在多跳移動無線網路(multihop MANETs)中，節點必須互相合作轉送彼此的封包。在本篇論文中，根據封包流動情況，節點可能是源頭(source)或是中繼節點(intermediate node)。每一個節點傳送封包的機率是相同的。因此，熱點(hop spot)可能會遭受運輸擁擠(Traffic Congestion)，導致封包遺失機率和傳送延遲都會增加，同時生產量也會漸少。由於每次傳送前都必須先和鄰近節點競爭共同使用的通道使用權，生產量不僅被通道能力所限制，也被附近節點的傳送影響。部分相關研究使用多個互不干擾的通道同時傳送封包來增加生產量。但當運輸量是大量時，上述的方法反而會導致更嚴重的封包遺失，因為它們並沒有考慮運輸擁擠的問題。在本篇論文，我們提出一個新的多通道媒介存取控制協定，並開發一個逐跳模式(hop-by-hop)的擁擠控制方法。主要是利用修改過的RTS/CTS控制封包預先在不同的通道下保留頻寬，同時解決多通道環境下的終端機隱匿問題(Hidden Terminal Problem)。另外，我們設定中繼節點比源頭有較高的優先權搶得通道的使用權，每個節點會監控流量的情況減少運輸擁擠的情況發生。從實驗模擬結果，我們可以發現使用我們的方法可以大幅改善整的網路的生產量。

In multihop MANETs, nodes have to cooperate to forward each other’s packets through the networks. Every node, including source and intermediate nodes, has a fair opportunity to transmit a packet. Thus, the hot spot may suffer traffic congestion. The packet loss rate and the transmission delay are increased, but the throughput is decreased. Due to the contention for the shared channel, the throughput of each single node is limited not only by the channel capacity, but also by the transmissions in its neighborhood (intraflow/interflow contention problem). Furthermore, the network throughput still restrict by the channel capacity. Some other related works using multiple channels simultaneously to transmit packets without interfering each other increases the throughput. But if the traffic load is heavy, these schemes may induce more serious packet loss on the contrary because they do not consider the congestion problem especially in multihop MANETs. In this thesis, we propose a new multichannel MAC protocol using multichannel transmission, and develop a hop-by-hop congestion control scheme, which is named “Efficient Flow Control with Multichannels” (EFCM). The EFCM scheme modifies the IEEE 802.11 RTS/CTS frame format to reserve bandwidth in different channels. It also solves the hidden terminal problem in the multichannel environment. The intermediate nodes have a higher priority than the source (or leaf) nodes to contend for the right of transmission to solve the intraflow contention. In order to solve the interflow contention, congestion control is taken in every node to construct a flow table, which restricts the number of packets of every flow passing by congested nodes. According to the simulation results, the whole network throughputs of EFCM are improved significantly.

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