Angle-Domain Partition Beam Pattern-Based Beam Training in Sub-THz Extremely Large-Scale Antenna Array Communication Systems

Sub-terahertz (sub-THz) communications is considered one of the critical techniques in 6G network. To enlarge the antenna effective aperture and guarantee the received power, the employment of an extremely large-scale antenna array to generate high-gain beams is essential in sub-THz communications. Obtaining accurate channel path directions of users is necessary for achieving high-gain beamforming and efficient user scheduling in both unicast and multicast scenarios. However, the existing beam training schemes for acquiring channel path directions suffer from a large beam training overhead in either time-domain or frequency-domain. To solve this problem, we propose an angle-domain partition beam pattern (APBP) based beam training scheme by considering the delay-phase precoding architecture. Specifically, a wideband beam pattern called APBP is defined which covers the entire angle-domain and is realized by generating beams that cover different angle-domain partitions through different radio-frequency chains. Then, the property of the APBP is revealed that the channel path direction can be uniquely determined by using the targeted direction difference of beams satisfying two different APBPs with coprime partition numbers. Based on this property, we propose a fast beam training scheme with two stages. In the coarse estimation stage, the channel path directions are coarsely estimated by utilizing beams satisfying two different APBPs with coprime partition numbers. After that, a fine-tuning stage is operated to accurately decide the channel path directions. The proposed scheme is able to achieve accurate beam training by utilizing pilots occupying only three time slots and a small part of subcarriers. Theoretical analyses and extensive simulations have shown that the proposed scheme can realize a 75% reduction in beam training overhead with the near-optimal achievable sum-rate.