近年來，利用收集器來進行資料收集的方式被廣泛的討論。在此類的作法中，感測器將偵測到的資料暫存在本身的記憶空間，等到收集器路由至各感測器的通訊範圍內進行資料的收集。此類作法中較值得關注的議題是，收集器在收集資料時的路由路徑該如何規劃，避免因收集器路由時間過長而造成資料的遺失。大部分的相關研究主要著重於單一收集器的議題，本論文中我們探討如何利用多個收集器進行有效的資料收集。多個獨立收集器的收集策略首先被提出來，收集器個別進行資料的收集，然後多個收集器合作收集的路由策略被設計來進一步降低資料遺失。同時，我們推導出計算最小資料遺失量的方程式，此方程式能夠被利用來找到最好的合作收集方式。實驗模擬的結果證明，合作收集的路由策略能有效降低資料的遺失量，而且在任何環境下都有很好的表現。

Recently, gathering data by collectors is widely discussed. This approach requires that sensors must keep data in their storage until collectors route into their communication range to gather the data. The major concern of collecting data by collectors is to find an efficient routing path for collectors in order to avoid or reduce the data loss caused by long routing time. Most related works have focused on single collector environment, in this thesis we explore how to gather data by multiple collectors in an efficient way. The strategies of collecting data with multiple individual collectors are first proposed and collectors go their separate ways to gather data. Then the routing strategies with multiple cooperative collectors are designed to further reduce the data loss. And we derive the equations of data loss so that the minimum data loss could be computed in order to find the best way of cooperative gathering. The experiment results show that the cooperative routing strategies can significantly reduce the data loss and perform well in any environment.

[1] S. Ratnasamy, B. Karp, S. Shenker, D. Estrin, R. Govindan, L. Yin, and F. Yu, “Data-Centric Storage in Sensornets with GHT, A Geographic Hash Table”, in Proceedings of Mobile Networks and Applications (MONET), Vol. 8, No. 4, pp. 427-442, Aug. 2003
[2] H. Du, X. Hu, and X. Jia, “Energy efficient routing and scheduling for real-time data aggregation in WSNs,” in Proceedings of Computer Communications, Vol. 29, No. 17, pp. 3527-3535, 8 Nov. 2006

[3] B. Deb, S. Bhatnagar, and B. Nath, “ReInForM: Reliable Information Forwarding Using Multiple Paths in Sensor Networks”, In Proceedings of the 28th Annual IEEE International Conference on Local Computer Networks (LCN’03), pp. 406–415, Germany, Oct. 20-24, 2003
[4] X. Li, Y. J. Kim, R. Govindan, and W. Hong, “Multi-dimensional Range Queries in Sensor Networks”, In Proceedings of the First ACM International Conference on Embedded Networked Sensor Systems (SenSys’03), Los Angeles, California, USA, November 5-7, 2003, pp. 63–75, 2003
[5] W. M. Lee, and V. W.S. Wong, “E-Span and LPT for data aggregation in wireless sensor networks,” in Proceedings of Computer Communications, Vol. 29 , No. 13-14, pp. 2506-2520, Aug. 2006
[6] R. W.N. Pazzi and A. Boukerche, “Mobile Data Collector Strategy for Delay-Sensitive Applications Over Wireless Sensor Networks,” in Proceedings of Computer Communications, Vol. 31, No. 5, pp. 1028-1039, 2008
[7] Y. Wang and C. Wu, “Robot-Assisted Sensor Network Deployment and Data Collection,” in Proceedings of Computational Intelligence in Robotics and Automation 2007(CIRA 2007), pp. 462-472, 2007
[8] M. Ma and Y. Yang, “SenCar: An Energy-Efficient Data Gathering Mechanism for Large-Scale Multihop Sensor Networks,” in IEEE Transactions on Parallel and Distributed Systems 2007, Vol. 18, No. 10, pp. 1476-1488, 2007
[9] A. A. Somasundara, A. Ramamoorthy, and M. B. Srivastava, “Mobile Element Scheduling for Efficient Data Collection in Wireless Sensor Networks with Dynamic Deadlines,” in Proceedings of IEEE International Real-Time Systems Symposium 2004(RTSS04), pp. 296-305, Washington DC USA, 2004
[10] A. A. Somasundara, A. Ramamoorthy, and M. B. Srivastava, “Mobile Element Scheduling with Dynamic Deadlines,” in IEEE Transactions on Mobile Computing 2007, Vol. 6, No. 4, pp.395-410, Piscataway, NJ, USA, Apr. 2007
[11] Y. Bi, J. Niu, L. Sun, W. Huangfum, and Y. Sun, “Moving Schemes for Mobile Sinks in Wireless Sensor Networks,” in Proceedings of Performance, Computing, and Communications Conference, pp. 101-108, May 2007
[12] Y. Gu, D. Bozdag, E. Ekici, Ozguner, F. Özgüner, and C.G. Lee, “Partitioning based mobile element scheduling in wireless sensor networks,” in Proceedings of Second Annual IEEE Communications Society Conference on Sensor and Ad Hoc Communications and Networks (SECON 2005), pp. 386-395, Santa Clara, California, USA, Sep. 2005.
[13] S. Acharya, R. Alonso, M. Franklin, and S. Zdonik, “Broadcast Disks: Data Management for Asymmetric Communication Environments,” in Proceedings of the ACM SIGMOD Conference, pp.199-210, San Jose, CA, May 1995
[14] T. H. Cormen, C. E. Leiserson, and R. L. Rivest, “Introduction to Algorithms,”in The MIT Press, 2002
[15] J. Bentley, “Fast algorithms for geometric traveling salesman problem,” in ORSA Journal on Computing, Vol. 4, No. 4, pp. 387–411, 1992.
[16] R. A. Finkel and J. L. Bentley, “Quad trees a data structure for retrieval on composite keys,” in Acta Informatica, Vol. 4, No. 1, pp. 1-9, 1 Mar. 1974
[17] M. Chen, T. Kwon, Y. Yuan, Y. Choi, and V. C.M. Leung, “Mobile Agent-Based Directed Diffusion in Wireless Sensor Networks,” in EURASIP Journal on Advances in Singal Procssing, Vol. 2007, No. 1, 13 pages, New York, USA, 2007
[18] M. Ma and Y. Yang, “Data Gathering in Wireless Sensor Network with Mobile Collectors,” in Parallel and Distributed Processing 2008(IPDPS2008), No. 14-18, pp. 1-9, Miami FL , 2008
[19] E. Shakshuki, X. Xing, and H. Malik, “Mobile Agent for Efficient Routing Among Source Nodes in Wireless Sensor Networks,” in Proceedings of International Conference on Autonomic and Autonomous Systems 2007(ICAS 07), pp .39-39, 2007
[20] Y. Tirta, Z. Li, Y.H. Lu, and S. Bagchi, “Efficient Collection of Sensor Data in Remote Fields Using Mobile Collectors,” in Proceedings of International Conference Computer Communications and Networks 2004(ICCCN 2004), pp. 515-519, Oct. 2004
[21] G. Xing, T. Wang, Z. Xie, and W. Jia, “Rendezvous Planning in Wireless Sensor Networks with Mobile Element,” in IEEE Transactions on Mobile Computing 2008, Vol. 7, No. 12, pp. 1430-1443, Dec. 2008