Studies Of Self-interference Cancellation In Single-channel Full-duplex Relay System

With the development trend of high-speed, wideband, ubiquity and heterogeneity of wireless communication network, the situation of the scarce radio spectrum resources becomes increasingly prominent. The traditional HDR(half-duplex relay) systems with low spectral efficiency are gradually unable to keep up with the demand for wireless communication. As one of the key technologies of 5G, FDR(full-duplex relay) technique attracts much attention owing to its characteristic of frequency reuse. The FDR systems can provide cost-effective coverage extension and throughput enhancement. However, serious loop interference resulting from its characteristic of sending and receiving signals at the same time and frequency becomes a major factor which restricts its development.With a core issue of SIC(Self-interference Cancellation) of FDR systems, this paper mainly adopts the spatial approach to suppress the MIMO relay self-interference, which can reduce the bit error rate and improve the system capacity, including:(1) Based on the model of full-duplex MIMO relay systems, a Null-space projection method is presented. By means of SVD(Singular value Decomposition) of the channel matrix, three methods of selecting relay code matrix are used to eliminate the self-interference. Simulation results show that this scheme can effectively eliminate self-interference, reduce bit error rate and improve the system capacity.(2) By the use of Null-space projection method, an optimization model is established with the capacity as the objective function. Transmit power of relay and zero self-interference are the constraints. Then two schemes namely improved scheme based on SVD and scheme of joint design of codec are proposed to obtain the optimal system capacity. The codecs can be designed respectively. Simulation results show that the improved schemes outperform the basic spatial SIC scheme on the reliability and the capacity improvement.(3) With the combination of FDR and two-way communication, a bidirectional FDR system model is set up. Based on the Null-space projection, this paper designs the codec of relay node to cancel the relay self-interference. The self-interference of the source nodes can be eliminated by the use of time-domain method. Simulation results show that the spatial method can effectively cancel the self-interference of the bidirectional FDR system and improve the system performance.