1. A bit error rate modeling method for quasi-linear communication systems, comprising: analytically calculating a combined covariance matrix for noise; computing probability distribution functions from the combined covariance matrix; numerically integrating the probability distribution functions to provide a modeled bit error rate; wherein the use of a split-step fast Fourier transformation is avoided for the simulation of long bit sequences and a numerical Fourier transformation is used only to transform a one bit waveform at an input and to compute an integral for a characteristic function at an output; and simulating and configuring a network using the modeled bit error rate.