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).
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.
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.
Ghoraishi M, Jiang W, Xiao P, Tafazolli R (2015) Subband Approach for Wideband Self-Interference Cancellation in Full-Duplex Transceiver, 2015 INTERNATIONAL WIRELESS COMMUNICATIONS & MOBILE COMPUTING CONFERENCE (IWCMC) pp. 1139-1143 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, (1) 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; (11) the
network location error gradually diminishes with spatial localization
cooperation procedures, due to the cooperative localization
information propagation; (111) the essence of spatial localization
cooperation among network nodes is the spatial propagation of
Zafar A, Imran MA, Xiao P, Cao A, Gao Y (2015) Performance Evaluation and Comparison of Different Multicarrier Modulation Schemes, 2015 IEEE 20TH INTERNATIONAL WORKSHOP ON COMPUTER AIDED MODELLING AND DESIGN OF COMMUNICATION LINKS AND NETWORKS (CAMAD) pp. 49-53 IEEE
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.
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.
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.
Xiao P, Lin Z, Mao J (2012) MIMO Transmit Diversity: Theoretical Analyses and Practical Applications, In: Le KN (eds.), 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.
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.
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
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.
Mao J, Lin Z, Xiao P (2012) Mobile WiMAX Downlink MIMO Beamforming Algorithms and Simulations, In: Le KN (eds.), 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 ...
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.
Lin Z, Xiao P, Wu Y, Schneider C (2013) Application of WLF to OFDMA MU-MIMO
Systems II: Frequency-Domain Packet
Scheduling, ISWCS 2013 VDE
Xiao P, Alina M, Gabbouj M (1996) Segmentation of Noisy Images with Watershed
Transformation, pp. 263-265
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.
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.
Al-Imari, Xiao P, Imarin M, Tafazolli R Uplink Non-Orthogonal Multiple Access for 5G Wireless Networks,
Xiao P, Strom E, Carrasco R (2005) Soft Demodulation with Interference Cancellation/Suppression for M-ary DS-CDMA System, (488) ACIT - Communication Systems - 2005 ACTA Press
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.
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.
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.
Chen G, Liang D, Ghoraishi M, Xiao P, Tafazolli R (2015) Optimum User Selection for Hybrid-Duplex Device-to-Device in Cellular Networks,
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.
Yue J, Lin Z, Vucetic B, Xiao P (2014) The Design of Degree Distribution for Distributed Fountain Codes in Wireless Sensor Networks, 2014 IEEE International Conference on Communications (ICC) pp. 5796-5801 IEEE
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.
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
© 2005-2012 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.
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.
Wu J, Xiao P (2009) OFDMA-based Mobile WiMAX, In: Song L, Jiang T, Zhang Y (eds.), Orthogonal Frequency Division Multiple Access Fundamentals and Applications 22 Auerbach Publications
Supported by the expert-level advice of pioneering researchers,Orthogonal Frequency Division Multiple Access Fundamentals and Applicationsprovides a comprehensive and accessible introduction to the foundations and applications of one of the ...
In this study, the authors analyse the temporal and spatial compression characteristics of retrodirective antenna systems wherein active phase conjugation (APC) is deployed. It is shown that under the APC Hermitian channel matrix properties result and these lead to opportunities for both temporal and spatial signal compression. The effects of additive channel noise, as well as compression assistance given by multipath richness are described. Some general properties of retrodirective antenna systems with respect to linear and circular polarised pilot signals are also discussed. The scheme elaborated here is compliant with a generic channel model and can therefore be easily incorporated into any readily available communication systems analysis or channel modelling software. The work presented in this study provides a theoretical foundation for the previous experimental findings in APC systems. © 2012 The Institution of Engineering and Technology.
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.
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.
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.
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.
Xiao P, Carrasco R, Wassell I (2006) AML Turbo Equalization for Space Time Block Coded Systems, The Mediterranean Journal of Computers and Networks 2 (2) pp. 40-49
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.
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).
Taheri S, Ghoraishi M, Xiao P (2015) Overhead Reduced Preamble-Based Channel Estimation for MIMO-FBMC Systems,
Al-Imari M, Xiao P, Imran M (2015) Receiver and Resource Allocation Optimization for Uplink NOMA in 5G Wireless Networks,
Sohail A, Al-Imari M, Xiao P, Evans B (2014) Power Allocation for Joint Interweave and Underlay Cognitive Radio Systems with Arbitrary Input Distributions, Wireless Communications and Networking Conference pp. 1838-1843 IEEE
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
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.
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.
Zhou B, Chen Q, Wymeersch H, Xiao P, Zhao L (2016) Variational Inference-based Positioning with Nondeterministic Measurement Accuracies and Reference Location Errors, 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.
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.
Cao A, Gao Y, Xiao P, Tafazolli R (2015) Performance Analysis of an Ultra Dense Network with and without Cell Cooperation,
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.
Al-Imari M, Ghoraishi M, Xiao P (2015) Radio Resource Allocation and System-Level Evaluation for Full-Duplex Systems, 2015 IEEE 20TH INTERNATIONAL WORKSHOP ON COMPUTER AIDED MODELLING AND DESIGN OF COMMUNICATION LINKS AND NETWORKS (CAMAD) pp. 103-107 IEEE
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.
Abdullahi M, Xiao P (2016) Performance Analysis and Soft Demapping for Coded MIMO-OFDM Systems, 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.
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.
The average channel capacity and the SINR distribution for multiuser multiple input multiple output (MIMO) systems in combination with the base station based packet scheduler are analyzed in this paper. The packet scheduler is used to exploit the available multiuser diversity in all the three physical domains (i.e., space, time and frequency). 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 multiuser (MU) MIMO schemes. The main contribution of this paper is the establishment of a mathematical model for the SINR distribution and the average channel capacity for multiuser SDM MIMO systems with frequency domain packet scheduler, which 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. © 2011 Zihuai Lin et al.
In the literature, researchers have evaluated optimal power loading algorithms under the Zero Mean Circularly Symmetric Complex Gaussian (ZMCSCG) constraint in OFDM based CR systems. The capacity of the Secondary User (SU) is maximized while keeping the interference introduced to the Primary User (PU) band remains within tolerable range. However the drawback of such an approach is that channel capacity increases with increasing Signal to Noise Ratio (SNR), which is not applicable to a practical scenario. Therefore, we propose an optimal power loading scheme under the Finite Symbol Alphabet (FSA) constraint, (i.e., QPSK, 8-PSK, 16-QAM and 64-QAM, etc.) to achieve realistic system performance especially under the high SNR region. Subsequently, Mutual Information (MI) is derived and compared against channel capacity which reveals that in the low SNR region, they are closely related. Conversely, MI saturates in the high SNR region which indicates maximum achievable data rates for practical systems. We further evaluate channel capacity and MI by varying the interference threshold and our observation is that the saturation value of the achievable SU data rate indicated by MI changes accordingly, but total achievable data rate remains constant. On the other hand, capacity increases with increasing interference threshold. © 2012 IEEE.
Mao J, Abdullahi M, Xiao P, Cao A (2016) A Low Complexity 256QAM Soft Demapper for 5G Mobile System,
Xiao P, Carrasco R, Wassell I (2004) Equalization and Decoding in BFWA Systems, PROCEEDINGS OF INTERNATIONAL SYMPOSIUM ON BROADBAND COMMUNICATIONS; 13 pp. 12-15
Xiao P, Carrasco R, Wassell I (2005) Turbo Equalization without MMSE Filtering, Eighth International Symposium on DSP and Communication Systems, DSPCS 2005 and 4th Workshop on the Internet Telecommunications and Signal Processing, WITSP 2005
DSP for Communication System
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
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
Perera R, Arachchi HK, Imran M, Xiao P (2016) Extrinsic Information Modification in the Turbo Decoder by Exploiting Source Redundancies for HEVC Video Transmitted over a Mobile Channel, IEEE Access
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.
Xiao P, Carrasco R, Wassell I (2005) Equalization and Decoding Algorithms in Broadband Fixed Wireless Access, 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.
Liang D, Xiao P, Chen G, Ghoraishi M, Tafazolli R (2015) Digital Self-Interference Cancellation for Full-Duplex MIMO Systems,
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.
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.
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.
Xiao P, Raitinen H, Gabbouj M (1998) Blind Deconvolution for Blurred Image Restoration with Simulated Annealing, pp. 170-173
Razavi R, Xiao P, Tafazolli R (2015) Information Theoretic Analysis of OFDM/OQAM
with Utilized Intrinsic Interference, IEEE Signal Processing Letters
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.
Xiao P, Carrasco R, Wassell I (2006) Improved Equalization Algorithm for Broadband Fixed Wireless Access,
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.
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
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.
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.
Yin W, Xiao P, Cowan C, Liu S, Huang Q (2010) ORL Scheme for WiMAX and LTE Systems with Convolutionally Coded Spatial Multiplexing, pp. 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.
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.
Xiao P, Fusco V, Cowan C (2010) Simulink Models for OFDM Based Wireless LAN System, Royal Irish Academy Colloquium Proceedings pp. 109-112
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.
Al-Imari M, Imran M, Xiao P (2016) Radio Resource Allocation for Multicarrier-Low Density Spreading Multiple Access, 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.
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.
Zhong J, Chen G, Xiao P (2015) Iterative Widely Linear Equalization for MIMO SC-FDMA Systems,
He C, Yang L-L, Xiao P, Imran MA (2015) DS-CDMA Assisted Visible Light Communications Systems, 2015 IEEE 20TH INTERNATIONAL WORKSHOP ON COMPUTER AIDED MODELLING AND DESIGN OF COMMUNICATION LINKS AND NETWORKS (CAMAD) pp. 27-32 IEEE
Cao A, Xiao P, Tafazolli R Frequency Offset Estimation Based on PRACH Preambles in LTE,
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.
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.
Xiao P, Carrasco R, Wassell I (2007) High Data Rate Broadband Fixed Wireless Access with Multilevel Modulation,
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.
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
Xiao P (2004) Iterative Detection, Decoding and Channel Parameter Estimation for Orthogonally Modulated DS-CDMA Systems,
In this thesis, we study iterative detection, decoding and channel parameter estimation
algorithms for asynchronous direct-sequence code division multiple access
(DS-CDMA) systems employing orthogonal signalling formats and long scrambling
Multiuser detection techniques are widely used to combat the detrimental
effects of multipath fading and multiple access interference (MAI), which are the
major impairments in CDMA communication systems. Although the emphasis is
placed on nonlinear interference cancellation schemes, several linear interference
filtering techniques are also discussed in the first part of the thesis. The multistage
parallel interference canceler (PIC) is evaluated analytically and compared
with simulation results. To prevent performance degradation of PIC due to error
propagation, some soft cancellation schemes using soft decision feedback are
Most multiuser detectors rely on accurate channel information, which needs
to be estimated in practice. For the purpose of channel estimation, both classic
and Bayesian methods are considered in this thesis, depending on whether prior
knowledge about the parameters to be estimated is available or not. We focus on
the decision directed approach when estimating the fading channel gains. That
is, the receiver estimates the channel parameters based on the detected data, no
training sequences are needed. The estimated channel coefficients are also used
to regenerate the signal of each user for the purpose of interference cancellation.
Another essential channel parameter to be estimated is the propagation delay.
Many studies show that multiuser detectors need very accurate delay estimates
to perform well. We propose some suboptimal synchronization algorithms that
achieve good acquisition performance in presence of MAI and have reduced complexity
compared to the optimum maximum likelihood estimator.
In the second part of the thesis, we employ the turbo processing principle
and study iterative demodulation and decoding of a convolutionally coded
and orthogonally modulated asynchronous DS-CDMA system. Several iterative
schemes based on soft demodulation and decoding algorithms are presented. The
performance of different strategies are evaluated and proved to achieve substantial
performance gains 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 whe
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.
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.
"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."
Wen L, Razavi R, Xiao P, Imran M (2014) Fast convergence and reduced complexity receiver design for LDS-OFDM system, 2014 IEEE 25th Annual International Symposium on Personal, Indoor, and Mobile Radio Communication pp. 918-922 IEEE
Xiao P, Carrasco R, Wassell I (2006) WLP for Broadband Fixed Wireless Access,
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.
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.
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.
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.
© 2014 IEEE.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.
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.
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.
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.
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.
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
Xiao P, Strom E (2003) Pilot-Aided Acquisition Algorithms for Asynchronous DS-CDMA Systems, European Transactions on Telecommunications 14 (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.
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.
Al-Imari M, Xiao P, Imran MA, Tafazolli R (2013) Low complexity subcarrier and power allocation algorithm for uplink OFDMA systems, EURASIP JOURNAL ON WIRELESS COMMUNICATIONS AND NETWORKING ARTN 98 SPRINGER INTERNATIONAL PUBLISHING AG
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.
Wu J, Xiao P, Sellahuai M, Blostein S (2009) Linear Dispersion Codes for Wireless Communications., In: Feng J (eds.), 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.
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
Liu Y, Zhong J, Xiao P, Zhao M (2015) A Novel Evidence Theory Based Row Message Passing Algorithm for LDS Systems, 2015 INTERNATIONAL CONFERENCE ON WIRELESS COMMUNICATIONS & SIGNAL PROCESSING (WCSP) IEEE
Mehran F, Nikitopoulos K, Xiao P, Chen Q (2015) Rateless wireless systems: gains, approaches, and challenges,
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.
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.
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.
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.
Al-Imari M, Ghoraishi M, Xiao P, Tafazolli R (2015) Game Theory Based Radio Resource Allocation for Full-Duplex Systems, IEEE 81st Vehicular Technology Conference (VTC Spring), 2015 pp. 1-5 IEEE
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.
Zhang G, Yang X, Xiao P, Lin Z (2012) Channel state information transmission method apparatus and system, 13/329027
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.
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.
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..
Lin Z, Xiao P, Sorensen TB, Vucetic B (2010) Spatial Frequency Scheduling for Uplink SC-FDMA based Linearly Precoded LTE Multiuser MIMO System, European Transactions on Telecommunications 21 (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.
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.
Xiao P, Chatzigeorgiou I, Rodrigues M, Carrasco R, Wassell I (2009) Design Considerations and Algorithms for Broadband Fixed WiMAX Systems, In: Watanabe K (eds.), 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.
Xiao P, Lin Z, Wu Y, Schneider C (2013) Application of WLF to OFDMA MU-MIMO
Systems I: Frequency-Domain Equalization, ISWCS 2013 VDE
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.
Cao A, Wang G, Ma Y, Xiao P, Tafazolli R Frequency Domain Pilot-based Carrier Frequency Offset Estimation in SC-FDMA system,
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Xiao P, Carrasco R, Wassell I (2007) On The Asymptotic Performance of The STBC Coded FWA Systems, Global Telecommunications Conference, 2006. GLOBECOM '06. IEEE 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.
Xiao P, Zhang H, Cowan C (2010) Widely Linear Equalization of Rotationally Variant Signals, ACIT - Information and Communication Technology - 2010 (691) ACTA Press
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 ?xed wireless access channels, and are shown to yield superior performance compared to the conventional linear schemes.
Zhou B, Chen Q, Xiao P (2015) On the Error Propagation of the Fast Time Varying Channel Tracking for MIMO System,
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.
Al-Imari M, Ghoraishi M, Xiao P (2015) Radio Resource Allocation for Full-Duplex Multicarrier Wireless Systems,
In time-varying frequency selective channels, to obtain high-rate joint time-frequency diversity, linear dispersion coded orthogo-nal frequency division multiplexing (LDC-OFDM), has recently been pro-posed. Compared with OFDM systems, single-carrier systems may re-tain the advantages of lower PAPR and lower sensitivity to carrier fre-quency offset (CFO) effects, which motivates this paper to investigate how to achieve joint frequency and time diversity for high-rate single-carrier block transmission systems. Two systems are proposed: linear dispersion coded cyclic-prefix single-carrier modulation (LDC-CP-SCM) and linear dispersion coded zero-padded single-carrier modulation (LDC-ZP-SCM) across either multiple CP-SCM or ZP-SCM blocks, respectively. LDC-SCM may use a layered two-stage LDC decoding with lower complexity. This paper analyzes the diversity properties of LDC-CP-SCM, and provides a sufficient condition for LDC-CP-SCM to maximize all available joint fre-quency and time diversity gain and coding gain. This paper shows that LDC-ZP-SCM may be effectively equipped with low-complexity minimum mean-squared error (MMSE) equalizers. A lower complexity scheme, lin-ear transformation coded SCM (LTC-SCM), is also proposed with good diversity performance. Copyright © 2012 The Institute of Electronics, Information and Communication Engineers.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
In this digital era, the usage of smart phones and mobile devices is becoming a norm in society with mobile communication quickly transitioned from voice oriented transmission to picture transmission to a more complex live video streaming. This latest development has demanded more
capacity and higher bandwidth in communication links. Static links, which are the focus of this thesis, are an integral part of this mobile system in delivering high capacity data transmission using backhauls or nomadic links. Multi polarised antennas with multiple-input multiple-output (MIMO) multiplexing can be employed to greatly enhance the capacity of a mobile system, especially at frequencies lower than 6 GHz, using their compact size.
A practical antenna inherently exhibits elliptical polarisation though it may be designed to form linear or circular polarisation. Little attention has been given to this aspect of polarised waves as they have always been deemed as unwanted polarisation, although in practice, any antenna is elliptically polarised as it can never be perfectly circularly or linearly polarised. This work therefore aims to deliberately exploit this opportunity by forming antennas with elliptical polarisation to identify the advantages of doing so in order to improve orthogonality in comparison with linear polarisation. It was found that in order to achieve perfect orthogonality, it was more practical to set the magnitudes and phases of the co-polar and cross-polar linear components, which resulted in an
improved co to cross polar ratio more than 20 dB better than linear polarisation in free space.
A dual elliptically polarised antenna prototype was designed and evaluated in this work, which was evaluated both in free space and within an indoor measurement campaign. Results concluded that at short distances with low scattering in the channel and directional antennas, elliptically polarised antennas provide improved multiplexing gain over dual linear polarisations.
Key words: Elliptical Polarisation, MIMO, Multiplexing, static wireless links, degrees of freedom, dual polarised antenna.
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.
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.
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 ?rst present a self organising, user-centric CoMP clustering algorithm in a control/data plane separation architecture (CDSA), proposed for 5G to maximise spectral ef?ciency (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 unsatis?ed users due to high load can be signi?cantly reduced with minimal impact on SE.
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.
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.
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.
The hype surrounding the 5G mobile networks is well justified in view of the explosive increase in mobile traffic and the inclusion of massive ?non-human? users that form the internet of things. Advanced radio features such as network densification, cloud radio access networks (C-RAN), and untapped frequency bands jointly succeed in increasing the radio capacity to accommodate the increasing traffic demand. However, a new challenge has arisen: the backhaul (BH), the transport network that connects radio cells to the core network. The BH needs to expand in a timely fashion to reach the fast spreading small cells. Moreover, the realistic BH solutions are unable to provide the unprecedented 5G performance requirements to every cell. To this end, this research addresses the gap between the 5G stipulated BH characteristics and the available BH capabilities. On the other hand, heterogeneity is a leading trait in 5G networks. First, the RAN is heterogeneous since it comprises different cell types, radio access technologies, and architectures. Second, the BH is composed of a mix of different wired and wireless technologies with different limitations. In addition, 5G users have a broader range of capabilities and requirements than any incumbent mobile network. We exploit this trait and develop a novel scheme, termed User-Centric-BH (UCB). The UCB targets the user association mechanism which is traditionally blind to users? needs and BH conditions. The UCB builds on the existing concept of cell range extension (CRE) and proposes multiple-offset factors (CREO) whereby each reflects the cell's joint RAN and BH capability with respect to a defined attribute (e.g., throughput, latency, resilience, etc.). In parallel, users associate different weights to different attributes, hence, they can make a user-centric decision. The proposed scheme significantly outperforms the state-of-the-art and unlocks the BH bottleneck by availing existing but misused resources to users in need.
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.
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.
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.
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
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.
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.
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.
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.
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.
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
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.
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.
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
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.
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
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.
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
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.
Non-orthogonal multiple access (NOMA) is an emerging technology for future cellular systems in order to accommodate more users via non-orthogonal resource allocation, especially when the number of users/devices exceeds the available degrees of freedom, resulting in an overloaded condition. To date, low density signature (LDS) and sparse code multiple access (SCMA) are two promising NOMA techniques. However, research in this area is still in its infancy and there are still several open issues in the LDS/SCMA transceiver design. This thesis aims to address some of these challenges. The contributions are summarized as follows.
1:-LDS-OFDM and low density parity check (LDPC) codes both can be represented by a bipartite graph. Inspired by their similar structure, we construct a joint sparse graph combining the single graphs of LDS-OFDM and LDPC codes, namely joint sparse graph for OFDM (JSG-OFDM). A joint detection and decoding scenario is proposed using message passing algorithm (MPA). Design guidelines for the joint sparse graph are derived through extrinsic information transfer (EXIT) chart analysis. Simulation results show that the JSG-OFDM outperforms existing techniques such as GO-MC-CDMA, LDS-OFDM and turbo structured LDS-OFDM.
2:-Due to the higher power and spectral efficiency, the filter-bank multi-carrier (FBMC) technique is a promising alternative to OFDM. We use a low density graph to model the weight matrix of intrinsic interference in the isotropic orthogonal transform algorithm (IOTA) filtered FBMC system. In addition, such graph is combined with LDS and LDPC codes to form a joint sparse graph for FBMC-IOTA (JSG-IOTA). Based on MPA, a joint detection and decoding scheme is designed for JSG-IOTA, and the joint sparse graph is optimized by EXIT chart analysis. Numerical results show the superiority of JSG-IOTA to conventional techniques.
3:-In SCMA, the processes of bit to symbol mapping and LDS spreading are combined together. We investigate multi-dimensional SCMA codebooks, and the design rules are derived to maximize the constellation shaping gain. Moreover, we propose to construct SCMA codebooks by copy-and-permute operation on protographs and three-dimensional (3D) constellation shaping. Simulation results show that SCMA outperforms LDS with high-order constellations, and the proposed optimization methods can further improve the SCMA performance.
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.
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 . 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.
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.
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.
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.
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.
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
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.
Ever increasing demands for higher data rates in mobile communication present an ultimate challenge to deliver a consistent service experience to users. Filter bank multicarrier (FBMC) systems with very low out of band radiation facilitate aggregation of non-adjacent bands and asynchronous transmissions to provide the service enhancement. The primary research objective in these systems is followed by the contributions provided in this thesis.
First of all, filter bank based multicarrier systems using fast convolution approach are investigated. We show that by applying FFT-based convolution without overlapped processing, the circular distortion can be discarded as a part of orthogonal interference term. The advantages of this property are spectral efficiency enhancement in the system and complexity reduction. The results show spectral efficiency enhancement by up to 15\% compared to conventional FBMC, while the complexity of the system is roughly half of conventional FBMC.
Secondly, two channel estimation methods for MIMO-FBMC are proposed. The first one is a preamble-based approach aiming to reduce the preamble duration overhead and peak to average power ratio compared to the existing methods. The results confirm that this method outperforms the existing methods in terms of the mentioned parameters with up to 55\% in the overhead reduction. The second approach is a comb-based method with avoiding the contamination of pilots with symbol interference and saving time-frequency resources compared to existing methods. The results show a comparable performance of this method with is OFDM counterpart.
Finally, we investigate the problems of transmitting complex symbols in FBMC systems. The challenge in these systems is designing appropriate filters to minimize the interference between adjacent subcarriers while maintaining the Nyquist property of the filter. We exploit fractional shift of the filtered symbols to compensate the deviation from the Nyquist property. The results show the proposed filter provides approximately 3 dB improvement of signal to interference ratio compared to the conventional filters.
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.
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 49.5æ
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.
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.
Filter bank based multicarrier (FBMC) systems are one of the promising waveform candidates to satisfy the requirements of future wireless networks. FBMC employs prototype filters with lower side lobe and faster spectral decay, which enables it to have the advantages of reduced out-of-band energy and theoretically higher spectral efficiency (SE) compared to conventional multicarrier scheme i.e., orthogonal frequency division multiplexing (OFDM). These systems also have the ability to facilitate aggregation of non-adjacent bands to acquire higher bandwidths for data transmission. They also support asynchronous transmissions to reduce signaling overhead to meet the ever increasing demand of high data rate transmission in future wireless networks. In this work, the primary research objective is to address some of the critical challenges in FBMC systems to make it viable for practical applications. To this end, the following contributions are provided in this thesis.
First of all, despite numerous advantages, FBMC systems suffers from long filter tails which may reduce the SE of the system. Filter output truncation (FOT) can reduce this overhead by discarding the filter tails but may also destroy the orthogonality in FBMC system. As a result, the signal to interference ratio (SIR) can be significantly degraded. To address this problem, we first presented a theoretical analysis on the effect of FOT in a multiple input multiple output (MIMO) FBMC system, when assuming that transmitter and receiver have the same number of antennas. 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. A general form of the compensation algorithm is then proposed to compensate all the symbols in a MIMO-FBMC block to improve the SIR values of each symbol for better detection at the receiver.
Secondly, transmission of quadrature modulated symbols using FBMC systems has been an issue due to the self-interference between the transmitted symbols both in the time and frequency domain (so-called intrinsic interference). To address this issue, we propose a novel low complexity interference-free FBMC system with QAM modulation (FBMC/QAM) using filter deconvolution. The proposed method is based on inversion of the prototype filters which completely removes the intrinsic interference at the receiver and allows the use of quadrature modulated signaling. The interference terms in FBMC/QAM with and without the proposed system are analyzed and compared in terms of mean square error (MSE). It is shown with theoretical and simulation results that the proposed method cancels the intrinsic interference and improves the output signal to interference plus noise ratio (SINR) at the expense of slight enhancement of residual interferences caused by multipath channel. The complexity of the proposed system is also analyzed along with performance evaluation in an asynchronous multi-service scenario. It is shown that the proposed FBMC/QAM system with filter deconvolution outperforms the conventional OFDM system.
Finally, subcarrier index modulation (SIM) a.k.a., index modulation (IM) has recently emerged as a promising concept for spectrum and energy-efficient next generation wireless communications systems due to the excellent trade-offs they offer among error performance, complexity, and SE. Although IM is well studied for OFDM, FBMC with index modulation (FBMC-IM) has not been thoroughly investigated. To address this topic, we shed light on the potential and implementation of IM technique for FBMC system. We first derived a mathematica
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.
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.
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.
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.
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.
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
Chu Zheng, Hao Wanming, Xiao Pei, Zhou Fuhui, Mi De, Zhu Zhengyu, Leung Victor C.M. (2018) Energy Efficient Hybrid Precoding in Heterogeneous Networks with Limited Wireless Backhaul Capacity, 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.
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.
Chen Hongzhi, Mi De, Fuentes Manuel, Garro Eduardo, Carcel Jose Luis, Mouhouche Belkacem, Xiao Pei, Tafazolli Rahim On the Performance of PDCCH in LTE and 5G New Radio, 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.
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.
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
Regarded as one of the most promising transmission techniques for future wireless communications, the discrete cosine transform based multicarrier modulation
(DCT-MCM) system hold several inherited advantages over the discrete Fourier transform (DFT) based one (DFT-MCM). However, various technical challenges that hinder practical use of DCT-MCM need to be addressed, e.g., enhanced transceiver design and extensions into several important 5th Generation (5G) communication scenarios. The overall objective of the proposed research is to
investigate some of the key practical challenges and optimise the receiver implementation of general DCT-MCM systems, by which effective solutions are
proposed for different future wireless communication scenarios.
First, an optimised transmitter structure for the pre-filtering based DCT-MCM system is established to improve the overall system performance. We therefore analyse the pre-filtering effect and investigate the output signal-to-noise ratio (SNR) gain among all subcarriers. Based on the derived instantaneous output SNR expression, the minimum-mean-square-error (MMSE) and maximum likelihood (ML) detections are re-designed to effectively compensate the coloured noise effect after pre-filtering at the receiver.
Second, we give the system model and performance analysis for the pre-filtering based DCT-MCM system in the presence of transceiver imperfections. In particular, an analytical expression in terms of desired signal, ICI and inter-symbol interference (ISI) is presented by considering carrier frequency offset (CFO), timing offset (TO) and insufficient guard sequence between symbols. In order to compensate for these imperfections, an advanced technique called zero forcing based (ZF-based) iterative channel detection algorithms are proposed to provide
significant gain compared with conventional detection methods in terms of BER performance.
Third, in order to render the DCT-MCM applicable to multiple-input multipleoutput (MIMO) systems, we trace back to the zero-padding based implementation method for DCT-MCM. Based on the double number of de-multiplexed symbols, we reformulated three effective detection algorithms to maximise the performance gain. Among of the three, we found that the equal gain combining (EGC) based
algorithm could successfully achieve the signal transmission on DCT-MCM in MIMO scenarios without interference introduced.
Finally, an enhanced structure of DCT-MCM with index modulation (IM) technique (which is called the EDCT-OFDM-IM) is proposed to further increase the spectral efficiency as well as its bit-error rate (BER) performance. Based on the approximate pairwise error probability, a theoretical upper bound on the average bit-error probability of EDCT-OFDM-IM is derived in closed form over frequency-selective Rayleigh fading channels. The achievable performance of our proposed EDCT-OFDM-IM scheme is analysed from several aspects including the spectral efficiency, corresponding Euclidean distance (ED), the peak-to-average power ratio (PAPR) value and its robustness against frequency offset. We demonstrate that the DCT-OFDM-IM scheme is comparable with the DFT-OFDM-IM counterpart in terms of PAPR but is more robust to the ICI effect.
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.
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.
Xiao Lixia, Xiao Pei, Xiao Yue, Wu Chaowu, Mi De, Hemadeh Ibrahim A. (2019) Rectangular Differential OFDM with index modulation, 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).
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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. Diýerent 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 diýcult 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.
Bashar Manijeh, Cumanan Kanapathippillai, Burr Alister G., Ngo Hien Quoc, Larsson Erik G., Xiao Pei (2019) On the Energy Efficiency of Limited-Backhaul Cell-Free Massive MIMO, 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.
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.
Bashar Manijeh, Cumanan Kanapathippillai, Burr Alister G., Ngo Hien Quoc, Hanzo Lajos, Xiao Pei (2019) NOMA/OMA Mode Selection-Based Cell-Free Massive MIMO, 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.