QPSK coherent detection
hi. i designed 150 km dual polarization QSPK with coherent detection in 4 WDM channel and use DSP for QPSK component in order to compensate impairments. obviously without EDFA the results are not good. but when i increase the length of fiber to 160km, the BER become very very good!!!
how can i describe this?
or where is the problem?
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