車載網路之結合碰撞的效能分析

Abstract

考慮車載隨意網路在控制通道上使用分時多工方法，為了避免隱藏節點的問題，某輛車可以挑選的時槽，只能從某輛車的one –hop 和 two-hop鄰居都沒有使用的時槽中挑選。但是隨著車輛位置不斷改變，可能產生新的時槽衝突，導致某輛車必須重新選擇時槽，這個問題被稱為結合碰撞。在本論文提出一個分析模型，用來計算某輛車發生結合碰撞的速率，本論文證明，在不同的交通密度下，分析結果與模擬結果非常接近。並且顯示，高速車發生結合碰撞的速率是高於低速車，且雙向高速公路的環境下發生的結合碰撞是高於單向高速公路的環境。

The vehicular ad hoc networks (VANETs) in which time division multiple access (TDMA) is employed on the control channel has been considered. In order to avoid the hidden terminal problem, a time slot can be reserved by a vehicle only when the time slot is unreserved by its one-hop and two-hop neighbors. However, frequent topology changes in VANETs may lead to conflicts between time slot reservations, causing reselection of time slots by vehicles. This problem is known as merging collision. An analytical model is thus proposed in this thesis to evaluate the rate of merging collision incurred by a vehicle. We show that the proposed analytical model can provide very accurate results, as compared with computer simulations, over a wide variety of vehicle traffic densities. In addition, it is shown that high-speed vehicles generally encounter a merging collision more often than low-speed ones, while the rate of merging collision incurred by a vehicle is higher on a bidirectional highway than on a unidirectional one.