A vactrain (or vacuum tube high-speed flying train) is considered as a novel proposed rail transportation approach in the ultra-high-speed scenario. The maglev train can run with low mechanical friction, low air resistance, and low noise mode at a speed exceeding 1000 km/h inside the vacuum tube regardless of weather conditions. Currently, there is no research on train-to-ground wireless communication system for vactrain. In this paper, we first summarize a list of the unique challenges and opportunities associated with the wireless communication for vactrain, then analyze the bandwidth and Quality of Service (QoS) requirements of vactrain’s train-to-ground communication services quantitatively. To address these challenges and utilize the unique opportunities, a leaky waveguide solution with simple architecture but excellent performance is proposed for wireless coverage for vactrains. The simulation of the leaky waveguide is conducted, and the results show the uniform phase distribution along the horizontal direction of the tube, but also the smooth field distribution at the point far away from the leaky waveguide, which can suppress Doppler frequency shift, indicating that the time-varying frequency-selective fading channel could be approximated as a stationary channel. Furthermore, the train-to-ground wireless access architectures based on leaky waveguide are studied and analyzed. Finally, the moving scheme is adopted based on centralized, cooperative, cloud Radio Access Network (C-RAN), so as to deal with the extremely frequent handoff issue.

This paper presents results from a wide band single-input-single-output (SISO) and 16 × 16 virtual multiple-input-multiple-output (MIMO) measurement campaign at a center frequency of 1.4725 GHz in a 100-meter long tunnel laboratory which is terminated by a vertical wall with a metallic door. The path loss, root-mean-square delay spread (RMS-DS) characteristics, and power delay profiles (PDPs) are described. In addition, we provide results for the MIMO channel amplitude matrix, which offers a new perspective in understanding MIMO characteristics in tunnel scenarios. Our measurement results are analyzed and compared to ray tracing simulations. The relationships among the angle spread, channel matrix singular values, and MIMO capacity at various link distances are illustrated, and these provide insights into MIMO system deployment.

Wireless channel modeling is regarded as a pivotal research topic, since the analysis and evaluation of the wireless communication system requires a reliable model of the channel impulse response (CIR). This paper presents a novel and practical study on the position-based radio propagation channel for high-speed vactrains in the vacuum tube scenarios using the propagation graph channel modeling theory. Based on the Lambertian scattering pattern, the propagation graph channel modeling method considers the diffusion effect of radio waves. A multiple-input multiple-output (MIMO) wideband system channel is emulated for obtaining the virtual channel data. During the emulation process, the line-of-sight (LoS), single-bounced and double-bounced components are considered to yield the virtual CIR. Then, small-scale fading properties such as K factor, time delay spread (DS), and Doppler frequency feature are parameterized particularly, which presents dynamic variances at different train locations. Moreover, the simulation performance analysis of the MIMO system focuses on the ergodic capacity and the singular value spread (SVS). The corresponding results indicate a MIMO capacity performance degradation in this scenario. The proposed model can facilitate the reliable simulation and evaluation of MIMO systems for the high-speed vactrains in the vacuum tube scenarios.

Based on realistic measurements in China, shadowing characteristics at the frequency of 2350 MHz were investigated in typical High-Speed Railway environments. After confirming that the measured shadowing satisfies wide-sense stationarity (assessed via the reverse arrangement test method), we quantify the shadowing correlation. Three types of correlation models are compared for the shadowing characterization, and the Normalized Mean Square Error is used to determine the best matching model: a single decaying exponential function. Decorrelation distances were found to be 11.9 m, 17.7 m, and 8.3 m in our three HSR scenarios, respectively. The results should be useful for the evaluation and verification of wireless communication in High-Speed Railway scenarios.