Multi-channel mac protocols with bandwidth utilization enhancement in wireless ad hoc networks

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Title:	Multi-channel mac protocols with bandwidth utilization enhancement in wireless ad hoc networks
Other Titles:	在隨建即連無線網路中提高頻寬利用率之多頻道媒體存取協定
Authors:	呂昀融;Lu, Yun-Jung
Contributors:	淡江大學資訊工程學系博士班張志勇;Chang, Chih-Yung
Keywords:	多頻道;媒體存取控制;無線網路;Multi-channel;MAC;Wireless network
Date:	2012
Issue Date:	2013-04-13 11:54:37 (UTC+8)
Abstract:	近年來，發展多頻道媒體存取協定已受到極大的關注與討論，並被認為是開發頻寬利用率的有效方法。在發展多頻道通訊協定時所遭遇最大的挑戰便是主機會面問題(Rendezvous Problem)與多頻道隱藏節點問題(Multi-Channel Hidden Terminal Problem)。為解決會面問題，有一些研究的作法，是讓所有主機週期性地在特定頻道的ATIM Window共同聚集，以安排資料交換的頻道，這樣的做法統稱Control Period Based(CPB)，然而，這樣的作法會造成其它頻道ATIM Window的頻寬利用率降低。為改善CPB的頻寬利用率，另一STEPWISE的頻道模型被提出[21]，其以階梯式的安排使得各頻道上的ATIM Window得以錯開，傳送節點能透過頻道對應函數取得接收節點所在的頻道，於接收者的頻道安排資料交換的時槽，但此類做法當遭遇網路頻道流量不均(Channel Traffic Unbalance Problem)時，將導致少數頻道壅擠，而其他頻道卻閒置的情形。本論文提出兩個多頻道MAC協定，以提昇頻寬利用率。首先，針對CPB頻道模型而言之其餘頻道ATIM Window頻寬利用率低的缺點，本論文提出一多頻道MAC協定(ECU-MAC)，其同樣基於CPB的頻道模型，使完成協調的通訊對能直接跳往資料頻道進行資料傳輸，同時克服衍伸性會面問題，進一步有效的利用所有頻道上的頻寬。實驗及分析顯示，ECU-MAC可有效增加頻寬利用率，並提升網路效能。除了CPB模型上的多頻道協定外，本論文亦針對STEPWISE的頻道模型現存的頻道流量不均的問題，進一步提出另一多頻道MAC協定(HSR-MAC)，其雖亦採用STEPWISE的頻道模型，但透過節點維護各自頻道上的資料時槽的使用狀況，使網路流量得以從擁擠的頻道上轉移至閒置的頻道上進行傳輸，促使頻道利用率提升。因此，透過兩個多頻道MAC協定，頻寬利用率確實能大幅地改善效能。 Multi-channel MAC protocols have recently attracted significant attention in wireless networking research because they possess the ability to boost the capacity of wireless ad hoc networks. However, the common challenges in developing multi-channel MAC protocol are the Multi-channel Hidden Terminal (MHT) problem and the Rendezvous problem. To avoid the two problems, a typical solution [15] proposed in literature is the CPB-based channel model which arranges an ATIM (Ad hoc Traffic Indication Messages) window in each beacon interval and asks all stations switch to the ATIM window of a predefined channel to cope with the rendezvous problem. Though all stations can negotiate the communication schedules in an ATIM window, however, the ATIM windows of all channels other than the predefined channel cannot be used for data exchange, leading to low channel utilization. To prevent the low utilization of ATIM windows as found in CPB-based channel model, a STEPWISE Channel Model is proposed in literature to fully utilize the ATIM window each channel. However, there exists the unbalanced traffic problem where some busy channels have contention and collision problems while the other idle channels have low channel utilization. This thesis presents two multi-channel MAC protocols. To improve the channel utilization problem as found in CPB-based channel model, this thesis proposes an ECU-MAC aims to increase the channel utilization and improve the network throughputs. The main idea of the proposed ECU-MAC is to exploit the bandwidth resource of ATIM windows of all channels for exchanging data such that the network throughput and channel utilization can be improved. As a result, the transmission delay can be significantly reduced. Performance evaluation and analytical results reveal that the proposed ECU-MAC outperforms existing MMAC and DCA protocols in terms of network throughput and average packet delay. This thesis also applies the STEPWISE channel model but improves the channel utilization by migrating the traffics from busy channels to the idle channels. The key concept of HSR-MAC is to construct the urgent zones of the idle channel and then migrate the traffics of busy channels to the urgent zones. As a result, the HSR-MAC could disperse the traffic from busy channel to idle channel and hence significantly improve the network throughputs. Compared with existing multi-channel MAC protocols, the proposed multi-channel MAC protocols prevents the MCHT and Rendezvous problems while improving the network throughput.
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