一種用於寬頻分碼多重進接上傳系統中非連續性傳輸之改良式碼擷取方法

Abstract

在直接序列/分碼多重進接系統中，碼擷取（Acquisition）的效能直接影響到系統的傳輸容量。在第三代行動通信中，非連續性的傳輸方式造成上傳系統要維持碼同步的困難度大增，所以快速而且高效率的碼擷取方式是必需的。 本論文主要是討論碼擷取系統中的後偵測積分（Post-detection Integration）對碼擷取效能的影響，比較傳統方式在不同通道下的優缺點，並針對個別的缺點提出一種較精確的改良方式。所提出的方法是以通道估測為著眼點，針對靜態與動態的通道提出一個穩健的架構，此架構運用到線性迴歸分析（Linear Regression）的理論。

In DS/CDMA communication systems, the capability of spreading code acquisition can decide the number of users affordable in a system. Moreover, in third-generation wireless communication system, bursty (non-continuous) transmissions in uplink network make the maintenance of synchronization more difficult. Thus, a fast acquisition algorithm with high detection probability is required. In this thesis, the effects of several post-detection integration (PDI) schemes in acquisition algorithm are discussed. Performances of each scheme under different channel environments are compared. A more robust scheme in both static and time-varying channel is proposed. We introduce a channel estimation algorithm based on linear regression to analyze PDI scheme. With more elegant channel estimation, the new scheme can adapt better to different channel environments. 2 Random Access Transmissions in W- CDMA Uplink System 3 2.1 Random Access Transmission Protocol 3 2.2 Spreading and Modulation 7 2.2.1 Channelization Code and Preamble Signature 7 2.2.2 Scrambling Code 9 3 Acquisition Methods 13 3.1 Preliminary 13 3.2 System Modeling 15 3.2.1 Noncoherent Reception in Acquisition 15 3.2.2 Effect of frequency Offset 19 3.3 Delay Searching 21 3.3.1 Searching Strategies 21 3.3.2 Searching Procedure 22 3.4 Despreading Schemes 24 3.4.1 Active Correlator 24 3.4.2 Matched Filter Correlator (MF) 24 3.4.3 Differential Matched Filter Correlator 25 3.5 Post-detection Integration (PDI) Schemes 27 3.5.1 Noncoherent PDI Scheme 27 3.5.2 Coherent PDI Scheme 27 3.6 False Alarm and Detection Probability 29 3.6.1 Likelihood Ratio 29 3.6.2 Threshold Setting by Neyman-Pearson Criterion 29 4 Post-detection Integration Scheme Based on Linear Regression Channel Estimation 31 4.1 Preliminary 31 4.2 Channel Estimation 33 4.2.1 Noncoherent PDI Scheme 33 4.2.2 Coherent PDI Scheme 34 4.2.3 Linear Regression Channel Estimation 37 4.3 Architecture of PDI Based on Linear Regression Channel Estimation 39 4.4 Background Noise Power Estimation 41 5 Computer Simulations 44 5.1 Simulation Environments 44 5.2 Simulation Results 46 5.2.1 AWGN Channel 46 5.2.2 Time-Varying Channel 48 5.2.3 Noise Power Estimation and Threshold Setting 50 6 Conclusions 52 References 54