Joint Antenna and Digital-Level Self-Interference Cancellation for 4(2) × 2 MIMO Full-Duplex Amplify and Forward Relay Systems

Abstract

Wireless relay systems have potentials to increase the spectral efficiency and to extend the cell coverage in cellular networks. There are various schemes of relay systems depending on the number of antennas, signal processing, and duplex modes. Among them, a full duplex amplify-and-forward relay is one of the most promising relaying schemes because the full-duplex mode is more efficient than the other duplex modes and the amplify-and-forward scheme is the closest to practical implementation. However, the full-duplex relay system has a self-interference problem because it transmits and receives signals at the same time through the same frequency band. Hence, the full duplex relay system implementation needs a method to solve the self-interference problem. For this reason, in this thesis, a joint antenna and digital-level self interference cancellation method for suppressing the self-interference is proposed. This method takes into account potential problems at the RF chain of the relay’s receiver but does not assume that the self interference channel state information is known. Hence the method is practical and facilitates the implementation of full-duplex relay systems. In proposed method, first, relay’s transmit and receive antennas are placed to suppress the self-interference at the EM level. Then the residual self-interference is eliminated at the digital-level using the self-interference channel information that is estimated in real time. By these procedures, the self-interference could be suppressed very effectively. In addition, the proposed method is for 4(2) × 2 MIMO relay systems. Hence, transmit signals from the relay can be beamformed to be sent in a desired direction. The transmit beamforming makes the proposed relay system suitable for the coverage extension of indoor space.