As the relay protection for power systems is growing more intelligent and digital,the test performance requirements of relay protection are becoming increasingly complex.The complexity of the protection equipment models puts forward higher requirements for the signal modulation compatibility of the test system.Therefore,this paper proposes a new modulation classification method to classify a variety of modulation signals,such as binary phase-shift keying,quadrature phase-shift keying,and 16 quadrature amplitude modulation.The proposed classification method can work in the presence of unknown frequency,time and phase offsets as well as without channel state information.First,the received signal is preprocessed to eliminate the effect of time offset.Second,key features are extracted by calculating the higher-order cumulants of the frequency-domain signal.Third,a likelihood ratio test is used to determine the threshold and perform a closed-form theoretical derivation of the probability of correct classification.Finally,the method is compared with other methods by simulation,and the results show that the proposed method outperforms other methods in terms of accuracy and computational speed,which verifies its effectiveness.
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