最近幾年，以位置資訊為基礎的服務持續發展中，像是搜尋、目標追蹤或是緊急搜救等；在無線感測網路中，精準且高效率的定位演算法是這些網路服務的關鍵．過去的文獻中已記載了許多不同類型的定位演算法．由於無線感測網路的布建範圍廣大，考量其成本和硬體的限制，range-free類型的定位演算法較為可行．此類型之演算法可分為兩個階段，分別是距離測量（distance estimation）和三角定位(triangulation)階段．若距離測量的精確性可以有所改進，便可增進定位的精準度．在這篇論文中，我們提出一套新的方法來測量單一躍點(single hop)間的距離；另外，在相距多個躍點(multi-hop)的情況下，也提出了一套修正的法則用以修正加總多個單一hop距離後的誤差．藉由模擬，我們將此方法和其他range-free的演算法加以比較，我們發現我們的距離測量方法可降低距離測量階段的誤差，在相同的設定下，我們的距離測量方法比起其他的方法準確，尤其是在錨點(anchor)數量低的情況下．

In recent years, a number of location - based services have been proposed, such as search, target tracking and rescue. An accurate and efficient localization algorithm is crucial in supporting all these services in wireless networks. There are many different localization algorithms proposed in the literature. Due to the cost and limitation of hardware on sensing nodes, range-free localization schemes have received great deal of attention. Such schemes include two phases: distance estimation and triangulation. A better distance estimation helps improve the accuracy of localization. In this thesis, we propose a novel scheme for single hop and range estimation. Additionally, we propose the first correction scheme to estimate multi-hop range by mean of single hop range estimations. Compared to other range-free distance estimation, our scheme reduces the error significantly, especially when the number of anchors is low.

[1] Suganya .S, “A Cluster-Based Approach for Collaborative Target Tracking in Wireless Sensor Networks”, in Emerging Trends in Engineering and Technology, ICETET, 2008, pp.276-282.
[2] Charles Bostian, Scott Midkiff, and Laurence W. "Bill" Carstensen, “Broadband wireless communications for disaster relief: A project of Virginia Tech''s Center for Wireless Telecommunications (CWT) Science Applications International Corporation”, in Proc. dg.o ''02 Proceedings of the 2002 annual national conference on Digital government research.
[3] Sheng-Po Kuo, Bing-Jhen Wu, Wen-Chih Peng, and Yu-Chee Tseng, “Cluster-Enhanced Techniques for Pattern-Matching Localization Systems”, in Proc. IEEE MOBHOC, 2007.
[4] J.C. Navas and T. Imielinski, “GeoCast-Geographic Addressing and Routing”, in Proc. of International Conference on MobiCom, 1997.
[5] Y.B. Ko and N.H. Vaidya, ”Location-aided routing (LAR) in monile ad hoc networks”, in Proc. ACM MobiCom.
[6] B. H. Wellenhoff, H. Lichtenegger and J. Collins, “Global Positions System: Theory and Practice”, Fourth Edition. Springer Verlag, 1997.
[7] P. Bahl and V. N. Padmanabhan, “RADAR: An In-Building RF-Based User Location and Tracking System”, in Proc. IEEE INFOCOM, 2000.
[8] A. Harter, A. Hopper and P. Steggles, “A. Ward and P.Webster, The anatomy of a context-aware application”, In Proc. ACM MOBICOM, 1999.
[9] J. Hightower, G. Boriello and R. Want, “SpotON: An indoor 3D Location Sensing Technology Based on RF Signal Strength”, University of Washington CSE Report #2000-02-02, 2000.
[10] N. Bulusu, J. Heidemann and D. Estrin, “GPS-less Low Cost Outdoor Localization for Very Small Devices”, IEEE Personal Communications Magazine,2000, pp. 7(5)28-34.
[11] D. Niculescu and B. Nath, “DV Based Positioning in Ad hoc Networks”, in Journal of Telecommunication Systems, 2003.
[12] D. Nicolescu and B. Nath, ”Ad-Hoc Positioning Systems(APS)”, in Proc. IEEE GLOBECOM, 2001.
[13] R. Nagpal, “Organizing a Global Coordinate System from Local Information on an Amorphous Computer”, A.I. Memo 1666, MIT A.I. Laboratory, 1999.
[14] Tian He, Chengdu Huang, Brian M. Blum, John A. Stankovic, Tarek Abdelzaher, “Range-Free Localization Schemes for Large Scale Sensor Networks”, in Proc. ACM MobiCom, 2003.
[15]Lingxuan Hu and David Evans, “Localization for Mobile Sensor Networks”, in Proc. ACM MobiCom, 2004.
[16]L.Kleinrock and J.Slivester, “Optimum transmission radii for packet radio networks or why six is a magic number”, in proc. National Telecomm conference, 1978, pp. 4.3.1-4.3.5.
[17]A. Savvides, C. C. Han and M. B. Srivastava, “Dynamic Fine-Grained Localization in Ad-Hoc Networks of Sensors”, in Proc. ACM MOBICOM, 2001.
[18] A. Savvides, H. Park and M. Srivastava, “The Bits and Flopsof the N-Hop Multilateration Primitive for Node Localization Problems”, in Proc. First ACM International Workshop on Wireless Sensor Networks and Application, 2002.