Finite-Order Space-Time Source and Relay Filter Design for Wideband Full-Duplex MIMO Relaying With MMSE Criterion

Recently, the full-duplex multiple-input multiple-output relay (FD-MIMO-R) has been widely considered a promising way to increase the spectrum efficiency of a cooperative communication network. Under frequency-selective fading channels, an FD-MIMO-R system simultaneously exhibits the self-interference (SI) and inter-symbol interference (ISI). Most existing transceiver designs aim to cancel or mitigate these two interferences by treating them as harmful signals. However, SI and ISI are inherently generated from the desired signal, which implies that further performance improvement is possible if they can be properly exploited. This concept motivates us to propose novel finite-order space-time source and relay filters so that the end-to-end mean-square error can be minimized. Our design is based on the following two phases. First we derive the optimum spectrums of the source and relay filters with a majorization theory and alternating optimization. The finite-order filters are then developed by applying the weighted least-square criterion. Numerical experiments show that our proposed filters are indeed able to significantly improve the system performance in either flat or frequency-selective fading channels.