在無線感測器網路(Wireless Sensor Networks)中，定位相關應用已經成為重要的議題並廣泛地被提出討論。對於這些應用而言，測距定位法面臨無線訊號傳遞的不規則性以及額外硬體裝置花費的挑戰，而無測距定位法不需要利用收到的訊號強度來估量距離，因此需要的硬體裝置簡單且花費少。若在不需求得太精確估計位置的前提下，無測距定位法較適用於無線感測器網路，而現存的無測距定位法有些計算太複雜，有些不夠精確。為了改進之前的定位方法，我們提出無線感測器網路中分散式之無測距定位法(Distributed Range-Free Localization Scheme)。我們假設只有一些感測器可以利用全球定位系統(Global Position System)獲得位置資訊，而其他感測器可藉由蒐集已定位感測器的位置資訊來估算自己的位置。首先我們先找出初始估計位置，再利用比較遠的已定位感測器與初始估計位置間的相對位置來修正初始估計位置。在模擬結果中可看出分散式之無測距定位法較其他定位法可獲得較精確的估計位置。

Location-related applications have become essential issues and have been widely proposed in wireless sensor networks (WSNs). For those applications, radio propagation irregularity and the cost of the additional devices on sensor nodes make range-based localization schemes in WSNs very challenging. Instead, range-free localization schemes don’t have to utilize received signal strength to estimate distances and only needs simple and costless hardware. Thus, range-free localization schemes are more suitable for WSNs if only coarse accuracy is required. However,existing range-free localization schemes are either too costly or not accurate enough. To improve previous works, we present DRLS, a fully distributed range-free
localization scheme for WSNs. We assume that only a few sensor nodes, called anchors, can get their locations by Global Positioning System (GPS) and the remaining nodes need to estimate their own locations by gathering the nearby neighboring information. We first find the coarse estimative locations of the nodes.
Furthermore, we derive a refinement method to correct the coarse estimative locations according to the relative position of the farther anchor and the coarse estimative locations. We show that our DRLS scheme performs well when random node placement is considered. Besides, our scheme is superior to previous range-free localization schemes via extensive simulations under a variety anchor densities.
Simulation results show that the proposed algorithm achieves better accuracy of
estimative locations.

[1] Andreas Savvides, ChihChieh Han, and Mani B. Strivastava, “Dynamic
Fine-Grained Localization in Ad-Hoc Networks of Sensors,” Proceedings of the
7th Annual ACM International Conference on Mobile Computing and
Networking (MobiCom 2001), pp. 166-179, Rome, Italy, July 2001.
[2] Nissanka B. Priyantha, Anit Chakraborty, and Hari Balakrishnan, “The Cricket Location-Support System,” Proceedings of the 6th Annual ACM International Conference on Mobile Computing and Networking (MobiCom 2000), pp. 32-43,Boston, MA, August 2000.
[3] Asis Nasipuri and Kai Li, ”A Directionality Based Location Discovery Scheme for Wireless Sensor Networks,” Proceedings of the first ACM international conference on Wireless sensor networks and applications (WSNA 2002), pp.105-111, September 2002.
[4] Mayuresh M. Patil, Umesh Shaha , U.B. Desai , and S. N. Merchant,
“Localization in Wireless Sensor Networks Using Three Masters,” Proceedings
of IEEE International Conference on Personal Wireless Communications
(ICPWC 2005), pp. 384-388, January 2005.
[5] Yoshikazu Ohta, Masashi Sugano, and Masayuki Murata, “Autonomous
Localization Method in Wireless Sensor Networks,” Proceedings of the first
IEEE International Workshop on Sensor Networks and Systems for Pervasive
Computing (PerSeNS 2005), pp. 379-384, March 2005.
[6] Nissanka B. Priyantha, Hari Balakrishnan, Erik Demaine, and Seth Teller,
“Anchor-Free Distributed Localization in Sensor Networks,” Proceedings of the
first International Conference on Embedded Networked Sensor Systems (SenSys
2003), pp. 340-341, Los Angeles, California, USA, November 2003.
[7] Joe Albowicz, Alvin Chen, and Lixia Zhang, ”Recursive Position Estimation in Sensor Networks,” Proceedings of the Ninth IEEE International Conference on
Network Protocols (ICNP 2001), pp. 35-41, Mission Inn, Riverside, California,
November 2001.
[8] Nirupama Bulusu, John Heidemann, and Deborah Estrin, ”GPS-less Low Cost
Outdoor Localization For Very Small Devices,” Proceedings of the IEEE
Personal Communications Magazine, vol. 7, no. 5, pp. 28-34, October 2000.
[9] Jan Blumenthal, Frank Reichenbach, and Dirk Timmermann, “Position
Estimation in Ad Hoc Wireless Sensor Networks with Low Complexity,”
Proceedings of IEEE Workshop on Positioning, Navigation, and
Communication (WPNC 2005), Hannover, Germany, March 2005.
[10] Dragos Niculescu and Badri Nath, ”Ad Hoc Positioning System (APS),”
Proceedings of IEEE Global Telecommunications Conference (Globecom 2001),
pp. 2926-2931, vol. 1, November 2001.
[11] Dragos Niculescu and Badri Nath, ”DV Based Positioning in Ad Hoc
Networks,”Journal of Telecommunication Systems, pp. 267-280, vol. 22, January-April 2003.
[12] Xiaoli Li, Hongchi Shi, and Yi Shang, “A Partial-range-aware Localization
Algorithm for Ad-hoc Wireless Sensor Networks,” Proceedings of the 29th
Annual IEEE International Conference on Local Computer Networks (LCN
2004), pp. 77-83, August 2004.
[13] Tian He, Chengdu Huang, Brian M. Blum, John A. Stankovic, and Tarek
abdelzher, ”Range-Free Localization Schemes for Large Scale Sensor
Networks,” Proceedings of the 9th Annual ACM International Conference on
Mobile Computing and Networking (MobiCom 2003), pp. 81-95, September 2003.
[14] Lance Doherty, Kristofer S. J. Pister, and Laurent El Ghaoui, ”Convex Position Estimation in Wireless Sensor Networks,” Proceedings of the 20th Annual Joint Conference of the IEEE Computer and Communications Societies (INFOCOM 2001), vol. 3, pp. 1655-1663, April 2001.
[15]Aram Galstyan, Bhaskar Krishnamachari, Sundeep Pattem, and Kristina
Lerman, ”Distributed Online Localization in Sensor Networks Using a Moving
Target,” Proceedings of IEEE/ACM 3rd International Symposium on
Information Processing in Sensor Networks (IPSN 2004), pp. 61-70, Berkeley,
CA, April 2004.
[16] Jeffrey Hightower and Gaetano Borriello, ”Location Systems for Ubiquitous
Computing,” in IEEE Computer, volume 34, issue 8, pp. 57-66, August 2001.
[17] Goran M. Djuknic and Robert E. Richton, “Geolocation and Assisted GPS,” in IEEE Computer, volume 34, issue 2, pp. 123-125, February 2001.
[18] G. J. Pottie and W. J. Kaiser, “Wireless Integrated Network Sensors,”
Communications of the ACM, volume 43, issue 5, pp. 51–58, May 2000.
[19] Katayoun Sohrabi, Jay Gao, Vishal Ailawadhi, and Gregory J. Pottie,
“Protocols for Self-Organization of A Wireless Sensor Network,” IEEE Personal
Communication, volume 7, issue 5, pp. 16–27, October 2000.
[20] “Garmin international: about GPS”, http://www.garmin.com/aboutGPS/
[21] “TinyOS Community Forum”, http://webs.cs.berkeley.edu/tos/
[22] Jason Hill, Robert Szewczyk, Alec Woo, Seth Hollar, David Culler, and
Kristofer Pister, ”System Architecture Directions for Networked Sensors,”
Proceedings of the 9th International Conference on Architectural Support for
Programming Languages and Operating Systems (ASPLOS 2000), pp. 93-104, Cambridge, MA, November 2000.
[23] B. H. Wellenhoff, H. Lichtenegger, and J. Collins, “Global Positions System: Theory and Practice”, Fourth Edition, Springer Verlag, 1997.
[24] Jang-Ping Sheu, Jian-Ming Li, and Chih-Shun Hsu, “A Distributed Location
Estimating Algorithm for Wireless Sensor Networks”, IEEE International
Conference on Sensor Networks, Ubiquitous, and Trustworthy Computing
(SUTC), June 2006.