寬頻分碼多工之複亂碼擷取系統的性能分析

Abstract

本篇論文探討一寬頻分碼多工（CDMA）之複亂碼粗調擷取系統(Code Acquistion System)在複徑衰褪（Multipath Fading）以及多工干擾（Multiple Access Interference）下的性能分析。 不論歐盟與日本之WCDMA或美國之cdma-2000，都採用complex spreading/QPSK以達到降低傳送訊號PAR (peak-to-average ratio)並提高功率效率之目的。在本篇論文的分析與傳統的分析主要相異，在於我們考慮了通道衰褪及多工干擾所造成的統計相關性。我們修正了早先較粗略的馬可夫模式並利用Royan 氏的結果來計算出精確的平均碼擷取時間 (Mean Acquisition Time)。 本論文所考慮的寬頻分碼多工系統為cdma2000上行鏈路（Reverse Link）系統。而所採用的擷取方法則為碼匹配濾波器（PN Code Matched filter）。這種方式可在寬頻多工的環境下迅速的完成亂碼擷取。

This thesis studies the code acquisition subsystem performance of the reverse link of the IS-2000 (previous known as cdma2000) radio interface in which complex sequence spreading is used to minimize the peak-to-average (PAR) ratio. Our work focuses on the analysis of the mean acquisition time performance, assuming a correlated Rayleigh multipath fading environment. Code acquisition is the most crucial step in setting up a direct sequence spread spectrum (DS/SS) communication link. Extensive researches have been carried out to study the performance of various code acquisition schemes. This thesis considers the one that uses pseudo-noise matched ?lter (PNMF) detectors for its rapid acquisition capability. Our analysis di?ers from earlier approaches in that we take into account the statistical correlation among the matched ?lter outputs corresponding to di?erent code phase positions. The correlation is due to the higher-than-1 sample/chip sampling rate and the channel e?ects such as multipath fading and multiple access interference from other users. We modify and extend the Markov chain model used by the conventional approach to take the detector output correlation into consideration. The results of Ruyen are then applied to evaluate the associated probabilities and whence the acquisition time performance. Numerical examples demonstrate that our analysis yields very accurate performance prediction while the conventional approach often gives too optimistic pre- diction.