A BLIND MODULATION CLASSIFICATION (BMC) METHOD FOR LINEARLY MODULATED SIGNAL OVER SINGLE CARRIER SYSTEMS

摘要

A blind modulation classification (BMC) method has been proposed and implemented for single carrier linearly modulated signals. The proposed method is feature based (FB) method, i.e., a combination of both elementary and cyclic cumulant approach is adopted which gives an optimal performance over a fading channel environment even at low signal to noise ratio (SNR) values. The elementary fourth order cumulant is used to decide whether the modulation constellation is from real, circular or rectangular, it is also known as macro modulation classifier. On the other hand, cyclic cumulant approach is used to classify modulation within a subclass of macro modulation classifier also known as micro modulation classifier. For the micro modulation classifier, we use different position of non-zero cyclic frequency of intermediate frequency (IF) signal. We have used fourth order cyclic cumulant to classify between PI/4-quadrature phase shift keying (PI/4-QPSK) and minimum shift keying (MSK) which are from the circular constellation. A second order cyclic cumulant has been used at baseband level to classify between QPSK and offset QPSK (OQPSK) which are remaining from the circular constellation. The proposed BMC method is implemented on a National Instrument (NI) software defined radio and results are verified through simulation and testbed measurement, and compared with the existing elementary approach. It has been observed that the proposed combined method works well in flat fading channel and is more robust than the elementary cumulant approach. For the simulation and experiment, we have considered a six class problem which includes binary phase shift keying (BPSK), QPSK, OQPSK, PI/4-QPSK, MSK and 16-quadrature amplitude modulation (16-QAM).