車載網路中
透過多重轉發緊急訊息策略

合作式車輛防撞機制係智慧型運輸系統(ITS)中的一項應用發展，利用車輛間無線通訊能力，將前方的交通事故透過傳送緊急訊息的方式迅速告知後方來車，使後方駕駛有足夠時間反應與迴避，以減少交通事故的發生。現有的緊急訊息策略多靠廣播傳遞的方式。然而，傳統氾濫式廣播會產生許多不必要的冗餘轉播，這不僅易導致封包碰撞且易產生封包延遲，並導致廣播風暴(Broadcast Storm)的發生。許多廣播策略為改善廣播風暴與隱藏節點問題，僅在廣播車輛的廣播範圍內限定一最佳車輛作為下一任轉播車輛，但於跨越路口時，仍只限定一車輛負責轉發緊急訊息，此舉將會導致緊急訊息無法於其它岔路繼續傳遞，而大為降低訊息傳遞率而危及交通疏導。有鑑於此，本論文提出車載網路中透過多重轉發緊急訊息策略(EMDM)，當廣播未跨路口時，僅限定一車輛負責轉播，以避免隱藏節點問題與廣播風暴；當廣播於跨越路口時，會依路口的岔路數量在每一條岔路競爭並產生一輛最佳車輛為下一任轉發車輛，使得緊急訊息能在每一條岔路上迅速傳遞。除此之外，當車輛稀少時，轉發者於廣播前等待時間易出現過久的缺點，透過本文提出的等待機制可減少競爭轉發權的等待時間，提升緊急訊息及時廣播之效率。根據模擬實驗結果，於廣播到達度評量，EMDM優於BPAB約高44.9 %，優於CBS約高46.6 %。於平均延遲時間評量，EMDM平均優於BPAB約低32.3 %，平均優於CBS約低69.1 %。

關鍵字

合作式車輛防撞機制；智慧型運輸系統；車載網路；緊急訊息；多重轉發

並列摘要

In recent years, based on the swift development of communication technology, Vehicular Ad-hoc Networks has been considered to provide for promoting road safety. Cooperative Collision Avoidance (CCA) was an application in the development of Intelligent Transportation System (ITS). Through broadcasting emergency messages to advice the vehicle behind accident, all drivers can slow down the speed of vehicle or put on the brake to avoid a car pileup. A lot of researches were proposed for broadcasting emergency messages and avoiding broadcast storm. However, the topology of VANET was restricted as the broadcast across the intersection, most schemes only have a forwarder for broadcasting. It caused that emergency messages could not be spread in other brand roads. In this paper, we proposed Emergency Message Dissemination by Multi-forwarding (EMDM) to elect multiple forwarders for each brand at the intersection. It showed that the emergency message could be propagated through each brand when the messages were broadcasted across as intersection. Moreover, the broadcast storm and hidden terminal problem issues were also avoided. According to the simulation results, the reachability of EMDM is 44.9 % better and higher than BPAB, 46.6 % better and higher than CBS. The average delay time of EMDM is 32.3 % better and lower than BPAB, 69.1 % better and lower than CBS.

並列關鍵字

Vehicular Ad-hoc Network ； Cooperative Collision Avoidance ； Intelligent Transportation System ； Emergency Message Dissemination ； Multi-forwarding

參考文獻

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國際替代計量

車載網路中透過多重轉發緊急訊息策略

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