Signal-to-noise ratio measurement for the signals with constant amplitude

A digital meter measuring the signal-to-noise ratio in the channel for transmitting discrete information with a constant amplitude of symbols that are the phase or frequency shift keyed signals is proposed. The desired value of the signal-to-noise ratio is determined based on the number of exceedings of the threshold level by the modulus of the logarithm of the ratio of the amplitudes of the received and previous symbols in the sample of a specified size, while the meter itself is invariant to the absolute levels of the signal and noise. It is shown that in the channel with Gaussian noise, this number depends only on the desired signal-to-noise ratio. The necessary calculation relations are successfully obtained; it is also established that the Gaussian approximation of the symbol amplitude probability density is valid. Statistical simulation of the meter operation has been carried out for receiving binary phase shift keyed signals. It is proven that the given theoretical meter characteristics are in satisfactory agreement with the corresponding experimental data and the small measurement error is provided within a wide range of signal-to-noise ratio values.