The third generation cellular mobile communication systems are expected to support several kinds of service, like voice, data, and video transmission. In other words, users will transmit their signal in different data rates. In this thesis, we choose Code Division Multiple Access (CDMA) using direct-sequence (DS) spread spectrum modulation to design a multi-rate system. MC and MPG access are used to reach the goal of multi-rate transmission. In MC access, a high rate user transmits using several spreading sequences. In MPG access, all signals are modulated to the same bandwidth, but the processing gain (PG) (and the symbol duration) of high rate users would be smaller than that of the lower rate users so that the high rate users can transmit more symbols in a given time.
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 multi-path effect. Both of them degrade the performance of the CDMA system. In order to suppress the interference, several multi-user detectors have been proposed, including the parallel interference cancellation (PIC) scheme. 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 this thesis, an algorithm, which combines the PIC scheme with the interference projection method, is proposed. By utilizing the interference projection method in the PIC scheme, the transmitting amplitude of every user can be estimated, and we can expect to have a better performance in the multi-rate multi-path CDMA system.

第三代蜂巢式行動通訊系統要能支援許多服務，如語音、資料及影像傳輸。換句話說，用戶會以多種傳輸速率來傳輸訊號。在這份論文中，我們選擇以直接序列(direct sequence)展頻技術調變之分碼多工存取系統，來設計一個多速率的通訊系統。我們使用MC及MPG技術來實踐多速率傳輸。在MC系統中，高傳輸速率使用者會使用多個展頻碼(spreading sequence)。在MPG系統中，所有訊號都被調變成相同的頻寬，但高速率使用者的展頻增益(processing gain)及符號區間(symbol duration)會小於低速率的使用者，如此高速率使用者才能在固定時間內傳輸較多的符號。
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，為了要抑制干擾，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）。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。在此論文裡，我們提出與干擾投影法相互結合之平行干擾消除偵測器。藉由應用干擾投影法於平行干擾消除偵測器中，我們可以估測出每個使用者的傳輸振幅，並能預期分碼多工存取系統在多速率多路徑情況下能有更佳的效能。

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