在基於802.11p的ETC系統中存在著兩個潛在的問題. 第一,在802.11p標準中,WSMP協定是用來進行OBU與RSU之間的傳輸. 不像有線網路,802.11p無線網路容易受到衰落,遮蔽效應及干擾的影響而導致高錯誤率,但是在WSMP協定中卻沒有可靠性機制. 第二,由於802.11a與802.11p的相似性,兩者所使用的頻段相近,因此存在著802.11a裝置干擾802.11p的ETC系統之可能性
為了解決第一個問題,在我們之前的成果中,我們開發了一個簡單的session層協定於WSMP的頂端,用以提供RSU與OBU之間可靠的訊息交換. 此協定成功地增加了車輛與ETC系統傳輸的成功率. 為了解決第二個問題,我們著重於了解802.11p的ETC傳輸被802.11a裝置干擾的可能性,以及當我們的協定實作於802.11p裝置上時,802.11a裝置會造成多少干擾
在這篇論文中,我們最先描述我們之前的成果: 一個簡單的session層協定,以及展示此協定對ETC系統的改良. 接著我們證明802.11a裝置對802.11p裝置干擾的存在性. 此外,我們模擬802.11a裝置對實裝了簡單協定的802.11p ETC系統之影響. 最後,我們討論訊號衰落現象對我們ETC系統的影響

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.

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