Double-RISs-Aided Predictable High-Speed Railway Communications With Doppler Effect Mitigation

Doppler mitigation method aided by reconfigurable intelligent surface (RIS) is essential for the high-speed rail (HSR) communications system, which, however, receives little attention. In this letter, a new anti-Doppler spread strategy in double RISs-aided HSR communication is proposed. The phase shift is designed according to the rail information (e.g., timetable, speed, and rail track) by optimizing a multiobjective problem with signal-to-noise ratio (SNR) maximization and Doppler and delay spread minimization. Numerical results verify the effectiveness of the proposed phase shifts design for double RISs, as compared to the various benchmark schemes, and proposed phase shifts design can eliminate the Doppler spread entirely.