n Systems Starting from the model reported in [75] and imposing the condition of small penalty, it is possible to determine the penalty in our conditions. For high power channels, XPM causes a plateau, not differently from other power depen- dent effects, but in the range of the possible power in this class of systems, the penalty is SO low that the plateau can be neglected. As far as FWM is concerned, the same model used in Chapter 6 can be reapplied here: FWM-induced crosstalk can be considered as an additional noise, due to its variability that is almost random for the effect of the walk-off. Reapplying the evaluation of Chapter 6, the FWM-induced penalty results to be about 0.5 dB. 9.5.1.2.4 Linear Crosstalk The analysis of the impact of the linear crosstalk can be done in complete analogy to what was done in Chapter 6 for IM systems. However it has to be taken into account that the worst case for linear crosstalk is constituted by a 100 Gbit/s channel with only 40 Gbit/s channels around, as a matter of fact, the binary 40 Gbit/s channels have a wider spectrum SO causing higher linear interference. The evaluation has been done with the method of [74] both for the case of all DPSK chan- nels and for the case of a single 100 Gbit/s channel with 40 Gbit/s channels around. The penalty curve is plotted in Figure 9.52. In our case, it results a penalty of about 0.15 dB for the case of complete substitution of the channels with 100 Gbit/s 8-DPSK (when /2R=6) and 0.3 in the case of an isolated 8-DPSK channel among a 40 Gbit/s comb (where Aw/2R=5). 9.5.1.2.5 Penalty Analysis Summary The summary of the penalty analysis is reported in Table 9.10. The estimated SN, required to reach the desired performances is 21 dB, smaller than the about 22.3 dB obtained from the draft design. Second step is the simulation, which here is carried out considering the evolution of the deterministic part of the signal and adding the effect of noise analytically. This confirms the effectiveness of the draft design and the fact that the 8-DP