# Efficient Dissemination of Safety Messages in Vehicle Ad Hoc Network Environments
## 4 Performance Evaluation
### Performance Evaluation Results  
#### 4.2.1 Comparison of Safety Message Packet Loss  
We compared the safety message packet loss rate with an existing scheme to demonstrate the superiority of the proposed scheme. The existing scheme, proposed by [PERSON] (PBE) [13], forms clusters for communication but does not maintain separate CH candidates. Therefore, when the CH departs from the cluster in the existing scheme, a new CH is selected from when it departs. However, during the operation of selecting a new CH in the existing scheme, safety message packets are lost. Conversely, the proposed scheme preselets and maintains CH candidates, so even if the CH departs from the cluster, it can be immediately replaced with a new CH. In the experimental evaluations, we measured the packet loss that occurred when the CH departed compared to the number of safety message packets that the CH could disseminate during the evaluation time and converted it into a percentage. In the first experimental evaluation, for the transmission cycle and message transmission rate, messages were assumed to be disseminated by performing a time sleep in units of ms. The vehicle departure was performed at intervals of 60 s.  
Figure 6 shows the safety message packet loss rate according to the CH departure cycle. In the V2V environment, the experimental evaluation was conducted by changing the departure cycle of the CH, the main agent of safety message dissemination, from 120 s to 10 s. The experimental evaluation time, number of vehicles, and maximum time, which is the time to wait for the disconnected CH and detect that the CH has departed, was 1.5 s. PBE compares scores among the CMs 1.5 s after the CH is disconnected to select a new CH. Therefore, in PBE, the more frequent the CH's departure from the cluster, the more score comparisons among CMs occur to select the next CH. The message exchanges required for this process result in substantial safety message packet loss. However, the proposed CH candidate algorithm enables the CM with the highest score in the cluster to immediately perform the new CH role 1.5 s after the CH is disconnected, resulting in packet loss for only the 1.5 s that they wait for the CH. Thus, the proposed CH candidate algorithm outperformed PBE by approximately 16.5% in terms of the packet loss rate.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Environment** & **Value** \\ \hline CPU & Intel(R) Core(TM) i5-9600 CPU 3.70 GHz \\ Memory & 32.0 GB \\ OS & Window 10 64-bit \\ Language & Python 3 \\ MAC Model & IEEE 802.11p WAVE \\ \hline \hline \end{tabular}
\end{table}
Table 1: Performance evaluation environments.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Time to wait for disconnected CH & 1.5 s \\ Message transmission rate & 6 Mbps \\ Channel synchronization period & 100 ms \\ Beacon size & 194 bytes \\ EM packet size & 170 bytes \\ \hline \hline \end{tabular}
\end{table}
Table 2: Performance evaluation parameters.  
Figure 7 shows the safety message packet loss rate according to the number of CM vehicles. In the V2V environment, the experimental evaluation was conducted by changing the number of CM vehicles forming the cluster to 10, 20, 30, 40, and 50. PBE and the proposed CH candidate algorithm showed little difference when the number of CM vehicles was relatively small; however, as the number of CM vehicles increased, more score comparisons between the CMs occurred, causing delays in selecting the next CH and increasing the packet loss. Thus, the proposed CH candidate algorithm outperformed PBE by up to 10%.