在水下感測網路中設計公平的MAC傳輸

雖然已有許多發展於陸地上無線感測網路傳輸的媒介存取控制協定，但這些協定在水下的環境中並不適用。水下環境具有較大傳輸延遲、低頻寬、節點移動…等特性，在協定的設計上面臨許多挑戰，例如空間與時間的不確定性以及空間的不公平性。本論文提出一種媒介存取控制協定解決空間的不公平性，利用機率法則探討每個競爭者最先傳送的機率。首先我們的方法是利用延遲RTS CP時間回覆CTS，避免一些不必要的碰撞。接收端考慮在RTS CP內收到的所有RTS，估計其可能的傳送時段，並透過我們所提出的機率法則與第一個收到的RTS比較，決定其中最先傳送的競爭者並回覆CTS，達到公平性的傳輸。由於我們的方法能夠在每一次競爭時，維持公平的傳輸；因此當多個傳送端傳送資料時，我們也能夠維持在網路中傳輸順序的公平性。此外我們的方法能夠確保在一次RTS/CTS交握之後，不會有任何資料碰撞的狀況發生，因而能夠避免多餘的競爭所產生的時間浪費，因此在頻道使用率與網路傳輸量的部分也能夠維持較好的表現。在移動式的感測網路中，我們的方法不需要計算其傳輸延遲或位置，因此也能避免因節點移動造成的傳輸碰撞的問題發生，使網路整體效率能有效改善。實驗結果顯示當競爭者越多，我們的方法仍能維持大約40%的準確率，以及90%的公平性，因而在公平性上能夠優於MACA、MACA-U以及T-Lohi。就頻道使用率而言，比起MACA、MACA-U以及T-Lohi更為有效率，在整體傳輸量也有較好的表現。

關鍵字

移動；水下感測網路；公平性

並列摘要

Many media access control protocols for the terrestrial networks have been proposed. When it comes to underwater environment, these protocols become not suitable. Long propagation delays, low bit rates and sensor mobility cause many challenge for MAC protocol design, such as space time uncertainty and spatial unfairness. Arriving time of packets are depend on both the sending time and distance from transmitter to receiver. It is difficult to avoid collision and guarantee the transmission fairness. In this thesis, we consider spatial unfairness problem in UWSN and proposed a spatial fairness MAC protocol: SF-MAC. SF-MAC can avoid collision through postponing CTS frame with a RTS CP. Receiver considers the potential sending time of each contender in RTS CP and determine the earliest transmitter with a probability rule that compare with the first RTS. SF-MAC can maintain more exact transmission order with multiple contenders to achieve fairness transmission because of responding CTS to the earliest transmitter in each contention. In addition, SF-MAC guarantees that the transmission can succeed while RTS/CTS handshake completely. Throughput can maintain better without unnecessary contention. In mobile sensor networks, the collision problem caused by sensor mobility can be avoid with considering the propagation delay or distance between each node, and make networks performance more efficiency. Simulation results show that while the contenders are increase, our protocol can maintain about 40% successful rate of responding CTS and 90% fairness index and better than MACA、MACA-U以及T-Lohi. SF-MAC can also make higher channel utilization with higher throughput to achieve well network performance.

並列關鍵字

mobile ； underwater sensor networks ； fairness

參考文獻

[1] I. F. Akyildiz, D. Pompili, and T. Melodia, “Underwater Acoustic Sensor Networks: Research Challenges,” Ad Hoc Networks, Vol. 3, No. 3, 2005, pp. 257-279.

[4] N. Chirdchoo, W.-S. Soh, and K.-C. Chua, “RIPT: A Receiver-initiated Reservation-based Protocol for Underwater Acoustic Networks,” IEEE Journal on Selected Areas in Communication (JSAC),Vol. 26, No. 9, 2008, pp. 1744-1753.

[5] N. Chirdchoo, W.-S. Soh, and K. C. Chua, “MACA-MN: A MACA-based MAC Protocol for Underwater Acoustic Networks with Packet Train for Multiple Neighbors,” IEEE Vehicular Technology Conference (VTC), 2008.

[6] I. Demirkol, C. Ersoy, and F. Alagöz, “MAC Protocols for Wireless Sensor Networks: A Survey,” IEEE Communications Magazine, Vol. 44, No. 4, 2006, pp. 115-121.

[7] P. Guo, T. Jiang, G. Zhu, and H.-H. Chen, “Utilizing Acoustic Propagation Delay to Design MAC Protocols for Underwater Wireless Sensor Networks,” Wireless Communications & Mobile Computing, Vol. 8, No. 8, 2008, pp. 1035-1044.

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在水下感測網路中設計公平的MAC傳輸

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