Optical True Time Delay Compensation Network-Based Beam Tracking for THz Massive MIMO Systems

Terahertz (THz) communication is one of the most important technologies of future 6G due to its ultra-bandwidth. In THz massive multiple-input multiple-output (MIMO) systems, the performance of beam tracking is significantly degraded due to the beam split effect. In this paper, we propose an optical true time delay compensation network (OTTDCN)-based beam tracking scheme. In the proposed OTTDCN-based beam tracking scheme, the OTTDCN is introduced between the radio-frequency (RF) chains and the phase shifter network to pre-generate the beam compensation modes. Then, OTTDCN controls the degree of the beam split effect through frequency-dependent phase compensation to create multiple beams to track the physical directions of multiple users. Meanwhile, we develop a beam compensation mode-based beam tracking (BCM-BT) algorithm, which considers the selection of the optimal beam compensation modes. The results show that the OTTDCN-based beam tracking scheme can effectively reduce beam tracking overhead and achieve near-optimal sum rate performance.