| Abstract: | 近年來網路的發達改變了人類的生活習慣；網路的服務類型豐富多變，也愈來愈貼近人們的生活。隨著網路技術的成熟與普及，網路應用層面也從一般的電子產品發展到車用電子。在這樣的演進之下，開始有一些車載通訊的標準或草案被訂定出來，例如由802.11發展而來的802.11p。
隨著802.11p草案的制定與發布，車載通訊也愈來愈廣為人知。因此車用隨意網路(Vehicular Ad Hoc Network, VANET)已經日益成熟，也有愈來愈多人投入相關研究。車用隨意網路的設備主要可以分為兩大類：一個是事前建置在道路旁的基地台(Road Site Unit, RSU又稱Infrastructure)；另一個是移動的車輛(Vehicle)。而通訊也可以分為兩大類：一類是車輛對車輛的通訊(Vehicle to Vehicle, V2V)，二是車輛對基地台的通訊(Vehicle to Infrastructure, V2I)。
由於建置RSU的成本高，因此在車載網路建置初期以及郊區人口稀疏的地方，為了節省成本，RSU的服務也許無法涵蓋所有路段。也就是說，車載網路中的RSU資源是相對珍貴的。為了更有效地利用RSU資源，我們提出了一個新的方法來提升車輛對基地台通訊的使用效率。
我們使用分散式排序機制(Distributed Sorting Mechanism, DSM)，讓網路中的所有車輛可以個別運算優先順序，經由我們所提出來的機制排序之後，可以讓較具有優勢的車輛能夠優先上傳資料。除了本身具有優勢的車輛可以優先使用V2I通訊資源外，我們另外也考慮到即將脫離服務範圍的車輛；在特定的情況下，我們的機制也具有先到期先服務(Deadline First)的特性。此外，使用分散式機制可以簡化交握（Handoff）過程，進而節省網路負荷，達到充分利用RSU資源的目的。
In recent years, the development of network technologies has greatly changed human being’s living habits, and the abundant network services are also getting more and more close to human lives. With the maturity and popularization of network technologies, the network applications have developed from household electronic products to products for mobile vehicles. In such an evolution, several vehicular network standards and drafts have been released, like 802.11p that is extended from 802.11.
Owing to the establishment and release of the draft of 802.11p, VANET is becoming well-known and more and more people have involved in related researches. Generally, the equipments of VANET can be divided into two categories: Road Site Units (RSU) or Infrastructure, and moving vehicles. The communication of VANET also can be divided into two types: Vehicle to Vehicle (V2V) and Vehicle to Infrastructure (V2I).
Because it is expensive to establish RSU, the number of RSU is usually too few to cover areas like suburbs or areas with sparse population. In other words, the resource of RSU is rather precious in VANET. In order to promote the utility of RSU, we propose a novel mechanism to improve the efficiency of communication between vehicles and RSU (Vehicle to Infrastructure, V2I).
Our proposed mechanism in this paper is called “Distributed Sorting Mechanism (DSM)”. In DSM, every vehicle can individually calculate its own priority of communication and the time to compete and obtain the channel can be reduced. We further consider the vehicles moving away from the coverage of communication and adjust their priorities of communication appropriately. Moreover, DSM owns the characteristic of “Deadline First” in specific situations. Using DSM can not only simplify the handoff procedure and reduce the network overhead, but also achieve the adequate utilization of RSU resource. |
