  Although Terahertz communication systems can provide high data rates, it
needs high directional beamforming at transmitters and receivers to achieve
such rates over a long distance. Therefore, an efficient beam training method
is vital to accelerate the link establishment. In this study, we propose a
low-complexity beam training scheme of terahertz communication system which
uses a low-cost small-scale hybrid architecture to assist a large-scale array
for data transmission. The proposed scheme includes two key stages: (1) coarse
AoAs/AoDs estimation for beam subset optimization in auxiliary array stage, and
(2) accurate AoAs/AoDs estimation by exploiting channel sparsity in data
transmission array stage. The analysis shows that the complexity of the scheme
is linear with the number of main paths, and thus greatly reduces the
complexity of beam training. Simulation results have verified the better
performance in spectral efficiency of the proposed scheme than that of the
related work.
