Research On Power Control And Relay Selection Algorithm Of Relay D2D Communication System

Device-to-Device(D2D)communication technology allows two mobile users to communicate directly without going through base stations or core networks.This significantly improves the overall system throughput and energy efficiency.Through the reuse of spectrum resources,D2D communication can also greatly improve the spectrum efficiency of the communication system and reduce the load on the communication network.In addition,relay-assisted D2D communication technology can improve signal interruption probability and error rate,and expand network coverage.As one of the key technologies of 5G,D2D relay transmission can serve as a practical solution for the spectrum scarcity and network congestion of 5G wireless networks.However,if not managed properly,interference between different users in the system may seriously affect the service quality of the cellular network.Therefore,reasonable allocation of user power and selection of appropriate relay nodes become the key to improving communication system performance and ensuring user service quality.Firstly,one of the main research questions of this paper is how to find the optimal power control scheme in a system scenario where cellular users coexist with direct Device-to-Device(D2D)users and relay D2D users.In this context,the paper models the optimization problem as a mixed integer nonlinear programming problem,with the objective of maximizing system throughput while ensuring Quality of Service(QoS)for users.The objective function is decomposed into two sub-problems,DMPC(Direct D2D Communication Mode Power Control)and RMPC(Relay D2D Communication Mode Power Control),based on the two communication modes of D2D communication in the cell.In the DMPC problem,the best transmission power of direct D2D communication users is obtained by discussing the feasible domain of the problem.In the RMPC problem,the fractional programming problem is solved using the Dinkelbach method and the Lagrange dual decomposition method.Finally,a relay selection algorithm based on maximizing system throughput is proposed based on previous work.Simulation results show that the power control scheme and relay selection algorithm proposed in this paper allocate the best transmission power to D2D users while ensuring QoS for users,and significantly improve the success probability of D2D communication.Secondly,this paper conducts research on the optimal relay node selection algorithm.A relay selection algorithm that considers both physical domain and social domain factors is proposed in this paper.Firstly,a preliminary selection is made to filter out nodes that cannot afford-relay forwarding based on the physical domain conditions of each device in the cell.Then,based on the multi-attribute decisionmaking approach,the paper uses the Intuitionistic Fuzzy Analytic Hierarchy Process(IFAHP)and entropy weight method to calculate the mixed weights of four social attributes,including interest similarity,interaction time,relative historical contribution,and compensation incentive,from both subjective and objective perspectives.Finally,the optimal relay node is explored using the Optimal Stopping Theory.Simulation results show that the relay selection algorithm proposed in this paper saves exploration time for the optimal relay node while maximizing system benefits.On the basis of ensuring the efficiency of exploring relay nodes,the algorithm selects the optimal relay node for D2D users.