Study Of The Joint Adaptive Equalization Technique In Time-and Frequency-Domain For OFDM Channel

Wireless communication systems are currently designed to provide high-data rates at high terminal speeds. Due to the increase of data-rate, multi-path effect gives rise to frequency selective fading of wireless channel. In addition, the relative mobility between the transmitter and receiver of wireless communication system will give rise to the Doppler shift of the receiving signal. As a result, the Doppler effect gives rise to time selective fading of wireless channel. The time- and frequency- selective fading channel is so-called doubly selective fading channel. In this thesis, we study equalization techniques for OFDM over the frequency selective fading channel and doubly selective fading channel respectively.In this thesis, we review the progress of OFDM and adaptive equalization technique. Then the characteristics and model of wireless channel and the basic principle , structure and characteristics of OFDM system are introduced. Finally, we focus on the joint channel equalization algorithm in time- and frequency- domain for OFDM over two types of multi-path fading channel respectively.First, for OFDM system over the frequency selective fading channel, a time- and frequency-domain adaptive equalization algorithm is proposed based on analyzing the generating mechanism of inter-carrier interference (ICI) and inter-symbol interference (ISI) by insufficient cyclic prefix. Theoretic analysis and simulation results demonstrate that the algorithm is effective and can increase frequency efficiency dramatically. On the other hand, for OFDM system over doubly selective fading channel, a time- and frequency- domain iterative ICI equalization algorithm is proposed based on analyzing and investigating the generating mechanism of ICI in detail. In addition, a design method of OFDM channel equalizer is proposed. Theoretic analysis and simulation results demonstrate that the algorithm is effective and can increase OFDM system's capability in reducing Doppler shift dramatically.