近年來，車用行動通訊網路(VANET)引起不少學者的注意，許多協定都因而提出，在這些協定研究中，緊急訊息傳遞(emergency message dissemination)是非常重要的議題，緊急訊息可以幫助駕駛者即時反應以防連環車禍，然而過去的方法鮮少同時考慮到訊息傳送的延遲(transmission latency)和封包量(packet overhead)，因此在我們方法的第一階段，我們提出一有效率的方法，考慮到傳送者(sender)的通訊範圍內中車輛的密度、多寡，進而盡量減低訊息傳送的延遲，同時只需要少量的封包數。此外，由於事件的狀態可能會改變，因此只傳送緊急訊息給靠近事件的車輛是比較有意義的，而不是那些離事件很遠的車輛。故在第二階段中，我們定義了兩個區域-緊急區域(emergency region)與警示區域(alarm region)，讓緊急訊息維持在定義的區域一段特定時間，我們使用生命週期(life cycle)一詞，代表緊急訊息維持在區域內的時間長短。只有當車輛(vehicles)進入定義的區域內才會接收到緊急訊息，我們盡可能延長緊急訊息的生命週期至黃金救援時間(critical time)，以便幫助靠近事件的駕駛者即時作出反應，避免後車追撞、連環車禍；此外，提醒靠近匝道的車輛可下匝道，避免前方塞車困在車陣中，同時也能節能減碳。簡而言之，我們結合了緊急訊息傳遞以及延長緊急訊息的生命週期兩者的概念，帶給駕駛者更佳的安全駕駛環境。我們的模擬環境為雙向的高速公路。從模擬結果中可得知，相較於先前的一些研究，不管在車輛密度低或高時，我們能大幅地減少訊息傳送的延遲，但不造成過多的封包量；另外一方面，我們延長了緊急訊息的生命週期的同時，也讓需要傳遞的封包數降至最少。

Recently, vehicular ad-hoc networks become an interesting research area due to safety-purpose applications, such as collision avoidance system. In such applications, emergency message dissemination is one of the most important issues
because shorter transmission time can advance driver’s response time. Previous protocols proposed for emergency message dissemination only consider either shortening transmission latency or minimizing packet overhead. In addition, we find that in real applications the usability of emergency messages will degrade with time and transmitted distance from events. Therefore, we propose an
efficient emergency message dissemination scheme whose goal is to minimize the transmission latency and low packet overhead. Considering the usability of emergency message, we define two regions; emergency region and alarm region,
where emergency region is close to emergency events and alarm region is close to the previous ramp closest to these events. Then emergency message with a predefined life time will be kept in these two regions. So, only vehicles entering into these two regions can receive emergency messages. Simulation results show that the proposed scheme can reduce the transmission latency immensely comparing
with previous works. Furthermore, we keep an emergency message for a critical time interval with low packet overhead.

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