  Provisioning reliable wireless services for railway passengers is becoming an
increasingly critical problem to be addressed with the fast development of high
speed trains (HST). In this paper, exploiting the linear mobility inherent to
the HST communication scenario, we discover a new type of spatial-temporal
correlation between the base station and moving antenna array on the roof top
of the train. Capitalizing on the new spatial-temporal correlation structure
and properties, an improved differential space-time modulation (DSTM) scheme is
proposed. Analytical expressions are obtained for the pairwise error
probability of the system. It is demonstrated that, the proposed approach
achieves superior error performance compared with the conventional DSTM scheme.
In addition, an adaptive method which dynamically adjusts the transmission
block length is proposed to further enhance the system performance. Numerical
results are provided to verify the performance of the proposed schemes.
