  In this paper, we study a new intelligent refracting surface (IRS)-assisted
high-mobility communication with the IRS deployed in a high-speed moving
vehicle to assist its passenger's communication with a static base station (BS)
on the roadside. The vehicle's high Doppler frequency results in a fast fading
channel between the BS and the passenger/user, which renders channel estimation
for the IRS with a large number of refracting elements a more challenging task
as compared to the conventional case with low-mobility users only. In order to
mitigate the Doppler effect and reap the full IRS passive beamforming gain with
low training overhead, we propose a new and efficient transmission protocol to
execute channel estimation and IRS refraction design for data transmission.
Specifically, by exploiting the quasi-static channel between the IRS and user
both moving at the same high speed, we first estimate the cascaded BS-IRS-user
channel with the Doppler effect compensated. Then, we estimate the
instantaneous BS-user fast fading channel (without IRS refraction) and tune the
IRS refraction over time accordingly to align the cascaded channel with the
BS-user direct channel, thus maximizing the IRS's passive beamforming gain as
well as converting their combined channel from fast to slow fading. Simulation
results show the effectiveness of the proposed channel estimation scheme and
passive beamforming design as compared to various benchmark schemes.
