WiMAX基頻時間同步電路設計｜國立清華大學博碩士論文庫

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研究生：	周俊宏 Chun-Hung Chou
論文名稱：	WiMAX基頻時間同步電路設計 Baseband Timing Synchronization Circuit Design for WiMAX Systems
指導教授：	吳仁銘 Jen-Ming Wu
口試委員:
學位類別：	碩士 Master
系所名稱：	電機資訊學院 - 通訊工程研究所 Communications Engineering
論文出版年：	2005
畢業學年度：	93
語文別：	英文
論文頁數：	82
中文關鍵詞：	時間同步、基頻、WiMAX
外文關鍵詞：	Timing Synchronization, Baseband, WiMAX
相關次數：	點閱：4 下載：0
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中文摘要

有別於傳統的單一載波通訊系統。正交分頻多工(OFDM)系統以多個正交載波同時傳送資料。其夾帶的好的好處包括：符元間干擾變小、資料的傳送速率提高、能夠達到最大的頻譜效益、以及可以用快速傅立葉轉換(FFT)簡單的實現調變..等。基於以上許多的優點，OFDM系統已經成為無線通訊的主流標準。在2004年IEEE所發佈的都會型無線通訊標準WiMAX (IEEE802.16-2004)中，實體層提供多種調變模式。本論文即是設計一個以OFDM調變模式為基礎的基頻時間同步演算法。
OFDM系統縱然有那麼多的優點，不過與傳統通訊系統比較起來，更容易因為頻率飄移以及時間不同步而使得整個系統效能大大降低。換句話說，OFDM系統的優點是建築在良好的同步機制上面。所以本篇論文將會專注在OFDM的時間同步演算法設計上，其中包括符元邊界的同步以及取樣頻率的同步。一開始我們會對OFDM系統以及WiMAX (IEEE802.16-2004)作一個介紹。再來我們會分析符元邊界以及取樣頻率不同步所帶來的影響，使我們了解問題所在。接著我們會介紹一些已經發表過的演算法，並且分析這些演算法的優點以及缺點。藉由分析這些演算法，我們試著提出兼顧低複雜度以及高效能的新演算法。最後是介紹模擬的方法以及結果。經由模擬的結果顯示，我們所提出的演算法擁有良好的效能且能適用於任何的OFDM系統。在硬體實作上，我們的演算法也提供了低複雜度的好處。

Abstract

Orthogonal frequency division multiplexing (OFDM) differs greatly from the traditional single carrier communication system. It is a multicarrier system with parallel transmission scheme by using a special set of orthogonal carrier frequencies. The advantages of OFDM include that Intersymbol Interference (ISI) becomes small relatively, bigger transmission rate of data, better spectral efficiency, and easy implementation by Fast Fourier Transform (FFT), etc. Therefore, OFDM becomes the main stream of the wireless communication. The WiMAX (IEEE802.16-2004) published in 2004 is an OFDM system.
However, the performance of OFDM system will be reduced seriously by the carrier frequency offset and the timing offset. In other words, the advantages of OFDM only base on the well synchronization schemes. In this thesis, we will focus on the timing synchronization algorithm design which includes symbol timing synchronization and sampling frequency synchronization. The simulation result shows that our proposed algorithm has better performance and is suitable for OFDM based systems. Our proposed algorithm also provides low complexity for hardware implementation.

Contents

Contents…………………………………………………………………………...i
List of Figures………………………………………………………………….iii
List of Tables………………………………………………………………….viii
Abstract…………………………………………………………………………...ix
Chapter 1 Introduction………………………………………………………..1
Chapter 2 OFDM and IEEE 802.16-2004……………………..............3
2.1    OFDM Basics…………………………………………………………...3
    2.1.1 OFDM Introduction………………………………………………….3
    2.1.2 Design of the OFDM Signal…………………………………………6
    2.1.3 OFDM System Model………………………………………………..9
2.2    Overview of IEEE 802.16-2004 PHY…………………...................11
    2.2.1 OFDM Symbol Description………………………………………...11
    2.2.2 OFDM Symbol Parameters and Transmitted Signal………………..13
    2.2.3 Modulation………………………………………………………….16
Chapter 3 Effects of the Timing Error for OFDM……………...…..20
3.1    Effects of Symbol Timing Offset……………………………………20
3.2    Effects of Sampling Frequency Offset……………………………..26
Chapter 4 Timing Synchronization Algorithms…………………..…32
4.1    Symbol Timing Synchronization Algorithm…………………........32
4.2    Sampling Frequency Synchronization Algorithm…………….......34
        4.2.1 Review of Some Sampling frequency Synchronization Algorithms...35
        4.2.2 Proposed Sampling frequency Synchronization Algorithms………...42
Chapter 5 Simulation Results……………………………………………...52
5.1    Simulation Platform…………………………….……………...............52
5.2    Simulation Results of Symbol Timing Synchronization……..….57
5.3    Simulation Results of Sampling Frequency Synchronization…..60
5.4    System Performance…………………………………………………...79
Chapter 6 Conclusion and Future Work………………………………..82















List of Figures

Figure 2-1 : Parallel transmission system…………………………………………….4
Figure 2-2 : PSD of single carrier system and multi-carrier system………………….4
Figure 2-3 : Structure of discrete time OFDM system………………………………..6
Figure 2-4 : Cyclic prefix insertion of the OFDM symbol…………………………....6
Figure 2-5 : Cyclic extension and windowing of the OFDM symbol………………....8
Figure 2-6 : Transfer function of the transmitter/receiver hardware and its impact on the design of an OFDM system………………………………………………………..9
Figure 2-7 : Idealized OFDM system model…………………………………………11
Figure 2-8 : OFDM symbol time structure…………………………………………...12
Figure 2-9 : OFDM frequency description…………………………………………...13
Figure 2-10 : OFDM symbol parameters…………………………………………….15
Figure 2-11 : BPSK, QPSK, 16-QAM, and 64-QAM constellations………………...16
Figure 2-12 : PRBS for pilot modulation…………………………………………….18
Figure 2-13 : Downlink and network entry preamble structure……………………...18
Figure 3-1 : Different kinds of symbol timing offset (  is the channel delay spread)………………………………………………………………………………..21
Figure 3-2 : The phase rotations of subcarriers when the symbol timing offset is
(a) 0 samples (b) 1 samples (c) 2 samples……………………………………………23
Figure 3-3 : Effect of STO (FFT Window 3)…………………………………………25
Figure 3-4 :  ……………………………..26
Figure 3-5 : The time domain block diagram of WiMAX receiver…………………..26
Figure 3-6 : OFDM symbol window drift due to sampling frequency offset………..27
Figure 3-7 : Subcarrier symbol rotation due to carrier and sampling frequency offsets………………………………………………………………………………...30
Figure 3-8 : Subcarrier symbol rotation (with time index) due to carrier and sampling frequency offsets……………………………………………………………………..30
Figure 4-1 : The representation of finding the symbol boundary and CP length in AWGN channel………………………………………………………………………33
Figure 4-2 : The representation of finding the symbol boundary and CP length in multipath channel…………………………………………………………………….34
Figure 4-3 : The relation between   and  ………………………………...35
Figure 4-4 : The system architecture of the method Ⅰ……………………………....37
Figure 4-5 : Interpretation of equation (4-8)…………………………………………40
Figure 4-6 : The block diagram of method Ⅱ……………………………………….41
Figure 4-7 : Widely used signal-plus-noise model…………………………………...42
Figure 4-8 : Block diagram of RLS algorithm……………………………………….44
Figure 4-9 : The system architecture of the method Ⅲ……………………………..45
Figure 4-10 : The subcarrier symbol rotation with symbol index   (the slope and
intercept are time-variant)……………………………………………………………47
Figure 4-11 : The behavior of LS algorithm of method Ⅳ………………………….48
Figure 4-12 : The representation of phase ambiguity problem………………………49
Figure 4-13 : The behavior of pre-compensation procedure…………………………50
Figure 4-14 : The phase rotation due to SFO and RCFO (SFO is positive or negative)……………………………………………………………………………...51
Figure 5-1 : Simulation environment of our WiMAX system………………………..52
Figure 5-2 : Magnitude plot of the SUI-3 (omni antenna) channel coefficients over time…………………………………………………………………………………...53
Figure 5-3 : Magnitude response of SUI-3 (omni antenna) channel…………………54
Figure 5-4 : Timing relations of resampling process…………………………………56
Figure 5-5 : FIR filter structure of the interpolator with sinc coefficients…………...56
Figure 5-6 : Calculation of symbol boundary and CP length (floating, no SUI)…….58
Figure 5-7 : Calculation of symbol boundary and CP length (floating, SUI-3)……...58
Figure 5-8 : Calculation of symbol boundary and CP length (Sign Bit, no SUI)……59
Figure 5-9 : Calculation of symbol boundary and CP length (Sign Bit, SUI-3)……..59
Figure 5-10 : One-Shot estimation of RCFO (Method Ⅰ)………………………….60
Figure 5-11 : Closed-loop RCFO estimation (Method Ⅰ)………………………….61
Figure 5-12 : One-Shot estimation of SFO (Method Ⅰ)……………………………61
Figure 5-13 : Closed-loop SFO estimation (Method Ⅰ)……………………………62
Figure 5-14 : RCFO estimation (Method Ⅲ)……………………………………….63
Figure 5-15 : Closed-loop RCFO estimation (Method Ⅲ)……….…………………63
Figure 5-16 : SFO estimation (Method Ⅲ)………………………………………….64
Figure 5-17 : Closed-loop SFO estimation (Method Ⅲ)……………………………64
Figure 5-18 :   and   (ICI only)……………………………………….65
Figure 5-19 :   and   (ICI only)………………………………………..66
Figure 5-20 : Compensated pilot and uncompensated pilot (ICI only)……………...66
Figure 5-21 : The 16-QAM constellation after compensation (ICI only)……………67
Figure 5-22 :   and   (RCFO=-200Hz, SFO=16ppm, Eb/No=20dB, SUI-3)………………………………………………………………………………..67
Figure 5-23 :   and   (RCFO=-200Hz, SFO=16ppm, Eb/No=20dB, SUI-3)………………………………………………………………………………..68
Figure 5-24 : Compensated pilot and uncompensated pilot (RCFO=-200Hz, SFO=16ppm, Eb/No=20dB, SUI-3)…………………………………………………68
Figure 5-25 : The 16-QAM constellation after compensation (RCFO=-200Hz, SFO=16ppm, Eb/No=20dB, SUI-3)………………………………………………….69
Figure 5-26 : Accumulated   and the residual phase rotation after pre-compensation (ICI only, without add/drop)………………………..…………….70
Figure 5-27 :   and   (ICI only, without add/drop)………………………...70
Figure 5-28 : The behavior of LS algorithm of one symbol in Figure 5-27…………71
Figure 5-29 : Compensated pilot and uncompensated pilot (ICI only, without add/drop)……………………………………………………………………………..71
Figure 5-30 : The 16-QAM constellation after compensation (ICI only, without add/drop)……………………………………………………………………………..72
Figure 5-31 : Original phase error before compensation and residual phase rotation after compensation (ICI only, without add/drop)……………………………………72
Figure 5-32 : Accumulated   and the residual phase error after pre-compensation (ICI only, with add/drop)…………………………………………………………….73
Figure 5-33 :   and   (ICI only, with add/drop)…………………………....73
Figure 5-34 : The behavior of LS algorithm of one symbol in Figure 5-33…………74
Figure 5-35 : Compensated pilot and uncompensated pilot (ICI only, with add/drop)……………………………………………………………………………..74
Figure 5-36 : The 16-QAM constellation after compensation (ICI only, with add/drop)……………………………………………………………………………..75
Figure 5-37 : The phase rotation of subcarrier index +64/-64 (ICI only, with add/drop)………………………………………………………………………….….75
Figure 5-38 : Original phase error before compensation and residual phase error after compensation (ICI only, with add/drop)……………………………………………..76
Figure 5-39 : Accumulated   and the residual phase error after pre-compensation (RCFO=46Hz, SFO=16ppm, Eb/No=20dB, SUI-3, with add/drop)………………...77
Figure 5-40 :   and   (RCFO=-110Hz, SFO=16ppm, Eb/No=20dB, SUI-3, with add/drop)………………………………………………………………………..77
Figure 5-41 : The behavior of LS algorithm of one symbol in Figure 5-40…………78
Figure 5-42 : Compensated pilot and uncompensated pilot (RCFO=-110Hz, SFO=16ppm, Eb/No=20dB, SUI-3, with add/drop)…………………………………78
Figure 5-43 : The 16-QAM constellation after compensation (RCFO=-110Hz, SFO=16ppm, Eb/No=20dB, SUI-3, with add/drop)…………………………………79
Figure 5-44 : The phase rotation of subcarrier index +64/-64 (RCFO=-110Hz, SFO=16ppm, Eb/No=20dB, SUI-3, with add/drop)…………………………………79
Figure 5-45 : Original phase error before compensation and residual phase error after compensation (RCFO=-110Hz, SFO=16ppm, Eb/No=20dB, SUI-3, with add/drop).80
Figure 5-46 : System performance in AWGN channel………………………………81
Figure 5-47 : System performance in multipath fading channel……………………..81











List of Tables

Table 4-1 : Summary of all methods…………………………………………………48
Table 5-1 : K factor, delay spread, and terrain type of SUI channel models………....53
Table 5-2 : The parameters used in simulation……………………………………….57

                                

Bibliography

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