6 dB Code gain (dB) Standard ITU-T code gain Total SNo precode 20 dB To confirm with simulation Total SN precode 20 dB The first is a Monte Carlo simulation that is able to simulate also the noise. This is a quite accurate program, but it is computationally very complex, especially when a great number of runs have to be carried out for statistical reasons. Running on a pc equipped with an i7 Intel processor, it is possible to arrive to an esti- mate of the error probability with a precision around 10% with few days of running, only if the BER is not smaller than 10-4, that means simulating the transmission of around 5 X 105 pseudorandom bits. We have also used a semianalytical program that simulates the propagation of the deter- ministic part of the signal and, at the end, evaluates the error probability by the saddle point approximation on the ground of the theoretical properties of the noise (naturally taking into account the real shape of the filters, and SO on). Both the programs are scalar, SO that all effects related to the vector nature of the field have to be inserted at the end in a phenomenological way. The two programs give results in a good agreement when they can be superimposed. The simulation result in terms of BER versus the SNo are reported in Figure 6.27a for both programs, where the simulation points are interpolated with a BER function of the form (Equation 6.65) fitting the free parameters with the simulation points. Transmission Systems Architectures and Performances (BER) log10 (BER) SN° (dB) SN° (dB) 10 Gbit/s 40 Gbit/s Semianalytic Semianalytic Monte Carlo Monte Carlo FIGURE 6.27 BER simulation of the system whose draft design reported in Table 6.4. Two types of simulation points are reported, Monte Carlo simulation and a semianalytic simulation where the signal propagation through the fiber and the different devices are simulated while the error probability is evaluated analytically on the ground of the theoretical noise distribution: (a) R =10 Gbit/s and (b) R = 40 Gbit/s. To attain the