| Summary: | 碩士 === 國立清華大學 === 動力機械工程學系 === 97 === 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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