Rotationally-Symmetrical Array for Self-Interference Reduction in Full-Duplex MIMO

Abstract

In order to realize a full-duplex wireless communication, the authors have proposed a spatial self-interference reduction technique with an end-fire array (EFA) which consumes only one degree of the multiple-input multiple-output (MIMO) freedom. However, this technique has a limited interference reduction performance due to an insufficient rank-degenerated interference channel because amplitude differences of the paths increase the rank of the channel in the EFA. In this letter, the authors propose a rotationally-symmetrical array (RSA) suitable for our conventionally proposing scenario to reduce the self-interference, where geometrical symmetry of the MIMO paths achieves a perfectly one-ranked channel and suppresses all of the self-interference in theory. Performance evaluation on the interference reduction level P_BF clarifies that the RSA reduces more interference than the EFA: P_BF = 47.3 dB (RSA), 23.0 dB (EFA) while array length of the transmitter (Tx), element spacing of the receiver (Rx), and distance between the Tx and Rx are 3.5 wavelengths, 0.5 wavelengths, and 5 wavelengths, respectively.