IEEE 802.11a 以及 IEEE 802.11p 車間通訊網路效能之比較

Abstract

IEEE 802.11p/1609 標準為了讓車與車 (V2V) 之間的 ad-hoc 網路做訊息的交換而定義了 WIBSS (WAVE Independent Basic Service Set) 。但是，這種設計無法善用 802.11p/1609 網路 multi-channel 的特性。如果我們想使用 multi-channel 勢必要有一種機制來溝通並且同步 nodes 所使用的 channel，但這可能會增加MAC layer 設計的複雜度。 有鑑於此，我們找設計一種更為簡單的方法來解決 channel 同步的問題。本篇論文首先利用模擬的方法來觀察常用的 ad-hoc 路由協定 (AODV，DSDV) 在 802.11p/1609 網路上的效能。在我們的模擬結果中發現，如果將一般路由協定所 傳送/廣播的控制訊息藉著 WBSS (WAVE Basic Service Set) 的建立來傳送，將造成路由協定的效能低落。為了解決此問題我們最終將這些路由協定所傳送/廣播的控制訊息以 WSM格式來包裝傳送。另外為了將封包正確的送達收端，我們在 WBSS-based 網路採用了兩種 MAC 層的 multi-hop forwarding 機制來幫助 WBSS 的建立。最後我們比較這兩種機制在 802.11p/1609 網路下運行的效能，並以 802.11a 網路為基準做比較。 我們的模擬結果顯示，在 802.11p/1609 networks 所運作的 routing protocol 效能上與 802.11a ad-hoc networks 並沒有太大的差異。這是由於我們將所有路由協定所 傳送/廣播 的控制訊息利用 WSM 的格式來發送。另外，雖然 WBSS-based V2V networks 相較於 802.11a 網路只能利用一半的頻寬來傳輸資料，但是因為運用到為 802.11p/1609 網路所設計的multi-channel，在某些情況下傳輸資料的效率反而優於 802.11a ad-hoc networks。

The IEEE 802.11p/1609 standards define the WAVE Independent basic service set (WIBSS) for vehicular ad-hoc networks to carry out vehicle-to-vehicle (V2V) communication. However, the design of a WIBSS cannot utilize the multi-channel property of an 802.11p/1609 network. To make use of these channels, an extra protocol is needed to negotiate and synchronize the channel used among nodes, which may complicate the design of the MAC layer. These observations motivated us to find an easy-to-implement solution for it.In this thesis, we first observed the performances of several common routing protocols (such as, AODV and DSDV) in 802.11p/1609 networks using simulations. From our simulation results, we concluded that transmitting/broadcasting control messages of routing protocols in WAVE Basic Service Sets (WBSSs) is inefficient for routing protocols. To solve this problem, we propose a framework that transmits/broadcasts routing control messages using WSMs while data are still transmitted in WBSSs. Based on this framework, we further propose two MAC-layer WBSS-creating schemes to realize multi-hop data forwarding in WBSS-based networks. We compare the performances of 802.11p/1609 networks using these two WBSS-creating schemes with those of 802.11a networks. Our simulation results show that the performances of routing protocols under 802.11p/1609 networks can be the same as those over 802.11a networks as long as in 802.11p/1609 networks routing control messages can be transmitted using WSMs. Because 802.11p/1609 networks only use a half of link bandwidth to transmit data, the bandwidth that can be used to transmit data is a half of the bandwidth that can be used in 802.11a networks. However, due to the multi-channel design WBSS-based V2V networks, can outperform 802.11a ad-hoc networks in several conditions.