Cooperative Transmission Scheme Of Loop Interference Suppression For OFDM Full-duplex Relay

With the rapid development of wireless communication, the relay cooperative communication technology has been widely used and has become one of the key technologies in the field of wireless communication. Compared to half-duplex(HD) relay system, full-duplex(FD) relay transmits and receives signals at the same time and over the same frequency band. So FD relay is capable of multiplying spectral efficiency and improving system capacity significantly. For the shortage of the spectrum resource nowadays, the FD relay cooperative system has quite good potential for development. However, the loop interference is the core factor that influences the system performance due to the characteristic of the FD wireless communication itself. For the inherent defects of the FD relay cooperative system, a variety of schemes has been proposed for the suppression of the self-interference, but the interference can still not be eliminated completely. These remaining loop interference signals would be accumulated continuously during the circulation of the transmitting and receiving process and influence the system cumulatively. For this reason, we consider a better scheme to deal with the residual loop interference(RLI) of the FD relay cooperative system.This thesis outlines the basic principles of FD relay cooperative communication system, presents various self-interference cancellation schemes, including conventional adaptive margin gain scheme, conventional maximum gain scheme for amplify-and-forward(AF) relay, and optimal gain scheme for single-frequency AF relay. Then a cooperative transmission scheme of FD relay is proposed to deal with RLI. This scheme can reduce the impact of RLI effectively, furthermore, the relay only needs to amplify and forward the received signal in analog domain by controlling the amplifying factor. That is, no further RLI cancellation is needed, which can simplify the processing at the relay greatly. First, by analyzing the transmission process of RLI at the relay node, we can see that the cyclic accumulation process of the signal through the loop channel can be treated as transmitting through a finite multipath channel. Thus, we can combat multipath effect caused by the strong part of RLI by taking advantage of OFDM. Then, the tail of RLI is degraded by the loop channel naturally only by optimizing the amplifying factor without any loop interference cancellation. Meanwhile, SINR can be maximized and BER performance of the system can be improved with optimal amplifying factor selection. Finally, the rationality of the theoretical optimal amplifying factor is verified by simulation results, the system influenced by the noise from relay node and destination node is shown and BER performance of the system while setting different amplifying factors is simulated.