  In this paper, we apply angle-domain Doppler compensation for high-mobility
wideband massive multi-input multi-output (MIMO) uplink transmission. The
time-varying multipath channel is considered between high-speed terminal and
static base station (BS), where multiple Doppler frequency offsets (DFOs) are
associated with distinct angle of departures (AoDs). With the aid of the
large-scale uniform linear array (ULA) at the transmitter, we design a
beamforming network to generate multiple parallel beamforming branches, each
transmitting signal pointing to one particular angle. Then, the transmitted
signal in each branch will experience only one dominant DFO when passing over
the time-varying channel, which can be easily compensated before transmission
starts. We theoretically analyze the Doppler spread of the equivalent uplink
channel after angle-domain Doppler compensation, which takes into account both
the mainlobe and sidelobes of the transmit beam in each branch. It is seen that
the channel time-variation can be effectively suppressed if the number of
transmit antennas is sufficiently large. Interestingly, the asymptotic scaling
law of channel variation is obtained, which shows that the Doppler spread is
proportional to the maximum DFO and decreases approximately as $1/\sqrt{M}$
($M$ is the number of transmit antennas) when $M$ is sufficiently large.
Numerical results are provided to corroborate the proposed scheme.
