Rotatable Antenna-Enabled Wireless Relaying for High-Speed Train Communications

Abstract

High-speed train (HST) communications face severe challenges in providing reliable data services to users due to the rapid channel variation and beam misalignment caused by high mobility. To address these issues, we propose a rotatable antenna (RA)-enabled HST relaying system, where both the base station (BS) and the train-mounted relay are equipped with RA arrays to enhance directional transmission through flexible boresight adjustment. Specifically, we formulate an optimization problem to maximize the received signal-to-noise ratio (SNR) at train-mounted relay by jointly optimizing the beamforming and RA orientations at the BS and relay. By exploiting the decomposable structure of the high-dimensional BS-relay channel matrix, the original non-convex problem is decomposed into two independent subproblems, for which closed-form solutions with low complexity are derived. Furthermore, we propose an efficient transmission protocol for HST communications to conduct channel estimation and beam/boresight tracking with low complexity. Simulation results demonstrate that the proposed RA-enabled HST relaying system achieves significant achievable rate gains over benchmark schemes.