A Hybrid Envelope-IQ Moment-Based Non-Data-Aided SNR Estimator for QPSK

In this work, we investigate non-data-aided (NDA) signal-to-noise ratio (SNR) estimation for quadrature phase-shift keying (QPSK) communications over the additive white Gaussian noise (AWGN) channel. We propose a moment-based estimator that exploits the 2nd and 4th-order moments of simultaneously the envelope and the complex values of the received signal. We show that the suggested estimator outperforms existing 2nd and 4th-order moment-based estimators and that it achieves asymptotically the non-data-aided normalized Cramér–Rao lower bound (NDA-NCRLB). Besides, we analytically justify the performance of the suggested estimator with respect to classical estimators, including in the presence of residual phase noise.