Fast Terahertz Beam Training Via Frequency-dependent Precoding

Terahertz (THz) communications in the 0.1-10 THz band are envisaged as an attractive way to attain richer spectrum resources and surmount the bandwidth desert. To overcome the severe propagation loss suffered in THz communications and thus achieve high beamforming gain, massive multiple-input multiple-output (MIMO) technique has received much attention. To realize highly directional communications, beam training procedure is indispensable but the beam training schemes de-signed for narrowband systems result in severe performance loss caused by the wideband beam squint effect. To address this problem, we propose a beam training scheme using frequency-dependent RF precoder. Specifically, we analyze the optimal phase shifts to obtain the frequency-dependent RF precoder and then propose a hierarchical beam training scheme using the frequency-dependent RF precoder. Numerical results including the achievable sum-rate and the beamforming gain are presented to demonstrate the effectiveness of the proposed scheme.