1997年國際電機電子工程師學會訂定了第一個無線區域網路標準IEEE 802.11，自此以來，無線通訊技術受到各方廣泛地研究。其中媒體（或媒介）存取控制（Medium Access Control，MAC）協定扮演舉足輕重的角色，左右整體網路效能之優劣。因此，MAC協定的改良與設計一直是多年來熱門的研究議題。另外，能源效率與能源管理亦是無線網路中相當重要的研究議題。尤其在無線感測網路中，大部分的感測節點都仰賴有限的電力（如電池），唯有調整適當的無線發射功率才可兼顧整體網路的連結性與延長感測節點的生命週期。
在IEEE 802.11無線區域網路標準中，以競爭模式為基礎的Distributed Coordination Function（DCF）最令人詬病的問題在於嚴峻的封包碰撞機率導致傳輸效能不彰、系統容量受限。而以輪詢模式為基礎的Point Coordination Function（PCF）雖然可達到較高的系統容量，但在系統負載度低的情況下，其效能卻又不如DCF。本論文第一部份以排隊理論M/G/1分析DCF及PCF於各種不同系統負載度下的效能，所分析的指標包含封包延遲時間、系統容量等。隨之提出Adaptive Coordination Function（ACF）根據數理分析結果，動態地切換使用DCF或PCF，使系統效能處於相對較佳的狀態。
理論上，ACF可根據數理分析的結果動態地切換DCF/PCF，但實際上確過於複雜且面臨諸多執行上的困難，於是本論文第二部份進一步研發簡潔有效的DCF/PCF動態切換技術。受物理光學波粒二象性（Wave-Particle Duality）的啟發，我們提出一套競爭/輪詢雙模並存協同傳輸協定（Contention-Polling Duality Coordination Function，CPDCF）。該協定利用polling ACK邀請指定的節點進行封包傳送，受邀者不需要進行任何的競爭程序即可傳送封包。在系統負載度低的情況下，CPDCF明顯地表現出DCF的特性。當系統負載度逐漸提升時，CPDCF自動地傾向PCF的特性。我們將CPDCF的概念導入並成功地改善IEEE 802.11e Enhanced Distributed Channel Access（EDCA）之效能。此協定已被驗證為實際可行、有效、並且容易與廣泛以DCF為基礎的無線通訊設備進行整合。
在封包傳送的過程當中，使用過大的發射功率不但耗電且容易造成其他非接收者的干擾。理想的情況為使用足夠的發射功率恰使接收者可正確地收到封包，本論文的第三部份針對無線網路的節能議題，提出一套多層次功率調節（Multilevel Power Adjustment，MLPA）機制。藉由多層次發射功率的使用，降低平均發射功率，達到節能的效果。所建立的數理模型可針對k層次功率調節（k-LPA）機制於不同的無線訊號衰減係數（γ）下，計算各個層次所對應的發射功率，以達到平均發射功率之最小化。
本論文所提出的CPDCF協定與MLPA機制皆經過完整的網路模擬（NS-2）、實驗、與數理分析，驗證其正確性與可行性。整體而言，本論文的貢獻可作為高效、節能無線網路的技術支撐，適用於廣泛的無線區域網路及無線感測網路。

The first standard of wireless local area network (WLAN), IEEE 802.11, was published in 1997. Since then, wireless communication technologies are widely discussed and studied. The Medium Access Control (MAC) protocol plays a significant role determining the performance of WLAN. In the last decade, the MAC protocol improvement and design have become hot research issues. Besides, the energy efficiency and energy management are important to wireless communication technology. In wireless sensor network (WSN), most sensor nodes are restricted to limited energy source, e.g. battery. Energy conservation and power control have become critical issues to prolong the node life-time while maintaining the network connectivity.
The IEEE 802.11 Distributed Coordination Function (DCF) suffers from serious collision probability under heavy-load condition. Thus the performance is degraded and the system capacity is reduced. The Point Coordination Function (PCF) can achieve a better performance in terms of saturation throughput, but under low-load condition, the performance in terms of delay is worse than that of DCF. The first work of this dissertation is to apply M/G/1 queuing model to analyze the performance of DCF and PCF under various load condition. The input variables are: the number of stations, packet arrival rate, packet payload size, and effective channel bit rate. The performance metrics include packet queuing delay, packet end-to-end delay, and saturation throughput. Moreover, the Adaptive Coordination Function (ACF) is proposed to adaptively invoke DCF or PCF according to the numerical results of our analytical model.
The second work is to research and develop a practical MAC protocol to take advantage of DCF and PCF. Inspired by the phenomenon of Wave-Particle Duality, we propose a novel coordination function called Contention-Polling Duality Coordination Function (CPDCF) to enhance the performance of DCF-based MAC protocol. A polling ACK mechanism is introduced to invite a designated station to transmit without performing any contention process. By eliminating collisions and preventing waste from idle backoff slots, the system capacity is increased effectively. Under low-load condition, the CPDCF is similar to the DCF. While traffic load increased, the CPDCF trends to the PCF. We also introduce the CPDCF to enhance the performance of IEEE 802.11e Enhanced Distributed Channel Access (EDCA). The proposed CPDCF is quite feasible, effective, and can be easily integrated with widespread DCF-based devices.
Finally, we study the energy conservation issue. Transmitting with excess power not only reduces the node lifetime, but also introduces immoderate interference in the shared radio channel. It is ideal to send packets with suitable transmission power. We propose a Multilevel Power Adjustment (MLPA) mechanism for WSNs to prolong the individual node lifetime and the overall network lifetime. Intuitively, the energy conservation is achieved by reducing the average transmission power. We build a mathematical model to minimize the average power for k distinct power levels (k-LPA) within various wireless environments (various path loss exponent γ). The optimal power configuration is derived as well.
In this dissertation, both proposed CPDCF protocol and MLPA mechanism are verified via extensive simulations and mathematical analyses. Overall speaking, the dissertation contributes the technical and theoretical support for developing wireless networks (WLANs and WSNs) with high-performance and low power consumption.

[AKK+01] S. Agarwal, R.H. Katz, S.V. Krishnamurthy, and S.K. Dao, “Distributed Power Control in Ad-Hoc Wireless Networks,” Proc. IEEE PIMRC, vol. 2, pp. 59-66, Sep. 2001.
[ASI] Agere Systems Inc., “WaveLAN 802.11b Chipset for Standard Form Factors,” Preliminary Product Brief, Dec. 2002.
[BDM99] R.O. Baldwin, N.J.I. Davis, and S.F. Midkiff, “A Real-Time Medium Access Control Protocol for Ad Hoc Wireless Local Area Networks,” ACM Mobile Computing and Communication Review, vol. 3, no. 2, pp. 20-27, Apr. 1999.
[BFO96] G. Bianchi, L. Fratta, and M. Oliveri, “Performance Evaluation and Enhancement of the CSMA/CA MAC Protocol for 802.11 Wireless LANs,” Proc. IEEE PIMRC, pp. 407-411, Oct. 1996.
[Bia98] G. Bianchi, “IEEE 802.11 Saturation Throughput Analysis,” IEEE Communications Letters, vol. 2, no. 12, pp. 318-320, Dec. 1998.
[Bia00] G. Bianchi, “Performance Analysis of the IEEE 802.11 Distributed Coordination Function,” IEEE JSAC, vol. 18, no. 3, pp. 535-547, Mar. 2000.
[Bin99] B. Bing, “Measured Performance of the IEEE 802.11 Wireless LAN,” Proc. of Conference on Local Computer Networks, LCN’99, pp. 34-42, Oct. 1999.
[BT03] G. Bianchi and I. Tinnirello, “Kalman Filter Estimation of the Number of Competing Terminals in an IEEE 802.11 Network,” Proc. IEEE INFOCOM, vol. 2, pp. 844-852, Apr. 2003.
[BZ02] C. Bettstetter and J. Zangl, “How to Achieve a Connected Ad Hoc Network with Homogeneous Range Assignment: An Analytical Study with Consideration of Border Effects,” Proc. IEEE Int’l Workshop Mobile and Wireless Comm. Network, pp. 125-129, Sep. 2002.
[CAS06] Chipcon AS, “CC2420 2.4 GHz IEEE 802.15.4/ZigBee-ready RF Transceiver,” Data Sheet, Rev. 1.4, 2006.
[CCG00] F. Cali, M. Conti, and E. Gregori, “IEEE 802.11 Protocol: Design and Performance Evaluation of an Adaptive Backoff Mechanism,” IEEE JSAC, vol. 18, no. 9, Sep. 2000.
[CCG00] F. Cali, M. Conti, and E. Gregori, “Dynamic Tuning of the IEEE 802.11 Protocol to Achieve a Theoretical Throughput Limit,” IEEE/ACM Transactions on Networking, vol. 8, no. 6, pp. 785-799, Dec. 2000.
[CG95] H.S. Chhaya and S. Gupta, “Throughput and Fairness Properties of Asynchronous Data Transfer Methods in the IEEE 802.11 MAC Protocol,” Proc. IEEE PIMRC, vol. 2, pp. 613-617, 1995.
[CG97] H.S. Chhaya and S. Gupta, “Performance Modeling of Asynchronous Data Transfer Methods of IEEE 802.11 MAC Protocols,” Wireless Networks, vol. 3, pp. 217-234, 1997.
[CL04] H. Chen and Y. Li, “Performance Model of IEEE 802.11 DCF with Variable Packet Length,” IEEE Communications Letters, vol. 8, no. 3, Mar. 2004.
[Chi06] Chipcon AS, “A True System-on-Chip Solution for 2.4 GHz IEEE 802.15.4/ZigBee,” Data Sheet, Rev. 2.01, 2006.
[Cho01] S. Choi, “PCF vs. DCF: Limitations and Trends,” IEEE 802.11-01/54, Jan. 2001.
[CS03] R.L. Cruz and A.V. Santhanam, “Optimal Routing, Link Scheduling and Power Control in Multi-Hop Wireless Networks,” Proc. IEEE INFOCOM, vol. 1, pp. 702-711, Apr. 2003.
[CYC+05] J. Choi, J. Yoo, S. Choi, and C. Kim, “EBA: An Enhancement of the IEEE 802.11 DCF via Distributed Reservation,” IEEE Transactions on Mobile Computing, vol. 4, no. 4, Jul. 2005.
[DW03] Q. Dai and J. Wu, “Computation of Minimal Uniform Transmission Power in Ad Hoc Wireless Networks,” Proc. IEEE ICDCS, pp. 680-684, May 2003.
[EE04] T. Elbatt and A. Ephremides, “Joint Scheduling and Power Control for Wireless Ad Hoc Networks,” IEEE Transactions on Wireless Communications, vol. 3, no. 1, pp. 74-85, Jan. 2004.
[EGH+99] D. Estrin, R. Govindan, J. Heidemann, and S. Kumar, “Next Century Challenges: Scalable Coordination in Sensor Networks,” Proc. ACM/IEEE MobiCom, pp. 263-270, Aug. 1999.
[Est02] D. Estrin, “Embedded Networked Sensing Research: Emerging Systems Challenges,” NSF Workshop on Distributed Communications and Signal Processing, Dec. 2002.
[GC07] J. Gomez and A.T. Campbell, “Variable-Range Transmission Power Control in Wireless Ad Hoc Networks”, IEEE Transactions on Mobile Computing, vol. 6, no. 1, pp. 87-99, Jan. 2007.
[GY07] S. Guo and O. Yang, “Localized Operations for Distributed Minimum Energy Multicast Algorithm in Mobile Ad Hoc Networks,” IEEE Transactions on Parallel and Distributed Systems, vol. 18, no. 2, pp. 186-198, Feb. 2007.
[HS95] H.S. Chhaya and S. Gupta, “Throughput and Fairness Properties of Asynchronous Data Transfer Methods in the IEEE 802.11 MAC Protocol,” Proc. IEEE PIMRC, pp. 613-617, vol. 2, 1995.
[IEE99] IEEE Standard for Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specification, Aug. 1999.
[IEE01] IEEE Std. 802.11e/D2.0a, “Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications: Medium Access Control (MAC) Enhancements for Quality of Service (QoS),” Nov. 2001.
[JCH84] R. Jain, D.-M. Chiu, and W. Hawe, “A Quantitative Measure of Fairness and Discrimination for Resource Allocation in Shared Systems,” Digital Equipment Corporation, Technical Report TR-301, Sep. 1984.
[PK02] K. Pahlavan, and P. Krishnamurthy, “Principles of Wireless Networks,” Prentice Hall PTR, 2002.
[KT75] L. Kleinrock and F. Tobagi, “Packet Switching in Radio Channels, Part II – The Hidden Terminal Problem in Carrier Sense Multiple Access and the Busy Tone Solution,” IEEE Transactions on Communications, vol. 23, no. 12, pp. 1417-1433, Dec. 1975.
[LZZ+06] S. Lin, J. Zang, G. Zhou, L. Gu, T. He, and J.A. Stankovic, “ATPC: Adaptive Transmission Power Control for Wireless Sensor Networks,” ACM Sensys, Nov. 2006.
[MCM+02] S. Mangold, S. Choi, P. May, O. Klein, G. Hiertz, and L. Stibor, “IEEE 802.11e Wireless LAN for Quality of Service,” Proc. European Wireless, pp. 32-39, Feb. 2002.
[NKS+02] S. Narayanaswamy, V. Kawadia, R.S. Sreenivas, and P.R. Kumar, “Power Control in Ad-Hoc Networks: Theory, Architecture, Algorithm and Implementation of the COMPOW Protocol,” Proc. European Wireless, pp. 156-162, Feb. 2002.
[NS] The Network Simulator – NS-2. http://www.isi.edu/nsnam/ns/.
[NV07] C.-F. Natali and N.H. Vaidya, “Expanding Horizon and Capture Effect in RFID Systems,” Technical Report, Wireless Networking Group, Coordinated Science Laboratory, University of Illinois at Urbana-Champaign, Dec. 2007.
[PFT06] S. Panichpapiboon, G. Ferrari, and O.K. Tonguz, “Optimal Transmit Power in Wireless Sensor Networks,” IEEE Transactions on Mobile Computing, vol. 5, no. 10, pp. 1432-1447, Oct. 2006.
[Rap02] T.S. Rappaport, “Wireless Communications: Principles and Practice,” Prentice Hall PTR, 2002.
[RR00] R. Ramanathan and R. Rosales-Hain, “Topology Control of Multihop Wireless Networks Using Transmit Power Adjustment,” Proc. IEEE INFOCOM, vol. 2, pp. 404-413, Mar. 2000.
[RM99] V. Rodoplu and T.H. Meng, “Minimum Energy Mobile Wireless Networks,” IEEE JSAC, vol. 17, no. 8, pp. 1333-1344, Aug. 1999.
[SK99] J.L. Sobrinho and A.S. Krishnakumar, “Quality-of-Service in Ad Hoc Carrier Sense Multiple Access Wireless Networks,” IEEE JSAC, vol. 17, no. 8, pp. 1353-1368, Aug. 1999.
[TC01] Y.C. Tay and K.C. Chua, “A Capacity Analysis for IEEE 802.11 MAC Protocol,” Wireless Networks, vol. 7, no. 2, pp. 159-171, Mar. 2001.
[TC04] C.-C. Tseng and K.-C. Chen, “Power Efficient Topology Control in Wireless Ad Hoc Networks,” Proc. IEEE WCNC, vol. 1, pp. 610-615, Mar. 2004.
[Tak91] H. Takagi, “Queueing Analysis,” in Vacation and Priority Systems. Amsterdam, the Netherlands: North-Holland, 1991.
[WEH+06] S. Wiethoelter, M. Emmelmann, C. Hoene, and A. Wolisz, “TKN EDCA Model for ns-2,” Telecommunication Networks Group, Technical University Berlin, Technical Report TKN-06-003, Jun. 2006.
[WRM] Wolfram Research: Mathematica. http://www.worlfram.com/.
[Xu02] Xu et al, “Revealing the Problems with 802.11 Medium Access Protocol in Multi-hop Wireless Ad Hoc Networks,” Computer Networks, vol. 38, pp. 531-548, Mar. 2002.
[ZA02] E. Ziouva and T. Antonakopoulos, “CSMA/CA Performance under High Traffic Conditions: Throughput and Delay Analysis,” Computer Communications, vol. 25, pp. 313-321, Feb. 2002.