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研究生:鄔侃陵
研究生(外文):Kei-Lin Wu
論文名稱:第三代行動通訊下鏈之等化器
論文名稱(外文):DOWNLINK EQUALIZER FOR 3G WCDMA SYSTEM
指導教授:李學智李學智引用關係
指導教授(外文):Hsueh-Jyh Li
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:2002
畢業學年度:90
語文別:英文
論文頁數:76
中文關鍵詞:等化器
外文關鍵詞:EqualizerEqualization
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在第三代行動通訊下鏈中,無線傳輸多路徑通道的效應會破壞不同使用者彼此展瑪(spreading code)間的正交性,也因此產生了多重存取干擾(MAI)的問題而使得系統效能隨之降低。面對在第三代行動通訊中高資料率的要求下,如何能有效地減輕多重存取干擾來提升系統的效能將是一個重要的課題。在本篇論文中,我們提出使用碎片層級等化器來對抗多路徑通道而使得不同使用者彼此間的正交性得以恢復。而更一進步地,我們建議搭配使用多樣性技術(diversity)來使得等化器能夠更有效率地運作。
對於一個等化器而言,最重要的部分是在於如何針對不同的通道特性來調整其中的係數。在這個部分,我們首先針對最小平均平方誤差準則(MMSE criteria)來推導出矩陣型式的演算法。而這個矩陣型式演算法需要事先知道有關於傳輸通道的資訊。因此,我們引進了一個最少平方通道估測器(least-square channel estimator)來估測無線傳輸通道。
雖然經由最少平方通道估測器和矩陣形式演算法的搭配可以讓這個碎片層級的等化器很有效地減輕多重存取干擾,但是在這其中需要運算到一個高秩矩陣的逆轉。這對於在硬體上的實現將會是一個很大的問題。因此在最後,我們針對降秩多階威靈濾波器(rank-reduced multi-stage Wiener filter)的架構提出了兩種可適性演算法來計算等化器的係數。經由這些可適性演算法的實現,我們可以在系統效能和運算複雜度上取得我們所想要的平衡點。

In 3G WCDMA downlink, the effect of the wireless communication multi-path channel will destroy the orthogonality of different user’s spreading code, thus the multiple-access interference (MAI) arises and degrades the system performance. In demand of high data rates in 3G cellular system, how to efficiently reduce the MAI to improve the system performance is the most important thing. In this thesis, we propose using a chip-level equalizer to oppose the multi-path channel and thus the orthogonality of different user can be recovered. Furthermore, we suggest using the diversity technique to help the equalizer perform much better.
The most important factor which will affect an equalizer’s performance is how to adjust the equalizer’s coefficients according to various communication channel. In this part, we first derive a matrix solution of equalizer’s coefficients. This matrix solution needs to know the information of communication channel. Thus, we introduce a least-square channel estimator to estimate the communication channel.
Although the chip-level equalizer with the matrix solution to calculate the equalizer’s coefficients can efficiently reduce the MAI, it will need to calculate the inversion of a large rank matrix. This is a big problem in implementing this chip-level equalizer on hardware. Thus, we establish two adaptive algorithms to calculate the equalizer’s coefficients based on the structure of rank-reduced multi-stage Wiener filter. From the implement of these adaptive algorithms, we can obtain the balance between the system performance and computational complexity.

Abstract....................................................I
List of Tables..............................................IV
List of Figures.............................................V
Chapter 1 Introduction...................................1
1.1 Motivation.................................1
1.2 Fundamental of Equalizer...................2
1.3 Thesis Overview............................3
Chapter 2 Overview of WCDMA Downlink.....................5
2.1 Main Parameters in WCDMA...................6
2.2 Spreading..................................7
2.3 Downlink Physical Layer....................9
2.3.1 Downlink Frame Structure.................9
2.3.2 Downlink Spreading and Modulation........10
2.3.3 Channelization Code......................11
2.3.4 Downlink Scrambling Code.................13
Chapter 3 WCDMA Downlink Discrete-time model.............14
3.1 Base-station Multi-user Chip
Signal Generation...............16
3.2 Wireless Communication Multi-path
Channel..........18
3.3 Equivalent Channel Model...................20
3.4 Receiving Sampling signal..................22
Chapter 4 Chip level MMSE Equalizer......................25
4.1 Equalizer coefficients Based
on MMSE Criterion...............26
4.2 Equalizer Delay and Length.................34
4.3 Rake Receiver..............................36
4.4 Simulation Results.........................37
Chapter 5 Least Square Channel Estimation................42
5.1 Solution for Least Square
Channel Estimator..................43
5.2 Requirement on Training Sequence...........45
5.3 Performance of Channel Estimator...........46
5.4 LS Channel Estimation on Downlink system...47
5.5 Simulation Results.........................51
Chapter 6 Reduced-Rank Adaptive MMSE Equalization........55
6.1 Multi-stage Nested Wiener Filter...........56
6.2 Rank Reduction Using the Multi-stage
Wiener Filter.......58
6.3 Block-adaptive Multi-stage Nested
Wiener Filter..........60
6.4 Accurate-adaptive Multi-stage Nested
Wiener Filter.......63
6.5 Simulation Results.........................66
Chapter 7 Conclusions....................................72
References.....................................75

[1]. Harri Holma and Antti Toskala, “WCDMA FOR UMTS , Radio Access for Third Generation Mobile Communications”
[2]. Third Generation Partnership Project Technical Specification Group Radio Access Network Working Group 1, “Spreading and Modulation (FDD) “, TS 25.213 V3.60
[3]. Irfan Ghauri and Dirk T.M. Slock “Linear Receivers for the DS-CDMA Downlink Exploiting Orthogonality of Spreading Sequences”, in Proc. 32nd Asilomar Conference on Signals, Systems and Computers, Pacific Grove, California, Nov. 1-4, 1998.
[4]. T.P. Krauss, M.D. Zoltowski, and S. Chowdhury, “Two channel Zero Forcing Equalization on CDMA Forward Link: Trade-Offs Between Multi-User Access Interference and Diversity Gains”, Conference Record of the 33rd Asilomar IEEE Conference on Signals, Systems, and Computers, October 25-27, 1999 (Invited)
[5]. A. Klein, G. K. Kaleh and P. W. Baier, “Zero forcing and Minimum Mean-Square-Error equalization for multiuser detection in Code-division Multiple-access channels”, IEEE Trans. Vehicular Technology, vol. 45(2), May 1996.
[6]. Stefan Wemer, Jorma Lilleberg “Downlink Channel Decorrelation in CDMA Systems with Long Codes”, Vehicular Technology Conference, 1999 IEEE 49th , Volume: 2 , 1999
[7]. T. S. Rappaport, Prentice Hall “Wireless Communications Principles and Practice”, Chapter 6
[8]. Mailaender,L “Low-complexity Implementation of CDMA Downlink Equalization”, 3G Mobile Communication Technologies, 2001. Second International Conference on (Conf. Publ. No. 477) , 2001
[9]. Fakhrul Alam , December 15 19999 , Blacksburg , Virginia, “Simulation of Third Generation CDMA Systems “
[10]. Thomas P. Krauss, Michael D. Zoltowski, and Geert Leus “Simple MMSE Equalizers for CDMA Downlink to restore chip sequence: Comparison to Zero-forcing and Rake”, Acoustics, Speech, and Signal Processing, 2000. ICASSP '00. Proceedings. 2000 IEEE International Conference on , Volume: 5 , 2000
[11]. Riera-Palou. F, Noras. J.M and Cruickshank “Variable Length Equalizers for Broadband Mobile Systems”, Vehicular Technology Conference, 2000. IEEE-VTS Fall VTC 2000. 52nd , Volume: 5 , 2000
[12]. Thomas P. Krauss and Michael D. Zoltowski “MMSE Equalization under Conditions of Soft Hand-off”, Spread Spectrum Techniques and Applications, 2000 IEEE Sixth International Symposium on , Volume: 2 , 2000
[13]. Laurence Mailaender, Bell Labs/Lucent Technologies Holmdel, NJ “CDMA Downlink Equalization with Imperfect Channel Estimation”, Vehicular Technology Conference, 2001. VTC 2001 Spring. IEEE VTS 53rd , 2001
[14]. Hu Rong, Huang Aiping, Wang Hongyu, Gu Weikang “Study on Channel Estimation Parameters of WCDMA”, Communication Technology Proceedings, 2000. WCC - ICCT 2000. International Conference on , Volume: 1 , 2000
[15]. J.S.Goldstein , I.S. Reed and L.L.Scharf , “A multistage representation of the wiener filter based on orthogonal projections”, Information Theory, IEEE Transactions on , Volume: 44 Issue: 7 , Nov. 1998
[16]. M.L.Honig and J.S.Goldstein , “Adaptive reduced-rank residual correlation algorithms for ds-cdma interference suppression”, Signals, Systems & Computers, 1998. Conference Record of the Thirty-Second Asilomar Conference on , Volume: 2 , 1998
[17]. Boon Chong NG, David Gesbert, Arogyswami Paulraj “A semi-blind Approach to Structured Channel Equalization”, Acoustics, Speech and Signal Processing, 1998. Proceedings of the 1998 IEEE International Conference on , Volume: 6 , 1998
[18]. Samina Chowdhury, Michael D. Zoltowski “Structured MMSE Equalization for Synchronous CDMA with Sparse Multipath Channels“, Acoustics, Speech, and Signal Processing, 2001. Proceedings. 2001 IEEE International Conference on , 2001
[19]. Samina Chowdhury, Michael D. Zoltowski “Reduced-Rank Adaptive MMSE Equalization for High-Speed CDMA Forward Link with Sparse Multipath Channels”, Signals, Systems and Computers, 2000. Conference Record of the Thirty-Fourth Asilomar Conference on , Volume: 2 , 2000
[20]. Irfan Ghauri and Dirk T: M. Slock “Structured Estimation of Sparse Channels in Quasi-Synchronous DS-CDMA”, Acoustics, Speech, and Signal Processing, 2000. ICASSP '00. Proceedings. 2000 IEEE International Conference on , Volume: 5 , 2000

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