Research On Detection And Tracking Of Low Altitude Target Based On OFDM Radar

Using stealthy aircraft or cruise missiles to achieve low altitude or ultra-low altitude penetration has become a commonly tactical means in modern warfare,so it has significant military value to investigate the technique of radar detection and tracking low altitude target.In this paper,we have studied the problem of target detection and tracking in low altitude with orthogonal frequency division multiplexing(OFDM)radar.The following issues are studied,including characteristics of OFDM radar signal and signal processing methods,OFDM waveform optimization algorithm for detection of extended target,adaptive OFDM radar for detection and tracking low altitude targt.The main contents are summarized as follows:Chapter 1 first clarifies the background and significance of the research work from a perspective of military requirements.Then,the main issues of target detection and tracking in low altitude are detailed analyzed and current research status in low altitude target detection and tracking and OFDM radar are also summarized.Finally,the main content and organization of this dissertation are presented.Chapter 2 first introduces the signal structure of OFDM and multi-carrier phase coded(MCPC)radar,and analyzes characteristics of their ambiguity function.Then,focusing on the problem of high range sidelobes produced by traditional pulse compression method,which would bring difficulty to detect weak target adjacent to the strong one,an adaptive pulse compression method with MCPC radar is proposed.The effect of encoding way on the performance of the algorithm is also analyzed.Simulation results show the proposed algorithm can effectively suppress the range sidelobe and improve the detection performance.Then utilizing the sensitivity of MCPC signal to time and frequency offset,a Doppler estimate algorithm based on single pulse is proposed.The algorithm has high unambiguous Doppler range and the estimates of range and Doppler are completely independent.Simulation results show that the Doppler frequency can be rapidly estimated within one single pulse and the algorithm can be applied in high-speed and multi-target scenario.Chapter 3 studies the waveform optimization based on OFDM radar for detection of extended target.Using the prior information of target,clutter and noise,the transmitted waveform could be optimized to impove the detection and tracking performance.First,assuming that the target signature and power sprctrum density of clutter and noise is known,a kind of marginal allocation algorithm based on mutual information criterion is proposed to acquire energy spectral density of the optimal waveform.Joint optimization functions of auto-correlation and energy spectrum density are established and the optimal transmitted OFDM parameters are acquired.Simulation results show the optimized waveform has better detection performance.Then,assuming that target impulse response is independent of interference(clutter,noise,etc.),an algorithm based on maximizing signal-to-noise ratio(SNR)criterion with deterministic and random target impulse response is proposed to optimize the OFDM multi-input multi-output(MIMO)waveform.The algorithm adopts cycle iteration to get the optimal weights of transmitted waveform and provides fast convergence.Simulation results show better signal-to-noise raio can be acquired in the receiver due to the waveform optimization.Chapter 4 studies adaptive OFDM radar for detection and tracking low altitude target.Multipath effect is utilized to enhance the detection performance and the detector is combined with waveform optimization to improve the detection performance.First,the multipath propagation model is modified under the consideration of atmosphere refraction,curved earth,etc.A general likelihood ratio test(GLRT)is derived.According to the characteristic of detector and statistical distribution of measurements,an adaptive waveform optimization algorithm based on Mahalanobis distance is proposed.Simulation results show detection performance can be improved by exploiting the multipath effect and frequency diversity of OFDM signal.Meanwhile,the waveform optimization method is validated by simulation experiment.Then,a GLRT detector under OFDM MIMO radar is derived.According to the asymptotic statistical characteristics of the detection test,a waveform optimization algorithm based on maximizing the noncentrality parameter is proposed to enhance the detection performance.Simulation results show the OFDM MIMO radar has better performance comparing with monostatic OFDM radar and the performance of waveform optimization method is also verified.Finally,on the assumption that the clutter follows compound Gaussian distribution,two detectors including GLRT and Rao are proposed.For GLRT detector,the detection test and the waveform optimization can be combined to improve the performance.The computation efficiency of the Rao detector is much higher than the GLRT detector.Chapter 5 studies adaptive OFDM radar for tracking of low altitude target.The posterior Cramér-Rao bound is minimized.The tracking procedure is combined with waveform optimization to improve the tracking perfroamnce.First,the target state and measurement model is derived with polarized transceivers and particle filter is used to solve the tracking problem.A waveform optimization method based the estimation of target state and measurement is proposed.Simulation results show the frequency diversity of OFDM signal and polarization can reduce the tracking error and the waveform optimization method can further improve the trakcing perforamnce.Then,a interacting multiple model based on particle filter is used to solve the issue of maneuvering target tracking.Simulation results validate the effectiveness of the algorithm.Chapter 6 summarized the dissertation and points out the future work.