Abstract
在本篇論文中，我們提出了一個可以提供服務品質(Quality of Service)無線區域網路媒體存取控制的協定(Medium Access Control protocol)。在設計無線區域網路中的一個重要要求就是能夠經由一個有彈性而且有效率 的媒體存取控制協定，在存取無線電頻道時能提供多種的服務型態。我們所 提出的媒體存取控制協定能支援多種要求服務品質保證的資料，並且可以有 效率以及動態地對於要求即時傳輸的連線分配頻寬。另外對於封包的排程亦 具有相當的彈性。在負載較輕的時候，我們也能增加預約時槽(reservation slot)的大小以提高建立連線及上傳封包的機率。模擬結果主要著重於和舊有的方法相比較即時傳輸連線的頻寬使用率。由模擬結果得知我們的方法平均在一個訊框中減少了空時槽 (empty slots)的數 目以及不必要的碰撞次數。而對於相同的資料流來說，我們的方法也只須使 用比較少的頻寬來傳送。 隨著無線區域網路的快速發展，以及連接著高速有線網路的同時，無線通訊 不再只是侷限於語音的收送，而要能夠整合語音、影像等多媒體資料。因此 在設計一個無線區域網路時要能夠滿足日見增長的服務需求並且對於無線電 媒介能夠有效的利用。在設計無線區域網路有幾個主要目標: (1) 能提供多 種的服務型態，(2)對於這多種型態的服務能提高好的服務品質，(3) 和現 存及未來的有線高速網路能相容，(4) 行動終端機能有較低的價錢、複雜度 以及能源消耗，(5) 網路架構要具有效率以及可擴充性。 而其中一個無線網路設計的主要議題就是在無線電界面中要有一個有效率 的媒體存取控制的協定。這樣的協定應該要能支援所有的服務而且對於每個 連線可以保證所要求的服務品質，同時具有公平性，又能有效率且動態地分 配頻寬。過去有關這方面的研究大致可分為下列幾類，它們分別是以Frequency-Division Multiple Access (FDMA)，Code-Division Multiple Access(CDMA) ，Time-Division Multiple Access (TDMA)或者是以上上列 三種的組合做為基礎。在以FDMA為基礎的研究中，由於上傳及下傳的頻寬是固定的，因此對於要 動態調整頻寬的變速率連線來說，在上傳及下傳負載不平均時，使用FDMA有 上傳及下傳頻寬的限制是比較沒有效率的。另一方面在以CDMA為基礎的研究 中，使用CDMA會使得每條連線的peak bitrate限制較大，對於寬頻應用程 式來說是一項問題。而大部分過去的研究主要是以TDMA為基礎。主要是因為 它能動態的分配頻寬。使用TDMA時槽可根據現在的資料流量狀況來因需求而 分配頻寬。而我們所提出來的方法也是以TDMA為基礎。A key requirement of the radio access design in a wireless localarea network is the ability to accommodate a variety of servicetypes via flexible and efficient medium access control (MAC)protocols.In this thesis we proposed a medium access controlprotocol with QoS guaranteed for wireless local area network.This protocol supports heterogeneous traffic with QoS guaranteesand allocates bandwidth dynamically for real-time connections inan efficient way. A simulation study is performed that focus onthe performance of bandwidth utilization for real-time traffictransmissions. The simulation results show that the proposedscheme can reduce the number of empty slots and collisions in aframe and thus utilize the bandwidth more efficiently. Wirelesspersonal communication has become an important field of activityin telecommunications. With the rapid development of thecellular or personal communication devices such as notebookcomputers and mobile handsets.the PCN (Personal CommunicationNetworks) terminal will be much more than just a mobiletelephone in the future.It will be able to integrate voice,video and data, giving to users more flexible services tocommunicate with each other. In addition, connecting to theexisting wired high-speed network will make the support of suchservices even more essential. Accordingly, the design of awireless local area network that is able to satisfy theincreased service requirements and at the same time lead toefficient use of the radio medium are needed.The main designobjectives include: (1) flexible multiservice capability (voice,data and multimedia),(2) good QoS for many service types, (3)compatibility with future high-speed networks, (4) low terminalcost/complexity/power consumption, and (5) efficient, scalableand moderate cost network architecture. One of theimportant system design issues in wireless LAN is the design ofan efficient medium access control (MAC) protocol for the radiointerface. This protocol should be able to support all theservices with often-conflicting requirements, and guarantee therequired QoS for each connection. It should also guaranteefairness and allocate bandwidth efficiently and dynamically.Accordingly, an advanced traffic-scheduling scheme is requiredto fulfill these requirements.The existing proposed MACprotocols are based on Frequency-Division Multiple Access(FDMA), Code-Division Multiple Access (CDMA), Time-DivisionMultiple Access (TDMA), or combinations of these techniques. Therequirement of dynamic bandwidth allocation for variable-bit-rate connections and lack of available bandwidth make the use ofFDMA inefficient.On the other hand, the use of CDMA techniquelimits the peak bit rate of connections. The limitation of peakbit rates is a problem for broadband applications. Most of theprevious works in this area employ an adaptive TDMA (Time-Division Multiple Access) scheme, due to its flexibility inchannel allocation. With adaptive TDMA, time slots can beallocated on demand according to the traffic load. Afterreviewing some existing TDMA based MAC protocols and outliningtheir problems, we propose a MAC protocol with QoS for wirelesslocal area networks. The proposed MAC protocol is designed basedon the framing strategy. The protocol can support the QoSrequirements for real-time traffic in an efficient way. To dothis, a novel traffic-scheduling scheme named FSURT (FramingStrategy for Upink Real-time traffic Transmissions) which canimprove bandwidth utilization for uplink real-time traffictransmissions is developed. The remainder of this thesis isorganized as follows. In chapter 2, some existing TDMA MACprotocols are discussed. In chapter 3, we propose a MAC protocolwith our new scheme FSURT. In chapter 4 the performance of FSURTis demonstrated through simulation experiments. And in chapter 5we present conclusions.