長程演進上傳系統單載波分頻多工通道估測與等化器

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研究生：	孫哲康 Che-Kang Sun
論文名稱：	長程演進上傳系統單載波分頻多工通道估測與等化器 Channel Estimation and Equalization of SC-FDMA for LTE Uplink System
指導教授：	林嘉慶 Jia-Chin Lin
口試委員:
學位類別：	碩士 Master
系所名稱：	資訊電機學院 - 通訊工程學系 Department of Communication Engineering
畢業學年度：	98
語文別：	英文
論文頁數：	70
中文關鍵詞：	正交分頻多工存取、塊狀引導信號編排、直接決策、通道估測、單載波分頻多工存取
外文關鍵詞：	decision directed, block-type pilot arrangement, SC-FDMA, channel estimation, OFDMA
相關次數：	點閱：14 下載：0
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近年來，無線通訊系統嚴重受到多重路徑通道干擾。由於正交分頻多工可以對抗頻選性衰弱通道，因此廣泛運用在通訊系統中。但正交分頻多工峰值因素過高，且無法抵抗頻率飄移。
單載波分頻多工傳送端使用單一載波調變，在接收端用頻域等化器，架構類似於正交分頻多工，因此效能也相似。單載波分頻多工為在正交分頻多工前加上離散傅立葉轉換前置編碼的系統。這方法可以降低峰值因素，且有效增加傳送功率效率。因此3GPP LTE
使用單載波分頻多工為上傳架構。
單載波分頻多工可視為單載波頻域均衡的延伸，但可更彈性分配資源。單載波分頻多工通常如正交分頻多工一般使用頻域等化器，但單載波分頻多工容易受到震盪器產生的頻率飄移干擾，造成載波間干擾降低系統效能。在這論文中我們使用資料域等化器與
時域等化器並且比較這些等化器的效能。並提出改進的直接決策方法增進原本直接決策方法的缺陷。此方法會與傳統頻域等化器在不同通道中比較單一與多使用者系統效能。

Orthogonal frequency-division multiplexing (OFDM), which is a multicarrier communication technique, has become popularly applicable because of its robustness against
frequency selective fading channels. Single-carrier frequency-division multiple access (SC-FDMA) is a technique which can achieve similar performance and essentially the same structure as OFDMA. SC-FDMA pre-codes its information-bearing symbols by discrete Fourier transform (DFT). This pre-coding operation can reduce PAPR and can benefit power efficiency and reduce manufacturing cost. SC-FDMA is adopted as the uplink multiple access
technique in the 3GPP LTE specification.
SC-FDMA can be considered to be an extension of SC-FDE but it has greater flexibility in resource allocation. SC-FDMA usually uses a frequency-domain equalizer the same as that in an OFDM system because it is simple and convenient. SC-FDMA is however highly sensitive to frequency offset which may be caused by oscillator inaccuracies or Doppler shift. It severely degrades the system performance. In this thesis, we use data-domain equalizers and time-domain equalizers and compare their performances. We also propose a modified decision-directed method to improve decision-directed method. These methods are compared with conventional frequency-domain equalizers over different channels and in multiuser environments.

Abstract…………………………………………………………………………i
List of Figures…………………………………………………………………vi
List of Tables…………………………………………………………………viii
Chapter 1 Introduction....................................................................................... 1
1 Background ....................................................................................................................... 1
2 Motivation........................................................................................................................ 2
3 Organization..................................................................................................................... 3
Chapter 2 Channel Characteristics ................................................................... 4
1 Preliminary....................................................................................................................... 4
2 AWGN channel model...................................................................................................... 4
3 Large scale fading ............................................................................................................. 5
3.1 Path loss ..................................................................................................................... 5
3.2 Shadowing.................................................................................................................. 6
4 Small scale fading ............................................................................................................. 7
4.1 Doppler shift .............................................................................................................. 8
4.2 Coherence bandwidth of the channel ......................................................................... 9
4.3 Coherence time of the channel................................................................................. 10
4.4 Categories of small-scale fading .............................................................................. 11
5 Rayleigh fading channel model ...................................................................................... 13
5.1 Channel mathematical models ................................................................................. 13
5.2 Simulation of fading channel ................................................................................... 15
6 Multipath fading channel model ..................................................................................... 19
iv
Chapter 3 System Description.......................................................................... 21
1 Preliminary..................................................................................................................... 21
2 Downlink multiple access scheme OFDMA................................................................... 21
2.1 Generation of subcarrier........................................................................................... 21
2.2 Guard time and cyclic prefix.................................................................................... 23
2.3 OFDM structure ....................................................................................................... 24
3 Uplink multiple access scheme SC-FDMA .................................................................... 25
3.1 SC-FDMA system.................................................................................................... 25
3.2 Subcarrier mapping .................................................................................................. 26
3.3 Time domain symbols of localized chunk ............................................................... 27
4 LTE frame and slot structures......................................................................................... 28
4.1 Frame structure types ............................................................................................... 28
4.2 Slot structure ............................................................................................................ 29
Chapter 4 Channel Estimation and Equalization.......................................... 32
1 Pilot signal arrangement ................................................................................................. 32
1.1 Block-type pilot........................................................................................................ 32
1.2 Comb-type pilot ....................................................................................................... 33
2 Reference signal in LTE uplink ...................................................................................... 34
2.1 Zadoff-Chu sequence ............................................................................................... 34
2.2 LTE uplink arrangement .......................................................................................... 36
3 Pilot estimation techniques ............................................................................................. 37
3.1 Time-domain least-square channel estimation......................................................... 38
3.2 Frequency-domain least-square channel estimation ................................................ 39
3.3 Frequency-domain minimum mean-square error channel estimation...................... 40
3.4 Frequency-domain least-square channel estimation with windowing ..................... 41
3.5 Frequency-domain least-square channel estimation with lowpass filtering ............ 43
v
3.6 Data-domain least-square channel estimation.......................................................... 43
4 Data block channel estimation techniques...................................................................... 44
4.1 Block data block channel estimation........................................................................ 44
4.2 Linear interpolation data block channel estimation ................................................. 45
4.3 Decision directed data block channel estimation ..................................................... 46
5 Equalization .................................................................................................................... 48
5.1 Time-domain zero-forcing equalization................................................................... 48
5.2 Frequency-domain equalization ............................................................................... 50
5.3 Data-domain zero-forcing equalization.................................................................... 50
Chapter 5 Simulation and Discussion ............................................................. 52
1 System and channel parameters ...................................................................................... 52
2 Multipath........................................................................................................................ 54
2.1 MSE performance .................................................................................................... 54
2.2 BER performance..................................................................................................... 59
3 Multiuser ......................................................................................................................... 62
3.1 MSE performance .................................................................................................... 63
3.2 BER performance..................................................................................................... 65
Chapter 6 Conclusion........................................................................................ 67
Bibliography ...................................................................................................... 68

                                

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