臺灣博碩士論文加值系統

近幾年來，無線區域網路(wireless local area network)的發展已日趨成熟，各種無線區域網路的規格也相繼出現。無線網路的優點為不需經由實體的纜線連接，架線的成本可大大的減少。尤其在一些廣大且無基礎佈線的區域更能顯出無線網路的便利性。此外，具有無線網路功能的裝置更能夠享受在移動中使用的好處。無線網路的應用不僅僅是連上網際網路，更可以作為各種無線裝置的連通與通訊。因此，無線網路所帶來的好處和實用性將會對傳統的網路環境有一定的衝擊。然而，無線網路的瓶頸在於它的有限頻寬及易受干擾的特性，因此要達到對資料流(data flow)有服務保證品質(quality of service, QoS)和增加系統的生產率(throughput)，仍然有待更新的技術出現。
美國電機電子工程師協會(Institute of Electrical and Electronic Engineers，IEEE)的802委員會在1997年正式制定802.11無線區域網路的標準。在最初的制定中，所傳送的資料傳送速率為每秒鐘1百萬位元(Mbps)或2百萬位元，但隨著各種應用程式與需求的成長，每秒鐘2百萬位元的資料傳送速率逐漸不敷使用。1999年，IEEE 802.11a及IEEE 802.11b的規格相繼被提出。IEEE 802.11a為在5GHz頻帶的高速無線區域網路規格，其資料傳送速率最高可達每秒鐘54百萬位元；IEEE 802.11b為在2.4GHz頻帶的高速無線區域網路規格，其資料傳送速率可達每秒鐘11百萬位元。
在此論文中我們提出一個在IEEE 802.11無線區域網路的環境下使用以等級限定為基礎的媒體存取機制來提供服務等級區分(service differentiation)，並且更進一步達到降低擁塞度(congestion)及減少碰撞機率(collision probability)，提高整個系統的生產率及對即時性(real-time)資料支援短延遲(latency)和減少變異度(jitter)。
經由模擬實驗的結果顯示，所提出的方法無論在網路交通擁塞與否的情況下都能夠對即時性的資料流有效率的達到短延遲和減少變異度，並且能使得生產率有一定程度的改善。

The wireless access network with the capability for people to access information anytime and anywhere has attracted much attention in recent years. The IEEE 802.11 wireless local area network (WLAN) can offer high data rates through IEEE 802.11a and IEEE 802.11b technologies [5].
In this thesis, we emphasize how to improve the performance of the 802.11 MAC protocol. We present a Priority-Based Contention Control (PCC) scheme to well manage the contention for the medium among the wireless stations (STA) in the IEEE 802.11 wireless LAN, and, the PCC scheme has the following advantages: providing service differentiation among the traffic flows with different priorities and easing off the serious collisions in high traffic loads.

CHAPTER 1 INTRODUCTION
CHAPTER 2 RELATED WORKS AND BACKGROUND
2.1 IEEE 802.11 MAC Access Schemes
2.2 Real-Time Communication
2.3 Service Differentiation Schemes
2.3.1 Adaptive Backoff Contention Window Differentiation Approaches
2.3.2 Differential Inter-Frame Spaces (IFS) Differentiation Approaches
2.3.3 Differential Frame Size Differentiation Approaches
CHAPTER 3 PRIORITY-BASED CONTENTION CONTROL SCHEME
3.1 Modified RTS / CTS / MAC / ACK Frame Formats
3.2 AP Behavior
3.3 STA Behavior
3.4 Contention Resolution Scheme
3.5 Algorithms
3.5.1 Basic Access Algorithm
3.5.2 Collision Resolution Algorithm
3.6 Analysis
CHAPTER 4 SIMULATION EXPERIMENTS
4.1 Simulation Results for the Conventional IEEE 802.11 WLAN
4.2 Simulation Results and Discussion
CHAPTER 5 CONCLUSIONS AND FUTURE WORKS

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