M-APSK (amplitude phase shift keying) signal to noise estimation method based on iterative decoding and decision feedback

The invention discloses an M-APSK (amplitude phase shift keying) signal to noise ration estimation method based on iterative decoding and decision feedback. The method includes subjecting a transport signal to utilize a variable bit rate decoder to obtain feedback result, modulating to obtain a receiving signal without noise, finding out relative position of the receiving signal on a constellation map, dividing into a plurality of circular rings, obtaining each circular ring receiving signal through solving rotation, calculating amplitude mean value of each circular ring receiving signal, calculating useful signal total power and transport signal total power according to the amplitude mean value, and calculating estimated value of signal to noise ratio. The concept of iterative estimation is adopted, iterative decoding output information bit is used for inverse modulation and constellation map division, and the data-aided algorithm is adopted to finish estimation of the signal to noise ratio, so that the prob