Thank you Alistu,now i am confused that in case of simple dwdm system results change when i change the SL without using any HOA.I think raman fiber cause this type of effects? If raman cause this then this also effects ither systems too where fsmf used.I got your point about ofdm and i think its correct.Damian explaines this better ,because as far as this paper is concerend ,it is also implemented in optisystem as i have full dessertation of author .Alistu how to now conclude this factor if i have explain this ?