Interference and Beam Squint Aware TTD-Aided Beamforming for Dual Wideband Massive MIMO

This letter investigates the design of an interference-aware (IA) and beam-squint-aware (BSA) true-time-delay (TTD)-aided statistical beamformer for spatial- and frequency-wideband (dual wideband) massive multiuser multiple-input multiple-output (MU-MIMO) systems. First, we provide the optimal unconstrained IA-BSA hypothetical frequency-dependent analog beamformer design, namely wideband generalized eigenbeamformer (WB-GEB), maximizing statistical mutual information for uplink beam division multiple access (BDMA) channels. Second, we propose IA-BSA TTD-aided quantized analog beamformers with double phase shifter (DPS) and single phase shifter (SPS) configurations, jointly optimizing phases and time delays for given radio-frequency (RF) chain allocation. These configurations are optimal least square (LS) approximations of the benchmark WB-GEB. The proposed designs employ quantized phase shifter (PS) and TTD networks and rely solely on slowly-varying channel covariance matrices (CCMs). Additionally, we determine the rank of the asymptotic mean CCM and its relation to the required number of TTD lines. Simulation results demonstrate the superiority of the proposed design in terms of outage capacity and spectral efficiency over existing approaches.