  High speed train system has proven to be a very flexible and attractive
system that can be developed under various circumstances and in different
contexts and cultures. As a result, high speed trains are widely deployed
around the world. Providing more reliable and higher data rate communication
services for high speed trains has become one of the most urgent challenges.
With vast amounts of spectrum available, the millimeter wave (mmWave) system is
able to provide transmission rates of several gigabits per second for high
speed trains. At the same time, mmWave communication also suffers from high
attenuation, thus higher energy efficiency should be considered. This paper
proposes an energy efficient power control scheme of train-ground mmWave
communication for high speed trains. Considering a beam switching method for
efficient beam alignment, we first establish position prediction model, the
realistic direction antenna model and receive power model. And then we allocate
the transmission power rationally through the power minimization algorithm
while ensuring the total amount of transmission data. Based on this, this paper
also develops a hybrid optimization scheme and finds the limit of total energy
consumption when the number of segments goes to infinity. Through simulation
with various system parameters and taking velocity estimation error into
account, we demonstrate the superior performance of our schemes.
