Research On Relay Strategies For The Full-duplex Two-way Relay System

The spectrum resources in the wireless communication system are limited.Faced with the increasing demand for data rates,it is urgent to improve spectrum efficiency and enhance transmission for the next-generation communication.Full-duplex(FD)technology supports concurrent transmitting and receiving signals on the same carrier frequency,which can double spectral efficiency.The relay technology operating in a cooperative manner can resist channel fading and increase cell coverage effectively.FD two-way relay system integrates the advantages of FD and relay technology.However,self-interference caused by FD limits the system performance.Therefore,the relay strategy of the FD two-way relay system is mainly studied.By designing different transmission strategies for different application scenarios,the residual self-interference is suppressed and the spectrum efficiency is improved.The research work of this paper mainly includes the following aspects:1.For a FD two-way multi-user multi-relay system,a joint user-relay selection strategy with low complexity is proposed.According to the channel state information of direct links,the user node is first selected based on the minimum SINR maximization,and the relay is selected based on outage probability minimization.The closed-form expression of the outage probability is derived,and it is compared with the conventional exhaustive strategy.The results show the proposed strategy can achieve system performance similar to the traditional exhaustive strategy.2.For the FD bidirectional MIMO relay system,a joint design of the transmit and receive beamforming vectors at the relay is proposed.The optimization problem is constructed to maximize the system capacity under the condition of power constraints of each node by jointly designing the transmit and receive beamforming vector.An iterative algorithm for solving the non-convex optimization problem is proposed.The main idea of the algorithm is to optimize the receive beamforming vector with the fixed transmit beamforming vector at the relay.The numerical solution and the closed solution are derived.The system capacity is then calculated.Fixed the receive beamforming vector,the transmit beamfonning vector is optimized in the same way.The iteration is repeated until achieving the convergence condition.The simulation analysis shows that the proposed design method can achieve better performance than traditional one.3.For a FD multi-user multi-relay system,N user pairs compete for M relays to accomplish bidirectional communication.A joint user pair and relay selection scheme is proposed based on minimum SINR maximization.Under the high SINR,the selection strategy is approximated to maximize the minimum channel coefficient modulus.The system outage performance is analyzed,and the closed-form expression of the outage probability is obtained and simulated.Simulation results show that the proposed scheme can achieve efficient information transmission between user pairs.As the increase of relays and user pairs,the diversity gain has a significant improvement.In summary,relay strategies corresponding to different application scenarios of full-duplex two-way communication are proposed in this paper,which provides a reference for the development and application of full-duplex technology.