無線直接序列展頻犛耙式接收器之設計

Abstract

無線通訊通道常有複徑衰褪的現象，而使得一般傳統的解調方式不再可行 。在這種環境下，使用寬頻信號為一種相當有效的方法。主要的原因是我 們可以使用類似犛耙式的接收器來提昇系統的性能。而犛耙式接收器在慢 速限頻衰褪環境中接近於最佳化表現，已引起廣泛的注意。本篇論文旨在 研究寬頻直接序列展頻系統中犛耙式接收器的設計。我們將探討兩種不同 架構的接收器。第一種為傳統之RAKE接收器。這種接收器需有通道測量以 及亂碼獲得線路來結合各個不同的路徑。第二種方法則是利用適應性濾波 器來同時完成路徑結合，通道等化以及某種程度亂碼獲得。有關設計這些 系統可能面臨之考量，像是亂碼獲得機率，亂碼獲得與通道等化以及位元 錯誤率之比較等，都是本文討論的主要議題。 Because of the presence of multipath fading, conventional narrowband signalings often suffer from severe performance degradation in a wireless communication environment. Wideband signaling is an alternative to mitigate fading if appropriate receiver design is in place, i.e, a RAKE-like receiver can be used to combine signals from distinct paths and provide much enhanced capability in a frequency-selective channel. On the other hand, RAKE receivers have been shown to achieve near optimal performance in slow frequency selective environments. This thesis concerned about the design of a RAKE-like direct sequence spread spectrum (DS/SS) receiver for wireless communication. Two receiver structures are discussed. The first one is the conventional RAKE structure which requires additional channel estimation and code acquisition circuits to combine different paths. The second alternative is realized by an adaptive filter which performs path combining, channel equalization and, to certain extent, code acquisition at the same time. We discuss issues related to the design of such systems like PN-code-acquisition probability, the relation between code acquisition and equalization, and bit error rate performance comparisons.