## 4 Simulation Results and Analysis
### Analysis of Simulation Results
#### 4.1.2 Analysis of Model Parameters Change on System Performance  
After conducting a thorough review of the relevant literature and establishing the effectiveness of the algorithm presented in this research, we proceed to investigate the influence of changes in system model parameters on the throughput of the VUEs system. This investigation is guided by the outcomes obtained from simulations. In the first stage, we examine the implications of different quantities of CUEs and their corresponding data rate demands on the throughput of VUEs, as illustrated in Figures 5 and 6, respectively. Significantly, when the number of VUEs increases, there is a corresponding increase in the overall throughput of VUEs. The analysis of Figures 5 and 6 demonstrates a noticeable pattern: when the data rate requirement is consistent, increasing the number of CUEs results in an increase in system throughput. On the other hand, if the quantity of CUEs remains constant while their data rate requirements increase, it leads to a decrease in the system throughput of VUEs. This issue occurs due to the limited number of subcarriers, resulting in a proportional increase in the number of occupied subcarriers by CUEs as their quantity increases. The increase in data rate requirements for CUEs necessitates a greater utilization of subcarriers in order to meet their data rate demands. Consequently, this leads to an increase in the exhaustion of unassigned subcarriers during the succeeding stage of the resource-allocation process. As a result, the capacity of VUEs to efficiently utilize the spectrum allocated to CUEs decreases, resulting in a decline in the total data transmission rate of VUEs. Secondly, we will delve into the influence of vehicle speed and the presence or absence of power control on VUEs' throughput, as illustrated in Figure 7. Initially, let us examine the effect of speed. As the vehicle speed escalates, the system throughput of VUEs experiences a decrease, regardless of the presence or absence of power control. This phenomenon arises  
Figure 5: Relationship between the CUEs quantity Y and VUE throughput. Figure 6: Relationship of throughput between \(\Psi^{size}\) (data rate) and VUEs systems. from the vehicle position modeling in this study, which considers the vehicle's safe distance. Consequently, the average distance between vehicles increases to ensure driving safety, leading to elevated path loss and subsequently a reduction in VUEs' throughput. Moving on to the comparison between the presence and absence of power control, the throughput of the system exhibits a higher value with power control in the comparison graph compared to the scenario without power control. This observation underscores the essentiality of power control in this research. The rationale behind this lies in the completion of spectrum resource allocation, wherein binary integer variables are determined. In the absence of power control, VUEs maintain their initial power size, while with power control, VUEs' power size can be automatically adjusted based on spectrum resource allocation without compromising the data rate requirements of CUEs. This adjustment mechanism contributes to an enhancement in the throughput of the VUEs system. Finally, this study aims to comprehensively analyze the impact of modifying the number of subcarriers on the throughput of VUE systems, as depicted in Figure 8. There is a clear correlation between the increase in the quantity of subcarriers V and the subsequent rise in the throughput of the VUE system. The origin of this phenomenon can be attributed to the algorithm's increased adaptability in allocating subcarriers to CUEs in the first stage, where the data rate requirements and the number of CUEs remain constant. By increasing the number of subcarriers, the algorithm is able to more efficiently identify the most suitable subcarriers for serving CUEs, which may result in a reduced need for a large number of subcarriers to meet their data rate demands.