在分碼多工存取(CDMA)行動通訊系統中，因比傳統的分頻多工存取(FDMA)和分時多工存取(TDMA)多了分碼傳輸的技術，在干擾上也增添了多重存取干擾(MAI)，因此在解調時需要考量消除干擾的技術。本篇論文即是以直接序列(direct sequence)展頻技術調變之分碼多工存取系統，並利用多載子傳輸搭配正交分頻多工(OFDM)來達到消除干擾的目的。另外在以往多路徑的考量之下，系統會有多路徑干擾的存在，因此抑制多路徑干擾也是CDMA所需解決的一大課題。本篇論文目前只考慮單一路徑，但經由多載子的傳輸之下，一個接收訊號會因而更加的準確，在未來加入多路徑頻道的情形，將會更接近現實的通訊狀況。
解調上本篇論文先使用干擾投影法做傳輸時的振幅估測，並假設頻道的各項變數已知方便解調。目前較常使用的解調技術有Maximal Ratio Combining (MRC)、Equal Gain Combining (EGC)、Selective Combining (SC)等等，再加入平行干擾消除偵測器（PIC）或是續列干擾消除偵測器(SIC)的技術，便可以達到消除干擾以及增加系統效能的目的。本論文將利用MRC與PIC技術進行解調。

Because the Code Division Multiple Access (CDMA) mobile communication systems has the code division scheme in the comparison with traditional frequency division multiple access (FDMA) and time division multiple access (TDMA), therefore, the system has more interference due to multiple access interference (MAI). Hence, the interference cancellation scheme should be considered in demodulation. This thesis will emphasize on the CDMA systems with direct-sequence (DS) spread spectrum modulation incorporating with the multi-carrier transmission and orthogonal frequency division multiplexing (OFDM) to get better interference cancellation. Besides, with the consideration of multipath, the systems will have multipath interference. Hence a huge task of suppressing multipath interference should be also solved in CDMA systems. For simplicity, in this thesis, we only consider single path environment and the received signal will be divided into several carriers to transmit.
In demodulation, we will use the interference projection method. Firstly, we estimate the transmitted amplitudes and assume that the channel parameters are known for demodulation conveniently. Up to present, there are several widely used demodulation schemes such as Maximal Ratio Combining (MRC), Equal Gain Combining (EGC), Selective Combining (SC), etc. In this thesis, we will add the scheme of interference cancellation such as parallel interference cancellation (PIC) to MRC scheme to obtain the goal of interference cancellation and increase the system’s performance.

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