目前Ad Hoc無線區域網路是一個在小區域範圍中相當方便的網路，不過由於存在著hidden terminal 及 exposed terminal 問題，發生封包碰撞的機率也相對地提高，因此容易造成頻道使用率不高的現象。也正因為如此，MAC層如何避免這些問題的發生，進而改善頻道的重用率就成為一個很關鍵的課題。目前已有一些相關的MAC協定被提出，例如：利用RTS / CTS機制為基礎的協定以及採用busy tone訊號的機制。
在我們這篇論文中，我們則是提出一個動態能量控制的機制，APC (Adjustable Power Control)。APC利用能量分層級方式為基礎，在配合每個工作站週期地廣播訊息收集到的資訊，期望傳送端資料傳遞時使用恰當的能量傳送，以不妨礙正在進行傳送的工作站為前提下，使封包可以在較為穩定的環境中傳送，避免封包之間產生碰撞。最後，透過模擬說明在同一時間內，APC的確可使多個工作站同時間使用頻道，提升頻道使用率。

In the present day, Ad Hoc wireless networks are quite convenient in a local area. But hidden terminal problems and exposed terminal problems exits in Ad Hoc networks. So how to avoid these problems and add channel bandwidth utilization efficiently in MAC (Medium Access Control) layer is a very critical topic. A number of MAC protocols have been presented to overcome these drawbacks, such as RTS / CTS – based and busy tone – based protocol.
In this paper, we proposed a dynamic power control scheme, Adjustable Power Control Protocol (APC). APC is based on the concept of power level with broadcasted message. The basic idea is sender should not interfere with other hosts’ going transmissions. Sender would use a suitable power level to send its data so as to overcome above problems. Our simulations show that the channel utilizations of APC is indeed increased in the same time.

Table of Contents……………………………………… i
List of Figures…………………………………………iii
List of Tables………………………………………… v

1.Introduction…………………………………………… 1

2.Background & Related works………………………… 5
2.1 Transmit Range……………………………………… 5
2.2 IEEE 802.11 Ad Hoc RTS/CTS-Based Protocols… 6
2.3 Power Control Routing for Ad Hoc Network…… 8
2.4 Channel Assignment………………………………… 9
2.4.1 Channel Hopping………………………………… 9
2.4.2 Multi-channel…………………………………… 10
2.5 Adaptive power control………………………… 10
2.5.1 PCMA…………………………………………………10
2.5.2 IBTPC……………………………………………… 11

3.Proposed Scheme……………………………………… 15
3.1 Assumptions………………………………………… 15
3.2 Power Level Table………………………………… 16
3.3 Adjust Power Control (APC)…………………… 18
3.4 Advantage…………………………………………… 28

4.Simulation…………………………………………… 29
4.1 Comparisons for three schemes……………… 29
4.2 Simulation Environment………………………… 29
4.3 Simulation Results……………………………… 31
4.3.1 Sessions and Collisions……………………… 31
4.3.2 Packet Arrival Rate…………………………… 35
4.3.3 Power……………………………………………… 36

5.Conclusion…………………………………………… 38

6.Reference……………………………………………… 39

[1]IEEE Standards Department, “Wireless LAN medium access control (MAC) and physical layer (PHY) specifications, IEEE standard 802.11-1997” 1997.

[2]Institution of Electrical and Electronic Engineers. Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications, Higher Speed Physical Layer Extension in the 2.4 GHz Band, 1999.

[3]K. Tsudaka, M. Kawahara, A. Matsumoto, and H. Okada, “Power control routing for multi hop wireless ad-hoc network,” IEEE GLOBECOM '01, vol. 5, pp. 2819 – 2824, 2001.

[4]J.P. Monks, V. Bharghavan, and W. Hwu, “A power controlled multiple access protocol for wireless packet networks,” IEEE INFOCOM. '01, vol.20, pp. 1 – 11, April 2001.

[5]S.-L. Wu, Y.-C. Tseng, and J.-P. Sheu, “Intelligent medium access for mobile ad hoc networks with busy tones and power control,” IEEE Journal on Selected Areas in Communications, vol.18, no.9, pp. 1647 – 1657, September 2000.

[6]Z.J. Haas and J. Deng, “Dual busy tone multiple access (DBTMA)-a multiple access control scheme for ad hoc networks,” IEEE Transactions on Communications, vol. 50, no. 6, pp. 975 – 985, Jun 2002.

[7]A. Lindgren and O. Schelen, “Infrastructured ad hoc networks,” In Proceedings of International Conference on Parallel Processing Workshops, pp. 64 – 70, August 2002.

[8]J.C. Cano and P. Manzoni, “A low power protocol to broadcast real-time data traffic in a clustered ad hoc network,” IEEE GLOBECOM '01, vol. 5, pp. 2916 – 2920, November 2001.

[9]A. Tzamaloukas and J.J. Garcia-Luna-Aceves, ”Channel-hopping multiple access,” IEEE International Conference on Communications, vol. 1, pp. 415 – 419, June 2000.

[10]M. Joa-Ng and I-Tai Lu, “Spread spectrum medium access protocol with collision avoidance in mobile ad-hoc wireless network,” In Proceedings of IEEE INFOCOM '99, vol. 2, pp. 776 – 783, March 1999.

[11]A. Nasipuri and S.R. Das, “Multichannel CSMA with signal power-based channel selection for multihop wireless networks,” IEEE VTS-Fall VTC 2000, vol. 1, pp. 211 – 218, September 2000.

[12]Bernhard H. Walke, “Mobile Radio Networks, Networking and Protocols,” WILEY, 2000.

[13]Ting-Chao Hou and Victor Li, “Transmission Range Control in Multihop Packet Radio Networks,” IEEE Transactions on Communications, vol. 34, no. 1, pp. 38 – 44, January 1986.

[14]T.A. ElBatt, S.V. Krishnamurthy, D. Connors, and S. Dao, “Power management for throughput enhancement in wireless ad-hoc networks,” 2000 IEEE International Conference on Communications, vol. 3, pp. 1506 – 1513, June 2000.

[15]Rong Zheng and R. Kravets, “On-demand power management for ad hoc networks,” IEEE INFOCOM ‘03, vol. 1, pp. 481 – 491, April 2003.