Frequency-Scanning-Based Fast Multiuser Beam Training for Wideband Massive MIMO

Beam squint effect causes severe performance degradation for wideband beamforming inside Internet of thing (IoT) communication, and the true-time-delay (TTD) line has been regarded as a promising enabler to address this issue. However, beam training becomes a challenging puzzle in TTD-aided transceivers, where enormous beam directions bring about unacceptable training overhead, especially for the overhead-efficient IoT devices. In this paper, based on a joint delay-phase beamforming structure, we provide enhanced frequency-scanning-based training schemes for remarkable overhead reduction. Simultaneous beams pointing to different physical directions over a set of OFDM subcarriers can be generated to reduce overhead. The pointing directions can be flexibly controlled following two subcarrier-angular mapping policies: forward-pairing and backward-pairing. Besides, the power leakage problem is retrieved via the compressive phase retrieval (CPR) method to avoid beam mismatch. Furthermore, we adopt it into the multiuser scenario and propose a frequency-scanning-based simultaneous multi-user beam training (FS-MBT) scheme. The different subcarriers' pencil beams illuminate a broad angular sector, while several sectors are merged into multi-finger wide beams for simultaneous multi-user training. Analytical and numerical results demonstrate the proposed schemes' superiority over existing methods in both single-user and multi-user scenarios.