Abstract
As a special micro-motion feature of rotor target, rotational angular velocity can provide a discriminant basis for target classification and recognition. In this paper, the authors focus on an efficient rotational angular velocity estimation method of the rotor target is based on the combination of the time–frequency analysis algorithm and Hough transform. In order to avoid the problems of low time–frequency resolution and cross-term interference in short-time Fourier transform and Wigner–Ville distribution algorithm, a modified short-time fractional Fourier transform (M-STFRFT) is proposed to obtain the time-FRFT domain (FRFD)-frequency spectrum with the highest time–FRFD–frequency resolution. In particular, an orthogonal matching pursuit (OMP)-based algorithm is proposed to reduce the computational complexity when estimating the matched transform order in the proposed M-STFRFT algorithm. Firstly, partial transform order candidates are selected randomly from the complete candidates. Then, a partial entropy vector corresponding to partial transform order candidates is calculated from the FRFT results and utilized to reconstruct the complete entropy vector via the OMP algorithm, and the matched transform order can be estimated by searching minimum entropy. Based on the estimated matched transform order, STFRFT is performed to obtain the time–FRFD–frequency spectrum. Moreover, Hough transform is employed to obtain the energy accumulation spectrum, and the micro-Doppler parameter of rotational angular velocity can be estimated by searching the peak value from the energy accumulation spectrum. Both simulated data and measured data collected by frequency modulated continuous wave radar validate the effectiveness of the proposed algorithm.
Highlights
The micro-Doppler (m-D) effect is a frequency modulation (FM) induced by the micromotion [1,2,3], including rotation, vibration, precession, and nutation, which widely exists in many objects or their structures, such as rotors of a helicopter, warhead in mid-phase, running vehicle engines, and so on
The complete procedure of the proposed method for rotational angular velocity estimation of rotor target is shown in Figure 6, in which the process in the blue dotted box is the matched transform order estimation based on the orthogonal matching pursuit (OMP) algorithm and the process in the red dashed box is the rotational angular velocity estimation based on the combination of the M-short-time fractional Fourier transform (STFRFT) algorithm and Hough transform
We can see that compared with the Hough–GSSbased STFRFT algorithm and other time–frequency analysis algorithms mentioned in this paper, the algorithm proposed in this paper has better rotational angular velocity estimation performance in the case of low SNR
Summary
The micro-Doppler (m-D) effect is a frequency modulation (FM) induced by the micromotion [1,2,3], including rotation, vibration, precession, and nutation, which widely exists in many objects or their structures, such as rotors of a helicopter, warhead in mid-phase, running vehicle engines, and so on. By contrast with the Fourier transform (FT), the time–frequency analysis class transforms provide joint distribution information in the time domain and frequency domain, and clearly describe the relationship between signal frequency and time They are widely employed in micro-motion parameter estimation [6,7]. The concept of SFT was introduced to STFRFT to achieve high time–FRFD–frequency resolution and low complexity of time–frequency distribution [32] These STFRFT-based algorithms do not give an effective solution to the estimation of the matched transform order. We propose a novel modified short-time fractional Fourier transform (MSTFRFT) algorithm to estimate the micro-Doppler parameter of rotational angular velocity.
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