Fig. 1 Anew HST communication cellular architecture.

To provide reliable communication services for high-speed train (HST) communication systems, key 5G communication technologies, such as mmWave and massive MIMO, and potential architectures, such as coordinated multipoint and mobile relay station, are considered in future railway communications. New technologies and architectures will bring new channel propagation characteristics. This article reviews the HST channel measurements conducted in different scenarios and frequency bands, and the advanced HST channel models. Then a novel HST channel model incorporating the mmWave and massive MIMO propagation characteristics is presented, and the space-time-frequency non-stationarity is analyzed. The new HST cellular architecture and typical channel statistical property are shown in Figs. 1 and 2. The proposed channel model can provide theoretical reference for constructing future railway communication systems. (Yu Liu, Cheng-Xiang Wang, and Jie Huang, “Recent developments and future challenges in channel measurements and models for 5G and beyond high-speed train communication systems,” IEEE Commun. Mag., vol. 57, no. 9, pp. 50-56, Sept. 2019.)

Fig. 2 Typical frequency non-stationarity analysis