Research On Processing Techniques Of High-speed/Accelerating Targets And Detectable Range Extension Based On LFMCW Radar

Unlike the traditional application fields, this dissertation is devoted to the detection and parameter estimation problem of targets with high dynamic range parameters in LFMCW (linear frequency-modulated continuous wave) radar. The so-called high dynamic range refers to long range, high-speed and acceleration. Upon the signal detection model constructed, rectification of MTRC (migration through range cell) for high-speed targets, parameter estimation of high-speed accelerating targets and extension of detectable range have been studied and been solved. And the properties of the method for detectable range extension are analyzed using the theory of ambiguity function.Based on the traditional structure of beat-Fourier analysis-MTD (moving target detection) processing, SNR (signal-to-noise ratio) improving factor is obtained in Chapter2, and hereby optimal detection metric is defined. Then quantitative analysis of the effect of high-speed and acceleration on the two-dimensional integration performance is carried out for high-speed/accelerating targets. Finally detection model under MTRC is established upon traditional processing flow.Aiming to parameter estimation of high-speed targets, rectification methods for MTRC are mainly focused in Chapter3. From the characteristic of the beat signal, a velocity precompensation method is proposed which accomplishes motion compensation by searching the optimal compensation velocity in its dynamic range. For the triangular LFMCW signal, MTRC of up-sweep beat signal and down-sweep part is symmetry, based on which secondary mixing-MTD processing is proposed. And recurring to the respective advantage of the above two methods, a combination processing for multi-targets is presented. Furthermore Keystone transform in SAR (synthetic aperture radar) and ISAR (inverse SAR) is introduced into LFMCW radar and a MTD processing based on Keystone transform is propounded which is developed to solve the range-velocity coupling problem in single chirp LFMCW signals. At the end of Chapter3, the applicability of these three rectification methods is discussed.Using the two-dimensional coupling signal model acquired in Chapter2, parameter estimation for high-speed accelerating targets is stressed in Chapter4. Firstly the maximum likelihood (ML) estimation model is derived and the Cramer Rao bound (CRB) in Gaussian white noise circumstance is obtained. Considering that the widening of the two-dimensional spectrum appeared in a local spectrum region, a velocity-acceleration template matching method based on partial compensation is proposed. The concept of partial compensation can effectively alleviate the computation burden during template matching course. And when some input SNR requirement is satisfied, the performance of ML estimation based on partial compensation can approach to the CRB. Then with the intention of decoupling, secondary mixing-DPT (discrete polynomial-phase transform) processing and direct phase differentiation (DPD) method are proposed respectively, which can realize the parameter estimation without searching and template matching operations. And when some modification is made in DPD method, DPT-CZT (Chirp-Z transform) method is produced which can achieve unambiguous velocity estimation without other ambiguity resolving processing. Therefore this method can be applied to parameter estimation for high-speed accelerating targets with single chirp LFMCW signal.To solve the ranging limitation problem in the beat-Fourier analysis-MTD structure, the objective of Chapter5 is to explore some technique to extend the detectable range of LFMCW radar and to investigate the corresponding problems. Considering the modulation symmetry and waveform repetition of triangular LFMCW signal, double beat-FFT processing is proposed in which the beat-FFT processing is performed twice. And by the analysis of the two complementary results, the measurable time-delay of targets is effectively extended to the whole repetition period. Then multi-cycle integration is discussed, and joint range-velocity pairing method for multi-targets is proposed according to the characteristics of range spectrum peaks. In virtue of the partial compensation concept in Chapter4, the parameter estimation problem of high-speed accelerating targets is solved in double beat-FFT processing.At last, the ambiguity function of triangular LFMCW signal adopting the double beat-FFT processing is derived in Chapter6. Under rational approximations, the symmetry and resolution properties are analyzed in detail and compared to those of the traditional processing. Some quantitative results for the double beat-FFT processing are obtained from the point of ambiguity function, which will provide theory foundation for the engineering applications.