Equalization of orthogonal frequency division multiplexing signals

An equalizer is generally a transversal filter which can be used either at the passband or the baseband. Adaptive equalizers adapt filter coefficients to cancel the channel response. We study two different frequency domain adaptive equalizers for orthogonal frequency division multiplexing systems (OFDM). After introducing some theoretical aspects we derive a lower bound for the signal-to-noise ratio reduction due to equalization. Comparisons between two different equalizer structures, the least-mean square (LMS) and proportional equalizers, are presented and tested by simulation in a terrestrial TV channel with strong microreflections.