在DS/CDMA系統中適應性多重使用者之碼擷取

Abstract

在直接序列分碼多重存取的系統中，通常使用匹配濾波器來完成碼之擷取。然而，在多重存取干擾的環境下，匹配濾波器的效能會大大地降低。為了解決這個問題，適應性濾波器的方法已經被提出。雖然這個方法有效的處理了多重存取干擾的問題，但是它的計算複雜度太高了。這篇論文提出了另一個方法“多率適應性匹配濾波器”之方法，這個方法能夠達到近似於原來適應性濾波器的效能但其計算複雜度卻大大地被降低了。為了進一步改善碼擷取的效能，多重使用者碼擷取的方法被提出，在這個方法中，所有的使用者同時處理碼的擷取。模擬的結果顯示出，當多率適應性匹配濾波器之方法能夠達到近似的擷取時間和錯誤率的情況下，它的計算複雜度是原來的適應性匹配濾波器之方法的三分之一或是二分之一。而且，多重使用者碼擷取之方法的效能是優於單一使用者碼擷取之方法的效能。

Code acquisition in direct sequence code division multiple access (DS/CDMA) systems is usually conducted using a matched filter. However, in a multi-user interference (MAI) environment, the performance of the matched filter is seriously degraded. The adaptive filtering approach has been proposed to overcome this problem. Although this approach can effectively deal with the MAI problem, its computational complexity can be very high. In this thesis, a multirate adaptive filtering method is proposed. This method can achieve similar acquisition performance as the original adaptive filter approach, however, the computational complexity is significantly lower. To further improve the acquisition performance, a multi-user acquisition scheme is also proposed. In this scheme, all users in acquisition are considered simultaneously. Simulations show that while the multirate adaptive filtering approach can achieve the similar acquisition time and error rate, its computational complexity is one third or half of the original adaptive filtering approach. Also, the multi-user acquisition can outperform the single-user one.