Signal power distribution based modulation format identification for coherent optical receivers

A simple modulation format identification (MFI) technique based on extracting features from the statistical distributions of normalized signal power is proposed for cognitive coherent optical receivers. The proposed MFI technique requires no prior training and is independent of phase noise or frequency offset. Furthermore, it also performs good identification of the polarization-multiplexed (PM) M-QAM signals even after insufficient equalization of the constant modulus algorithm (CMA). Simulation results demonstrate successful MFI among PM-QPSK, PM-8-QAM, PM-16-QAM, PM-32-QAM and PM-64-QAM signals within OSNR range of practical system. Experimental verification using PM-QPSK/16-QAM/64-QAM signals also confirms the feasibility of the proposed MFI technique after long distance fiber transmission.