Fast Codeword Design for Asymmetric Millimeter-Wave MIMO Systems under Mutual Coupling

Asymmetric mmWave massive multiple-input multiple-output (MIMO) systems have attracted much interest due to the massive available spectrum and lower power consumption. In these systems, once a communication link has been established in the beam training stage, part of the array can be deactivated to support asymmetric uplink-downlink (UL-DL) traffic in the data transmission stage. For this array with deactivated elements, however, the phase of the original ideal codeword requires further perturbation to overcome the pattern distortion caused by mutual coupling between the activated and deactivated elements. We therefore propose a phase perturbation method, which perturbs the phase of ideal codeword based on the effective channel including the coupling effect. In this method, we propose a fast search (FS)-based alternative optimization algorithm that alternatively adjusts each activated antenna phase to apply to the effective channel. Simulation results show that the proposed phase perturbation method can make up for the angular distortion.