Extra-Large Scale Reconfigurable Refracting Surfaces for High-Speed Railway Networks

The operational high-speed rail (HSR) communication network has become increasingly unable to satisfy the explosive throughput requirements of the ever-increasing number of people traveling by high-speed trains. To acquire the immersive user experience of in the next generation smart and immersive HSR communications, this paper presents a powerful application of reconfigurable intelligent surfaces (RISs) technique, namely the employment of reconfigurable refracting surfaces (RRSs) that are installed on the shells or windows of trains, which can sufficiently enhance the signal power within the carriages with the aid of high-gain beamforming. Specifically, we first compare the regular RISs and RRSs for highlighting the advantages of RRSs. Then, we conceive the XL-RRS architecture applied in the next generation HSR networks, and propose an extra-large scale (XL)-RRS-aided train-to-trackside (T2T) transmission scheme. By exploiting the features of the uplink and downlink channel models between trackside base station and intra-wagon users, the proposed XL-RRS-aided T2T solution involves a grouped multi-user interleave-division multiple access based uplink transmission for higher system throughput and a zero-forcing based downlink transmit precoding for reliability. Simulation results show that the proposed XL-RRS-aided solution achieves superior throughput and bit error rate performance compared with the conventional single-hop and mobile relay station modes.