Transmission Design For Relay System With Finite-alphabet Inputs

How to improve the transmission capacity of the wireless relay communication system is a current research hotspot.Most of the existing studies assume that the inputs are ideal Gaussian signals.However,the inputs of practical wireless relay communication system are non-Gaussian distributed finite-alphabet signals,such as phase shift keying(PSK)and quadrature amplitude modulation(QAM)signals,which leads to a large gap between the practical performance of the transmission technology based on Gaussian signals in the wireless relay system and the theoretically expected performance.To improve the practical transmission performance of the wireless relay system,this thesis studies the transmission technology in relay systems with finite-alphabet inputs.The main contents and contributions of this thesis are as follows:First,this thesis studies the joint transmission technology in a simultaneous wireless information and power transfer(SWIPT)-enabled multi-relay cooperative system,whose goal is to jointly optimize the source precoder and power splitting(PS)ratio to maximize the mutual information.In order to solve the considered nondeterministic polynomial-time(NP)-hard problem,the optimal PS ratio is theoretically analyzed,and then an approximately optimal precoding design based on semi-definite relaxation(SDR)is proposed;in addition,a precoding design based on search technology was developed with lower complexity.The simulation results show that,compared with the traditional design,the proposed transmission design has a significant performance gain.Then,this thesis studies the joint optimization of source precoder,relay precoder,and energy harvesting(EH)ratio in a SWIPT-enabled multiple-input multiple-output(MIMO)relay system.In two EH schemes,the feasible regions of the PS and time switching(TS)ratios are analyzed,and an algorithm based on linear backtracking search is proposed to solve PS and TS ratios.Then,the necessary condition for the optimal relay precoding matrix is derived and a joint source and relay precoding algorithm based on SDR and Karush-Kuhn-Tucker(KKT)theorem is designed.In addition,the optimal precoder structure for energy transmission under the TS scheme is theoretically proved.The simulation results show that the proposed joint optimization algorithm outperforms the optimization algorithm based on Gaussian signals.Subsequently,this thesis considers the joint design of source and multi-relay precoders in a multi-hop cognitive MIMO relay system.First,for the problems with perfect channel state information(CSI)and statistical CSI,the solving frameworks including the iterative rank penalty(IRP)algorithm and the customized Uzawa algorithm are proposed,respectively.Then,the convergence of the proposed solving framework is theoretically analyzed.The simulation results show that,compared with the precoding design with Gaussian signals,the proposed precoding design can greatly improve the achievable rate.Finally,this thesis studies the secure transmission problem in a cache-aided relay system,whose goal is to maximize the achievable secrecy rate by designing beamforming vectors and power control at the source and relays.In order to solve the difficult problem with combinatorial optimization variables,the optimal beamforming vector and power control parameter is theoretically analyzed for the source;for the relay,a joint solving algorithm is developed by introducing Moreau-Yosida regularization(MYR)and rank-one decomposition procedure(RDP)techniques,and the optimal caching coefficient is discussed.Simulation results show that the performance of the proposed algorithm exceeds that of the existing traditional algorithms.