車載網路中協調式多通道媒體存取控制通訊規約之設計

Abstract

車載網路(Vehicular Ad Hoc Networks, VANETs)為有前景的無線通訊技術，能提供安全性應用與娛樂資訊。車載網路的主要標準之一，為汽車環境無線存取(Wireless Access in Vehicular Environments, WAVE)。在WAVE中定義同步區間(Synchronization Interval)與多通道(Multichannel)存取。多通道包含一個控制通道及六個服務通道。在先前的研究中如C-MAC，提到協調式多通道媒體存取控制通訊規約作法。C-MAC是透過路邊基地台居中協調，包含安全訊息的傳送、傳輸預約、車輛辨識等等。C-MAC的作法中可確保安全訊息的傳送是免碰撞，但在傳輸預約及車輛辨識方面，它的通道使用卻是欠缺效率。換言之，在C-MAC作法中，這兩個部分是透過競爭過程來完成，是導致通道頻寬被浪費的主要原因。我們提出兩種作法：作法一為有辨識過程、作法二為沒有辨識過程。兩種作法在傳輸預約上都採用免競爭的方式，以確保通道有效地被使用。模擬結果顯示，我們提出的作法在通道頻寬與吞吐量上都優於C-MAC的作法。Vehicular Ad Hoc Networks (VANETs) have widely considered as a promising wireless communication technology that can simultaneously provide vehicle safety and infotainment. In view of this, Wireless Access in Vehicular Environments (WAVE) has been standardized, in which synchronization intervals and multichannel access are defined. To be more specific, there are one control channel (CCH) and six service channels (SCHs). In previous works, e.g. C-MAC, a coordinated multichannel MAC control protocol has been designed, in which road side units (RSUs) play the role of a coordinator and arrange for the delivery of safety messages, transmission reservations, vehicle identifications, and so on. Though collision-free delivery of safety messages is guaranteed in C-MAC, it has the drawback that channel utilization is inefficient in transmission reservations and vehicle identifications. That is, they are done by means of a contention-based process, which can easily result in waste of channel bandwidth. In order to remedy this, we have proposed two designs in this thesis: one with an identification process of vehicles and another without. In both our designs, transmission reservations are all performed in a collision-free manner, ensuring that channel is efficiently utilized. Simulation results demonstrate that our proposed designs can outperform C-MAC in terms of channel bandwidth and throughput.