Digital modulation classification: the BPSK versus QPSK case

The authors report on a novel BPSK/QPSK classifier and compare it to the more traditional, ad-hoc techniques of-a-square-law classifier and phase-based classifiers (weighting on the phase histogram). The proposed classifier is derived by an approximation of the likelihood-ratio functionals of phase modulated digital signals in white Gaussian noise, called a quasi-log-likelihood-ratio (qLLR) rule. It is shown analytically that its performance is significantly better than that of intuitively designed phased-based rules or the conventional square-law classifier