Frequency-domain signal reconstruction for wideband dynamic time-domain weighting hybrid precoding

Dynamic time-domain weighting (DTW) hybrid precoding has been proposed to approximate the performance of fully digital (FD) precoding by maintaining the phase shifter (PS)-based structure, especially in wideband scenario with beam squint. The DTW framework does not depend on steering vectors, and hence is applicable to far- and near-field scenarios. However, existing DTW is originally designed for a single radio frequency (RF) chain. Directly extension to multi-chains involves matrix inversion, which leads to numerical instability. To solve these issues, we propose a frequency-domain DTW hybrid precoding. Different from the existing DTW solving the analog matrices in time domain, we solve the frequency component of these matrices instead, which avoids the ill-conditioned pseudo-inverse operation in fully-connected multi-chains. Furthermore, we approximate the optimal analog precoder by utilizing the user channels instead of the overall channel, which introduces additional dimension of users/RF chains and useful information to improve the performance. Considering the practical constraints on PS, we design the slow-switching analog precoders with a smaller time dimension by incorporating the Discrete Fourier Transform (DFT) matrix and reshaping the signal reconstruction equation. Extensive simulation results with different channel models, system parameters, and practical concerns demonstrate the superiority of the proposed method compared with conventional wideband precoding and existing DTW hybrid precoding in terms of spectrum efficiency, energy efficiency, and gain spectrum.