臺灣博碩士論文加值系統

儘管正交分頻多工對干擾敏感，但仍被廣泛的應用在無線寬頻通訊系統中。在窄頻干擾下，首先研究其在同步碼符號輔助之下的時間與頻率偏移估測的效果。同時，時頻交錯正交分頻多工被普遍擬用在（相對地）受到窄頻干擾的環境下所操作的超寬頻通訊系統。這篇論文，主要是在利用時頻交錯的協助，發展出在干擾環境下有效的頻率偏估測方法。正交分頻多工系統經由不同的次頻帶的同步碼符號，在時域，使用適應性雜訊消除法技術來估測消除干擾後的關聯樣本；在頻域，透過頻域轉換去取得關聯次載波，使得所估測的頻率偏移更為強健。同時亦顯示出頻域方法在強干擾下較時域方法來的強健，其原因為當所有的次頻帶的同步碼都被窄頻干擾的情況下，在高信號雜訊比的地方會有明顯有效抑制其錯誤地板效應的能力。

OFDM, in spite of being sensitive to interference, is widely applied in wireless broadband communications. The effect of preamble symbol aided timing and frequency offset estimation in the presence of narrowband interference is investigated. Time-frequency interleaving OFDM has been generally considered for ultra-wide band communications, which must operate under (relatively) narrow-band interferences. By mitigation with the aid of time-frequency interleaving, we develop effective frequency offset estimation under interference in this thesis. Applying adaptive noise cancellation and frequency domain transformation technique, both time-domain and frequency-domain algorithms to estimate frequency offset via correlating samples and correlating subcarriers respectively of repeated preamble symbols from different sub-bands are shown robust to interference in OFDM systems. It can be shown that frequency-domain approach is much robust than time-domain approach when preamble symbol are affected by severe NBI over all sub-bands since the error floor effect is suppressed much efficiently at high SNR region.

Abstract i
Contents iii
List of Figures vii
List of Tables xi
1 Introduction 1
2 Technical Background 5
2.1 Orthogonal Frequency Division Multiplexing Systems ﹒﹒﹒﹒﹒﹒﹒﹒ 5
2.1.1 Fundamental of Orthogonal Frequency Division Multiplexing ﹒﹒﹒﹒ 6
2.1.2 Transmission over Frequency-Selective Fading Channels ﹒﹒﹒﹒﹒﹒ 6
2.2 Degradation due to Timing and Frequency Offset ﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒ 7
2.2.1 Transmission Model ﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒ 7
2.2.2 Effects of Timing (or Frame) Offset ﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒ 8
2.2.3 Effects of Carrier and Sampling Clock Frequency Offsets ﹒﹒﹒﹒﹒11
2.2.4 Sensitivity of OFDM symbol to carrier frequency offset ﹒﹒﹒﹒﹒﹒13
2.3 Degradation due to Narrowband Interference ﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒14
2.3.1 Narrowband Interference Model ﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒14
2.3.2 Synchronization in the Presence of Narrowband Interference ﹒﹒﹒15
2.3.3 Effect of Narrowband Interference on Pilot Symbol Detection ﹒﹒﹒17
2.3.4 Effect of Narrowband Interference on Frequency Offset Estimation ﹒18
3 Robust Timing and Frequency Offset in the Presence of Narrowband Interference 21
3.1 Autoregressive Modeling and Linear Prediction Filtering of Narrowband Interference ﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒21
3.1.1 Introduction to Narrowband Interference suppression ﹒﹒﹒﹒﹒﹒﹒﹒21
3.1.2 Autoregressive Modeling ﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒23
3.1.3 Linear Prediction Filtering ﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒24
3.2 Time Domain Approach of Frequency Offset Estimation ﹒﹒﹒﹒﹒﹒﹒26
3.2.1 Normalized Least Mean Square Algorithm ﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒26
3.2.2 Performance analysis of frequency offset estimation ﹒﹒﹒﹒﹒﹒﹒27
3.3 Narrowband Interference Identification in Frequency Domain ﹒﹒﹒﹒31
3.3.1 Order-statistic Algorithm of NBI Identification ﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒31
3.3.2 Performance Analysis of Narrowband Interference Identification ﹒34
3.4 Frequency Domain Approach of Frequency Offset Estimation ﹒﹒﹒﹒36
3.4.1 Windowing of Frequency domain transformation ﹒﹒﹒﹒﹒﹒﹒﹒﹒36
3.4.2 Laplacian Approximation of Non-Gaussian Noise Modeling ﹒﹒﹒38
3.4.3 Median Selection of Frequency Offset Estimation ﹒﹒﹒﹒﹒﹒﹒﹒39
3.4.4 Computation Complexity of N-LMS and Median Selection ﹒﹒﹒﹒43
4 Robust Frequency Offset Estimation on Ultra-Wide Band Environment 45
4.1 Introduction to Ultra-Wide Band Environment ﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒45
4.2 Time-Frequency Interleaved OFDM Systems ﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒49
4.2.1 Architecture for a TFI-OFDM System ﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒49
4.2.2 Frequency Planning and Synthesize Architecture ﹒﹒﹒﹒﹒﹒﹒﹒﹒52
4.2.3 TFI-OFDM and NBI Signal Model ﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒54
4.3 BLUE of Frequency Offset Estimation in TFI-OFDM Systems ﹒﹒﹒﹒56
4.3.1 N-LMS Over TFI-OFDM Systems ﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒56
4.3.2 Frequency Offset Estimation Performance Analysis using BLUE ﹒58
4.4 Frequency Domain Median Selection of Frequency Offset Estimation ﹒62
4.4.1 Windowing and Overlap-Add Effect of Frequency Domain
Transformation ﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒62
4.4.2 Simple Median Selection Tracking Algorithm ﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒65
4.4.3 Other Non-Gaussian Noise Modeling ﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒66
5 Computer Simulations 71
5.1 Effect of N-LMS on Synchronization ﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒71
5.2 Time Domain Approach ﹒﹒﹒﹒﹒﹒﹒﹒74
5.3 Frequency Domain Approach ﹒﹒﹒﹒﹒79
5.4 Performance Comparison over Different SIR Level ﹒﹒﹒﹒﹒﹒﹒﹒﹒84
5.5 Simple Median Selection Tracking ﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒﹒88
6 Conclusion 91
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