Residual self-interference in full-duplex MIMO relays after null-space projection and cancellation

Practical full-duplex MIMO relays require efficient mitigation of the relay self-interference signal propagating from the transmit antenna array to the receive antenna array; this paper concentrates on time-domain cancellation (TDC) and spatialdomain suppression by null-space projection (NSP). Both schemes can eliminate all self-interference in the idealistic case where the relay has perfect side information on the self-interference channel and signal. Thus, it is of practical interest to analyze their performance in more realistic cases where the side information is non-ideal. In particular, our contribution is to evaluate the additional isolation given by the mitigation schemes w.r.t. natural isolation between spatially separated antenna arrays. We also show how NSP (as opposed to TDC) can be made immune to errors in information on the self-interference signal.