The Study Of Multi-carrier Spread Spectrum Communication Technology

Multiple access system based on CDMA has been greatly favored in mobile communication applications. However, the performance of CDMA system is limited by both multiple access interference and inter-symbol interference(ISI). At the same time, OFDM technology has been more and more mature while its performance on resisting multipath fading is outstanding.Multi Carrier-Code Division Multiple Access(MC-CDMA) is a new Multi-carrier modulating technology for broadband mobile wireless communication. It combined the advantage of OFDM and CDMA, it can convert the frequency selective attenuation channel of the broadband to flat channel of the sub-carrier. It has adaptive flexibility, high capacity, high bandwidth efficiency and interference robustness. It can be used for high speed data transmission, has attracted much attention in recent years. So it is considered as the core technique of the future 4G wireless communication system.In this paper, the development of MC-CDMA and related technology are first introduced, and the basic principle of CDMA, OFDM and OFDM-CDMA are illuminated. Based on the analyzing and comparing of three solutions of OFDM-CDMA, it can be conclued that MC-CDMA is superior to others in performace.Then the predigested MC-CDMA system model is established and its simulation flow chart in Matlab are proposed, include the model of transmitter,wireless channel and receiver, and then its key techniques are analyzed. Some technologies of MC-CDMA and their functions in MC-CDMA system are emphasized, such as frequency spread of data in frequency domain, IFFT/FFT and Cyclic Prefix, and so on. Last, the multiple access interference of MC-CDMA system receiver will be analyzed, and the corresponding detection techniques will be introduced. It can be classified as signal-user detection and multi-user detection. The mathematics models are independently built, system simulation and theoretic performance analysis are done. Also, this paper adopts two-class detection to modify MMSE scheme, named MMSE-PIC scheme. The parallel interference cancellation(PIC) technique is adopted to realize multi-user detection. The results of the computer simulation illustrate that MMSE-PIC scheme with two stages could be a good compromise between system performance and computational complexity.