Measurement and Simulation-Based Channel Characterization in Extra-Wagon Scenarios for 5G-R Communications

5G-Railway (5G-R) is the pivotal infrastructure to ensure the railway safety and support the development of intelligent railway. The design, optimization, and performance evaluation of communication systems rely on accurate channel characterization. This paper analyzes the channel characteristics for three scenarios in the railway environment: wagon-side, wagon-blocked, and wagon-moving scenarios, employing measurements and simulations. The channel measurements are firstly carried out in the wagon-side scenario at the 5G-R private network band. The large-scale and small-scale fading parameters are analyzed. A large-scale parameters table is proposed. The results reveal that there are 8 clusters, which is smaller than the reference values in existing channel standards. This indicates a limited number of rays in railway environment. Second, the channel characteristics in the wagon-blocked scenario are analyzed experimentally at the 5G-R private network band to analyze the signal variation from blocked to unblocked states. The results demonstrate that wagon blocking causes an additional loss of 4.62 dB, and there is more significant delay spread at the blocking critical point. Third, the ray-tracing simulations are performed in the wagon-moving scenario based on the measurement scenario. In a scenario similar to the measurement, time-varying channel characteristics and Doppler effect are analyzed when the train moves at a speed of 350 km/h. It is found that the wagon can increase the delay spread because the wagon brings more reflective and diffractive paths. These results are crucial for informing the design and deployment of 5G-R communication systems in railway environment.