WDM channels

(b)

Since the advent of coherent detection and DSP for coherent optical receivers, CD can be effectively compensated by digital equalization in the electric domain ad thereby, eliminating the need for dispersion compensating fibers (DCF). However, nonlinear mitigation in the dispersion managed (DM) links is also vital in order to upgrade existing links. Although, the computational complexity of DBP is quite high, for DM links, the DBP algorithm can be simplified by assuming that the nonlinear behavior repeats itself every span and therefore, the total nonlinearity after N spans of transmission can be approximated to N times the nonlinearity from a single span [70]. This is termed as distance folded DBP [70] and it reduces the complexity by a factor of N assuming the step size of DBP is equal to the span length and the span length is assumed to be constant. Assuming the dispersion is fully compensated in each span, only the nonlinear term in the nonlinear Schrödinger equation (NLSE) can be solved in the time domain avoiding the Fourier and inverse Fourier transformation (FFT/IFFT) pairs which reduces the computational cost of DBP drastically. We call this approach single step nonlinearity mitigation (SSNL). Similar to the unmanaged links as discussed in the earlier section

3.3. EKF for mitigation of nonlinearities in dispersion managed links

can be observed in Figure 5(b).

transmission at launch power of 3 dBm [58].

6

8

Q-factor (dB) 10

12

0 0*.*2 0*.*4 0*.*6 0*.*8 1

ODBP EKF OCDBP+EKF ODBP+EKF SSMF NZ-DSF

218 Kalman Filters - Theory for Advanced Applications
