Robust Parameters Estimation Algorithm For Advanced Polarimetric Array

The polarization sensitive array can measure the electromagnetic field components of incident waves,which can not only significantly improve the estimation accuracy of the spatial angles of sources,but also accurately estimate the polarization angles of incident signals,whose performance is superior to that of traditional scalar arrays.Therefore,it has applications in radar,communications,sonar,navigation and other fields.Parameters estimation is an important issue of polarization sensitive array signal processing,and most of the existing parameters estimation methods for polarization sensitive array are aiming at far-field sources.However,with the increasingly extensive application of large(ultra-large)scale arrays and distributed arrays in practice,they have become a research hotspot in recent years.In such applications,the signals received by an array are often the mixture of nearfield(NF)sources and far-field(FF)sources,and the conventional pure FF or pure NF signal model may become invalid in this scenario,which leads to the mixed source signal model and related signal processing algorithm of polarization sensitive array become more complicated.In practice,there will inevitably exist array gain/phase errors and mutual coupling errors,which will lead to the performance degradation or even failure of the conventional polarization sensitive array signal processing algorithms.Therefore,it is of practical significance to study robust parameters estimation algorithm for polarization sensitive array to effectively reduce the impact of various array errors.In addition,since multiple-input multiple-output(MIMO)array can increase the degree of freedom of the system and form virtual aperture,it has obvious advantages in parameters estimation and has received considerable attention in the past decades.Thus,it is extremely important to study the parameters estimation algorithm of polarimetric MIMO array by combining waveform diversity provided by MIMO system with polarization diversity provided by polarization sensitive array.Focusing on these aspects,by fully exploiting the advantages of polarization sensitive array and applying it to large-scale arrays and MIMO system,and considering the array errors in practice,the robust parameters estimation algorithms for advanced polarimetric array is studied in this dissertation.The main works can be summarized as the following three parts.The first part studies the problem of parameters estimation for polarization sensitive array.Firstly,aiming at tackling the problem of parameters estimation performance degradation of subspace based algorithms at low SNRs,a novel method is proposed for DOA and polarization parameters estimation using COLD array.By combining the ROOT-MUSIC algorithm with modified resampling technique,the proposed approach achieves high parameters estimation accuracy even at low SNRs.Secondly,a sparse nonuniform rectangular array(SNRA-SSEMVS)based on spatially spread electromagnetic vector sensor is introduced,and a novel method for estimating 2D-DOA and polarization angles is devised.According to the structure of the sparse nonuniform rectangular array,a set of accurate but ambiguous direction-cosine estimates can be obtained.Then the steering vector of spatially spread electromagnetic vector sensor(SSEMVS)can be extracted from the array manifold to obtain the coarse but unambiguous direction-cosine estimates.With these estimates,the disambiguation approach can be used to get the final accurate estimates of 2D-DOA and polarization angles.Compared with some existing methods,the sparse nonuniform rectangular array configuration extends the spatial aperture and refines the parameters estimation accuracy without adding any redundant antennas,as well as highly reduces the mutual coupling effect.Finally,in order to simplify the array configuration,reduce the serious mutual coupling effect,and further improve the parameter estimation accuracy,a Sparsely Stretched L-shaped Polarization Sensitive Array(SSL-PSA)is proposed,and a novel method for estimating the azimuth-elevation angles as well as polarization parameters is presented accordingly.By dividing the SSL-PSA into 6 subarrays,the ESPRIT algorithm can be utilized to estimate the Rotational Invariant Factors(RIFs).On this basis,a set of fine but ambiguous estimates and four sets of unambiguous coarse estimates of direction cosine are obtained by a series of mathematical operations.Then,the correct coarse direction-cosine estimation can be determined according to the orthogonality of the steering vector and the noise subspace.After disambiguation,the estimation of DOA and polarization parameters can be achieved.Compared to the existing polarization sensitive array consists of collocated vector sensor array,the proposed one has no collocated configuration,which can reduce the mutual coupling effect.Additionally,the proposed method can also extend the spatial aperture and refine the direction-finding accuracy without adding any redundant antennas.The second part studies the mixed FF and NF source localization algorithm using polarization sensitive array.The existing mixed source localization methods can only measure the spatial information of the reflected signals,whereas the polarization of electromagnetic signal is not taken into account.To deal with this problem,a novel algorithm for mixed FF and NF source localization using a linear tripole array is presented.By constructing several special fourth-order cumulants and deriving a matrix equation,the sources types can be classified,both the spatial and polarization information of mixed sources can also be estimated.Compared to the existing methods,the proposed one provides improved parameters estimation accuracy without any spectral search,as well as realizes a more reasonable classification of the signal types.Moreover,it overcomes the limitation of inter-sensor spacing be within ?/4 or ?/8(? is the wavelength)and only needs to know the position of three tripoles.Then,the issue of mixed source localization using linear array when the signal sources are in 3D space is discussed.By extending the aforementioned algorithm to the situation that signal sources scattered in 3D space,the signal model in 3D space is established,and the estimation of 2D-DOA,range as well as polarization parameters is achieved for the first time.Finally,in practice,the antenna arrays are usually suffering from various uncertainties such as the unknown gains and phases.This will results in a serious degradation of estimation accuracy or even failure of the mixed source localization methods.To cope with this issue,a novel algorithm for mixed source localization using a linear electromagnetic-vector-sensor array with gain/phase uncertainties is proposed.By designing several special fourth-order cumulant matrices and using the special structure of the presented array,the DOA,range and polarization parameters of mixed sources can be estimated.According to the orthogonality between the noise subspace and array steering vector,a matrix equation can be developed to generate the unknown gain/phase errors.The proposed approach can estimate the DOA and polarization angles of mixed sources as well as unknown gains/phases without performing any spectral search,and has no restriction on EMVSs placement.The third part studies the problem of parameters estimation for polarimetric MIMO array.Firstly,a typical DOD and DOA estimation algorithm for bistatic MIMO system using a uniform linear array(ULA)composed of multiple collocated EMVSs in transmitter and receiver is introduced.However,due to the use of EMVS,there exists serious mutual coupling which decreases the parameters estimation performance significantly,and the array configuration is restricted to be ULA.Moreover,the spatial diversity of the components of EMVS is not utilized and the parameters estimation accuracy can be further improved.To overcome these drawbacks,a MIMO system with vector arrays composed of spatially spread dipole quints is proposed,and a new method for estimating the azimuth-elevation angles and polarization parameters is devised.Particularly,both the transmit and receive arrays are divided into five subarrays,then the directions-of-departure(DODs)and DOAs can be estimated by making use of the shift invariant properties.The proposed approach makes full use of the waveform diversity offered by MIMO system and the polarization diversity offered by polarized sensitive array simultaneously,improves parameter estimation accuracy with fewer antennas,reduces the mutual coupling,resolves more targets and has attractive computational complexity.Moreover,the proposed method does not require the information of the spacing among dipole quints,and it is applicable to arrays with dipole quints at inexactly known locations.