Research On Parameter Estimation Of Complex Modulation LPI Radar Signal

As the modulation of radar signal becoming more complex, the Electronic reconnaissance technologues face new challenge. Currently, the low probability of intercept(LPI) technologues are widely used, and there are practical significance and application value to study the parameter estimation of LPI radar signals. In this paper, the main work and research results are as follows:Firstly, the basic theory of time-frequency analysis is briefly introduced, four kinds of typical LPI radar signals are also introduced, including the binary phase shift keying(BPSK) signal, polyphase coded signal, linear frequency modulation and binary phase shift keying(LFM-BPSK) signal, linear frequency modulation continuous wave(LFMCW) signal. Secondly, for the above four kinds of LPI radar signals, the parameter estimation algorithms are studied respectively.For BPSK signals, the construction statistics algorithm based on periodic ambiguity function(PAF) is studied. Select a set of delay vector to construct statistics, which can improve performance and suppress noise. For polyphase coded signal, if the signal is a complete period, the PAF is used to estimate parameters. For the case that signal is not a complete period, the quadratic phase function(QPF) and the ambiguity function(AF) are used to estimate parameters. The algorithm can find the spike after the Radon transform at low SNR, improving parameter estimation performance.For LFM-BPSK signal, the denoising algorithm based on Discrete Chirp-Fourier Transform(DCFT) is studied. Squared denoised signal, the signal becomes LFM signal, then use Lv’s Distribution(LVD) and DCFT to estimated parameters. Demodulate the denoised signal, the signal becomes BPSK, the construction statistics algorithm based on PAF is used to estimate symbol rate. By DCFT denoising algorithm, the performances of following algorithms are improved at low SNR. For LFMCW signal, the inter-frame correlation mehod is used to estimate the period of signal. For the case that the beginning of signal exists dely, DCFT is used to estimate the dely, then intercept a complete period signal to estimate carrier ferquency and time-frequency rate.