## 4 Simulation Verification  
In establishing the three-dimensional electromagnetic model, we configured the vehicle-mounted receiving 4G and GNSS antennas as excitation ports 1 and 2 to accurately simulate their operating states within the vehicle. Meanwhile, to recreate the authentic communication environment, the simulated base station transmitting antenna was set as excitation ports 3 and 4. Additionally, to meet satellite communication requirements, the simulated satellite transmitting antenna was set as excitation ports 5, 6, 7, and 8. This port  
Figure 11: Typical throughput measurement result schematic. Figure 10: MIMO wireless communication schematic and definition of downlink power. configuration scheme is shown in Figure 12, which comprehensively reflects the interactions among various antennas and their influence on signal propagation. S-parameters, as coupling parameters between transmitting and receiving antennas, play a crucial role in our simulation process. To calculate the transmission coefficients from the transmitting antenna to the receiving antenna, we need to solve all relevant parameters listed in Table 1. It is particularly noteworthy that since the three-dimensional electromagnetic model we constructed involved signal transmission between multiple transmitting and receiving antennas, this simulation experiment was conducted within the framework of MIMO systems. Although this research focused on communication transmission performance between the base station and the vehicle's 4G antenna, as well as between satellites and the vehicle's global navigation satellite system antenna, it should be emphasized that these data do not equate to conclusions derived from SISO studies. In the MIMO environment, the simultaneous use of multiple antennas greatly enhances the capacity of the signal transmission, effectively improving the reliability and capacity of the communication system. Therefore, the results we obtained not only reflect the performance between base stations and antennas, but also encompass the effects of multi-node interactions in complex channel environments. S-parameters, or scattering parameters, are critical metrics in microwave transmission, utilized to characterize the frequency domain properties of transmission channels. In passive devices, they represent interference and isolation, whereas in wireless transmission, they can denote the communication between antennas. The S-parameters consist of four fundamental reference quantities, namely S11, S12, S21, and S22, each encompassing distinct signal behaviors. S11 represents the reflection coefficient, characterizing the proportion of the signal reflected back from port 1. S12 denotes the reverse transmission coefficient, describing the signal transmission capability from port 2 to port 1. S21 signifies the transmission coefficient, illustrating the signal transmission capability from port 1 to port 2. S22, analogous to S11, represents the reflection coefficient, depicting the proportion of the signal reflected back from port 2. Given that this study focused on the signals transmitted from the base station and satellite to the vehicle-mounted antenna, the signal behavior of S21, which describes the signal transmission capability from port 1 to port 2, aligns well with the specific configuration of our designed transmitter and receiver. The reference values of the S-parameters required for our analysis are tabulated in Table 1. S23 describes the signal transmission capability from base station 3 to the vehicle-mounted 4G antenna, while S15