在車載隨意行動網路中跨層式壅塞避免之路由機制

Abstract

由於現存的細胞網路無法完全適用於車輛間通訊，利用車載隨意行動網路及多跳傳輸方式來傳輸資料有其必要性。因為車載隨意行動網路以具避免碰撞的載波感測多重存取技術為基礎，多媒體存取層的碰撞問題會增加封包的傳輸延遲時間。因此，為了提升路由的效能，在設計車載隨意行動網路的路由機制時將多媒體存取層的碰撞問題列入考量是必要的。 在本篇論文中，我們以車用環境無線存取協定為基礎，針對車載隨意行動網路提出一個跨層式壅塞避免之路由(cross-layer congestion avoidance routing,CCAR)機制。由於網路拓撲的快速改變，在CCAR 機制中每一個節點只選擇他的下一個轉送站。首先，CCAR 機制動態地調整轉送站候選人的數量，讓傳送者可以有較高的機率找到合適的轉送站。然後，CCAR 機制依據每一個服務通道的負載量動態地調整每一個服務通道被選為指定通道的機率來平衡服務通道的負載量。最後，CCAR 機制將各個服務通道的使用人數、可能被選為轉送站的節點的負載量，以及車輛行進方向都列入考量，選擇一個最適合的車輛當作轉送站。模擬結果顯示在車輛密度較密集的情況下，我們提出的CCAR 機制可以達到比對照的機制低的封包傳送延遲時間及比對照的機制高的系統傳輸量。

Since current cellular networks do not have a good fit for vehicular communications, vehicular ad hoc networks (VANETs) and multi-hop communications are needed. Due to VANETs are based on carrier sense multiple access with collision avoidance (CSMA/CA) technique, MAC layer collision problems increase packet delay. To improve the routing efficiency, it is necessary for us to take the MAC layer collision problem into account when designing routing scheme for VANETs. In this thesis, we propose a cross-layer congestion avoidance routing (CCAR) scheme for VANETs based on wireless access in vehicular environment (WAVE) protocol. Due to highly dynamic network topology, the forwarders are selected one by one. First, the CCAR scheme adaptively adjust the number of candidates so that senders have high probability of finding a candidate as the forwarder. Second, the CCAR scheme dynamically adjusts the selection probability of each SCH based on traffic load of SCHs to balance channel loads. Final, the CCAR scheme takes the number of co-channel senders, the loads of each possible forwarder, and the vehicular moving direction into account to determine the most appropriate route for senders. Simulation results show that the proposed CCAR scheme achieves lower packet delay and higher system uplink throughput than the compared schemes when the vehicular density is dense.