非同步無線感測網路下的連續性精確top-k查詢於執行後，基地台會持續取得環境中數值最高的k筆數值與回饋這些數值的感測節點。劉宗瑋曾經提出一個實作連續性精確top-k查詢的方法，此方法使用所謂的候選點來減少感測節點的資料傳輸次數，以減少電量消耗而延長網路生命週期。
本研究進一步改良劉宗瑋所提出的方法，做法是設置長度為c的快取區，每次基地台執行廣播時等同於執行top-(k+c)查詢，然而當快取區的資料耗盡時才進行廣播。另外，我們保存快取區中的最小值當作門檻值，來減少基地台廣播門檻值與探測值的情況發生。如此一來，雖然少量感測節點的上傳資料次數上升，然而因廣播次數下降，整體來說仍可減少感測節點的傳送與接收資料的次數，而增加無線感測網路的網路生命週期。
我們在10種拓樸中以模擬的方式將本論文的方法與劉的方法進行比較。實驗結果顯示在k=3、4、5、7、10中，本研究的方法最高可增加約43%的網路生命週期。

After running the continuous exact top-k query in asynchronous wireless sensor networks, base station will continue to get the top-k sensors and their values. Zong-Wei Liu had proposed a method for continuous exact top-k query, this method use what so called candidate for reducing the number of sensor's transmission in order to lower power comsumption and to extend network lifetime.
This research improved Zong-Wei Liu's method by setting a cache with length of c, running top-(k+c) query in every base station's broadcast, and then doing the broadcast when the cache data is depleted. Besides, we use minimum value of the cache as a threshold in order to lower base station broadcast's threshold and probe value. Consequently, although some sensors' upload data frequency is increased, the broadcast frequency is decreased. Overall, sensors transmission frequency is reduced and the network lifetime is extended.
We compare our method with Liu's method on ten types of topology. As a result, for k = 3, 4, 5, 7, and 10, our method could increase network lifetime by 43%.

[1] Sang Hyuk Lee, Soobin Lee, Heecheol Song, and Hwang Soo Lee, "Wireless sensor network design for tactical military applications: Remote large-scale environments," in Proceedings of the IEEE Military Communications Conference, pp. 1–7, October 2009.
[2] Ian F. Akyildiz, Weilian Su, Yogesh Sankarasubramaniam, and Erdal Cayirci, "A survey on sensor networks," IEEE Comniunications Magazine, vol. 40, no. 8, pp. 102-114, August 2002.
[3] 賴勇勳，《在無線感測網路下以等級式資料聚集之研究》，朝陽科技大學碩士論文，2008。
[4] Baljeet Malhotra, Mario A. Nascimento, and Ioanis Nikolaidis, "Exact top-k queries in wireless sensor networks," IEEE Transactions on Knowledge and Data Engineering, Vol. 23 IEEE Press, pp. 1513-1525, 2011.
[5] 劉宗瑋，《在非同步無線感測網路環境底下連續Top-k 查詢之研究》，國立台灣科技大學碩士論文，2014。
[6] Xueyan Tang and Jianliang Xu, "Extending Network Lifetime for Precision-Constrained Data Aggregation in Wireless Sensor Networks," in Proceedings of the IEEE INFOCOM, April 2006.
[7] Ossama Younis and Sonia Fahmy, "Distributed Clustering for Ad-Hoc Sensor Networks: A Hybrid Energy-Efficient Approach," in Proceedings of the IEEE INFOCOM, March 2004.
[8] Samuel Madden, Michael J. Franklin, Joseph M. Hellerstein and Wei Hong, "TAG: A Tiny AGgregation Service for Ad Hoc Sensor Networks," in Proceedings of the Usenix Fifth Symp. Operating Systems Design and Implementation, pp. 131-146, December 2002.
[9] Minji Wu, Jianliang Xu, Xueyan Tang and Wang-Chien Lee, "Top-k Monitoring in Wireless Sensor Networks," IEEE Transactions on Knowledge and Data Engineering, vol. 19, no. 7, pp. 962-976, July 2007.
[10] Jianping Pan, Y. Thomas Hou, Lin Cai, Yi Shi, and Sherman X. Shen, "Topology Control for Wireless Sensor Networks," in Proceedings of the ACM MobiCom'03, pp. 286-299, September 2003.
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[11] Y. Thomas Hou, Yi Shi and Hanif D. Sherali, "Rate Allocation in Wireless Sensor Networks with Network Lifetime Requirement," in Proceedings of the ACM MobiHoc’04, pp. 67–77, May 2004.
[12] Wendi Beth Heinzelman, "Application-Specific Protocol Architectures for Wireless Networks," PhD dissertation, Massachusetts Institute of Technology, 2000