在Ad Hoc網路中，當兩個網路節點要互相通訊時，若節點 不在彼此的傳輸範圍內，可以藉由其他節點來轉送封包到 達目的地，因此Ad Hoc網路必須使用多跳路由的方式來傳 送資料。 目前Ad Hoc路由協定都承襲傳統有線網路的路由演算法， 假設最少轉送節點(minimum hop count)就是最佳的衡量 指標，在支援多速率的無線網路環境中，連結速率與傳輸 距離成反比，具有最少轉送節點的路徑代表節點之間的距 離較遠，封包只能以較低的連結速率傳送，受到干擾的因 素也跟著增加，因此在無線網路中最少轉送節點的路徑並 不一定是最好的選擇。 本論文所提出的路由協定基於距離向量演算法，以提升網 路的吞吐量為目標，利用跨層設計的概念來改善路由選擇 方式，考量IEEE 802.11多速率的特性，同時也考慮到相 鄰節點的負載情形，在連結速率及負載變化之間取得平衡 ，能夠有效地減少封包端點對端點的延遲以及改善延遲抖 動的情況。 模擬結果顯示，本論文所提的方法能夠克服以最少轉送次 數為路徑選擇的缺陷，確保路由協定能夠找出最佳的封包 傳送路徑。 In ad hoc networks, when two nodes want to communicate may not be within wireless transmission range of each other, nodes could be enlist the aid of other nodes in forwarding packets to each other. In order to facilitate communication within the ad hoc network, a multi hop routing protocol is used to discover routes between nodes. Most conventional ad hoc routing protocols primarily carry over from wired networks that using the minimum hop count as the metric to make routing decisions. However, in the wireless networks with multiple data rates, the data rate of wireless network is inversely proportional to the transmission distance. And each hop in paths chosen by minimum hop count metric will tend to have a longer physical span and also be associated with a lower data rate. Therefore, the conventional minimum hop count approach will be not suitable for the multi-rate wireless networks. In this thesis, we will propose a routing protocol based on distance vector algorithm. We investigate the cross layer design methods that take into account both IEEE 802.11 multi- rate capacity as well as the load condition of neighboring nodes, thus aiming to achieve higher network throughput. Referring from the link rate and variation of load, the proposed scheme can effectively minimize the transfer delay from source to destination and delay jitter. Simulation results show that the drawback of conventional minimum hop count approach is largely overcome by the proposed scheme. Furthermore the proposed routing protocol can find the better routing path for packets.
