無線感測網路(wireless sensor network；WSN)是由多個感測節點所組成的網路型態，IEEE 802.15.4 標準定義了低速率無線個人區域網路之規範，相當適合於無線感測網路之應用。IEEE 802.15.4標準可選擇性的使用免競爭週期(contention-free period；CFP)來傳送資料，使得無線感測網路於負載較高或需服務品質要求(quality of service；QoS)時，傳輸間所造成的碰撞機率減少，進而提升整體網路的有效流量。
IEEE 802.15.4標準中所定義的免競爭週期部份，感測節點使用免競爭的方式進行資料的傳輸，但此種方式是以單位時槽為基本的配置單位，故容易發生部份頻寬未使用而導致浪費的問題。此種問題於低網路負載中更為明顯，且隨著超碼框級數(superframe order；SO)值漸增，上述的現象將更加嚴重。
為了解決免競爭週期頻寬浪費的問題，本論文提出了有效保證時槽配置機制(efficient mechanism for GTS allocation；EMGA)，本機制可有效提升感測節點在免競爭週期內傳送資料時，保證時槽之使用率。如此，可明顯改善整體網路的效能。由模擬結果可知，本論文之機制與IEEE 802.15.4標準及新保證時槽配置機制之文章相較下，在整體網路之有效產能和免競爭週期的使用率都有大幅的提升，且配置的保證時槽中由於頻寬未使用而導致浪費的問題也將減少。

Wireless sensor network (WSN) is composed of many sensor nodes. IEEE 802.15.4 standard defines some specifications for low-rate wireless personal area networks (WPAN), and it can apply in WSN. IEEE 802.15.4 standard can optionally use contention-free period (CFP) to transmit data. CFP can reduce the probability of collision from transmission and promote overall goodput, when WSN is heavy-loaded or need quality of service (QoS).
IEEE 802.15.4 standard defines the portion of CFP, so sensor nodes will transmit data without contention. However, CFP allocate guaranteed time slots (GTSs) based on unit time slot, and then CFP shall have the waste problem because the partial bandwidth has not been used. This problem is more obvious in the low-loaded network, and when the value of superframe order (SO) gradually increases, which results in the partial bandwidth has not been used, so waste problem will become worse.
In order to solve the bandwidth waste of CFP, we propose efficient mechanism for GTS allocation (EMGA). This mechanism can promote utilization of GTSs when sensor nodes transmit data in CFP. Thus, GTSs can promote utilization of CFP and improve overall network’s efficiency. By simulations, we compare our mechanism with IEEE 802.15.4 standard and a new GTS allocation scheme, the goodput and utilization of CFP are promoted a lot in overall network, and the waste portion of GTS’s bandwidth is also reduced.

[1] F. Bouabdallah, N. Bouabdallah, R. Boutaba, “On Balancing Energy Consumption in Wireless Sensor Networks,” IEEE Transactions on Vehicular Technology, Vol. 58, issue 6, pp.2909-2924, July 2009.
[2] D. Puccinelli, M. Haenggi, “Wireless Sensor Networks : Applications and Challenges of Ubiquitous Sensing,” IEEE Circuit and Systems Magazine, Vol. 5, issue 3, pp. 19-31, 2005.
[3] M. Ulema, “Wireless sensor networks: architectures, protocals , and management,” in Proceeding of Network Operations and Management Symposium’04, Vol. 1, pp. 931, April 2004.
[4] M. A. M. Vieira, D. C. S. Junior, “Survey on Wireless Sensor Network Devices,” in Proceeding of Emerging Technologies and Factory Automation’03, Vol. 1, pp. 537-544, September 2003.
[5] J. L. Wong, M. Potkonjak, “Search in sensor networks : challenges, techniques, and applications,” in Proceeding of Acoustics, Speech, and Signal Processing, Vol. 4, pp. 3752-3755, 2002.
[6] D. Digon, N. Medrano, B. Calvo, M. T. Sanz, S. Celma, “Practical experience for designing a power-efficient wireless sensor network,” in Proceeding of EAEEIE Annual Conference’08, pp. 118-122, June-July 2008.
[7] H. Bai, M. Atiquzzaman, D. Lilja, “Wireless Sensor Network for Aircraft Health Monitoring,” in Proceeding of Broadband Networks’04, pp. 748-750, October 2004.
[8] D. Steere, A. Baptista, D. McNamee, C. Pu, J. Walpole, “Research challenges in environmental observation and forecasting systems,” in Proceeding of ACM/IEEE MOBICOM Conference, Boston, pp. 292-299, August 2000.
[9] J. A. Guierrez, “On the use of IEEE 802.15.4 to enable wireless sensor networks in building automation,” in Proceeding of IEEE PIMRC’04, Vol. 3, pp. 1869-1869, September 2004.
[10] L. Q. Zhuang, K. M. Goh, J. B. Zhang, “The wireless sensor networks for factory automation : Issue and challenges,” in Proceeding of Emerging Technologies & Factory Automation’07, pp. 141-148, September 2007.
[11] J. J. Evans, “Wireless sensor networks in electrical manufacturing,” in Proceeding of Electrical Insulation Conference and Electrical Manufacturing Expo, pp. 460-465, October 2005.
[12] K. Sha, W. Shi, O. Watkins, “Using Wireless Sensor Networks for Fire Rescue Applications : Requirements and Challenges,” in Proceeding of Electro/information Technology, pp. 239-244, May 2006.
[13] Hu. Jingtao, “The Application of Wireless Sensor Networks to In-Service Motor Monitoring and Energy Management,” in Proceeding of Intelligent Networks and Intelligent Systems, 2008. ICINIS’08, pp. 165-169, November 2008.
[14] Shao-Yen Tseng, Chung-Han Tsai, Yu-Sheng Lai, Wai-Chi Fang, “A wireless biomedical sensor network using IEEE802.15.4,” in Proceeding of Life Science Systems and Applications Workshop, 2009. LiSSA 2009, IEEE/NIH, pp. 183-186, April 2009.
[15] S. Misra, V. Tiwari, M. Obaidat, “Lacas: learning automata-based congestion avoidance scheme for healthcare wireless sensor networks,” IEEE Journal on Selected Areas in Communications, Vol. 27, issue 4, pp. 466-479 , May 2009.
[16] L. Schwiebert, S. K. S. Gupta, J. Weinmann, “Research challenges in wireless networks of biomedical sensors,” in Proceeding of ACM/IEEE MOBICOM Conference, pp. 151-165, 2001
[17] C. L. Yau, W. Y. Chung, “IEEE 802.15.4 Wireless Mobile Application for Healthcare System,” in Proceeding of Convergence Information Technology, 2007, pp. 1433-1438, November 2007.
[18] IEEE 802 Working Group, “Standard for Part 15.4: Wireless Medium Access Control(MAC) and Physical(PHY) Specifications for Low Rate Wireless Personal Area Networks(LR-WPANs),” ANSI/IEEE 802.15.4, October 2003.
[19] IEEE 802 Working Group, “Standard for Part 15.4: Wireless Medium Access Control(MAC) and Physical(PHY) Specifications for Low Rate Wireless Personal Area Networks(LR-WPANs),” ANSI/IEEE 802.15.4, September 2006.
[20] G. Lu, B. Krishnamachari, C. S. Raghavendra, “Performance evaluation of the IEEE 802.15.4 MAC for low-rate low power wireless Networks,” in Proceeding of IEEE IPCCC, pp. 701-706, April 2004.
[21] J. A. Gutierrez, M. Naeve, E. Callaway, M. Bourgeois, V. Mitter, B. Heile, “IEEE 802.15.4 : A Developing Standard for Low-Power Low-Cost Wireless Personal Area Networks,” IEEE Network Magazine, Vol. 15, issue 4, pp. 12-19, September-October 2001.
[22] J. S. Lee, “An Experiment on Performance Study of IEEE 802.15.4 Wireless Networks,” in Proceeding of Emerging Technologies and Factory Automation, 2005. ETFA 2005. 10th, Vol. 2, pp. 451-458, September 2005.
[23] J. T. Adams, “An Introduction to IEEE STD 802.15.4,” in Proceeding of Aerospace Conference, March 2006.
[24] Tae Rim Park, M. J. Lee, “Power saving algorithms for wireless sensor networks on IEEE 802.15.4,” IEEE Communications Magazine, Vol. 46, pp.148-155, June 2008.
[25] S. Wielens, M. Galetzka, P. Schneider, “Design support for Wireless Sensor Networks based on the IEEE 802.15.4 standard,” in Proceeding of Personal, Indoor and Mobile Radio Communications, 2008. PIMRC 2008, pp. 1-5, September 2008.
[26] A. Koubaa, M. Alves, E. Tovar, “i-GAME: an implicit GTS allocation mechanism in IEEE 802.15.4 for time-sensitive wireless sensor networks,” in Proceeding of the 18th Euromicro Conference on Real-Time Systems (ECRTS’06), pp. 183-192, 2006
[27] Liang Cheng, A. G. Bourgeois, Xin Zhang “A new GTS allocation scheme for IEEE 802.15.4 networks with improved bandwidth utilization,” in Proceeding of Communications and Information Technologies, 2007. ISCIT’07, pp. 1143-1148, October 2007.
[28] Liang Cheng, A. G. Bourgeois, Xin Zhang, “A Performance Comparison Study of GTS Allocation Schemes in IEEE 802.15.4,” in Proceeding of Future Generation Communication and Networking (FGCN 2007), Vol. 2, pp. 356-361, December 2007.
[29] Liang Cheng, A.G. Bourgeois, “Energy efficiency of different data transmission methods in IEEE 802.15.4: study and improvement,” in Proceeding of Wireless Pervasive Computing, 2007. ISWPC’07, pp. 395-400, February 2007.
[30] Amitabh Mishra, Chewoo Na, Dwayne Rosenburgh, “On Scheduling Guaranteed Time Slots for Time Sensitive Transactions in IEEE 802.15.4 Networks,” in Proceeding of Military Communications Conference, 2007. MILCOM 2007, PP. 1-7, October 2007.
[31] Yu-Kai Huang, Ai-Chun Pang, Tei-Wei Kuo, “AGA: Adaptive GTS Allocation with Low Latency and Fairness Considerations for IEEE 802.15.4,” IEEE Communications Magazine, Vol. 9, pp. 3929-3934, June 2006.
[32] Yu-Kai Huang, Ai-Chun Pang, Hui-Nien Hung, “An Adaptive GTS Allocation Scheme for IEEE 802.15.4,” IEEE Transactions on Parallel and Distributed Systems, Vol. 19, issue 5, pp. 641-651, May 2008.
[33] Seong-eun Yoo, Daeyoung Kim, Minh-Long Pham, Yoonmee Doh, Eunchang Choi, Jae-doo Huh, “Scheduling support for guaranteed time services in IEEE 802.15.4 low rate WPAN,” in Proceeding of the 11th IEEE International Conference on Embedded and Real-Time Computing Systems and Applications (RTCSA’05), pp. 400-406, August 2005.