attached here a file comparing the performance of DSP and DCF, the difference in the performance can be seen from the constellation visualizer.
i don’t know where is the problem, the frequency domain filter just multiply the signal by the conjugate of {exp(j*[(beta2*omega^2/2)+(beta3*omega^3/6)]), beta2,3: second and third order dispersion, omega: angular frequency} to compensate dispersion.