Comparison of OFDM and frequency domain equalization for dispersive optical channels with direct detection

In this paper, advanced block-transmission schemes for dispersive optical channels with intensity modulation and direct detection are discussed and compared. In the framework of orthogonal frequency division multiplex or its real valued base-band derivate discrete multitone transmission (DMT) we analyze DC-biased DMT, pulse-amplitude modulated DMT as well as asymmetrically clipped DMT. The results are compared to those of base-band pulse-amplitude modulation with frequency domain equalization. The dispersive optical channel is modeled as a Gaussian type low-pass filter. Closed-form expressions to estimate the required optical power are presented. Under the constraint of using power loading and no bit loading, we show that frequency domain equalization outperforms DMT.