MIMO array for space division duplex

We propose a novel self-interference cancellation (SIC) technique for space-division-duplex (SDD) multiple-input multiple-output (MIMO) array. The proposed SIC approach is as follows; first, an one-rank channel matrix, called a SI matrix in the paper, having only one dominant mode is formed between multiple transmitting (Tx) and receiving (Rx) antennas in a same SDD array. Then, the Tx/Rx ports are spatially isolated by cutting off the dominant mode giving eigenweight excitation to either the Tx or Rx array, that is, SIC is achieved at a cost of only one degree of freedom (DOF). For this SIC approach, we present a simple analog implementation using a cuboidal array configuration for the one-rank SI matrix and hybrid couplers for the eigenweight excitation. In this paper, theoretical aspects of the proposed technique are mainly focused on, and some numerical results are given demonstrating a good SIC effect even in some practical models.