US Patent 9425908 Method and apparatus for estimating the current signal-to-noise ratio

A method of estimating current SNR in a sequence of symbols, including receiving a signal representing an additive mixture y(t)=s(t)+n(t) of a sequence of phase-modulated symbols with fixed length and phase modulation s(t) and including white Gaussian noise (AWGN) n(t); separating quadrature components IY and QY of the received signal in a quadrature mixer; determining a mean-square IY2 of IY; determining a mean-square QY2 of QY; determining a square/squared value of mean absolute value (modulus) |IY|2; determining a square of mean value for quadrature component ]QY[2, where values of the quadrature component QY are averaged taking into account a sign of a symbol received in a channel; determining a current absolute value (vector length) for Iy2+Qy2; determining the current SNR based on IY2, QY2, |IY|2, ]QY[2 and √{square root over (Iy2+Qy2)}; and compensating for a systematic error of the current SNR.