此論文在平交道警示系統設計一個通訊協定，使火車駕駛藉由平交道的監測影像資料做出更精確的安全決策。安全性影像資料需要較高的封包傳輸率、足夠的吞吐量與較低的延遲時間，並且此安全影像資料必需較其他非安全性的影像資料擁有較高的優先權。論文中的平交道警示系統設備都是雙介面WAVE設備，包含Road Side Units (RSUs)與火車，其間使用無線車用隨機網路來做溝通。根據雙介面的特性，此論文也為平交道警示系統的RSU設計出每三個頻道做循環的TCPC頻道分配演算法(TCPC channel allocation)。並且為了解決附近其他使用WAVE設備車子所造成的干擾，此論文也設計跨車輛服務品質機制(Inter-QoS scheme)。最後，此論文使用NS-2模擬，呈現即刻式頻道切換(immediate access)在平交道警示系統(GCAS)的情境下，較交換式頻道切換(alternating access)有好的效能，有更低的延遲、更高的封包傳輸率並提供較多吞吐量。使用即刻式頻道切換，可成功讓火車駕駛得到從平交道而來的高品質串流影像資料。

This thesis designs a communication protocol for streaming video data that are captured from a grade crossing. The corresponding communication protocol can be used in the Grade Crossing Alarm System (GCAS) to deliver the monitored video of a grade crossing as an aid for train drivers to make more precise decision for driving through grade crossings. This safety video data have requirements of a higher packet delivery ratio, higher throughput and lower delay and need to have the higher priority than other non-safety video data. Road Side Units (RSUs) and On Board Units (OBUs) used in GCAS adopt dual-interface WAVE devices. Road Side Units (RSUs) and OBUs, which are allocated in trains, used in the proposed GCAS communicate with each other using the wireless Vehicular Ad Hoc Networks (VANET) scenario. According to the dual-interface characteristics, this thesis also proposes a three channel per cycle (TCPC) channel allocation algorithm for RSUs in GACS and an Inter-QoS scheme for other vehicles out of GCAS. Finally, the NS-2 simulation results show that the immediate access performances is better than that of the alternating access in this grade crossing scenario: lower delay, higher packet delivery ratio and higher throughput. Using immediate channel access, train driver can successfully receive the high quality streaming video data from a grade crossing.

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