寬頻CDMA系統反鏈通道資訊之取得模擬

Abstract

為了要在多路徑衰減(multipath fading)環境下實現同調檢測技術，可靠的通道資訊諸如每一衰減通道路徑的傳輸延遲及複振幅都必須被估計。在cdma2000反鏈(reverse link)系統中，有一專用的領航通道(pilot channel)同時與資料通道一起被傳送來實現同調檢測技術。這個領航訊號可以用來估計在執行犛耙式組合(Rake combining)時所需要的通道傳輸延遲或複振幅。對於傳輸延遲的估計，我們使用了一粗調碼取得(code acquisition)系統及一微調碼追蹤(code tracking)系統。在碼取得方面我們使用了一連續搜尋的(serial-search)匹配濾波器來執行粗略的傳輸延遲估計，而在碼追蹤方面則使用了一數位鎖延遲迴路(digital delay-locked loop)來執行較小的傳輸延遲追蹤。對於通道複振幅的估計，接收的領航訊號強度直接地被用來作為測量。為了要消除多路徑干擾及雜訊，我們使用了無限脈衝響應(IIR)與有限脈衝響應(FIR)的濾波器。使用這些濾波器的問題主要在輸入及輸出之間的群延遲(group delay)特性。對於即時的補償而言，輸入與輸出必須同步，為此，我們分析並比較了無限脈衝響應濾波器及有限脈衝響應濾波器應用在不同環境下的相位靈敏度及延遲特性。

In order to achieve coherent detection under multipath fading environment, reliable channel information such as delay and complex amplitude of each path in fading channel must be estimated. In cdma2000 reverse link, a dedicated pilot channel is transmitted with data channels simultaneously for coherent detection. This pilot signal can be used to estimate the channel delay or complex amplitude for Rake combining. For channel delay estimation, a coarse code acquisition and a fine code tracking are used. A serial-search matched filter is used for coarse delay estimation and a digital delay-locked loop (DDLL) is used for fine delay tracking in the synchronization system. For channel complex amplitude estimation, the received pilot signal strength is used directly as a measure of the channel behavior. To remove the multipath interference and noise, both the IIR and FIR filters are used. The problem with this filtering is the group delay between the input and the output of the filter. For real time compensation, the input and output must be synchronized. For this, the sensitivity of phase and the delay for both the IIR and the FIR are analyzed and compared for use in different environments.