Intercarrier interference suppression and channel estimation for OFDM systems in time-varying frequency-selective fading channels

In orthogonal frequency division multiplexing (OFDM) systems, channel variations within an OFDM block destroy orthogonality between subcarriers, resulting in intercarrier interference (ICI), which increases an error floor in proportional to normalized Doppler frequency. To mitigate the effects of channel variations, many schemes have been proposed, but they are computationally complex or at the price of sacrificing spectral efficiency. In this paper, we first provide an ICI analysis in both time- and frequency- domain while existing literatures analyze the ICI effects mainly in frequency domain. Based on this analysis, we then propose a novel ICI suppression technique, which uses iterative ICI cancellation in time domain and has a computation complexin linear in the OFDM symbol length. Channel estimation in rapidly time-varying scenarios is critical for ICI suppression and coherent demodulation, and we also propose a scheme for estimating channel parameters varying within an OFDM block. Along with the channel estimation scheme, we investigate the issue of optimum pilot tone placement. Theoretical analysis and simulation results show, that the proposed ICI suppression method and channel estimation scheme have low computational complexity and good performance for most Doppler frequency of practical importance.