Antenna Arrangement Suitable for Full-Duplex MIMO

In this paper, we introduce an interference suppression technique that combines a multiple-input multiple-output antenna arrangement with eigen-beamforming suitable for space division duplex relay that uses separate transmitter (Tx) and receiver (Rx) in relay stations (RSs) to realize full-duplex communication. The proposed technique degenerates the rank of the interference channel matrix to basically one at the RSs by careful arrangement of the antenna, which allows the Tx and Rx arrays to use nearly zero space weights. This scheme offers significant interference suppression while consuming only one degree of spatial division multiplexing freedom. To implement this scheme, we adopt the end-fire arrangement, where all antenna elements are arranged in line. In line-of-sight environments, this arrangement degenerates the rank of the interference channel matrix. The results of a numerical analysis and an experiment show that the proposed method can reduce the interference by up to 75.2 and 36.5 dB, respectively. The simulation using measured data clarifies that the proposed system attains 1.81 times higher capacity (12.1 b/s/Hz) than the conventional system.