  Reconfigurable intelligent surface (RIS) has received increasing attention
due to its capability of extending cell coverage by reflecting signals toward
receivers. This paper considers a RIS-assisted high-speed train (HST)
communication system to improve the coverage probability. We derive the
closed-form expression of coverage probability. Moreover, we analyze impacts of
some key system parameters, including transmission power, signal-to-noise ratio
threshold, and horizontal distance between base station and RIS. Simulation
results verify the efficiency of RIS-assisted HST communications in terms of
coverage probability.
