臺灣博碩士論文加值系統

由於無線通訊提供使用上的彈性和便利性，近年無線通訊儼然形成一股潮流。過去這幾年許多研究特別針對一種不需固有的基礎架構的多點跳躍式網路感到興趣。這種各行動點之間就能夠互相通訊的網路，可以和現有的蜂巢式細胞行動通訊系統搭配，延伸通訊的涵蓋範圍。
衰減和干擾是無線環境既有的問題，除此之外，隱藏點 (hidden node) 問題是在無線多點跳躍式網路所發生的特有干擾現象。IEEE 802.11是無線區域網路的標準，它定義了分散式協調功能 (DCF) 的機制， 可以應用在多點跳躍式網路上。本篇論文主要分析IEEE 802.11 DCF 用在媒介存取控制 (MAC) 機制上的效能分析。我們以不同的載波偵測範圍和不同的訊框資料長度來討論在無線多點跳躍式網路的隱藏點和曝露點 (exposed node) 的問題。

In recent years there has been an increasing trend toward wireless communications. Wireless communication networks are gaining special interest as they provide flexibility and convenience. Much research has focused on one kind of multi-hop ad hoc wireless networks where there is no stationary infrastructure, such as a base station, and nodes communicate with each other through other mobile nodes. It may work together with the existing mobile cellular system to extend the communication coverage.
In a wireless environment, there are the inherent fading and
interference problems. The hidden node problem is a unique
interference phenomenon in wireless multi-hop networks. IEEE
802.11 is a wireless LAN standard which defines a DCF mechanism
that may be used in a multi-hop networks. This thesis work
analyzes the throughput of a wireless multi-hop network when the
IEEE 802.11 DCF mechanism is used as the MAC access scheme. We
discuss the hidden node problem and the exposed node problem when different carrier sense ranges and packet sizes are adopted in a multi-hop WLAN.

Table of Contents iv
List of Tables vi
List of Figures vii
Abstract x
1 Introduction 1
2 IEEE 802.11 DCF 6
2.1 CarrierSenseMechanism.........................6
2.1.1 PhysicalCarrierSense ......................7
2.1.2 VirtualCarrierSense.......................7
2.2 RandomBacko Time ..........................9
2.3 DCF Access Procedure ..........................11
3 Mathematical Analysis 13
3.1 OverviewoftheSingle-hopAnalysis...................13
3.1.1 Packet Transmission Probability .................13
3.1.2 Throughput Analysis .......................16
3.2 MultihopNetworkAnalysis .......................17
3.3 Calculation of Equilibrium τ .......................21
3.4 TheAnalyticalResult ..........................21
4 Simulation study 24
4.1 NS-2Introduction.............................24
4.2 SimulationModel.............................26
4.3 TheSimulationResult ..........................27
5 Multihop Topology in One Dimension 32
5.1 Three Baseline Connection Patterns with Four Nodes .........32
5.2 Three Transmission Pairs in One-Dimensional Topology ........47
6 Conclusions 55
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