Performance degradation of OFDM system over time-varying fading channel

The paper considers the performance degradation of an orthogonal frequency division multiplexing (OFDM) system over frequency-selective time-varying fading channels. The time variations of the channel during one OFDM frame destroy the orthogonality of the different subcarriers and generate power leakage among the subcarriers, known as intercarrier interference (ICI). A novel and suitable channel model for OFDM is introduced and serves as the basis for the derivation of the ICI. The bivariate probability density function (PDF) of the ICI is shown to be a weighted Gaussian mixture. A two-dimensional Gram-Charlier representation for the bivariate probability density of the ICI is established; it is shown that its truncated version, of order 4,6, provides a very good approximation. Finally, the degradation in the performance of OFDM resulting from Doppler effects caused by a time-varying, frequency selective Rayleigh fading channel is obtained by averaging the approximated ICI statistics over the fading channel statistics.