Research On The Anti-fading Approaches In WFRFT-OFDM Systems

Orthogonal frequency-division multiplexing (OFDM) is a method of encoding digital data on multiple carrier frequencies. And channel state information is needed to be estimated by channel estimation algorithms, which is crucial for achieving reliable communication with high rates. An improved transform domain channel estimation method is proposed to enhance the quality of channel estimation of wireless fading environment with impulsive noise. On the other hand, to cope with time-frequency selective, as it usually happens in the rapidly fading wireless channel, a new multicarrier system is designed in which the weighted fractional Fourier transform replaces the traditional Fourier transform.Firstly, areas of channel estimation of OFDM systems are investigated in the first chapter. There are already plenty of studies engaged in estimation methods for calculating the channel state information in the receiver; however, few researchers have taken consideration of the particular condition with impulsive noise. Besides, theoretical analysis of the ICI in WFRFT-OFDM system is lacking.Secondly, the proposed transform estimation algorithm, composed of impulse equalization, flexible threshold of filter, is designed and implemented in the second chapter. Mathematical simulation illustrates that the proposed method outperforms the conventional one under impulsive noisy wireless channel.Thirdly, we have derived theoretical expression of ICI of WFRFT-OFDM system which is useful for selecting optimal fractional order. We find that OFDM with fractional order equals one has the worst ICI performance compared with the system with fractional order ranging from zero to one. Finally, by choosing the proper fractional order, WFRFT-OFDM system outperforms single-carrier and OFDM schemes in time-frequency selective fading channel.