Joint Iterative Delay-Phase Precoding for THz UM-MIMO with Finite-Resolution and Limited-Range True Time Delay

Beam squint becomes a real challenge for the conventional wideband hybrid beamformers in ultra massive multiple input multiple output (UM-MIMO) systems at Terahertz (THz) band, as it causes serious beam gain loss and, hence, impedes the full utilization of the huge vacant bandwidths at this band. With the aim of combating this effect, delay-phase precoding has emerged as an energy-efficient solution, in which a mixture of true time delay (TTD) elements and phase shifters (PSs) are proposed to convert phase-controlled analog precoding into delay-phase controlled analog precoding. Nevertheless, existing infinite-resolution and large-range TTD elements are impractical due to the hardware cost and power consumption. In this paper, we propose a joint iterative optimization of the TTD and PS values based on alternating minimization considering low-resolution and limited-range TTD elements. Simulation results reveal the supremacy and robustness of the proposed algorithm in dealing with the hardware limitations of TTDs.