Research On The Identification And The Treatment Of The Composite Modulation Radar Signal

The identification and the parameters estimation of the radar signals based on the phase unwrapping are discussed in this dissertation.First, the phase of the common radar signals is studied in this dissertation, and a method of the phase unwrapping is put forward. Through discussing the impact of noise, the method of phase unwrapping has the best performance, when the phase difference between adjacent samples is pi; in other words, when there are only two samples in each cycle. Because the phase unwrapping that in each cycle there are only two samples can not be guaranteed, a suboptimal algorithm is put forward: First, the center frequency and the bandwidth of the radar signal are estimated, then the frequency of the signal is moved to one half of the sampling frequency and the phase is unwrapped. The instantaneous phase under the conditions of low SNR can be obtained with this method.Second, the identification of the radar signal modulation mode is also discussed in this dissertation, and a complete identification process is put forward. The time-frequency curve of the signal is obtained from the Nth-order difference of the phase. Based on the phase unwrapping. Effective identification of the signal can be achieved based on the characteristics of the time-frequency curve and the techniques including curve fitting, coefficient of frequency modulation, peak detection, amplitude comparison etc. The algorithm can get a high rate of identification at 3 dB.In the end, the parameters of the multi-linear frequency modulation signal and the second phase frequency shift keying signal are estimated. In parameter estimation of the multi-linear frequency signal, the frequency jumping positions is estimated based on the time-frequency curve then the initial frequency and other parameters are estimated based on the frequency jumping positions. In parameter estimation of the second frequency shift keying signal, an exact estimation algorithm of the frequency jumping positions is put forward, and then the width of the code element and the carrier frequency of 2FSK are estimated.A large amount of computer simulations prove that the algorithms of the phase unwrapping, the identification of the radar signal modulation mode and the parameters estimation presented in this dissertation are feasible and effective and the performance of the algorithms is good.