## 2 Channel Measurement and Simulation
### Ray-Tracing Simulation  
The ray-tracing simulation can calibrate material property parameters such as relative permittivity, conductivity, and roughness based on the received power data from actual measurements. This paper uses Wireless Insite's ray-tracing simulation tool to simulate the HSR seat path loss. Based on the measured scenario and the 3D train model, the wireless channel simulation model in the HSR plain scenario is built, as shown in Figure 4. In the simulation scenario, there are four carriages; the transmitter antenna is located at the center of the connection between Carriage 1 and Carriage 2, the antenna height is 3.6 m, and the distance between the station rails is 5 m. The measured data calibrates the wireless channel model constructed.  
Figure 5 illustrates the received power values obtained through the ray-tracing method after several adjustments to the material property parameters, compared with both the measured results and theoretical values. The path loss results from the simulation closely align with the measured data, demonstrating the high accuracy and reliability of our ray-tracing model. To further highlight the consistency between the simulation and measurement data, we present the following comparison in Table 1. This table provides a detailed statistical comparison of key parameters between the simulated and actual measured received power data. The mean difference between the measured and simulated data is 1.52 dB, the standard deviation difference is 0.86 dB, and the K-S test value is 0.7406, all of which indicate a high level of consistency between the two data. The optimized material parameters for the compartments are provided in Table 2.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Method** & **Mean (dBm)** & **Standard Deviation (dB)** & **K-S** \\ \hline Measurement & \(-77.96\) & 8.25 & 0.7406 \\ Simulation & \(-79.48\) & 9.11 & 0.7406 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Statistical comparison of received power data between simulation and measurement.  
Figure 4: RT simulation scenario.  
Based on the calibrated model, further simulations were conducted to obtain a high-precision data set of path loss for the seats in the high-speed train carriage. The distance between the transmitting antenna and the train tracks (D) is 100 m, with the transmitting antenna placed at a height of 25 m, aligned with the x-axis coordinates of the first row of seats in the first carriage. The train consists of 8 carriages, and the frequency is 2.6 GHz. As shown in Figure 6a, the receiving antennas are omnidirectional, with six spatial sampling points arranged in each row of seats. The aisle position is labeled as E, and the seat positions are labeled as ABCDF, following the train's seat numbering system. Above each seat and aisle position, five receiving antennas with different heights (I, II, III, IV, V) are installed at heights of 2.376 m, 2.476 m, 2.576 m, 2.676 m, and 2.776 m, respectively, to reflect the typical usage scenarios of high-speed train passengers. Position A refers to the antenna on the side farthest from the transmitting antenna, while position F refers to the antenna closest to the transmitting antenna. Figure 6b shows that the receiving antennas are placed in rows 1 to 18 of the carriage seats, excluding connections such as through-paths between adjacent carriages. A total of 4320 receiving points were established, creating a high-precision data set with 4320 samples through simulation.  
Figure 5: Comparison of Received Power: Theoretical (Based on Two-path Model in Section 2.2, see Equation (1)), Measurement (Section 2.3), and Simulation (Ray tracing with parameters adjusted in Section 2.4).