| Frequency-hopping(FH) signal has been widely used in military communication for its strong anti-jamming and anti-interception capability. Therefore it is very important for us to study the interception of FH signal. This paper deeply studies the detection and frequency search and parameters estimation of FH signal utilizing time-frequency analysis, and an Ultra Short Wave FH signal detection and analysis system has been designed.The paper proposes a new method for detection of FH signal using the spectrogram. Firstly the factors which impact time and frequency resolution of spectrogram are studied, and an adaptive short time Fourier transform is proposed. An adaptive time-frequency local threshold is applied to predispose the spectrogram; And by the means such as power-detection and time-statistic, we can get rid of most of the interferences, and remove the effect of the swept-signal and the random noise from the spectrogram. And finally the detection of FH signal is realized.We propose two strategies for the frequency search of FH signal: one is based on the spectrogram and the other is based on the algorithm of Goertzel. Both the applicability and performance comparison is analyzed for these two strategies. The mathematical model of the frequency interception is studied, and it has been found that improving the searching speed is the only way to increase the interception probability.With respect to the estimation of the characteristic parameters, an algorithm using the wavelet-ridge and its fast algorithm is studied. The algorithm of multi-window non-overlapped Smooth Pseudo Wigner-Ville Time-Frequency Distribution based on instantaneous frequency is proposed. And the comparison is made between these two methods, the result shows that the latter algorithm has better performance than the former one. And an adaptive complex modulated Zoom-FFT algorithm is studied to zoom the spectrum of every hopping period, which reduces the unitary frequency error of estimation to 10-6. |
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