A New LFM-Signal Detector Based on Fractional Fourier Transform
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Parameter Estimation for Linear FM Signal Liran Shen, Qingbo Yin
Tian’en Shen
Lili Guo
College of Information Science and Technology Dalian Maritime University Dalian, 116026, China
School of Economics and Management, Dalian Ocean University Dalian, 116023, China
School of Information and Communication Engineering Harbin Engineering University Harbin, 150001, China
on FRFT have been proposed to detect LFM-signal and estimate its parameters [13–17]. An effective method for parameter estimation and recovery of time-varying signals including LFM-signal by using FRFT is proposed in [13]. According to the equivalence relationship between RWT and the fractional power spectrum [18, 19], a LFM signal detection and parameters estimation method based on FRFT has been presented [14-16]. But, those methods must search the fractional order parameter in the whole angle space (or fractional order space), and therefore, have a drawback, heavy computational burden. In this paper, we propose a new scheme for parameter estimation of LFM signals, which consists of a coarse search and a fine search. In the initial stage(the coarse search), the line of ridge energy is tracked in the STFT domain, and the parameters of LFM signal can be estimated coarsely by overdetermined equation (by minimum mean square error). In the second stage, the fine search for correct parameters is implemented in the FRFT domain using Gaussian model to fit the impulse response of the LFM signals under the guidance of the estimated parameters from the above stage by the property of monotonicity in the limited neighborhood of the optimal value.
Abstract—A new method is introduced for parameter estimation of linear frequency modulated (LFM) signals, which consists of a coarse search and a fine search. In the initial stage, the window length for short time Fourier transform (STFT) is selected to get the right time-frequency resolution and concentrate the energy to a line in spectrogram according to the LFM signal characteristic, then the line of ridge energy is tracked in the spectrogram, and the parameters of LFM signal can be estimated coarsely. In the second stage, the fine search for correct parameters is implemented in the fractional Fourier transform (FRFT) domain using Gaussian model to fit the impulse response of the LFM signals under the guidance from the above stage by the property of monotonicity in the limited neighborhood of the optimal value. Computer simulations have verified the effectiveness of the new method. Keywords- Linear frequency modulated signl; Fractional Fourier transform; Parameter estimation; Short time Fourier transform
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INTRODUCTION
Linear frequency modulated (LFM) signals have many applications such as radar, sonar, communications, and seismic analysis. Detection and estimation of the LFM signal are extremely important in a noisy environment, and have gained considerable attention in recent years. Many efforts were done and proposed based on timefrequency (TF) analysis for LFM signals in noise，including the dechirping tech
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