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研究生:闞啟安
研究生(外文):Chi-Ann Kang
論文名稱:寬頻分碼多工系統的基站搜尋
論文名稱(外文):Cell Search in W-CDMA
指導教授:蘇炫榮
指導教授(外文):Hsuan-Jung Su
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:2004
畢業學年度:92
語文別:英文
論文頁數:55
中文關鍵詞:基站搜尋
外文關鍵詞:fast power controlweighted combininingcell searchdifferential combining
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在寬頻分碼多工系統下,不同的基地台之間不需要同步.因此必須要用不同的擾亂碼來區別基地台.基站搜尋所要作的就是要找到能到提供最好的服務品質的基地台.基站搜尋發生在手機剛開機時尋找服務品質最好的基地台,或者是已經維持跟基地台之間的聯繫但是希望能切換到服務品質更好的.此外,低成本的振盪器會造成在手機剛開機的時候有蠻大的一個頻率偏移,這會影響到搜尋基地台的效能.一般而言,搜尋基地台可以分成五個階段,第一階段是訊槽同步,第二階段是訊框同步和找到擾亂碼所在的分組,第三階段是確認擾亂碼,第四階段是掌握到頻率偏移,第五個階段是接收基地台的資訊.在本篇論文中,吾人研究前三個階段,它們遭受到頻率偏移以及都普勒效應.為了避免第一階段的解展頻器受到頻率偏移的影響,吾人考慮將解展頻的展頻碼分成幾個區塊以減少相位翻轉.吾人亦在第一階段使用differential combining 來增加訊雜比,同時可以粗估手機剛開機時遭受到的頻率偏移.第一個階段粗估的頻率偏移可以用到第二和第三階段去抵消掉一部分的相位翻轉,增加偵測效能.此外.為了克服FPC (fast power control) 所造成隨時間改變的干擾,吾人提出了在第一跟第二階段使用weighted combining 的方法.在論文中提到的改進方法都會用電腦模擬在不同的通道底下加以驗證
In W-CDMA system, synchronization among base stations is not necessary. Each cell is identified by a unique primary scrambling code. Cell search is the process of the mobile station searching for a best cell and achieving time synchronization to its downlink primary scrambling code. Cell search is performed when 1) the mobile station is just switched on and tries to find a best serving cell (initial cell search) 2) when the mobile station has camped on a cell, and is looking for another that has a better transmission quality to it, in order to switch to (target cell search) or in idle mode. In addition, the low cost oscillator used in the mobile station usually incurs a large frequency offset when the mobile station is switched on. This practical defect further complicates the initial cell search.
In general, the cell search process is divided into five stage process:1) slot synchronization 2) frame synchronization and scrambling code group identification 3) scrambling code identification 4) frequency acquisition 5) cell identification . In this thesis, we investigated the first three stages of the initial cell search where large frequency offset and possible Doppler effect are the major obstacles. To avoid the match filtering performance degradation induced by the frequency offset, we considered using a partial correlating match filter which has a length smaller than the coherence time of the channel. Differential combining of the partial correlated segments is then applied to increase the stage 1 signal-to-noise ratio (SNR). The differential technique can also be used to roughly estimate the frequency offset which can be used at stage 2 and stage 3 to correct the phase rotation and improve the detection. In addition, a weighted combining at stage 1, and stage 2 was proposed to overcome the time-varying interference due to fast power control of the traffic and control channels. These proposed enhancements were firstly tested with a single-path Rayleigh fading channel, then applied to the multi-path fading channel models specified in the 3GPP standards. It was shown through simulation that the proposed enhancements improve the initial cell search performance significantly.
Contents

Chinese Abstract I
English Abstract II
Acknowledgement IV
Contents V
List of Figures VII
List of Tables IX
Acronym Glossary X
1 Introduction 1
2 Synchronization Channels and Cell Search
Algorithms in W-CDMA 4
2.1 Introduction to Synchronization Channels in W-
CDMA 4
2.2 Primary Synchronization Channel 5
2.3 Secondary Synchronization Channel 8
2.4 Common Pilot Channel 10
2.4.1 Channelization Codes 10
2.4.2 Common Pilot Channel 11
2.5 Cell Search Procedure 11
3 Stage 1 Process 17
3.1 System Model 17
3.2 Slot Synchronization with Noncoherent Combining 19
3.3 Slot Synchronization with Differential Combining23
3.4 Computer Simulations 24
3.5 Slot Synchronization with Weighted Combining
under Fast Power Control 28
3.6 Computer Simulations withr Fast Power Control 28
4 Stage2 and Stage3 Process 32
4.1 Frame Synchronization and Scrambling Code Group
Identification 32
4.1.1 Noncoherent Detection with 0 Hz Frequency Error 33
4.1.2 Noncoherent Detection with 20 KHz Frequency Error
37
4.1.3 Coherent Detection with 0 Hz Frequency Error 42
4.1.4 Coherent Detection with 20 KHz Frequency Error 42
4.1.5 Computer Simulations 43
4.1.6 Weighted Coherent Combining with Fast Power
Control 44
4.1.7 Computer Simulations under with Power Control 45
4.2 Scrambling Code Identification 46
4.2.1 Computer simulations 47
4.3 Average Acquisition Time in Serial Cell Search 48
5 Conclusion 54
Bibliography 56



List of Figures

Figure 2.1 Synchronization channels in cell search 5
Figure 2.2 Recursive pruned Golay complementary sequence generator 7
Figure 2.3 Pruned efficient Golay correlator for the generalized hierarchical Golay (GHG) sequence 8
Figure 2.4 Spreading for physical channels 10
Figure 2.5 Code-tree for generation of Orthogonal Variable Spreading Factor (OVSF) codes 11
Figure 2.6 Serial search 13
Figure 2.7 Pipelined search 13
Figure 3.1 System model used for evaluating the performance of the cell search process 17
Figure 3.2 Slot boundary detector 19
Figure 3.3 SNR vs M when the frequency offset is 20 KHz. 21
Figure 3.4 Structure of the hierarchical correlator(64-chip partial correlation) 22
Figure 3.5 Noncoherent combining 22
Figure 3.6 Phase rotation between consecutive 64-chip partial correlations values 23
Figure 3.7 Intra-slot differential combining 24
Figure 3.8 Synchronization probability comparison in 256-chip and 64-chip dispreading (flat fading, 5 km/h synchronization channels) 26
Figure 3.9 Synchronization probability with noncoherent combining 26
Figure 3.10 Synchronization probability with intra-slot differential combining 27
Figure 3.11 Differential vs noncoherent combining 27
Figure 3.12 Intra-cell interference average power variation within one frame interval 30
Figure 3.13 Differential, weighted v.s. conventional combining with flat fading 5 km/h synchronization channels, 30km/h traffic channels 31
Figure 3.14 Synchronization probability with weighted differential combining comparison in 3km/h, 30km/h, and 120km/h traffic channels, flat fading 5 km/h synchronization channels 31
Figure 4.1 The structure of frame synchronization and scrambling code group identification 34
Figure 4.2 Butterfly structure of computing partial correlation 42
Figure 4.3 Frame boundary detection and code group identification performance (flat fading, 5 km/h synchronization channels) 44
Figure 4.4 Stage 2 performance under FPC (30 km/h traffic channels, and 5km/h synchronization channels) 45
Figure 4.5 Synchronization probability with weighted coherent combining comparison in 3km/h, 30km/h, and 120km/h traffic channels, 5km/h synchronization channels 46
Figure 4.6 Miss probability for the scrambling code identification in a flat fading channel with 5 km/h synchronization channels, 48
Figure 4.7 Average acquisition time in a flat fading channel with 5 km/h synchronization channels 49
Figure 4.8 Stage 1 performance in serial cell search (30ms synchronization time) 51
Figure 4.9 Initial frequency offset estimation performance (flat fading, 3km/h synchronization channels) 51
Figure 4.10 Average acquisition time for initial serial cell search in various W-CDMA test channels 52
Figure 4.11 Average acquisition time for initial serial search in Case 2 channel with 20 KHz frequency offset, 30 km/h traffic channels 53




List of Tables
Table 2.1 Allocation of SSCs for secondary SCH 14
Table 4.1 Detection threshold 47
Table 4.2 Delay profiles W-CDMA test channels 50
























Acronym Glossary
2G The Second Generation
3G The Third Generation
3GPP Third Generation Partnership Project
AWGN Additive White Gaussian Noise
BS Base Station
CDMA Code Division Multiple Access
CP Cyclically Permutable
CPICH Common Pilot Channel
DS-CDMA Direct Sequence-Code Division Multiple Access
EGC Efficient Golay Correlator
FDD Frequency Division Duplex
FHT Fast Hadamard Transform
FPC Fast Power Control
GHG Generalized Hierarchical Golay
GPS Global Position System
IEEE Institute of Electrical and Electronics Engineers
ML Maximum Likelihood
MRC Maximal Ratio Combining
MS Mobile Station
OVSF Orthogonal Variable Spreading Factor
PEGC Pruned Efficient Golay Correlator
PFHT Partial Fast Hadamard Transform
P-SCH Primary Synchronization Channel
PSC Primary Synchronization Codes
RS Reed Solomon
SCH Synchronization Channel
SF Spreading Factor
SNR Signal-to-Noise Ratio
SSC Secondary Synchronization Code
S-SCH Secondary Synchronization Channel
W-CDMA Wideband-Code Division Multiple Access
[1] Y.P.E. Wang and T. Ottosson, ‘‘Cell Search in W-CDMA’’, IEEE journal on
Selected Areas Commun., vol. 18, pp. 1470-1482, Aug 2000
[2] 3rd Generation Partnership Project, “Spreading and Modulation”, 3GPP Tech Spec.
TS25.213, V3.30, June 2000
[3] June Moon and Yong-Hwan Lee, “Cell search robust to initial frequency offset in
W-CDMA systems”, Personal, Indoor and Mobile Radio Communications, 2002. The 13th IEEE International Symposium on, Volume: 5, 15-18, Pages: 2039 - 2043 vol.5, Sept. 2002
[4] Siemens and Texas Instruments, “Generalized hierarchical Golay sequence for
PSC with low complexity correlation using pruned efficient Golay correlators”, 3GPP Tech. Doc., Tdoc R1-99554, Cheju, Korea, June 1999
[5] K. Higuchi, M. Sawahashi, and F. Adachi, “Fast cell search algorithm using long code masking in DS-CDMA asynchronous cellular system”, Tech. Rep. IEICE, pp.57-62, Jan. 1997
[6]K. Higuchi, M. Sawahashi, and F. Adachi, “Fast cell search algorithm in DS-CDMA mobile radio using long spreading codes”, in Proc. IEEE 1997 Vehicular Technology Conference, 4-7, Pages: 1430 - 1434 vol.3, May 1997
[7] J. Nystrom; K. Jamal; Y.P.E. Wang; R. Esmailzadeh, “Comparison of cell search methods for asynchronous wideband CDMA cellular system”, in Proc. IEEE 1998 Int. Conf. Universal Personal Communications, Italy Oct. 1998
[8] B.M. Popovic, “Efficient Golay correlator”, Electronics Letters, 19 Pages: 1427 – 1428, Aug. 1999
[9] S. Sriram.; S. Hosur. “Cyclically permutable codes for rapid acquisition in DS-CDMA systems with asynchronous base stations”, Selected Areas in Communications, IEEE Journal on, Volume: 19, Issue: 1, Jan 2001
[10] Y.P.E. Wang and T. Ottosson, “Initial frequency acquisition in W-CDMA”, in Proc. IEEE Veh. Technol. Conf, Amsterdam, pp 1013-1-1017, Sept. 1999
[11]A. Cerdeira Estrada.; M. Lunardon; L. Marcato; M. Pierasco; S. Marsi, “Initial synchronization procedure for UMTS-FDD mode in FPGA”, Microelectronics, 2002. MIEL 2002. 23rd International Conference on, Volume: 2, 12-15, Pages:663 – 666, May 2002
[12] Kai Niu ; Qun-Feng He ;Wei-Ling Wu, “Improvements on acquisition of secondary synchronization channel in W-CDMA”, Info-tech and Info-net, 2001. Proceedings. ICII 2001 - Beijing. 2001 International Conferences on vol.2 Volume: 2, Pages:632 - 641, 29, Oct.-1 Nov. 2001
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