Optimal eigenbeamforming for suppressing self-interference in full-duplex MIMO relays

We address the main technical challenge encountered in the practical implementations of full-duplex MIMO relays, i.e., how to mitigate efficiently the self-interference that loops back from the relays transmit antenna array to its receive antenna array. In particular, we consider spatial-domain suppression using optimal eigenbeamforming that minimizes the power of the residual self-interference signal by pointing the transmit and receive beams to the minimum eigenmodes of the self-interference channel. As a special case, the scheme covers also the null-space projection approach discussed in earlier papers. To demonstrate the feasibility of full-duplex relaying, we have previously built prototype antenna arrays for a full-duplex MIMO relay and measured an extensive set of real-world self-interference channels in different deployment scenarios. Using the measurement data, we now evaluate the natural isolation between separated antenna arrays and the additional isolation given by optimal eigenbeamforming.