車載網路(Vehicular ad hoc network，簡稱VANET)是行動隨意網路(Mobile Ad Hoc Network,簡稱MANET)的一種。在VANET中的通訊架構可分成Vehicle-to-Vehicle (V2V)和Vehicle-to-Road Side Unit (V2R)。V2V網路特色是車輛高速的移動、車輛行駛受限於道路的設計、通訊設備無能源消耗限制、及容易改變的網路拓墣環境。由於V2V網路中易改變的網路拓墣環境和不均勻的車輛分佈狀況，形成車輛間彼此距離超過彼此的通訊半徑，造成車輛間彼此暫時通訊斷線。為了解決此問題，許多論文提出在傳送封包的時候採取carry-and-forward的策略以應付此種暫時性通訊斷線，即封包被車輛所持有，直到遇見另一部車輛才將封包送出。 在車載網路內傳輸資訊前，傳送封包的最佳路由路徑須靠路由協定找出，所謂最佳路由路徑可取決於道路上的車輛密度或路由路徑距離最短來降低封包傳輸時間或是升高封包送達率，採用歷史道路交通資料來找尋最佳路由路徑來傳送封包而並沒有考慮到動態交通狀況改變，歷史道路交通資料的時效性會影響到路由協定在評估封包路由路徑所需時間。 本論文提出一個基於道路交叉口為基礎適用於不同交通狀況的無線路由協定於車載網路中。結合了封包路由路徑的方向性及車輛的移動性，使得封包路由能夠盡量保持和車輛移動方向同向，以減少封包路由過程中被不同於路由路徑方向的行駛車輛給載走，導致路由時間拉長，進而達到縮短封包路由的傳輸時間。並提出一評估封包無線路由所需時間，面對不同的交通狀況時，預估封包路由所需的時間也會不同。為了能夠使用即時的交通狀況作為評估封包路由所需時間，提出當車輛交會時，交換彼此所收集到的交通資訊以用來評估封包路由時間。在最後提供模擬結果，證明相較於其他無線路由協定，封包路由時間是可以被縮短的。 Vehicular ad hoc network (VANET) is a form of mobile ad hoc network (MANET). Features of VANET are high mobility of vehicles, vehicles move on predefined roads, no power constrains, and rapid topology changes. VANET can be classified into vehicle-to-vehicle (V2V) and vehicle-to-road side unit (V2R). Rapid topology changes uneven distribution of vehicles, and inter-vehicle space is greater than transmission range, resulting in network disconnection. In order to overcome problem, strategy called carry-and-forward is adopt; a moving vehicle holds packets until meeting a new vehicle Before delivering data, vehicles need a routing protocol to select routing paths. Routing path depends on vehicle density or short distance to reduce routing delay and increase packet delivery ratio. Routing path selection is usually based on historical traffic data to find a routing path with minimum routing delay regardless of dynamic traffic condition changes. Routing delay estimation is thus affected by timeliness of historical traffic data. In this paper we propose a routing protocol based on intersections for various vehicular traffic, combines routing path of packets and mobility of vehicles, to reduce probability that packets are carried by vehicles that move toward road segments different from routing paths, the event which results in increase routing delay. We also propose routing delay estimation based on different traffic conditions. In order to obtain traffic conditions to estimate routing delay, while vehicles at the intersection, would exchange collected traffic data from road segments which they have moved through, to estimate routing delay. Simulation results show our routing protocol has better performance in shortening routing delay.
