# A Design of a Lightweight In-Vehicle Edge Gateway for the Self-Diagnosis of an Autonomous Vehicle
## 4 The Performance Analysis  
The model shown in Figure 10 uses one gateway connected to two CAN buses, two FlexRay buses, two MOST buses and one Ethernet backbone to verify the LI-VEG performance proposed in this paper and each bus has four nodes. The Main Processor of the LI-VEG uses ARM Cortex-A7 (900 Mhz) and is simulated in the RAM with these two experiments in PC. In the first simulation environment, the transmission delay caused by message translation was measured while messages are transferred between four protocols (CAN, MOST, FlexRay and Ethernet). The transmission delay was measured based on the eight Message transmissions from CAN to FlexRay, the eight Message transmissions from CAN to Ethernet, and the eight Message transmissions from CAN to MOST. The transmission cycle of each message uses 14 ms. The transmission delay between the existing message mapping translation system not using a lightweight header and the message translation system using a lightweight header was compared. Table 2 shows the simulation environment of the first simulation. In the second simulation environment, the transmission delay caused by overhead was measured. The overhead happens in each protocol bus because of the continuous signal from the CAN. Transmission delay between the existing message translation system and the proposed message translation system was compared according as network traffic increases. In the same way as the first experiment, transmission delay was measured in the case the CAN messages are translated to the other three protocols. Figure 11a-c shows maximum transmission delay and its stabilization time when the CAN messages are transferred to the other protocols. The transmission delay means the time that it takes for a source message to be translated into a destination message in the LI-VEG. The stabilization time means the time between when translation overhead occurs and when its overhead disappears. Figure 11a shows the transmission delay and stabilization time when messages are transferred from the CAN bus to the FlexRay bus. In the transmission, it takes maximum 278 \(\upmu\)s transmission delay for the existing method to store and translate a message and about 8 ms to stabilize the transmission delay. It takes a maximum of 274 \(\upmu\)s for the proposed method to store and transform a message and about 6 ms to stabilize the transmission delay. Therefore, the maximum transmission delay is improved by about 2% and its stabilization time about 25%. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Source Protocol** & **CAN** & **CAN** & **CAN** \\ \hline destination protocol & FlexRay & MOST & Ethernet \\ the number of message transmissions & 8 & 8 & 8 \\ transmission cycle & 14 ms & 14 ms & 14 ms \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The Simulation Environment. Figure 10: The simulation Model. Figure 11b shows the transmission delay and stabilization time when messages are transferred from CAN bus to MOST bus. In the transmission, it takes maximum 3.03 ms transmission delay for the existing method to store and transform a message and 11 ms to stabilize the transmission delay. It takes a maximum of 2.84 ms for the proposed method to store and transform a message and 11 ms to stabilize the transmission delay. Therefore, the maximum transmission delay is improved by about 7% and its stabilization time is the same. Figure 11c shows the transmission delay and stabilization time when messages are transferred from CAN bus to Ethernet bus. In the transmission, it takes maximum 1.47 ms transmission delay for the existing method to store and translate a message and 9 ms to stabilize the transmission delay. It takes a maximum of 1.29 ms for the proposed method to store and transform a message and 7 ms to stabilize the transmission delay. Therefore, the maximum transmission delay is improved by about 11% and its stabilization time about 20%. Table 3 shows how much the proposed method is improved in comparison to the existing method.