Research On Blind Analysis Of Hybrid Modulation Signals

With the current development of modulated signals in the communication field,the traditional single modulation signal has been unable to meet the complex communication needs,so the research of hybrid modulation signal becomes more and more important.Hybrid modulation signal is a signal that has been modulated twice or more.The inner modulation is called subcarrier modulation,and the outer modulation is the main carrier modulation.At present,hybrid modulation signals are used in military and civil fields widely,but there is no universal discrimination method for modulation recognition of hybrid modulation signals.In thesis,according to the modulation method of hybrid modulation signals and its related characteristics,a universal modulation model of hybrid modulation signals is established.For PCM-BPSK-PM,PCM-QPSK-PM,PCM-2FSKPM,PCM-BPSK-FM,PCM-FM and PCM-PM signals,thesis carries out power spectrum formula derivation,judgment of whether it belongs to hybrid modulation or not,recognition of inner and outer modulation modes and parameter estimation.The major work is as below.1.According to the spectral peak-line interval of hybrid modulation signals,thesis presents an algorithm based on SPL-LSEC to judge whether the signal is compound or not.SPL and LSEC are two characteristic parameters,namely,spectral peak line joint parameter(SPL)and line spacing energy concentration(LSEC).The experimental results show that the algorithm can achieve recognition accuracy of more than 98% when the SNR is greater than 7d B.2.After accurately judging whether the signal is a hybrid modulation signal,thesis proposes an FM\PM main carrier discrimination method based on the the difference of spectral line characteristics between PM and FM modulated signals at the main carrier frequency.This method can distinguish the signal with PM modulation as the main carrier modulation mode and the signal with FM modulation as the main carrier modulation.In addition,in view of the modulation mode discrimination of subcarrier,thesis proposes a method of subcarrier modulation method based on direct filtering,and compares it with the one based on the main carrier demodulation.The analysis results show that although this method needs higher SNR conditions than the direct filtering method,its main advantage is that it does not need to demodulate the main carrier of the signal.Therefore,this method has obvious advantages in higher SNR conditions.3.According to the characteristic that the peak-line of hybrid modulation signals are separated by the subcarrier frequency,thesis summarizes a universal process of modulation type recognition of hybrid modulation signals.According to this process,PCM-PM,PCM-FM,PCM-BPSK-PM and PCM-2FSK-PM signals can achieve more than98% recognition accuracy when SNR is greater than-5d B,and PCM-BPSK-FM and PCM-QPSK-PM signals can achieve more than 90% recognition accuracy when SNR is greater than 10 d B.