Research On Anti-interference Techniques And Time Allocation For Time Reversal Wireless Powered Communication Networks

The fast development of wireless communication and the rapid growth of the number of terminals access the network make a large number of Internet of things(Io T)devices represented by sensor nodes in wireless communication system in future.Thus,how to ensure stable and continuous power supply of these ubiquitous devices is an urgent problem that the Io T needs to solve.The core of wireless powered communication network(WPCN)is wireless energy transfer(WET)technology,which can effectively solve the problem that traditional batteries cannot continuously supply power in wireless networks.However,when the coverage of WPCN expanded and the structure of WPCN complicated,the inevitable interference will affect the system performance.Time reversal(TR)can effectively enhance the strength of the target signal and suppress the interference in the system because of its unique space-time focusing characteristics.Therefore,this thesis combines WPCN and TR to optimize system performance and two resource allocation methods are also proposed to improve system performance while suppressing interference.Specific research content is as follows:First,in multi-user WPCN,when users transmit uplink information at the same time,inter-user interference(IUI)occurs.In order to solve the IUI during the transmission,an interference solution based on TR is constructed and the "Tunneling effect" of TR is used to increase the uplink throughput of the system.TR is introduced into a multi-user WPCN system firstly,and the space-time focusing characteristic is used to suppress the interference of system.Based on this,the system's signal-to-interference-noise ratio(SINR)and system capacity expressions are derived theoretically,and an optimized objective function is set with the goal of maximizing the system throughput.Finally,the non-convex function is convexly transformed by successively optimizing the variables.Thus the optimal solution of time allocation can be obtained by combining the dichotomy method.The Monte Carlo simulation proves that the proposed time allocation scheme can effectively improve the throughput of TR-WPCN system.Second,in actual situations,the situation of WPCN systems in each cell is different and the uplink transmission is not synchronized,so cross-link interference will occur between cells.Aiming at the cross-link interference in asynchronous multi-user WPCN system,a joint optimization of uplink and downlink time allocation and power allocation scheme based on TR is proposed to maximize uplink weighted-sum rate(WSR).First,the unique space-time focus of TR is used to suppress cross-link interference.Then,an optimization model is built and the complex WSR problem is converted into the weighted minimum mean square error(WMMSE)problem.Finally,the variables are successively optimized through classification,and the optimal solutions of power and time are obtained respectively.Simulations verify that the system's average WSR is significantly improved after introducing TR to suppress the cross-link interference of the system.