A systematic approach to improve fiber-wireless access network in high speed railway tunnels

Wireless access networks over high speed railway (HSR) encounters many challenges, e.g., the fluctuations of wireless channels, frame synchronization, and geographical obstacles. Since increasing signal quality can bring benefit against channel impairments, the key to solve these challenges is to enhance radio signal strength over HSR. Combining radio over fiber with distributed antennas system (RoF-DAS) can improve radio link quality on a high speed train over HSR, especially in tunnels and underground. Compared to leaky cable, RoF-DAS is easier to be deployed and lower cost. However, the effects of multipath fading and Doppler shift can seriously degrade the performance of RoF-DAS. In this paper, we present a systematic methodology to determine the enhanced configuration for RoFDAS, such as power attenuation values and propagation time. The proposed systematic methodology takes the joint effect of channel dispersion and Doppler effect, and different deployment scenarios into account to determine the RoF-DAS configuration. Our simulation results also show that performance of RoF-DAS with configuration by the proposed methodology are better than the other configurations.