近年來，由於有著較高容量、較佳抗干擾功能，分碼多工存取系統（CDMA）已成為一重要之通訊系統機制。然而，分碼多工系統中之主要缺點之一為多重存取干擾（MAI）。這是由於在此系統中，多位使用者同時在相同的頻帶上傳送訊息所造成。另一個形成干擾的原因則為多路徑干擾。此兩原因降低了系統的效能，為了要消除干擾，數種多用戶偵測器曾被提出，其中包括了平行干擾消除偵測器（PIC）。在此論文裡，我們提出與向量投影法相互結合之平行干擾消除偵測器。
　　平行干擾消除偵測器的結構是由多個傳統的匹配濾波器（matched filter）一層層組成，藉由層級上的疊代而改善傳統匹配濾波器的效能。在傳統的平行干擾消除結構內，使用者的傳送功率必須事先知曉以便能在干擾消除的過程中進行估測多重存取干擾的動作。藉由向量投影法，可以在使用者的傳送功率無法事先知曉的情形下估測多重存取干擾，並使接收器的效能仍然維持在不錯的範圍內。

　　Code Division Multiple Access (CDMA) has become an important access scheme in recent years because of its several advantages such as higher capacity, anti-jamming, etc. However, one of the serious shortcomings of CDMA system is the multiple access interference (MAI). The multiple access interference is produced when there are multiple users using the same frequency band simultaneously in the CDMA system. The other source of interference is the multipath effect. Both of them degrade the performance of the CDMA system. In order to suppress the interference, several multiuser detectors have been proposed, including the parallel interference cancellation (PIC) scheme. In this thesis, an algorithm is proposed, which combines the parallel interference cancellation scheme with the interference projection method.
　　The PIC scheme, which is constructed by several matched filters stage-by-stage, makes use of the adaptive iteration to improve the performance of the conventional receiver. In the conventional PIC scheme, the transmission power of every user must be known beforehand to arrive at a correct MAI estimation in the cancellation process. By utilizing the interference projection method in the PIC scheme, the transmission power of every user can be estimated, and a good performance of the receiver is retained.

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