Pei Xiao

Professor Pei Xiao


Professor of Wireless Communications
+44 (0)1483 689489
14 CII 02

Biography

Biography

Pei Xiao is a Professor in Wireless Communications at ICS, home of 5GIC. He received the B. Eng, MSc and PhD degree from Huazhong University of Science & Technology, Tampere University of Technology, Chalmers University of Technology, respectively. Prior to joining Surrey in 2011, he worked at Newcastle University and Queen's University Belfast and had held positions at Nokia Network in Finland. He is the technical manager of 5GIC, leading and coordinating research activities and overseeing major projects in 5GIC. His main research interests and expertise span a wide range of areas in communications theory and signal processing for wireless communications.

Teaching

  • EEEM061 Advanced 5G Wireless Technologies
  • EEEM020 Microwave Engineering
  • EEEM004 MSc Project Coorindator

Research projects

My publications

Publications

SALMAN BEHBOUDI AMLASHI, MOHSEN KHALILY, TIM W C BROWN, PEI XIAO, RAHIM TAFAZOLLI (2021)Graphene-based Reconfigurable Reflecting Surface for Future Communications

—In this paper, a reflecting metasurface is proposed to control the reflection angle by manipulating the chemical potential (CP) of graphene. The surface can operate in three anomalous reflection modes for θ = 45 • , 60 • and 75 • while it is illuminated with a normal incident electromagnetic wave (EMW). Moreover, by tuning the chemical potential of graphene sheets the proposed surface can switch off the reflection mode of operation by absorbing the incident EM power.

ALEXANDR KUZMINSKIY, Yuri I. Abramovich, PEI XIAO, RAHIM TAFAZOLLI, Jinliang Huang (2021)Maximum Likelihood Optimization of Adaptive Asynchronous Interference Mitigation Beamformer, In: IEEE Transactions on Signal Processing Institute of Electrical and Electronics Engineers (IEEE)

In asynchronous (intermittent) interference scenarios, the content of co-channel interference sources over the data interval may be different from the interferers content over the training interval, typically with extra interference sources presented over the data interval. Under such conditions, conventional adaptive beamformer designed over the training interval may lose its efficiency when applied to the data interval. In this paper, we address the problem by 1) formulating a family of the second order statistics adaptive beamformers regularized by the covariance matrix estimated over the data interval; 2) proposing a maximum likelihood methodology for optimization of the combined (mixed) covariance matrix based on maximization of a product of a likelihood ratio that checks the accuracy of the recovered training signals and a likelihood ratio on equality of the eigenvalues in complementary to the signal subspace defined over the data interval; 3) demonstrating efficiency and robustness of the proposed solution as a linear adaptive beamformer and as an initialization for iterative beamformer with projections to the finite alphabet in different asynchronous interference scenarios comparing with the basic training and data based interference rejection combining receivers.

Qi Zeng, Zilong Liu, Xing Liu, Jun Zhong, PEI XIAO (2021)Frequency-Hopping Based SCMA for Massive Connectivity in Multi-cell Networks

—Sparse code multiple-access (SCMA) is an emerging technique to support massive connectivity in 5G networks and beyond. In SCMA transmissions, some resource-blocks may undergo certain contamination due to deep fading and/or jamming attacks, thus leading to severe performance degradation over such contaminated ones. Besides, the current SCMA infrastructure is normally deployed in single-cell. To deploy the SCMA into multi-cell networks under contaminated/jamming channels, we propose a novel frequency-hopping based SCMA (FH-SCMA) for quasi-synchronous multi-cell networks, in which the entire subcarrier-channels of every codeword keep hopping over the multiple resource-blocks according certain hopping pattern. We propose and design a pseudo-randomly orthogonal hopping pattern to adapt to the specific requirements of quasi-synchronous FH-SCMA multi-cell networks. Our analysis and simulation results indicate that the proposed FH-SCMA leads to both improved user capacity and error-rate performance, whilst remaining resilient to the inter-cell interference.

Jing Zhu, Lixia Xiao, Pei Xiao, Atta ul Quddus, Chang He, Lei Lu (2021)Differential STBC-SM Scheme for Uplink Multi-user Massive MIMO Communications: System Design and Performance Analysis, In: IEEE Transactions on Vehicular Technology Institute of Electrical and Electronics Engineers (IEEE)

In this paper, a novel differential space-time block coded spatial modulation (differential STBC-SM) is proposed for uplink multi-user massive multiple-input multiple-output (MIMO) communications, which combines the concept of differential coding and STBC-SM to enhance the diversity benefits in the absence of the channel state information (CSI). The transmission structure of the proposed system is on a block basis, where each block contains two sub-blocks. More specifically, the first sub-block only conveys amplitude and phase modulation (APM) symbol bits, since its transmit antennas (TAs) obey a pre-designed activation pattern, which do not carry any information bit. For the second sub-block, the input bits are modulated to STBCSM matrices, which are then differentially coded between two adjacent sub-blocks. Moreover, a novel block-by-block based non-coherent detector is presented. Finally, we derive an upper bound on the average bit error probability (ABEP) by using the moment generating function (MGF). Our simulation results show that the proposed differential STBC-SM transmission structure is able to acquire considerable bit error rate (BER) performance improvements compared to both the conventional differential spatial modulation (DSM) and differential Alamouti schemes.

Judith Nkechinyere Njoku, Manuel Eugenio Morocho-Cayamcela, Angela Caliwaga, PEI XIAO, Wansu Lima (2021)Predicting target data rates for dynamic spectrum allocation using Gaussian process regression, In: ICT Express Elsevier

Issues in spectrum allocation between wireless network users have arisen due to the fast increase in the number of broadband services. Such issues include the failure to maximize the performance of all users by considering only a particular category of users. Specifically, a previously adopted selfish algorithm for spectrum allocation considers only the performance of the weakest user. To resolve this issue, we propose a new target data rate setting algorithm for dynamic spectrum allocation. In this algorithm, a Gaussian process regression model is trained to predict the target data rate. All users that perform below the defined target rate will have their frequency band allocations changed to one that guarantees a better performance. Through simulations, we show that the maximum data rate achieved by the weakest user in our algorithm is 121.7% higher than the selfish algorithm.

A Ijaz, L Zhang, P Xiao, R Tafazolli (2016)Analysis of Candidate Waveforms for 5G Cellular Systems, In: Towards 5G Wireless Networks - A Physical Layer Perspective(1) InTech

Choice of a suitable waveform is a key factor in the design of 5G physical layer. New waveform/s must be capable of supporting a greater density of users, higher data throughput and should provide more efficient utilization of available spectrum to support 5G vision of “everything everywhere and always connected” with “perception of infinite capacity”. Although orthogonal frequency division multiplexing (OFDM) has been adopted as the transmission waveform in wired and wireless systems for years, it has several limitations that make it unsuitable for use in future 5G air interface. In this chapter, we investigate and analyse alternative waveforms that are promising candidate solutions to address the challenges of diverse applications and scenarios in 5G.

Zilong Liu, Ping Yang, Yong Liang Guan, Pei Xiao (2020)Cross Z-Complementary Pairs (CZCPs) for Optimal Training in Spatial Modulation Over Frequency Selective Channels, In: IEEE Transactions on Signal Processing Institute of Electrical and Electronics Engineers

The contributions of this paper are twofold: Firstly, we introduce a novel class of sequence pairs, called “cross Zcomplementary pairs (CZCPs)”, each displaying zero-correlation zone (ZCZ) properties for both their aperiodic autocorrelation sums and crosscorrelation sums. Systematic constructions of perfect CZCPs based on selected Golay complementary pairs (GCPs) are presented. Secondly, we point out that CZCPs can be utilized as a key component in designing training sequences for broadband spatial modulation (SM) systems. We show that our proposed SM training sequences derived from CZCPs lead to optimal channel estimation performance over frequency-selective channels.

Manijeh Bashar, Alister G. Burr, Katsuyuki Haneda, Kanapathippillai Cumanan, Mehdi M. Molu, Mohsen Khalily, Pei Xiao (2019)Evaluation of Low Complexity Massive MIMO Techniques Under Realistic Channel Conditions, In: IEEE Transactions on Vehicular Technology Institute of Electrical and Electronics Engineers (IEEE)

A low complexity massive multiple-input multipleoutput (MIMO) technique is studied with a geometry-based stochastic channel model, called COST 2100 model. We propose to exploit the discrete-time Fourier transform of the antenna correlation function to perform user scheduling. The proposed algorithm relies on a trade off between the number of occupied bins of the eigenvalue spectrum of the channel covariance matrix for each user and spectral overlap among the selected users. We next show that linear precoding design can be performed based only on the channel correlation matrix. The proposed scheme exploits the angular bins of the eigenvalue spectrum of the channel covariance matrix to build up an “approximate eigenchannels” for the users. We investigate the reduction of average system throughput with no channel state information at the transmitter (CSIT). Analysis and numerical results show that while the throughput slightly decreases due to the absence of CSIT, the complexity of the system is reduced significantly.

Manijeh Bashar, Ali Akbari, Kanapathippillai Cumanan, Hien Quoc Ngo, Alister G. Burr, Pei Xiao, Merouane Debbah, Josef Kittler (2020)Exploiting Deep Learning in Limited-Fronthaul Cell-Free Massive MIMO Uplink, In: IEEE Journal on Selected Areas in Communications Institute of Electrical and Electronics Engineers

A cell-free massive multiple-input multiple-output (MIMO) uplink is considered, where quantize-and-forward (QF) refers to the case where both the channel estimates and the received signals are quantized at the access points (APs) and forwarded to a central processing unit (CPU) whereas in combinequantize- and-forward (CQF), the APs send the quantized version of the combined signal to the CPU. To solve the non-convex sum rate maximization problem, a heuristic sub-optimal scheme is exploited to convert the power allocation problem into a standard geometric programme (GP). We exploit the knowledge of the channel statistics to design the power elements. Employing largescale-fading (LSF) with a deep convolutional neural network (DCNN) enables us to determine a mapping from the LSF coefficients and the optimal power through solving the sum rate maximization problem using the quantized channel. Four possible power control schemes are studied, which we refer to as i) small-scale fading (SSF)-based QF; ii) LSF-based CQF; iii) LSF use-and-then-forget (UatF)-based QF; and iv) LSF deep learning (DL)-based QF, according to where channel estimation is performed and exploited and how the optimization problem is solved. Numerical results show that for the same fronthaul rate, the throughput significantly increases thanks to the mapping obtained using DCNN.

Manijeh Bashar, Hien Quoc Ngo, Kanapathippillai Cumanan, Alister G Burr, Pei Xiao, Emil Bjornson, Erik G Larsson (2020)Uplink Spectral and Energy Efficiency of Cell-Free Massive MIMO with Optimal Uniform Quantization, In: IEEE Transactions on Communicationspp. 1-1 IEEE

This paper investigates the performance of limited-fronthaul cell-free massive multiple-input multiple-output (MIMO) taking account the fronthaul quantization and imperfect channel acquisition. Three cases are studied, which we refer to as Estimate&Quantize, Quantize&Estimate, and Decentralized, according to where channel estimation is performed and exploited. Maximum-ratio combining (MRC), zero-forcing (ZF), and minimum mean-square error (MMSE) receivers are considered. The Max algorithm and the Bussgang decomposition are exploited to model optimum uniform quantization. Exploiting the optimal step size of the quantizer, analytical expressions for spectral and energy efficiencies are presented. Finally, an access point (AP) assignment algorithm is proposed to improve the performance of the decentralized scheme. Numerical results investigate the performance gap between limited fronthaul and perfect fronthaul cases, and demonstrate that exploiting relatively few quantization bits, the performance of limited-fronthaul cell-free massive MIMO closely approaches the perfect-fronthaul performance.

Manijeh Bashar, Kanapathippillai Cumanan, Alister G. Burr, Hien Quoc Ngo, Lajos Hanzo, Pei Xiao (2019)On the Performance of Cell-Free Massive MIMO Relying on Adaptive NOMA/OMA Mode-Switching, In: IEEE TRANSACTIONS ON COMMUNICATIONSpp. 1-1 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

The downlink (DL) of a non-orthogonal-multiple-access (NOMA)-based cell-free massive multiple-input multipleoutput (MIMO) system is analyzed, where the channel state information (CSI) is estimated using pilots. It is assumed that the users are grouped into multiple clusters. The same pilot sequences are assigned to the users within the same clusters whereas the pilots allocated to all clusters are mutually orthogonal. First, a user’s bandwidth efficiency (BE) is derived based on his/her channel statistics under the assumption of employing successive interference cancellation (SIC) at the users’ end with no DL training. Next, the classic max-min optimization framework is invoked for maximizing the minimum BE of a user under per-access point (AP) power constraints. The max-min user BE of NOMA-based cell-free massive MIMO is compared to that of its orthogonal multiple-access (OMA) counter part, where all users employ orthogonal pilots. Finally, our numerical results are presented and an operating mode switching scheme is proposed based on the average per-user BE of the system, where the mode set is given by Mode = { OMA, NOMA }. Our numerical results confirm that the switching point between the NOMA and OMA modes depends both on the length of the channel’s coherence time and on the total number of users.

P Xiao, R Tafazolli, W Yin, SW Shaker (2011)Enhanced subspaced approach to interference mitigation, In: 11th International Symposium on Communications and Information Technologies, ISCIT 2011pp. 13-17

In this paper, we study an enhanced subspace based approach for the mitigation of multiple access interference (MAI) in direct-sequence code-division multiple-access (DS-CDMA) systems over frequency-selective channels. Blind multiuser detection based on signal subspace estimation is of special interest in mitigating MAI in CDMA systems since it is impractical to assume perfect knowledge of parameters such as spreading codes, time delays and amplitudes of all the users in a rapidly changing mobile environment. We develop a new blind multiuser detection scheme which only needs the priori knowledge of the signature waveform and timing of the user of interest. By exploiting the improper nature of multiple access interference (MAI) and intersymbol interference (ISI), the enhanced detector shows clear superiority to the conventional subspace-based blind multiuser detector. The performance advantages are shown to be more obvious in heavily loaded systems when the number of active users is large. © 2011 IEEE.

Lei Wen, Pei Xiao, R Razavi, Muhammad Imran, M AL-Imari, A Maaref, J Lei (2018)Joint sparse graph for FBMC/OQAM systems, In: IEEE Transactions on Vehicular Technology67(7)pp. 6098-6112 IEEE

As an advanced non-orthogonal multiple access (NOMA) technique, the low density signature (LDS) has never been used in filter bank multicarrier (FBMC) systems. In this paper, we model a low density weight matrix (LDWM) to utilize the intrinsic interference in FBMC systems when single-tap equalization is employed, and propose a LDS-FBMC scheme which applies LDS to FBMC signals. In addition, a joint sparse graph for FBMC named JSG-FBMC is proposed to combine single graphs of LDS, LDWM and low density parity-check (LDPC) codes which respectively represent techniques of NOMA, multicarrier modulation and channel coding. By employing the message passing algorithm (MPA), a joint receiver performing detection and decoding simultaneously on the joint sparse graph is designed. Extrinsic information transfer (EXIT) charts and construction guidelines of the joint sparse graph are studied. Simulations show the superiority of JSG-FBMC to state-of-theart techniques such as OFDM, FBMC, LDS-OFDM, LDS-FBMC and turbo structured LDS-FBMC.

Lei Zhang, Ayesha Ijaz, Pei Xiao, Rahim Tafazolli (2017)Channel Equalization and Interference Analysis for Uplink Narrowband Internet of Things (NB-IoT), In: IEEE communications Letters21(10)pp. 2206-2209 IEEE

We derive the uplink system model for In-band and Guard-band narrowband Internet of Things (NB-IoT). The results reveal that the actual channel frequency response (CFR) is not a simple Fourier transform of the channel impulse response, due to sampling rate mismatch between the NB-IoT user and Long Term Evolution (LTE) base station. Consequently, a new channel equalization algorithm is proposed based on the derived effective CFR. In addition, the interference is derived analytically to facilitate the co-existence of NB-IoT and LTE signals. This work provides an example and guidance to support network slicing and service multiplexing in the physical layer.

P Xiao, R Carrasco, I Wassell (2007)A Novel Multistage Equalization Algorithm, In: Communications, 2007. ICC '07. IEEE International Conference onpp. 2630-2634

A novel equalization algorithm utilizing improper nature of the intersymbol interference (ISI) is introduced in this paper. We show that full exploitation of the available information on the second-order statistics of the observed signal entails widely linear processing and that previously known linear minimum mean square error (MMSE) equalizers represent sub-optimum solutions. The proposed scheme is generally applicable for both real and complex signal constellations. The results show that accounting for the improper nature of the ISI leads to significant performance gain compared to conventional equalization schemes.

Wanming Hao, Ming Zeng, Gangcan Sun, Pei Xiao (2019)Edge Cache-assisted Secure Low-Latency Millimeter Wave Transmission, In: IEEE Internet of Things Journal IEEE

In this paper, we consider an edge cache-assisted millimeter wave cloud radio access network (C-RAN). Each remote radio head (RRH) in the C-RAN has a local cache, which can prefetch and store the files requested by the actuators. Multiple RRHs form a cluster to cooperatively serve the actuators, which acquire their required files either from the local caches or from the central processor via multicast fronthaul links. For such a scenario, we formulate a beamforming design problem to minimize the secure transmission delay under transmit power constraint of each RRH. Due to the diffculty of directly solving the formulated problem, we divide it into two independent ones: i) minimizing the fronthaul transmission delay by jointly optimizing the transmit and receive beamforming; ii) minimizing the maximum access transmission delay by jointly designing cooperative beamforming among RRHs. An alternatively iterative algorithm is proposed to solve the first optimization problem. For the latter, we first design the analog beamforming based on the channel state information of the actuators. Then, with the aid of successive convex approximation and S -procedure techniques, a semidefinite program (SDP) is formulated, and an iterative algorithm is proposed through SDP relaxation. Finally, simulation results are provided to verify the performance of the proposed schemes.

Mahmoud Abdullahi, Aijun Cao, Adnan Zafar, Pei Xiao, Ibrahim Hemadeh (2020)A Generalized Bit Error Rate Evaluation for Index Modulation Based OFDM System, In: IEEE Access Institute of Electrical and Electronics Engineers

Orthogonal frequency division multiplexing (OFDM-IM) is a multicarrier transmission technology that modulates information bits not just onto subcarriers by means of Mary constellation mapping but also onto selected (active) subcarrier indices. Consequently, errors can occur in OFDMIM systems indices in addition to the errors of M-ary symbols. This paper analyzes the error scenarios and derives mathematical expressions for the error performance based on the maximum likelihood (ML) detection. In evaluating the bit error rate (BER) in the additive white Gaussian noise (AWGN) channel, some assumptions are made and our analytical result show that the BER of OFDM-IM system is a weighted sum of exponential functions and Q-functions. Our general BER expression has been shown to be in excellent agreement with numerical simulation and proven to be accurate and can serve as a reference for the design and evaluation of any arbitrary size and configuration of OFDM-IM systems.

Pei Xiao, R Carrasco, I Wassell (2007)High Data Rate Broadband Fixed Wireless Access with Multilevel Modulation, In: Proceedings World Wireless Congress 2007pp. 85-90 Delson Group

A spectrally efficient equalization scheme with multilevel modulation is proposed in this paper for combating intersymbol interference caused by the broadband fixed wireless access (BFWA) channel. The complexity of the existing MMSE equalization schemes increases drastically with the channel memory, which make them impractical to implement when signal transmission rate goes beyond a certain limit. The proposed low complexity scheme enables the system to operate at very high data rate, and its complexity does not increase with data rate, which makes it suitable for high data rate BFWA applications.

Chunxu Mao, Mohsen Khalily, Vikrant Singh, Pei Xiao (2020)Low-Profile Vertically Polarized Wearable Antenna with Omni-Directional Radiation, In: 2020 IEEE International Symposium on Antennas and Propagation and North American Radio Science Meeting

In this paper, a single-layer planar antenna with vertical polarization and omni-directional radiation is proposed for wearable applications. The antenna consists of two identical shorted patches which are face-to-face located and fed by a microstrip line at the center. Due to the structural symmetry, the current distribution and electric-field distribution are symmetrical regarding the feed, which result in vertical linear polarization normal to the antenna and omni-directional radiation pattern in the azimuthal plane. To verify the design concept, an antenna prototype operating at 2.45 GHz is designed, fabricated and tested. Measured results concur well with the simulations, showing that the antenna has a good impedance matching, omnidirectional radiation pattern, and vertical polarization in the band of interest. The proposed antenna can be a good candidate for wearable and other wireless communication systems.

Zeina Mheich, Lei Wen, Pei Xiao, Amine Maaref (2018)Design of SCMA Codebooks Based on Golden Angle Modulation, In: IEEE Transactions on Vehicular Technology IEEE

In this paper, we propose to use golden angle modulation (GAM) points to construct codebooks for uplink and downlink sparse code multiple access (SCMA) systems. We provide two categories of codebooks with one and two optimization parameters respectively. The advantages of the proposed design method are twofold: 1) the number of optimization variables is independent of codebook and system parameters; 2) it is simple to implement. In the downlink, we use GAM points to build a multidimensional mother constellation for SCMA codebooks, while in the uplink GAM points are directly mapped to user codebooks. The proposed codebooks exhibit good performance with low peak to average power ratio (PAPR) compared to the codebooks proposed in the literature based on constellation rotation and interleaving.

P Xiao, R Tafazolli, BK Khoo, SY Le Goff (2011)Theoretical analysis of repetition time-switched transmit diversity scheme, In: 11th International Symposium on Communications and Information Technologies, ISCIT 2011pp. 211-216

The conventional transmit diversity schemes, such as Alamouti scheme, use several radio frequency (RF) chains to transmit signals simultaneously from multiple antennas. In this paper, we propose a low-complexity repetition time-switched (RTSTD) transmit diversity algorithm, which employs only one RF chain as well as a low-complexity switch for transmission. A mathematical model is developed to assess the performance of the proposed scheme. In order to make it applicable for practical applications, we also investigate its joint application with orthogonal frequency division multiplexing (OFDM) and channel coding techniques to combat frequency selective fading. © 2011 IEEE.

Chunxu Mao, Mohsen Khalily, Pei Xiao (2020)Integrated Design of Dual-Band Antenna with Uni-/Omni-Directional Radiations, In: Proceedings 14th European Conference on Antennas and Propagation IEEE

A multifunctional antenna with diverse radiation patterns in different frequency bands (2.45/5.8 GHz) is presented in this paper. The antenna has a low profile but exhibits an omni-directional radiation pattern in the low-band operation and uni-directional pattern in the high-band operation. For the high-band operation, a 2 × 2 patch arrays are designed by employing a out-of-phase feeding method. The low-band operation with the omni-directional pattern is achieved by exciting four open-ended slots in-phase. The four slots are slit in the ground of the high-band array and in this way, this footprint of the antenna is maintained. The operating principles of the antenna are studied with the aid of equivalent circuit model and the current distribution. The antenna is prototyped and measured, demonstrating good results in terms of bandwidths, inter-channel isolation, radiation characteristics.

Ahmed Almradi, Pei Xiao (2018)Energy Beamforming for MIMO WIPT Relaying with Arbitrary Correlation, In: IEEE Access Institute of Electrical and Electronics Engineers (IEEE)

This paper investigates the negative impact of spatial fading correlation in multiple-input multiple-output (MIMO) relaying systems on the performance of energy beamforming. Namely, a source and destination nodes equipped with multiple antennas which have a general correlation structures and arbitrary eigenvalue multiplicities, exchanging information through a dual-hop amplify-and-forward (AF) single antenna energyconstrained relay. To facilitate longer-distance wireless power transfer, the overall scavenged energy needs to be maximized. Hence, the energy-constrained relay harvest energy from the source radio-frequency (RF) signal through energy beamforming, the harvested energy is then used to forward the source information symbol to the destination. The time switching-based receiver (TSR) along with the power splitting-based receiver (PSR) protocols are examined in order to perform wireless information and power transfer at the relay. To this end, tight closed-form lower and upper bounds for the outage probability and ergodic capacity are derived, and used to examine the throughput of the delay-constrained and delay-tolerant transmission modes, respectively. Numerical results supported by simulations manifest the tightness of the presented analytical formulas. The effect of several parameters like energy harvesting ratio, source transmit power, number of antennas and spatial fading correlation on the overall throughput is investigated. It is shown that increasing the number of antennas could be used to improve the system throughput or facilitate longer-distance wireless power transfer. On the other hand, the ramification of spatial correlation on the system throughput is also studied for arbitrary correlation structure. Moreover, it is revealed that the performance of powersplitting receiver outperforms the time-switching receiver at high signal-to-noise ratio. Finally, simulation results for the case of statistical CSI is also included for comparison purposes.

ZU Abidin, P Xiao, M Amin, V Fusco (2012)Circular polarization modulation for digital communication systems, In: Communication Systems, Networks & Digital Signal Processing (CSNDSP), 2012 8th International Symposium onpp. 1-6

Conventional approaches of digital modulation schemes make use of amplitude, frequency and/or phase as modulation characteristic to transmit data. In this paper, we exploit circular polarization (CP) of the propagating electromagnetic carrier as modulation attribute which is a novel concept in digital communications. The requirement of antenna alignment to maximize received power is eliminated for CP signals and these are not affected by linearly polarized jamming signals. The work presents the concept of Circular Polarization Modulation for 2, 4 and 8 states of carrier and refers them as binary circular polarization modulation (BCPM), quaternary circular polarization modulation (QCPM) and 8-state circular polarization modulation (8CPM) respectively. Issues of modulation, demodulation, 3D symbol constellations and 3D propagating waveforms for the proposed modulation schemes are presented and analyzed in the presence of channel effects, and they are shown to have the same bit error performance in the presence of AWGN compared with conventional schemes while provide 3dB gain in the flat Rayleigh fading channel. © 2012 IEEE.

P Xiao, J Wu, CFN Cowan (2011)MIMO Detection Schemes with Interference and Noise Estimation Enhancement, In: IEEE Transactions on Communications59(1)pp. 26-32 IEEE

Different detection schemes for multiple-input, multiple-output (MIMO) systems are investigated. By enhancing the interference and noise estimation, we propose a novel MIMO receiver strategy, which is shown to achieve superior performance with moderate increase in computational complexity compared to conventional MIMO detection schemes.

P Xiao, R Carrasco, I Wassell (2007)Theoretical Analysis of Single and Multiple antenna FWA Systems, In: IET Communications1(3)pp. 496-506 IET
P Xiao, R Carrasco, I Wassell (2007)EXIT Chart Anlaysis of Space-Time Turbo Equalizer, In: Information Theory Workshop, 2006. ITW '06pp. 631-635

In this paper, we study the performance of the turbo equalization schemes for systems with space-time block code (STBC) using the extrinsic information transfer (EXIT) chart, which is shown to be very useful for analyzing the convergence behavior of turbo equalizers, predicting the expected BER performance of the STBC coded systems, determining the SNR threshold for a target BER, as well as facilitating the proper choice of equalizers and channel codes for specific channel conditions

P Xiao, R Carrasco, I Wassell (2007)On The Asymptotic Performance of The STBC Coded FWA Systems, In: Global Telecommunications Conference, 2006. GLOBECOM '06. IEEE

The asymptotic performance of the space-time block coded systems using two transmit antennas over a broadband wireless fixed access (FWA) frequency selective channel is studied in this paper. The conducted theoretical analysis gives us an insight into the physical limitations imposed by the FWA channels and suggests solutions to improve the capacity and performance of future FWA systems.

P Xiao, V Fusco, P Sundaralingam (2011)Analysis of temporal compression characteristics using active phase conjugation in systems with multiple antenna elements, In: Antennas and Propagation (EUCAP), Proceedings of the 5th European Conference onpp. 297-300

In this paper we give first account of a simple analysis tool for modeling temporal compression for automatic mitigation of multipath induced intersymbol interference through the use of active phase conjugation (APC) technique. The temporal compression characteristics of an APC system is analyzed using a simple discrete channel model, and numerical results are provided to justify the theoretical findings. © 2011 EurAAP.

P Xiao, I Chatzigeorgiou, R Carrasco, I Wassell (2007)Comparison of Frequency And Time Domain Schemes for MIMO Broadband Fixed Wireless Accesspp. 3051-3056

Broadband fixed wireless access (BFWA) is an ideal solution for providing high data rate communications where traditional landlines are either unavailable or too costly to be installed. In this paper we consider a number of alternative techniques to achieve high data rate and high quality of services requirements in these systems, including orthogonal frequency division multiplexing (OFDM), turbo equalization as well as multiple-input multiple-output (MIMO) techniques. In particular, the frequency domain OFDM scheme and time domain turbo equalization will be studied and compared in a MIMO BFWA context, in an attempt to provide some guidelines on how to design high data rate BFWA applications.

H.R.D. Filgueiras, I. F. da Costa, S. Jr. Arismar Cerqueira, James R. Kelly, Pei Xiao (2018)A Novel Approach for Designing Omnidirectional Slotted-Waveguide Antenna Array, In: Proceedings of ICEAA - IEEE APWC - FEM 2018 Institute of Electrical and Electronics Engineers (IEEE)

This paper presents a novel design of a high-gain omnidirectional slotted-waveguide antenna array for 5G mmwave applications. The structure is based on a circular waveguide filled with teflon for manipulating its dimension. It provides 12,1 dBi gain and omnidirectional coverage in the azimuth plane with only 1.3 dB deviation, which is ensured by making use of a twisting technique for proper placing the slots into the waveguide walls. A bandwidth of 1.61 GHz centered at 26.2 GHz has been numerically demonstrated.

Ali Araghi, Mohsen Khalily, Pei Xiao, Rahim Tafazolli (2020)Holographic-Based mmW-Wideband Bidirectional Frequency Scanning Leaky Wave Antenna, In: EUCAP 2020

Utilizing the holography theory, a bidirectional wideband leaky wave antenna in the millimetre wave (mmW) band is presented. The antenna includes a printed pattern of continuous metallic strips on an Alumina 99:5% sheet, and a surface wave launcher (SWL) to produce the initial reference waves on the substrate. To achieve a bidirectional radiation pattern, the fundamental TE mode is excited by applying a Vivaldi antenna (as the SWL). The proposed holographic-based leaky wave antenna (HLWA) is fabricated and tested and the measured results are aligned with the simulated ones. The antenna has 22:6% fractional bandwidth with respect to the central frequency of 30 GHz. The interference pattern is designed to generate a 15 deg backward tilted bidirectional radiation pattern with respect to the normal of the hologram sheet. The frequency scanning property of the designed HLWA is also investigated.

P Xiao, LG Barbero, M Sellathurai, T Ratnarajah (2008)On the Uncoded BER Performance Bound of the IEEE 802.16d Channel, In: IEEE Signal Processing Letters15pp. 561-564 IEEE

In this letter, the performance bound of the IEEE 802.16d channel is examined analytically in order to gain an insight into its theoretical potential. Different design strategies, such as orthogonal frequency division multiplexing (OFDM) and single-carrier frequency-domain equalization (SC-FDE), time-domain decision feedback equalization (DFE), and sphere decoder (SD) techniques are discussed and compared to the theoretical bound.

Bogdan Dorneau, Mohamed Heshmat, Abdelrahim Mohamed, Hang Ruan, Yang Gao, Pei Xiao, Harvey Arellano-Garcia (2020)Stepping towards the industrial Sixth Sense, In: ESCAPE30

This contribution introduces the development of an intelligent monitoring and control framework for chemical processes, integrating the advantages of Industry 4.0 technologies, cooperative control and fault detection via wireless sensor networks. Using information on the process’ structure and behaviour, equipment information, and expert knowledge, the system is able to detect faults. The integration with the monitoring system facilitates the detection and optimises the controller’s actions. The results indicate that the proposed approach achieves high fault detection accuracy based on plant measurements, while the cooperative controllers improve the control of the process.

X Zhang, P Xiao, D Ma, J Wei (2014)Variational Bayes Assisted Joint Signal Detection, Noise Covariance Estimation and Channel Tracking in MIMO-OFDM Systems, In: IEEE Transactions on Vehicular Technology IEEE

This paper introduces a robust variational bayes (Robust-VB) receiver algorithm for joint signal detection, noise covariance matrix estimation and channel impulse response (CIR) tracking in multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems over time varying channels. The variational bayes (VB) framework and turbo principle are combined to accomplish the parameter estimation and data detection. In the proposed Robust-VB receiver, a modified linear minimum mean-square-error interference cancellation (LMMSE-IC) soft detector is developed based on the VB theory, which adaptively sets the log-likelihood ratio (LLR) clipping value according to the reliability of detection on each subcarrier to mitigate the error propagation. Following the signal detection, an adaptive noise covariance matrix estimator is derived for the effective noise covariance estimation. Furthermore, in order to track time varying channels, a VB soft-input Kalman filter (VB-Soft-KF) is first derived. However, unreliable soft symbols introduce outliers, which degrade the performance of VB-Soft-KF. To tackle this problem, we propose a robust VB soft-input Kalman filter (VB-Robust-KF) based on the Huber M estimation theory. Finally, the performance of the proposed algorithm is assessed via simulations, showing the superior performance of the Robust-VB receiver compared to the other benchmark receiver algorithms.

P Xiao, R Carrasco, I Wassell (2007)Estimation of FWA MIMO Channelspp. 641-645

Channel estimation schemes for fixed wireless access (FWA) multiple-input, multiple-output (MIMO) systems are considered in this study. The use of multiple antennas in combination with advanced detection techniques, such as turbo equalization is an effective means for a FWA system to provide high quality and high data rate services. Accurate knowledge, i.e., a good estimate of the underlying channel is essential for turbo equalization to achieve good performance. In this paper, we investigate some algorithms that are suitable for estimating FWA MIMO channels. The proposed schemes are evaluated and compared using different training sequences. Based on our analysis and numerical results, some recommendations are made on how to design appropriate channel estimator and how to choose training sequences for practical FWA systems

J Du, P Xiao, J Wu, Q Chen (2012)Design of isotropic orthogonal transform algorithm-based multicarrier systems with blind channel estimation, In: IET COMMUNICATIONS6(16)pp. 2695-2704 INST ENGINEERING TECHNOLOGY-IET
P Xiao, R Carrasco, I Wassell (2007)Iterative Equalization and TCM Decoding with Refined Channel Value, In: IEEE Transactions on Wireless Communications6(11)pp. 3920-3925
Chun Xu Mao, Mohsen Khalily, Pei Xiao, Long Zhang, Rahim Tafazolli (2020)High-Gain Phased Array Antenna with End-Fire Radiation for 26 GHz Wide-Beam-Scanning Applications, In: IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

In this paper, a high-gain phased array antenna with wide-angle beam-scanning capability is proposed for fifth- generation (5G) millimeter-wave applications. First, a novel, end-fire, dual-port antenna element with dual functionalities of radiator and power splitter is designed. The element is composed a substrate integrated cavity (SIC) and a dipole based on it. The resonant frequencies of the SIC and dipole can be independently tuned to broaden the impedance bandwidth. Based on this dual-port element, a 4-element subarray can be easily constructed without resorting to a complicated feeding network. The end-fire subarray features broad beam-width of over 180 degrees, high isolation, and low profile, rendering it suitable for wide-angle beam-scanning applications in the H-plane. In addition, the methods of steering the radiation pattern downwards or upwards in the E-plane are investigated. As a proof-of-concept, two phased array antennas each consisting of eight subarrays are designed and fabricated to achieve the broadside and wide-angle beam-scanning radiation. Thanks to the elimination of surface wave, the mutual coupling between the subarrays can be reduced for improving the scanning angle while suppressing the side-lobe level. The experimental predictions are validated by measurement results, showing that the beam of the antenna can be scanned up to 65 degrees with a scanning loss only 3.7 dB and grating lobe less than -15 dB.

Abdelrahim Mohamed, Hang Ruan, Mohamed Abdelwahab, Bogdan Dorneanu, Pei Xiao, Harvey Arellano-Garcia, Yang Gao, Rahim Tafazolli (2020)An Inter-disciplinary Modelling Approach in Industrial 5G/6G and Machine Learning Era, In: IEEE International Conference on Communications (ICC) IEEE

Recently, the fifth-generation (5G) cellular system has been standardised. As opposed to legacy cellular systems geared towards broadband services, the 5G system identifies key use cases for ultra-reliable and low latency communications (URLLC) and massive machine-type communications (mMTC). These intrinsic 5G capabilities enable promising sensor-based vertical applications and services such as industrial process automation. The latter includes autonomous fault detection and prediction, optimised operations and proactive control. Such applications enable equipping industrial plants with a sixth sense (6S) for optimised operations and fault avoidance. In this direction, we introduce an inter-disciplinary approach integrating wireless sensor networks with machine learningenabled industrial plants to build a step towards developing this 6S technology. We develop a modular-based system that can be adapted to the vertical-specific elements. Without loss of generalisation, exemplary use cases are developed and presented including a fault detection/prediction scheme, and a sensor density-based boundary between orthogonal and non-orthogonal transmissions. The proposed schemes and modelling approach are implemented in a real chemical plant for testing purposes, and a high fault detection and prediction accuracy is achieved coupled with optimised sensor density analysis.

Zheng Chu, Wanming Hao, Pei Xiao, Mohsen Khalily, Rahim Tafazolli (2020)Resource Allocations for Symbiotic Radio with Finite Block Length Backscatter Link, In: IEEE Internet of Things Journal Institute of Electrical and Electronic Engineers

This paper exploits a generic downlink symbiotic radio (SR) system, where a Base Station (BS) establishes a direct (primary) link with a receiver having an integrated backscatter device (BD). In order to accurately measure the backscatter link, the backscattered signal packets are designed to have finite block length. As such, the backscatter link in this SR system employs the finite block-length channel codes. According to different types of the backscatter symbol period and transmission rate, we investigate the non-cooperative and cooperative SR (i.e., NSR and CSR) systems, and derive their average achievable rate of the direct and backscatter links, respectively. We formulate two optimization problems, i.e., transmit power minimization and energy efficiency maximization. Due to the non-convex property of these formulated optimization problems, the semidefinite programming (SDP) relaxation and the successive convex approximation (SCA) are considered to design the transmit beamforming vector. Moreover, a low-complexity transmit beamforming structure is constructed to reduce the computational complexity of the SDP relaxed solution. Finally, the simulation results are demonstrated to validate the proposed schemes.

P Xiao, R Carrasco, I Wassell (2007)Turbo Equalization For Space-Time Block Coded FWA Systemspp. 626-630

The use of multiple antennas in combination with advanced detection techniques, such as turbo equalization is an effective means for a Fixed Wireless Access (FWA) system to provide high quality and high data rate services. Alamouti's space-time block code (STBC) with two transmit antennas and one or two receive antennas over frquency selective FWA SUI-3 channels is considered in this paper. We propose a turbo equalization algorithm that aims at exploiting the multipath diversity and reducing the effect of intersymbol iterference (ISI), and in the meantime, keeping the desired feature of the original Alamouti detection algorithm, i.e, achieving spatial diversity with simple linear processing.

Manijeh Bashar, Ali Akbari, Kanapathippillai Cumanan, Hien Quoc Ngo, Alister G. Burr, Pei Xiao, Merouane Debbah (2020)Deep Learning-Aided Finite-Capacity Fronthaul Cell-Free Massive MIMO with Zero Forcing, In: IEEE ICC 2020

We consider a cell-free massive multiple-input multiple-output (MIMO) system where the channel estimates and the received signals are quantized at the access points (APs) and forwarded to a central processing unit (CPU). Zero-forcing technique is used at the CPU to detect the signals transmitted from all users.. To solve the non-convex sum rate maximization problem, a heuristic sub-optimal scheme is proposed to convert the problem into a geometric programme (GP). Exploiting a deep convolutional neural network (DCNN) allows us to determine both a mapping from the large-scale fading (LSF) coefficients and the optimal power by solving the optimization problem using the quantized channel. Depending on how the optimization problem is solved, different power control schemes are investigated; i) small-scale fading (SSF)-based power control; ii) LSF use-and-then-forget (UatF)-based power control; and iii) LSF deep learning (DL)-based power control. The SSF-based power control scheme needs to be solved for each coherence interval of the SSF, which is practically impossible in real time systems. Numerical results reveal that the proposed LSF-DL-based scheme significantly increases the performance compared to the practical and well-known LSF-UatF-based power control, thanks to the mapping obtained using DCNN.

Lixia Xiao, Da Chen, Ibrahim Hemadeh, Pei Xiao, Tao Jiang (2020)Graph Theory assisted Bit-to-Index-Combination Gray Coding for Generalized Index Modulation, In: IEEE Transactions on Wireless Communications Institute of Electrical and Electronics Engineers (IEEE)

Generalized index modulation (GIM) which implicitly conveys information by the activated indices is a promising technique for next-generation wireless networks. Due to the prohibitive challenge of bit-to-index combination (IC) mapping optimization, conventional GIM system obtains the bit-to-IC mapping table randomly, which may suffer from some performance loss. To circumvent this issue, we propose a low-complexity graph theory assisted bit-to-IC gray coding for GIM systems by minimizing the average hamming distance (HD) between any two ICs having one different value. Specifically, we decompose and transform the optimization problem into two subproblems using the graph theory, i.e., 1) Select an IC set whose corresponding graph has the minimum degree; 2) Design a bit-to-IC mapping principle to minimize the weight of the selected graph. Low complexity algorithms are developed to solve the subproblems with a significant reduced complexity. Both simulation and theoretical results are shown that the GIM systems with our proposed mapping table are capable of providing significant performance gains over the conventional counterparts without the need for any additional feedback-link and without extra computational complexity. It is also shown that the proposed bit-to-IC mapping table is straightforward for any GIM systems over generalized fading channels.

P Xiao, I Chatzigeorgiou, M Rodrigues, R Carrasco, I Wassell (2009)Design Considerations and Algorithms for Broadband Fixed WiMAX Systems, In: VLSI and Computer Architecture(3) Nova Science Publishers

This is expected to become more commonplace as semiconductor fabrication moves from thecurrent generation of 65 nm processes to the next 45 nm generations.

P Xiao, Z Lin, Y Wu, C Schneider (2013)Application of WLF to OFDMA MU-MIMO Systems I: Frequency-Domain Equalization, In: ISWCS 2013

This paper presents a novel iterative receiver strategy incorporating widely linear filtering for uplink Orthogonal Frequency Division Multiple Access (OFDMA) multiuser multiple-input, multiple-output (MIMO) systems. The proposed iterative receiver scheme achieves better performance without the loss of spectrum efficiency compared to the conventional iterative receivers; The superiority of the investigated scheduler coupled with the innovative iterative receiver scheme over conventional solutions is verified by both simulation and analytical results. © VDE Verlag GMBH.

P Xiao, J Wu, M Sellathurai, T Ratnarajah (2009)On The Performance of Space-Time Coded Multiuser MIMO Systems with Iterative Receivers, In: IEEE 69th Vehicular Technology Conference Spring 2009

This paper considers multiuser MIMO CDMA systems with high rate space-time linear dispersion codes (LDC) and orthogonal space-time block codes (O-STBC) in time-varying Rayleigh fading MIMO channels. We propose a multi-function process integrating multi-user detection, space-time decoding and symbol demodulation, which can be coupled with soft channel decoding to improve the system performance in an iterative fashion. We show that the space-time coded CDMA systems approach the single-user bound with only two iterations, and full diversity LDCs enable the systems to utilize the time diversity inherent in fast fading channels. The space-time coded CDMA systems are also compared to the MIMO CDMA system based on spatial multiplexing, some recommendations are made on how to design a practical MIMO CDMA system based on the comparative studies.

Arunprakash Jayaprakash, Barry G. Evans, Pei Xiao, Adegbenga Awoseyila, Yingnan Zhang (2020)New Radio Numerology and Waveform Evaluation for Satellite Integration into 5G Terrestrial Network, In: IEEE International Conference on Communications

This paper analyses the New Radio (NR) air interface waveforms and numerologies in the context of current activities and studies of 3GPP related to the feasibility and standardisation of necessary adaptations for the 5G NR to support integrated-satellite-terrestrial networks with low earth orbit (LEO) satellites. Frequency-localized orthogonal frequency division multiplexing (OFDM)-based candidate waveforms are recommended by 3GPP as the waveforms for the NR in order to preserve the advantages of OFDM as well as maintain backward compatibility. 5G New Radio enables diverse service support, efficient synchronization and channel adaptability using a multinumerology concept, which defines a family of parameters of the parent waveform, that are related to each other by scaling. The major design challenges in the LEO satellite scenario are power limited link budget and high Doppler effects which can be addressed by choosing waveforms with small peak to average power ratio (PAPR) and sub-carrier bandwidth adaptation respectively. Hence, the selection of the right waveform and numerology is of prime relevance for the proper adaptation of 5G NR for LEO satellite terrestrial integration. The performance evaluation of the new air interface waveforms, with different numerologies, are carried out under the effect of carrier frequency offset (CFO), multipath effects, non-linearity, phase noise and additive white Gaussian noise (AWGN).

G Chen, Pei Xiao, Rahim Tafazolli (2016)Dual Antenna Selection in Self-Backhauling Multiple Small Cell Networks, In: IEEE Communications Letters20(8)pp. 1611-1614 IEEE

This paper investigates self-backhauling with dual antenna selection at multiple small cell base stations. Both half and full duplex transmissions at the small cell base station are considered. Depending on instantaneous channel conditions, the full duplex transmission can have higher throughput than the half duplex transmission, but it is not always the case. Closed-form expressions of the average throughput are obtained, and validated by simulation results. In all cases, the dual receive and transmit antenna selection significantly improves backhaul and data transmission, making it an attractive solution in practical systems.

P Xiao, Z Lin, C Cowan (2010)Analysis of Channel Capacity for LTE Downlink Multiuser MIMO Systems, In: Vehicular Technology Conference Fall (VTC 2010-Fall)pp. 1-6

The average channel capacity for 3GPP LTE downlink multiuser Multiple Input Multiple Output (MIMO) systems is analyzed in this paper. A packet scheduler is used to exploit the available multiuser diversity in all the three physical domains (i.e., space, time and frequency). A mathematical model is established to derive the channel capacity of multiuser MIMO systems with the frequency domain packet scheduler (FDPS). This work provides a theoretical reference for the future version of the LTE standard and a useful source of information for the practical implementation of the LTE systems.

I da Costa, H Filgueiras, James Kelly, S Arismar Cerqueira, Pei Xiao (2018)Mechanical Beam Steering Circular Patch Antenna, In: EuCAP 2018 Proceedings

This work reports preliminary results and a prototype of an innovative mechanical beam steering circular patch antenna for 5G indoor cellular access networks with sub6 GHz operation. The beam steering is achieved using 18 screws installed around the circular patch radiator, working as a reflector by proper managing the screws position and height. The new antenna can steer its main beam over 360º in azimuth plane and from -30º to 30º in the elevation plane with gain up to 8.01 dBi at 4.6 GHz.

Alexandr Kuzminskiy, Pei Xiao, Rahim Tafazolli (2018)Good Neighbor Distributed Beam Scheduling in Coexisting Multi-RAT Networks, In: Proceedings of WCNC 2018 IEEE

Spectrum sharing and employing highly directional antennas in the mm-wave bands are considered among the key enablers for 5G networks. Conventional interference avoidance techniques like listen-before-talk (LBT) may not be efficient for such coexisting networks. In this paper, we address a coexistence mechanism by means of distributed beam scheduling with minimum cooperation between spectrum sharing subsystems without any direct data exchange between them. We extend a “Good Neighbor” (GN) principle initially developed for decentralized spectrum allocation to the distributed beam scheduling problem. To do that, we introduce relative performance targets, develop a GN beam scheduling algorithm, and demonstrate its efficiency in terms of performance/complexity trade off compared to that of the conventional selfish (SLF) and recently proposed distributed learning scheduling (DLS) solutions by means of simulations in highly directional antenna mm-wave scenarios.

B Zhou, Q Chen, J Li, P Xiao (2014)Online Variational Bayesian Filtering-Based Mobile Target Tracking in Wireless Sensor Networks, In: Sensors14pp. 21281-21315

Online variational bayesian filtering-based mobile target tracking in wireless sensor networks. Abstract: The received signal strength (RSS)-based online tracking for a mobile node in wireless sensor networks (WSNs) is investigated in this paper. Firstly, a multi-layer dynamic Bayesian network (MDBN) is introduced to characterize the target mobility with either directional or undirected movement. In particular, it is proposed to employ the Wishart distribution to approximate the time-varying RSS measurement precision's randomness due to the target movement. It is shown that the proposed MDBN offers a more general analysis model via incorporating the underlying statistical information of both the target movement and observations, which can be utilized to improve the online tracking capability by exploiting the Bayesian statistics. Secondly, based on the MDBN model, a mean-field variational Bayesian filtering (VBF) algorithm is developed to realize the online tracking of a mobile target in the presence of nonlinear observations and time-varying RSS precision, wherein the traditional Bayesian filtering scheme cannot be directly employed. Thirdly, a joint optimization between the real-time velocity and its prior expectation is proposed to enable online velocity tracking in the proposed online tacking scheme. Finally, the associated Bayesian Cramer-Rao Lower Bound (BCRLB) analysis and numerical simulations are conducted. Our analysis unveils that, by exploiting the potential state information via the general MDBN model, the proposed VBF algorithm provides a promising solution to the online tracking of a mobile node in WSNs. In addition, it is shown that the final tracking accuracy linearly scales with its expectation when the RSS measurement precision is time-varying.

Z Lin, P Xiao, Y Wu, C Schneider (2013)Application of WLF to OFDMA MU-MIMO Systems II: Frequency-Domain Packet Scheduling, In: ISWCS 2013
L Wen, R Razavi, P Xiao, M Imran (2014)Fast convergence and reduced complexity receiver design for LDS-OFDM system, In: 25th International Symposium on Personal, Indoor and Mobile Radio Communications Proceedingspp. 918-922
Hugo Rodrigues Dias Filgueiras, James R. Kelly, Pei Xiao, I. F. da Costa, Arismar Cerqueira S. Jr. (2019)Wideband Omnidirectional Slotted-Waveguide Antenna Array Based on Trapezoidal Slots, In: International Journal of Antennas and Propagation Hindawi

This manuscript presents a novel approach for designing wideband omnidirectional slotted-waveguide antenna arrays, which is based on trapezoidal-shaped slots with two different electrical lengths, as well as a twisted distribution of slot groups along the array longitudinal axis. The trapezoidal section is formed by gradually increasing the slot length between the waveguide interior and exterior surfaces. In this way, a smoother impedance transition between waveguide and air is provided in order to enhance the array operating bandwidth. Additionally, we propose a twisting technique, responsible to improve the omnidirectional pattern, by means of reducing the gain ripple in the azimuth plane. Experimental results demonstrate 1.09 GHz bandwidth centered at 24 GHz (4.54% fractional bandwidth), gain up to 14.71 dBi over the operating bandwidth and only 2.7 dB gain variation in the azimuth plane. The proposed antenna array and its enabling techniques present themselves as promising solutions for mm-wave application, including 5G enhanced mobile broadband (eMBB) communications.

Z Lin, P Xiao, B Vucetic, C Cowan (2010)Multiuser Scheduler and FDE Design for SC-FDMA MIMO Systems, In: 2010 IEEE International Conference on Communications (ICC)

This paper presents a novel spatial frequency domain packet scheduling and frequency domain equalization (FDE) algorithm for uplink Single Carrier (SC) Frequency Division Multiple Access (FDMA) multiuser MIMO systems. Our analysis model is confined to 3GPP uplink SC-FDMA transmission with Multi-user (MU) Spatial Division Multiplexing (SDM). The results show that the proposed MU-MIMO scheduler in conjunction with the new FDE singificantly increases the maximum achievable rate and improves the bit error rate (BER) performance for the system under consideration.

P Xiao, C Toal, D Burns, V Fusco, C Cowan (2010)Transmit and Receive Filter Design For OFDM Based WLAN Systems, In: International Conference on Wireless Communications and Signal Processing (WCSP), 2010
Bin Li, Zesong Fei, Zheng Chu, Fuhui Zhou, Kai-Kit Wong, Pei Xiao (2018)Robust Chance-Constrained Secure Transmission for Cognitive Satellite-Terrestrial Networks, In: IEEE Transactions on Vehicular Technology67(5)pp. 4208-4219 Institute of Electrical and Electronics Engineers (IEEE)

Cognitive satellite-terrestrial networks (CSTNs) have been recognized as a promising network architecture for addressing spectrum scarcity problem in next-generation communication networks. In this paper, we investigate the secure transmission for CSTNs where the terrestrial base station (BS) serving as a green interference resource is introduced to enhance the security of the satellite link. Adopting a stochastic model for the channel state information (CSI) uncertainty, we propose a secure and robust beamforming framework to minimize the transmit power, while satisfying a range of outage (probabilistic) constraints concerning the signal-to-interference-plus-noise ratio (SINR) recorded at the satellite user and the terrestrial user, the leakage-SINR recorded at the eavesdropper, as well as the interference power recorded at the satellite user. The resulting robust optimization problem is highly intractable and the key observation is that the highly intractable probability constraints can be equivalently reformulated as the deterministic versions with Gaussian statistics. In this regard, we develop two robust reformulation methods, namely S-Procedure and Bernstein-type inequality restriction techniques, to obtain a safe approximate solution. In the meantime, the computational complexities of the proposed schemes are analyzed. Finally, the effectiveness of the proposed schemes are demonstrated by numerical results with different system parameters.

Zeina Mheich, Wenjuan Yu, Pei Xiao, Atta Quddus, Amine Maaref (2020)On the Performance of HARQ Protocols With Blanking in NOMA Systems, In: IEEE Transactions on Wireless Communications Institute of Electrical and Electronics Engineers

In this paper, we investigate the throughput performance of single-packet and multi-packet hybrid-automatic repeat request (HARQ) with blanking for downlink non-orthogonal multiple access (NOMA) systems. While conventional singlepacket HARQ achieves high throughput at the expense of high latency, multi-packet HARQ, where several data packets are sent in the same channel block, can achieve high throughput with low latency. Previous works have shown that multi-packet HARQ outperforms single-packet HARQ in orthogonal multiple access (OMA) systems, especially in the moderate to high signal-tonoise ratio regime. This work amalgamates multi-packet HARQ with NOMA to achieve higher throughput than the conventional single-packet HARQ and OMA, which has been adopted in the legacy mobile networks. We conduct theoretical analysis for the throughput per user and also investigate the optimization of the power and rate allocations of the packets, in order to maximize the weighted-sum throughput. It is demonstrated that the gain of multi-packet HARQ over the single-packet HARQ in NOMA systems is reduced compared to that obtained in OMA systems due to inter-user interference. It is also shown that NOMAHARQ cannot achieve any throughput gain with respect to OMAHARQ when the error propagation rate of the NOMA detector is above a certain threshold.

P Xiao, R Tafazolli, K Moessner, A Gluhak (2012)Codebook based single-user MIMO system design with widely linear processing, In: IEEE Transactions on Communications60(9)pp. 2408-2414

This work addresses joint transceiver optimization for multiple-input, multiple-output (MIMO) systems. In practical systems the complete knowledge of channel state information (CSI) is hardly available at transmitter. To tackle this problem, we resort to the codebook approach to precoding design, where the receiver selects a precoding matrix from a finite set of pre-defined precoding matrices based on the instantaneous channel condition and delivers the index of the chosen precoding matrix to the transmitter via a bandwidth-constraint feedback channel. We show that, when the symbol constellation is improper, the joint codebook based precoding and equalization can be designed accordingly to achieve improved performance compared to the conventional system. © 2012 IEEE.

W Yin, P Xiao, C Cowan (2010)Grubbs and Wright Algorithms for WiMAX and LTE Systems, In: International Conference on Wireless Communications and Signal Processing (WCSP), 2010

In this paper, we address the problem of interference mitigation with data pre-processing in the 4G uplink systems, and propose to use the Grubbs/Wright algorithm to detect and remove the interference contaminated data. The Markov algorithm is also applied to correct the system errors. The pre-processed data are used for channel estimation and data detection in base stations

L Barbero, P Xiao, T Ratnarajah, M Sellathurai (2010)A Sphere Decoder with Approximate QR Decomposition for Frequency-Selective Channels, In: 2010 IEEE International Conference on Communications (ICC)

This paper presents a method to significantly reduce the preprocessing complexity of the sphere decoder (SD) in frequency-selective channels. The method consists of calculating an approximate QR decomposition (AQRD) of the channel matrix, making use of its special Toeptliz and block-Topelitz structure in single and multiple-antenna frequency-selective channels, respectively. The AQRD obtains the QR decomposition of a small submatrix of the channel matrix and extends that result to the rest of the matrix, resulting in a considerable complexity reduction compared to the original full QR decomposition (FQRD). Simulation results show that, despite the lower complexity of the AQRD, it causes only a small bit error rate (BER) performance degradation in the SD.

Z Lin, P Xiao, B Vucetic, M Sellathurai (2010)Analysis of Receiver Algorithms for LTE SC-FDMA Based Uplink MIMO Systems, In: IEEE Transactions on Wireless Communications9(1)pp. 60-65 IEEE

This letter derives mathematical expressions for the received signal-to-interference-plus-noise ratio (SINR) of uplink Single Carrier (SC) Frequency Division Multiple Access (FDMA) multiuser MIMO systems. An improved frequency domain receiver algorithm is derived for the studied systems, and is shown to be significantly superior to the conventional linear MMSE based receiver in terms of SINR and bit error rate (BER) performance.

L Tian, M Zhao, J Zhong, Pei Xiao, L Wen (2017)A Low Complexity Detector for Downlink SCMA Systems, In: IET Communications11(16)pp. 2433-2439 Institution of Engineering and Technology

Sparse Code Multiple Access (SCMA) is a novel non-orthogonal multiple access scheme for 5G systems, in which the logarithm domain message passing algorithm (Log-MPA) is applied at the receiver to achieve near-optimum performance. However, the computational complexity of Log-MPA detector is still a big challenge for practical implementation, especially for energysensitive user equipments in the downlink scenario. In this paper, a Region-Restricted detector with an improved Log-MPA (RRL detector) is proposed for downlink SCMA systems, in which the complexity is reduced from two perspectives. To avoid unnecessary calculations when searching the superposition constellation exhaustively, the proposed RRL detector updates the function nodes only within a restricted search region. While constellation points outside the search region are neglected, the performance is well maintained which is verified by simulations. Besides, the original Log-MPA heavily relies on exponential operations, resulting in high computational complexity. To solve this problem, an improved Log-MPA is also put forward in this paper to make a better compromise between complexity and performance. Simulation results show that the complexity of the RRL detector is reduced considerably while the bit error rate (BER) performance degrades unnoticeably.

P Xiao, R Carrasco, I Wassell (2005)Turbo Equalization without MMSE Filtering, In: Eighth International Symposium on DSP and Communication Systems, DSPCS 2005 and 4th Workshop on the Internet Telecommunications and Signal Processing, WITSP 2005

The filter-based turbo equalization scheme has been proposed in several papers to avoid the prohibitive complexity imposed by the trellis-based turbo equalization. In the existing literature,the filter-based approach has been solely implemented by a linear MMSE filter, the coeffi cients of which are updated to minimize the mean-square error for every output symbol of the equalizer. A new turbo equalization algorithm is introduced in this paper. It has a lower computational complexity compared to most of the existing MMSE filter-based turbo equalization schemes. The complexity reduction is accomplished by deriving log-likelihood ratios (LLRs) directly from the output of an interference canceler, thus avoiding the MMSE filtering and its inherent matrix inversion for each symbol estimate. Numerical results show that the proposed scheme enables ISI-free transmission for some frequency selective channels.

P Xiao, E Strom (2002)Synchronization Algorithms for Iterative Demodulated M-ary DS-CDMA Systems, In: GLOBECOM'012pp. 1371-1375

In this paper, we developed several algorithms to combat the impact of synchronization errors on demodulating M-ary orthogonal signaling formats in asynchronous DS-CDMA systems. The system under study resembles the uplink of an IS-95 system. The channel is assumed to be a time-varying flat Rayleigh-fading channel. Investigation shows that synchronization errors severely deteriorate the performance of multi-user detectors. We proposed an adaptive algorithm to estimate the errors in synchronization. Based on this information, remedial actions are taken to alleviate the performance degradation caused by sampling the received signals at the incorrect timing. Simulation results show considerable capacity gains when the proposed algorithms are performed to erroneously sampled signals

Sohail Taheri, Mir Ghoraishi, Pei Xiao, Lei Zhang (2017)Efficient Implementation of Filter Bank Multicarrier Systems Using Circular Fast Convolution, In: IEEE Access5pp. 2855-2869 IEEE

In this paper, filter bank based multicarrier systems using fast convolution approach are investigated. We show that exploiting offset quadrature amplitude modulation enables us to perform FFT/IFFT based convolution without overlapped processing and the circular distortion can be discarded as a part of orthogonal interference terms. This property has two advantages. Firstly, it leads to spectral efficiency enhancement in the system by removing the prototype filter transients. Secondly, the complexity of the system is significantly reduced due to using efficient FFT algorithms for convolution. The new scheme is compared with the conventional waveforms in terms of out of band radiation, orthogonality, spectral efficiency and complexity. The performance of the receiver and the equalization methods are investigated and compared with other waveforms through simulations. Moreover, based on the time variant nature of the filter response of the proposed scheme, a pilot based channel estimation technique with controlled transmit power is developed and analysed through lower bound derivations. The proposed transceiver is shown to be a competitive solution for future wireless networks.

P Xiao, W Yin, C Cowan, V Fusco (2011)VBLAST Detection Algorithms Utilizing Soft Symbol Estimate and Noncircular CAI, In: IEEE Transactions on Signal Processing59(5)pp. 2441-2447 IEEE

We address the problem of error propagation inherent in the VBLAST detection process. To this end, two improved VBLAST schemes are proposed. The first one replaces hard decision with soft decision; whereas the other also utilizes soft symbol estimate, but in the meantime exploits the noncircular nature of the residual co-antenna interference (CAI) and noise, it involves refining the error criterion and nulling filter. Simulation results show that both schemes outperform their conventional counterpart and utilization of noncircular CAI significantly alleviates the error propagation problem and improves the performance of the VBLAST detection.

Abdelrahim Mohamed, O Onireti, Muhammad Imran, Haris bin Pervaiz, Pei Xiao, Rahim Tafazolli (2017)Predictive Base Station Activation in Futuristic Energy-Efficient Control/Data Separated RAN, In: IEEE Globecom 2017 Proceedings IEEE

Nowadays, system architecture of the fifth generation (5G) cellular system is becoming of increasing interest. To reach the ambitious 5G targets, a dense base station (BS) deployment paradigm is being considered. In this case, the conventional always-on service approach may not be suitable due to the linear energy/density relationship when the BSs are always kept on. This suggests a dynamic on/off BS operation to reduce the energy consumption. However, this approach may create coverage holes and the BS activation delay in terms of hardware transition latency and software reloading could result in service disruption. To tackle these issues, we propose a predictive BS activation scheme under the control/data separation architecture (CDSA). The proposed scheme exploits user context information, network parameters, BS sleep depth and measurement databases to send timely predictive activation requests in advance before the connection is switched to the sleeping BS. An analytical model is developed and closed-form expressions are provided for the predictive activation criteria. Analytical and simulation results show that the proposed scheme achieves a high BS activation accuracy with low errors w.r.t. the optimum activation time.

P Xiao, VF Fusco (2012)Passive Phase Conjugation Applied to an OFDM-Based Terrestrial Communication System, In: IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY61(5)pp. 2120-2129 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
Chang He, Lei Zhang, Juquan Mao, Aijun Cao, Pei Xiao, Muhammad Imran (2018)Performance Analysis and Optimization of DCT-Based Multicarrier System on Frequency-Selective Fading Channels, In: IEEE Access6pp. 13075-13089 IEEE

Regarded as one of the most promising transmission techniques for future wireless communications, the discrete cosine transform (DCT) based multicarrier modulation (MCM) system employs cosine basis as orthogonal functions for real-modulated symbols multiplexing, by which the minimum orthogonal frequency spacing can be reduced by half compared to discrete Fourier transform (DFT) based one. With a time-reversed prefilter employed at the front of the receiver, interference-free one-tap equalization is achievable for the DCT-based systems. However, due to the correlated pre-filtering operation in time domain, the signal-to-noise ratio (SNR) is enhanced as a result at the output. This leads to reformulated detection criterion to compensate for such filtering effect, rendering minimum-meansquare- error (MMSE) and maximum likelihood (ML) detections applicable to the DCT-based multicarrier system. In this paper, following on the pre-filtering based DCT-MCM model that build in the literature work, we extend the overall system by considering both transceiver perfections and imperfections, where frequency offset, time offset and insufficient guard sequence are included. In the presence of those imperfection errors, the DCTMCM systems are analysed in terms of desired signal power, inter-carrier interference (ICI) and inter-symbol interference (ISI). Thereafter, new detection algorithms based on zero forcing (ZF) iterative results are proposed to mitigate the imperfection effect. Numerical results show that the theoretical analysis match the simulation results, and the proposed iterative detection algorithms are able to improve the overall system performance significantly.

P Xiao, C Cowan, T Ratnarajah, V Fusco, A Fagan (2010)Soft Demapping for IEEE 802.11 OFDM System, In: Royal Irish Academy Colloquium Proceedingspp. 43-46
H Zhou, P Xiao, C Cowan (2010)Robust Adaptive Multiuser Detection for CDMA Frequency-Selective Fading Channels, In: Vehicular Technology Conference Fall (VTC 2010-Fall)pp. 1-6

Robust adaptive multiuser detection schemes are developed for direct-sequence code-division multiple-access (DS-CDMA) multipath frequency-selective fading channels. Multiple access interference (MAI) and intersymbol interference (ISI) are presented in identical format in the expanded signal subspace, which provides convenience for symbol-by-symbol multiuser detection. The proposed multiuse detectors are designed in the expanded signal subspace, and subspace estimation and Kalman filtering algorithms are developed for their adaptive implementation. It is demonstrated by simulation that these adaptive detectors are robust against subspace estimation error and can effectively suppress both MAI and ISI and converge to the optimum SINR.

Zilong Liu, Ping Yang, Yong Liang Guan, Pei Xiao (2020)Cross Z-Complementary Pairs (CZCPs) for Optimal Training in Broadband Spatial Modulation Systems, In: 2020 IEEE International Symposium on Information Theory

Spatial modulation (SM) is a new multiple-input multiple-output (MIMO) paradigm in which only one transmit antenna is activated over every symbol duration. So far, efficient SM training sequences (different from the existing design for conventional MIMO systems) remain largely open. Motivated by this research problem, we introduce a novel class of sequence pairs, called “cross Z-complementary pairs (CZCPs)", each displaying zero-correlation zone (ZCZ) properties for both their aperiodic autocorrelation sums and crosscorrelation sums. A CZCP may be transmitted in two non-orthogonal SM channels and hence proper design should be conducted to minimize the cross-interference of the two constituent sequences. We construct perfect CZCPs based on selected Golay complementary pairs. We show that the training sequences derived from our proposed CZCPs lead to optimal channel estimation performance over frequency-selective SM channels.

Universal filtered multi-carrier (UFMC) systems offer a flexibility of filtering arbitrary number of subcarriers to suppress out of band (OoB) emission, while keeping the orthogonality between subbands and subcarriers within one subband. However, subband filtering may affect system performance and capacity in a number of ways. In this paper, we first propose the conditions for interference-free one-tap equalization and corresponding signal model in the frequency domain for multi-user (MU) UFMC system. Based on this ideal interference-free case, impact of subband filtering on the system performance is analyzed in terms of average signal-to-noise ratio (SNR) per subband, capacity per subcarrier and bit error rate (BER) and compared with the orthogonal frequency division multiplexing (OFDM) system. This is followed by filter length selection strategies to provide guidelines for system design. Next, by taking carrier frequency offset (CFO), timing offset (TO), insufficient guard interval between symbols and filter tail cutting (TC) into consideration, an analytical system model is established. New channel equalization algorithms are proposed by considering the errors and imperfections based on the derived signal models. In addition, a set of optimization criteria in terms of filter length and guard interval/filter TC length subject to various constraints is formulated to maximize the system capacity. Numerical results show that the analytical and corresponding optimal approaches match the simulation results, and the proposed equalization algorithms can significantly improve the BER performance.

P Xiao, E Strom, R Carrasco (2005)Soft Demodulation with Interference Cancellation/Suppression for M-ary DS-CDMA System, In: (488) ACIT - Communication Systems - 2005

The system under study is a convolutionally coded M-ary orthogonal DS-CDMA system in time-varying frequency selective Rayleigh fading channels. With emphasis on the development of several soft demodulation algorithms, we propose an iterative multi-function process integrating demodulation,decoding and multiuser detection in this paper. The performance of the proposed algorithms are evaluated numerically and proved to achieve substantial performance gain compared to the conventional demodulation and decoding scheme, especially when the soft demodulator is assisted by interference cancellation or suppression techniques.

Two approaches of multistage gradient robustification for image contour detection are presented in this paper: two stages of Difference of Estimates and Difference of Estimate followed by an optimal filtering. Watershed transformation is then applied to these robusti ed gradient images to effectively detect image contours which are guaranteed to be in closed form. Multistage gradient robustification provides the flexibility of using different image processing techniques and produces good detection results for the images highly corrupted with noise.

P Xiao, R Carrasco, I Wassell (2005)Performance Analysis of Conventional Detection in BFWA Systems, In: Wireless and Optical Communications Networks, 2005. WOCN 2005. Second IFIP International Conference onpp. 447-452

The systems under study are broadband wireless fixed access (BFWA) systems over multipath fading channels. Conventional detection methods like coherent and non-coherent detection are examined theoretically for both QPSK and 16-QAM modulated BFWA systems in this paper and shown to yield unsatisfactory performance. The theoretical analysis for different algorithms are validated by Monte-Carlo simulations and proved to be accurate. They give us an insight into the physical limitations of the BFWA channels and suggest solutions to improve the capacity and performance of future BFWA systems.

P Xiao, C Cowan, T Ratnarajah, A Fagan (2010)Time Synchronization Algorithms for IEEE 802.11 OFDM Systems, In: IET International Communication Conference on Wireless Mobile and Computing (CCWMC 2009)pp. 287-290

Time synchronization algorithms for OFDM systems using the short and long training symbols are investigated in this paper. We only consider efficient low complexity schemes that are feasible for practical implementations. Different algorithms are compared in the context of IEEE 802.11Wireless Local Area Network (WLAN) systems. Based on the simulation results, some recommendations are made as to how the short and long training symbols can be effectively utilized for synchronization purposes.

Pei Xiao, R Carrasco, I Wassell (2005)Equalization and Decoding Algorithms in Broadband Fixed Wireless Access, In: ACIT - Communication Systems (ACIT-CS 2005) ACTA Press

Broadband Fixed Wireless Access (BFWA) has attracted considerable attention as a promising approach for the next generation high quality and high speed wireless access in frastructure. However, previous studies have shown that BFWA channels are dispersive, they introduce intersym bol interference (ISI) to the transmitted signals, which greatly deteriorates the system performance. In this pa per, we show that the effect of ISI can be greatly alleviated by proper equalization and decoding design, the system performance and capacity can be significantly improved compared to the conventional equalization and decoding scheme.

P Xiao, M Sellathurai (2008)Application of Jacobi Algorithm in Frequency Selective Channels, In: IEEE International Conference on Communications, 2008. ICC '08pp. 886-890

In this paper, we apply the Jacobi iterative algorithm to combat intersymbol interference caused by frequency selective channels. An analytical bound of the proposed equalizer is analyzed in order to gain an insight into its asymptotic performance. Due to the error propagation problem, the potential of this algorithm is not reached in an uncoded system. However, its extension to a coded system with the application of the turbo processing principle results in a new turbo equalization algorithm which demonstrates comparable performance with reduced complexity compared to some existing filter based turbo equalization schemes.

Manijeh Bashar, Kanapathippillai Cumanan, Alister G. Burr, Hien Quoc Ngo, Erik G. Larsson, Pei Xiao (2019)Energy Efficiency of the Cell-Free Massive MIMO Uplink With Optimal Uniform Quantization, In: IEEE Transactions on Green Communications and Networking3(4)pp. 971-987 Institute of Electrical and Electronics Engineers (IEEE)

A cell-free Massive multiple-input multiple-output (MIMO) uplink is considered, where the access points (APs) are connected to a central processing unit (CPU) through limited-capacity wireless microwave links. The quantized version of the weighted signals are available at the CPU, by exploiting the Bussgang decomposition to model the effect of quantization. A closed-form expression for spectral efficiency is derived taking into account the effects of channel estimation error and quantization distortion. The energy efficiency maximization problem is considered with per-user power, backhaul capacity and throughput requirement constraints. To solve this non-convex problem, we decouple the original problem into two sub-problems, namely, receiver filter coefficient design, and power allocation. The receiver filter coefficient design is formulated as a generalized eigenvalue problem whereas a successive convex approximation (SCA) and a heuristic sub-optimal scheme are exploited to convert the power allocation problem into a standard geometric programming (GP) problem. An iterative algorithm is proposed to alternately solve each sub-problem. Complexity analysis and convergence of the proposed schemes are investigated. Numerical results indicate the superiority of the proposed algorithms over the case of equal power allocation.

X Zhang, Lei Zhang, Pei Xiao, D Ma, J Wei, Y Xin (2018)Mixed Numerologies Interference Analysis and Inter-Numerology Interference Cancellation for Windowed OFDM Systems, In: IEEE Transactions on Vehicular Technology67(8)pp. 7047-7061 IEEE

Extremely diverse service requirements are one of the critical challenges for the upcoming fifth-generation (5G) radio access technologies. As a solution, mixed numerologies transmission is proposed as a new radio air interface by assigning different numerologies to different subbands. However, coexistence of multiple numerologies induces the inter-numerology interference (INI), which deteriorates the system performance. In this paper, a theoretical model for INI is established for windowed orthogonal frequency division multiplexing (W-OFDM) systems. The analytical expression of the INI power is derived as a function of the channel frequency response of interfering subcarrier, the spectral distance separating the aggressor and the victim subcarrier, and the overlapping windows generated by the interferer’s transmitter windows and the victim’s receiver window. Based on the derived INI power expression, a novel INI cancellation scheme is proposed by dividing the INI into a dominant deterministic part and an equivalent noise part. A soft-output ordered successive interference cancellation (OSIC) algorithm is proposed to cancel the dominant interference, and the residual interference power is utilized as effective noise variance for the calculation of loglikelihood ratios (LLRs) for bits. Numerical analysis shows that the INI theoretical model matches the simulated results, and the proposed interference cancellation algorithm effectively mitigates the INI and outperforms the state-of-the-art W-OFDM receiver algorithms.

P Xiao, R Carrasco, I Wassell (2006)Filter-Based Turbo Equalization for TCM Signals, In: Global Telecommunications Conference, 2005. GLOBECOM '05.pp. 1407-1411

In this paper, we presents a novel method of turbo equalization and decoding multi-level trellis coded modulation (TCM) signals over frequency selective channels. Results show that the proposed algorithm achieves better performance with reduced complexity compared to previous work on the MMSE filter-based turbo equalization for non-binary coded modulation scheme. The performance gain is accomplished by passing the refined signal from different paths to the TCM decoder as channel value in addition to the a prior information. While the computational complexity is reduced by avoiding matrix inversion for each symbol estimate.

T Yu, M Zhao, J Zhong, J Zhang, P Xiao (2017)Low-complexity graph-based turbo equalization for single-carrier and multi-carrier FTN signaling, In: IET Signal Processing11(7)pp. 838-845 Institution of Engineering and Technology

We propose a novel turbo detection scheme based on the factor graph serial-schedule belief propagation equalization algorithm with low complexity for single-carrier faster-than-Nyquist (FTN) and multicarrier FTN signaling. In this work, the additive white Gaussian noise channel and multi-path fading channels are both considered. The iterative factor graph-based equalization algorithm can deal with severe intersymbol interference and intercarrier interference introduced by the generation of single-carrier and multi-carrier FTN signals, as well as the effect of multi-path fading. With the application of Gaussian approximation, the complexity of the proposed equalization algorithm is significantly reduced. In the turbo detection, Low density parity check code is employed. The simulation results demonstrate that the factor graph-based turbo detection method can achieve satisfactory performance with low complexity.

P Xiao, R Carrasco, I Wassell (2005)Equalization of BFWA Channels: Theory and Analysis, In: IEEE Proceedings of the Eighth International Symposium on Communication Theory and Applications (ISCTA)pp. 404-408

Broadband Fixed Wireless Access (BFWA) is quickly emerging as a strong network access alternative for the delivery of voice, data, Internet, video and multimedia type applications to business and residential customers. However,the physical limitations of the wireless channel present a fundamental technical challenge to system capacity and reliable communications. Previous studies have shown that BFWA channels are dispersive, they introduce intersymbol interference (ISI) to the transmitted signals, which greatly deteriorates the system performance. An equalization algorithm based on the algebra matrix is introduced and theoretically analyzed in this paper. The results show that this algorithm exhibits a good potential to combat ISI under certain conditions, which suggests the solutions for the future BFWA systems.

Z Lin, P Xiao, B Vucetic (2009)SINR Distribution for LTE Downlink Multiuser MIMO Systems, In: IEEE International Conference on Acoustics, Speech and Signal Processing, 2009. ICASSP 2009pp. 2833-2836

The LTE downlink multiuser multiple input multiple output (MIMO) systems are analyzed in this paper. Two spatial division multiplexing (SDM) multiuser MIMO schemes are investigated: Single User (SU) and Multi-user (MU) MIMO schemes. The main contribution of this paper is the establishment of a mathematical model for the Signal to Interference plus Noise Ratio (SINR) distribution for multiuser SDM MIMO systems with frequency domain packet scheduler

R Fa, P Xiao (2009)Joint Data Detection and Phase Recovery for Downlink MC-2D-CDMA Systems, In: IEEE Transactions on Communications57(9)pp. 2782-2789 IEEE

The performance of a downlink synchronous MCCDMA system with joint frequency-time domain spreading (MC-2D-CDMA) is investigated in this paper. We propose a two dimensional adaptive minimum mean square error (MMSE) receiver, which works in decision-directed mode after an initial training period. A subcarrier phase tracker, which comprises a bank of phase locked-loops (PLLs), is employed in the receiver to track the fading phase variability. Furthermore, a simplified phase tracker structure is proposed to reduce the system complexity. The performance of the data detector and the behavior of the phase tracker are analyzed theorectically in this paper and are shown to match the simulation results. Both analysis and simulation indicate that the proposed system outperforms the conventional MC-DS-CDMA systems by exploiting frequency diversity and facilitating subcarrier synchronization.

P Xiao, M Sellathurai (2008)Analysis of A Simplified Channel Estimator for MIMO Frequency Selective Channels, In: IEEE Vehicular Technology Conference,VTC Spring 2008pp. 988-993

Channel estimation for multiple-input, multiple-output (MIMO) systems is studied in this paper. In particular, we present a simplified MIMO channel estimator based on orthogonal design. The performance of the proposed scheme is theoretically analyzed and compared to that of the optimum maximum likelihood estimator. The effect of non-orthogonality of the training sequences is investigated. Some modifications of the proposed estimator with sample stacking and averaging are introduced to further improve the estimation performance. This simplified scheme is evaluated in the context of the WiMAX MIMO systems in terms of mean square error for the channel estimation and bit error rate for the space-time turbo equalization. Both analytical and simulation results indicate that despite of its low computational complexity, this simplified estimator leads to minimum variance unbiased estimation and achieves identical performance to that of the maximum likelihood estimator.

P Xiao, E Strom, R Carrasco (2005)Comparison of Different Soft Demodulation and Decoding Algorithms in Coded M-ary Orthogonal DS-CDMA Systems, In: Wireless and Optical Communications Networks, 2005pp. 578-583

The system under study is a convolutionally coded and orthogonally modulated DS-CDMA system in time-varying frequency selective Rayleigh fading channels. In this paper, we investigate several iterative schemes based on soft demodulation and decoding algorithms. The performance of different strategies are evaluated numerically and proved to achieve substantial performance gain compared to the conventional hard decision based scheme, especially when the soft demodulator is assisted by decision directed channel estimation and interference cancellation techniques, and also when demodulation and decoding are performed jointly in an iterative manner.

P Xiao, M Sellathurai (2009)Iterative Receiver Design for MIMO Systems with Improper Signal Constellations, In: IEEE International Conference on Communications, 2009. ICC '09.

In this paper, we propose a novel iterative receiver strategy for uncoded multiple-input, multiple-output (MIMO) systems employing improper signal constellations. The proposed scheme is shown to achieve superior performance and faster convergence without the loss of spectrum efficiency compared to the conventional iterative receivers. The superiority of this novel approach over conventional solutions is verified by both simulation and analytical results.

Mehdi Ghorbani, Mohsen Khalily, Pei Xiao, Rahim Tafazolli (2019)A Wideband High Flat Gain Waveguide-Fed Aperture Antenna Using Superstrate and Shield, In: IEEE Xplore Digital Library IEEE

In this paper, a high flat gain waveguide-fed aperture antenna has been proposed. For this purpose, two layers of FR4 dielectric as superstrates have been located in front of the aperture to enhance the bandwidth and the gain of the antenna. Moreover, a conductive shield, which is connected to the edges of the ground plane and surrounding aperture and superstrates, applied to the proposed structure to improve its radiation characteristics. The proposed antenna has been simulated with HFSS and optimized with parametric study and the following results have been obtained. The maximum gain of 13.0 dBi and 0.5-dBi gain bandwidth of 25.9 % (8.96 – 11.63 GHz) has been achieved. The 3-dBi gain bandwidth of the proposed antenna is 40.7% (8.07-12.20 GHz), which has a suitable reflection coefficient (≤-10dBi) in whole bandwidth. This antenna comprises a compact size of (1.5λ×1.5λ), easy structure and low-cost fabrication.

P Xiao, E Strom (2002)Performance of Iterative DS-CDMA M-ary Demodulation in The Presence of Synchronization Errors, In: IEEE 53rd VTC Spring 20013pp. 1703-1707

The robustness of different interactive schemes for demodulating M-ary orthogonal signaling formats in asynchronous DS-CDMA systems to the synchronization errors is addressed. The system under study resembles the uplink of an IS-95 system. The channel is assumed to be a time-varying flat Rayleigh-fading channel. Our simulation results show that the performance degradation for the considered multi-user detectors increase linearly with synchronization errors and eventually converge to that of conventional matched filter. In order to see the impact of channel estimation on the performance of multi-user detectors, we made some comparisons between non-coherent and coherent variants of the detection algorithms

P Xiao, E Strom, R Carrasco (2006)BER Performance Analysis of Multistage PIC Scheme in Asynchronous DS-CDMA System over Unbalanced Multipath Fading Channels, In: IEEE Global Telecommunications Conference, 2005. GLOBECOM '05.pp. 3763-3767

In this paper, we provide a theoretical evaluation for the multistage parallel interference cancellation (PIC) scheme in a DS-CDMA system with orthogonal modulation and long scrambling codes. The studied system operates on the reverse link in a time-varying multipath Rayleigh fading channel. Unequal powers are assumed among different paths, which is usually the case in practical situations. The proposed analysis gives insight into the performance and capacity one can expect from the PIC based receivers under different situations

J Wu, SD Blostein, Q Chen, P Xiao (2012)Joint Time-Frequency Diversity for Single-Carrier Block Transmission in Frequency Selective Channels, In: IEICE TRANSACTIONS ON FUNDAMENTALS OF ELECTRONICS COMMUNICATIONS AND COMPUTER SCIENCESE95A(11)pp. 1912-1920 IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG
Alexandr M. Kuzminskiy, Pei Xiao, Rahim Tafazolli (2019)Spectrum Sharing with Decentralized Occupation Control in Rule Regulated Networks, In: IEEE Transactions on Cognitive Communications and Networking(99) Institute of Electrical and Electronics Engineers (IEEE)

Decentralized dynamic spectrum allocation (DSA) that exploits adaptive antenna array interference mitigation diversity at the receiver, is studied for interference-limited environments with high level of frequency reuse. The system consists of base stations (BSs) that can optimize uplink frequency allocation to their user equipments (UEs) to minimize impact of interference on the useful signal, assuming no control over resource allocation of other BSs sharing the same bands. To this end“, good neighbor” (GN) rules allow effective trade-off between the equilibrium and transient decentralized DSA behavior if the performance targets are adequate to the interference scenario. In this paper, we 1) extend the GN rules by including a spectrum occupation control that allows adaptive selection of the performance targets; 2) derive estimates of absorbing state statistics that allow formulation of applicability areas for different DSA algorithms; 3) define a semi-analytic absorbing Markov chain model and study convergence probabilities and rates of DSA with occupation control including networks with possible partial breaks of the GN rules. For higher-dimension networks, we develop simplified search GN algorithms with occupation and power control and demonstrate their efficiency by means of simulations.

P Xiao, R Carrasco, I Wassell (2004)Equalization and Decoding in BFWA Systems, In: PROCEEDINGS OF INTERNATIONAL SYMPOSIUM ON BROADBAND COMMUNICATIONS; 13pp. 12-15
Arunprakash Jayaprakash, Hongzhi Chen, Pei Xiao, Barry G. Evans, Yingnan Zhang, Jing Yuan Li, Adegbenga Awoseyila (2019)Analysis of Candidate Waveforms for Integrated Satellite-Terrestrial 5G Systems, In: Proceedings of the 2019 IEEE 2nd 5G World Forum (5GWF’19)

Satellites will play an indispensable part in 5G roll out and the common use of new radio (NR) air interface will enable this. Satellite-terrestrial integration requires adaptations to the existing NR standards and demands further study on the potential areas of impact. From a physical layer perspective, the candidate waveform has a critical role in addressing design constraints to support non-terrestrial networks (NTN). In this paper, the adaptability of frequency-localized orthogonal frequency division multiplexing (OFDM)-based candidate waveforms and solutions are discussed in the context of physical layer attributes of non-linear satellite channel conditions. The performance of the new air interface waveforms are analysed in terms of spectral confinement, peak-to-average power ratio (PAPR), power amplifier efficiency, robustness against non-linear distortions and carrier frequency offset (CFO).

P Xiao, E Strom, R Carrasco (2004)Estimation of Time-Varying Multipath Rayleigh Fading Channels in Asynchronous DS-CDMA Systems, In: Personal, Indoor and Mobile Radio Communications, 2004. PIMRC 2004. 15th IEEE International Symposium on (Volume:4 )4pp. 2570-2575

We present the channel estimation algorithms for the asynchronous direct-sequence code-division multiple access (DS-CDMA) systems employing the orthogonal signalling formats and long scrambling codes. The performance of a communication system depends largely on its ability to retrieve an accurate measurement of the underlying channel. We investigated channel estimation algorithms under different conditions. The estimated channel information is used to enable the coherent data detection to combat the detrimental effect of multipath propagation of the transmitted signal as well as multiple access interference (MAI). Different channel estimation schemes are evaluated and compared in terms of mean square error (MSE) of the channel estimate and the bit error rate (BER) performance. Based on our analysis and numerical results, some recommendations are made on how to choose appropriate channel estimators in practical systems.

P Xiao, E Strom (2003)Multiuser Detection and Channel Estimation Algorithms for M-ary DS-CDMA Systems in Multipath Rayleigh Fading Channels, In: Personal, Indoor and Mobile Radio Communications, 2003. PIMRC 2003. 14th IEEE Proceedings on2pp. 1829-1834

In this paper, we present different linear and nonlinear iterative data detection schemes for the asynchronous direct-sequence code-division multiple access (DS-CDMA) systems employing orthogonal signalling formats and long scrambling codes. Compared to the conventional receiver and other noncoherent multiuser detectors, coherent multiuser detection schemes achieve much better performance provided that the channels are accurately estimated. To this end, we proposed several channel estimation algorithms to estimate multipath Rayleigh fading channels. Different data detection and channel estimation schemes are compared in terms of BER performance. Based on the numerical results, some recommendations are made on how to choose multiuser detectors and channel estimation algorithms in practical CDMA systems.

Zheng Chu, Fuhui Zhou, Pei Xiao, hengyu Zhu, De Mi, Naofal Al-Dhahir, Rahim Tafazolli (2018)Resource Allocation for Secure Wireless Powered Integrated Multicast and Unicast Services with Full Duplex Self-Energy Recycling, In: IEEE Transactions on Wireless Communications IEEE

This paper investigates a secure wireless powered integrated service system with full duplex self-energy recycling. Specifically, an energy-constrained information transmitter (IT), powered by a power station (PS) in a wireless fashion, broadcasts two types of services to all users: a multicast service intended for all users, and a confidential unicast service subscribed to by only one user while protecting it from any other unsubscribed users and an eavesdropper. Our goal is to jointly design the optimal input covariance matrices for the energy beamforming, the multicast service, the confidential unicast service, and the artificial noises from the PS and the IT, such that the secrecy-multicast rate region (SMRR) is maximized subject to the transmit power constraints. Due to the non-convexity of the SMRR maximization (SMRRM) problem, we employ a semidefinite programmingbased two-level approach to solve this problem and find all of its Pareto optimal points. In addition, we extend the SMRRM problem to the imperfect channel state information case where a worst-case SMRRM formulation is investigated. Moreover, we exploit the optimized transmission strategies for the confidential service and energy transfer by analyzing their own rank-one profile. Finally, numerical results are provided to validate our proposed schemes.

Zeina Mheich, Zilong Liu, Pei Xiao, Amine Maaref (2020)Delayed Bit Interleaved Coded Sparse Code Multiple Access, In: IEEE Transactions on Vehicular Technologypp. 1-1 Institute of Electrical and Electronics Engineers (IEEE)

Targeting to provide reliable short-packet communications with tens of bits in machine-type networks, we investigate a novel sparse code multiple access (SCMA) scheme called delayed bit-interleaved coded SCMA (DBIC-SCMA). At the transmitter side, a delay module is introduced between each channel encoder and SCMA mapper such that data bits from different channel codewords can be mapped to an identical SCMA codeword. We present the main components and principles for the transmitter of DBIC-SCMA, followed by a pre-decoding assisted receiver design which exploits systematic and rate-adaptive properties of certain channel codes. Our simulation results show that the proposed DBIC-SCMA leads to significant improvements in error rate performance over the classical BIC-SCMA scheme.

M Al-Imari, M Ghoraishi, P Xiao, R Tafazolli (2015)Game Theory Based Radio Resource Allocation for Full-Duplex Systems, In: IEEE 81st Vehicular Technology Conference (VTC Spring), 2015pp. 1-5

Full-duplex transceivers enable transmission and reception at the same time on the same frequency, and have the potential to double the wireless system spectral efficiency. Recent studies have shown the feasibility of full-duplex transceivers. In this paper, we address the radio resource allocation problem for full-duplex system. Due to the self-interference and inter-user interference, the problem is coupled between uplink and downlink channels, and can be formulated as joint uplink and downlink sum-rate maximization. As the problem is non-convex, an iterative algorithm is proposed based on game theory by modelling the problem as a noncooperative game between the uplink and downlink channels. The algorithm iteratively carries out optimal uplink and downlink resource allocation until a Nash equilibrium is achieved. Simulation results show that the algorithm achieves fast convergence, and can significantly improve the full-duplex performance comparing to the equal resource allocation approach. Furthermore, the full-duplex system with the proposed algorithm can achieve considerable gains in spectral efficiency, that reach up to 40%, comparing to half-duplex system.

Lei Zhang, A Ijaz, Pei Xiao, Rahim Tafazolli (2017)Multi-service System: An Enabler of Flexible 5G Air-Interface, In: IEEE Communications Magazine55(10)pp. 152-159 IEEE

Multi-service system is an enabler to flexibly support diverse communication requirements for the next generation wireless communications. In such a system, multiple types of services co-exist in one baseband system with each service having its optimal frame structure and low out of band emission (OoBE) waveforms operating on the service frequency band to reduce the inter-service-band-interference (ISvcBI). In this article, a framework for multi-service system is established and the challenges and possible solutions are studied. The multi-service system implementation in both time and frequency domain is discussed. Two representative subband filtered multicarrier (SFMC) waveforms: filtered orthogonal frequency division multiplexing (F-OFDM) and universal filtered multi-carrier (UFMC) are considered in this article. Specifically, the design methodology, criteria, orthogonality conditions and prospective application scenarios in the context of 5G are discussed. We consider both single-rate (SR) and multi-rate (MR) signal processing methods. Compared with the SR system, the MR system has significantly reduced computational complexity at the expense of performance loss due to inter-subband-interference (ISubBI) in MR systems. The ISvcBI and ISubBI in MR systems are investigated with proposed low-complexity interference cancelation algorithms to enable the multi-service operation in low interference level conditions.

B Zhou, Q Chen, H Wymeersch, P Xiao, L Zhao (2016)Variational Inference-based Positioning with Nondeterministic Measurement Accuracies and Reference Location Errors, In: IEEE Transactions on Mobile Computing

Cooperative network localization plays an important role in wireless sensor network (WSN), wherein neighboring sensor nodes will help each other to calibrate their locations. However, due to the dynamic wireless propagation environment and different surroundings, the measurement accuracy at different network nodes is different and varies over time. In this paper, the uncertainties in both measurement accuracy and reference node locations are considered to account for the impact of different surrounding environments and the initial node location errors on the cooperative network localization. A mean-field variational inference-based positioning (VIP) algorithm is proposed for cooperative network localization. The mechanism of the proposed VIP algorithm, the convergence properties, implementation complexity, and the parallel implementation structure are presented to show that the VIP algorithm provides an effective mechanism to incorporate and share the localization information among all network nodes for an improved localization performance. Finally, a concise Cramer-Rao lower bound (CRLB) is derived to reveal the principle of localization error propagation. It is disclosed that the localization error propagation principle is similar to the Ohm’s Law in circuit theory, which provides a new insight into the impact of the measurement accuracy, the reference node location errors and the number of reference nodes on the cooperative network localization performance.

Hongzhi Chen, De Mi, Zheng Chu, Pei Xiao, Rahim Tafazolli (2018)Rate-Splitting for Multigroup Multicast Beamforming in Multicarrier Systems, In: Proceedings of 19th IEEE international workshop on signal processing advances in wireless communications (SPAWC) Institute of Electrical and Electronics Engineers (IEEE)

In this paper, we consider multigroup multicast transmissions with different types of service messages in an overloaded multicarrier system, where the number of transmitter antennas is insufficient to mitigate all inter-group interference. We show that employing a rate-splitting based multiuser beamforming approach enables a simultaneous delivery of the multiple service messages over the same time-frequency resources in a non-orthogonal fashion. Such an approach, taking into account transmission power constraints which are inevitable in practice, outperforms classic beamforming methods as well as current standardized multicast technologies, in terms of both spectrum efficiency and the flexibility of radio resource allocation.

Bogdan Dorneanu, Hang Ruan, Abdelrahim Mohamed, Mohamed Heshmat, Yang Gao, Pei Xiao, Harvey Arellano-Garcia (2019)Towards fault detection and self-healing of chemical processes over wireless sensor networks, In: Industry 4.0 – Shaping the Future of the Digital World Taylor & Francis

This contribution introduces a framework for the fault detection and healing of chemical processes over wireless sensor networks. The approach considers the development of a hybrid system which consists of a fault detection method based on machine learning, a wireless communication model and an ontology-based multi-agent system with a cooperative control for the process monitoring.

The system under study is a convolutionally coded and orthogonally modulated DS-CDMA system in time-varying frequency selective Rayleigh fading channels. After convolutional encoding and block interleaving, information bits are mapped to M- ary orthogonal Walsh sequences. In conventional systems, Mary symbol demodulation and convolutional decoding are conducted separately in the receiver, only hard decisions are passed between these two blocks. In this paper, we propose an integrated scheme based on some soft demodulation and decoding algorithms. Instead of making hard decision on the transmitted M-ary symbols from the received observations, we compute the reliability value for the code bits from which orthogonal symbols are formed. This soft information is then deinterleaved and decoded. The detected bits are fed back to demodulator for channel estimation and multiuser detection. For channel decoding, we use Log-MAP algorithm instead of VA (Viterbi algorithm) for better performance. Maximum achievable performance for the system is obtained by iterating this joint soft demodulation and Log-MAP decoding process. The performance of this strategy is evaluated numerically and proved to significantly outperform the conventional partitioned and hard decision based scheme.

P Xiao, E Strom (2003)Delay Estimation and Data Detection in Long-Code DS-CDMA System, In: Communications, 2003. APCC 2003. The 9th Asia-Pacific Conference on2pp. 584-589

In this paper, we aim at solving the problem of joint delay estimation and data detection of the orthogonal modulated signals in the asynchronous DS-CDMA system employing aperiodic long spreading codes over fading channels. The general system requirement of low error rate in data demodulation necessitates the reliable synchronization mechanisms. Synchronization of CDMA signals with long spreading codes is a more challenging task than that of CDMA signals with short spreading codes. In this work, two algorithms are introduced to perform acquisition and tracking of orthogonal modulated signals with long spreading codes, followed by data detection. The numerical results show that when applying to the asynchronous system with random propagation delays, the proposed algorithms approximate the performance that is attainable in the synchronized and chip-aligned system.

Y Wu, P Xiao, H Zhang, W Yin, Z Lin (2012)Blind Multiuser Detection Based on Subspace Estimation, In: Journal of Communication and Computer2012(9)pp. 1038-1044 David publishing
Ahmed Almradi, Michail Matthaiou, Pei Xiao, Vincent F. Fusco (2020)Hybrid Precoding for Massive MIMO with Low Rank Channels: A Two-Stage User Scheduling Approach, In: IEEE Transactions on Communications Institute of Electrical and Electronics Engineers (IEEE)

To fully reap the benefits of massive multiple-input multiple-output hybrid analog and digital precoding in frequency division duplexing single-cell systems, a two-stage precoder is developed utilizing the signal-to-leakage-plus-noise ratio metric. The main idea of this technique is to jointly design the analog precoder based only on the long-term channel statistics information at the transmitter, i.e., the channel mean and reconstructed reduced rank covariance statistics, while the digital precoder is designed based on the instantaneous channel state information of the reduced dimensionality effective reconstructed channel. Consequently, we can significantly reduce the downlink training and uplink feedback overhead analogously to the rank of the resultant effective channel. The two extremes of full channel state information at the transmitter (CSIT) and statistical CSIT are also investigated. The performance gap between the full and statistical CSIT corroborates the importance of the proposed two-stage CSIT approach. These precoders are then extended to multi-cell systems. It is shown that the digital baseband precoder design problem reduces to the generalized Rayleigh quotient problem, while the analog precoder design problem reduces to the quotient trace problem, also known as the ratio trace problem. These dimensionality reduction problems are solved via the generalized eigenvalue decomposition method. Finally, in the presence of multiuser diversity where only a subset of the users are scheduled, to considerably alleviate the channel estimation and feedback overhead burden, a low-complexity one-stage and two-stage CSIT joint user scheduler and precoder algorithms are developed.

Hongzhi Chen, De Mi, Manuel Fuentes, David Vargas, Eduardo Garro, Jose Luis Carcel, Belkacem Mouhouche, Pei Xiao, Rahim Tafazolli (2018)Pioneering studies on LTE eMBMS: Towards 5G Point-to-Multipoint Transmissions, In: Proceedings of The Tenth IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM2018) Institute of Electrical and Electronics Engineers (IEEE)

The first 5G (5th generation wireless systems) New Radio Release-15 was recently completed. However, the specification only considers the use of unicast technologies and the extension to point-to-multipoint (PTM) scenarios is not yet considered. To this end, we first present in this work a technical overview of the state-of-the-art LTE (Long Term Evolution) PTM technology, i.e., eMBMS (evolved Multimedia Broadcast Multicast Services), and investigate the physical layer performance via link-level simulations. Then based on the simulation analysis, we discuss potential improvements for the two current eMBMS solutions, i.e., MBSFN (MBMS over Single Frequency Networks) and SCPTM (Single-Cell PTM). This work explicitly focus on equipping the current eMBMS solutions with 5G candidate techniques, e.g., multiple antennas and millimeter wave, and its potentials to meet the requirements of next generation PTM transmissions.

P Xiao, M Sellathurai, T Ratnarajah (2007)A Low Complexity Scheme for Transmit Diversity Over Frequency Selective Channels, In: GLOBECOM '07pp. 4086-4090

A low complexity transmit diversity scheme is derived in this paper in order to overcome the prohibitive complexity imposed by the maximum likelihood detection for the systems with space-time block code (STBC) over frequency selective channels. By taking advantage of multipath propagation and exploiting temporal diversity gain, the proposed turbo equalization algorithm significantly improves the system performance compared to the original Alamouti algorithm as well as the conventional minimum mean square error (MMSE) detection scheme.

M Al-Imari, P Xiao, MA Imran, R Tafazolli (2014)Radio Resource Allocation for Uplink OFDMA Systems with Finite Symbol Alphabet Inputs, In: IEEE Transactions on Vehicular Technology63(4)pp. 1917-1921 IEEE

In this paper, we consider the radio resource allocation problem for uplink OFDMA system. The existing algorithms have been derived under the assumption of Gaussian inputs due to its closed-form expression of mutual information. For the sake of practicality, we consider the system with Finite Symbol Alphabet (FSA) inputs, and solve the problem by capitalizing on the recently revealed relationship between mutual information and Minimum Mean-Square Error (MMSE). We first relax the problem to formulate it as a convex optimization problem, then we derive the optimal solution via decomposition methods. The optimal solution serves as an upper bound on the system performance. Due to the complexity of the optimal solution, a low-complexity suboptimal algorithm is proposed. Numerical results show that the presented suboptimal algorithm can achieve performance very close to the optimal solution and outperforms the existing suboptimal algorithms. Furthermore, using our proposed algorithm, significant power saving can be achieved in comparison to the case when Gaussian input is assumed.

P Xiao, E Strom (2003)Pilot-Aided Acquisition Algorithms for Asynchronous DS-CDMA Systems, In: European Transactions on Telecommunications14(1)pp. 89-96 Wiley

The problem of estimating propagation delays of orthogonally modulated signals in asynchronous DS-CDMA systems over time-varing Rayleigh-fading channels is treated in this paper. The maximum likelihood (ML) estimator and its unaffordable complexity for implementation are discussed. Some suboptimal solutions, e.g., whitened sliding correlator, MMSE estimator, subspace-based estimator, approximate ML estimator, are proposed to combat the multiple access interference in the fading channels. The performance of these estimators are evaluated with the computer simulations and shown to have better acquisition performance than the standard sliding correlator. They also achieve reduced computational complexity compared with the ML estimator, while maintaining an acceptable performance degradation.

In this paper, we tackle the problem of theoretical evaluation for the multistage parallel interference cancellation (PIC) scheme in a direct-sequence code division multiple access (DS-CDMA) system with orthogonal modulation and long scrambling codes. The studied system operates on the reverse link in a time varying multipath Rayleigh fading channel. By applying the Central Limit Theorem and some other approximations to multiple access interference (MAI) and intersymbol interference (ISI), as well as assuming identically distributed chips from a single interferer, the bit error rate (BER) performance of the PIC scheme at any stage can be recursively computed from the signal-to-noise ratio, number of users, the number of path per user, processing gain of the CDMA system, and the average received power of each path. For completeness, the BER expression is derived for chip synchronous and chip asynchronous systems over both equal and unequal power multipath channels. The proposed analysis is validated by the Monte Carlo simulations and proved to be reasonably accurate, and it gives insight into the performance and capacity one can expect from PIC-based receivers under different situations. For instance, the analytical results can be used to examine the convergence property, multipath diversity gains, and near-far resistance of the PIC scheme.

Lei Zhang, Chang He, Juquan Mao, Ayesha Ijaz, Pei Xiao (2017)Channel Estimation and Optimal Pilot Signals for Universal Filtered Multi-carrier (UFMC) Systems, In: 28th PIMRC Workshop 2017 Proceedings IEEE

We propose channel estimation algorithms and pilot signal optimization for the universal filtered multi-carrier (UFMC) system based on the comb-type pilot pattern. By considering the least square linear interpolation (LSLI), discrete Fourier transform (DFT), minimum mean square error (MMSE) and relaxed MMSE (RMMSE) channel estimators, we formulate the pilot signals optimization problem by minimizing the estimation MSE subject to the power constraint on pilot tones. The closed-form optimal solutions and minimum MSE are derived for LSLI, DFT, MMSE and RMMSE estimators.

Arooj Mubashara Siddiqui, Barry Evans, Yingnan Zhang, Pei Xiao (2020)Capacity Enhancement of High Throughput Low Earth Orbit Satellites in a constellation (HTS-LEO) in a 5G network, In: Advances in Intelligent Systems and Computing Springer-Verlag

The global telecommunication market aims to fulfil future ubiquitous coverage and rate requirements by integrating terrestrial communications with multiple spot beam high throughput satellites (HTS). In this paper a new scheme is proposed to connect multiple Low Earth Orbit (LEO) satellites in a constellation to a single gateway to support integrated-satellite-terrestrial networks. A single gateway with multiple steerable antenna arrays is proposed for reduction in gateway numbers and cost. Using a power allocation strategy, the target is to maximize the gateway link capacity of the HTS-LEO satellites for operation including feasible used cases studies of 3GPP for necessary adaptations in a 5G system. Firstly, an objective function is established to find the optimal power levels required. Secondly the interference from neighbouring satellite beams is considered to achieve maximum capacity. Mathematical formulations are developed for this non-convex problem. Simulation results show that the proposed system architecture improves capacity and meets the dynamic demand better than traditional methods.

P Xiao, E Strom (2004)Soft Interference Cancellation and Channel Estimation in Uncoded Asynchronous DS-CDMA System, In: Vehicular Technology Conference, 2004. VTC 2004-Spring. 2004 IEEE 59th3pp. 1688-1692

The conventional interference cancellation receiver is subject to performance degradation due to incorrect decisions on interference subtracted from the received signal. This paper aims at deriving algorithms to improve the performance of interference cancellation and channel estimation in an uncoded asynchronous DS-CDMA system with orthogonal modulation. Two soft cancellation schemes, one based on the maximum a posterior (MAP), the other based on the nonlinear minimum mean square error (MMSE) criterion are presented and proved to be superior to the conventional PIC scheme with minor increase in complexity. Furthermore, the best system performance (2dB gain in a 21-user system) is observed when the derived soft information is also used for channel estimation.

Lixia Xiao, Pei Xiao, Zilong Liu, Wenjua Yu, Harald Haas, Lajos Hanzo (2020)A Compressive Sensing Assisted Massive SM-VBLAST System: Error Probability and Capacity Analysis, In: IEEE Transactions on Wireless Communicationspp. 1-1 IEEE

The concept of massive spatial modulation (SM) assisted vertical bell labs space-time (V-BLAST) (SM-VBLAST) system [1] is proposed, where SM symbols (instead of conventional constellation symbols) are mapped onto the VBLAST structure. We show that the proposed SM-VBLAST is a promising massive multiple input multiple output (MIMO) candidate owing to its high throughput and low number of radio frequency (RF) chains used at the transmitter. For the generalized massive SM-VBLAST systems, we first derive both the upper bounds of the average bit error probability (ABEP) and the lower bounds of the ergodic capacity. Then, we develop an efficient error correction mechanism (ECM) assisted compressive sensing (CS) detector whose performance tends to achieve that of the maximum likelihood (ML) detector. Our simulations indicate that the proposed ECM-CS detector is suitable both for massive SM-MIMO based point-to-point and for uplink communications at the cost of a slightly higher complexity than that of the compressive sampling matching pursuit (CoSaMP) based detector in the high SNR region.

P Xiao, R Carrasco, I Wassell (2007)Bit Error Rate Evaluation of Linear Equalization in BFWA Systems, In: International Journal of Communication Systems20(2)pp. 235-246 Wiley

The bit error rate performance of broadband wireless fixed access (FWA) systems over multipath fading channels is investigated in this paper. Linear MMSE equalization is examined theoretically for 16-QAM and QPSK modulated FWA systems and shown to yield unsatisfactory performance. The theoretical analysis is validated by Monte-Carlo simulations and proved to be reasonably accurate. It provides us an insight into the physical limitations imposed by the FWA channels and suggest solutions to improve the capacity and performance of future FWA systems. Copyright © 2006 John Wiley & Sons, Ltd.

P Xiao, E Strom (2006)Correction of Extrinsic Information for Iterative Decoding in Serially Concatenated DS-CDMA Systems, In: IEEE Transactions on Wireless Communications5(3)pp. 591-602 IEEE
P Xiao, E Strom (2002)Applications of Maximum Likelihood Algorithm in Asynchronous CDMA Systems, In: Spread Spectrum Techniques and Applications, 2002 IEEE Seventh International Symposium on1pp. 208-213

We treat the problems of propagation delay and channel estimation as well as data detection of orthogonally modulated signals in an asynchronous DS-CDMA system over fading channels using the maximum likelihood (ML) approach. The overwhelming computational complexity of the ML algorithm makes it unfeasible for implementation. The emphasis of this paper is to reduce its complexity by some approximation methods. The derived approximative ML schemes are compared with conventional algorithms as well as some others, e.g., the parallel interference cancellation (PIC) for data detection and the subspace-based algorithm for acquisition

The present disclosure is related to a transmitter, a receiver, a method for transmitting information, and a method of receiving information in a system which simplifies receiver structure and improves the performance in an orthogonal frequency-division multiplexing (OFDM) system. The transmitter comprises a module for generating a passive phase conjugation probe signal for transmission. The receiver comprises a passive phase conjugation module. The method for transmitting information comprises generating a passive phase conjugation probe signal for transmission. The method for receiving information comprises extracting OFDM symbols from a received signal using a method which comprises performing passive phase conjugation on the received signal.

P Xiao, E Strom (2004)BER Performance Analysis of Multistage PIC Scheme in An Asynchronous DS-CDMA System with Long Scrambling Codes, In: Vehicular Technology Conference, 2004. VTC 2004-Spring. 2004 IEEE 59th2pp. 952-957

We tackle the problem of theoretical evaluation of the multistage parallel interference cancellation (PIC) scheme in a DS-CDMA system with orthogonal modulation and long scrambling codes. The studied system operates on the reverse link in a time-varying multipath Rayleigh fading channel. By applying the central limit theorem to multiple access interference (MAI) and intersymbol interference (ISI), as well as identically distributed chips from a single interferer, the bit error rate (BER) performance of the PIC scheme at any stage can be recursively computed from the signal-to-noise ratio, number of users, the number of paths per user, processing gain of the CDMA system, as well as the average received power of each path. The proposed approximative analysis is validated by Monte-Carlo simulations and proved to be accurate, and it gives insight into the performance and capacity one can expect from the PIC based receivers under different situations.

De Mi, Lei Zhang, Mehrdad Dianati, Sami Muhaidat, Pei Xiao (2018)A Self-Calibration Scheme for TDD Massive MIMO with Imperfect Channel Estimation, In: Proceedings of The Tenth IEEE Sensor Array and Multichannel Signal Processing Workshop (SAM2018) Institute of Electrical and Electronics Engineers (IEEE)

Exploiting channel reciprocity, time-divisionduplexing (TDD) operated massive multiple-input multipleoutput (MIMO) systems are able to acquire the channel state information with a reasonable overhead of channel estimation. However, in practical scenarios, the imperfections in channel reciprocity can significantly degrade the system performance. In this work, we propose a novel self calibration scheme for the maximum ratio transmission in TDD multi-user massive MIMO systems to compensate for the imperfect channel reciprocity, with considerations of imperfect channel estimation. The proposed scheme shows the greater robustness to a compound effect of channel reciprocity error and channel estimation error, compared with the traditional self calibration scheme that is widely used in massive MIMO systems.

Matthew Bridges, Mohsen Khalily, Mohammad Abediankasgari, Demos Serghiou, Pei Xiao, Rahim Tafazolli (2020)High Isolation 8×8 MIMO Antenna Design for 5G Sub-6 GHz Smartphone Applications, In: 2020 International Conference on UK-China Emerging Technologies (UCET)

In this paper, an 8×8 Multiple Input Multiple Output (MIMO) antenna design for Fifth Generation (5G) sub- 6GHz smartphone applications is presented. The antenna elements are based off a folded quarter wavelength monopole that operate at 3.4-3.8GHz. Isolation between antenna elements is provided through physical distancing. The fabricated antenna prototype outer casing is made from Rogers R04003C with dimensions based on future 5G enabled phones. Measured results show an operating bandwidth of 3.32 to 3.925GHz (S11 < 6dB) with a transmission coefficient < -14.7dB. A high total efficiency for an antenna array is also obtained at 70-85.6%. The design is suitable for MIMO communications exhibited by an Envelope Correlation Coefficient (ECC) < 0.014. To conclude a Specific Absorption Rate (SAR) model has been constructed and presented showing the user’s effects on the antenna’s Sparameter results. Measurements of the amount of power absorbed by the head and hand during operation have also been simulated.

Viet Hung Nguyen, S Ng, W Liang, Pei Xiao, L Hanzo (2018)A Network-Coding Aided Road-Map of Large-scale Near-capacity Cooperative Communications, In: IEEE Access6(1)pp. 21592-21620 IEEE

In the paper, we present a road-map towards a Nearcapacity Large-scale Multi-user Cooperative-communications (NLMC) system, where all the evolution paths converge to the construction of the NLMC system. More specifically, we will summarise all relevant schemes appearing on the road-map in the unified frame-work of forward error correction (FEC). Various Network Coding (NC) design paradigms are highlighted for illustrating how the NLMC systems might be designed for meeting diverse design criteria in the context of cooperative and cognitive communications, where the channel capacity of the NLMC systems is used for comparing the different design paradigms.

Lei Zhang, A Ijaz, Juquan Mao, Pei Xiao, Rahim Tafazolli (2017)Multi-service Signal Multiplexing and Isolation for Physical-Layer Network Slicing (PNS), In: VTC2017-Fall Proceedings

Network slicing has been identified as one of the most important features for 5G and beyond to enable operators to utilize networks on an as-a-service basis and meet the wide range of use cases. In physical layer, the frequency and time resources are split into slices to cater for the services with individual optimal designs, resulting in services/slices having different baseband numerologies (e.g., subcarrier spacing) and / or radio frequency (RF) front-end configurations. In such a system, the multi-service signal multiplexing and isolation among the service/slices are critical for the Physical-Layer Network Slicing (PNS) since orthogonality is destroyed and significant inter-service/ slice-band-interference (ISBI) may be generated. In this paper, we first categorize four PNS cases according to the baseband and RF configurations among the slices. The system model is established by considering a low out of band emission (OoBE) waveform operating in the service/slice frequency band to mitigate the ISBI. The desired signal and interference for the two slices are derived. Consequently, one-tap channel equalization algorithms are proposed based on the derived model. The developed system models establish a framework for further interference analysis, ISBI cancelation algorithms, system design and parameter selection (e.g., guard band), to enable spectrum efficient network slicing.

W Liu, M Sellathurai, P Xiao, C Tang, J Wei (2009)Improved Design of Two and Four-group Decodable STBCs with Larger Diversity Product for Eight Transmit Antennas, In: IEEE International Conference on Acoustics, Speech and Signal Processing, 2009. ICASSP 2009pp. 2737-2740

Recently, full rate and full diversity two-group (2 Gp) and four-group (4 Gp) decodable space-time block codes (STBC) derived from quasi-orthogonal STBC (QSTBC) and designed under diversity product maximization criterion have been proposed. In this paper, we derive an upper bound of diversity product for those STBCs and discover that the diversity product of the current 2 Gp-QSTBC and 4 Gp-QSTBC has the potential to approach the upper bound for 8 transmit antennas. To this end, we propose an improved design of 2 Gp and 4 Gp STBC with increased diversity product for 8 transmit antennas by allowing sufficient number of dimensions for constellation rotation. The diversity product of the proposed two-group decodable STBC achieves the derived upper bound.

B Zhou, Q Chen, Pei Xiao (2017)The Error Propagation Analysis of the Received Signal Strength-based Simultaneous Localization and Tracking in Wireless Sensor Networks, In: IEEE Transactions on Information Theory63(6)pp. 3983-4007 IEEE

Simultaneous localization and tracking (SLAT) in wireless sensor networks (WSNs) involves tracking the mobile target while calibrating the nearby sensor node locations. In practice, a localization error propagation (EP) phenomenon will arise, due to the existence of the latest tracking error, target mobility, measurement error and reference node location errors. In this case, the SLAT performance limits are crucial for the SLAT algorithm design and WSN deployment, and the study of localization EP principle is desirable. In this paper, we focus on the EP issues for the received signal strength-based SLAT scheme, where the measurement accuracy is assumed to be spatialtemporal- domain doubly random due to the target mobility, environment dynamics and different surroundings at different reference nodes. Firstly, the Cramer-Rao lower bound (CRLB) is derived to unveil both the target tracking EP and the node location calibration EP. In both cases, the EP principles turn out to be in a consistent form of the Ohm’s Law in circuit theory. Secondly, the asymptotic CRLB analysis is then presented to reveal that both EP principles scale with the inverse of sensor node density. Meanwhile, it is shown that, the tracking and calibration accuracy only depends on the expectation of the measurement precision. Thirdly, the convergence conditions, convergence properties and the balance state of the target tracking EP and the location calibration EP are examined to shed light on the EP characteristics of the SLAT scheme. Finally, numerical simulations are presented to corroborate the EP analysis.

P Xiao, M Alina, M Gabbouj (1996)Segmentation of Noisy Images with Watershed Transformationpp. 263-265
Chang He, Lei Zhang, Juquan Mao, Aijun Cao, Pei Xiao, Muhammad Imran (2016)Output SNR Analysis and Detection Criteria for Optimum DCT-Based Multicarrier System, In: Proceedings of ISWCS'2016 IEEE

The discrete cosine transform (DCT) based multicarrier system is regarded as one of the complementary multicarrier transmission techniques for 5th Generation (5G) applications in near future. By employing cosine basis as orthogonal functions for multiplexing each real-valued symbol with symbol period of T , it is able to reduce the minimum orthogonal frequency spacing to 1/(2T ) Hz, which is only half of that compared to discrete Fourier transform (DFT) based multicarrier systems. Critical to the optimal DCT-based system design that achieves interference-free single-tap equalization, not only both prefix and suffix are needed as symmetric extension of information block, but also a so-called front-end pre-filter is necessarily introduced at the receiver side. Since the pre-filtering process is essentially a time reversed convolution for continuous inputs, the output signal-to-noise ratio (SNR) for each subcarrier after filtering is enhanced. In this paper, the impact of pre-filtering on the system performance is analyzed in terms of ergodic output SNR per subcarrier. This is followed by reformulated detection criterion where such filtering process is taken into consideration. Numerical results show that under modified detection criteria, the proposed detection algorithms improve the overall bit error rate (BER) performance effectively.

A Sohail, M Al-Imari, P Xiao, BG Evans (2014)Theoretical Analysis of Power Saving in Cognitive Radio with Arbitrary Inputs, In: IEEE Transactions on Vehicular Technology IEEE

In Orthogonal Frequency Division Multiplexing (OFDM) based cognitive radio systems, power optimization algorithms have been evaluated to maximize the achievable data rates of the Secondary User (SU). However, unrealistic assumptions are made in the existing work, i.e. a Gaussian input distribution and traditional interference model that assumes frequency division multiplexing modulated Primary User (PU) with perfect synchronization between the PU and the SU. In this paper, we first derive a practical interference model by assuming OFDM modulated PU with imperfect synchronization. Based on the new interference model, the power optimization problem is proposed for the Finite Symbol Alphabet (FSA) input distribution (i.e., M-QAM), as used in practical systems. The proposed scheme is shown to save transmit power and to achieve higher data rates compared to the Gaussian optimized power allocation and the uniform power loading schemes. Furthermore, a theoretical framework is established in this paper to estimate the power saving by evaluating optimal power allocation for the Gaussian and the FSA input. Our theoretical analysis is verified by simulations and proved to be accurate. It provides guidance for the system design and gives deeper insights into the choice of parameters affecting power saving and rate improvement.

Zilong Liu, Pei Xiao, Su Hu (2019)Low-PAPR Preamble Design for FBMC Systems, In: IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

This paper presents a family of training preambles for offset QAM (OQAM) based filter-bank multi-carrier (FBMC) modulations with low peak-to-average power ratio (PAPR) property. We propose to use binary Golay sequences as FBMC preambles and analyze the maximum PAPR for different numbers of zero guard symbols. For both the PHYDYAS and Hermite prototype filters with overlapping factor of 4, as an illustration of the proposed preambles, we show that a preamble PAPR less than 3 dB can be achieved with probability of one, when three or more zero guard symbols are inserted in the vicinity of each preamble.

Amir Alizadeh Ghannad, Mohsen Khalily, Pei Xiao, Rahim Tafazolli, Ahmed A. Kishk (2019)Enhanced Matching and Vialess Decoupling of Nearby Patch Antennas for MIMO System, In: IEEE Antennas and Wireless Propagation Letterspp. 1-1 Institute of Electrical and Electronics Engineers (IEEE)

Simultaneous improvement of matching and isolation for a modified two-element microstrip patch antenna array is proposed. Two simple patch antennas in a linear array structure are designed, whereas, the impedance matching and isolation are improved without using any conventional matching networks. The presented low profile multifunctional via-less structure comprises of only two narrow T-shaped stubs connected to feed lines, a narrow rectangular stub between them, and a narrow rectangular slot on the ground plane. This design provides a simple, compact structure with low mutual coupling, low cost and no adverse effects on the radiation and resonance. To validate the design, a compact very-closely-spaced antenna array prototype is fabricated at 5.5 GHz which is suitable for multiple-input-multiple-output (MIMO) systems. The measured and simulated results are in good agreement with a 16 dB, and 40 dB of improvements in the matching and isolation, respectively.

Juquan Mao, Lei Zhang, Pei Xiao, Konstantinos Nikitopoulos (2020)Filtered OFDM: An Insight into Intrinsic In-Band Interference and Filter Frequency Response Selectivity, In: IEEE Access8 Institute of Electrical and Electronics Engineers

The future mobile networks will face challenges in support of heterogeneous services over a unified physical layer, calling for a waveform with good frequency localization. Filtered orthogonal frequency division multiplexing (f-OFDM), as a representative subband filtered waveform, can be employed to improve the spectrum localization of orthogonal frequency-division multiplexing (OFDM) signal. However, the applied filtering operations will impact the performance in various aspects, especially for narrow subband cases. Unlike existing studies which mainly focus its benefits, this paper investigates two negative consequences inflicted on single subband f-OFDM systems: in-band interference and filter frequency response (FFR) selectivity. The exact-form expression for the in-band interference is derived, and the effect of FFR selectivity is analyzed for both single antenna and multiple antenna cases. The in-band interference-free and nearly-free conditions for f-OFDM systems are studied. A low-complexity blockwise parallel interference cancellation (BwPIC) algorithm and a pre-equalizer are proposed to tackle the two issues caused by the filtering operations, respectively. Numerical results show that narrower subbands suffer more performance degradation compared to wider bands. In addition, the proposed BwPIC algorithm effectively suppresses interference, and pre-equalized f-OFDM (pf-OFDM) considerably outperforms f- OFDM in both single antenna and multi-antenna systems.

A Sohail, M Al-Imari, Pei Xiao, B Evans (2014)Power Allocation for Joint Interweave and Underlay Cognitive Radio Systems with Arbitrary Input Distributions, In: Wireless Communications and Networking Conference Proceedingspp. 1838-1843 Institute of Electrical and Electronics Engineers (IEEE)

In the literature, the Gaussian input is assumed in power optimization algorithms. However, this assumption is unrealistic, whereas practical systems use Finite Symbol Alphabet (FSA) input, (e.g., M-QAM). In this paper, we consider the optimal power for joint interweave and underlay CR systems given FSA inputs. We formulated our problem as convex optimization and solved it through general convex optimization tools. We observed that the total SU transmit power is always less than the power budget and remains in interference limited region only over the considered distance range. Therefore, we re-derive optimal power with interference constraint only in order to reduce the complexity of the algorithm by solving it analytically. Numerical results reveal that, for the considered distance range, the transmit power saving and the rate gain with the proposed algorithm is in the range 16-92% and 7-34%, respectively, depending on the modulation scheme (i.e., BPSK, QPSK and 16-QAM) used.

Hongzhi Chen, De Mi, Zheng Chu, Pei Xiao (2020)Link-Level Performance of Rate-splitting based Downlink Multiuser MISO Systems, In: IEEE International Symposium on Personal, Indoor and Mobile Radio Communications
C He, L-L Yang, P Xiao, MA Imran (2015)DS-CDMA Assisted Visible Light Communications Systems, In: 2015 IEEE 20TH INTERNATIONAL WORKSHOP ON COMPUTER AIDED MODELLING AND DESIGN OF COMMUNICATION LINKS AND NETWORKS (CAMAD)pp. 27-32
A Zafar, MA Imran, P Xiao, A Cao, Y Gao (2015)Performance Evaluation and Comparison of Different Multicarrier Modulation Schemes, In: 2015 IEEE 20TH INTERNATIONAL WORKSHOP ON COMPUTER AIDED MODELLING AND DESIGN OF COMMUNICATION LINKS AND NETWORKS (CAMAD)pp. 49-53
P Xiao, R Carrasco, I Wassell (2006)AML Turbo Equalization for Space Time Block Coded Systems, In: The Mediterranean Journal of Computers and Networks2(2)pp. 40-49
M Abdullahi, P Xiao (2016)Performance Analysis and Soft Demapping for Coded MIMO-OFDM Systems, In: Proceedings of the Thirteenth International Symposium on Wireless Communication Systems

Multiple input multiple output-Orthogonal frequency division multiplexing (MIMO-OFDM) is a viable solution for providing high data rate services in harsh channel environments. The optimum receivers for them are those based on the maximum likelihood criterion. However, they have a prohibitive complexity especially when channel dimensions are high and coding is employed. Zero Forcing (ZF) and Linear Minimum Mean Square Error (MMSE) receivers on the other hand provide practicable and low complexity solutions for detection, but require soft demappers to deduce the soft bits information contained in each of the received symbols. In this work, we present the ZF and MMSE receiver analysis of a bit interleaved and coded MIMO-OFDM system and propose a soft output demapper based on MMSE equalizer output to demap the information needed for viterbi decoding. A comparison of the proposed soft demapper with conventional soft demappers in literature show a significant performance improvement. We also noticed that it is more advantageous to apply the proposed demapper on a MIMO-OFDM system employing higher modulation schemes.

Lixia Xiao, Pei Xiao, Hang Ruan, Naoki Ishikawa, Lei Lu, Yue Xiao, Lajos Hanzo (2020)Differentially-encoded rectangular spatial modulation approaches the performance of its coherent counterpart, In: IEEE Transactions on Communications IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

A simplified rectangular differential spatial modulation (S-RDSM) scheme is conceived for massive multiple-input multiple-output (MIMO) systems dispensing with the channel state information (CSI). In the proposed S-RDSM scheme, the information bits are first mapped to a conventional SM symbol and then rectangular differential encoding is invoked between a pair of SM symbols. Then a non-coherent detector relying on a forgetting factor is developed, which requires no CSI at the receiver. Explicitly, a low-complexity hard limited maximum likelihood (HL-ML) detector is conceived for our generalized SRDSMscheme,whichischaracterizedbyourtheoreticalanalysis. Furthermore, we derive the optimal forgetting factor in closed form, which is capable of significantly reducing the complexity of the associated optimization. Finally, the upper bounds of the average bit error probability (ABEP) are derived using the moment generating function (MGF), and are validated by our simulation results. Both the theoretical and simulation results have shown that the proposed S-RDSM system outperforms the existing non-coherent schemes, despite operating at 10% of the benchmarker’s complexity, whilst approaching the performance of its coherent SM counterpart at a comparable complexity.

Wanming Hao, Gangcan Sun, Jiankang Zhang, Pei Xiao, Lajos Hanzo (2020)Secure Millimeter Wave Cloud Radio Access Networks Relying on Microwave Multicast Fronthaul, In: IEEE Transactions on Communications Institute of Electrical and Electronics Engineers

In this paper, we investigate the downlink secure beamforming (BF) design problem of cloud radio access networks (C-RANs) relying on multicast fronthaul, where millimeter-wave and microwave carriers are used for the access links and fronthaul links, respectively. The base stations (BSs) jointly serve users through cooperating hybrid analog/digital BF. We first develop an analog BF for cooperating BSs. On this basis, we formulate a secrecy rate maximization (SRM) problem subject both to a realistic limited fronthaul capacity and to the total BS transmit power constraint. Due to the intractability of the non-convex problem formulated, advanced convex approximated techniques, constrained concave convex procedures and semidefinite programming (SDP) relaxation are applied to transform it into a convex one. Subsequently, an iterative algorithm of jointly optimizing multicast BF, cooperative digital BF and the artificial noise (AN) covariance is proposed. Next, we construct the solution of the original problem by exploiting both the primal and the dual optimal solution of the SDP-relaxed problem. Furthermore, a per-BS transmit power constraint is considered, necessitating the reformulation of the SRM problem, which can be solved by an efficient iterative algorithm. We then eliminate the idealized simplifying assumption of having perfect channel state information (CSI) for the eavesdropper links and invoke realistic imperfect CSI. Furthermore, a worst-case SRM problem is investigated. Finally, by combining the so-called S-Procedure and convex approximated techniques, we design an efficient iterative algorithm to solve it. Simulation results are presented to evaluate the secrecy rate and demonstrate the effectiveness of the proposed algorithms.

W Yin, P Xiao (2009)Optimal Power Allocation Strategy for TBLAST based 4G System, In: Engineering1(2)pp. 91-98 Scientific Research Publishing Inc

There is a big demand for increasing number of subscribers in the fourth generation mobile communication systems. However, the system performance is limited by multi-path propagations and lack of efficient power allocation algorithms in conventional wireless communication systems. Optimal resource allocation and interference cancellation issues are critical for the improvement of system performance such as throughput and transmission reliability. In this paper, a turbo coded bell lab space time system (TBLAST) with optimal power allocation techniques based on eigen mode, Newton and convex optimization method and carrier-interference-and-noise ratio (CINR) are proposed to improve link reliability and to increase throughput with reasonable computational complexity. The proposed scheme is evaluated by Monte-Carlo simulations and is shown to outperform the conventional power allocation scheme.

P Xiao, E Strom (2002)Acquisition of Orthogonal Modulated Signals in Rayleigh-Fading Channels, In: European Wireless 2002pp. 811-816

The problem of estimating propagation delays of the orthogonal modulated signals in asynchronous DS-CDMA system over fading channels is treated in this paper. The system under study resembles the uplink of an IS-95 system. The channel is assumed to be a time-varing flat Rayleigh-fading channel. The shortcoming of the sliding correlator as the standard method of code acquisition is examined and three robustified versions of delay estimators,namely whitened sliding correlator, subspace based delay estimator and MMSE based delay estimator are proposed to combat the multiple access interference (MAI) in the Rayleigh-fading channels. The performance of these estimators are compared with the computer simulations as a function of different parameters, e.g., the number of pilots, near-far resistance, signal to noise ratio,etc..

Yasin Kabiri, Alejandro L. Borja, James Kelly, Pei Xiao (2019)A technique for MIMO antenna design with flexible element number and pattern diversity, In: IEEE Accesspp. 1-1 Institute of Electrical and Electronics Engineers (IEEE)

This paper presents a new technique for designing Multiple Input Multiple (MIMO) Output antennas having pattern diversity. Massive MIMO is expected to form part of 5G communications and will require antennas having a very large number of elements. However, due to the size limitation, it is highly challenging to preserve high isolation between the ports. Pattern diversity technique are also highly desirable and can facilitate MIMO systems with diversity gain. However, achieving that within a compact antenna where there is limited space between the elements is also challenging. In this paper a technique is introduce and applied to 4-element and 6-element MIMO antennas. This technique can improve the isolation between the ports and it also yields pattern diversity for MIMO antennas with various numbers of elements. The technique is verified via experimental measurement.

Su Fong Chien, Charilaos C. Zarakovitis, Qiang Ni, Pei Xiao (2019)Stochastic Asymmetric Blotto Game Approach for Wireless Resource Allocation Strategies, In: IEEE Transactions on Wireless Communications Institute of Electrical and Electronics Engineers (IEEE)

The development of modellings and analytical tools to structurise and study the allocation of resources through noble user competitions become essential, especially considering the increased degree of heterogeneity in application and service demands that will be cornerstone in future communication systems. Stochastic asymmetric Blotto games appear promising to modelling such problems, and devising their Nash equilibrium (NE) strategies by anticipating the potential outcomes of user competitions. In this regard, this paper approaches the generic energy efficiency problem with a new stochastic asymmetric Blotto game paradigm to enable the derivation of joint optimal bandwidth and transmit power allocations by setting multiple users to compete in multiple auction-like contests for their individual resource demands. The proposed modelling innovates by abstracting the notion of fairness from centrally-imposed to distributed-competitive, where each user’s pay-off probability is expressed as quantitative bidding metric, so as, all users’ actions can be interdependent, i.e., each user attains its utility given the allocations of other users, which eliminates the chance of low valued carriers not being claimed by any user, and, in principle, enables the full utilisation of wireless resources. We also contribute by resolving the allocation problem with low complexity using new mathematical techniques based on Charnes-Cooper transformation, which eliminate the additional coefficients and multipliers that typically appear during optimisation analysis, and derive the joint optimal strategy as a set of linear single-variable functions for each user. We prove that our strategy converges towards a unique, monotonous and scalable NE, and examine its optimality, positivity and feasibility properties in detail. Simulation comparisons with relevant studies confirm the superiority of our approach in terms of higher energy efficiency performance, fairness index and quality-of-service provision.

Shadi Danesh, Ali Araghi, Mohsen Khalily, Pei Xiao, Rahim Tafazolli (2020)Millimeter Wave Phased Array Antenna Synthesis Using a Machine Learning Technique for Different 5G Applications, In: Proceedings of the 2020 IEEE International Symposium on Networks, Computers and Communications (ISNCC'20) Institute of Electrical and Electronics Engineers (IEEE)

A machine learning (ML) technique has been used to synthesis a linear millimetre wave (mmWave) phased array antenna by considering the phase-only synthesis approach. For the first time, gradient boosting tree (GBT) is applied to estimate the phase values of a 16-element array antenna to generate different far-field radiation patterns. GBT predicts phases while the amplitude values have been equally set to generate different beam patterns for various 5G mmWave transmission scenarios such as multicast, unicast, broadcast and unmanned aerial vehicle (UAV) applications.

Chang He, Aijun Cao, Lixia Xiao, Lei Zhang, Pei Xiao, Konstantinos Nikitopoulos (2019)Index modulation assisted DCT-OFDM with Enhanced Transceiver Design, In: Proceedings of the 53rd IEEE International Conference on Communications (IEEE ICC 2019) Institute of Electrical and Electronics Engineers (IEEE)

An index modulation (IM) assisted Discrete Cosine Transform based Orthogonal Frequency Division Multiplexing (DCT-OFDM) with Enhanced Transmitter Design (termed as EDCT-OFDM-IM) is proposed. It amalgamates the concept of Discrete Cosine Transform assisted Orthogonal Frequency Division Multiplexing (DCT-OFDM) and Index Modulation (IM) to exploit the design freedom provided by the double number of available subcarrier under the same bandwidth. In the proposed EDCT-OFDM-IM scheme, the maximum likelihood (ML) detector used for symbol bits and index bits recovering is derived and the sophisticated designing guidelines for EDCTOFDM-IM are provided. Based on the derived pairwise error event probability, a theoretical upper bound on the average biterror probability (ABEP) of EDCT-OFDM-IM is provided over multipath fading channels. Furthermore, the maximum peak-toaverage power ratio (PAPR) of our proposed EDCT-OFDM-IM scheme is derived and compared to than the general Discrete Fourier Transform (DFT) based OFDM-IM counterpart.

Chang He, Pei Xiao, Lei Zhang, Juquan Mao, Aijun Cao, Konstantinos Nikitopoulos (2017)Efficient DCT-MCM Detection for Single and Multi-Antenna Wireless Systems, In: Proceedings of the 2017 IEEE 28th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC) IEEE

The discrete cosine transform (DCT) based multicarrier modulation (MCM) system is regarded as one of the promising transmission techniques for future wireless communications. By employing cosine basis as orthogonal functions for multiplexing each real-valued symbol with symbol period of T , it is able to maintain the subcarrier orthogonality while reducing frequency spacing to 1/(2T ) Hz, which is only half of that compared to discrete Fourier transform (DFT) based multicarrier systems. In this paper, following one of the effective transmission models by which zeros are inserted as guard sequence and the DCT operation at the receiver is replaced by DFT of double length, we reformulate and evaluate three classic detection methods by appropriately processing the post- DFT signals both for single antenna and multiple-input multipleoutput (MIMO) DCT-MCM systems. In all cases, we show that with our reformulated detection approaches, DCT-MCM schemes can outperform, in terms of error-rate, conventional OFDMbased systems.

M Ghoraishi, W Jiang, P Xiao, R Tafazolli (2015)Subband Approach for Wideband Self-Interference Cancellation in Full-Duplex Transceiver, In: 2015 INTERNATIONAL WIRELESS COMMUNICATIONS & MOBILE COMPUTING CONFERENCE (IWCMC)pp. 1139-1143
Mohammad Abediankasgari, Mohsen Khalily, Shadi Danesh, Pei Xiao, Rahim Tafazolli (2020)Reconfigurable Dielectric Resonator Antenna Using an Inverted U-shaped Slot, In: Proceedings of the 2020 IEEE International Symposium on Networks, Computers and Communications (ISNCC'20) Institute of Electrical and Electronics Engineers (IEEE)

A novel reconfigurable dielectric resonator antenna (DRA) employed a T-Shaped microstrip-fed structure in order to excite the dielectric resonator is presented. By carefully adjusting the location of the inverted U-shaped slot, switches, and length of arms, the proposed antenna can support WLAN wireless system. In addition, the presented DRA can be proper for cognitive radio because of availability switching between wideband and narrowband operation. The proposed reconfigurable DRA consisting of a Roger substrate with relative permittivity 3 and a size of 20 mm × 30 mm × 0.75 mm and a dielectric resonator (DR) with a thickness of 9 mm and the overall size of 18 mm × 18 mm. Moreover, the antenna has been fabricated and tested, which test results have enjoyed a good agreement with the simulated results. As well as this, the measured and simulated results show the reconfigurability that the proposed DRA provides a dual-mode operation and also three different resonance frequencies as a result of switching the place of arms.

Lixia Xiao, Pei Xiao, Y Xiao, C Wu, Hung Nguyen, Ibrahim Hemadeh, L Hanzo (2018)Transmit Antenna Combination Optimization for Generalized Spatial Modulation Systems, In: IEEE Access6pp. 41866-41882 IEEE

Generalized Spatial Modulation (GSM), where both the Transmit Antenna Combination (TAC) index and the Amplitude Phase Modulation (APM) symbols convey information, is a novel low-complexity and high efficiency Multiple Input Multiple Output (MIMO) technique. In Conventional GSM (C-GSM), the legitimate TACs are selected randomly to transmit the APM symbols. However, the number of the TACs must be a power of two, hence the excess TACs are discarded, resulting in wasting some resource. To address these issues, in this paper, an optimal TAC set-aided Enhanced GSM (E-GSM) scheme is proposed, where the optimal TAC set is selected with the aid of the Channel State Information (CSI) by maximizing the Minimum Euclidean Distance (MED). Furthermore, a Hybrid Mapping GSM (HM-GSM) scheme operating without CSI knowledge is investigated, where the TAC selection and bit-to-TAC mapping are both taken into consideration for optimizing the Average Hamming Distance (AHD). Finally, an Enhanced High Throughput GSM (E-HT-GSM) scheme is developed, which makes full use of all the TACs. This scheme is capable of achieving an extra one bit transmission rate per time slot. Moreover, rotated phase is employed and optimized for the reused TACs. Our simulation results show that the proposed E-GSM system and HM-GSM system are capable of outperforming the CGSM system. Furthermore, the E-HT-GSM system is capable of obtaining one extra bit transmission rate per time slot compared to the C-GSM system.

F. Mehran, K. Nikitopoulos, P. Xiao, Q. Chen (2015)Rateless wireless systems: gains, approaches, and challenges, In: 2015 IEEE China Summit and International Conference on Signal and Information Processing (ChinaSIP) Proceedingspp. 751-755 IEEE

State-of-the-art channel coding schemes promise data rates close to the wireless channel capacity. However, efficient link adaptation techniques are required in order to deliver such throughputs in practice. Traditional rate adaptation schemes, which are reactive and try to “predict” the transmission mode that maximizes throughput based on “transmission quality indicators”, can be highly inefficient in an evolving wireless ecosystem where transmission can become increasingly dynamic and unpredictable. In such scenarios, “rateless” link adaptation can be highly beneficial. Here, we compare popular rateless approaches in terms of gains and practicality in both traditional and more challenging operating scenarios. We also discuss challenges that need to be addressed to make such systems practical for future wireless communication systems.

Shujun Han, Xiaodong Xu, Zilong Liu, Pei Xiao, Klaus Moessner, Xiaofeng Tao, Ping Zhang (2019)Energy-Efficient Short Packet Communications for Uplink NOMA-based Massive MTC Networks, In: IEEE Transactions on Vehicular Technology Institute of Electrical and Electronics Engineers (IEEE)

The 5th generation (5G) mobile networks and beyond need to support massive machine-type communications (MTC) devices with limited available radio resources. In this paper, we study the power-domain non-orthogonal multiple access (NOMA) technology to support energy-efficient massive MTC networks, where MTC devices exchange information using sporadic and low-rate short packets. We investigate the subchannel allocation and power control policy to maximize the achievable effective energy efficiency (EE) for uplink NOMA-based massive MTC networks, taking into account of short-packet communication characteristics. We model the subchannel allocation problem as a multi-agent Markov decision process and propose an efficient Q-learning algorithm to solve it. Furthermore, we obtain the optimal transmission power policy by approximating the achievable effective rate of uplink NOMA-based short packet communications. Compared with the existing OFDMA scheme, simulations validate that the proposed scheme can improve the achievable effective EE of massive MTC networks with 5.93%.

Ali Araghi, Mohsen Khalily, Amirhossein Alizadeh Ghannad, Pei Xiao, Rahim Tafazolli (2019)Compact Dual Band Antenna for Off-Body-Centric Communications, In: Proceedings of the 13th European Conference on Antennas and Propagation (EuCAP 2019) European Association on Antennas and Propagation

A compact size, dual-band wearable antenna for off-body communication operating at the both 2.45 and 5.8 GHz industrial, scientific, and medical (ISM) band is presented. The antenna is a printed monopole on an FR4 substrate with a modified loaded ground plane to make the antenna profile compact. Antennas’ radiation characteristics have been optimized while the proposed antenna placed close to the human forearm. The fabricated antenna operating on the forearm has been measured to verify the simulation results.

A Sohail, M Al-Imari, P Xiao, B Evans (2013)Cognitive Radio Systems: Multicarrier Modulation and Power Allocation Challenges, In: Journal of Electrical & Electronic Systems3(1)pp. 1-6

The rapid development of modern communication services results in high data rate requirements from the end user. It is challenging to meet high data rate requirements because of prevailing issues such as spectrum scarcity and spectrum underutilization due to fixed spectrum assignment policy. Cognitive Radio (CR), being the enabler of dynamic spectrum management techniques, has the capability to tackle these issues by proficiently implementing spectrum sharing schemes using Multicarrier Modulation (MCM) techniques. In CR system, where the Primary User (PU) and the Secondary User (SU) co-exist in the same frequency band, mutual interference (i.e., from SU to PU and vice versa) is a limiting factor on the achievable capacity of both the PU and the SU. Power allocation in MCM based CR systems aims to dynamically control the transmit power on each subcarrier of the SU in order to reduce the mutual interference. Furthermore, combining multiple antennas with MCM is regarded as a very attractive solution for the CR communications to effectively enhance data rate without demanding additional bandwidth and transmit power.

Chun Xu Mao, Mohsen Khalily, Long Zhang, Pei Xiao, Yuhang Sun, Douglas H. Werner (2020)Compact Patch Antenna with Vertical Polarization and Omni-Directional Radiation Characteristics, In: IEEE Transactions on Antennas and Propagation Institute of Electrical and Electronics Engineers

This communication proposes a compact, low-profile patch antenna with omni-directional radiation pattern and vertical polarization. A pair of shorted patches are excited in-phase to achieve the omni-directivity and the vertical polarization, simultaneously. The principle is to excite two back-to-back arranged shorted patches to generate symmetrical electric field (E-field) distributions normal to the ground plane. Analytical study on how to generate the omni-directional radiation pattern is carried out. Base on this study, we found the spacing in-between the two patches have little influence on the radiation characteristics, which provides another flexibility in the design. In addition, the shape of the patch and the corresponding field distribution are investigated to further improve the omni-directivity. To improve the impedance bandwidth, resonant structures are inserted in-between the patches, producing the 2nd order response in frequency. The antenna has been fabricated and characterized, and the measured results are in a reasonable agreement with the simulations, showing that the proposed antenna is suitable for potential surface-mount wireless applications.

An iterative turbo decoder based cross layer error recovery scheme for compressed video is presented in this paper. The soft information exchanged between two convolutional decoders are reinforced both by channel coded parity and video compression syntactical information. An algorithm to identify the video frame boundaries in corrupted compressed sequences is formulated. The paper continues to propose algorithms to deduce the correct values for selected fields in the compressed stream. Modifying the turbo extrinsic information using these corrections act as reinforcements in the turbo decoding iterative process. The optimal number of turbo iterations suitable for the proposed system model is derived using EXIT charts. Simulation results reveal that a transmission power saving of 2.28% can be achieved using the proposed methodology. Contrary to typical joint cross layer decoding schemes, the additional resource requirement is minimal since the proposed decoding cycle does not involve the decompression function.

Yusha Liu, Lie-Liang Yang, Pei Xiao, Harald Haas, Lajos Hanzo (2019)Spatial modulated multicarrier sparse code-division multiple access, In: IEEE Transactions on Wireless Communications Institute of Electrical and Electronics Engineers (IEEE)

This paper proposes a novel spatial-modulated multicarrier sparse code-division multiple access (SM/MC-SCDMA) system for achieving massive connectivity in device-centric wireless communications. In our SM/MC-SCDMA system, the advantages of both MC signalling and SM are amalgamated to conceive a low-complexity transceiver. Sparse frequency-domain spreading is utilized to mitigate the peak-to-average power ratio (PAPR) of MC signalling, as well as to facilitate low-complexity detection using the message passing algorithm. We then analyze the single-user bit error rate performance of SM/MC-SCDMA systems communicating over frequency-selective fading channels. Furthermore, the performance of SM/MC-SCDMA systems is evaluated based on both Monte-Carlo simulations and analytical results. We demonstrate that our low-complexity SM/MCSCDMA transceivers are capable of achieving near-maximum likelihood (ML) performance even when the normalized userload is as high as two, hence constituting a variable solution to support massive connectivity in device-centric wireless systems.

Wanming Hao, Gangcan Sun, Fuhui Zhou, De Mi, Jia Shi, Pei Xiao, Victor C. M. Leung (2019)Energy-Efficient Hybrid Precoding Design for Integrated Multicast-Unicast Millimeter Wave Communications with SWIPT, In: IEEE Transactions on Vehicular Technology Institute of Electrical and Electronics Engineers (IEEE)

In this paper, we investigate the energy-efficient hybrid precoding design for integrated multicast-unicast millimeter wave (mmWave) system, where the simultaneous wireless information and power transform is considered at receivers. We adopt two sparse radio frequency chain antenna structures at the base station (BS), i.e., fully-connected and subarray structures, and design the codebook-based analog precoding according to the different structures. Then, we formulate a joint digital multicast, unicast precoding and power splitting ratio optimization problem to maximize the energy efficiency of the system, while the maximum transmit power at the BS and minimum harvested energy at receivers are considered. Due to its difficulty to directly solve the formulated problem, we equivalently transform the fractional objective function into a subtractive form one and propose a two-loop iterative algorithm to solve it. For the outer loop, the classic Bi-section iterative algorithm is applied. For the inner loop, we transform the formulated problem into a convex one by successive convex approximation techniques and propose an iterative algorithm to solve it. Meanwhile, to reduce the complexity of the inner loop, we develop a zero forcing (ZF) technique-based low complexity iterative algorithm. Specifically, the ZF technique is applied to cancel the inter-unicast interference and the first order Taylor approximation is used for the convexification of the non-convex constraints in the original problem. Finally, simulation results are provided to compare the performance of the proposed algorithms under different schemes.

Abdelrahim Mohamed, Muhammad Imran, Pei Xiao, Rahim Tafazolli (2018)Memory-full Context-aware Predictive Mobility Management in Dual Connectivity 5G Networks, In: IEEE Access6pp. 9655-9666 Institute of Electrical and Electronics Engineers (IEEE)

Network densification with small cell deployment is being considered as one of the dominant themes in the fifth generation (5G) cellular system. Despite the capacity gains, such deployment scenarios raise several challenges from mobility management perspective. The small cell size, which implies a small cell residence time, will increase the handover (HO) rate dramatically. Consequently, the HO latency will become a critical consideration in the 5G era. The latter requires an intelligent, fast and light-weight HO procedure with minimal signalling overhead. In this direction, we propose a memory-full context-aware HO scheme with mobility prediction to achieve the aforementioned objectives. We consider a dual connectivity radio access network architecture with logical separation between control and data planes because it offers relaxed constraints in implementing the predictive approaches. The proposed scheme predicts future HO events along with the expected HO time by combining radio frequency performance to physical proximity along with the user context in terms of speed, direction and HO history. To minimise the processing and the storage requirements whilst improving the prediction performance, a user-specific prediction triggering threshold is proposed. The prediction outcome is utilised to perform advance HO signalling whilst suspending the periodic transmission of measurement reports. Analytical and simulation results show that the proposed scheme provides promising gains over the conventional approach.

Lei Zhang, Pei Xiao, Adnan Zafar, Atta Quddus, Rahim Tafazolli (2016)FBMC System: An Insight into Doubly Dispersive Channel Impact, In: IEEE Transactions on Vehicular Technology66(5)pp. 3942-3956 IEEE

It has been claimed that the filter bank multicarrier (FBMC) systems suffer from negligible performance loss caused by moderate dispersive channels in the absence of guard time protection between symbols. However, a theoretical and systematic explanation/analysis for the statement is missing in the literature to date. In this paper, based on one-tap minimum mean square error (MMSE) and zero-forcing (ZF) channel equalizations, the impact of doubly dispersive channel on the performance of FBMC systems is analyzed in terms of mean square error (MSE) of received symbols. Based on this analytical framework, we prove that the circular convolution property between symbols and the corresponding channel coefficients in the frequency domain holds loosely with a set of inaccuracies. To facilitate analysis, we first model the FBMC system in a vector/matrix form and derive the estimated symbols as a sum of desired signal, noise, inter-symbol interference (ISI), inter-carrier interference (ICI), inter-block interference (IBI) and estimation bias in the MMSE equalizer. Those terms are derived one-by-one and expressed as a function of channel parameters. The numerical results reveal that in harsh channel conditions, e.g., with large Doppler spread or channel delay spread, the FBMC system performance may be severely deteriorated and error floor will occur.

Zheng Chu, Wenjuan Yu, Pei Xiao, Fuhui Zhou, Naofal Al-Dhahir, Atta ul Quddus, Rahim Tafazolli (2019)Opportunistic Spectrum Sharing for D2D-Based URLLC, In: IEEE Transactions on Vehicular Technologypp. 1-1 Institute of Electrical and Electronics Engineers (IEEE)

A device-to-device (D2D) ultra reliable low latency communications (URLLC) network is investigated in this paper. Specifically, a D2D transmitter opportunistically accesses the radio resource provided by a cellular network and directly transmits short packets to its destination. A novel performance metric is adopted for finite block-length code. We quantify the maximum achievable rate for the D2D network, subject to a probabilistic interference power constraint based on imperfect channel state information (CSI). First, we perform a convexity analysis which reveals that the finite block-length rate for the D2D pair in short-packet transmission is not always concave. To address this issue, we propose two effective resource allocation schemes using the successive convex approximation (SCA)-based iterative algorithm. To gain more insights, we exploit the mono- tonicity of the average finite block-length rate. By capitalizing on this property, an optimal power control policy is proposed, followed by closed-form expressions and approximations for the optimal average power and the maximum achievable average rate in the finite block-length regime. Numerical results are provided to confirm the effectiveness of the proposed resource allocation schemes and validate the accuracy of the derived theoretical results.

Alexandr Kuzminskiy, Pei Xiao, Rahim Tafazolli (2020)Good Neighbor Alternative to Best Response and Machine Learning Based Beamforming and Power Adaptation for MIMO Ad Hoc Networks, In: 2020 IEEE 31st Annual International Symposium on Personal, Indoor and Mobile Radio Communications: Track 2: Networking and MAC Institute of Electrical and Electronics Engineers

Decentralized joint transmit power and beam- forming selection for multiple antenna wireless ad hoc net- works operating in a multi-user interference environment is considered. An important feature of the considered environ- ment is that altering the transmit beamforming pattern at some node generally creates more signicant changes to in- terference scenarios for neighboring nodes than variation of the transmit power. Based on this premise, a good neighbor algorithm is formulated in the way that at the sensing node, a new beamformer is selected only if it needs less than the given portion of the transmit power required for the current beamformer. Otherwise, it keeps the current beamformer and achieves the performance target only by means of power adaptation. Equilibrium performance and convergence be- havior of the proposed algorithm compared to the best re- sponse and regret matching solutions is demonstrated by means of semi-analytic Markov chain performance analysis for small scale and simulations for large scale networks.

Ahmed Almradi, Pei Xiao, Khairi Ashour Hamdi (2018)Hop-by-Hop ZF Beamforming for MIMO Full-Duplex Relaying with Co-Channel Interference, In: IEEE Transactions on Communications Institute of Electrical and Electronics Engineers (IEEE)

In this paper, a comprehensive design and analysis of multiple-input multiple-output (MIMO) full-duplex (FD) relaying systems in a multi-cell environment are investigated, where a multi-antenna amplify-and-forward (AF) FD relay station serves multiple half-duplex (HD) multi-antenna users. The pivotal obstacles of loopback self-interference (LI) and multiple co-channel interferers (CCI) at the relay and destination when employing FD relaying in cellular networks are addressed. In contrast to the HD relaying mode, the CCI in the FD relaying mode is predicted to double since the uplink and downlink communications are simultaneously scheduled via the same channel. In this paper, the optimal layout of transmit (receive) precoding (decoding) weight vectors which maximizes the overall signal-to-interefernce-plusnoise ratio (SINR) is constructed by a suitable optimization problem, then a closed-form sub-optimal formula based on null space projection is presented. The proposed hop-by-hop rank- 1 zero-forcing (ZF) beamforming vectors are based on added ZF constraints used to suppress the LI and CCI channels at the relay and destination, i.e., the source and relay perform transmit ZF beamforming, while the relay and destination employ receive ZF combining. To this end, unified accurate expressions for the outage probability and ergodic capacity are derived in closed-form. In addition, simpler tight lower-bound formulas for the outage probability and ergodic capacity are presented. Moreover, the asymptotic approximations for outage probability is considered to gain insights into system behavior in terms of the diversity order and array gain. Numerical and simulation results show the accuracy of the presented exact analytical expressions and the tightness of the lower-bound expressions. The case of hopby- hop maximum-ratio transmission/maximal-ratio combining beamforming is included for comparison purposes. Furthermore, our results show that while multi-antenna terminals improve the system performance, the detrimental effect of CCI on FD relaying is clearly seen. Therefore, our findings unveil that MIMO FD relaying could significantly improve the system performance compared to its conventional MIMO HD relaying counterpart.

P Xiao, M Sellathurai (2010)Improved Linear Transmit Processing for Single-User and Multi-User MIMO Communications Systems, In: IEEE Transactions on Signal Processing58(3)pp. 1768-1779 IEEE

In this paper, we propose a novel linear transmit precoding strategy for multiple-input, multiple-output (MIMO) systems employing improper signal constellations. In particular, improved zero-forcing (ZF) and minimum mean square error (MMSE) precoders are derived based on modified cost functions, and are shown to achieve a superior performance without loss of spectrum efficiency compared to the conventional linear and nonlinear precoders. The superiority of the proposed precoders over the conventional solutions are verified by both simulation and analytical results. The novel approach to precoding design is also applied to the case of an imperfect channel estimate with a known error covariance as well as to the multi-user scenario where precoding based on the nullspace of channel transmission matrix is employed to decouple multi-user channels. In both cases, the improved precoding schemes yield significant performance gain compared to the conventional counterparts.

G Chen, Y Gong, P Xiao, J Chambers (2016)Dual Antenna Selection in Secure Cognitive Radio Networks, In: IEEE Transactions on Vehicular Technology

This paper investigates data transmission and physical layer secrecy in cognitive radio network. We propose to apply full duplex transmission and dual antenna selection at secondary destination node. With the full duplex transmission, the secondary destination node can simultaneously apply the receiving and jamming antenna selection to improve the secondary data transmission and primary secrecy performance respectively. This describes an attractive scheme in practice: unlike that in most existing approaches, the secrecy performance improvement in the CR network is no longer at the price of the data transmission loss. The outage probabilities for both the data transmission and physical layer secrecy are analyzed. Numerical simulations are also included to verify the performance of the proposed scheme.

Md. Noor-A-Rahim, Zilong Liu, Haeyoung Lee, G. G. Md. Nawaz Ali, Dirk Pesch, Pei Xiao (2020)A Survey on Resource Allocation in Vehicular Networks, In: IEEE Transactions on Intelligent Transportation Systems Institute of Electrical and Electronics Engineers (IEEE)

Vehicular networks, an enabling technology for Intelligent Transportation System (ITS), smart cities, and autonomous driving, can deliver numerous on-board data services, e.g., road-safety, easy navigation, traffic efficiency, comfort driving, infotainment, etc. Providing satisfactory quality of service (QoS) in vehicular networks, however, is a challenging task due to a number of limiting factors such as hostile wireless channels (e.g., high mobility or asynchronous transmissions), increasingly fragmented and congested spectrum, hardware imperfections, and explosive growth of vehicular communication devices. Therefore, it is highly desirable to allocate and utilize the available wireless network resources in an ultra-efficient manner. In this paper, we present a comprehensive survey on resource allocation (RA) schemes for a range of vehicular network technologies including dedicated short range communications (DSRC) and cellular based vehicular networks. We discuss the challenges and opportunities for resource allocations in modern vehicular networks and outline a number of promising future research directions.

J Xiong, Y Tang, D Ma, P Xiao, K Wong (2015)Secrecy Performance Analysis for TAS-MRC System with Imperfect Feedback, In: IEEE Transactions on Information Forensics and Security10(8)pp. 1617-1629 IEEE

In this paper, we investigate the secrecy performance for a multiple-input multiple-output (MIMO) wiretap channel in the presence of a multiantenna eavesdropper. In particular, the legitimate transmitter uses transmit antenna selection (TAS) to transmit on a single antenna with the largest signal-to-noise ratio (SNR) while both the legitimate receiver and the eavesdropper adopt maximal ratio combining (MRC) for reception. We derive exact closed-form expressions for the probabilities of achieving positive secrecy rate and secrecy outage in the case of imperfect feedback due to feedback delay and/or feedback error. Furthermore, we derive the asymptotic secrecy outage probability at high SNR, which accurately reveals the secrecy diversity loss due to imperfect feedback. Simulation results are provided to verify our analytical results and illustrate the impact of imperfect feedback on the secrecy performance of such a wiretap system.

HONGZHI CHEN, DE MI, ZHENG CHU, PEI XIAO (2021)Rate-Splitting for Multicarrier Multigroup Multicast: Precoder Design and Error Performance, In: IEEE transactions on broadcasting.

Employing multi-antenna rate-splitting (RS) at the transmitter and successive interference cancellation (SIC) at the receivers, has emerged as a powerful transceiver strategy for multi-antenna networks. In this paper, we design RS precoders for an overloaded multicarrier multigroup multicast downlink system, and analyse the error performance. RS splits each group message into degraded and designated parts. The degraded parts are combined and encoded into a degraded stream, while the designated parts are encoded in designated streams. All streams are precoded and superimposed in a non-orthogonal fashion before being transmitted over the same time-frequency resource. We first derive the optimized RS-based precoder, where the design philosophy is to achieve a fair user group rate for the considered scenario by solving a joint max-min fairness and sum subcarrier rate optimization problem. Comparing with other precoding schemes including the state-of-the-art multicast transmission scheme, we show that the RS precoder outperforms its counterparts in terms of the fairness rate, with Gaussian signalling, i.e., idealistic assumptions. Then we integrate the optimized RS precoder into a practical transceiver design for link-level simulations (LLS), with realistic assumptions such as finite alphabet inputs and finite code block length. The performance metric becomes the coded bit error rate (BER). In the system under study, low-density parity-check (LDPC) encoding is applied at the transmitter, and iterative soft-input soft-output detection and decoding are employed at the successive interference cancellation based receiver, which completes the LLS processing chain and helps to generate the coded error performance results which validate the effectiveness of the proposed RS precoding scheme compared with benchmark schemes, in terms of the error performance. More importantly, we unveil the corresponding relations between the achievable rate in the idealistic case and coded BER in the realistic case, e.g., with finite alphabet input, for the RS precoded multicarrier multigroup multicast scenario. Index Terms—Downlink multiuser MISO, multicarrier multi-group multicast, rate-splitting, optimization, coded bit error rate BER.

Z Lin, P Xiao, TB Sorensen, B Vucetic (2010)Spatial Frequency Scheduling for Uplink SC-FDMA based Linearly Precoded LTE Multiuser MIMO System, In: European Transactions on Telecommunications21(3) Wiley

This paper investigates the performance of the uplink single carrier (SC) frequency division multiple access (FDMA) based linearly precoded multiuser multiple input multiple output (MIMO) systems with frequency domain packet scheduling. A mathematical expression of the received signal to interference plus noise ratio (SINR) for the studied systems is derived and a utility function based spatial frequency packet scheduling algorithms is investigated. The schedulers are shown to be able to exploit the available multiuser diversity in time, frequency and spatial domains.

Aijun Cao, Lixia Xiao, Pei Xiao, Chang He, Rahim Tafazolli (2020)A Tight Upper Bound for Enhanced DCT-OFDM with Index Modulation, In: IEEE Transactions on Vehicular Technology69(12)pp. 16213-16217 IEEE

Orthogonal frequency division multiplexing (OFDM) with index modulation (IM) (OFDM-IM), which employs the activated sub-carrier indices to convey information, exhibits higher energy efficiency and lower peak-to-average power ratio (PAPR)thanconventionalOFDMsystems.Tofurtherimprovethe throughput of discrete Fourier transform (DFT) based OFDM-IM (DFT-OFDM-IM),discretecosinetransform(DCT)basedOFDMIM (DCT-OFDM-IM) can be employed with double subcarriers giventhesamebandwidth.However,oneofthemaindisadvantage of DCT-OFDM-IM is its lack of circular convolutional property over a dispersive channel. To address this issue, an enhanced DCT-OFDM-IM(EDCT-OFDM-IM)systemhasbeenproposedby introducing symmetric prefix and suffix at the transmitter and a pre-filter at the receiver leading to better performance than DFTOFDM-IM in terms of bit error rate (BER). However, due to its special structure, it is difficult to derive the accurate absolute bit error probability (ABEP) upper bound, which is essential for the performance evaluation. In this paper, a tight ABEP upper bound is derived using the moment-generating-function (MGF). Our theoretical analysis is validated by simulation results and proven to be very accurate. Consequently the advantages of the EDCT-OFDM-IM system over the classic OFDM-IM system are further demonstrated analytically.

ZHENG CHU, PEI XIAO, DE MI, HONGZHI CHEN, Wanming Hao (2020)Intelligent Reflecting Surfaces Enabled Cognitive Internet of Things Based on Practical Pathloss Model, In: China Communications 17(12)pp. 1-16 IEEE

In this paper, we aim to unlock the potential of intelligent reflecting surfaces (IRSs) in cognitive internet of things (IoT). Considering that the secondary IoT devices send messages to the secondary access point (SAP) by sharing the spectrum with the primary network, the interference is introduced by the IoT devices to the primary access point (PAP) which profits from the IoT devices by pricing the interference power charged by them. A practical path loss model is adopted such that the IRSs deployed between the IoT devices and SAP serve as diffuse scatterers, but each reflected signal can be aligned with its own desired direction. Moreover, two transmission policies of the secondary network are investigated without/with a successive interference cancellation (SIC) technique. The signal-to-interference plus noise ratio (SINR) balancing is considered to overcome the near-far effect of the IoT devices so as to allocate the resource fairly among them. We propose a Stackelberg game strategy to characterize the interaction between primary and secondary networks. For the proposed game, the Stackelberg equilibrium is analytically derived to optimally obtain the closed-form solution of the power allocation and interference pricing. Numerical results are demonstrated to validate the performance of the theoretical derivations.

Mohsen Khalily, Rahim Tafazolli, Pei Xiao, Ahmed A. Kishk (2018)Broadband mm-Wave Microstrip Array Antenna with Improved Radiation Characteristics for Different 5G Applications, In: IEEE Transactions on Antennas and Propagation44(9)pp. 4641-4647 Institute of Electrical and Electronics Engineers (IEEE)

A Ka-band inset-fed microstrip patches linear antenna array is presented for the fifth generation (5G) applications in different countries. The bandwidth is enhanced by stacking parasitic patches on top of each inset-fed patch. The array employs 16 elements in an H-plane new configuration. The radiating patches and their feed lines are arranged in an alternating out-of-phase 180-degree rotating sequence to decrease the mutual coupling and improve the radiation pattern symmetry. A (24.4%) measured bandwidth (24.35 to 31.13 GHz)is achieved with -15 dB reflection coefficients and 20 dB mutual coupling between the elements. With uniform amplitude distribution, a maximum broadside gain of 19.88 dBi is achieved. Scanning the main beam to 49.5◦ from the broadside achieved 18.7 dBi gain with -12.1 dB sidelobe level (SLL). These characteristics are in good agreement with the simulations, rendering the antenna to be a good candidate for 5G applications.

—Multi-numerology multi-carrier (MN-MC) techniques are considered as essential enablers for RAN slicing in fifth-generation (5G) communication systems and beyond. However, utilization of mixed numerologies breaks the or-thogonality principle defined for single-numerology orthogonal frequency division multiplexing (SN-OFDM) systems with a unified subcarrier spacing. This leads to interference between different numerologies, i.e., inter-numerology interference (INI). This paper develops metrics to quantify the level of the INI using a continuous-time approach. The derived analytical expressions of INI in terms of mean square error (MSE) and error vector magnitude (EVM) directly reveal the main contributing factors to INI, which can not be shown explicitly in a matrix form INI based on discrete-time calculations. Moreover, the study of power offset between different numerologies shows a significant impact on INI, especially for high order modulation schemes. The finding in this paper provides analytical guidance in designing multi-numerology (MN) systems, for instance, developing resource allocation schemes and interference mitigation techniques.

Lisu Yu, Zilong Liu, Miaowen Wen, Donghong Cai, Shuping Dang, Yuhao Wang, PEI XIAO (2021)Sparse Code Multiple Access for 6G Wireless Communication Networks: Recent Advances and Future Directions, In: IEEE Communications Standards Magazine Institute of Electrical and Electronics Engineers (IEEE)

As 5G networks are rolling out in many different countries nowadays, the time has come to investigate how to upgrade and expand them towards 6G, where the latter is expected to realize the interconnection of everything as well as the development of a ubiquitous intelligent mobile world for intelligent life. To enable this epic leap in communications, this article provides an overview and outlook on the application of sparse code multiple access (SCMA) for 6G wireless communication systems, which is an emerging disruptive non-orthogonal multiple access (NOMA) scheme for enabling massive connectivity. We propose to apply SCMA to a massively distributed access system (MDAS), whose architecture is based on fiber-based visible light communication (FVLC), ultra-dense network (UDN), and NOMA. Under this framework, we consider the interactions between optical front-hauls and wireless access links. In order to stimulate more upcoming research in this area, we outline a number of promising directions associated with SCMA for faster, more reliable, and more efficient multiple access in future 6G communication networks.

Qu Luo, Pengyu Gao, Zilong Liu, Lixia Xiao, Zeina Mheich, Pei Xiao, Amine Maaref (2021)An Error Rate Comparison of Power Domain Non-Orthogonal Multiple Access and Sparse Code Multiple Access, In: IEEE Open Journal of the Communications Society2pp. 500-511 IEEE

Non-orthogonal Multiple Access (NOMA) has been envisioned as one of the key enabling techniques to fulfill the requirements of future wireless networks. The primary benefit of NOMA is higher spectrum efficiency compared to Orthogonal Multiple Access (OMA). This paper presents an error rate comparison of two distinct NOMA schemes, i.e., power domain NOMA (PD-NOMA) and Sparse Code Multiple Access (SCMA). In a typical PD-NOMA system, successive interference cancellation (SIC) is utilized at the receiver, which however may lead to error propagation. In comparison, message passing decoding is employed in SCMA. To attain the best error rate performance of PD-NOMA, we optimize the power allocation with the aid of pairwise error probability and then carry out the decoding using generalized sphere decoder (GSD). Our extensive simulation results show that SCMA system with " 5\times 10 " setting (i.e., ten users communicate over five subcarriers, each active over two subcarriers) achieves better uncoded BER and coded BER performance than both typical " 1\times 2 " and " 2\times 4 " PD-NOMA systems in uplink Rayleigh fading channel. Finally, the impacts of channel estimation error on SCMA, SIC and GSD based PD-NOMA and the complexity of multiuser detection schemes are also discussed.

HAEYOUNG LEE, HAMIDREZA BAGHERI, Md. Noor-A-Rahim, Zilong Liu, Dirk Pesch, KLAUS MOESSNER, PEI XIAO (2021)5G NR-V2X: Towards Connected and Cooperative Autonomous Driving, In: IEEE communications standards magazine Institute of Electrical and Electronics Engineers (IEEE)

5G New Radio (NR) is touted as a pivotal enabling technology for the genuine realization of connected and cooperative autonomous driving. Despite numerous research efforts in recent years, a systematic overview on the role of 5G NR in future connected autonomous communication networks is missing. To fill this gap and to spark more future research, this paper introduces the technology components of 5G NR and discusses the evolution from existing cellular vehicle-to-everything (V2X) technology towards NR-V2X. We primarily focus on the key features and functionalities of physical layer, Sidelink communication and its resource allocation, architecture flexibility, security and privacy mechanisms, and precise positioning techniques. Moreover, we envisage and highlight the potential of machine learning for further performance enhancement in NR-V2X services. Lastly, we show how 5G NR can be configured to support advanced V2X use cases.

Christopher Husmann, Chathura Jayawardena, Amine Maaref, Pei Xiao, Konstantinos Nikitopoulos (2020)Low-Complexity SCMA Detection for Unsupervised User Access, In: IEEE Communications Letterspp. 1-1 IEEE

Non-orthogonal multiple access schemes (NOMA), such as sparse code multiple access (SCMA), are among the most promising technologies to support massive numbers of connected devices. Still, to minimize the transmission delay and to maximize the utilization of the transmission channel, "grant-free" NOMA techniques are required that eliminate any prior information exchange between the users and the base-stations. However, if a large number of users transmit simultaneously in an "unsupervised" manner, (i.e., without any prior signaling for controlling the number of users and the corresponding transmission patterns), it is likely that a large number of users may share the same frequency-resource element, rendering the corresponding user detection impractical. In this context, we present a new multi-user detection approach, which aims to maximize the detection performance, with respect to given processing and latency limitations. We show that our approach enables practical detection for grant-free SCMA schemes that support hundreds of interfering users, with a complexity that is up to two orders of magnitude less than that of conventional detection approaches.

(2021)Robust Design for Intelligent Reflecting Surface Assisted MIMO-OFDMA Terahertz IoT Networks, In: IEEE Internet of Things Journal Institute of Electrical and Electronics Engineers (IEEE)

Terahertz (THz) communication has been regarded as one promising technology to enhance the transmission capacity of future internet-of-things (IoT) users due to its ultra-wide bandwidth. Nonetheless, one major obstacle that prevents the actual deployment of THz lies in its inherent huge attenuation. Intelligent reflecting surface (IRS) and multiple-input multipleoutput (MIMO) represent two effective solutions for compensating the large pathloss in THz systems. In this paper, we consider an IRS-aided multi-user THz MIMO system with orthogonal frequency division multiple access, where the sparse radio frequency chain antenna structure is adopted for reducing the power consumption. The objective is to maximize the weighted sum rate via jointly optimizing the hybrid analog/digital beamforming at the base station and reflection matrix at the IRS. Since the analog beamforming and reflection matrix need to cater all users and subcarriers, it is difficult to directly solve the formulated problem, and thus, an alternatively iterative optimization algorithm is proposed. Specifically, the analog beamforming is designed by solving a MIMO capacity maximization problem, while the digital beamforming and reflection matrix optimization are both tackled using semidefinite relaxation technique. Considering that obtaining perfect channel state information (CSI) is a challenging task in IRS-based systems, we further explore the case with the imperfect CSI for the channels from the IRS to users. Under this setup, we propose a robust beamforming and reflection matrix design scheme for the originally formulated non-convex optimization problem. Finally, simulation results are presented to demonstrate the effectiveness of the proposed algorithms.

J Mao, Z Lin, P Xiao (2012)Mobile WiMAX Downlink MIMO Beamforming Algorithms and Simulations, In: Orthogonal Frequency Division Multiplexing with Diversity for Future Wireless Systems(11) Bentham Science Publisher

MIMO. Transmit. Diversity: Theoretical. Analyses. and. Practical. Applications. Pei Xiao1, Zihuai Lin2 and Jian Mao3 Abstract: In this chapter, we study transmit diversity scheme employed in multipleinput, multiple-output (MIMO) systems and ...

Pei Xiao, J Wu, Q Chen (2012)Decoding algorithms for 3-D space-time-frequency codes, In: Proceedings of the 5th International Workshop on Signal Design and Its Applications in Communications, IWSDA'11pp. 185-188

In this paper, we propose a joint complex diversity coding (CDC) and channel coding based space-time-frequency codes (STFCs) to increase diversity gains over space, time and frequency. Both non-iterative and iterative decoding of joint channel coding and 3-dimensional CDC transmission are investigated. The simulation results show that the minimum mean square error (MMSE) based iterative soft decoding achieves the performance of the soft sphere decoding (SD) with reduced complexity.

Hang Ruan, Pei Xiao, Lixia Xiao, James Kelly (2021)Joint Iterative Optimization Based Low-Complexity Adaptive Hybrid Beamforming for Massive MU-MIMO Systems, In: IEEE Transactions on Communications IEEE

This paper proposes a joint iterative optimization based hybrid beamforming technique for massive MU-MIMO systems. The proposed technique jointly and iteratively optimizes the transmitter precoders and combiners, aiming to approach the global optimum solution for the system sum-rate maximization problem. The proposed technique develops an adaptive algorithm exploiting the stochastic gradients (SG) of the local beamformers and provides low-complexity closed-form solutions. Furthermore, an efficient adaptive scheme is developed based on the proposed adaptive algorithm and the closed-form solutions. The proposed algorithm requires the signal-to-interference-plus-noise ratio (SINR) feedback from each user and a limited size transition vector to be exchanged between the transmitter and receivers at each step to update beamformers locally. Analytic result shows that the proposed adaptive algorithm achieves low-complexity when the array size is large and is able to converge within a small number of iterations. Simulation result shows that the proposed technique is able to achieve superior performance comparing to the existing state-of-art techniques. In addition, the knowledge of instantaneous channel state information (CSI) is not required as the channels are also adaptively estimated with each coherence time which is a practical assumption since the CSI is usually unavailable or have time-varying nature in real-time applications.

Pei Xiao, Z Lin, J Mao (2012)MIMO Transmit Diversity: Theoretical Analyses and Practical Applications, In: Orthogonal Frequency Division Multiplexing with Diversity for Future Wireless Systems(5) Bentham Science Publisher

The book examines several aspects of Orthogonal Frequency Division Multiplexing (OFDM) employing linear diversity techniques such as inter-carrier interference, bit error rate, peak to average power and inter-block interference.

Zheng Chu, Wanming Hao, Pei Xiao, De Mi, Zilong Liu, Mohsen Khalily, James R Kelly, Alexandros P Feresidis (2020)Secrecy Rate Optimization for Intelligent Reflecting Surface Assisted MIMO System, In: IEEE transactions on information forensics and security16pp. 1655-1669 IEEE

This paper investigates the impact of intelligent reflecting surface (IRS) enabled wireless secure transmission. Specifically, an IRS is deployed to assist multiple-input multiple-output (MIMO) secure system to enhance the secrecy performance, and artificial noise (AN) is employed to introduce interference to degrade the reception of the eavesdropper. To improve the secrecy performance, we aim to maximize the achievable secrecy rate, subject to the transmit power constraint, by jointly designing the precoding of the secure transmission, the AN jamming, and the reflecting phase shift of the IRS. We first propose an alternative optimization algorithm (i.e., block coordinate descent (BCD) algorithm) to tackle the non-convexity of the formulated problem. This is made by deriving the transmit precoding and AN matrices via the Lagrange dual method and the phase shifts by the Majorization-Minimization (MM) algorithm. Our analysis reveals that the proposed BCD algorithm converges in a monotonically non-decreasing manner which leads to guaranteed optimal solution. Finally, we provide numerical results to validate the secrecy performance enhancement of the proposed scheme in comparison to the benchmark schemes.

Li Zhen, Ali Kashif Bashir, Keping Yu, Yasser D Al-Otaibi, Chuan Heng Foh, Pei Xiao (2020)Energy-Efficient Random Access for LEO Satellite-Assisted 6G Internet of Remote Things, In: IEEE internet of things journalpp. 1-1 IEEE

Satellite communication system is expected to play a vital role for realizing various remote internet of things (IoT) applications in 6G vision. Due to unique characteristics of satellite environment, one of the main challenges in this system is to accommodate massive random access (RA) requests of IoT devices while minimizing their energy consumptions. In this paper, we focus on the reliable design and detection of RA preamble to effectively enhance the access efficiency in high-dynamic low-earth-orbit (LEO) scenarios. To avoid additional signaling overhead and detection process, a long preamble sequence is constructed by concatenating the conjugated and circularly shifted replicas of a single root Zadoff-Chu (ZC) sequence in RA procedure. Moreover, we propose a novel impulse-like timing metric based on length-alterable differential cross-correlation (LDCC), that is immune to carrier frequency offset (CFO) and capable of mitigating the impact of noise on timing estimation. Statistical analysis of the proposed metric reveals that increasing correlation length can obviously promote the output signal-to-noise power ratio, and the first-path detection threshold is independent of noise statistics. Simulation results in different LEO scenarios validate the robustness of the proposed method to severe channel distortion, and show that our method can achieve significant performance enhancement in terms of timing estimation accuracy, success probability of first access, and mean normalized access energy, compared with the existing RA methods.

G Chen, Y Gong, P Xiao, JA Chambers (2015)Physical Layer Network Security in the Full-Duplex Relay System, In: IEEE TRANSACTIONS ON INFORMATION FORENSICS AND SECURITY10(3)pp. 574-583 IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

This paper investigates the secrecy performance of full-duplex relay (FDR) networks. The resulting analysis shows that FDR networks have better secrecy performance than half duplex relay networks, if the self-interference can be well suppressed. We also propose a full duplex jamming relay network, in which the relay node transmits jamming signals while receiving the data from the source. While the full duplex jamming scheme has the same data rate as the half duplex scheme, the secrecy performance can be significantly improved, making it an attractive scheme when the network secrecy is a primary concern. A mathematic model is developed to analyze secrecy outage probabilities for the half duplex, the full duplex and full duplex jamming schemes, and the simulation results are also presented to verify the analysis.

X Long, Q Chen, P Xiao, J Wu (2012)On the design of PS-RCPT codes for LTE system, In: GLOBECOM - IEEE Global Telecommunications Conferencepp. 4238-4243

The optimized weight spectrum sequence (OWSS) is utilized as a design criterion in this paper to determine the periodic puncturing pattern and the non-periodic puncturing pattern of partially systematic RCPT (PS-RCPT) codes for LTE systems. It is shown that the OWSS-criterion based PS-RCPT codes outperform the pseudo-random puncturing (PRP) based PS-RCPT codes. Meanwhile, it is unveiled that, the puncturing ratio of information bits should be carefully determined in PS-RCPT codes generation to achieve reasonable tradeoff between the waterfall region and the error floor region performance. © 2012 IEEE.

J Wu, Pei Xiao (2010)OFDMA-based Mobile WiMAX, In: Orthogonal Frequency Division Multiple Access Fundamentals and Applicationspp. 595-622 Auerbach Publications

Supported by the expert-level advice of pioneering researchers, Orthogonal Frequency Division Multiple Access Fundamentals and Applications provides a comprehensive and accessible introduction to the foundations and applications of one of the most promising access technologies for current and future wireless networks. It includes authoritative coverage of the history, fundamental principles, key techniques, and critical design issues of OFDM systems. Covering various techniques of effective resource management for OFDM/OFDMA-based wireless communication systems, this cutting-edge reference: Addresses open problems and supplies possible solutions. Provides a concise overview of key techniques for adaptive modulation. Investigates radio channel modeling in OFDMA-based wireless communication systems. Details detection strategies of frequency-domain equalization for broadband communications. Introduces a novel combination of OFDM and the orbital angular momentum of the electromagnetic field to improve performance. Contains extensive treatment of adaptive MIMO beamforming suitable for multiuser access. This valuable resource supplies readers with a macro-level understanding of OFDMA and its key issues, while providing a systematic manual for those whose work is directly related to practical OFDMA and other multiuser communication systems projects.

M Al-Imari, Pei Xiao, Muhammad Imran, Rahim Tafazolli (2014)Uplink Non-Orthogonal Multiple Access for 5G Wireless Networks, In: 11th International Symposium on Wireless Communications Systems (ISWCS) 2014pp. 781-785 IEEE

Orthogonal Frequency Division Multiple Access (OFDMA) as well as other orthogonal multiple access techniques fail to achieve the system capacity limit in the uplink due to the exclusivity in resource allocation. This issue is more prominent when fairness among the users is considered in the system. Current Non-Orthogonal Multiple Access techniques (NOMA) introduce redundancy by coding/spreading to facilitate the users' signals separation at the receiver, which degrade the system spectral efficiency. Hence, in order to achieve higher capacity, more efficient NOMA schemes need to be developed. In this paper, we propose a NOMA scheme for uplink that removes the resource allocation exclusivity and allows more than one user to share the same subcarrier without any coding/spreading redundancy. Joint processing is implemented at the receiver to detect the users' signals. However, to control the receiver complexity, an upper limit on the number of users per subcarrier needs to be imposed. In addition, a novel subcarrier and power allocation algorithm is proposed for the new NOMA scheme that maximizes the users' sum-rate. The link-level performance evaluation has shown that the proposed scheme achieves bit error rate close to the single-user case. Numerical results show that the proposed NOMA scheme can significantly improve the system performance in terms of spectral efficiency and fairness comparing to OFDMA.

Zheng Chu, Pei Xiao, De Mi, Wanming Hao, Mohsen Khalily, Lie-Liang Yang (2021)A Novel Transmission Policy for Intelligent Reflecting Surface Assisted Wireless Powered Sensor Networks, In: IEEE Journal of Selected Topics in Signal Processing Institute of Electrical and Electronics Engineers (IEEE)

This paper proposes a novel transmission policy for an intelligent reflecting surface (IRS) assisted wireless powered sensor network (WPSN). An IRS is deployed to enhance the performance of wireless energy transfer (WET) and wireless information transfer (WIT) by intelligently adjusting phase shifts of each reflecting elements. To achieve its self-sustainability, the IRS needs to collect energy from the ES to support its control circuit operation. Our proposed policy for the considered system is called IRS assisted harvest-then-transmit time switching (IRS-HTT-TS) which schedules the transmission time slots by switching between energy collection and energy reflection modes. We study the performance of the proposed transmission policy in terms of the achievable sum throughput, and investigate a joint design of the transmission time slots, the power allocation, as well as the discrete phase shifts of the WET and WIT. This formulates the problem as a mixed-integer non-linear program (MINLP), which is NP-hard and non-convex. To deal with this problem, we first relax it to the one with continuous phase shifts. Consequently, we propose a two-step approach and decompose the original problem into two sub-problem, each being solved separately. Specifically, we independently solve the first sub-problem with respect to the phase shifts of the WIT in terms of closed-form expression. Then, we consider two cases to solve the second sub- problem. For the special case without the circuit power of each sensor node, the Lagrange dual method and the Karush-Kuhn- Tucker (KKT) conditions are applied to derive the optimal closed- form transmission time slots, power allocation, and phase shift of the WET. Moreover, we exploit the second sub-problem for the general case with the circuit power of each sensor node, which can be solved via employing a semi-definite programming (SDP) relaxation.

Yuan Zhang, Zilong Liu, PEI XIAO, Fucheng Guo (2021)A Novel SCMA Codebook Design Method Based on Low Error Probability Criteria

—In this paper, we propose a method to construct codebooks for downlink sparse code multiple access (SCMA) systems. Different from the traditional methods in which codebooks are designed for each user, we allocate codebooks for each sub-channel based on the most common modulation QAM. Then, low error probability criteria to measure the SCMA codebook performance in AWGN channel and Rayleigh fading channel are proposed. And simulated annealing algorithm is used to optimize the codebooks based on the criteria. Simulation results prove that the proposed codebooks exhibit good performance in both Rayleigh fading channel and AWGN channel, especially for high order SCMA systems.

Long Cheng, Guangrong Yue, PEI XIAO, Ning Wei, Shaoqian Li (2021)Fast Beam Alignment for Millimeter Wave Time-Varying Channels Using Sparse Codes, In: IEEE Transactions on Vehicular Technology Institute of Electrical and Electronics Engineers (IEEE)

In this paper, a novel beam alignment algorithm based on the sparse graph coding theory is proposed for millimeter wave (mmWave) time-varying channels. Firstly, a pilot design method is introduced to transform the mmWave timevarying beam alignment into a sparse-graph design and detection problem. Inspired by Low-Density-Parity-Check (LDPC) codes and fountain codes, a multi-stage sparse coding method is proposed for the design of the measurement matrix and the theoretical bound of the probability of success is derived to guide the design of the sparse-graph. A beam alignment algorithm is subsequently proposed to detect the beam index and estimate the carrier frequency offset (CFO). Then, the Carme´r-Rao Lower Bound (CRLB) is derived. Simulation results demonstrate that the proposed beam alignment algorithm achieves significant performance improvements over the conventional counterparts in both the noiseless and noise cases.

SALMAN BEHBOUDI AMLASHI, MOHSEN KHALILY, VIKRANT SINGH, PEI XIAO, JAMES DAVID CAREY, RAHIM TAFAZOLLI (2021)Surface Electromagnetic Performance Analysis of a Graphene-Based Terahertz Sensor Using a Novel Spectroscopy Technique, In: IEEE journal on selected areas in communications : a publication of the IEEE Communications Society Institute of Electrical and Electronics Engineers (IEEE)

In this paper, a novel terahertz (THz) spectroscopy technique and a new graphene-based sensor is proposed. The proposed sensor consists of a graphene-based metasurface (MS) that operates in reflection mode over a broad range of frequency band (0.2 -6 THz) and can detect relative permittivity of up to 4 with a resolution of 0.1 and a thickness ranging from 5 μm to 600 μm with a resolution of 0.5 μm. To the best of author’s knowledge, such a THz sensor with such capabilities has not been reported yet. Additionally, an equivalent circuit of the novel unit cell is derived and compared with two conventional grooved structures to showcase the superiority of the proposed unit cell. The proposed spectroscopy technique utilizes some unique spectral features of a broadband reflection wave including Accumulated Spectral power (ASP) and Averaged Group Delay (AGD), which are independent to resonance frequencies and can operate over a broad range of spectrum. ASP and AGD can be combined to analyse the magnitude and phase of the reflection diagram as a coherent technique for sensing purposes. This enables the capability to distinguish between different analytes with high precision which, to the best of author’s knowledge, has been accomplished for the first time.

Long Cheng, Guangrong Yue, PEI XIAO, Ning Wei, Shaoqian Li (2021)Beam Alignment for Millimeter Wave Multiuser MIMO Systems Using Sparse-Graph Codes, In: Science China Information sciences = 中国科学:信息科学(英文版) Springer Verlag

In order to achieve millimeter wave (mmWave) beam alignment , a class of beam scanning and searching schemes have been extensively studied [1–3]. Recently, to address the problems of the traditional algorithms have a high sample complexity, some adaptive beam scanning approaches utilize the hierarchical beamforming codebook to reduce the training time at the cost of frequent feedback [2]. Then, to eliminate the feedback link, a random beam alignment algorithm is proposed by utilizing the pseudo-random spreading codes [3]. However, it needs a Pseudo-Noise (PN) sequences with sufficient length to ensure the good correlation properties of different beams. Furthermore, in addition to the above disadvantages, most of the existing algorithms require either a separate pilot sequence per user or long beam scanning time when considering mmWave multiuser uplinking systems. To solve the above problems, a novel class of beam alignment algorithms based on the sparse graph coding theory are proposed in this paper. Firstly, we investigate the uplink mmWave beam training structure. Based on the analysis, the mmWave multiuser beam alignment problem is transformed into the sparse-graph design and detection problem. Secondly, a beam alignment algorithm framework based on sparse-graph coding and decoding is proposed. Furthermore , we derive the theoretical bound to chose the optimal parameters of the designed coding matrix. Finally, two beam alignment algorithms are proposed to detect the beam index in different settings. Simulation results confirm that our beam algorithms outperform the conventional beam training methods. Proposed Uplink Beam Training Scheme. This paper considers a typical uplink mmWave MU-MIMO system, where the BS communicates with K UEs simultaneously. Suppose that the BS is equipped with N R antennas and N RF RF chains, while the k-th UE has M T antennas and M RF RF chains. Then, the channel associated with the k-th UE can be given by [4]

Zheng Chu, Pei Xiao, Mohammad Shojafar, De Mi, Juquan Mao, Wanming Hao (2020)Intelligent Reflecting Surface Assisted Mobile Edge Computing for Internet of Things, In: IEEE Wireless Communications Letterspp. 1-1 IEEE

This paper studies the impact of an intelligent reflecting surface (IRS) on computational performance in a mobile edge computing (MEC) system. Specifically, an access point (AP) equipped with an edge server provides MEC services to multiple internet of thing (IoT) devices that choose to offload a portion of their own computational tasks to the AP with the remaining portion being locally computed. We deploy an IRS to enhance the computational performance of the MEC system by intelligently adjusting the phase shift of each reflecting element. A joint design problem is formulated for the considered IRS assisted MEC system, aiming to optimize its sum computational bits and taking into account the CPU frequency, the offloading time allocation, transmit power of each device as well as the phase shifts of the IRS. To deal with the non-convexity of the formulated problem, we conduct our algorithm design by finding the optimized phase shifts first and then achieving the jointly optimal solution of the CPU frequency, the transmit power and the offloading time allocation by considering the Lagrange dual method and Karush-Kuhn-Tucker (KKT) conditions. Numerical evaluations highlight the advantage of the IRS-assisted MEC system in comparison with the benchmark schemes.

MANIJEH BASHAR, PEI XIAO, RAHIM TAFAZOLLI, Kanapathippillai Cumanan, Alister G Burr, Emil Bjornson (2021)Limited-Fronthaul Cell-Free Massive MIMO with Local MMSE Receiver under Rician Fading and Phase Shifts, In: IEEE Wireless Communications Letters Institute of Electrical and Electronics Engineers (IEEE)

A cell-free Massive multiple-input multiple-output (MIMO) system is considered, where the access points (APs) are linked to a central processing unit (CPU) via the limited-capacity fronthaul links. It is assumed that only the quantized version of the weighted signals are available at the CPU. The achievable rate of a limited fronthaul cell-free massive MIMO with local minimum mean square error (MMSE) detection is studied. We study the assumption of uncorrelated quantization distortion, which is commonly used in literature. We show that this assumption will not affect the validity of the insights obtained in our work. To investigate this, we compare the uplink per-user rate with different system parameters for two different scenarios; 1) the exact uplink per-user rate and 2) the uplink per-user rate while ignoring the correlation between the inputs of the quantizers. Finally, we present the conditions which imply that the quantization distortions across APs can be assumed to be uncorrelated.

J Wu, P Xiao, M Sellahuai, S Blostein (2009)Linear Dispersion Codes for Wireless Communications., In: Wireless Networks: Research, Technology, and Applications(4) Nova Science Pub Inc

An intelligent authentication and key agreement mechanism for e-Hospital applications is proposed in this book. In addition, a mathematical model for calculating the coverage fraction in wireless sensor networks (WSNs) is addressed.

Chun Xu Mao, Long Zhang, Mohsen Khalily, Yue Gao, Pei Xiao (2021)A Multiplexing Filtering Antenna, In: IEEE Transactions on Antennas and Propagationpp. 1-1 IEEE

In this paper, a compact, highly integrated multiplexing filtering antenna operating at 4.7/5.2/6.0/6.6 GHz is proposed for the first time. Different from traditional antennas, the proposed antenna has one shared radiator but four ports working in different frequency bands and thus, it can simultaneously support four different transmission channels. The proposed multiplexing antenna is composed of a patch with a U-shaped slot, two substrate integrated waveguide (SIW) cavities, and four resonator-based frequency-selective paths. The resonator-based paths can not only enhance the inter-channel isolations but also improve the impedance bandwidth. The design principles and the methods of controlling the four operating bands are studied. Measurement results agree reasonably well with the simulations, showing four channels from 4.5 to 4.8 GHz, 5.1 to 5.3 GHz, 5.85 to 6.3 GHz, and 6.4 to 6.6 GHz, respectively. The antenna also exhibits a high isolation of over 25 dB between the channels. In addition, the proposed antenna has a consistent broadside radiation pattern and polarization in the four bands, manifesting the proposed multiplexing filtering antenna can be a promising candidate for multi-service wireless communication systems.

Mehdi Ghorbani, Mohsen Khalily, Habib Ghorbaninejad, Pei Xiao, Rahim Tafazolli (2019)Bandwidth Enhancement and Radiation Characteristics Improvement of Triangular Dielectric Resonator Antenna, In: Proceedings of The 2019 International Symposium on Networks, Computers and Communications (ISNCC'19) Institute of Electrical and Electronics Engineers (IEEE)

In this paper, an ultra-wideband, Dielectric Resonator Antenna (DRA) has been proposed. The proposed antenna is based on isosceles triangular DRA (TDRA), which is fed from the base side using a 50Ω probe. For bandwidth enhancement and radiation characteristics improvement, a partially cylindrical-shape hole is etched from its base side which approached probe feed to the center of TDRA. The dielectric resonator (DR) is located over an extended conducting ground plane. This technique has significantly enhanced antennas bandwidth from 48.8% to 80% (5.29-12.35 GHz), while the biggest problem was radiation characteristics. The basis antenna possesses negative gain in a wide range of bandwidth from 7.5 GHz to 10.5 GHz down to -13.8 dBi. Using this technique improve antenna gain over 1.6 dBi for whole bandwidth, while peak gain is 7.2 dBi.

K. Yahya Alqurashi, H.R.D. Filgueiras, I. F. da Costa, Arismar Cerqueira S. Jr., Pei Xiao, Zhe Chen, Hang Wong, J.R. Kelly (2018)Millimeter Wave Beam Steerable/Reconfigurable Liquid Metal Array Antenna, In: Proceedings of ICEAA - IEEE APWC - FEM 2018pp. 814-815 Institute of Electrical and Electronics Engineers (IEEE)

Users within mobile networks require ever increasing data rates. However, the frequency spectrum, reserved for mobile networks, is highly saturated. The millimeter wave spectrum, by contrast is relatively under utilised. Nonetheless, this area of the spectrum suffers from higher propagation losses, necessitating the use of highly directional antennas. To support mobility these antennas require beam steering capabilities. For several applications wide beam scanning capability is required. A valuable approach for increasing the beam scanning range is to use element factor plus array factor control [1]. Although several authors have presented designs based on this approach the lobe performance of those antennas is generally quite poor. In this paper we seek to address that issue.

In Cognitive Radio (CR) systems, the data rate of the Secondary User (SU) can be maximized by optimizing the transmit power, given a threshold for the interference caused to the Primary User (PU). In conventional power optimization algorithms, the Gaussian input distribution is assumed, which is unrealistic, whereas the Finite Symbol Alphabet (FSA) input distribution, (i.e., M-QAM) is more applicable to practical systems. In this paper, we consider the power optimization problem in multiple input multiple output orthogonal frequency division multiplexing based CR systems given FSA inputs, and derive an optimal power allocation scheme by capitalizing on the relationship between mutual information and minimum mean square error. The proposed scheme is shown to save transmit power compared to its conventional counterpart. Furthermore, our proposed scheme achieves higher data rate compared to the Gaussian optimized power due to fewer number of subcarriers being nulled. The proposed optimal power algorithm is evaluated and compared with the conventional power allocation algorithms using Monte Carlo simulations. Numerical results reveal that, for distances between the SU transmitter and the PU receiver ranging between 50m to 85m, the transmit power saving with the proposed algorithm is in the range 13-90%, whereas the rate gain is in the range 5-31% depending on the modulation scheme (i.e., BPSK, QPSK and 16-QAM) used.

P Xiao, BK Khoo, SY Le Goff, W Scanlon (2012)BER evaluation of a low complexity transmit diversity scheme and its application to MIMO-BICM, In: Communication Systems, Networks & Digital Signal Processing (CSNDSP), 2012 8th International Symposium on

In this paper, we first provide a theoretical validation for a low-complexity transmit diversity algorithm which employs only one RF chain and a low-complexity switch for transmission. Our theoretical analysis is compared to the simulation results and proved to be accurate. We then apply the transmit diversity scheme to multiple-input and multiple-output (MIMO) systems with bit-interleaved coded modulation (BICM). © 2012 IEEE.

T Zeng, Q Chen, P Xiao, J Wu (2012)MSINR based precoding design for non-regenerative MIMO relay system, In: 2012 1st IEEE International Conference on Communications in China, ICCC 2012pp. 508-513

The maximum signal-to-interference plus noise ratio (MSINR) design criterion is proposed in this paper to maximize the geometric product of signal-to-interference plus noise ratio (GEOM-SINR) in non-regenerative MIMO relay system. It is shown that the optimal MSINR based precoding at relay will diagonalize the equivalent source-relay-destination channel into parallel sub-channels, and the MSINR based MIMO relay precoding design will be transformed into the MSINR criterion based power allocation among multiple sub-channels. Simulation results are presented to corroborate the MSINR-based MIMO relay precoding design. It is unveiled that, compared with the existing maximal mutual information (MMI) based MIMO relay precoding design and the minimal mean square error (MMSE) based MIMO relay precoding design, MSINR-based MIMO relay precoding design is able to achieve a better tradeoff between the communication reliability and the realized ergodic capacity. © 2012 IEEE.

Ibrahim Hemadeh, Pei Xiao, Yasin Kabiri, Lixia Xiao, Vincent Fusco (2020)Polarization Modulation Design for Reduced RF Chain Wireless, In: IEEE Transactions on Communications Institute of Electrical and Electronics Engineers

In this treatise, we introduce a novel polarization modulation (PM) scheme, where we capitalize on the reconfigurable polarization antenna design for exploring the polarization domain degrees of freedom, thus boosting the system throughput. More specifically, we invoke the inherent properties of a dual polarized (DP) antenna for transmitting additional information carried by the axial ratio (AR) and tilt angle of elliptic polarization, in addition to the information streams transmitted over its vertical (V) and horizontal (H) components. Furthermore, we propose a special algorithm for generating an improved PM constellation tailored especially for wireless PM modulation. We also provide an analytical framework to compute the average bit error rate (ABER) of the PM system. Furthermore, we characterize both the discrete-input continuousoutput memoryless channel (DCMC) capacity and the continuous-input continuous-output memoryless channel (CCMC) capacity as well as the upper and lower bounds of the CCMC capacity. The results show the superiority of our proposed PM system over conventional modulation schemes in terms of both higher throughput and lower BER. In particular, our simulation results indicate that the gain achieved by the proposed Q-dimensional PM scheme spans between 10dB and 20dB compared to the conventional modulation. It is also demonstrated that the PM system attains between 54% and 87.5% improvements in terms of ergodic capacity. Furthermore, we show that this technique can be applied to MIMO systems in a synergistic manner in order to achieve the target data rate target for 5G wireless systems with much less system resources (in terms of bandwidth and thenumber of antennas) compared to existing MIMO techniques.

Lixia Xiao, Pei Xiao, Yue Xiao, Chaowu Wu, De Mi, Ibrahim A. Hemadeh (2019)Rectangular Differential OFDM with index modulation, In: Proceedings of the 2019 IEEE 89th Vehicular Technology Conference: VTC2019-Spring Institute of Electrical and Electronics Engineers (IEEE)

Orthogonal Frequency Division Multiplexing (OFDM) with Index Modulation (OFDM-IM), which conveyed information bits via the activated indices and constellation symbols is a promising technique in the next wireless communications. In the OFDM-IM scheme, only part of subcarriers are activated to transmit information, the inactive subcarriers transmit zero symbols, so that the conventional differential coding is not suitable for the adjacent subcarriers. In order to address this issue, in this paper, a novel Rectangular Differential OFDM-IM (RD-OFDM-IM) scheme is proposed to exploit the benefits of OFDM-IM dispensing with Channel State Information (CSI). In the proposed RD-OFDM-IM scheme, N subcarriers are partitioned into G subblocks and index modulation is employed in each subblock first. Then rectangular differential coding is invoked during two adjacent subblocks, so that nocoherent detection can be employed for the proposed RD-OFDM-IM scheme. Simulation results are shown that the proposed RD-OFDM-IM scheme is capable of providing considerable performance gain over conventional Differential OFDM (D-OFDM) scheme with lower Peak Average Power Ratio (PAPR).

Y Chen, Z Lin, P Xiao, M Dianati (2012)Average per-user rate for MIMO systems with SDM-FDPS, In: IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRCpp. 698-702

In this paper, we introduce the concept of average per-user rate to the multiuser Multiple-Input, Multiple-Output (MIMO) system with the frequency domain packet scheduler (FDPS) at base stations, which provides an estimate of the rate that the system could provide for each admitted user. The proposed admission control is designed by comparing the user's quality of service (QoS) requirements with the transmission rate that the system can offer. The analytical model is based on the generalized 3GPP LTE downlink transmission for which two Spatial Division Multiplexing (SDM) multiuser MIMO schemes are investigated, namely, Single User (SU) and Multi-user (MU) MIMO schemes. The main contribution of this paper is the derivation of the achievable rate for each user in the SDM MIMO systems based on a mathematical model of the Signal to Interference plus Noise Ratio (SINR) distribution with the frequency domain packet scheduler. The achievable rate provides insights into the system's performance from a different perspective. © 2012 IEEE.

J Wu, P Xiao, M Sellathurai, S Blostein, T Ratnarajah (2011)Joint complex diversity coding and channel coding over space, time and frequency, In: IET SIGNAL PROCESSING5(7)pp. 643-651 IET

This study provides a general diversity analysis for joint complex diversity coding (CDC) and channel coding-based space-time-frequency codeing is provided. The mapping designs from channel coding to CDC are crucial for efficient exploitation of the diversity potential. This study provides and proves a sufficient condition of full diversity construction with joint three-dimensional CDC and channel coding, bit-interleaved coded complex diversity coding and symbol-interleaved coded complex diversity coding. Both non-iterative and iterative detections of joint channel code and CDC transmission are investigated. The proposed minimum mean-square error-based iterative soft decoding achieves the performance of the soft sphere decoding with reduced complexity.

Chang He, Aijun Cao, Lixia Xiao, Lei Zhang, Pei Xiao, Konstantinos Nikitopoulos (2019)Enhanced DCT-OFDM System With Index Modulation, In: IEEE Transactions on Vehicular Technology Institute of Electrical and Electronics Engineers (IEEE)

Discrete cosine transform (DCT) based orthogonal frequency division multiplexing (OFDM), which has double number of subcarrier compared to the classic discrete fourier transform (DFT) based OFDM (DFT-OFDM) at the same bandwidth, is a promising high spectral efficiency multicarrier techniques for future wireless communication. In this paper, an enhanced DCT-OFDM with index modulation (IM) (EDCT-OFDM-IM) is proposed to further exploit the benefits of the DCT-OFDM and IM techniques. To be more specific, a pre-filtering method based DCT-OFDM-IM transmitter is first designed and the non-linear maximum likelihood (ML) is developed for our EDCT-OFDM-IM system. Moreover, the average bit error probability (ABEP) of the proposed EDCT-OFDM-IM system is derived, which is confirmed by our simulation results. Both simulation and theoretical results are shown that the proposed EDCT-OFDM-IM system exhibits better bit error rate (BER) performance over the conventional DFT-OFDM-IM and DCT-OFDM-IM counterparts.

Lixia Xiao, Pei Xiao, Yue Xiao, Ibrahim Hemadeh, Abdelrahim Mohamed, Lajos Hanzo (2018)Bayesian Compressive Sensing Assisted Space Time Block Coded Quadrature Spatial Modulation, In: IEEE Transactions on Vehicular Technology67(10)pp. 10044-10048 Institute of Electrical and Electronics Engineers (IEEE)

A novel Multiple-Input and Multiple- Output (MIMO) transmission scheme termed as Space- Time Block Coded Quadrature Spatial Modulation (STBC-QSM) is proposed. It amalgamates the concept of Quadrature Spatial Modulation (QSM) and Space- Time Block Coding (STBC) to exploit the diversity benefits of STBC relying on sparse Radio Frequency (RF) chains. In the proposed STBC-QSM scheme, the conventional constellation points of the STBC structure are replaced by the QSM symbols, hence the information bits are conveyed both by the antenna indices as well as by conventional STBC blocks. Furthermore, an efficient Bayesian Compressive Sensing (BCS) algorithm is developed for our proposed STBCQSM system. Both our analytical and simulation results demonstrated that the proposed scheme is capable of providing considerable performance gains over the existing schemes. Moreover, the proposed BCS detector is capable of approaching the Maximum Likelihood (ML) detector’s performance despite only imposing a complexity near similar to that of the Minimum Mean Square Error (MMSE) detector in the high Signal to Noise Ratio (SNR) regions.

A Sohail, P Xiao, BG Evans (2012)Optimal Power Allocation Scheme under FSA Constraint for OFDM Based Cognitive Radio Systems, In: IV INTERNATIONAL CONGRESS ON ULTRA MODERN TELECOMMUNICATIONS AND CONTROL SYSTEMS 2012 (ICUMT)pp. 195-200
Zheng Chu, Wanming Hao, Pei Xiao, Fuhui Zhou, Rose Qingyang Hu (2019)Low-Latency Driven Energy Efficiency for D2D Communications, In: IEEE ICC Conference Proceedings IEEE

Low latency and energy efficiency are two important performance requirements in various fifth-generation (5G) wire-less networks. In order to jointly design the two performance requirements, in this paper a new performance metric called effective energy efficiency (EEE) is defined as the ratio of the effective capacity (EC) to the total power consumption in a cellular network with underlaid device to device (D2D) communications. We aim to maximize the EEE of the D2D network subject to the D2D device power constraints and the minimum rate constraint of the cellular network. Due to the non-convexity of the problem, we propose a two-stage difference-of-two-concave (DC) function approach to solve this problem. Towards that end, we first introduce an auxiliary variable to transfer the fractional objective function into a subtractive form. We then propose a successive convex approximation (SCA) algorithm to iteratively solve the resulting non-convex problem. The convergence and the global optimality of the proposed SCA algorithm are both analyzed. The numerical results are presented to demonstrate the effectiveness of the proposed algorithm.

"The authors propose some robust adaptive multiuser detection schemes for direct-sequence code-division multipleaccess multipath frequency-selective fading channels. Multiple access interference (MAI) and intersymbol interference (ISI) are presented in an identical format using expanded signal subspace, which facilitates multiuser detection in a symbol-bysymbol fashion. This study contributes to the theoretical aspect of adaptive multiuser detection by proving that the optimum linear multiuser detectors that achieve maximum signal-to-interference-plus-noise ratio (SINR) must exist in the signal subspace, and the theoretic SINR upper bound is also derived. Another contribution of this study is to propose the design of multiuser detectors in an expanded signal subspace, and introduce subspace estimation and Kalman filtering algorithms for their adaptive implementation. To robustify the adaptive detectors against subspace estimation and channel estimation errors, a modified projection approximation subspace tracking (PAST) algorithm is proposed for subspace tracking. It is demonstrated by simulations that these adaptive detectors effectively suppress both MAI and ISI and converge to the optimum SINR. They are robust against subspace estimation errors and channel estimation errors compared to the conventional Wiener minimum mean square error (MMSE) detector."

Xiaoying Zhang, Lei Zhang, Pei Xiao, Jibo Wei (2019)Fine Timing Synchronization Based on Modified Expectation Maximization Clustering Algorithm for OFDM Systems, In: IEEE Wireless Communications Letters Institute of Electrical and Electronics Engineers (IEEE)

A novel fine timing synchronizaton method based on the modified expectation-maximization (EM) clustering algorithm is proposed for OFDM systems. Using the cross-correlation metrics of one preamble symbol, the cross-correlation peaks corresponding to the channel arriving paths are identified by the proposed modified EM clustering algorithm, the position of the first coherent cross-correlation peak is then chosen as the start of the frame. Computer simulations show that the proposed method is robust in multipath dispersive channels and achieves superior performance to existing techniques in terms of timing accuracy.

Manijeh Bashar, Kanapathippillai Cumanan, Alister G. Burr, Hien Quoc Ngo, Erik G. Larsson, Pei Xiao (2019)On the Energy Efficiency of Limited-Backhaul Cell-Free Massive MIMO, In: Proceedings of the 2019 IEEE International Conference on Communications (ICC): Green Communication Systems and Networks Symposium Institute of Electrical and Electronics Engineers (IEEE)

We investigate the energy efficiency performance of cell-free Massive multiple-input multiple-output (MIMO), where the access points (APs) are connected to a central processing unit (CPU) via limited-capacity links. Thanks to the distributed maximum ratio combining (MRC) weighting at the APs, we propose that only the quantized version of the weighted signals are sent back to the CPU. Considering the effects of channel estimation errors and using the Bussgang theorem to model the quantization errors, an energy efficiency maximization problem is formulated with per-user power and backhaul capacity constraints as well as with throughput requirement constraints. To handle this non-convex optimization problem, we decompose the original problem into two sub-problems and exploit a successive convex approximation (SCA) to solve original energy efficiency maximization problem. Numerical results confirm the superiority of the proposed optimization scheme.

Wanming Hao, Zheng Chu, Fuhui Zhou, Pei Xiao, Victor C. M. Leung, Rahim Tafazolli (2019)Hybrid Precoding Design for SWIPT Joint Multicast-Unicast mmWave System with Subarray Structure, In: IEEE ICC Conference Proceedings

In this paper, we investigate the hybrid precoding design for joint multicast-unicast millimeter wave (mmWave) system, where the simultaneous wireless information and power transform is considered at receivers. The subarray-based sparse radio frequency chain structure is considered at base station (BS). Then, we formulate a joint hybrid analog/digital precoding and power splitting ratio optimization problem to maximize the energy efficiency of the system, while the maximum transmit power at BS and minimum harvested energy at receivers are considered. Due to the difficulty in solving the formulated problem, we first design the codebook-based analog precoding approach and then, we only need to jointly optimize the digital precoding and power splitting ratio. Next, we equivalently transform the fractional objective function of the optimization problem into a subtractive form one and propose a two-loop iterative algorithm to solve it. For the outer loop, the classic Bi-section iterative algorithm is applied. For the inner loop, we transform the formulated problem into a convex one by successive convex approximation techniques, which is solved by a proposed iterative algorithm. Finally, simulation results are provided to show the performance of the proposed algorithm.

Lixia Xiao, Pei Xiao, Chao Xu, Ibrahim A. Hemadeh, De Mi, Wanming Hao (2019)Generalized Space Time Block Coded Spatial Modulation Systems, In: Proceedings of the 2019 Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (IEEE PIMRC 2019) Institute of Electrical and Electronics Engineers (IEEE)

In this paper, Generalized Space-Time Block Coded Spatial Modulation (GSTBC-SM) is proposed for Multiple-Input and Multiple-Output (MIMO) system, which can be extended into an arbitrary even number of Transmit Antennas (TAs). The proposed GSTBC-SM scheme employs the hybrid concepts of Generalized Space-Time Block Coding (GSTBC) and Spatial Modulation (SM) to further exploit the diversity benefits of GSTBC using sparse Radio Frequency (RF) chains. To be more specific, the information bits are divided into Nu groups and each group is modulated by SM scheme. Finally, the Nu symbols are invoked for GSTBC structure. In order to demonstrated the advantages of our proposed GSTBCSM schemes, the theoretical Average Bit Error Probability (ABEP) of our proposed GSTBC-SM is derived. Both our analytical and simulation results demonstrated that the proposed GSTBC-SM scheme is capable of providing considerable performance gains over the corresponding GSTBC schemes at the same transmit rate associated with the same number of RF chains.

Wanming Hao, Fuhui Zhou, Zheng Chu, Pei Xiao, Rahim Tafazolli, Naofal Al Dhahir (2019)Beam Alignment for MIMO-NOMA Millimeter Wave Communication Systems, In: IEEE International Conference on Communications (ICC) Conference Proceedings

Abstract—Millimeter wave (mmWave) communication is a promising technology in future wireless networks because of its wide bandwidths that can achieve high data rates. However, high beam directionality at the transceiver is needed due to the large path loss at mmWave. Therefore, in this paper, we investigate the beam alignment and power allocation problem in a nonorthogonal multiple access (NOMA) mmWave system. Dierent from the traditional beam alignment problem, we consider the NOMA scheme during the beam alignment phase when two users are at the same or close angle direction from the base station. Next, we formulate an optimization problem of joint beamwidth selection and power allocation to maximize the sum rate, where the quality of service (QoS) of the users and total power constraints are imposed. Since it is dicult to directly solve the formulated problem, we start by fixing the beamwidth. Next, we transform the power allocation optimization problem into a convex one, and a closed-form solution is derived. In addition, a one-dimensional search algorithm is used to find the optimal beamwidth. Finally, simulation results are conducted to compare the performance of the proposed NOMA-based beam alignment and power allocation scheme with that of the conventional OMA scheme.

Lei Zhang, A Ijaz, Pei Xiao, Atta Quddus, Rahim Tafazolli (2016)Single-rate and Multi-rate Multi-service Systems for Next Generation and Beyond Communications, In: IEEE 27th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications

To flexibly support diverse communication requirements (e.g., throughput, latency, massive connection, etc.) for the next generation wireless communications, one viable solution is to divide the system bandwidth into several service subbands, each for a different type of service. In such a multi-service (MS) system, each service has its optimal frame structure while the services are isolated by subband filtering. In this paper, a framework for multi-service (MS) system is established based on subband filtered multi-carrier (SFMC) modulation. We consider both single-rate (SR) and multi-rate (MR) signal processing as two different MS-SFMC implementations, each having different performance and computational complexity. By comparison, the SR system outperforms the MR system in terms of performance while the MR system has a significantly reduced computational complexity than the SR system. Numerical results show the effectiveness of our analysis and the proposed systems. These proposed SR and MR MS-SFMC systems provide guidelines for next generation wireless system frame structure optimization and algorithm design.

J Yue, Z Lin, B Vucetic, P Xiao (2014)The Design of Degree Distribution for Distributed Fountain Codes in Wireless Sensor Networks, In: 2014 IEEE International Conference on Communications (ICC)pp. 5796-5801

In this paper, we first analyse bit error rate (BER) bounds of the distributed network coding (DNC) scheme based on the Luby-transform (LT) codes, which is a class of fountain codes, for wireless sensor networks (WSNs). Then we investigate the effect from two parameters of the degree distributions, i.e., the degree value and the proportion of odd degree, to the performance of the LT-based DNC scheme. Based on the analysis and investigation results, a degree distribution design criteria is proposed for the DNC scheme based on fountain codes over Rayleigh fading channels. We compare the performance of the DNC scheme based on fountain codes using degree distributions designed in this paper with other schemes given in the literature. The comparison results show that the degree distributions designed by using the proposed criteria have better performance.

Juquan Mao, Chin-Liang Wang, Lei Zhang, Chang He, Pei Xiao, Konstantinos Nikitopoulos (2018)A DHT-based Multicarrier Modulation System with Pairwise ML Detection, In: Proceedings of the 2017 IEEE 28th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC)pp. 1-6 IEEE

This paper proposes a complex-valued discrete multicarrier modulation (MCM) system based on the real-valued discrete Hartley transform (DHT) and its inverse (IDHT). Unlike conventional discrete Fourier transform (DFT), DHT can not diagonalize the multipath fading channel due to its inherent properties, which results in the mutual interference between subcarriers in the same mirror-symmetrical pair.We explore the interference pattern in order to seek an optimal solution to utilize the channel diversity for the purpose of enhancing system bit error performance (BEP). It is shown that the optimal channel diversity gain can be achieved via a pairwise maximum likelihood (ML) detection, taking into account not only the subcarrier’s own channel quality but also the channel state of its mirror-symmetrical peer. Performance analysis indicates that DHT-based MCM mitigates the fast fading effect by averaging the channel power gain on the mirror-symmetrical subcarriers. Simulation results show that the proposed system has a substantial improvement in BEP over conventional DFT-Based MCM.

Jing Zhang, Su Hu, Zilong Liu, Pei Wang, Pei Xiao, Yuan Gao (2019)Real-Valued Orthogonal Sequences for Iterative Channel Estimation in MIMO-FBMC Systems, In: IEEE Access4pp. 1-10 Institute of Electrical and Electronics Engineers (IEEE)

In this paper, we present a novel sequence design for efficient channel estimation in multiple input multiple output filterbank multicarrier (MIMO-FBMC) system with offset QAM modulation. Our proposed sequences, transmitted over one FBMC/OQAM symbol, are real-valued in the frequency domain and display zero-correlation zone properties in the time-domain. The latter property enables optimal channel estimation for a least-square estimator in frequency-selective fading channels. To further improve the system performance, we mitigate the data interference by an iterative feedback loop between channel estimation and FBMC demodulation. Simulation results validate that our proposed real-valued orthogonal sequences and the iterative channel estimation and demodulation scheme provide a practical solution for enhanced performance in preamble-based MIMO-FBMC systems.

Manijeh Bashar, Kanapathippillai Cumanan, Alister G. Burr, Hien Quoc Ngo, Lajos Hanzo, Pei Xiao (2019)NOMA/OMA Mode Selection-Based Cell-Free Massive MIMO, In: Proceedings of the 2019 IEEE International Conference on Communications (ICC): Wireless Communications Symposium Institute of Electrical and Electronics Engineers (IEEE)

In this paper, non-orthogonal-multiple-access (NOMA)-based cell-free massive multiple-input multiple-output (MIMO) is investigated, where the users are grouped into multiple clusters. Exploiting conjugate beamforming, the bandwidth efficiency (BE) of the system is derived while the assumption that the users performing realistic successive interference cancellation (SIC) based on only the knowledge of channel statistics. The max-min fairness problem of maximizing the lowest user BE is investigated and an iterative bisection method is developed to determine the optimal solution to the max-min BE problem. Numerical results are presented for validating the proposed design’s performance, and a mode switching scheme is conceived for selecting a specific Mode = f OMA, NOMA g that maximizes the system’s BE.

Ke Lai, Lei Wen, Jing Lei, Gaojie Chen, Pei Xiao, Amine Maaref (2018)Codeword Position Index based Sparse Code Multiple Access System, In: IEEE Wireless Communications Letterspp. 1-1 Institute of Electrical and Electronics Engineers (IEEE)

In this letter, a novel variant of sparse code multiple access (SCMA), called codeword position index based SCMA (CPI-SCMA), is proposed. In this scheme, the information is transmitted not only by the codewords in a M-point SCMA codebook, but also by the indices of the codeword positions in a data block. As such, both the power and transmission efficiency (TE) can be improved. Furthermore, CPI-SCMA can achieve better error rate performance compares to conventional SCMA (C-SCMA) in the region of moderate and high SNRs.

Lei Zhang, Ayesha Ijaz, Pei Xiao, Kezhi Wang, Deli Qiao, Muhammad Ali Imran (2019)Optimal Filter Length and Zero Padding Length Design for Universal Filtered Multi-carrier (UFMC) System, In: IEEE Access Institute of Electrical and Electronics Engineers (IEEE)

Universal filtered multi-carrier (UFMC) systems offer a flexibility of filtering arbitrary number of subcarriers to suppress out of band (OoB) emission, while keeping the orthogonality between subcarriers and robustness to transceiver imperfections. Such properties enable it as a promising candidate waveform for Internet of Things (IoT) communications. However, subband filtering may affect system performance and capacity in a number of ways. In this paper, we first propose the conditions for interference-free one-tap equalization and corresponding signal model in the frequency domain for UFMC system. The impact of subband filtering on the system performance is analyzed in terms of average signal-to-noise ratio (SNR), capacity and bit error rate (BER) and compared with the orthogonal frequency division multiplexing (OFDM) system. This is followed by filter length selection strategies to provide guidelines for system design. Next, by taking carrier frequency offset (CFO), timing offset (TO), insufficient guard interval between symbols and filter tail cutting (TC) into consideration, an analytical system model is established. In addition, a set of optimization criteria in terms of filter length and guard interval/filter TC length subject to various constraints is formulated to maximize the system capacity. Numerical results show that the analytical and corresponding optimal approaches match the simulation results, and the proposed equalization algorithms can significantly improve the BER performance.

A Sohail, M Al-Imari, P Xiao, BG Evans (2014)Theoretical Analysis of Power Saving In Cognitive Radio with Arbitrary Inputs, In: IEEE Transactions on Vehicular Technology

In Orthogonal Frequency Division Multiplexing (OFDM) based cognitive radio systems, power optimization algorithms have been evaluated to maximize the achievable data rates of the Secondary User (SU). However, unrealistic assumptions are made in the existing work, i.e. a Gaussian input distribution and traditional interference model that assumes frequency division multiplexing modulated Primary User (PU) with perfect synchronization between the PU and the SU. In this paper, we first derive a practical interference model by assuming OFDM modulated PU with imperfect synchronization. Based on the new interference model, the power optimization problem is proposed for the Finite Symbol Alphabet (FSA) input distribution (i.e., M-QAM), as used in practical systems. The proposed scheme is shown to save transmit power and to achieve higher data rates compared to the Gaussian optimized power allocation and the uniform power loading schemes. Furthermore, a theoretical framework is established in this paper to estimate the power saving by evaluating optimal power allocation for the Gaussian and the FSA input. Our theoretical analysis is verified by simulations and proved to be accurate. It provides guidance for the system design and gives deeper insights into the choice of parameters affecting power saving and rate improvement.

Juquan Mao, Lei Zhang, Pei Xiao (2020)Interference Analysis and Power Allocation in the Presence of Mixed Numerologies, In: IEEE Transactions on Wireless Communications Institute of Electrical and Electronics Engineers

The flexibility in supporting heterogeneous services with vastly different technical requirements is one of the distinguishing characteristics of the fifth generation (5G) communication systems and beyond. One viable solution is to divide the system bandwidth into several bandwidth parts (BWPs), each having a distinct numerology optimized for a particular service. However, multiplexing of mixed numerologies over a unified physical infrastructure comes at the cost of induced interference. In this paper, we develop an analytical system model for inter-numerology interference (InterNI) analysis in orthogonal frequency-division multiplexing (OFDM) systems with and without filter processing in the presence of mixed numerologies. With the analytical model, the level of InterNI is quantified by the developed analytical metric, which is expressed as a function of several system parameters. This leads to an analysis and evaluation of these parameters for meeting a given distortion target. Moreover, a case study on power allocation utilizing the derived analysis is presented, where an optimization problem of maximizing the sum rate is formulated, and a solution is also provided. It is also demonstrated that a filtered-OFDM system better accommodates the coexistence of mixed numerologies. The proposed model provides an accurate analytical guidance for the multi-service design in 5G and beyond systems.

Lixia Xiao, Da Chen, Ibrahim Hemadeh, Pei Xiao, Tao Jiang (2020)Generalized Space Time Block Coded Spatial Modulation for Open-Loop Massive MIMO Downlink Communication Systems, In: IEEE Transactions on Communications Institute of Electrical and Electronics Engineers

In this paper, we propose a generalized space-time block coded spatial modulation (GSTBC-SM) scheme for openloop massive multiple-input and multiple-output (MIMO) downlink communication systems. Specifically, we firstly partition the information bits into multiple groups with each group modulated by the spatial modulation (SM), where the SM symbols are invoked for orthogonal STBC (OSTBC) and quasi-orthogonal STBC (Q-OSTBC) structures. Then, message passing (MP) and block minimum mean square equalization (B-MMSE) detectors are designed for our GSTBC-SM systems, to achieve near-optimal performance with significantly reduced complexity in massive MIMO configurations. Finally, we derive the theoretical average bit error probability (ABEP) of the proposed scheme. The main contribution is that the propose scheme achieves high transmission rate and diversity gain even with small number of radio frequency (RF) chains at the transmitter. Simulation results verify the theoretical derivations and show that the proposed GSTBCSM scheme provides near 20 dB gain over the conventional GSTBC scheme under massive MIMO configurations. Index Terms—Spatial Modulation (SM), Space Time Block Coding (STBC), High throughput, Diversity gain.

Lei Zhang, Pei Xiao, Atta Quddus (2016)Cyclic Prefix Based Universal Filtered Multi-carrier System and Performance Analysis, In: IEEE Signal Processing Letters23(9)pp. 1197-1201 IEEE

Recently proposed universal filtered multi-carrier (UFMC) system is not an orthogonal system in multipath channel environments and might cause significant performance loss. In this paper, we propose a cyclic prefix (CP) based UFMC system and first analyze the conditions for interference-free one-tap equalization in the absence of transceiver imperfections. Then the corresponding signal model and output SNR (signal-tonoise ratio) expression are derived. In the presence of carrier frequency offset (CFO), timing offset (TO) and insufficient CP length, we establish an analytical system model as a summation of desired signal, inter-symbol interference (ISI), intercarrier interference (ICI) and noise. New channel equalization algorithms are proposed based on the derived analytical signal model. Numerical results show that the derived model matches the simulation results precisely, and the proposed equalization algorithms improve the UFMC system performance in terms of bit error rate (BER).

Zilong Liu, Pei Xiao, Zeina Mheich (2019)Power-Imbalanced Low-Density Signatures (LDS) From Eisenstein Numbers, In: Proceedings of The 16th IEEE Asia Pacific Wireless Communications Symposium 2019 (APWCS 2019) Institute of Electrical and Electronics Engineers (IEEE)

As a special case of sparse code multiple access (SCMA), low-density signatures based code-division multiple access (LDS-CDMA) was widely believed to have worse error rate performance compared to SCMA. With the aid of Eisenstein numbers, we present a novel class of LDS which can achieve error rate performances comparable to that of SCMA in Rayleigh fading channels and better performances in Gaussian channels. This is achieved by designing power-imbalanced LDS such that variation of user powers can be seen both in every chip window and the entire sequence window. As LDS-CDMA is more flexible in terms of its backwards compatibility, our proposed LDS are a promising sequence candidate for dynamic machine-type networks serving a wide range of communication devices.

Xiaoran Liu, Xiaoying Zhang, Lei Zhang, Pei Xiao, Jibo Wei, Haijun Zhang, Victor C.M Leung (2020)PAPR Reduction Using Iterative Clipping/Filtering and ADMM Approaches for OFDM-Based Mixed-Numerology Systems, In: IEEE Transactions on Wireless Communications

Mixed-numerology transmission is proposed to support a variety of communication scenarios with diverse requirements. However, as the orthogonal frequency division multiplexing (OFDM) remains as the basic waveform, the peak-to average power ratio (PAPR) problem is still cumbersome. In this paper, based on the iterative clipping and filtering (ICF) and optimization methods, we investigate the PAPR reduction in the mixed numerology systems.We first illustrate that the direct extension of classical ICF brings about the accumulation of inter-numerology interference (INI) due to the repeated execution. By exploiting the clipping noise rather than the clipped signal, the noiseshaped ICF (NS-ICF) method is then proposed without increasing the INI. Next, we address the in-band distortion minimization problem subject to the PAPR constraint. By reformulation, the resulting model is separable in both the objective function and the constraints, and well suited for the alternating direction method of multipliers (ADMM) approach. The ADMM-based algorithms are then developed to split the original problem into several subproblems which can be easily solved with closedform solutions. Furthermore, the applications of the proposed PAPR reduction methods combined with filtering and windowing techniques are also shown to be effective.

In the literature, optimal power assuming Gaussian input has been evaluated in OFDM based Cognitive Radio (CR) systems to maximize the capacity of the secondary user while keeping the interference introduced to the primary user band within tolerable range. However, the Gaussian input assumption is not practical and Finite Symbol Alphabet (FSA) input distributions, i.e., M-QAM are used in practical systems. In this paper, we consider the power optimization problem under the condition of FSA inputs as used in practical systems, and derive an optimal power allocation strategy by capitalizing on the relationship between mutual information and minimum mean square error. The proposed scheme is shown to save transmit power in a CR system compared to its conventional counterpart, that assumes Gaussian input. In addition to extra allocated power, i.e., power wastage, the conventional power allocation scheme also causes nulling of more subcarriers, leading to reduced transmission rate, compared to the proposed scheme. The proposed optimal power algorithm is evaluated and compared with the conventional algorithm assuming Gaussian input through simulations. Numerical results reveal that for interference threshold values ranging between 1 mW to 3 mW, the transmit power saving with the proposed algorithm is in the range between 55-75%, 42-62% and 12-28% whereas the rate gain is in the range between 16.8-12.4%, 13-11.8% and 3-5.8% for BPSK, QPSK and 16-QAM inputs, respectively.

Aijun Cao, Y Gao, Pei Xiao, Rahim Tafazolli (2015)Performance Analysis of an Ultra Dense Network with and without Cell Cooperation, In: 2015 12th International Symposium on Wireless Communication Systems (ISWCS) Procedingspp. 51-55 IEEE

This paper presents an analysis on performance of an ultra dense network (UDN) with and without cell cooperation from the perspective of network information theory. We propose a UDN performance metric called Total Average Geometry Throughput which is independent from the user distribution or scheduler etc. This performance metric is analyzed in detail for UDN with and without cooperation. The numerical results from the analysis show that under the studied system model, the total average geometry throughput reaches its maximum when the inter-cell distance is around 6 ~ 8 meters, both without and with cell cooperation. Cell cooperation can significantly reduce inter-cell interference but not remove it completely. With cell cooperation and an optimum number of the cooperating cells the maximum performance gain can be achieved. Furthermore, the results also imply that there is an optimum aggregate transmission power if considering the energy cost per bit.

J Zhong, G Chen, Juquan Mao, S Dang, Pei Xiao (2018)Iterative Frequency Domain Equalization for MIMO-GFDM Systems, In: IEEE Access6pp. 19386-19395 IEEE

This paper proposes a new iterative frequency domain equalization (FDE) algorithm for multiple-input multipleoutput (MIMO)-frequency division multiplexing (GFDM) systems. This new FDE scheme is capable of enhancing the system fidelity by considering the complete frequency-domain second order description of the received signal. In addition, a new nulling filter design is also proposed for MIMO-GFDM systems to remove the residual interference, which further improves the system fidelity compared to the traditional scheme. Simulation results are presented to verify the effectiveness and efficiency of the proposed FDE algorithm.

G Chen, D Liang, M Ghoraishi, Pei Xiao, Rahim Tafazolli (2015)Optimum User Selection for Hybrid-Duplex Device-to-Device in Cellular Networks, In: 2015 International Symposium on Wireless Communication Systems (ISWCS) Proceedingspp. 16-20

This paper studies the optimum user selection scheme in a hybrid-duplex device-to-device (D2D) cellular networks. We derive an analytical integral-form expression of the cumulative distribution function (CDF) for the received signal-to-noise-plus-interference-ratio (SINK) at the D2D node, based on which the closed-form of the outage probability is obtained. Analysis shows that the proposed user selection scheme achieves the best SINK at the D2D node with interference to base station being limited by a pre-defined level. Hybrid duplex D2D can be switched between half and full duplex according to different residual self-interference to enhance the throughput of D2D pair. Simulation results are presented to validate the analysis.

Abdelrahim Mohamed, Atta Quddus, Pei Xiao, Bernard Hunt, Rahim Tafazolli (2020)5G and LTE-TDD Synchronized Coexistence with Blind Retransmission and Mini-Slot Uplink, In: 91st IEEE Vehicular Technology Conference VTC2020-Spring

The fifth-generation (5G) new radio (NR) cellular system promises a significant increase in capacity with reduced latency. However, the 5G NR system will be deployed along with legacy cellular systems such as the long-term evolution (LTE). Scarcity of spectrum resources in low frequency bands motivates adjacent-/co-carrier deployments. This approach comes with a wide range of practical benefits and it improves spectrum utilization by re-using the LTE bands. However, such deployments restrict the 5G NR flexibility in terms of frame allocations to avoid the most critical mutual adjacent-channel interference. This in turns prevents achieving the promised 5G NR latency figures. In this we paper, we tackle this issue by proposing to use the minislot uplink feature of 5G NR to perform uplink acknowledgement and feedback to reduce the frame latency with selective blind retransmission to overcome the effect of interference. Extensive system-level simulations under realistic scenarios show that the proposed solution can reduce the peak frame latency for feedback and acknowledgment up to 33% and for retransmission by up to 25% at a marginal cost of an up to 3% reduction in throughput.

S Bassoy, Mona Jaber, Muhammad Imran, Pei Xiao (2016)Load Aware Self-Organising User-Centric Dynamic CoMP Clustering for 5G Networks, In: IEEE Access4pp. 2895-2906 IEEE

Coordinated multi-point (CoMP) is a key feature for mitigating inter-cell interference, improve system throughput and cell edge performance. However, CoMP implementation requires complex beamforming/scheduling design, increased backhaul bandwidth, additional pilot overhead and precise synchronisa-tion. Cooperation needs to be limited to a few cells only due to this imposed overhead and complexity. Hence, small CoMP clusters will need to be formed in the network. In this paper, we first present a self organising, user-centric CoMP clustering algorithm in a control/data plane separation architecture (CDSA), proposed for 5G to maximise spectral efficiency (SE) for a given maximum cluster size. We further utilise this clustering algorithm and introduce a novel two-stage re-clustering algorithm to reduce high load on cells in hotspot areas and improve user satisfaction. Stage-1 of the algorithm utilises maximum cluster size metric to introduce additional capacity in the system. A novel re-clustering algorithm is introduced in stage-2 to distribute load from highly loaded cells to neighbouring cells with less load for multi-user (MU) joint transmission (JT) CoMP case. We show that unsatisfied users due to high load can be significantly reduced with minimal impact on SE.

Lixia Xiao, Pei Xiao, Yue Xiao, Harald Haas, Abdelrahim Mohamed, Lajos Hanzo (2019)Compressive Sensing Assisted Generalized Quadrature Spatial Modulation for Massive MIMO systems, In: IEEE Transactions on Communicationspp. 1-1 Institute of Electrical and Electronics Engineers (IEEE)

A novel Multiple-Input and Multiple- Output (MIMO) transmission scheme termed as Generalized Quadrature Spatial Modulation (G-QSM) is proposed. It amalgamates the concept of Quadrature Spatial Modulation (QSM) and spatial multiplexing for the sake of achieving a high throughput, despite relying on low number of Radio Frequency (RF) chains. In the proposed G-QSM scheme, the conventional constellation points of the spatial multiplexing structure are replaced by the QSM symbols, hence the information bits are conveyed both by the antenna indices as well as by the classic Amplitude/Phase Modulated (APM) constellation points. The upper bounds of the Average Bit Error Probability (ABEP) of the proposed G-QSM system in high throughput massive MIMO configurations are derived. Furthermore, an Efficient Multipath Orthogonal Matching Pursuit (EMOMP) based Compressive Sensing (CS) detector is developed for our proposed G-QSM system. Both our analytical and simulation results demonstrated that the proposed scheme is capable of providing considerable performance gains over the existing schemes in massive MIMO configurations.

Zheng Chu, Wanming Hao, Pei Xiao, Jia Shi (2019)Intelligent Reflecting Surface Aided Multi-Antenna Secure Transmission, In: IEEE Wireless Communications Letters Institute of Electrical and Electronics Engineers (IEEE)

In this paper, we propose intelligent reflecting surface (IRS) aided multi-antenna physical layer security. We present a power efficient scheme to design the secure transmit power allocation and the surface reflecting phase shift. It aims to minimize the transmit power subject to the secrecy rate constraint at the legitimate user. Due to the non-convex nature of the formulated problem, we propose an alternative optimization algorithm and the semidefinite programming (SDP) relaxation to deal with this issue. Also, the closed-form expression of the optimal secure beamformer is derived. Finally, simulation results are presented to validate the proposed algorithm, which highlights the performance gains of the IRS to improve the secure transmission.

BK Khoo, P Xiao, S Le Goff, B Sharif, C Tsimenidis (2010)A Low Complexity Transmit Diversity Scheme Using Moderate-Sized Constellations, In: IET Electronic Letters46(6)pp. 460-462 IET

In the conventional space-time coding technique, nT radio frequency (RF) chains are employed to transmit signals simultaneously from nT transmit antennas. A low-complexity transmit diversity scheme with nT=2 transmit antennas is proposed, which employs only one RF chain as well as a low-complexity switch for transmission.

P Xiao, Z Lin, A Fagan, C Cowan, B Vucetic, Y Wu (2011)Frequency-domain equalization for OFDMA-based multiuser MIMO systems with improper modulation schemes, In: EURASIP JOURNAL ON ADVANCES IN SIGNAL PROCESSINGARTN 7pp. 73-?
P Xiao, R Tafazolli, K Moessner, A Gluhak (2012)Codebook Based Single-User MIMO System Design with Widely Linear Processing, In: IEEE Transactions on CommunicationsPP(99)pp. 1-7 IEEE

This work addresses joint transceiver optimization for multiple-input, multiple-output (MIMO) systems. In practical systems the complete knowledge of channel state information (CSI) is hardly available at transmitter. To tackle this problem, we resort to the codebook approach to precoding design, where the receiver selects a precoding matrix from a finite set of pre-defined precoding matrices based on the instantaneous channel condition and delivers the index of the chosen precoding matrix to the transmitter via a bandwidth-constraint feedback channel. We show that, when the symbol constellation is improper, the joint codebook based precoding and equalization can be designed accordingly to achieve improved performance compared to the conventional system.

M Al-Imari, M Imran, P Xiao (2016)Radio Resource Allocation for Multicarrier-Low Density Spreading Multiple Access, In: IEEE Transactions on Vehicular Technology IEEE

Multicarrier-low density spreading multiple access (MC-LDSMA) is a promising multiple access technique that enables near optimum multiuser detection. In MC-LDSMA, each user’s symbol spread on a small set of subcarriers, and each subcarrier is shared by multiple users. The unique structure of MC-LDSMA makes the radio resource allocation more challenging comparing to some well-known multiple access techniques. In this paper, we study the radio resource allocation for single-cell MC-LDSMA system. Firstly, we consider the single-user case, and derive the optimal power allocation and subcarriers partitioning schemes. Then, by capitalizing on the optimal power allocation of the Gaussian multiple access channel, we provide an optimal solution for MC-LDSMA that maximizes the users’ weighted sum-rate under relaxed constraints. Due to the prohibitive complexity of the optimal solution, suboptimal algorithms are proposed based on the guidelines inferred by the optimal solution. The performance of the proposed algorithms and the effect of subcarrier loading and spreading are evaluated through Monte Carlo simulations. Numerical results show that the proposed algorithms significantly outperform conventional static resource allocation, and MC-LDSMA can improve the system performance in terms of spectral efficiency and fairness in comparison with OFDMA.

R Liu, P Xiao, J Elmirghani, C Cowan (2009)Interference Cancellation Schemes for MIMO MC-CDM in Fading Channels, In: IET Electronic Letters45(24)pp. 1229-1231 IET

A novel interference cancellation (IC) scheme for MIMO MC-CDM systems is proposed. It is shown that the existing IC schemes are suboptimum and their performance can be improved by utilising some special properties of the residual interference after interference cancellation.

Chunxu Mao, Mohsen Khalily, Pei Xiao, Tim Brown, Steven Gao (2019)Planar Sub-Millimeter-Wave Array Antenna with Enhanced Gain and Reduced Sidelobes for 5G Broadcast Applications, In: IEEE Transactions on Antennas and Propagation67(1)pp. 160-168 IEEE

In this paper, a compact, broadband, planar array antenna with omnidirectional radiation in horizontal plane is proposed for the 26 GHz fifth-generation (5G) broadcast applications. The antenna element is composed of two dipoles and a substrate integrated cavity (SIC) as the power splitter. The two dipoles are placed side-by-side at both sides of the SIC and they are compensated with each other to form an omni-directional pattern in horizontal plane. By properly combing the resonant frequencies of the dipoles and the SIC, a wide impedance bandwidth from 24 to 29.5 GHz is achieved. To realize a large array while reducing the complexity, loss and size of the feeding network, a novel dual-port structure combined with radiation and power splitting functions is proposed for the 1st time. The amplitude and phase on each element of the array can be tuned, and therefore, the grating lobes level can be significantly reduced. Based on the dual-port structure, an 8-element array with an enhanced gain of over 12 dBi is designed and prototyped. The proposed antenna also features low profile, low weight and low cost, which is desirable for 5G commercial applications. Measured results agree well with the simulations, showing that the proposed high-gain array antenna has a broad bandwidth, omni-directional pattern in horizontal plane, and low side-lobes.

P Xiao, R Liu (2008)Multi-user Detector for Multi-carrier CDMA Systems, In: IET Electronic Letters44(23)pp. 1366-1368 IET

A novel blind multi-user detection scheme is developed, which shows clear superiority to the conventional subspace-based blind multi-user detector by improving the condition of the signal subspace. The performance advantages are shown to be more obvious as the number of active users increases, which makes it an attractive solution in heavily loaded systems.

Wanming Hao, Gangcan Sun, Zheng Chu, Pei Xiao, Zhengyu Zhu, Shouyi Yang, Rahim Tafazolli (2019)Beamforming Design in SWIPT-Based Joint Multicast-Unicast mmWave Massive MIMO with Lens-Antenna Array, In: IEEE Wireless Communications Letterspp. 1-1 Institute of Electrical and Electronics Engineers (IEEE)

In this letter, we study the beamforming design in a lens-antenna array-based joint multicast-unicast millimeter wave massive MIMO system, where the simultaneous wireless information and power transfer at users is considered. First, we develop a beam selection scheme based on the structure of the lens-antenna array and then, the zero forcing precoding is adopted to cancel the inter-unicast interference among users. Next, we formulate a sum rate maximization problem by jointly optimizing the unicast power, multicast beamforming and power splitting ratio. Meanwhile, the maximum transmit power constraint for the base station and the minimum harvested energy for each user are imposed. By employing the successive convex approximation technique, we transform the original optimization problem into a convex one, and propose an iterative algorithm to solve it. Finally, simulation results are conducted to verify the effectiveness of the proposed schemes.

W Liu, M Sellathurai, P Xiao, J Wei (2008)A New Restricted Full-Rank Single-Symbol Decodable Design for Four Transmit Antennas, In: IEEE Signal Processing Letters15pp. 765-768 IEEE

Recently, a single-symbol decodable transmit strategy based on preprocessing at the transmitter has been introduced to decouple the quasi-orthogonal space-time block codes (QOSTBC) with reduced complexity at the receiver. Unfortunately, it does not achieve full diversity, thus suffering from significant performance loss. To tackle this problem, we propose a full diversity scheme with four transmit antennas in this letter. The proposed code is based on a class of restricted full-rank single-symbol decodable design (RFSDD) and has many similar characteristics as the coordinate interleaved orthogonal designs (CIODs), but with a lower peak-to-average ratio (PAR).

Chin-Liang Wang, Yu-Ching Wang, Pei Xiao (2019)Power Allocation Based on SINR Balancing for NOMA Systems with Imperfect Channel Estimation, In: Proceedings of the 13th International Conference on Signal Processing and Communication Systems (ICSPCS 2019) Institute of Electrical and Electronics Engineers (IEEE)

This paper investigates power allocation for a downlink non-orthogonal multiple access (NOMA) system with a base station and two users under imperfect channel estimation, where the variance of the channel estimation error for each transmission link is assumed to be known. We first present approximated user capacity expressions according to the error variance information, and then formulate a power allocation optimization problem between the two users for maximizing the minimum approximated user capacity under a total power constraint. Since such a max-min problem is equivalent to maximizing the minimum approximated received signal-to-interference-plusnoise ratio (SINR), a closed-form power allocation solution can be derived based on SINR balancing between the two users. The proposed method involves solving a quadratic equation, and only low implementation complexity is required for practical applications. Computer simulation results show that the proposed max-min power allocation scheme is more robust against channel estimation errors and achieves better worst bit-error-rate performance for the two users, as compared with the conventional fixed power allocation approach and the related max-min method derived according to perfect channel state information.

Wenjuan Yu, Leila Musavian, Atta ul Quddus, Qiang Ni, Pei Xiao (2018)Low latency driven effective capacity analysis for non-orthogonal and orthogonal spectrum access, In: Proceedings of 2018 IEEE Global Communications Conference (GLOBECOM) Institute of Electrical and Electronics Engineers (IEEE)

In this paper, we theoretically investigate the performance of non-orthogonal and orthogonal spectrum access protocols (more generically known as NOMA) in supporting ultra-reliable low-latency communications (URLLC). The theory of effective capacity (EC) is adopted as a suitable delayguaranteed capacity metric to flexibly represent the users’ delay requirements. Then, the total EC difference between a downlink user-paired NOMA network and a downlink orthogonal multiple access (OMA) network is analytically studied. Exact closed-form expressions and the approximated closed-forms at high signal-tonoise ratios (SNRs) are derived for both networks and validated through simulation results. It is shown that for a user pair in which two users with the most distinct channel conditions are paired together, NOMA still achieves higher total EC (compared to OMA) in high SNR regime as the user group size becomes larger, although the EC performance of both NOMA and OMA reduces with the increase in group size. It is expected that the derived analytical framework can serve as a useful reference and practical guideline for designing favourable orthogonal and nonorthogonal spectrum access schemes in supporting low-latency services.

Lei Zhang, A Ijaz, Pei Xiao, Atta Quddus, Rahim Tafazolli (2017)Subband Filtered Multi-carrier Systems for Multi-service Wireless Communications, In: IEEE Transactions on Wireless Communications16(3)pp. 1893-1907 IEEE

Flexibly supporting multiple services, each with different communication requirements and frame structure, has been identified as one of the most significant and promising characteristics of next generation and beyond wireless communication systems. However, integrating multiple frame structures with different subcarrier spacing in one radio carrier may result in significant inter-service-band-interference (ISBI). In this paper, a framework for multi-service (MS) systems is established based on subband filtered multi-carrier system. The subband filtering implementations and both asynchronous and generalized synchronous (GS) MS subband filtered multi-carrier (SFMC) systems have been proposed. Based on the GS-MS-SFMC system, the system model with ISBI is derived and a number of properties on ISBI are given. In addition, low-complexity ISBI cancelation algorithms are proposed by precoding the information symbols at the transmitter. For asynchronous MS-SFMC system in the presence of transceiver imperfections including carrier frequency offset, timing offset and phase noise, a complete analytical system model is established in terms of desired signal, intersymbol-interference, inter-carrier-interference, ISBI and noise. Thereafter, new channel equalization algorithms are proposed by considering the errors and imperfections. Numerical analysis shows that the analytical results match the simulation results, and the proposed ISBI cancelation and equalization algorithms can significantly improve the system performance in comparison with the existing algorithms.

J Zhang, M Zhao, J Zhong, Pei Xiao, T Yu (2017)An Optimized Index Modulation for Filter Bank Multicarrier (FBMC) System, In: IET Communications11(4)pp. 459-467 Institution of Engineering and Technology

Orthogonal frequency division multiplexing with index modulation (OFDM-IM) has attracted considerable interest recently. The technique uses the subcarrier indices as a source of information. In FBMC system, doubledispersive channels lead to inter-carrier interference (ICI) and/or inter-symbol interference (ISI), which are caused by the neighboring symbols in the frequency and/or time domain. When we introduce index modulation to the FBMC system, the interference power will be smaller comparing to that of the conventional FBMC system as some subcarriers carry nothing but zeros. In this paper, the advantages of FBMC with index modulation (FBMC-IM) are investigated by comparing the signal to interference ratio (SIR) with that of the conventional FBMC system. However, the bit error rate (BER) performance is affected since there exists interference in the FBMC-IM system. To improve the BER performance, we propose an optimal combination-selection algorithm and an optimal combinationmapping rule. By abandoning some combinations whose error probability are larger and by mapping the remaining combinations into specified bits, a better BER performance can be achieved compared with that without optimization. The theoretical analysis and simulation results clearly show the FBMC-IM system has a good BER performance under double-dispersive channels.

Z Lin, P Xiao, Y Wu (2011)Performance analysis for linearly precoded LTE downlink multiuser MIMO, In: Eurasip Journal on Wireless Communications and Networking2011
F Zhou, Zheng Chu, Y Wu, N Al-Dhahir, Pei Xiao (2018)Enhancing PHY Security of MISO NOMA SWIPT Systems With a Practical Non-Linear EH Model, In: Proceedings of 2018 IEEE ICC Workshop IEEE

Non-orthogonal multiple-access (NOMA) and simultaneous wireless information and power transfer (SWIPT) are promising techniques to improve spectral efficiency and energy efficiency. However, the security of NOMA SWIPT systems has not received much attention in the literature. In this paper, an artificial noise-aided beamforming design problem is studied to enhance the security of a multiple-input single-output NOMA SWIPT system where a practical non-linear energy harvesting model is adopted. The problem is non-convex and challenging to solve. Two algorithms are proposed to tackle this problem based on semidefinite relaxation (SDR) and successive convex approximation. Simulation results show that a performance gain can be obtained by using NOMA compared to the conventional orthogonal multiple access. It is also shown that the performance of the algorithm using a cost function is better than the algorithm using SDR at the cost of a higher computation complexity.

Alexandr Kuzminskiy, Y Abramovich, Pei Xiao, Rahim Tafazolli (2016)Spectrum Sharing Efficiency Analysis in Rule Regulated Networks with Decentralized Occupation Control, In: IEEE PIMRC 2016 Proceedings

Decentralized dynamic spectrum allocation (DSA) that exploit adaptive antenna array interference mitigation (IM) diversity at the receiver, is studied for interference-limited environments with high level of frequency reuse. The system consists of base stations (BSs) that can optimize uplink frequency allocation to their user equipments (UEs) to minimize impact of interference on the useful signal, assuming no control over band allocation of other BSs sharing the same bands. To this end, “good neighbor” (GN) rules allow effective trade off between the equilibrium and transient decentralized DSA behavior if the performance targets are adequate to the interference scenario. In this paper, we extend the GN rules by including a spectrum occupation control that allows adaptive selection of the performance targets corresponding to the potentially “interference free” DSA; define the semi-analytic absorbing Markov chain model for the GN DSA with occupation control and study the convergence properties including effects of possible breaks of the GN rules; and for higher-dimension networks, develop the simplified search GN algorithms with occupation and power control (PC) and demonstrate their efficiency by means of simulations in the scenario with unlimited requested network occupation.

Ke Lai, Lei Wen, Pei Xiao, Amine Maaref, Muhammad Ali Imran (2018)Sub-graph based Joint Sparse graph for Sparse Code Multiple Access Systems, In: IEEE Access6pp. 25066-25080 Institute of Electrical and Electronics Engineers (IEEE)

Sparse code multiple access (SCMA) is a promising air interface candidate technique for next generation mobile networks, especially for massive machine type communications (mMTC). In this paper, we design a LDPC coded SCMA detector by combining the sparse graphs of LDPC and SCMA into one joint sparse graph (JSG). In our proposed scheme, SCMA sparse graph (SSG) defined by small size indicator matrix is utilized to construct the JSG, which is termed as sub-graph based joint sparse graph of SCMA (SG-JSG-SCMA). In this paper, we first study the binary-LDPC (B-LDPC) coded SGJSG- SCMA system. To combine the SCMA variable node (SVN) and LDPC variable node (LVN) into one joint variable node (JVN), a non-binary LDPC (NB-LDPC) coded SG-JSG-SCMA is also proposed. Furthermore, to reduce the complexity of NBLDPC coded SG-JSG-SCMA, a joint trellis representation (JTR) is introduced to represent the search space of NB-LDPC coded SG-JSG-SCMA. Based on JTR, a low complexity joint trellis based detection and decoding (JTDD) algorithm is proposed to reduce the computational complexity of NB-LDPC coded SGJSG- SCMA system. According to the simulation results, SG-JSGSCMA brings significant performance improvement compare to the conventional receiver using the disjoint approach, and it can also outperform a Turbo-structured receiver with comparable complexity. Moreover, the joint approach also has advantages in terms of processing latency compare to the Turbo approaches.

Amir Arayeshnia, Ali Araghi, Mohsen Khalily, Pei Xiao, Rahim Tafazolli (2020)Trapped Microstrip-Ridge Gap Waveguide for Standalone Millimeter Wave Structures, In: EUCAP 2020

This paper presents a novel design of trapped microstrip-ridge gap waveguide by using partially filled air gaps in a conventional microstrip-ridge gap waveguide. The proposed method offers an applicable solution to obviate frustrating assembly processes for standalone high-frequency circuits employing the low temperature co-fired ceramics technology which supports buried cavities. To show the practicality of the proposed approach, propagation characteristics of both trapped microstrip and microstrip-ridge gap waveguide are compared first. Then, a right-angle bend is introduced, followed by designing a power divider. These components are used to feed a linear 4-element array antenna. The bandwidth of the proposed array is 13 GHz from 64~76 GHz and provides the realized gain of over 10 dBi and the total efficiency of about 80% throughout the operational band. The antenna is an appropriate candidate for upper bands of WiGig (63.72~70.2) and FCC-approved 70 GHz band (71~76 GHz) applications.

Ali Araghi, Mohsen Khalily, Pei Xiao, Rahim Tafazolli (2020)Study on the Location of mmWave Antenna for the Autonomous Car’s Detection and Ranging Sensors, In: EUCAP 2020

The effect of vehicle’s proximity on the radiation pattern when the RADAR’s antenna is mounted on the body of autonomous cars is analysed. Two directional radiation patterns with different specifications are placed at different locations of a realistic car body model. The simulation is performed based on ray-tracing method at 77 GHz, the standard frequency for self-driving applications. It is shown that to obtain a robust RADAR sensor, the antenna radiation pattern is better to have relatively higher gain and lower side-lobe-level (SLL), than narrower halfpower- beamwidth (HPBW) and higher front-to-back (F/B) ratio. Both academia and industry can benefit from this study.

P Xiao, M Sellathurai (2009)Application of Jacobi Algorithm for ISI Channels, In: IET Signal Processing3(2)pp. 119-132 IET

Here, the Jacobi iterative algorithm is applied to combat intersymbol interference (ISI) caused by frequency-selective channels. The performance bound of the equaliser is analysed in order to gain an insight into its asymptotic behaviour. Because of the error propagation problem, the potential of this algorithm is not reached in an uncoded system. However, its extension to a coded system with the application of the turbo-processing principle results in a new turbo equalisation algorithm, which demonstrates comparable performance with reduced complexity compared with some existing filter-based turbo equalisation schemes; and superior performance compared with some frequency domain solutions, such as orthogonal frequency division multiplexing and single-carrier frequency domain equalisation.

J Perez, I Soto, M Alfaro, F Cubillos, P Xiao (2013)Real-Time Modeling in Pervasive Miningpp. 60-66
Zeina Mheich, Ibrahim A. Hemadeh, Zilong Liu, Pei Xiao (2020)Low-Complexity Expectation Propagation Detection for Uplink MIMO-SCMA Systems, In: 2020 International Conference on UK-China Emerging Technologies (UCET)

We consider uplink sparse code multiple access (SCMA) systems associated with multiple input multiple output (MIMO), where the transmitters and the receiver are equipped with multiple antennas, for enhanced reliability (diversity gain) or improved data rate (multiplexing gain). For each diversity or multiplexing based MIMO scheme combined with SCMA, we develop low-complexity iterative detection algorithms based on the message passing algorithm (MPA) and the expectation propagation algorithm (EPA). We show that the MIMO-SCMA under EPA enjoys the salient advantage of linear complexity (in comparison to the MPA counterpart with exponential complexity) as well as enhanced error rate performances due to the MIMO transmission. We also show that the performance of EPA depends on the codebook size and the number of antennas.

Zeina Mheich, Lei Wen, Pei Xiao, Amine Maaref (2019)Unequal Error Protection SCMA Codebooks, In: the IEEE Transactions on Vehicular Technology IEEE

This paper investigates the design of unequal error protection (UEP) codebooks for sparse code multiple access (SCMA) systems. We propose a joint LDPC code and SCMA codebook design approach by incorporating cloud-partitioning of codewords in the design of SCMA codebooks with different protection levels. The protection levels of the SCMA codebooks could be optimized based on the existing error correction code. Simulation results show that significant gains could be obtained using code-aware UEP SCMA codebooks compared to codebooks designed independently of the channel code.

P Xiao, V Fusco (2012)Active phase conjugation with multiple antenna array element, In: IET MICROWAVES ANTENNAS & PROPAGATION6(4)pp. 482-488 INST ENGINEERING TECHNOLOGY-IET
Rui Chen, Jia Shi, Long Yang, Chao Wang, Zan Li, Pei Xiao, Gaojie Chen (2020)Performance Analysis for User Scheduling in Covert Cognitive Radio Networks, In: IEEE International Symposium on Personal, Indoor and Mobile Radio Communications Institute of Electrical and Electronics Engineers

Covert communication provides high-level security for protecting users’privacy information. In this paper, we analyze the joint impact of an external jammer and channel uncertainty on covert communication in multi-user cognitive radio networks. Meanwhile, to fairly schedule the covert communication over multi-user cognitive radio networks, we propose a fairness secondary user (SU) scheduling scheme, which enables each SU to have the same probability for sending information covertly with the aid of an external jammer. Then, the closed-form expression for the covert rate of the scheduled SU can be obtained. Our results show that the minimal detection error probability and covert rate of the scheduled SU can be significantly improved by exploiting the channel uncertainty and random variation of interference power. Moreover, the impact of interference power on the probability of detection error and the covert rate is noticeable when channel uncertainty is large.

Yun Wen, Makoto Yoshida, Junqing Zhang, Zheng Chu, Pei Xiao, Rahim Tafazolli (2019)Machine Learning Based Attack Against Artificial Noise-aided Secure Communication, In: Proceedings of the 2019 IEEE International Conference on Communications (ICC): Communication and Information Systems Security Symposium (IEEE ICC 2019 - CISS Symposium) Institute of Electrical and Electronics Engineers (IEEE)

Physical layer security (PLS) technologies have attracted much attention in recent years for their potential to provide information-theoretically secure communications. Artificial Noise (AN)-aided transmission is considered as one of the most practicable PLS technologies, as it can realize secure transmission independent of the eavesdropper’s channel status. In this paper, we reveal that AN transmission has the dependency of eavesdropper’s channel condition by introducing our proposed attack method based on a supervised-learning algorithm which utilizes the modulation scheme, available from known packet preamble and/or header information, as supervisory signals of training data. Numerical simulation results with the comparison to conventional clustering methods show that our proposed method improves the success probability of attack from 4.8% to at most 95.8% for the QPSK modulation. It implies that the transmission to the receiver in the cell-edge with low order modulation will be cracked if the eavesdropper’s channel is good enough by employing more antennas than the transmitter. This work brings new insights into the effectiveness of AN schemes and provides useful guidance for the design of robust PLS techniques for practical wireless systems.

R Razavi, M Imran, P XIAO, R Tafazolli (2013)Effect of Forward Error Correction Codes on the Performance of LDS-OFDM, In: 19th European Wireless Conference 2013

In this paper, selection criteria of Forward Error Correction (FEC) codes, in particular, the convolutional codes are evaluated for a novel air interface scheme, called Low Density Signature Orthogonal Frequency Division Multiple Access (LDS-OFDM). In this regard, the mutual information transfer characteristics of turbo Multiuser Detector (MUD) are investigated using Extrinsic Information Transfer (EXIT) charts. LDS-OFDM uses Low Density Signature structure for spreading the data symbols in frequency domain. This technique benefits from frequency diversity in addition to its ability of supporting parallel data streams more than the number of subcarriers (overloaded condition). The turbo MUD couples the data symbols’ detector of LDS scheme with users’ FEC decoders through the message passing principle. Index Terms — Low density signature, Multiuser detection, Iterative decoding.

Mohsen Khalily, Rahim Tafazolli, Pei Xiao, Ahmed A. Kishk (2018)Microstrip Array Antenna with Improved Radiation Characteristic for Different 5G Applications, In: IEEE Transactions on Antennas and Propagation66(9)pp. 4641-4647 Institute of Electrical and Electronics Engineers (IEEE)

A Ka-band inset-fed microstrip patches linear antenna array is presented for the fifth generation (5G) applications in different countries. The bandwidth is enhanced by stacking parasitic patches on top of each inset-fed patch. The array employs 16 elements in an H-plane new configuration. The radiating patches and their feed lines are arranged in an alternating out-of-phase 180-degree rotating sequence to decrease the mutual coupling and improve the radiation pattern symmetry. A (24.4%) measured bandwidth (24.35 to 31.13 GHz)is achieved with -15 dB reflection coefficients and 20 dB mutual coupling between the elements. With uniform amplitude distribution, a maximum broadside gain of 19.88 dBi is achieved. Scanning the main beam to 49.5° from the broadside achieved 18.7 dBi gain with -12.1 dB sidelobe level (SLL). These characteristics are in good agreement with the simulations, rendering the antenna to be a good candidate for 5G applications.

Hongzhi Chen, De Mi, Bruno Clerckx, Zheng Chu, Jia Shi, Pei Xiao (2019)Joint Power and Subcarrier Allocation Optimization for Multigroup Multicast Systems with Rate Splitting, In: IEEE Transactions on Vehicular Technology69(2)pp. 2306-2310 IEEE

In this article, we investigate a resource allocation problem for multicarrier multiuser MISO (multiple-input-Single-output) downlink systems, where multiple co-channel multicast groups are served simultaneously. We consider a rate-splitting transmission scheme to address the inevitable inter-group interference under an overloaded multigroup multicast scenario, where the insufficient number of transmit antennas prevents the conventional schemes from neutralizing the interference. We first formulate an optimization problem for maximizing the minimum multicast group rate among all groups on all available subcarriers. This problem involves a joint power and subcarrier allocation optimization, and is non-convex. We apply an iterative scheme based on successive convex approximation (SCA) to find the locally optimal solution. Simulation results demonstrate the performance gain of the proposed scheme compared to the state-of-the-art transmission schemes.

P Shang, J Wu, Y Zeng, P Xiao (2013)A novel resource scheduling algorithm to improve TCP performance for 3GPP LTE systems, In: IEEE Wireless Communications and Networking Conference, WCNCpp. 1898-1902

The Long Term Evolution (LTE) may provide ubiquitous mobile broadband services with all IP architecture, however, the quality of service (QoS) of LTE systems is seriously affected by the network congestions, packet losses, jitters, latencies and other QoS issues in all IP networks. Thus it is valuable to investigate and design efficient resource scheduling algorithms to improve the performance of data services and end-user experiences. In this paper we propose an improved radio resource scheduling algorithm over the existing semi-continuous scheduling algorithm for the voice over Internet Protocol (VoIP) data packets. Through mapping the TCP (transmission control protocol) ACK (acknowledgement) packets into a higher priority logical channel, the probability of both the discarded ACK packets and congestions in the wireless channels are reduced. As the result, the scheme may avoid frequently opening the TCP congestion control mechanism. The simulation results have shown the advantages of our proposed algorithm, such as the RTT (Round-Trip Time) packet delay reduction, improved throughput, acceptable stability, desirable performance, and son on © 2013 IEEE.

P Xiao, Q Chen (2011)Optimization of MIMO transceiver with limited feedback channel, In: Signal Design and its Applications in Communications (IWSDA), 2011 Fifth International Workshop onpp. 169-172

This work addresses joint transceiver optimization for multiple-input, multiple-output (MIMO) systems. In practical systems the complete knowledge of channel state information (CSI) is hardly available at transmitter. To tackle this problem, we resort to the codebook approach to precoding design, where the receiver selects a precoding matrix from a finite set of predefined precoding matrices based on the instantaneous channel condition and delivers the index of the chosen precoding matrix to the transmitter via a bandwidth-constraint feedback channel. In this paper, the codebook based precoding design at transmitter is optimized jointly with decoding design at receiver. © 2011 IEEE.

Sohail Taheri, Mir Ghoraishi, Pei Xiao, L Zhang, Yu Xin (2018)Square-Root Nyquist Filter Design for QAM-Based Filter Bank Multicarrier Systems, In: IEEE Transactions on Vehicular Technology IEEE

Filter bank multicarrier systems with quadrature amplitude modulation (FBMC/QAM) have drawn attentions to get the advantage of complex symbol transmission, as well as very low out of band radiation and relaxed synchronization requirements for asynchronous scenarios. In order to make this system viable for practical deployment, the biggest challenge is designing appropriate filters to minimize the interference between adjacent subcarriers, while maintaining the Nyquist property of the filter. We show that the deviation from the Nyquist property can be compensated through the fractional shift of the filtered symbols, which provides flexibility to optimize the stopband of the filter. The proposed design method shows advantages over the state of the art designs, and provides guidance for the filter design in practical FBMC/QAM systems.

Ali Araghi, Mohsen Khalily, Pei Xiao, Arash Kosari, Houman Zarrabi, Rahim Tafazolli (2018)Millimeter-Wave MIMO Balanced Antipodal Vivaldi Antenna Design for Autonomous Cars, In: IEEE ISNCC 2018 : 2018 IEEE International Symposium on Networks, Computers and Communications Institute of Electrical and Electronics Engineers (IEEE)

This paper introduces a millimeter-wave multipleinput- multiple-output (MIMO) antenna for autonomous (selfdriving) cars. The antenna is a modified four-port balanced antipodal Vivaldi which produces four directional beams and provides pattern diversity to cover 90 deg angle of view. By using four antennas of this kind on four corners of the car’s bumper, it is possible to have a full 360 deg view around the car. The designed antenna is simulated by two commercially full-wave packages and the results indicate that the proposed method can successfully bring the required 90 deg angle of view.

Samineh Sarbazi Golazari, Mohsen Khalily, Fariborz Entezami, Pei Xiao (2018)Performance Analysis of the Loop-Shaped Plasma Antenna Under Different Pressure Conditions, In: IEEE ISNCC 2018 : 2018 IEEE International Symposium on Networks, Computers and Communications Institute of Electrical and Electronics Engineers (IEEE)

This study examines the effect of different pressures on the radiation characteristics of the loop-shaped plasma antenna filled by two gases; Argon and Nitrogen. Proposed loop plasma antennas operating at LTE and Wi-Fi frequency bands have been designed and its performance studied at three different pressures of 2.28, 5 and 10 Torr. The radiation characteristics of the both loop-shaped plasma antennas have been investigated and presented for three different pressures. To analyze the performance of the proposed antenna, full-wave simulation were run using the finite integral method software, CST Microwave Studio.

S Hu, J Zhang, W Tang, Zilong Liu, Pei Xiao, Y Gao (2018)Real-Valued Orthogonal Sequences for Ultra-Low Overhead Channel Estimation in MIMO-FBMC Systems, In: Machine Learning and Intelligent Communications. MLICOM 2018pp. 162-171 Springer

Multiple-input multiple-output filterbank multicarrier communication (MIMO-FBMC) is a promising technique to achieve very tight spectrum confinement (thus, higher spectral efficiency) as well as strong robustness against dispersive channels. In this paper, we present a novel training design for MIMO-FBMC system which enables efficient estimate of frequency-selective channels (associated to multiple transmit antennas) with only one non-zero FBMC symbol. Our key idea is to design real-valued orthogonal training sequences (in the frequency domain) which displaying zero-correlation zone properties in the time-domain. Compared to our earlier proposed training scheme requiring at least two non-zero FBMC symbols (separated by several zero guard symbols), the proposed scheme features ultra-low training overhead yet achieves channel estimation performance comparable to our earlier proposed complex training sequence decomposition(CTSD). Our simulations validate that the proposed method is an efficient channel estimation approach for practical preamble-based MIMO-FBMC systems.

J Wu, P Xiao, Q Chen, SD Blostein (2011)Three-dimensional combined diversity coding and error control coding: Code design and diversity analysis, In: 11th International Symposium on Communications and Information Technologies, ISCIT 2011pp. 7-12

This paper investigates joint complex diversity coding (CDC) and error control coding (ECC) to increase diversity gains across multiple antennas, OFDM blocks, and OFDM sub-carriers. A general diversity analysis for joint CDC and ECC based space-time-frequency codes (STFCs) is provided. The mapping designs from ECC to CDC are crucial for efficient exploitation of the diversity potential. This paper provides and proves a sufficient condition of full diversity construction with joint 3D CDC and ECC, bit-interleaved coded complex diversity coding (BICCDC) and symbol-interleaved coded complex diversity coding (SICCDC). A multi-stream architecture is also introduced to reduce the complexity and latency of the decoding process. © 2011 IEEE.

Zheng Chu, Wanming Hao, Pei Xiao, Fuhui Zhou, De Mi, Zhengyu Zhu, Victor C.M. Leung (2018)Energy Efficient Hybrid Precoding in Heterogeneous Networks with Limited Wireless Backhaul Capacity, In: Proceedings of the IEEE Global Communications Conference, Abu Dhabi, UAE, 9-13 Dec 2018 Institute of Electrical and Electronics Engineers (IEEE)

This paper investigates a two-tier heterogeneous networks (HetNets) with wireless backhaul, where millimeter wave (mmWave) frequency is adopted at the macro base station (MBS), and the cellular frequency is considered at small cell BS (SBS) with orthogonal frequency division multiple access (OFDMA). Subarray structure based hybrid analog/digital precoding scheme is investigated to reduce the hardware cost and energy consumption. Our goal is to maximize the energy efficiency (EE) of the HetNets with limited wireless backhaul capacity and all users’ quality of service (QoS) constraints. The formulated problem is non-convex mixed integer nonlinear fraction programming (MINLFP), which is non-trivial to solve directly. In order to circumvent this issue, we propose a two-loop iterative resource allocation algorithm. Specifically, we transform the outer-loop problem into a difference of convex programming (DCP) by employing integer relaxation and Dinkelback method. In addition, the first-order approximation is considered to linearize this inner-loop DCP problem into a convex optimization framework. Lagrange dual method is adapted to achieve the optimal closed-form power allocation. Furthermore, we analyze the convergence of the proposed iterative algorithm. Numerical results are presented to demonstrate our proposed schemes.

P Xiao, H Zhang, C Cowan (2011)Equalization of rotationally variant signals, In: Optoelectronics, Instrumentation and Data Processing47(3)pp. 253-263 Springer

Several equalization algorithms utilizing the rotationally variant nature of the received signals are presented in this paper to combat the detrimental effect of intersymbol interference (ISI) introduced by frequency selective channels. Their adaptive implementations and application to a time-reversal space-time block coded (TR-STBC) system are also considered. In addition, a turbo equalization algorithm is derived for systems employing the error correction code. The proposed equalizers and turbo equalizer are evaluated over broadband fixed wireless access channels, and are shown to yield superior performance compared to the conventional equalization schemes.

P Xiao, R Carrasco, IJ Wassell (2009)Generalized Equalization Algorithm Utilizing Improper ISI., In: IEEE Transactions on Vehicular Technology58(2)pp. 788-789 IEEE

The improper nature of intersymbol interference (ISI) for signals transmitted over frequency-selective channels is investigated in this paper. Our analysis reveals that for real signals, the improperness originates from both improper signal modulation and the interference cancellation process, whereas for most complex signals, the improperness is only a characteristic of the residual ISI due to interference cancellation. To utilize the improperness of ISI, a multistage widely linear equalization algorithm is introduced, and it is generally applicable for both real and complex signal constellations. The results reveal that accounting for the improper nature of the ISI at both the input and output of the equalizer leads to a noticeable performance gain compared with conventional equalization schemes.

P Xiao, E Strom (2010)Soft Demodulation Algorithms for Orthogonally Modulated and Convolutionally Coded DS-CDMA System, In: IEEE Transactions on Communications58(3)pp. 742-747 IEEE

A convolutionally coded M-ary orthogonal direct sequence code division multiple access (DS-CDMA) system in time-varying frequency-selective Rayleigh fading channels is considered in this work. We propose several novel soft demodulation algorithms based on interference cancellation and suppression techniques that can be coupled with soft decoding to improve the system performance in an iterative manner. The performance of the proposed demodulation algorithms is evaluated numerically and proved to achieve substantial bit error rate (BER) performance gain compared with the conventional detection schemes.

Yikun Mei, Zhen Gao, De Mi, Pei Xiao, Mohamed-Slim Alouini (2020)Compressive Sensing Based Grant-Free Random Access for Massive MTC, In: Proceedings of the IEEE International Conference on UK-China Emerging Technologies (UCET) 2020 Institute of Electrical and Electronics Engineers (IEEE)

Massive machine-type communications (mMTC) are expected to be one of the most primary scenarios in the next-generation wireless communications and provide massive connectivity for Internet of Things (IoT). To meet the demanding technical requirements for mMTC, random access scheme with efficient joint activity and data detection (JADD) is vital. In this paper, we propose a compressive sensing (CS)-based grant-free random access scheme for mMTC, where JADD is formulated as a multiple measurement vectors (MMV) CS problem. By leveraging the prior knowledge of the discrete constellation symbols, we develop an orthogonal approximate message passing (OAMP)-MMV algorithm for JADD, where the structured sparsity is fully exploited for enhanced performance. Moreover, expectation maximization (EM) algorithm is employed to learn the unknown sparsity ratio of the a priori distribution and the noise variance. Simulation results show that the proposed scheme achieves superior performance over other state-of-the-art CS schemes.

De Mi, Lei Zhang, Mehrdad Dianati, Sami Muhaidat, Pei Xiao, Rahim Tafazolli (2018)Self-Calibration for Massive MIMO with Channel Reciprocity and Channel Estimation Errors, In: Proceedings of the IEEE Global Communications Conference, Abu Dhabi, UAE, 9-13 Dec 2018 Institute of Electrical and Electronics Engineers (IEEE)

In time-division-duplexing (TDD) massive multipleinput multiple-output (MIMO) systems, channel reciprocity is exploited to overcome the overwhelming pilot training and the feedback overhead. However, in practical scenarios, the imperfections in channel reciprocity, mainly caused by radiofrequency mismatches among the antennas at the base station side, can significantly degrade the system performance and might become a performance limiting factor. In order to compensate for these imperfections, we present and investigate two new calibration schemes for TDD-based massive multi-user MIMO systems, namely, relative calibration and inverse calibration. In particular, the design of the proposed inverse calibration takes into account a compound effect of channel reciprocity error and channel estimation error. We further derive closedform expressions for the ergodic sum rate, assuming maximum ratio transmissions with the compound effect of both errors. We demonstrate that the inverse calibration scheme outperforms the traditional relative calibration scheme. The proposed analytical results are also verified by simulated illustrations.

Mohsen Khalily, Sohail Taheri, Pei Xiao, Fariborz Entezami, Timothy Hill, Rahim Tafazolli (2018)26 GHz Indoor Wideband Directional Channel Measurement and Analysis in LoS and NLoS Scenarios, In: Proceedings of EuCAP 2018 IEEE

This paper presents details of the indoor wideband and directional propagation measurements at 26 GHz in which a wideband channel sounder using a millimeter wave (mmWave) signal analyzer and vector signal generator was employed. The setup provided 2 GHz bandwidth and the mechanically steerable directional lens antenna with 5 degrees beamwidth provides 5 degrees of directional resolution over the azimuth. Measurements provide path loss, delay and spatial spread of the channel. Angular and delay dispersion are presented for line-of-sight (LoS) and non-line-of-sight (NLoS) scenarios.

Hongzhi Chen, De Mi, Manuel Fuentes, Eduardo Garro, Jose Luis Carcel, Belkacem Mouhouche, Pei Xiao, Rahim Tafazolli (2018)On the Performance of PDCCH in LTE and 5G New Radio, In: Proceedings of the IEEE Global Communications Conference, Abu Dhabi, UAE, 9-13 Dec 2018 (GlobeComm 2018)

5G New Radio (NR) Release 15 has been specified in June 2018. It introduces numerous changes and potential improvements for physical layer data transmissions, although only point-to-point (PTP) communications are considered. In order to use physical data channels such as the Physical Downlink Shared Channel (PDSCH), it is essential to guarantee a successful transmission of control information via the Physical Downlink Control Channel (PDCCH). Taking into account these two aspects, in this paper, we first analyze the PDCCH processing chain in NR PTP as well as in the state-of-the-art Long Term Evolution (LTE) point-to-multipoint (PTM) solution, i.e., evolved Multimedia Broadcast Multicast Service (eMBMS). Then, via link level simulations, we compare the performance of the two technologies, observing the Bit/Block Error Rate (BER/BLER) for various scenarios. The objective is to identify the performance gap brought by physical layer changes in NR PDCCH as well as provide insightful guidelines on the control channel configuration towards NR PTM scenarios.

BK Khoo, SL Goff, P Xiao (2011)Repetition time-switched transmit diversity as an alternative to Alamouti space-time coding for wireless communication systems, In: 2011 the 14th International Symposium on Wireless Personal Multimedia Communications: Communications, Networking and Applications for the Internet of Things, WPMC'11pp. 1-5

We present a simple transmit diversity technique, called repetition time-switched transmit diversity (R-TSTD), which is a modified version of the well-known time-switched transmit diversity (TSTD) algorithm. Throughout the paper, we focus on the scenario of a transmitter with n = 2 antennas. The idea behind R-TSTD is to use only one antenna at a time while still ensuring that all constellation symbols are transmitted via both antennas. Thus, unlike the classical TSTD technique, R-TSTD does provide a transmit diversity effect similar to that achieved with space-time coding (STC) algorithms. The error performance of the proposed R-TSTD system is compared to that of the Alamouti STC scheme via Monte Carlo computer simulations. It is shown that, in the absence of any outer error-correcting code, Alamouti STC slightly outperforms R-TSTD. However, when a near-capacity channel code is employed as an outer code, the error performance achieved using R-TSTD is significantly better than that obtained with Alamouti STC, provided that the desired spectral efficiency is sufficiently low. © 2011 National Institute of Inform.

De Mi, Hongzhi Chen, Zhen Gao, Lei Zhang, Pei Xiao (2020)Massive MIMO in Mobile Networks: Self-Calibration with Channel Estimation Error, In: Proceedings of the ACM MobiArch 2020 The 15th Workshop on Mobility in the Evolving Internet Architecturepp. 30-35 Association for Computing Machinery (ACM)

Time-division-duplexing (TDD) massive multiple-input multiple-output (MIMO) systems will play a crucial role in the deployment of emerging mobile networks in 5G and beyond. Such systems heavily rely on the reciprocity-based channel estimation for its scalability. However, the imperfect channel reciprocity, mainly caused by radio-frequency mismatches among the base station antennas, can contaminate the estimate of the effective channel response thus become a performance-limiting factor. In practice, self-calibration schemes are often applied to compensate for this type of imperfections. This work investigates two self-calibration schemes, namely relative calibration and inverse calibration. Considering a TDD massive multi-user MIMO system in the presence of both channel reciprocity error and imperfect channel estimation, we derive closed-form expressions for the receive mean-square error and provide an in-depth comparative analysis of the post-equalisation performance of two calibration schemes. The proposed analytical results are verified via Monte-Carlo simulations.

C Toal, S Sezer, D Burns, Pei Xiao, V Fusco (2012)A 1Gbps FPGA-based wireless baseband MIMO transceiver, In: Proceedings IEEE International SOC Conference (SOCC), 2012pp. 202-207 IEEE

This paper presents the design and implementation of a high performance baseband transceiver targeted for System on a Chip (SoC). The presented architecture utilizes a 4×4 Multiple-Input Multiple-Output Orthogonal Frequency Division Multiplexing (MIMO-OFDM) system and is capable of enabling greater than 1Gbps wireless transmission. A complex channel equalization circuit is realized using matrix inversion via high-resolution QR decomposition. Full synthesis results are included as this MIMO-OFDM transceiver has been proved on standard FPGA technology.

P Xiao, Z Lin, Y Wu (2013)Mutual Information Based Packet Scheduling for Linearly Precoded Multiuser MIMO Systems, In: 19th European Conference 2013

In this paper, we present a novel Mutual Information (MI) based spatial frequency domain packet scheduling for downlink Orthogonal Frequency Division Multiple Access (OFDMA) multiuser MIMO systems. The proposed scheduler is designed to exploit the available multiuser diversity in time, frequency and spatial domains. The analysis model is based on the generalized 3GPP LTE downlink transmission for which two Spatial Division Multiplexing (SDM) multiuser MIMO schemes are investigated: Single User (SU) and Multi-user (MU) MIMO schemes. The results show that the proposed MU-MIMO scheduler is a more realistic solution and provides fairness among users for the system under consideration.

Zheng Chu, Zhou Fuhui, Zhengyu Zhu, Rose Qingyang Hu, Pei Xiao (2017)Wireless Powered Sensor Networks for Internet of Things: Maximum Throughput and Optimal Power Allocation, In: IEEE Internet of Things Journal5(1)pp. 310-321 Institute of Electrical and Electronics Engineers (IEEE)

This paper investigates a wireless powered sensor network (WPSN), where multiple sensor nodes are deployed to monitor a certain external environment. A multi-antenna power station (PS) provides the power to these sensor nodes during wireless energy transfer (WET) phase, and consequently the sensor nodes employ the harvested energy to transmit their own monitoring information to a fusion center (FC) during wireless information transfer (WIT) phase. The goal is to maximize the system sum throughput of the sensor network, where two different scenarios are considered, i.e., PS and the sensor nodes belong to the same or different service operator(s). For the first scenario, we propose a global optimal solution to jointly design the energy beamforming and time allocation. We further develop a closed-form solution for the proposed sum throughput maximization. For the second scenario in which the PS and the sensor nodes belong to different service operators, energy incentives are required for the PS to assist the sensor network. Specifically, the sensor network needs to pay in order to purchase the energy services released from the PS to support WIT. In this case, the paper exploits this hierarchical energy interaction, which is known as energy trading. We propose a quadratic energy trading based Stackelberg game, linear energy trading based Stackelberg game, and social welfare scheme, in which we derive the Stackelberg equilibrium for the formulated games, and the optimal solution for the social welfare scheme. Finally, numerical results are provided to validate the performance of our proposed schemes.

R Razavi, Pei Xiao, Rahim Tafazolli (2015)Information Theoretic Analysis of OFDM/OQAM with Utilized Intrinsic Interference, In: IEEE Signal Processing Letters22(5)pp. 618-622 Institute of Electrical and Electronics Engineers

In this paper, the capacity of OFDM/OQAM with isotropic orthogonal transfer algorithm (IOTA) pulse shaping is evaluated through information theoretic analysis. In the conventional OFDM systems the insertion of a cyclic prefix (CP) decreases the system’s spectral efficiency. As an alternative to OFDM, filter bank based multicarrier systems adopt proper pulse shaping with good time and frequency localisation properties to avoid interference and maintain orthogonality in real field among sub-carriers without the use of CP. We evaluate the spectral efficiency of OFDM/OQAM systems with IOTA pulse shaping in comparison with conventional OFDM/QAM systems, and our analytical model is further extended in order to gain insights into the effect of utilizing the intrinsic interference on the performance of our system. Furthermore, the spectral efficiency of OFDM/OQAM systems is analyzed when the effect of inter-symbol and inter-carrier interference is considered.

Ke Lai, Lei Wen, Jing Lei, Gaojie Chen, Pei Xiao, Amine Maaref (2018)Secure Transmission with Interleaver for Uplink Sparse Code Multiple Access System, In: IEEE Wireless Communications Letters IEEE

Sparse code multiple access (SCMA) is a promising air interface candidate technique for next generation mobile networks. By introducing the Tent map in the Chaos theory, we propose a novel physical layer transmission scheme with codeword level interleaving at the transmitter in this letter, which is termed as interleaver based SCMA (I-SCMA). Simulation results and analysis show that I-SCMA can provide high security performance without any loss in performance and transmission rate, thus constitutes a viable solution for the next generation wireless networks to provide secure communications.

M Al-Imari, P Xiao, MA Imran, R Tafazolli (2013)Low complexity subcarrier and power allocation algorithm for uplink OFDMA systems, In: Eurasip Journal on Wireless Communications and NetworkingAprilpp. ?-? Springer

In this article, we consider the joint subcarrier and power allocation problem for uplink orthogonal frequency division multiple access system with the objective of weighted sum-rate maximization. Since the resource allocation problem is not convex due to the discrete nature of subcarrier allocation, the complexity of finding the optimal solution is extremely high. We use the optimality conditions for this problem to propose a suboptimal allocation algorithm. A simplified implementation of the proposed algorithm has been provided, which significantly reduced the algorithm complexity. Numerical results show that the presented algorithm outperforms the existing algorithms and achieves performance very close to the optimal solution.

G Chen, Pei Xiao, James Kelly, B Li, Rahim Tafazolli (2017)Full-Duplex Wireless-Powered Relay in Two Way Cooperative Networks, In: IEEE Access5pp. 1548-1558 IEEE

This paper investigates a full duplex wirelesspowered two way communication networks, where two hybrid access points (HAP) and a number of amplify and forward (AF) relays both operate in full duplex scenario. We use time switching (TS) and static power splitting (SPS) schemes with two way full duplex wireless-powered networks as a benchmark. Then the new time division duplexing static power splitting (TDD SPS) and full duplex static power splitting (FDSPS) schemes as well as a simple relay selection strategy are proposed to improve the system performance. For TS, SPS and FDSPS, the best relay harvests energy using the received RF signal from HAPs and uses harvested energy to transmit signal to each HAP at the same frequency and time, therefore only partial self-interference (SI) cancellation needs to be considered in the FDSPS case. For the proposed TDD SPS, the best relay harvests the energy from the HAP and its self-interference. Then we derive closed-form expressions for the throughput and outage probability for delay limited transmissions over Rayleigh fading channels. Simulation results are presented to evaluate the effectiveness of the proposed scheme with different system key parameters, such as time allocation, power splitting ratio and residual SI.

A novel hybrid multiuser detection scheme that jointly uses linear and nonlinear interference suppression techniques is developed for high-speed direct-sequence code-division multiple-access communications in multipath frequency-selective fading channels. The detector detects signals in a symbol-by-symbol style. Conventional decorrelating detectors suffer from the noise enhancement problem, which becomes more serious for dispersive multipath channels. The proposed detector uses interference cancellation technology to reduce the rank of the expanded signal subspace and hence it preserves the advantages of the expanded decorrelating detector in terms of complete multiple access interference and intersymbol interference suppression and meanwhile avoids its disadvantage in terms of noise enhancement. Computer simulation shows clear superiority of the new detector to other existing methods.

Manijeh Bashar, Kanapathippillai Cumanan, Alister G Burr, Hien Quoc Ngo, Pei Xiao (2019)Max-Min Rate of Cell-Free Massive MIMO Uplink with Optimal Uniform Quantization, In: IEEE TRANSACTIONS ON COMMUNICATIONS IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

Cell-free Massive multiple-input multiple-output (MIMO) is considered, where distributed access points (APs) multiply the received signal by the conjugate of the estimated channel, and send back a quantized version of this weighted signal to a central processing unit (CPU). For the first time, we present a performance comparison between the case of perfect fronthaul links, the case when the quantized version of the estimated channel and the quantized signal are available at the CPU, and the case when only the quantized weighted signal is available at the CPU. The Bussgang decomposition is used to model the effect of quantization. The max-min problem is studied, where the minimum rate is maximized with the power and fronthaul capacity constraints. To deal with the non-convex problem, the original problem is decomposed into two sub-problems (referred to as receiver filter design and power allocation). Geometric programming (GP) is exploited to solve the power allocation problem whereas a generalized eigenvalue problem is solved to design the receiver filter. An iterative scheme is developed and the optimality of the proposed algorithm is proved through uplink-downlink duality. A user assignment algorithm is proposed which significantly improves the performance. Numerical results demonstrate the superiority of the proposed schemes.

M Al-Imari, M Ghoraishi, P Xiao (2015)Radio Resource Allocation and System-Level Evaluation for Full-Duplex Systems, In: 2015 IEEE 20TH INTERNATIONAL WORKSHOP ON COMPUTER AIDED MODELLING AND DESIGN OF COMMUNICATION LINKS AND NETWORKS (CAMAD)pp. 103-107
P Xiao, Z Lin, C Cowan (2011)Suboptimal and Optimal MIMO-OFDM Iterative Detection Schemes, In: Proceedings of the Global Communications Conference, 2010. GLOBECOM 2010pp. 1-5

A novel iterative detection scheme for MIMO-OFDM systems is proposed in this work. We show that the existing detection schemes are sub-optimum and the iterative process can be optimized by utilizing the non-circular property of the residual interference after interference cancellation. Results show that the proposed iterative scheme outperforms the conventional iterative soft interference cancellation (ISIC) and V-BLAST schemes by about 1.7 and 4.0 dB, respectively, in a 4 × 4 antennas system over exponentially distributed eleven path channels.

Yang Tian, Jie Zhong, Xiaoxiang Lin, Pei Xiao, Haifeng Yang, Yu Zhong, Dongpeng Kang (2019)A High-dynamic Wavelength Tracking and Millimeter-level Ranging Inter-satellite Laser Communication Link with Feedback-Homodyne Detection, In: Applied Optics Optical Society of America

The Integrated Laser Communication/Ranging System, which uses coded signal as the ranging information carrier, is of great importance to the next large-capacity inter-satellite information network. In this paper, a system design with high-sensitivity feedback-homodyne detection scheme and asynchronous ranging algorithm is demonstrated with real-time FPGA implementation. The parallel FFT estimation is applied to improve the speed and range of wavelength drift tracking, which can handle dynamic wavelength drift up to 2.4 pm/s (300 MHz/s). Meanwhile, for clock sources with subtle dynamic frequency offset and sufficient stability, the proposed fractional symbol ranging method is proven to achieve millimeter-level measurement accuracy. The designed system is shown to perform well in terms of both laser linewidth tolerance and noise resistance.

Mehdi M. Molu, Pei Xiao, Mohsen Khalily, Kanapathippillai Cumanan, Lei Zhang, Rahim Tafazolli (2017)Low-Complexity and Robust Hybrid Beamforming Design for Multi-Antenna Communication Systems, In: IEEE Transactions on Wireless Communications17(3)pp. 1445-1459 Institute of Electrical and Electronics Engineers (IEEE)

This paper proposes a low-complexity hybrid beamforming design for multi-antenna communication systems. The hybrid beamformer comprises of a baseband digital beamformer and a constant modulus analog beamformer in radio frequency (RF) part of the system. As in Singular-Value-Decomposition (SVD) based beamforming, hybrid beamforming design aims to generate parallel data streams in multi-antenna systems, however, due to the constant modulus constraint of the analog beamformer, the problem cannot be solved, similarly. To address this problem, mathematical expressions of the parallel data streams are derived in this paper and desired and interfering signals are specified per stream. The analog beamformers are designed by maximizing the power of desired signal while minimizing the sum-power of interfering signals. Finally, digital beamformers are derived through defining the equivalent channel observed by the transmitter/receiver. Regardless of the number of the antennas or type of channel, the proposed approach can be applied to wide range of MIMO systems with hybrid structure wherein the number of the antennas is more than the number of the RF chains. In particular, the proposed algorithm is verified for sparse channels that emulate mm-wave transmission as well as rich scattering environments. In order to validate the optimality, the results are compared with those of the state-of-the-art and it is demonstrated that the performance of the proposed method outperforms state-of-the-art techniques, regardless of type of the channel and/or system configuration.

W Yin, P Xiao, C Cowan, S Liu, Q Huang (2010)ORL Scheme for WiMAX and LTE Systems with Convolutionally Coded Spatial Multiplexingpp. 173-176

In 4G systems such as Wimax and LTE, system performance suffers from interferences and lack of low complexity algorithms for interference cancellation as well as utilization of optimal resource. In this paper, we propose a PCINR and EM based optimal resource allocation scheme to improve the performance of 4G systems and compensate the performance loss due to spatial correlation and interferences. Furthermore, the SIC technique is employed to mitigate interferences. The performance of the proposed system is evaluated by computer simulations and is shown to outperform the conventional schemes.

D Liang, P Xiao, G Chen, M Ghoraishi, R Tafazolli (2015)Digital Self-Interference Cancellation for Full-Duplex MIMO Systems
L Wen, R Razavi, M Imran, P Xiao (2014)Design of joint sparse graph for OFDM (JSG-OFDM) system, In: IEEE Transactions on Wireless Communications

Low density signature orthogonal frequency division multiplexing (LDS-OFDM) and low density parity-check (LDPC) codes are multiple access and forward error correction (FEC) techniques, respectively. Both of them can be expressed by a bipartite graph. In this paper, we construct a joint sparse graph combining the single graphs of LDS-OFDM and LDPC codes, namely joint sparse graph for OFDM (JSG-OFDM). Based on the graph model, a low complexity approach for joint multiuser detection and FEC decoding (JMUDD) is presented. The iterative structure of JSG-OFDM receiver is illustrated, and its extrinsic information transfer (EXIT) chart is researched. Furthermore, design guidelines for the joint sparse graph are derived through the EXIT chart analysis. By offline optimization of the joint sparse graph, numerical results show that the JSG-OFDM brings about 1.5 – 1.8 dB performance improvement at bit error rate (BER) of 10 5 over similar well-known systems such as grouporthogonal multi-carrier code division multiple access (GO-MCCDMA), LDS-OFDM and turbo structured LDS-OFDM.

P Xiao, M Sellathuai, C Cowan (2010)Advanced Linear Processing for 2-Hop Fixed MIMO Relaying, In: International Conference on Signal Processing and Communications (SPCOM), 2010

In this paper, we consider a 2-hop downlink point-to-multipoint fixed relay systems and propose a novel linear processing strategy at the base station and relay station to improve the reliability of the source-relay and relay-to-destination links. When coupled with a soft-decode-and-forward protocol, the proposed scheme leads to significant performance gain compared to the conventionl solutions for fixed relay networks.

P Xiao, J Wu, M Sellathurai, T Ratnarajah, E Strom (2009)Iterative Multi-User Detection and Decoding for DS-CDMA System with Space-Timer Linear Dispersion, In: IEEE Transactions on Vehicular Technology58(5)pp. 2343-2353 IEEE

This paper considers a Q-ary orthogonal direct-sequence code-division multiple-access (DS-CDMA) system with high-rate space-time linear dispersion codes (LDCs) in time-varying Rayleigh fading multiple-input-multiple-output (MIMO) channels. We propose a joint multiuser detection, LDC decoding, Q-ary demodulation, and channel-decoding algorithm and apply the turbo processing principle to improve system performance in an iterative fashion. The proposed iterative scheme demonstrates faster convergence and superior performance compared with the V-BLAST-based DS-CDMA system and is shown to approach the single-user performance bound. We also show that the CDMA system is able to exploit the time diversity offered by the LDCs in rapid-fading channels.

P Xiao, H Zhang, C Cowan (2010)Widely Linear Equalization of Rotationally Variant Signals, In: ACIT - Information and Communication Technology - 2010(691)pp. 48-?

Several widely linear equalization algorithms utilizing the rotationally variant nature of the received signals are pre sented in this paper to combat the detrimental effect of in tersymbol interference (ISI) introduced by frequency selec tive channels. Their adaptive implementations and appli cation to the time-reversal space-time coded (TR-STBC) system are also considered. In addition, a widely linear approach to turbo equalization is derived for systems em ploying error correction code. The widely linear equaliz ers and turbo equalizer are evaluated over broadband fixed wireless access channels, and are shown to yield superior performance compared to the conventional linear schemes.

Y Liu, J Zhong, P Xiao, M Zhao (2015)A Novel Evidence Theory Based Row Message Passing Algorithm for LDS Systems, In: WCSP 2015 Conference Proceedings
Adnan Zafar, Lei Zhang, Pei Xiao, Muhammad Imran (2017)Spectrum Efficient MIMO-FBMC System using Filter Output Truncation, In: IEEE Transactions on Vehicular Technology67(3)pp. 2367-2381 Institute of Electrical and Electronics Engineers (IEEE)

Due to the use of an appropriately designed pulse shaping prototype filter, filter bank multicarrier (FBMC) system can achieve low out of band (OoB) emissions and is also robust to the channel and synchronization errors. However, it comes at a cost of long filter tails which may reduce the spectral efficiency significantly when the block size is small. Filter output truncation (FOT) can reduce the overhead by discarding the filter tails but may also significantly destroy the orthogonality of FBMC system, by introducing inter carrier interference (ICI) and inter symbol interference (ISI) terms in the received signal. As a result, the signal to interference ratio (SIR) is degraded. In addition, the presence of intrinsic interference terms in FBMC also proves to be an obstacle in combining multiple input multiple output (MIMO) with FBMC. In this paper, we present a theoretical analysis on the effect of FOT in an MIMO-FBMC system. First, we derive the matrix model of MIMO-FBMC system which is subsequently used to analyze the impact of finite filter length and FOT on the system performance. The analysis reveals that FOT can avoid the overhead in time domain but also introduces extra interference in the received symbols. To combat the interference terms, we then propose a compensation algorithm that considers odd and even overlapping factors as two separate cases, where the signals are interfered by the truncation in different ways. The general form of the compensation algorithm can compensate all the symbols in a MIMO-FBMC block and can improve the SIR values of each symbol for better detection at the receiver. It is also shown that the proposed algorithm requires no overhead and can still achieve a comparable BER performance to the case with no filter truncation.

Aijun Cao, Pei Xiao, Rahim Tafazolli (2014)Frequency Offset Estimation Based on PRACH Preambles in LTE, In: The Eleventh International Symposium on Wireless Communication Systems, ISWCS'2014 Proceedingspp. 27-32 IEEE

This paper presents a novel method to estimate the frequency offset between a mobile phone and the infrastructure when the mobile phone initially attaches to the LTE network. The proposed scheme is based on PRACH (Physical Random Access Channel) preambles and can significantly reduce the complexity of preamble detection at the eNodeB side.

Ke Lai, Jing Lei, Lei Wen, Gaojie Chen, Wei Li, Pei Xiao (2017)Secure Transmission with Randomized Constellation Rotation for Downlink Sparse Code Multiple Access System, In: IEEE Access6pp. 5049-5063

Sparse code multiple access (SCMA) is a promising candidate air interface of next-generation mobile networks. In this paper, we focus on a downlink SCMA system where a transmitter sends confidential messages to multiple users in the presence of external eavesdroppers. Consequently, we develop a novel secure transmission approach over physical layer based on a highly structured SCMA codebook design. In our proposed scheme, we rotate the base constellations (BCs) with random angles by extracting channel phases from the channel state information (CSI). By employing randomized constellation rotation (RCR), the security of downlink SCMA can be ensured. In addition, a tight SCMA upper bound is introduced to guide the design of the encrypted codebook. As a result, we propose an approach to avoid the significant error rate performance loss caused by using codebooks that are designed using our method. The proposed upper-bound-aided codebook design scheme can select relatively good codebooks with low complexity. By combining SCMA codebook design and secure communication, our scheme ensures security for massive quantities of users with low encrypted and decrypted complexity at the cost of transmission rate and possible error rate performance loss. Moreover, the proposed scheme can achieve robustness against channel estimation errors. Analyses and Monte Carlo simulations confirm the effectiveness of our scheme.

P Xiao, R Carrasco, I Wassell (2007)Time Reversal Space-Time Block Coding for FWA Systems, In: Wireless and Mobile Communications, 2006. ICWMC '06.pp. 51-?

The aim of this paper is to present the application of the time-reversal space-time coding (TR-STBC) on the broadband fixed wireless access (FWA) systems. In addition to the transmit diversity obtained from the TR-STBC scheme, we also consider the concatenation of TR-STBC and an outer channel code in order to provide coding gain for the FWA systems. A turbo equalization scheme is proposed for the concatenated systems. Different receiver strategies are compared, and their performance/complexity tradeoff is discussed.

B Zhou, Q Chen, P Xiao, L Zhao (2016)On the Spatial Error Propagation Characteristics of Cooperative Localization in Wireless Networks, In: IEEE Transactions on Vehicular Technology IEEE

Cooperative localization is an important technique in wireless networks. However, there are always errors in network node localization, which will spatially propagate among network nodes when performing network localization. In this paper, we study the spatial error propagation characteristics of network localization, in terms of Fisher information. Firstly, the spatial propagation function is proposed to reveal the spatial cooperation principle of network localization. Secondly, the convergence property of spatial localization information propagation is analyzed to shed light on the performance limits of network localization through spatial information propagation. It is shown that, (ı) the network localization error propagates in a way of the Ohm’s law in electric circuit theory, where the measurement accuracy, node location accuracy and geometric-resolution information behave like the resistances connected in parallel or series; (ıı) the network location error gradually diminishes with spatial localization cooperation procedures, due to the cooperative localization information propagation; (ııı) the essence of spatial localization cooperation among network nodes is the spatial propagation of localization information.

Hongzhi Chen, De Mi, Zilong Liu, Pei Xiao, Rahim Tafazolli (2020)Rate-Splitting for Overloaded Multigroup Multicast: Error Performance Evaluation, In: IEEE ICC 2020

In this work, we provide the first attempt to evaluate error performance of Rate-Splitting (RS) based transmission strategies with constellation-constrained coding/modulation. The consider scenario is an overloaded multigroup multicast, where RS can mitigate the inter-group interference thus achieve a better max-min fair group rate over conventional transmission strategies. We bridge the RS-based rate optimization with modulationcoding scheme selection, and implement them in a developed transceiver framework with either linear or non-linear receiver, where the latter equips with a generalized sphere decoder. Simulation results of a coded bit error rate demonstrate that, while the conventional strategies suffer from the error floor in the considered scenario, the RS-based strategy delivers a superior performance even with low complexity receiver techniques. The proposed analysis, transceiver framework and evaluation methodology provide a generic baseline solution to validate the effectiveness of the RS-based system design in practice. Index Terms—Rate-splitting, overloaded system, multigroup multicast, rank-deficient, generalized sphere decoder, coded bit error rate.

Jia Shi, Pei Xiao, W Liang, G Pan, Z Li (2018)High-Reliability and Low-Complexity Resource Allocation for Future Multicarrier Spread Spectrum Systems, In: Transactions on Emerging Telecommunications Technologies29(10)e3457 Wiley

In this paper, we investigate resource allocation in the multicarrier spread spectrum systems, especially in the multicell downlink multicarrier direct-sequence code division multiple-access (MC DS-CDMA) systems. The allocation of resources including subcarriers and spreading codes aims to maximize the system reliability, thereby resulting in the high-reliability mutlicarrier systems. For the sake of achieving low-complexity, we develop the novel resource allocation framework. We propose two resource allocation algorithms, which are the simplified heuristic subcarrier- and code-allocation (SHSC) algorithm and the enhanced heuristic subcarrier- and code-allocation (EHSC) algorithm. The two proposed algorithms can find the promising sub-optimum solutions to the mixed integer nonconvex resource allocation problem. The SHSC algorithm has lower complexity and demands less backhaul resources than the EHSC algorithm. In return, the EHSC algorithm performs better than the SHSC algorithm. Nevertheless, we show that both algorithms significantly outperform the existing algorithms, while approaching the optimal algorithm of high complexity

MM Molu, Pei Xiao, Mohsen Khalily, Lei Zhang, Rahim Tafazolli (2017)A Novel Equivalent Definition of Modified Bessel Functions for Performance Analysis of Multi-Hop Wireless Communication Systems, In: IEEE Access5pp. 7594-7605 IEEE

A statistical model is derived for the equivalent signal-to-noise ratio of the Source-to-Relay-to-Destination (S-R-D) link for Amplify-and-Forward (AF) relaying systems that are subject to block Rayleigh-fading. The probability density function and the cumulated density function of the S-R-D link SNR involve modified Bessel functions of the second kind. Using fractional-calculus mathematics, a novel approach is introduced to rewrite those Bessel functions (and the statistical model of the S-R-D link SNR) in series form using simple elementary functions. Moreover, a statistical characterization of the total receive-SNR at the destination, corresponding to the S-R-D and the S-D link SNR, is provided for a more general relaying scenario in which the destination receives signals from both the relay and the source and processes them using maximum ratio combining (MRC). Using the novel statistical model for the total receive SNR at the destination, accurate and simple analytical expressions for the outage probability, the bit error probability, and the ergodic capacity are obtained. The analytical results presented in this paper provide a theoretical framework to analyze the performance of the AF cooperative systems with an MRC receiver.

Ali Araghi, Mohsen Khalily, Pei Xiao, Rahim Tafazolli (2020)Multiple-Beam mmW-Slotted-Waveguide Leaky Wave Antenna with Control on Polarization, In: 2020 IEEE International Symposium on Antennas and Propagation and North American Radio Science Meeting Institute of Electrical and Electronics Engineers (IEEE)

By performing the Floquet-mode analysis of a periodic slotted waveguide, a multiple-beam leaky wave antenna is proposed in the millimetre-wave (mmW) band. Considering the direction of surface current lines on the broad/side-walls of the waveguide, the polarization of constructed beams are also controlled. The simulation results are well matched with the initial mathematical analysis.

Bowen Yang, Lei Zhang, Oluwakayode Onireti, Pei Xiao, Muhammad Ali Imran, Rahim Tafazolli (2020)Mixed-numerology Signals Transmission and Interference Cancellation for Radio Access Network Slicing, In: IEEE Transactions on Wireless Communicationspp. 1-14 Institute of Electrical and Electronics Engineers (IEEE)

A clear understanding of mixed-numerology signals multiplexing and isolation in the physical layer is of importance to enable spectrum efficient radio access network (RAN) slicing, where the available access resource is divided into slices to cater to services/users with optimal individual design. In this paper, a RAN slicing framework is proposed and systematically analyzed from a physical layer perspective. According to the baseband and radio frequency (RF) configurations imparities among slices, we categorize four scenarios and elaborate on the numerology relationships of slices configurations. By considering the most generic scenario, system models are established for both uplink and downlink transmissions. Besides, a low out of band emission (OoBE) waveform is implemented in the system for the sake of signal isolation and inter-service/slice-band-interference (ISBI) mitigation. We propose two theorems as the basis of algorithms design in the established system, which generalize the original circular convolution property of discrete Fourier transform (DFT). Moreover, ISBI cancellation algorithms are proposed based on a collaboration detection scheme, where joint slices signal models are implemented. The framework proposed in the paper establishes a foundation to underpin extremely diverse user cases in 5G that implement on a common infrastructure.

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