Research On Transceiver Design Method Of RIS-Assisted Symbiotic Radio Communication System

Due to the supermassive connectivity requirements of future communication networks,energy efficiency(EE)and spectrum efficiency(SE)have become the two key performance indicators of the sixth generation of wireless communication networks.The symbiotic radio(SR)based on the reconfigurable intelligent surface(RIS)has been widely studied as a technology to achieve both high EE and SE.It is worth noting that secure transmission is an important issue for SR systems.In this thesis,the transceiver design improves the existing RIS-assisted SR system.The proposed system not only supports RIS enabling secondary user(SU)communication,but also can effectively reduce the energy consumption of the primary transmitter(PT),and enhance the security of private information transmission of the primary user(PU).In view of the design of transceiver for RIS-assisted SR communication system,this thesis proposes a receiving scheme based on hypothesis testing for SU.SU does not need to demodulate the master information and directly receive RIS information.The PT emission power is minimized by combining the constraints of the Signal-to-Noise-to-noise ratio(SNR),the bit error rate(BER)of SU and the phase shift coefficient of RIS.Since the stated problem is non-convex,the alternating optimization(AO)algorithm is used to decompose the non-convex original problem into two sub-problems of optimization PT precoding vector and RIS phase shift coefficient,and the suboptimal solution is obtained by combining the semidefinite relaxation(SDR)technology and Gaussian randomization method.The simulation results show that the proposed system effectively reduces the energy consumption and has certain safety.To solve the high complexity of RIS phase shift subproblem when the number of RIS antennas is large,this thesis proposes a low complexity algorithm based on coordinate descent(CD)to solve the phase shift subproblem.This algorithm can obtain the closed solution of the subproblem by fixing the residual phase shift coefficient by optimizing a phase shift coefficient at a time,and the proposed algorithm greatly reduces the problem complexity.The simulation results show that the proposed algorithm outperformed the benchmark scheme and reduces the complexity effectively.