Research On Feature Extraction For Target With Micro-motion Based On New OFDM Radar Signals

Micro-motion is the mechanical vibration or rotation of a target or its components in addition to its bulk translation. The micro-motion status of a target reflects the fine feature of the target, and provides new approaches for radar target feature extraction and target recognition. With the research background of target recognition for the new OFDM radar, this dissertation addresses micro-Doppler and high resolution feature extraction for targets with micro-motions, and OFDM waveform design optimization, based on the modulation effects analysis of the OFDM radar echoes.In chapter 1, it illustrates the background and significance of this dissertation, and introduces the present status of research on OFDM radar and feature extraction for micro-motion targets. The current trend of each research areas and the problems exists are especially analyzed. The main content of this dissertation is also presented.In chapter 2, several typical micro-motion forms, such as vibration/rotation, precession, and tumbling, are analyzed to induce the uniform model of micro-Doppler signature. With the form of OFDM radar signal, the OFDM radar echo model of micro-motion targets is presented. The approaches are proposed to get Doppler course and high resolution range profile (HRRP) sequence of micro-motion targets from the echo. It shows that OFDM radar can obtain micro-Doppler and HRRP sequence simultaneously, which is proved by mathematical derivations and simulation experiments. It reveals the micro-Doppler and high range resolution feature of OFDM radar echo of micro-motion targets. That lays the foundation for feature extraction of micro-motion targets.In chapter 3, the Cramer-Rao lower band (CRLB) for the variances of the micro-Doppler signature parameters estimation is derived at first. A method based on cyclostationary characteristics for parameters estimation of the micro-motion is proposed, which has advantage of good precision and anti-noise performance. And then, making use of micro-Doppler curves in the time-frequency plane, the methods based on extended Hough transform (EHT) and coherent Doppler interference (CDI) are exploited for micro-motion parameters estimation. Making use of curves in the HRRP sequences plane, a method based on single range cell phase characteristics and a method based on back projection of range-time domain are proposed for micro-motion parameters estimation, which fit for the condition that the radial amplitude of micro-motion is smaller and larger than range resolution cell, respectively. For the characteristic that OFDM radar can obtain micro-Doppler and high range resolution feature simultaneously, the concept of combined feature is proposed, based on which the physical feature extraction of micro-motion targets is developed. At last, the imaging of micro-motion targets is researched. When the radial amplitude of micro-motion is smaller than range resolution cell, an imaging method for micro-motion targets based on CDI is proposed. When the radial amplitude of micro-motion is larger than range resolution cell, a segmental pseudo Keystone transform (SPKT) is designed to realize migration through resolution cells (MTRC), and based on SPKT, a novel imaging method for fast rotating targets is proposed. The method has advantage of low computation complexity and high resolution performance.In chapter 4, waveform design of OFDM radar signal is investigated firstly for lower peak-to-mean envelope power ratio (PMEPR). Based on deriving the ambiguity function of OFDM signal, a method to design the spectrum for a better autocorrelation function (ACF) is proposed. And then, the relationship between the OFDM radar performance and the OFDM signal parameters is analysized. The relationship among the modulation feature of micro-motion, OFDM signal parameters, and the parameters of micro-motion targets is presented, and the design of OFDM radar signal parameters for feature extraction of micro-motion targets is investigated. Adaptive waveform design approaches for OFDM cognitive radar based on the improved wideband ambiguity function (WAF) and based on maximizing the output signal-to-interference-plus-noise ratio (SINR) are proposed, to realize the function that the cognitive radar adjusts emitted signal parameters intelligently for best performance, according to the varying scattering characteristic of the target and the environment clutter. At last, a new radar signal named OFDM phase-coded stepped-frequency (OFDM-PCSF) is proposed to solve the problem that large instantaneous bandwidth of OFDM wideband radar leads to high requirement of the radar receiving technique. The properties of OFDM-PCSF signals are analyzed, and the principle and the performance of synthesizing HRRP are investigated.Chapter 5 summarizes the dissertation and discusses the further work.