Detection of LFM Radar Signals and Chirp Rate Estimation Based on Time-Frequency Rate Distribution.

Ewa Swiercz,Dariusz Janczak,Krzysztof Konopko

doi:10.3390/s21165415

Ewa Swiercz, Dariusz Janczak + Show 1 more

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https://doi.org/10.3390/s21165415

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Abstract

Linear frequency-modulated (LFM) signals are the most significant example of waveform used in low probability of intercept (LPI) radars, synthetic aperture radars and modern communication systems. Thus, interception and parameter estimation of the signals is one of the challenges in Electronic Support (ES) systems. The methods, which are widely used to accomplish this task are mainly based on transformations from time to time-frequency domain, which concentrate the energy of signals along an instantaneous frequency (IF) line. The most popular examples of such transforms are the short time Fourier transform (STFT) and Wigner-Ville distribution (WVD). However, for LFM waveforms, methods that concentrate signal energy along a line in the time-frequency rate domain may allow to obtain better detection and estimation performance. This type of transformation can be obtained using the cubic phase (CP) function (CPF). In the paper, the detection of LFM waveform and its chirp rate (CR) parameter estimation based on the extended forms of the standard CPF is proposed. The CPF was originally introduced for instantaneous frequency rate (IFR) estimation for quadratic frequency modulated (QFM) signals i.e., cubic phase signals. Summation or multiplication operations on time cross-sections of the CPF allow to formulate the extended forms of the CPF. Based on these forms, detection test statistics and the estimation procedure of LFM signal parameters have been proposed. The widely known estimation methods assure satisfying accuracy for high SNR levels, but for low SNRs the reliable estimation is a challenge. The proposed approach based on joint analysis of detection and estimation characteristics allows to increase the reliability of chirp rate estimates for low SNRs. The results of Monte-Carlo simulation investigations on LFM signal detection and chirp rate estimation evaluated by the mean squared error (MSE) obtained by the proposed methods with comparisons to the Cramer-Rao lower bound (CRLB) are presented.

Highlights

low probability of intercept (LPI) radars are a class of radar systems that are designed to be difficult to detect by today’s electronic support measures (ESM) [1]
The results for TSCPF statistics and N = 63 can be directly compared with the detection characteristics using the CPF-based detector and the directly compared with the detection characteristics using the CPF-based detector and the integrated CPF (ICPF)-based detector presented in [29]
This paper has presented the new approach for both detection and parameter estimation of Linear frequency-modulated (LFM) signals based on time-frequency rate distributions with use of developed

Summary

Introduction

LPI radars are a class of radar systems that are designed to be difficult to detect by today’s electronic support measures (ESM) [1]. Such signals are addressed in Electronic Intelligence (ELINT). Systems with non-cooperative transmitters, such as those operating in ultra high frequency (UHF) and very high frequency (VHF) bands, forces incrisingly advanced analysis of frequency modulated (FM) signals, including LFM signals [5]. LFM signals belong to the class of polynomial phase signals, which are intensively used in imaging of moving and non-moving targets in modern synthetic aperture radar (SAR) imaging systems [6]. The rapid development of modern communication systems including wireless sensor network applications entails the need to develop energy-efficient transmission techniques, especially dedicated to large, low-power networks (LPWAN) [7,8,9]. A promising approach seems to be the technique using the linear chirp spread spectrum (CSS) [10]

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