無線區域網路上傳輸多媒體資料是一個熱門且有急迫需要的一個重要課題。高速無線區域網路挾帶著他安裝容易，低成本，移動性，高頻寬的優勢，已經被廣泛應用在辦公室及校園之中；而多媒體資料的應用及在網路上的傳輸的需求又日趨重要，如何在高速無線區域網路上有效地傳送多媒體資料流就歸結到如何設計一個有提供品質保證服務的無線媒體存取控制層 。
在無線區域網路的標準方面，我們採用的是IEEE 所制訂的802.11。其中媒體存取控制協定所制訂的PCF ( Point Coordination Function )可以用來傳送有時間性限制的資料，如一些即時性的資料，但以往的研究顯示在傳送聲音的效能不彰，而且也只有討論聲音傳送的效能而已，並沒有討論到影像傳送的問題。
在我的論文中，我們採用了演算法來達到以更有效率的方法來傳送異質性資料(影像，聲音，一般性資料)的混合式傳輸，透過佇列的管理(Queue Management)以符合影像的高頻寬需求，透過輪詢表單的管理(Polling list management)來使傳送聲音時更有效地使用有限的頻寬。結果證明用我們的方式比在規格中所制訂原始的方式還更適合來傳送混合適的多媒體資料。

In order to grapple with the continuously increasing demand on the multimedia traffic over high speed wireless LAN, we need a QoS-oriented MAC for wireless multimedia system.
The IEEE 802.11's PCF is an optional capability, which is connection-oriented, and provides contention-free service, but some papers have proved that it is not efficient when use PCF to transmit voice. And there are no any efficient bandwidth allocation scheme for more high bandwidth requirement source like video in PCF.
In this thesis, we will propose a efficient centralized scheduled access MAC approach in IEEE 802.11 to satisfy heterogeneous traffic mix. There are two main algorithms to achieve the goal, queue management algorithm for downlink and uplink to satisfy video traffic's high bandwidth requirement, polling list management method enhance the efficiency of the polling scheme for transmitting voice traffic.
We evaluate the system performance by the network simulator OPNET, we use the MPEG-1 and ITU G.711 PCM standard as the video and voice traffic . The result shows that the centralized scheduled access MAC approach we propose has excellent efficient and compelling performance.

Contents
Chaper1 Introduction 9
1.1 Background 9
1.2 Motivation 10
1.3 Objective 12
Chapter 2 Wireless Medium Access Control(MAC) Protocols 13
2.1 ALOHA 13
2.2 Carrier Sense Multiple Access(CSMA) 14
2.3 IEEE 802.11 14
2.3.1 The Distributed Coordination Function 17
2.3.2 Point coordination Function 18
2.3.3 Real-time Medium Access Control (MAC) Protocols 19
2.4 Traffic and Channel Models 22
2.4.1 Traffic Models 22
2.4.2 Channel Models 23
2.5 Related research Efforts 23
2.5.1 Voice over IEEE 802.11 schemes 24
2.5.2 Performance Comparison 25
2.5.3 Summary 26
Chapter 3 Objectives and Methodology 28
3.1 Problem Definition 28
3.2 Objectives 29
3.3 Methodology delineation 30
3.3.1 Remote Deficit Round-robin scheme 30
3.2.2 Polling List management 34
Chaper 4 Simulation Model 35
4.1 Traffic Models 37
4.2 System parameters 39
4.2.1 Boundary conditions 39
4.3 Result 42
Chapter 5 Conclusion and future work
Reference 50

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