臺灣博碩士論文加值系統

數據資料傳輸在第三代行動通訊系統中，是一項重要的服務．第三代行動通訊系統提供不同的數據資料傳輸速率 (data transmission rate)，用以滿足不同需求的數據服務．例如語音訊號傳輸速率較低，而影像訊號對於傳輸速率則有較高的需求．
第三代行動通訊系統使用展頻 (Spread Spectrum) 與分碼多重接取 (CDMA) 的技術，每個使用者擁有相同的展頻頻寬．在此條件下，高傳輸速率的用戶所使用的展頻因子較小，導致於對抗干擾的能力降低．當用戶在遠離提供服務的基地台的同時，因受到其他同頻細胞發射的干擾逐漸增大，高傳輸率用戶的傳輸品質會較低傳輸率用戶者為差，甚至導致傳輸中斷的情況產生．由此可知，對於不同的資料傳輸率，所對應的細胞涵蓋範圍並不一樣．它們之間的關係，亦會由於各種環境與系統因素而有所變動．而當使用者在長距離使用高傳輸率的服務，不僅達不到服務品質，也會降低系統的容量．
在這篇論文中，我們主要利用系統模擬與數值分析方法，考慮第三代行動通訊系統之下行傳輸　(downlink transmission)，在可加性白高斯通道 (AWGN channel) 與雷利衰減通道 (Rayleigh fading channel) 中，去找出最大可提供資料傳輸率與細胞涵蓋範圍之間的關係．我們也針對各種影響因子，包括環境與系統的變數，分析其對於涵蓋範圍所產生的效應．在不影響精確度的前提下，我們也使用一些方法，用以簡化計算量．

Many data services are available in third-generation (3G) mobile communication systems and may have different data rates on transmission. It is important to maintain the link quality and performance when higher data rate is served. For example, real time video service is one of the services which require high data rate and high transmission quality. Unfortunately, the higher data rate we use, the lower processing gain we get, and fewer ability of anti-multiple- access-interference (MAI) we will have. Not only the processing gain, but also the carrier-to-interference ratio (CIR) will influence system performance. Simply speaking, when the CIR degrades due to either traveling away from the base-station (BS) or being shadowed by structures, the service rate must decrease to increase the processing gain for better link quality. By observing BER, we can discuss the relationship between propagation length and maximum available data rate under the forward link assumption for 3G systems. The results can be used to limit user’s data rates according to user’s positions. It is a helpful reference to resource management problems.

Abstract i
Contents ii
1 Introduction 1
2 System & Channel Models 4
2.1 System Model …………………………………………………………4
2.1.1 Assumptions and Simplifications on System Model …………6
2.2 Channel Model …………………………………………………………8
2.3 The Received Signal ……………………………………………………10
3 Review of Performance Calculations 11
3.1 Receiver Structure & Received Signal Statistics …………………………11
3.2 Review of BER Calculation Methods over An AWGN Channel …………13
3.2.1 Central Limit Theorem Approximation …………………………14
3.2.1.1 The MAI Variance Expression …………………………14
3.2.1.2 Standard Gaussian Approximation …………………………15
3.2.1.3 Improved Gaussian Approximation &
Simplified Improved Gaussian Approximation …………16
3.2.2 The Exact BER Calculation for a DS/CDMA system over
AWGN Channel ………………………………………………19
3.3 Accuracy Comparison among BER Calculation Methods ………………21
4 Cell Coverage & Maximum Available Data Rate 27
4.1 Performance Calculations over Large Scale Fading Channel
Using CLT ………………………………………………………………27
4.1.1 Using SGA in Large Scale Fading ………………………………28
4.1.2 Using SIGA in Large Scale Fading ………………………………29
4.1.3 Representations for Distance Terms by …………31
4.2 Performance Calculations over Large & Small Scale Fading
Channel Using CLT ……………………………………………………35
4.2.1 Using SGA in Large & Small Scale Fading ……………………36
4.2.2 Using SIGA in Large & Small Scale Fading ……………………37
4.3 Relationship between Total Transmission Power and Noise Density ……39
4.3.1 Noise Raise Concept …………………………………………40
4.3.2 BER analyses using the noise raised factor representation ……41
4.4 Accuracy Comparison among BER Calculation Methods ………………42
4.4.1 Accuracy Comparison over Large Scale Fading Channel ……43
4.4.2 Accuracy Comparison over Large & Small Scale
Fading Channel ………………………………………………45
4.5 Summation of Lognormal Random Variables …………………………46
4.5.1 Review of The Moment Matching Methods ……………………46
4.5.1.1 Fenton-Wilkinson Method ………………………………47
4.5.2 Simplifications for SGA by Fenton-Wilkinson Method …………49
4.5.3 Accuracy for Moment Matching Method ……………………52
4.6 Cell Coverage And Maximum Available Data Rate ……………………53
4.6.1 Performance Gains for RAKE Combiner, Soft Handoff
and Coding ……………………………………………………54
4.6.2 Numerical Results ………………………………………………56
5 Discussions, Simulations & Numerical Results 64
5.1 Different Environment Parameters …………………………………………64
5.2 Variance of Data Rate ……………………………………………………68
5.3 Choosing Total Transmission Power ……………………………………72
5.4 Channel Reservation for High Data Rate Services …………………………75
6 Conclusion 80
Bibliography 81

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