Wireless communication networks have become an essential part in our life these days, due to its flexibility and mobility. Researchers have shown that energy and security are fundamental factors in wireless networks, and can degrade the network performance. Recently, radio frequency (RF) energy harvesting (EH) in wireless cooperative systems has attracted significant attention; this technology is based on the fact that RF signals can concurrently carry information and energy, hence allowing energy-constrained nodes to harvest energy from the received RF signals. Furthermore, a promising method to achieve secure wireless communication is by applying physical layer security techniques, which exploit the physical characteristics of the communication channels to perform secure transmission; based on this concept, there has been considerable amount of research on improving the physical layer security in wireless cooperative systems. The purpose of this thesis is to investigate EH and physical layer security in cooperative systems. The major aim of the thesis is to introduce techniques to increase the EH and/or security of amplify-and-forward (AF) relaying systems, and provide an accurate theoretical performance evaluation of the proposed techniques. Firstly, a two-way wireless-powered communication network is considered, and the impact of the channel state information in the charging time on the system performance is investigated. In light of this, efficient power transmission techniques are proposed, and new expressions of the spectral and energy efficiencies are derived in different cases. Secondly, an EH-based AF relay system is analyzed; an appropriate jamming strategy to increase the EH and security is presented, and a comparison between the traditional EH-relaying protocols is also provided in terms of secrecy capacity. Thirdly, a new adaptive receiver and adaptive relaying (AR) protocol for EH and information processing are proposed, and exact expressions of throughput are derived. Furthermore, new mathematical expressions are derived for the secrecy capacity and secrecy outage probability of AF multi-input multi-output relaying systems, when the zero-forcing scheme is used in different locations in the system. Finally, a joint cooperative beam-forming and jamming technique in the two phases of AF relaying system is proposed. The new analytical expressions and algorithms derived in this thesis provide new insights into EH and secrecy performance in various practical scenarios.
|Date of Award||1 Aug 2018|
- The University of Manchester
|Supervisor||Khairi Hamdi (Supervisor) & Ka Chun So (Supervisor)|