Transmission schemes for high-speed railway: Direct or relay?

Two transmission schemes exist in wireless communication system for high-speed railway: the direct transmission and relay-based transmission. The main purpose of this paper is to evaluate the performance of these two transmission schemes. Specifically, the closed-form expressions of ergodic capacity for each transmission scheme are derived. By comparing these obtained capacity expressions, we find that the relay-based transmission has better performance in the low and intermediate SNR, while the direct transmission becomes a better choice at high SNR. It is also shown that the signal amplitude loss resulted from signal traversing through the carriage is a key parameter in determining the ergodic capacity for direct transmission scheme. Finally, the simulation results demonstrate an exact match with our theoretical findings.