Study On MC-CDMA And Its Key Technologies

MC-CDMA is one of the key technologies in next generation mobile communication. It combines the advantages of OFDM and CDMA. So it can convert the frequency selective channel propagation of the broadband to flat channel of the sub-carriers. It has adaptive flexibility, high capacity, high bandwidth efficiency and interference robustness. Therefore, MC-CDMA and its key technologies are deeply studied in this paper. The fundamental principle and performance of OFDM and CDMA technologies are introduced and compared in the paper firstly. Then three solutions of OFDM-CDMA are set forth and analyzed. On the basis of these analyzing and comparing of three solutions, it can be concluded that MC-CDMA is superior to others in comprehensive performance. As MC-CDMA is a multi-carrier modulation method presented for broadband mobile communication, the principles, schemes and performances of the system are illustrated firstly. Then the signal models and the FFT realization of the system are also analyzed in the paper. In MC-CDMA system, we exploit multi-carriers to transmit high-speed data, which is sensitive to the errors of synchronization, so synchronization is much important to the system, especially to those fast acquisition systems. Therefore, as one of the key technologies of MC-CDMA system, the synchronization of MC-CDMA system is mainly studied in this paper. Due to the multi-carrier transmission technology used in MC-CDMA system, almost all the previous synchronization algorithms in MC-CDMA system are derived from that in OFDM system. The data symbols transmitted in MC-CDMA system have the structure of CDMA signal, which is greatly different from normal binary signal in OFDM system. So a new synchronization technology based on the correlation property of PN sequence of MC-CDMA system is introduced and discussed in detail, in which synchronization is performed before FFT conversion in order to make full use of the transmitted CDMA signal structure. This paper discusses this acquisition technology based on the correlation property of PN sequence in MC-CDMA system. It carries out the comprehensive analysis of the principles and the acquisition performances in no fading AWGN channel and in Rayleigh fading channel. On the basis of these analysis, the paper points out that there are some disadvantages of this basic acquisition system based on the correlation property of PN sequence in MC-CDMA system, and puts forth some amelioration schemes to resist these disadvantages. On the basis of these amelioration schemes and the basic correlation property of PN sequence, a rapid hybrid acquisition system is proposed in this paper, which is based on the correlation property of PN sequence with adaptive decision threshold control in MC-CDMA system .The amelioration system utilizes the hybrid acquisition method to search the whole uncertainty phases. And the constant false alarm rate (CFAR) method is introduced to estimate the background power level and to set the detection threshold adaptively. The mathematics models and the detail performance analysis of this hybrid acquisition system are put forward in no fading AWGN channel and in Rayleigh fading channel. The theoretical analysis and computer simulation show that the amelioration system proposed in this paper has much shorter acquisition mean time than that of the basic scheme based on the correlation property of PN sequence in MC-CDMA system. So the conclusion may be drawn that the amelioration scheme has superior comprehensive synchronization performance to that of the basic scheme. Lastly the paper further analyzes that how does the mean acquisition time of the amelioration system change with the number of the parallel detectors.