Self-interference Cancellation For Wireless Full-duplex MIMO-OFDM System

This paper focused on the adaptive echo cancellation technique in wireless full-duplex(FD) multiple input multiple output(MIMO)- orthogonal frequency division multiplexing(OFDM) systems. Two typical adaptive echo self-interference cancellation schemes were studied including the passive adaptive echo cancellation in digital baseband domain and an active echo cancellation using beamforming algorithm.First of all, the evolution of wireless full-duplex systems as well as existing problems is briefly summarized. The mathematical MIMO-OFDM model and its corresponding theoretical foundation on full-duplex echo cancellation were then illustrated, followed by the description for the causes, represents and performances impacts. Specially, the methods of full-duplex capacity under various channel state information were analyzed in depth. Furthermore, two classical full-duplex echo cancellation techniques in analog domain and analog domain and their advantages and disadvantages were subsequently elaborated and analyzed in details. Implementation issues are considered, including the existing full-duplex scheme was illustrated on single input single output(SISO) system and in perfect channel states. Considering the defects, a FD-MIMO-OFDM method for passive echo cancellation was applied in this investigation. This novel echo cancellation was joint separating antenna, analog domain cancellation method and digital domain cancellation method by using normalized least mean squares(NLMS) algorithm. Furthermore, the relevant BER(Bit Error Rate) and its system capacity were evaluated by computer simulation. It is shown that the performance based echo cancellation can be 30 d B. Comparing with ideal half-duplex(HD) system, BER can be decreased around 0.4d B, while its system capacity can be increased by a factor of up to 1.5. Meanwhile although its BER had a little loss, the capacity could still achieve 80 percent of ideal FD-MIMO-OFDM system.Moreover, since the passive echo cancellation method with high complexity and the limited performance of echo cancellation suppression, this paper employs another adaptive echo cancellation with beamforming method. Computer simulations were conducted, and the results illustrated that, compared with passive echo cancellation FD-MIMO-OFDM system, the proposed scheme perform better comprehensively. It can be observed that the capacity can be creased 0.7 times than ideal HD-MIMO-OFDM system. In addition, the proposed method can be raised by a factor of up to 1.2 than passive echo cancellation FD-MIMO-OFDM system, in the mean time, had a little influence on the BER.