Research On Full Duplex Technique In Broadband Wireless MIMO System

Wireless full-duplex(FD) can double spectral efficiency potentially and shows a good application foreground. Its major limiting factor is strong echo self-interference. This paper focused on the self interference cancellation technique in wireless full duplex multiple input multiple output(FD-MIMO) systems. Two typical self interference cancellation technique schemes were studied including the passive echo cancellation and an active echo cancellation using spatial time domain precoding algorithm.First of all, the evolution of wireless full-duplex systems was introduced in detailed. The main existing problems is briefly summarized. The self-interference problem is analyzed under the mathematical MIMO-OFDM model. The cause of self-interference is analyzed, followed by the description for the performances impacts. Specially, the theory system capacity of full-duplex system is analyzed. Furthermore, different implementations of full-duplex system and their system scenarios are described in depth. Their advantages and disadvantages, including system bit error rate, system capacity, algorithm complexity are subsequently elaborated and analyzed in details.Since the least squared(LS) interference suppression algorithm has the drawback of poor stability and high complexity. Aiming at the problem of LS algorithm, a passive echo self-interference suppression algorithm for FD-MIMO-OFDM system is proposed based on wireless local area network(WLAN) framework. This novel echo cancellation is performed by using normalized least mean squares(NLMS) algorithm and shows higher stability and lower algorithm complexity. The system model and detailed signal processing flow are presented. The feasibility of proposed scheme is argued in bit error rate(BER), system capacity and algorithm complexity. The theory achievable system capacity fomula is derived. Computer simulation is performed under different antenna configuration and channel types. Simulation reseult shows that, the proposed FD-MIMO system can achieve a capacity of 1.85 times the ideal half duplex MIMO(HD-MIMO) system, with signal noised ratio(SNR) loss of only 0.3~0.5d B. Moreover, the paper propose an FD-Massive MIMO relay aided wireless communication system. Theory analysis and computer simulation verify that the system capacity of FD-Massive MIMO system increase with system antennas. FD-Massive MIMO system achieves higher system capacity than HD-Massive MIMO system when self-interference strength is low.Further more, due to the limited performance of passive echo self-interference suppression and its poor use of spatial-time structure of signal, a joint spatial-time precoding algorithm for FD-MIMO system is presented. The proposed algorithm avoids the power loss problem of desired signal by beamforming with the channel side information(CSI) of the desired signal. The papar analyses the feasibility of proposed algorighm by BER, system capacity, algorithm complexity. Theory analysis and computer simulation results show that, the proposed method increases the signal to interference and noise ratio(SINR) by 6d B with perfect CSI feedback under 8x8 MIMO.