Orthogonal Waveform Design And Target Detection For MIMO Radar Based On Chaos Theory

Orthogonal waveform design and optimization is a basic research issue for MIMOradar, which takes up quite an important status for colocated and statistic MIMO radaras well. Chaos presentes inherent property in orthogonal signal design for its easygeneration, easy copy, great number, randomicity, ergodicity and aperiodicity.Thus, thisthesis investigates the MIMO radar waveform design and optimization based on chaosand fractal theory which is also extended to MIMO radar target detection inunheterogeneous fractal clutter.Background and siginificance of this thesis are first expounded, and then someMIMO radar sytem development and waveform design technique are introduced. Thestudy development of chaos is listed, especially its application in radar waveform isreviewed in detail and its feasibility for MIMO radar waveform is pointed out as well,followed with the main content introduction.In charpter2, the relationship between transmitting unideal orthogonal waveformsand localization and detection performance of MIMO radar is investigated guiding forMIMO radar orthogonal waveform design and optimization. The general measuredsignal model is introduced, the course of matched processing is then presented, and thesufficient statistic for parameters estimation is induced in theory. Relationships betweenunideal orthogonal transmitting waveforms and MIMO radar beamforming, targetdetection in Gaussion noise and DOA estimation are mainly investigated. It can befound out that the sidelobe level is increased though its width is sustained fortransmit-receive beam with the correlation increases, which trend is similar to targetdetection and DOA estimation performance. Therefore, there is no necessary forpursuing fully orthogonal tramsmitting signals, which should be chosen, design andoptimizasion according to requirements of MIMO radar localization and detection.Based on the analysis in chapter2, performances of chaos based modulated signalsincluding average ambiguity function, correlation, spectrum, range and velocityresolution, and echo waveform signal processing are mainly investigated in chapter3,and their feasibility and superiority are also pointed out. As to the chaos basedfrequence modulated signal, the signal model is introduced, statistic characteristic basedon ergodicity theory is investigated, based on these, its spectrum, average ambiguityfunction, and psudo-orthogonality are induced in theory. As to the chaos based discretefrequency coded signal, its chaotic coding method is presented, then performancesincluding the ambiguity function, the range and velocity resolution, and orthogonalityare investigated. Numerical simulation based on four chaotic maps has validated theanalyzing. As to the chaos based frequency stepped signal, an echo signal processingmethod is proposed, which carries our matched saving before pluse compression. Whenthere is no range velocity, FFT is utilized for pluse compression; otherwise, it takes the correlation processing.In charpter4, MIMO radar orthogonal waveform design based on chaos theory ismainly inveatigated. Taking the poly phase coded signal as an example, the probabilitydensity, coding method and chaos chosn and construction are synthetically considered,which provides a design guidance for MIMO radar orthogonal waveform design. Basedon the ergodicity and independence theory, a chaos series sampling method is proposedfor orthogonal waveform set design. It is found out that, when the sampling distance islarge enough, two chaotic signals generated from the same chaos system are notcorrelated, which show better modulated orthogonal performance. Further, a sufficientcondition for chaos sustaining for chaotic frequency modulated signals is induced andan inititial condition sensitivity function for chaotic coded signals is defined. Thereasons for varying performance of different chaos are thus analyzed, which can guidefor MIMO radar chaotic orthogonal waveform design.In charpter5, MIMO radar orthogonal waveform optimization based on chaostheory is mainly inveatigated. Velocity and accelerate velocity intolerance are firstanalyzed for poly phase coded waveforms. An improved clonal seneltion algorithm isproposed by introducing chaos. Based on this algorithm combining more flexiblecoding to increase signal design freedom, a combined optimization method is thusproposed and waveforms with lower sidelobe level, more velocity and acceleratevelocity intolerance are obtained. Based on the complementary coding idea, a chaosbased complementary codes are transmitted for MIMO radar after transmitting itcorresponding chaos codes and much lower sidelobe level is obtained shown bynumerical simulations. Further, a multiple hypothesis testing at MIMO radartransmitters is proposed for Doppler tolerance increasing,which carrys out Dopplerfiltering and gets a Doppler estimation firstly, and then is is feeded back to MIMO radartransmitters in a closed loop for Doppler precompensation. Numerical simulations showgreatly improvements have been obtained.Fractal geometry has been used as an effective tool to improve target detectionperformance in radar system, since most non-homogeneous clutter generated by naturalsurface is demonstrated to be fractal by recent researches. In charpter6, we mainlyconsider MIMO radar target detection in fractal clutter. Target and clutter model isproposed for high resolution MIMO radar. Based on this model, a fractal dimensionestimation method is discussed, which is further investigated and deduced inmulti-channel systems with antennas being placed colocated and distributed,respectively. Fractal detectors for both colocated and statistical MIMO radars are thendesigned based on the statistic theory. The likelihood ratio threshold, false alarmprobability and detection probability are deduced according to the Neyman-Pearson (NP)Criteria, and the relationship between detection performances and the transmit-receivechannel number is analyzed as well. Additionally, we show that the fractal detector presents great capabilities in rejection of non-homogeneous clutter for MIMO radarsystem.In charpter7, the summarization and the probable future work of this dissertationare discussed.What need to be pointed out for supplement is that the study of this dissertation isof both theoretical and engineering sense. On one hand, it can promote the developmentof the new radar system-MIMO radar and provide waveform set for engineeringapplication. On the other hand, it can deepen and widen the non-linear science-chaosand fractal research in theory and engineering. Additionally, the research results canilluminate orthogonal waveform design of netted radars, electronic warfare, andelectromagnetism concealment. The obtained orthogonal waveform set can evendirectly be used in netted radar system.