A Research On Simultaneous Wireless Information And Power Transfer In Relay Systems

Simultaneous wireless information and power transfer(SWIPT) is a frontier research direction, which combines the technology of wireless information transfer and wireless energy transfer. Since radio signal can carry information as well as energy at the same time, we can achieve the parallel transmission of information and energy. SWIPT can improve the utilization of transmission power thus meeting the requirements of green communication.The realization of SWIPT depends on the operating strategy of the receiver, including the Time-Switching and Power-Splitting strategy. Thereby, we investigate three practical structure designs of receiver, namely time switching, power splitting and separated. The time switching and power splitting receiver architectures are studied in single antenna systems, which enable the energy-limited node to harvest energy and process information at the same time. But in multi-antenna systems, we mainly consider the separated receiver architectures. Using spatial degrees of freedom in multi-antenna systems, we design the beamforming vector to meet the requirements of rate and the constraints of energy harvesting.This thesis studies the SWIPT technology in relay systems. We focus on the receiver structure designs of energy harvesting relay in single antenna relay systems. And in multi-antenna relay systems, the relay beamforming problem is studied. Also, we apply the SWIPT technology in secure relay system, which combines green communication and information security.Firstly, practical receiver structures of energy harvesting relay are investigated in single antenna relay systems. Based on the power splitting and time switching receiver structures, we propose two relaying protocols, i.e. the power splitting-based relaying protocol and the time switching-based relaying protocol to enable the energy-limited relay to harvest energy and process information at the same time. We derive that the achievable rate is a convex function with regard to energy harvesting time ratio and power splitting ratio. The optimal energy harvesting time and power splitting ratio are designed to maximize the achievable rate.Secondly, we study the optimal relay beamforming problem, which maximizes the achievable rate subject to the transmit power constraint at relay and the energy harvesting constraint at energy harvesting receiver. As the high complexity of CVX-based solution, we propose a simple linear precoding based method, and present the rate-energy region.Finally, based on the above research, two aspects are involved in secure relay systems with SWIPT. On one hand, the power splitting-based relaying protocol is discussed at the secure relays. We investigate the joint design of power splitting and secure relay beamforming, aiming to achieve the maximal secrecy rate. To reduce complexity, the secure relay beamforming problem under the fixed power splitting ratio is also considered. On the other hand, we study the optimal relay beamforming problem which maximizes the secrecy rate under the constraints of transmit power at relay and the harvesting energy at energy harvesting receiver. Also, the suboptimal null space beamforming scheme is proposed.