# A Novel Base-Station Selection Strategy for Cellular Vehicle-to-Everything (C-V2X) Communications
## 7 Simulation Results  
Due to the limited speed of the vehicle, if the vehicle is closer to the macrocell base station, the probability of a handover to the femtocell base station in the next second is small. Similarly, if the vehicle is very close to the femtocell base station, the next second is less likely to move to the macrocell base station, but the vehicle could prefer the femtocell base station. In the existing selection method, the user selects the larger predicted RSS of the two base stations. Therefore, we mainly discuss the choice of vehicles at critical locations in the coverage of macrocell and femtocell base stations. Since the vehicle reward function is related to the running speed of the vehicle and the motion direction, base station selection of the vehicle is according to different running speeds and the motion direction. In this critical area, we discuss the average RSS in the system when using the Markov decision policy and the non-Markov decision policy if the vehicle selecting the femtocell base station exceeds the user limit. We assumed that there were 150 randomly-distributed vehicles in the coverage of the femtocell base station, which can be used by up to 100 vehicles. We set vehicle speeds at 2, 4.5, and 30 m/s. At the speed of the previous step, the marked dot in the figure represents the real value obtained by the simulation; then, values are normalized to the line in the figure. We simulated the base station selection problem using MATLAB. All parameters we used in this simulation are presented in Table 1. Here, we set \(h_{M}=h_{F}\). We assumed that mobility speed was 2 m/s (low speed), where \(\theta_{0}\) is the user's displacement angle of the previous step, randomly setting these variables. In Figures 7-9, the three different colors \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Path-loss exponent \(\beta\) & 2 \\ Transmitting power of macrocell \(E_{M}\) & 300 w \\ Transmitting power of femtocell \(E_{F}\) & 300 mw \\ Coverage of macrocell & 1000 m \\ Coverage of femtocell & 100 m \\ High probability \(P_{H}\) & 0.6 \\ Normal probability \(P_{M}\) & 0.3 \\ Low probability \(P_{L}\) & 0.1 \\ Reward of femtocell \(P_{F}\) & 0.7 \\ High probability \(P_{H}\) & 0.6 \\ Normal probability \(P_{M}\) & 0.3 \\ Low probability \(P_{L}\) & 0.1 \\ Speed of user’s mobility & 2, 4.5, 30 m/s \\ High probability of vehicle displacement \(\widehat{M_{Hj}}\) & 120\({}^{\circ}\) \\ Normal probability of vehicle displacement \(\widehat{M_{Mj}}\) & 120\({}^{\circ}\) \\ Low probability of vehicle displacement \(\widehat{M_{Lj}}\) & 120\({}^{\circ}\) \\ High probability of vehicle displacement \(\widehat{F_{Hj}}\) & 120\({}^{\circ}\) \\ Normal probability of vehicle displacement \(\widehat{F_{Mj}}\) & 120\({}^{\circ}\) \\ Low probability of vehicle displacement \(\widehat{F_{Lj}}\) & 120\({}^{\circ}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Simulation parameters. represent the different locations where the macrocell and the femtocell base stations are located. Figure 7 shows, with the choice of a macrocell base station, the expected RSS we get in low speed. Figure 8 shows the expected RSS we get in low speed with the choice of a femtocell base station. As the traditional base station choice policy, the system chose the larger one. As Figure 9 shows, the expected signal strength of macrocell and femtocell base stations remained stable under low speed. This means that the advantage of traditional base station selection policy is not obvious in a low-speed environment. We can see from the results of Figures 7 and 8 that low-speed mobility through traditional base station selection cannot obviously change the RSS. Here, we changed r to 4.5 m/s (middle speed), \(\theta_{0}\) was randomly set, and the three different colors represent the different locations where the macrocell and femtocell base stations were located. Figure 10 shows the expected RSS we obtained at middle speed with the choice of the macrocell base station.