一種於車載隨意網路之MAC通道擁塞控制機制

A MAC Channel Congestion Control Mechanism in VANETs

徐志偉(Chih-Wei Hsu) ； 何平凡(Ping-Fan Ho)

《電腦與通訊》 142期 (2011/12) Pp. 83-90

https://doi.org/10.29917/CCLTJ.201112.0012

摘要

IEEE 802.11p／WAVE（Wireless Access in Vehicular Environments）為車載隨意網路（Vehicular Ad Hoc Networks；VANETs）下新興的標準之一。於車載環境下廣播資料與控制封包變得更為重要，特別是安全性與非安全性應用下廣播資料封包與狀態交換。IEEE 1609.4標準有定義廣播封包於控制通道（Control Channel；CCH）區間內被傳送，但在車載隨意網路下車輛做通道交換（channel switch）時會經歷高於平均的通道擁塞週期。因此，本論文提出動態位移間隔（Adaptive Offset Slot；AOS）機制。此機制每輛車先利用廣播Hello訊息封包估計鄰近車輛的數目，之後計算期望的位移間隔值並預先加到初始MAC Contention Window（CWmin）之前。透過AOS機制可降低封包碰撞情況並改善傳輸的效能。

關鍵字

車載隨意網路 ； 擁塞控制 ； 媒體擷取層 ； 通道交換

並列摘要

IEEE 802.11p/WAVE (Wireless Access in Vehicular Environments) is an emerging family of standards intended to support wireless access in Vehicular Ad Hoc Networks (VANETs). Broadcasting of data and control packets is expected to be crucial in this environment. Both safety-related and non-safety applications rely on broadcasting for the exchange of data or status and advertisement messages. Most of the broadcasting packet is designed to be delivered on a given frequency during the control channel (CCH) interval set by the IEEE 1609.4 standard. In an IEEE 802.11p VANET, vehicles that perform channel switching may experience a period of above-average channel congestion immediately following a channel switch. However, the AOS (Adaptive Offset Slot) mechanisms is firstly developed based on the estimation of potential neighboring vehicles through broadcasting Hello messages, and then calculating the expected offset slots for reducing the collision situations, and thus improve transmission performance.

並列關鍵字

Vehicular Ad Hoc Networks ； VANETs ； Congestion Control ； Media Access Control ； MAC ； Channel Switch