Two-Stage Beamforming Design for High-Speed Train mmWave Communications

Millimeter wave (mmWave) communications can achieve high data-rate transmission for high-speed trains (HSTs). However, the rapid change in path loss during the fast movement of HSTs poses a significant challenge to the mmWave beamforming design. In this paper, a two-stage beamforming (TSB) scheme is proposed to address this challenge for downlink HST mmWave communications. In the first stage, an algorithm based on semi-definite relaxation (SDR) and alternating minimization (AM) is proposed to stabilize the instantaneous receive signal-to-noise ratio (SNR) above a predefined threshold when the HSTs travel along the railway. In the second stage, the coverage of each beam used by the base station (BS) is widened to reduce the number of beam switches. Simulation results demonstrate that the proposed scheme requires fewer BS beams to cover the same railway range than the existing schemes while keeping the instantaneous receive SNR of the HSTs above the predefined threshold.