FIELD: digital data exchange over digital phase-modulation communication channels; digital data transmission systems. SUBSTANCE: information about signal quality in receiver is obtained by executing following operations with signal: first estimate of phase ϕ1 is generated in receiver for each respective phase-modulated digital character; second estimate of phase ϕ2 is calculated in receiver for each phase-modulated digital character from formula ϕ2 = ϕ1+ϕ3, where ϕ3 = const; decisions are taken using first and second calculated estimates of phases ϕ1 and ϕ2 on respective first and second m-bit codes, where m = log2M; distance is found according to Hamming as difference in number of bits between first and second m-bit codes and distances found according to Hamming for preset number of phase-modulated digital characters are summed up; information about quality of phase-modulated digital characters is determined by sum obtained. EFFECT: enhanced precision and equal time for measuring all values of input signal-to- noise ratio. 1 cl, 3 dwg
