Optimum relay node selection for two-relay networks in railway environments

Relay networks enhance the system performance by creating cooperative diversity gain and extend communication range by relaying the received signal to other devices. Recently, Long Term Evolution-Railway (LTE-R) is applied in railway communication to increase capacity by keeping reliability, and 3rd Generation Partnership Projects (3GPP) adopts relay function for data transmission. In this paper, the performance of two-relay networks is analyzed in railway environments. We adopt decode-and-forward (DF) protocol for relaying using partially differential modulation to bypass channel estimation at the destination. We first analyze the effect of relay location in the system performance. Based on this, we find the optimum relay selection which minimizes the symbol error rate (SER).