  As a potential development direction of future transportation, the vacuum
tube ultra-high-speed train (UHST) wireless communication systems have newly
different channel characteristics from existing high-speed train (HST)
scenarios. In this paper, a three-dimensional non-stationary millimeter wave
(mmWave) geometry-based stochastic model (GBSM) is proposed to investigate the
channel characteristics of UHST channels in vacuum tube scenarios, taking into
account the waveguide effect and the impact of tube wall roughness on channel.
Then, based on the proposed model, some important time-variant channel
statistical properties are studied and compared with those in existing HST and
tunnel channels. The results obtained show that the multipath effect in vacuum
tube scenarios will be more obvious than tunnel scenarios but less than
existing HST scenarios, which will provide some insights for future research on
vacuum tube UHST wireless communications.
