因為車載網路興起，許多與車輛相關的安全性及非安全性的應用被提出。安全性相關的應用，主要是用來改善駕駛安全，減少意外的發生；非安全性的應用主要是用來提供乘客，有更好的乘車體驗。車載網路使用了IEEE 802.11p 當做通訊協定，定義了一個控制頻道以及六個服務頻道。為了要讓更多的服務能夠使用車載網路，以及讓安全性相關的應用能夠有效且快速的廣播給其他車輛，同時考慮緊急訊息的傳遞，要如何有效的使用多個頻道是非常重要的。這篇論文中，我們提出了一個分散式頻道選擇機制，並且搭配緊急狀態轉換機制，主要是透過接收端所在的相對位置決定使用哪個服務頻道，以及在緊急事件發生的時候，藉由不同的狀態轉換，將可用的頻道用於傳送緊急訊息，因此能夠快速的傳遞緊急訊息且更頻繁的更新緊急事件。透過我們的方法，能夠達到有效的使用服務頻道，以及讓安全性相關的訊息能夠在不發生碰撞的環境下傳送，以及能夠對於緊急事件有快速的反應。從模擬結果可以看出，我們的方法改善了27%的資料傳輸量。

In vehicular ad-hoc network (VANET), safety services have been proposed to improve driving safely and non-safety services provide comfort for passengers. VANET employs IEEE 802.11p as transmission protocol that provides a control channel (CCH) and six service channels (SCHs). How to use multiple service channels efficiently has significant effects on how many non-safety services can be accommodated in a VANET. IEEE 802.11p MAC is a contention-based protocol that has the drawback that reduces channel utilization. When the traffic flow is heavy, there are collisions and resources wasted. On the other hand, safety applications are the major concern in VANET. One of the important issues of safety-related services is the dissemination of emergency messages. In order to warn the drivers after emergency events, the dissemination of emergency messages should be as fast as possible. This thesis proposes Distributed Channel Assignment Scheme (DCAS) and emergency state transition mechanism to solve these problems. DCAS assigns service channels in a distributed manner and uses service channels efficiently. To avoid hidden terminal problem when assign SCHs, we propose a channel assignment scheme which increases the successful reservation rate so that increases channel utilization. Emergency state transition mechanism has three different states. Through transition among states, our proposed method can update emergency messages efficiently and reduce the latency. Through simulations with ns-3, our approach shows that the utilization of service channels is better and vehicles are able to get slots to transmit safety message and therefore increases driving safety.

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