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

Beam squint effect causes severe performance degradation for wideband beamforming inside Internet of Things (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 article, 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: 1) forward pairing and 2) 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 multiuser beam training (FS-MBT) scheme. The different subcarriers’ pencil beams illuminate a broad angular sector, while several sectors are merged into multifinger wide beams for simultaneous multiuser training. Analytical and numerical results demonstrate the proposed schemes’ superiority over existing methods in both single-user and multiuser scenarios.