 Gbit/s taps, LMS adaptation algorithm with ATC is also reported for comparison. (After Xia, C. and Rosenkranz, W., IEEE Photon. Technol. Lett., 19(13), 1041, 2007.) DL (ps/nm) ASN,(dB) Uncompensated 10 Gbit/s FFE9/DFE2 FIGURE 5.61 10 Gbit/s Performance of an electronic equalizer implementing MLSE equalization with the Viterbi algorithm at 10 and 20 Gbit/s 20 Gbit/s on a fiber line with polarization dispersion. The performances of an FFE-DFE with nine FFE taps and two DFE taps, and LMS adaptation algorithm with ATC is also reported for comparison. (After Xia, C. and Rosenkranz, W., IEEE Photon. Technol. Lett., 19(13), 1041, 2007.) PMD (ps) The performance of such an equalizer is shown in Figure 5.60 for a link affected by chro- matic dispersion and in Figure 5.61 for a link affected by PMD [71]. As in the case of the FFE-DFE, the performances of the equalizer are measured through the increment of the optical signal to noise ratio (ASN) needed to overcome the effect of dispersion. In both cases, and both at 10 and 20 Gbit/s, MLSE outperforms the considered FFE-DFE as soon as the distortion becomes relevant. The MLSE has also been demonstrated to be effective in mitigating the impact of non- linear distortion in DWDM systems. Both four-wave mixing (FWM) [83] and self-phase modulation/cross-phase modulation (SPM/XPM) [84,85] effects can be attenuated, con- temporary to PMD and chromatic dispersion compensation. As an example, let us consider the structure proposed in [84] where the MLSE digital equalizer comprises a 3 bit analog-to-digital converter operating at up to 25 Gsamples/s and a four-state (two bits per sample, one sample per transmitted bit) Viterbi decoder. This is a case of extreme reduction of the Viterbi algorithm, quite far from the unconstrained working. Nevertheless, it is effective in mitigating both linear and nonlinear fiber distortions. This is demonstrated in Figure 5.62, where the performance of the MLSE EDC is compared with that of a similar uncompensated receiver in the case of 10 Gbit/s spe