hi fayiqa naqshbandi… thanks for the reply
the link u had posted has designed a system where it has used loop control fr both fiber link as vl as opt. amplifier….i am using it only fr optical fiber bt here it is bit complicated and it has used 2 fibers in between…i am using a single fiber and my distance is 150 km and i hv kept loops = 3..can u tel me why BER shows variation….thanking u in advnce