Study Of Channel Equalization Technique For OFDM Wireless Communication Systems

Orthogonal Frequency Division Multiplexing (OFDM) is a high efficiency multi-carrier transmission technology. Currently, because of nice ability against multi-path interference and high bandwidth efficiency, OFDM gets more and more attention and has already been one of key techniques in 4G mobile communication systems.However, to achieve this goal, there are still a lot of problems to be resolved, and channel equalization technology is one of them. When there is a higher carrier frequency offset or the Doppler frequency shift caused by the relative movement between the transmitter and receiver is larger, the orthogonality between subcarriers will be destroyed, resulting in a serious inter-carrier interference (ICI), and lead to greatly degrade system performance. To mitigate the ICI, this paper makes an in-depth research on the channel equalization problems in the OFDM wireless communication systems.Firstly, the characteristics and model of wireless channel and the basic principle, structure and characteristics of OFDM systems are introduced.Then some frequency domain equalization algorithms and ICI self-cancellation schemes are proposed based on analyzing the generating mechanism of ICI in detail. In order to improve bandwidth efficiency, we also propose a modified ICI self-cancellation scheme.On the other hand, for OFDM systems over time-variant channel, we propose a zero-forcing equalization method based on linear precoding technique. First, we analyze the bit error rate (BER) performance of this system without introducing redundancy and derive the optimal criterion for the design of non-redundant linear precoders. In order to achieve maximum diversity gain, we then derive the criterion in designing the optimal redundant precoders. Finally, we propose a block precoded method. This method can effectively reduce the designing complexity and computing complexity. Theoretic analysis and simulation results demonstrate that in a higher signal-to-noise ratio (SNR), our equalization technologies are capable of mitigating the ICI and improving the BER performance.