Design Of Orthogonal Waveforms With Multiple Diversities And Its Application In MIMO HFSWR

Since the beginning of the 21 st century,Multiple-Input Multiple-Output(MIMO)radar has become a research focus in the radar field due to its multi-diversity and multidegree of freedom.The MIMO radar virtual aperture technology provides a feasible theoretical solution for improving the angular resolution of radars.However,studies have shown that the virtual aperture technique,which assumes that the transmitted waveform is completely orthogonal at any delay–Doppler,is completely unachievable.In order to obtain better orthogonality between waveforms,researchers are working to design waveforms with lower cross-correlation or cross ambiguity level.In these waveform designs,the popular radar system application background is microwave phased array radar,and the designed waveform can not be directly applied to other radars,i.e.,High Frequency Surface Wave Radar(HFSWR).The HFSWR operating in the high frequency band(3?30 MHz)is one of the main means of sea surface vessel target detection and sea state parameter remote sensing over-the-horizon,but its narrow bandwidth and large dynamic range presents a major challenge for orthogonal waveform design.Therefore,the orthogonal waveform design with HFSWR as the application background will be beneficial to enrich the MIMO radar orthogonal waveform system,and it is beneficial to improve the angle measurement and even locating performance of HFSWR and promote the popularization and application of HFSWR.In this thesis,multiple diversities is used as the starting point.Several researches have been carried out on waveform system design,waveform design method and performance analysis.These studies are based on HFSWR,but their methods,ideas and results can also be applied to other radar systems.Details as follows:First,the design of the multiple diversities waveform structure.Diversity is the basis of the orthogonality between waveforms.Recently,the most popular orthogonal waveform design is based on frequency diversity,phase diversity,time diversity,frequency modulation diversity or polarization diversity.However,one common feature of these designs is that they are almost all single diversity waveforms,i.e.,the waveforms can only obtain the benefits from degree-of-freedom provided by a single diversity in the design process.Based on the idea that high degree-of-freedom is beneficial to improving the orthogonality of waveforms,this thesis proposes the idea of using multiple diversities for orthogonal waveform design.Combining phase diversity and frequency diversity,we design Discrete Frequency Phase Coding Waveform(DFPCW)and continuous-Phase Frequency-coding Pulse-train Waveform(PFPW),and combining frequency diversity and frequency modulation,we design Discrete Frequency Chirp-rate Coding Waveform(DFCCW).In the meanwhile,we prove that DFCCW with frequency and frequency modulation diversity can achieve lower cross-correlation level than pure frequency diversity waveform.Second,the simplified approaches of waveform design process based on waveform properties.The general orthogonal waveform design process is to propose a new waveform system(or use the existing waveform system),derive its ambiguity function,set the objective function,and design the optimization algorithm to solve the optimization problem.For a given waveform system,the performance of the waveform depends on the direct solution of the optimization algorithm.In the process of designing PFPW waveforms,several properties of the waveform are found,and four theorems of the waveform's ambiguity function are given.Using the property 3.1,it is possible to realize that the multiple PFPW waveforms designed have identical auto-correlation properties.Based on this,the objective function of the waveform design can be simplified or the constraints of the optimization problem can be reduced,so that the PFPW design can be expressed as a special linear constraint sum-of-ratios programming problem.Then the Numerator Denominator Cyclic(NDC)algorithm is proposed to tackle the problem.If the arrangement of the frequency and phase of the PFPW waveform satisfies the precondition of the property 3.2?3.4,we prove that there is a cross ambiguity null region between the waveforms,and this region can be shifted along the Doppler-axis by controlling phase coding sequence.Based on this,a continuous-Phase Stepped-frequency Pulse-train Waveform(PSPW)and its simplified design method are proposed.Third,the waveform design idea based on multi(many)-objective optimization algorithm.Orthogonal waveform design of MIMO radar and even traditional waveform design are essentially multi-objective(multiple criteria),such as narrow auto-correlation main lobe,low peak sidelobe,low integral sidelobe and low cross-correlation peak.The traditional approach is to weight the sum of the criteria,convert multiple objective functions into a single objective function and solve it using single objective optimization algorithms.This approach requires a certain prior knowledge of the setting of the weight,or the selection of multiple sets of weights for optimization,which is not conducive to the understanding of the performance of waveforms and engineering applications.This paper introduces the Pareto optimal concept and multi-objective optimization algorithm,and performs non-dominated sorting on the achievable criteria of different waveforms,and then uses the proposed Nondominated Sorting Genetic Algorithm with Differential Evolution(NSGA/ DE)to obtain a set of DFCCWs that are optimal in the Pareto category.Through the set of waveforms,the magnitude of the criteria of each waveform achieved can be clearly recognized and the contradiction between different criteria can also be observed.The radar system designer can select the appropriate waveform in the set according to practical requirements.Finally,the analysis of target location performance of MIMO HFSWR.Although the waveform designed in this paper can achieve relatively good orthogonality,the application effect in the actual system still needs analysis.Here,the MIMO radar ambiguity function is used as a means to analyze the target location performance of MIMO HFSWR in monostatic/shipborne and bistatic system scenarios.The results show that MIMO HFSWR can realize virtual aperture and significantly improve the azimuth resolution of target when transmitting and receiving co-located.In the case of bistatic system,grating lobes are observed in MIMO HFSWR,but the target resolution is better than the monostatic situation.Based on in-situ data,this paper proves the orthogonality of the designed PSPW.Furthermore,by employing virtual aperture technique of MIMO radar,the MIMO HFSWR is able to provide better azimuth measurement accuracy then traditional HFSWR.