Phase noise suppression for realistic LOS-MIMO microwave backhaul systems

Phase noise (PN) in microwave (MW) systems greatly deteriorates Line-of-Sight (LOS) Multi-input Multioutput (MIMO) performance. To address the PN impairment, a least squares (LS) estimator for LOS-MIMO is derived based on a flat channel assumption, and the MIMO phase compensation strategy is also deduced to suppress the vital PNs. Then, more realistic radio frequency front-ends (RFFEs) with non-flatness in frequency response are considered in a MW LOS-MIMO system. The normally shallow notches in RFFEs' bandwidth introduce some inter-symbol interference (ISI) into the system. Based on the ISI polluted MIMO system model, we prove that the effectiveness of LS MIMO PN suppression (PNS) is largely deteriorated by the fast varying component in adjacent symbols. A novel matrix-inversion-based method is then proposed to address the ISI impairment on MIMO PNS. The two PNS methods are evaluated in our MW LOS-MIMO receiver. Effectiveness of both methods on ideal RFFEs and the superior of the latter one on realistic RFFEs are verified.