stor- tion, Proceedings of Optical Fiber Conference, OSA, s.l., 2006.) Telecommunication Networks Starting from the propagation equation (Equation 4.39) it is demonstrated that the reverse propagation is obtained just from the forward propagation equation with negative parameters. In this way, the signal attenuation is transformed into a gain and the operators working on the phase of the signal induce a rotation into the opposite direction. Thus, to obtain the input signal corresponding to a certain output (i.e., the unperturbed signal) it is sufficient to "invert" the parameters of the propagation equation and to apply the split-step Fourier method, the same that is used to simulate fiber propagation in nor- mal conditions [91]. From a processing complexity point of view, the signal processing block at the transmit- ter is one of the critical components. In a practical system this block can be either implemented as an ASIC or by using a DSP or an FPGA. It is worth noting that in this case the ASIC solution could prevail even if it is more expensive and time-consuming due to its optimization, which could allow the con- sumed power to be reduced reentering within the system limits while achieving higher processing speed. If the pulse distortion is mainly caused by linear propagation and nonlinear effects are negligible, the complexity of this device is mainly driven by the number of complex taps necessary for the FIR filter to compensate for the chromatic dispersion. Several studies have been done to optimize the number of taps that can be adopted in this case [92] and it is demonstrated that the complexity scales linearly with the amount of accumulated dispersion to be compensated. It was shown that the complexity grows quadratically with an increasing bit rate [90]. In the presence of substantial nonlinear effects, nonlinear filtering has to be used. When a look-up table is used for filtering, the number of entries is determined by the number S of symbols that significantly interfere with each other. In particul