臺灣博碩士論文加值系統

正交分頻多重接取系統於近年來廣泛應用於多種通訊系統上，有著非常重要的地位。但由於正交分頻多重接取系統是基於一項技術正交分頻多工的基礎所設計的，因此相同的，對於傳送端與接收端之間的載波頻率偏移非常的敏感，如果沒有順利的解決載波頻率偏移之問題，則會造成載波間干擾以及用戶間干擾等狀況，這些現象都將會使得整個通訊系統的品質與表現大幅下降。
本篇論文將基於現有的改善頻率偏移狀況的方法，延伸至多天線正交分頻多重接取系統，並提出利用多天線所估測之頻率偏移量之線性組合的方法來大幅改善頻率偏移所造成的影響。論文中也提出一些參數標準之參考值，可以僅透過簡單的計算與判斷得出最適當的線性組合結果，其改善結果相當優秀且簡易快速。本論文的章節後有附上多種情況下之實驗模擬圖來驗證目標方法的效果與表現。

Orthogonal frequency division multiplexing (OFDM) and orthogonal frequency division multiple access (OFDMA) techniques has been widely adopted in many wireless communication standards in recent years. Although the invention of OFDMA has improved many communication systems, but the performance of OFDMA-based systems still limited by many factors, such as carrier frequency offset (CFO) since the OFDMA-based systems are sensitive to the frequency synchronization error. If the problem of CFO is not solved or improved, it may cause intercarrier interference (ICI) among all subcarrier as well as intersymbol interference (ISI). In order to reduce the effect of CFO, we need to have an accurate estimate CFO and compensate its effect at the receiver.
In this thesis, we propose to study the blind estimation of CFO in uplink OFDMA system with multiple antennas. We will first introduce the existing blind estimator using the constant modulus (CM) constellation and virtual carrier (VC) based and joint CM-VC. Then, we propose a blind estimation of CFO in uplink OFDMA systems with multiple antennas. By exploiting the multiple signals from these antennas, we show how to combine the CFO estimates from these antennas to obtain more accurate estimates of CFOs. The optimal parameter that gives the best estimate will be derived. Numerical simulations are provided to verify the performance of the proposed methods.

CONTENTS i
LIST OF FIGURES iii
Acknowledgement v
中文摘要 vi
Abstract vii
Chapter 1 Introduction 1
Chapter 2 OFDMA Systems and CFO Compensation 4
2.1 OFDMA Systems 4
2.2 CFO Effect and Its Compensation in OFDMA Systems 5
2.2.1 Least-Square Compensation of CFO in Time Domain 5
2.2.2 Least-Square Compensation of CFO in Frequency Domain 6
Chapter 3 Blind Estimation of CFO in Uplink OFDMA Systems 7
3.1 Subcarrier Assignment 7
3.2 Constant-Modulus (CM) Based Estimator [9] 8
3.2.1 Iterative Algorithm 10
3.3 Virtual-Carriers (VC) Based Estimator [11] 10
3.3.1 Iterative Algorithm 12
3.4 Proposed CM-VC Based Estimator 12
3.4.1 Iterative Algorithm 13
3.5 Simulation Results and Comparisons 13
3.6 Concluding Remarks 14
Chapter 4 Blind Estimation of CFO in Uplink OFDMA Systems with Multiple Antennas 22
4.1 Blind Estimation of CFO in Uplink OFDMA System with Two Antennas 22
4.1.1 Solving for The Optimal λ 23
4.2 Extension to The More General Case 24
4.2.1 Solving for The Optimal λk 25
4.3 Blind Estimation of CFO in Uplink OFDMA System with Four Antennas 25
4.3.1 Solving For The Optimal λ 27
4.4 Simulation Results and Comparisons 28
4.5 Concluding Remarks 32
Chapter 5 Conclusions 46
REFERENCE 47

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