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研究生:李佩學
研究生(外文):Pei-Hsueh Li
論文名稱:多輸入多輸出正交分頻多工系統應用於無線區域網路之基頻收發機架構設計
論文名稱(外文):MIMO-OFDM system baseband transceiver architecture design for WLAN applications
指導教授:曹恆偉曹恆偉引用關係
學位類別:碩士
校院名稱:國立臺灣大學
系所名稱:電信工程學研究所
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:2005
畢業學年度:93
語文別:英文
論文頁數:118
中文關鍵詞:多輸入多輸出正交分頻多工通道模型時間同步頻率同步通道估測
外文關鍵詞:MIMOOFDMchannel modeltiming synchronizationfrequency synchronizationchannel estimation
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在最近這幾年,因為無線通訊的方便性以及實用性,使得其變成人門日常生活中一個不可或缺的元素。商用市場上對於手機的巨大需求就是一個最好的例子。以無線區域網路來說,IEEE 802.11/a/b/g的成功同時也代表著無線傳輸的趨勢,然而就現行的無線區域網路標準來看,傳輸效能以及訊號所能涵蓋的範圍 對於現今急速發展的應用來說急需改進。由於多輸入多輸出的技術在學術界以及工業界已為廣泛證實其技術在一般合理的訊雜比條件下,可以達到快速的資料傳輸速度,或是等效上在同樣的傳輸速度條件下可以達到更大的傳輸距離。因此,在傳統的正交分頻多工系統上,為了改善系統的效能,充分利用這項有力的技術變成一個適當的選擇。在這個論文裡,我們利用模擬去設計並且驗證一個應用在無線區域網路上2×2多輸入多輸出正交分頻多工的基頻收發機系統,其傳輸機的架構主要是依據IEEE802.11a的標準,但是額外加入了一個空間多工器來將原本單一的傳輸資料分配成多數個空間上的傳輸資料,使得多根天線傳輸變成可能,除此之外,在通道模型中我們採用了IEEE 802.11工作小組N所提出的架構並且考慮在實際傳輸上的效應。在接收機的架構設計上,針對時間以及頻率同步上面所會遇到的問題,我們加以分析以及考慮其對於系統所造成的影響,並且提出了有效的方法來改善。另外,在通道估測以及空間上多輸入多輸出的訊號處理方式也都會在這篇論文裡面加以討論,最後,整個系統我們在安捷倫ADS還有MATLAB的環境下加以模擬以及驗證。
Wireless communication becomes vital for our daily life in recent years since it provides not only great convenience but also high practicability for us. The enormous demand for mobile phones in the commercial market is the best example. In terms of WLAN applications, the success of IEEE 802.11a/b/g also shows the tendency toward wireless communication. However, the throughput or the covering range supplied by the existing WLAN standards reveals insufficiently and inadequately for current swift-growing applications and is needed to improve. As the MIMO technology had been proved to have a great potential for achieving a very high data rate with a practical SNR or equivalently a larger covering range with an acceptable throughput, it is reasonable to apply the powerful technology to the existing OFDM based wireless transceiver to enhance the system performance. As a result, in this thesis, we designed and verified by simulations a 2X2 MIMO-OFDM baseband transceiver mainly for WLAN applications. The architecture of the transmitter is based on the IEEE 802.11a standard but is introduced a spatial multiplexer to distribute the single data stream to multiple spatial streams such that the transmission via multiple antennas is feasible. Besides, the channel models are used those provided by the IEEE 802.11 task group N with practical considerations. The architecture of the receiver is designed to deal with the synchronization problems such as timing and frequency offset errors. In addition, the channel estimation and spatial MIMO signal processing are also including in the receiver design.
At last, the entire system is verified with the aid of simulation tools such as Agilent advanced design system (ADS) and MATLAB.
1 Introduction 1
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Organization of This Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2 OFDM Basics 3
2.1 OFDM Signal Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 Orthogonality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3 FFT-based OFDM System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.4 Guard Interval . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3 Transmitter Architecture 11
3.1 Packet Preamble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.1.1 Legacy Short Training Field . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.1.2 Legacy Long Training Field . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.1.3 Legacy SIGNAL Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.1.4 HT-SIGNAL Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.1.5 HT-Short Training Field . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.1.6 HT-Long Training Field . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.2 Scrambler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.3 Convolutional Encoder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.4 Interleaver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.5 Constellation Mapper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.6 Pilot Generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.7 IFFT Mapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
4 MIMO Channel Model 37
4.1 Path Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4.2 Shadowing (Slow Fading) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
4.3 Multipath Fading (Fast Fading) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.3.1 Equivalent Baseband Representation of Multipath Channels . . . . . . . . 41
4.3.2 Statistical Characterization of the Time Variant Behavior . . . . . . . . . . 42
4.3.3 The WSSUS Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
4.4 MIMO Channel Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.4.1 Channel Matrix Formulation . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.4.2 Power Azimuth Spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . 50
4.4.3 Channel Spatial Correlation Matrix . . . . . . . . . . . . . . . . . . . . . 52
4.4.4 Generation of Correlated Channel Samples . . . . . . . . . . . . . . . . . 54
4.5 Simulation Flow Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
5 Receiver Architecture 63
5.1 Timing Synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
5.1.1 Effects of The Timing Offset Errors . . . . . . . . . . . . . . . . . . . . . 64
5.1.2 Compensation Technique for Timing Offset Errors . . . . . . . . . . . . . 67
5.2 Frequency Synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
5.2.1 Effects of The Frequency Offset Errors . . . . . . . . . . . . . . . . . . . 71
5.2.2 Compensation Techniques for Frequency Offset Errors . . . . . . . . . . . 74
5.3 Channel Estimator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
5.3.1 Least Squares Channel Estimator . . . . . . . . . . . . . . . . . . . . . . 79
5.3.2 Minimum Mean Square Error Channel Estimator . . . . . . . . . . . . . . 80
5.4 MIMO Spatial Decoder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
5.4.1 Zero Forcing Spatial Decoding . . . . . . . . . . . . . . . . . . . . . . . . 84
5.4.2 Maximum Likelihood Spatial Decoding . . . . . . . . . . . . . . . . . . . 85
5.4.3 Minimum Mean Square Error Spatial Decoding . . . . . . . . . . . . . . . 85
5.5 Constellation Demapper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
5.6 Deinterleaver and Spatial Multiplexer . . . . . . . . . . . . . . . . . . . . . . . . 88
5.7 Viterbi Decoder and Descrambler . . . . . . . . . . . . . . . . . . . . . . . . . . 89
6 Simulation Results 91
6.1 Timing Synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
6.1.1 Timing Offset Estimation in Different Channel Models . . . . . . . . . . . 91
6.2 Frequency Synchronization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
6.2.1 Integer Frequency Offset Estimation . . . . . . . . . . . . . . . . . . . . . 95
6.2.2 Frequency Offset Estimation in Different Channel Models . . . . . . . . . 97
6.3 Channel Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
6.3.1 Channel Estimation in Different Channel Models . . . . . . . . . . . . . . 100
6.4 Bit Error Rate Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
6.4.1 BER in ZF-Spatial Decoding . . . . . . . . . . . . . . . . . . . . . . . . . 102
6.4.2 BER in MMSE-Spatial Decoding . . . . . . . . . . . . . . . . . . . . . . 104
7 Conclusion 107
A ADS and Matlab Co-Simulation 109
A.1 Environment Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
A.2 The Simplest Method of Co-Simulation . . . . . . . . . . . . . . . . . . . . . . . 110
A.3 Matlab LibLink in Script Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
A.4 Matlab LibLink in Compile/Auto Mode . . . . . . . . . . . . . . . . . . . . . . . 113
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