  We consider channel estimation for high-speed railway communication systems,
where both the transmitter and the receiver are equipped with large-scale
antenna arrays. It is known that the throughput of conventional training
schemes monotonically decreases with the mobility. Assuming that the moving
terminal employs a large linear antenna array, this paper proposes a
position-aided channel estimation scheme whereby only a portion of the transmit
antennas send pilot symbols and the full channel matrix can be well estimated
by using these pilots together with the antenna position information based on
the joint spatial-temporal correlation. The relationship between mobility and
throughput/DoF is established. Furthermore, the optimal selections of transmit
power and time interval partition between the training and data phases as well
as the antenna size are presented accordingly. Both analytical and simulation
results show that the system throughput with the position-aided channel
estimator does not deteriorate appreciably as the mobility increases, which is
sharply in contrast with the conventional one.
