Research On Multi-carrier Modulation And MC-CDMA Interference Cancellation

Multi-carrier modulation technology, which has high spectral efficiency and can effectively combat the negative effect of multipath transmission, has become a key technology of High-speed data transmission. Most researches focus on Orthogonal Frequency Division Multiplex (OFDM), Wavelet Multi-carrier Modulation technique (WT-OFDM) and the combination of multi-carrier modulation technology and CDMA. However, the Doppler frequency shift, the frequency offset of transmitting and receiving carriers, the phase noise of oscillator and the effect of other time-varying factors can break the inter-carrier orthogonality, and cause Inter-carrier Interference (ICI) to multi-carrier modulation system, which may significantly reduce system performance. In a mobile environment, ICI is mainly caused by Doppler frequency shift. While, when combined with CDMA, Multiple Access Interference (MAI) is another key factor affecting system performance. In this paper, we research on the key technologies of the multi-carrier modulation system, ICI and MAI interference cancellation based on the interference generating model of multi-carrier modulation system.This paper first introduces the multi-path channel model. Using ray tracing techniques, we establish a ray distance and incident angle model of rectangular tunnel multi-path channel; through the model we can calculate the multi-path loss, delay, Doppler frequency shift, and the number of rays, which can provide reference for the subsequent research. In the multi-path channel environment, this paper establish Doppler frequency shift of OFDM system of ICI model, we propose a kind algorithm about Doppler frequency shift and time delay compensation for ICI cancellation according the signal to interference ratio, and give the performance analysis of the algorithm.In the MC-DS-CDMA system, we analyze the MC-DS-CDMA system model based on cooperative communication, and propose a joint MMSE multiuser detector according to the model. The theoretical analysis and the simulation results show that with the joint MMSE multiuser detector the proposed model can increase the system capacity and suppress the MAI effectively under the flat Rayleigh fading channel.For the wavelet multi-carrier modulation system, this article analyzes the principle of ICI caused by Doppler frequency shift and its mathematical expression based on polyphase decomposition M-band Wavelet Multi-carrier Modulation system model. Through analysis of mathematical expression, combining with the conditions of perfect reconstruction of M-band Wavelet multi-carrier modulation system, we propose the design conditions of M-band filter to reduce ICI and present methods to eliminate it. The impulse response model of the filter design conditions and iterative algorithms to eliminate ICI is also established. The simulation results show that the proposed ICI reduction and elimination methods can effectively improve the system performance.This paper also discuss the analytical methods in OFDM system, we analyze the spectral model of several kinds of anthropogenic interference using cyclic spectrum characteristics, combining the model we present the interference identification method by cyclic frequency.