Frequency-Domain Signal Reconstruction for Dynamic Time-Domain Weighting Hybrid Precoding with Beam Squint

Abstract

Hybrid precoding is considered in wideband mm-Wave massive MIMO-OFDM systems with beam squint. Traditional wideband hybrid precoding schemes cannot achieve near-optimal sum rate as digital precoding/beamforming (DBF) and may induce high hardware cost. Dynamic time-domain weighting hybrid precoding (DTW-HBF) updates the analog weights during an OFDM symbol, realizing equivalent frequency-dependent analog precoding and approximating DBF with a low cost. Directly reconstructing the time-domain signals, however, involves pseudo-inverse operations, which may cause numerical instability. In this work, the frequency-domain spectrum is reconstructed by introducing the optimal frequency-domain analog precoder and using the cyclic convolution property of Discrete Fourier Transform (DFT). The proposed method can approximately approach the performance of DBF while maintaining the hardware structure based on phase shifters (PSs). As shown by simulation results, an increased sum rate has been achieved.