Performance analysis of OFDM in frequency selective time-variant channels with application to IEEE 802.16 broadband wireless access

In this paper, the performance of orthogonal frequency division multiplexing systems in frequency selective and time-variant Rayleigh fading channels is analyzed. Channel variations severely degrade the performance of OFDM by introducing both a complicated multiplicative distortion and an additive intercarrier interference. The IEEE 802.16 standard is designed to provide broadband wireless-services for fixed and pedestrian terminals, and hence, the channel is assumed to be slowly variant during one OFDM symbol. Under this assumption, the multiplicative distortion can be simplified as a sum of two correlated Rayleigh random variables. Based on this simplification, and by observing that the signal-to-interference-plus-noise ratio of the OFDM system is similar to the expression of the signal-to-noise ratio at the output of an equal gain combiner, we derive a closed form analytical expression for the symbol error rate. The proposed analytical expression is verified through numerical evaluation using the parameters of the IEEE 802.16 standard