ed by the scheme of Figure 5.63 is quite effective in compensating large amounts of chromatic dispersion. However, the pre-compensation technique allows the received pulse to be dispersion- free, but causes during propagation the broadening of the transmitted signals due to the combined effect of pre-distortion and dispersion. This complex evolution, almost unavoidably, causes the apparition in some points along the link of complex structures with high maxima and deep depleted minima. The high-power density maxima create a strong nonlinear effect, thus the pre-distorted signal is more prone to the nonlinear effect impairments with respect to a standard, non- compensated signal. Nonlinear effects compensation can be operated in principle through the use of the so- called look-up table-based pre-distortion. This technique conceptually consists of the fol- lowing steps: A physical model of propagation through the link is implemented in a DSP, based on a nonlinear propagation equation like Equation 4.39; this model depends on a set of parameters that are specific to the link under operation. At the beginning, in a set-up phase, the propagation model parameters are tuned by observing the link behavior when a set of known bit patterns is transmitted through the link. When a good estimate of the link parameters is reached they are used to fit the link behavior with the propagation algorithm. Once the algorithm is tuned on the real link characteristics it is used to construct the inverse of the propagation operator through virtual pulse back-propagation through the link. The inverse propagation operator is thus stored as a set of parameters in a look-up table that is used for fast pre-distortion during link operation. The link enters operation and the transmitted pulses are pre-distorted using the data stored in the look-up table. An adaptive algorithm adapts the look-up table parameters to the slow channel changes by repeating the link parameters identification periodically. Technology for Telecommunications: Integrated