A New Time-Frequency Spectrogram Analysis of FH Signals by Image Enhancement and Mathematical Morphology

Abstract

A new method is proposed to extract the parameters of frequency hopping (FH) signals. After short-time Fourier transform (STFT), the time-frequency spectrogram of FH signals is treated as a kind of digital image with special contents. The spectrogram analysis is investigated to detect and extract FH parameters by useful image enhancement techniques and mathematical morphology. First, the spectrogram image is enhanced by contrast stretch and binarization. Then, morphological closing and opening cascaded operations are manipulated using rectangular structure elements horizontally and vertically. After morphological image processing, the spectrogram edges are extracted by boundary tracking and extraction. Finally, the important FH parameters, such as hopping carrier frequency, hop timing and hop rate can be estimated, which lay the foundations for later finer hopping frequency location. The experimental results and analysis on the short-wave FH signals show the good performance of the proposed method.