網際網路的迅速發展，令無線網路得到重大突破，協作任務的執行就是重要應用之一；也就是有足夠多個行動節點組成一個群組，並相互分享運算資源，使原本無法在同一個行動裝置下完成的任務，能順利達成。
近期對於動態群組上的研究多半著重於分群，並未考慮協作任務，群組成員數量必須有定量限制，同時任務必須持續一段執行時間。但是，在動態環境下，行動節點的位置將隨著時間變動而改變，群組成員可能會遺失，因此需要一個維護機制以確保群組成員數量能夠達到需求。
是以本研究旨在開發一個有效率的動態群組維護機制，使花費較少的維護成本，獲取較高的群組品質。利用計算條件機率的方式，估算各節點會在群組傳輸範圍內的機率，據此，我們可以決定如何選擇群組成員。論文中提出兩種方法，以計算期望值的方式，分別達到可得到最久的群組維持時間或單位時間遞補節點成本最少的兩種目的。
最後我們搭配模擬，在不同的環境之下，比較我們的方法與直觀方法的優缺點，結果顯示我們的方法皆能比直觀方式來得有效，且各能在不同的環境下各有不同的優勢。

Following the shift development of World Wide Web, wireless network technology and its applications has risen dramatically. Especially, collaborative task management is an important issue among them. Basically, a collaborative task cannot be accomplished by only mobile device. However, with the help of several devices and sharing their resources with each other, the task can now be finished efficiently.
Researches in this field basically focus on clustering instead of the collaboration task in these decades. The number of group members in a task will be restricted quantitatively; and their execution time has to keep continuously awhile as well. However, under the dynamic mobile environment, the topology of mobile nodes will change over time and the members will be cut down probably; therefore, a maintenance mechanism to ensure the number of group members is required.
This thesis aims to develop an efficient mechanism for maintaining a dynamic group, which with less maintenance cost, and better group quality. Based on conditional probability , our method estimates the probability that a mobile node will stay within coordinator's transmission range. Using these values, we can decide how to choose the group members. We have proposed two strategies to achieve best expected group formation time or less maintenance cost in this thesis.
Last, we have built a simulation and compared our methods with naive one. Results show that our strategies are more effective and have different advantages in different network environments.

[1]K. Kihwan, C. Ying, and W. Tavanapong, "Safe-Time: Distributed Real-Time Monitoring of cKNN in Mobile Peer-to-Peer Networks," in Proc. 9th International Conference on Mobile Data Management (MDM '08), pp. 124-131, 2008.
[2]D. H. Kim, M. R. Lee, L. Han, and H. P. In, "Efficient Data Dissemination in Mobile P2P Ad-Hoc Networks for Ubiquitous Computing," in Proc. International Conference on Multimedia and Ubiquitous Engineering (MUE '08), pp. 384-389, 2008.
[3]Y. Luo, O. Wolfson, and B. Xu, "A Spatio-Temporal Approach to Selective Data Dissemination in Mobile Peer-to-Peer Networks," in Proc.International Conference on Wireless and Mobile Communications (ICWMC '07), pp. 50b, 2007.
[4]L. Tang, Y. Zheng, J. Yuan, J. Han, A. Leung, C. Hung, and W. Peng, "On Discovery of Traveling Companions from Streaming Trajectories, " IEEE 28th International Conference on Data Engineering (ICDE '12), pp. 186-197, 2012.
[5]O. Wolfson, B. Xu, and R. M. Tanner, "Mobile Peer-to-Peer Data Dissemination with Resource Constraints," International Conference on Mobile Data Management (MDM '07), pp.16-23, 2007.
[6]S. Kim, Y. Yonglk, I. Minkyo, L. Kangchan, and L. Seungyun, "The evolution of standardization for mobile cloud, "International Conference on ICT Convergence (ICTC '011), pp.578-579, 2011
[7]M. Armbrust, A. Fox, R. Griffith, A. D. Joseph, R. Katz, A. Konwinski, G. Lee, D. Patterson, A. Rabkin, I. Stoica, and M. Zaharia, "Above the Clouds: A Berkeley View of Cloud Computing," Technical Report No. UCB/EECS-2009-28, EECS Department, University of California, Berkeley, February 10, 2009.
[8]M. A. Cheema, L. Brankovic, X. Lin, W. Zhang, and W. Wang, "Continuous Monitoring of Distance-Based Range Queries," IEEE Transactions on Knowledge and Data Engineering, vol. 23, pp. 1182-1199, 2011.
[9]T. T. Do, K. A. Hua, and Chow-Sing Lin , "ExtRange: Continuous Moving Range Queries in Mobile Peer-to-Peer Networks," 10th International Conference on Mobile Data Management (MDM '09), pp. 317-322, 2009.
[10]J. Zhang, M. Zhu, D. Papadias, Y. Tao, and D. L. Lee, "Location-based Spatial Queries," in Proc. ACM International Conference on Management of Data (SIGMOD), pp. 443-454, 2003.
[11]M. A. Cheema, L. Brankovic, X. Lin, W. Zhang, and Wei Wang, "Multi-Guarded Safe Zone: An Effective Technique to Monitor Moving Circular Range Queries," in Proc. IEEE 26th International Conference on Data Engineering, pp. 189-200, 2010.
[12]Z. Song and N. Roussopoulos, "K-nearest Neighbor Search for Moving Query Point," Advances in Spatial and Temporal Databases, pp. 79-96, 2001.
[13]B. Zheng, and D. L. Lee, "Semantic Caching in Location-dependent Query Processing," Advances in Spatial and Temporal Databases, pp. 97-113, 2004.
[14]H. Hu, J. Xu, and D. L. Lee, "A Generic Framework for Monitoring Continuous Spatial Queries over Moving Objects," in Proc. ACM International Conference on Management of Data (SIGMOD), Baltimore, Maryland, pp. 479-490, 2005.
[15]P. Kalnis, G. Ghinita, K. Mouratidis, and D. Papadias, "Preventing Location-Based Identity Inference in Anonymous Spatial Queries," IEEE Transactions on Knowledge and Data Engineering, vol. 19, pp. 1719-1733, 2007.
[16]H. Qingfeng, C. Julien, and G. Roman, "Relying on Safe Distance to Achieve Strong Partitionable Group Membership in Ad Hoc Networks, " IEEE Transactions on Mobile Computing, pp. 192-205, 2004.
[17]L. Tang, Y. Zheng, J. Yuan, J. Han, A. Leung, C. Hung, and W. Peng, "On Discovery of Traveling Companions from Streaming Trajectories, " IEEE 28th International Conference on Data Engineering (ICDE '12), pp. 186-197, 2012.
[18]D. Papadias, Q. Shen, Y. Tao, and K. Mouratidis, " Group Nearest Neighbor Queries ," in Proc. International Conference on Data Engineering (ICDE '04), pp. 301-312, 2004.
[19]K. Deng, S. Sadiq, X. Zhou, H. Xu, G. P. C. Fung, and Y. Lu, " On Group Nearest Group Query Processing," IEEE Transaction on Knowledge and Data Engineering, vol. 24, no. 2, pp. 295-308, 2012.
[20]K. Deng, H. Xu, S. Sadiq, Y. Lu, G. Fung, and H.T. Shen, " Processing Group Nearest Group Query," IEEE 25th International Conference on Data Engineering (ICDE '09), pp. 1144-1147, 2009.
[21]H. Xu, Y. Lu,and Z. Li, " Continuous Group Nearest Group Query on Moving Objects," Second International Workshop on Education Technology and Computer Science (ETCS '10), pp. 350-353, 2010.
[22]Yan Zhang, and Jim Mee Ng, "A Distributed Group Mobility Adaptive Clustering Algorithm for Mobile Ad Hoc Networks," IEEE International Conference on Communications (ICC '08), pp.3161-3165, 2008.