直接序列/分碼複接系統中之辨識碼快速擷取方法研究

Abstract

在直接序列/分碼複接系統中，唯有保證辨識碼的同步化之後才能正確無 誤地接收傳輸資料。 這項辨識碼的同步化工作通常被分為二個步驟來進 行︰第一個步驟稱為擷取 (Acquisiton)僅負責達成粗略的同步，當擷取 成功後第二個步驟稱為追蹤 (Tracking)，它緊接著利用一些迴授電路來 完成更精準的同步。本論文主要研究一種名為辨識碼匹配濾波器的快速擷 取方法， 並分別在 AWGN 通道和 Rayleigh 衰減通道中檢視其平均擷取 時間， 錯誤警示機率 (False Alarm Propability)，和臨界值三者之間 的關係。 另外為解決載波相位失準問題，一種差分式 (differential)的 架構在本論文中被提出，並和傳統的同相位/ 90度相位 (I-phase/Q- phase) 架構作比較，分別討論各別的優缺點。 In DS/CDMA systems, the extraction of information from the carrier requires the synchronization of a pseudonoise(PN) code at the receiver for correlation detection. The process of synch- ronization is usually accomplished in two steps. The first step, called acquisition, is to bring the locally generated PN code in the receiver into corse alignment withe the PN code superimposed on the incoming waveform. ONce the acquisition is achieved, the second step, called tracking, takes over and continuously maintains the best possible waveform fine alignment by means of a feedback loop. In this thesis, we focus attention on rapid acquisition scheme called PN matched filter. The relations between acquisi- tion mean time, false alarm probability, and threshold setting are both examined on the AWGN channel and on the Rayleigh fading channel. In addition, the matched filters employing the differential structure is proposed to reduce the hardware complexity of traditional I-Q noncoherent matched filters with little loss of performance.