802.11a 對基於DSRC技術之ETC通訊影響

Abstract

In 802.11p-based ETC (Electronic Toll Collection) system, there are two potential problems. First, in 802.11p standard, the WSMP protocol is used for the communication between OBU and RSU. Unlike wired network, 802.11p wireless network is prone to fading, shadowing and interferences, which might result in high error rates, but there is no reliability mechanism embedded in the WSMP protocol. Second, because of the similarity between 802.11a & 11p, their frequency band are near, so there exists the possibility that 802.11a-based devices could interfere the 802.11p-based ETC communication and ruin the service. To solve the first problem, in our previous work, we developed a simple session-layer protocol on the top of WSMP to provide reliable message exchanges between RSU and OBU. The protocol successfully increases the success rate of cars communicate with ETC system. To solve the second problem, we focus on understanding the possibility that 802.11p-based ETC communication is interfered by 802.11a-based devices and how much the interference is when our protocol is already implemented on the 802.11p device. In this thesis, we first describe our previous work: a simple session-layer protocol and present the improvement on ETC system. Then we prove the existence of the interference on 802.11p-based devices due to 802.11a-based device and verify the possibility in practice. Moreover, we simulate the effect of 802.11a-based device on 802.11p-based ETC communication which is implemented with our simple reliability protocol. Finally, we discuss the effect of fading on our ETC system.