Research On Modulation Recognition Method Of Telemetry Signal Based On Composite Modulation Characteristics

In the field of satellite communication telemetry,the modulation types involved are very rich,including secondary modulation,continuous phase modulation and other complex modulation signals,which brings some challenges to the field of modulation recognition.In this paper,a mathematical model is established for the concept of compound modulation characteristics.The secondary modulation set {PCM/FM ?BPSK/PM?QPSK/PM?OQPSK/PM?2FSK/PM},and the continuous phase modulation(CPM)set {FM,MSK,GMSK} are studied.The identification problem of the system is designed based on decision tree classifier.The main work is as follows.For the secondary modulation set which can be extracted by demodulating,a set of processing methods are given,which are demodulated first and then identified.Aiming at FM and PM signals,a PCM/FM signal recognition method based on the characteristics of cyclic spectral lines is proposed.The modulation type is effectively distinguished when the SNR is greater than 0d B.The spectral line generation characteristics of modulation signals are analyzed.The recognition of BPSK/PM,QPSK/PM,OQPSK/PM,2FSK/PM is realized by using spectral line ratio as classification feature.The recognition success rate is over 95% in signal-to-noise ratio of 7d B.In this paper,the phase locked loop is proposed to improve the carrier synchronization effect before extracting phase angle.For the estimation of carrier bandwidth and other parameters involved in demodulation,a simple estimation method is given.For the frequency modulation and continuous phase modulation which is difficult to extract the composite modulation feature directly in phase,this paper analyzes whether FM and CPM modulation contain digital symbol information.A feature parameter based on cyclic spectrum extraction symbol rate spectral line is proposed to realize the recognition of two modulation types in signal-to-noise ratio of 0d B.For the modulation types of MSK and GMSK,which are also CPM modulation,the signal model and its cyclic stability characteristics are sorted out.It is found that due to the difference of frequency pulse forming function,the number of spectral lines in different cycle frequency sections of the cycle spectrum is different after the frequency doubling.A method of extracting discrete spectral line characteristics based on frequency doubling cycle spectrum is proposed.The spectral line ratio is used as the feature parameter,which can distinguish the two modulation types effectively at 7d B.Finally,FM,CPM are placed in modulation set {CW,AM,FM,BPSK,QPSK,OQPSK,8PSK,DBPSK,DQPSK,CPM}.By using the information spectral lines of envelope spectrum symbols,instantaneous amplitude characteristics and high-order cumulants,the modulation recognition scheme based on decision tree is given.The recognition success rate is more than 95% when the SNR is more than 8d B.