陸上無線感測網路 (terrestrial wireless sensor network) 發展已有很長的時間，也已經廣泛地運用在生活上，而最近幾年水下無線感測網路（underwater sensor network）開始受到重視，相對於陸上無線感測網路，水下無線感測網路不管在技術與應用上仍有很大的進步空間，主要是水下無線感測網路使用聲波 (acoustic waves) 作為傳輸的媒介，不同於陸上無線感測網路使用無線電波(radio waves)，也由於聲波與無線電波兩者特性截然不同，因此傳統陸地上的方法無法運用在無線水底感測網路，必須重新發展針對無線水底感測網路的新方法與技術。
本論文我們提出N level binary tree的路由協定，N level binary tree利用感測器彼此的深度差來決定路由的方向，再使用簡單的區塊定位，透過多點跳躍 (muti-hop)的方式，使感測資料能送達海面上的基地站。N level binary tree採用多路徑 (mutipath)來傳送感測資料，N level binary tree會限制傳送次數，因此不會產生過多的傳送次數而且封包到達率不會太低。
聲波在水中通訊容易受到破壞導致發生封包遺失 (packet loss)，陸地上常用的解決方法是採用自動重傳請求 (automatic repeat request, ARQ) 機制，在我們的模擬實驗中，N level binary tree不使用ARQ機制，我們將與單一路徑且使用ARQ的Greedy short sink方法來比較，由實驗結果得知，在不需要極高的封包到達率 ( Packet Delivery Ratio)，N level binary tree能有較低的傳送次數，因此N level binary tree能節省感測器的電力，增加整個網路生命週期 (network lifetime )。

In the last few years there has been are intensive study in routing protocols for terrestrial wireless sensor networks. Terrestrial wireless sensor networks have been used extensively in many land-based applications. Underwater Sensor Networks (UWSNs) have attracted a lot of attention recently. Since data packets in Underwater Sensor Networks are transmitted by acoustic signals, the characteristics of a Underwater Sensor Networks are different from those of a terrestrial wireless sensor networks. However, due to the different nature of the underwater environment and applications, there are drawbacks with respect to the suitability of the existing solutions for underwater acoustic networks.
In this paper, we propose a N level binary tree protocol. Sinks are usually situated at the water surface. The based on the depth information of each sensor, N level binary tree forwards data packet towards the water surface. We make use of multipath data delivery. N level binary tree will limit the number of transmissions, it does not produce excessive transmission times and packet arrival rate is not too low.
Acoustic communications vulnerable to damage in the water result in packet loss, land used solution is to use automatic repeat request (ARQ) techniques. In our simulations, N level binary tree does not use ARQ, we will work with a single path and use the ARQ Greedy short sink method to compare. The results indicate that, without the need for high packet arrival rate, N level binary tree can have a lower number of transmissions, the N level binary tree can save electricity sensor, increasing the network lifetime.

[1] I. F. Akyildiz, D. Pompili, and T. Melodia, “Underwater Acoustic SensorNetworks: Research Challenges,” Ad Hoc Networks Journal (Elsevier), Vol. 3, pp. 257–281, March 2005.

[2] I. F. Akyildiz, D. Pompili, and T. Melodia, “ Challenges for efficient communication in underwater acoustic sensor networks,” ACM SIGBED Review 1(1) , July 2004.

[3] I. F. Akyildiz, D. Pompili, and T. Melodia, “State of the Art in Protocol Research for Underwater Acoustic Sensor Networks,” ACM International Workshop on UnderWater Networks (WUWNet), Los Angeles, CA, September 2006.

[4] I. F. Akyildiz, D. Pompili, and T. Melodia, “ Challenges for efficient communication in underwater acoustic sensor networks,” ACM SIGBED Review 1(1) , July 2004.

[5] M.J.Buckingham, “Ocean-acoustic progation models.”1992.

[6] Vijay Chandrasekhar, Winston KG Seah Yoo Sang Choo, How Voon Ee, “Localization in Underwater Sensor Networks — Survey and Challenges,” ACM WUWNet’06, September 25, 2006.

[7] N. Chirdchoo, W.-S. Soh, and K. C. Chua, “Aloha-based mac protocols with collision avoidance for underwater acoustic networks,” INFOCOM 2007. 26th IEEE International Conference on Computer Communications. IEEE, pages 2271–2275, May 2007.

[8] J.H.Cui, J.Kong, M.Gerla, and S.Zhou, “Challenges: Building Scalable Mobile Underwater Wireless Sensor Networks for Aquatic Applications,” IEEE Network, Special Issue on Wireless Sensor Networking, 20(3):12–18, May June 2006.

[9] J. Heidemann, W. Ye, J. Wills, A. Syed, and Y. Li, “Research Challenges and Applications for Underwater Sensor Networking,” Proceedings of IEEE Wireless Communications and Networking Conference, (Las Vegas, Nevada, USA), pp. 228–235, April 2006.

[10] C.-C. Hsu, K.-F. Lai, C.-F. Chou, and K.-J. Lin, “St-mac: Spatial-temporal mac scheduling for underwater sensor networks,” INFOCOM 2009. The 28th Conference on Computer Communications. IEEE, pages 1827–1835, April 2009.

[11] J. Heidemann, Y. Li, A. Syed, J. Wills, and W. Ye, “Underwater sensor networking: Research challenges and potential applications,” USC/ISI Technical Report ISI-TR- 2005-603, 2005.

[12] Daniele Puccinelli and Martic Haenggi, “Wireless Sensor Networks: Applications and Challenges of Ubiquitous Sensing,” IEEE Circuits and Systems Magazine, pp. 19-31. 2005.

[13] Xie, P., Cui, J.-H., Lao, “Vbf: Vector-based forwarding protocol for underwater sensor networks,” Proceedings of IFIP Networking ,May 2006.

[14] J. Proakis, J. Rice, E. Sozer, and M. Stojanovic, “Shallow water acoustic networks,” Encyclopedia of Telecommunications, J. G. Proakis, Ed. John Wiley and Sons, 2003.

[15] J. Partana, J. Kurosea, and B. Neil Levinea, “A Survey of Practical Issues in Underwater Networks,” ACM, WUWNet’06, September 25, 2006.

[16] D.Pompili and T.Melodia, “Three­Dimensional Routing in Underwater Acoustic Sensor Networks,” ACM, PE­WASUN, 2005.

[17] Y-H.Pickard, George L. and William J. Emery, “Descriptive Physical Oceanography: An Introduction,” Oxford: Pergamon Press,1990.

[18] M. Molins and M. Stojanovic, “Slotted fama: a mac protocol for underwater acoustic networks,” OCEANS 2006 - Asia Pacific, pages 1–7, May 2006.

[19] Melike E.-K., Sema Oktuga, Luiz Vieirab and Mario Gerla, “Performance evaluation of distributed localization techniques for mobile underwater acoustic sensor networks,” Ad Hoc Networks Volume 9, Issue 1, Pages 61-72, January 2011.

[20] Nicolaou, N., See, A., Xie, P., Cui, J.-H., Maggiorini, “Improving the robustness of location-based routing for underwater sensor networks,” Proceedings of IEEE OCEANS 2007 (June 2007).

[21] N. Ramanathan, M. Yarvis, J. Chhabra, N. Kushalnagar, L. Krishnamurthy, and D. Estrin, “A stream-oriented power management protocol for low duty cycle sensor network applications,” Proceedings of the IEEE Workshop on Embedded Networked Sensors, Sydney, Australia, May 2005.

[22] M. Stojanovic, “Acoustic (underwater) communications,” Encyclopedia of Telecommunications, J. G. Proakis, Ed. John Wiley and Sons, 2003.

[23] Seach, W.K., Tan, H.X, “Multipath virtual sink architecture for underwater sensor networks,” OCEANS, May 2006.

[24] M.L.Sichitiu and V. Ramadurai, “Location of wireless sensor networks with a mobile beacon,” Proceedings of the IEEE International Conference on Mobile Ad-hoc and Sensor Systems (MASS2004), Fort Lauderdale, FL,USA, Oct 25-27, 2004.

[25] UNOLS day rates, 2005. www.unols.org/ publications/reports/budget_impacts/Fleet_Cost_Estimates.xls.

[26] R. J. Urick, Principles of Underwater Sound. McGraw-Hill, 1983.

[27] Y-H. Wang, C-H. Tsai, and H.-J. Mao, “A Hierarchical Multiple-Choice Routing Path Protocol for Wireless Sensor Networks,” JOURNAL OF INFORMATION SCIENCE AND ENGINEERING 24, 277-291 ,2008.

[28] Hai Yan, Zhijie Jerry Shi, and Jun-Hong Cui, “DBR: Depth-Based Routing for Underwater Sensor Networks,” IFIP International Federation for Information Processing 2008.

[29] Z. Zhou, J.-H. Cui, and S. Zhou, “Localization for Large-Scale Underwater Sensor Networks,” Proceedings of the 6th international IFIP-TC6 conference on Ad Hoc and sensor networks, wireless networks, next generation internet Springer-Verlag Berlin, Heidelberg , 2007.

[30] Z. Zhou,Z. Peng,J.-H. Cui,and Z.Jiang, “Handling Triple Hidden Terminal Problems for Multi-Channel MAC in Long-Delay Underwater Sensor Networks,” IEEE INFOCOM’10, San Diego, CA, USA,2010.