Wireless body area networks : enabling robust coexistence and interference management

Abstract

The global trends for dramatic population growth and an ageing society are likely to increase the strain on scarce medical resources in the coming decades. The next generation of personal area networks, Wireless Body Area Networks (BANs), provide a promising solution to this problem with advantages of, e.g. high flexibility, low cost, location independence, real-time monitoring etc... Hence the use of BAN is becoming pervasive. However, the increasing number of active BAN units is a challenge as significant co-channel radio interference is generated, which often causes severe performance degradation and harms system reliability. Because of the difficulty of global coordination amongst multiple, coexisting and uncoordinated, BANs, due to significant dynamics, effective interference management schemes are urgently needed to enable reliable coexistence. Here the main theme is the investigation of the feasibility and efficiency of some co-channel interference mitigation schemes for BANs. The schemes we study in this thesis are based on the following: 1) cooperative communications with relays; 2) transmit power control; and 3) a cross layer design that integrates 1) and 2). Two types of power control methods are investigated: a) the first is a light-weight prediction-based power control method, which adaptively adjusts transmit power, at the sensors and relays, with respect to channel condition variations; b) the second method employs game theory and models the coexistence as a non-cooperative game. These techniques have been studied for other conventional wireless networks in the literature. However, there is very-limited work for radio interference mitigation for BANs. Another main contribution here is, instead of using channel models as presented in the literature, many open-access empirical body-centric channel measurements are used for the investigation of interference mitigation schemes proposed. These measurements contain subjects performing different {u0300}{u0300}everyday'' activities over many hundreds of hours in various environments. The use of the measurements in our study further enhances this by capturing factors that can significantly influence the on-body and inter-body channels. These factors include variations in body shapes and sizes of different subjects, subjects' local and spatial movement, body orientation and the effect of the surrounding environment. The performance, of the proposed schemes, is compared with traditional single-hop star-topology BANs for the same coexisting scenarios and BANs employing other conventional power control methods commonly used in the literature. We analyse their effectiveness with respect to first- and second-order statistics, particularly outage probability, level crossing rate, and average outage/non-outage duration, of the received packets' SINR at the hub of a BAN. The power consumption of using the proposed schemes is also compared with other schemes. Finally, it is shown that employing relays and the proposed power control schemes can greatly enhance a BAN's ability to mitigate co-channel radio interference. The use of a non-cooperative power control game enforces BANs to minimise the interference they create in the coexisting environment while maintaining reliability requirements. Importantly, there is fast convergence to a socially optimum outcome. Overall, there is significant impetus to using the schemes proposed here in future, practical, BAN implementations, as elucidated in this dissertation.