Comparison of four SNR estimators for QPSK modulations

Four signal-to-noise ratio (SNR) estimators for quaternary phase-shift keying (QPSK)-like signaling are proposed and examined. Two are based on receiver statistics directly related to the SNR while two others are based on receiver statistics inversely related to the SNR. The results show that the estimators based on the inverse of the SNR perform better than the estimators based on the SNR.