The Research Of Automatic Digital Modulation Recognition

Automatic modulation recognition of communication signals is a new research direction in the signal analysis field, and it has a very widely applied foreground, especially, in the military communication realm. With the development of the technical research on the electronical countermeasures, it urgently needs the technical research on the automatic modulation recognition which is applied extensively in the realms, such as the signal confirm, the interference identify, wireless interception, signal monitor and so on.This dissertation studies digital modulation to make a way of blind identify, without any information before recoginiton.Firstly, after analyzing the different modulation recogniton methods proposed in the literature carefully, we adopt the statistical modulation recognition method basing on the decision-theoretic approach to recognize the modulation signals corrupted by the channel noises properly. After analyzing some methods of carrier frequency withdrawing, we adopt the mehtod of estimating the carrier frequency from the signal's instantaneous frequency which is extracted from the instantaneous linear phase. Then we list many characteristic parameters of modulation recogniton. According to the subsampling theory, digital quadrature processor based on polyphase filters is proposed in this dissertation to substitute the conventional lowpassing quadrature processor to extract the typical instantaneous features.Secondly, comparing with the algorithm that was given by English scholars A.K.Nandi and E.E.Azzouz in 1995, this dissertation presents a modified automatic recognition algorithm of six kind of digital modulation types such as 2ASK, 4ASK, 2PSK, 4PSK, 2FSK and 4FSK, which only uses four key features, and has a very great exaltation in the rate of correct recognition and the performance of signal to noise, we puts forward the constitution of the best threshold which is applicable to the signal that changes within the scope of the signal to noise rate (SNR) from 5dB to 30dB, and the overall success rate is not lower than 92% when SNR is over 7dB.