無線網路下以分散式演算法選擇夥伴的合作式媒體存取協定

在無線網路中，每個工作站(station)都可以聽到鄰近工作站所發出的訊號，而加以解碼並分析其中的標頭(header)，並判斷這個訊框(frame)是不是傳送給它，所以利用無線訊號這個特性，合作式通訊(cooperative communication)就被提出來可以創造空間多樣性(spatial diversity)，但不需要通訊裝置必須有多根天線的限制。在這篇論文中，我們針對在一個無線網路中，所有無線工作站共享一個無線頻道，所以要讓所有工作站能夠平均合理的存取媒介，例如在802.11中，利用分散式協調功能(DCF)讓工作站能夠公平的存取無線媒介，但有一個問題是由於傳輸效能會隨著工作站間的環境狀況或彼此間的距離而有所差異，因此，相較於傳輸速率較快的工作站，當傳輸速率較差的工作站獲得媒介使用權時，需要更多的時間來傳送同樣的大小的訊框，這使得其他節點要等待更有的時間才能競爭媒介使用權，此現象使得網路整體效能低落。所以我們提出一個利用合作式通訊的方法來解決這個問題，藉由一個工作站的加入(我們稱之為夥伴或中繼站)，使得原本透過直接傳輸所花費較長的時間縮短，而替來源和目的地工作站找尋夥伴是透過一個分散式的方法，是鄰近工作站透過所獲得的資訊，然後由他們自己決定誰將成為夥伴，但並不是每次工作站要傳送訊框時都需要選擇夥伴一次，在來源工作站要傳送訊框給目的地工作站時，會依據一個表格，這個表格會記錄目前這個目的地工作站是否有一個夥伴，如果沒有夥伴的話，才需要去觸發鄰近工作站去互相競爭誰能成為夥伴透過NS-2模擬工具評估我們所提出的方法，像較於傳統的802.11協定，網路的整體效能有大幅的改善，而在討論行動性(mobility)方面，我們的方法也比其他的方法，在校能低落方面也改善不少。

關鍵字

合作式通訊；合作式媒體存取協定；夥伴選擇

並列摘要

In wireless networks, stations can overhear frames that are sent by their neighboring stations. However, this broadcast nature of wireless signals can allow cooperative transmission to achieve spatial diversity without the need for multiple antennas. When a station with a low transmission rate accesses the shared wireless channel, the overall network throughput is reduced. Here we propose a cooperative MAC protocol called PocMAC that uses a distributed method to select relay stations for forwarding the traffic of such low-transmission-rate stations to improve overall throughput. Before each transmission, stations determine whether cooperative transmission through a relay station would be beneficial. Furthermore, the source must know whether the destination has a partner (relay). If the destination is not assigned a relay before a data frame is transmitted, the relay selection process will be performed during transmission. Then, one relay station will be automatically selected to forward the data frame; its MAC address will be stored in the RelayTable of the source station. For a future transmission to the same destination, the appropriate relay station may thus be directly found in the RelayTable instead of performing relay selection again. We performed a simulation to comparing our mechanism with traditional IEEE 802.11 and another cooperative MAC protocol, CoopMAC. The simulation results show that our mechanism improves overall network throughput, especially in dynamic topologies caused by mobility.

並列關鍵字

無資料

參考文獻

[1] A. Nosratinia, T.E. Hunter, and A. Hedayat, “Cooperative Communication in Wireless Networks,” IEEE Communications Magazine, 2004.

[2] A. Stefanov, and E. Erkip, “Cooperative Coding for Wireless Networks,” IEEE Transaction on Communicaions, Vol. 52, No. 9, September 2004.

[3] J. Nicholas Laneman, David N. C. Tse, and Gregory W. Wornell, “Cooperative Diversity in Wireless Networks: Efficient Protocols and Outage Behavior,” IEEE Transactions on Information Theory, Vol. 50, No. 12, December 2004.

[4] M. Yu and J. Li, “Is Amplify-and-Forward Practically Better Than Decode-and-Forward or Vice Versa?” IEEE Transaction on Acoustics, Speech, and Signal Processing, March 2005.

[7] Chun-Ting Chou, Jun Yang, and Dong Wang, “Cooperative MAC Protocol with Automatic Relay Selection in Distributed Wireless Networks,” in Proceedings of the Fifth Annual IEEE International Conference on Pervasive Computing and Communications Workshops (PerComW’07).

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無線網路下以分散式演算法選擇夥伴的合作式媒體存取協定

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