Fupin Yao

The concept of sensing-as-a-service is proposed to enable a unified way of accessing and controlling sensing devices for many Internet of Things based applications. Existing techniques for Web service computing are not sufficient for this class of services that are exposed by resource-constrained devices. The vast number of distributed and redundantly deployed sensors necessitate specialised techniques for their discovery and ranking. Current research in this line mostly focuses on discovery, e.g., designing efficient searching methods by exploiting the geographical properties of sensing devices. The problem of ranking, which aims to prioritise semantically equivalent sensor services returned by the discovery process, has not been adequately studied. Existing methods mostly leverage the information directly associated with sensor services, such as detailed service descriptions or quality of service information. However, assuming the availability of such information for sensor services is often unrealistic. We propose a ranking strategy by estimating the cost of accessing sensor services. The computation is based on properties of the sensor nodes as well as the relevant contextual information extracted from the service access process. The evaluation results demonstrate not only the superior performance of the proposed method in terms of ranking quality measure, but also the potential for preserving the energy of the sensor nodes.

The extensive utilization of wireless networks requires research in the field of mitigating wireless interference to be urgent and necessary. As the standard designed for low data rate and low cost wireless personal area network, the IEEE 802.15.4 standard is widely employed to construct wireless connectivity among the inexpensive devices. However, the characteristics of low transmission power and narrow bandwidth make the IEEE 802.15.4 system vulnerable to wireless interference. The interference varies in time, frequency and is not able to be recognized since the modulation schemes are usually different. This paper proposes an interference mitigation strategy for IEEE 802.15.4 system to maintain communications during times of interference by adjusting the transmission parameters. The adjustment is made according to the energy detection on the relevant radio frequencies that is used to determine the pattern of idle slots in the interfering signals. This enables the IEEE 802.15.4 system to commence communications within the detected idle slots and thus the communication links are possible to be maintained even under serious interference circumstance. © 2012 IEEE.