A Study On Secure Transmission Schemes For Simultaneous Wireless Information And Power Transfer Systems

Simultaneous Wireless Information and Power Transfer(SWIPT)is a frontier research field,which is a combination of wireless communication technology and wireless energy transfer.Recently,there has been an upsurge of research interests in simultaneous wireless information and power transfer(SWIPT),where energy and information are jointly transmitted using the same radio waveform.It's a promising new solution to provide convenient and perpetual energy supplies to wireless networks.However,SWIPT faces challenges of fading and secure communications.Therefore,the study on how to realize efficient energy transfer and secure communication in SWIPT system has important practical significance.In traditional wireless networks,multi-antenna precoding and physical layer security technologies can effectively reduce the impact of channel fading and ensure the security of communications,respectively.Consequently,by combining these two technologies,the thesis mainly focus on the topic of robust secure beamforming for MISO SWIPT broadcast channels with confidential messages,cooperative precoding design for cognitive wireless energy transfer networks.The detailed contents and main contributions of this thesis are listed as follows:Firstly,the thesis propose a secure and robust beamforming design for the scenario of secure message propagation in SWIPT broadcasting channel,where the transmitter only knows part of channel state information(CSI).The thesis aim at minimizing the total transmit power of the system by jointly optimizing the beamforming vector,the noise covariance matrix and the power allocation factor of the receiver,subject to the achievable secrecy rate and energy harvesting constraints.The proposed robust beamforming design corresponds mathematically to a non-convex optimization problem which is difficult to solve.To solve this problem,the thesis first use Lagrange method to accurately calculate the upper and lower bounds of the original optimization problem,and then use semi-definite relaxation technology to transform the original non-convex problem into convex problem.Finally,the robustness of the proposed scheme is verified by simulation results.Secondly,the thesis propose a cooperative precoding design for a coexisting wireless energy transfer(WET)and cognitive radio(CR)system.Unlike traditional wireless networks,co-channel interference here is useful,rather than harmful resources.By jointly optimizing the transmission covariance matrix,the proposed scheme maximizes the security rate of cognitive links while guaranteeing the energy acquisition needs of energy receivers.To solve the above problems,the thesis propose an iterative algorithm based on Block Coordinate Descent(BCD)to deal with the original non-convex optimization problem.Thesimulation results show that the proposed cooperative precoding scheme outperforms the non-cooperative precoding scheme in terms of security rate and energy collection.