Unambiguous Estimation Research Articles

Устранение неоднозначности оценок направлений прихода широкополосных сигналов в многосигнальном режиме пеленгования

Direction finding of wideband signals overlapping in the spectral domain by a fixed antenna array requires the correction of steering vector ambiguity and phase differences corresponding to different spectral components. The spectral components of the same signal correspond to unequal values of the distance in wavelengths between the antennas in the array. A method of steering vector ambiguity correction suitable for subspace methods such as MUSIC and ESPRIT is proposed. The ambiguity in the presence of multiple signals is resolved by correcting phase diffe-rences between antennas for each spectral component, with preliminary correlation of the ambiguous steering vector with unambiguous ones obtained for the low-frequency range of the spectrum using maximum correlation. The corrected steering vector for each spectral component is obtained from the adjusted phase differences between the antennas and is used in the direction finding correlation algorithm to obtain unambiguous estimates of the directions of arrival of the wideband signals. Simulation results for direction finding of five sound wideband signals using a square internally filled antenna array consisting of 16 antennas, based on ESPRIT with the proposed method of ambiguity correction, are presented. The proposed method for correcting the steering vector ambiguity caused by different spectral components of wideband signals in the antenna array allows estimation of their directions of arrival, as is done for narrowband radio signals.

Multi-qubit gates and Schrödinger cat states in an optical clock.

Many-particle entanglement is a key resource for achieving the fundamental precision limits of a quantum sensor1. Optical atomic clocks2, the current state of the art in frequency precision, are a rapidly emerging area of focus for entanglement-enhanced metrology3-6. Augmenting tweezer-based clocks featuring microscopic control and detection7-10 with the high-fidelity entangling gates developed for atom-array information processing11,12 offers a promising route towards making use of highly entangled quantum states for improved optical clocks. Here we develop and use a family of multi-qubit Rydberg gates to generate Schrödinger cat states of the Greenberger-Horne-Zeilinger (GHZ) type with up to nine optical clock qubits in a programmable atom array. In an atom-laser comparison at sufficiently short dark times, we demonstrate a fractional frequency instability below the standard quantum limit (SQL) using GHZ states of up to four qubits. However, because of their reduced dynamic range, GHZ states of a single size fail to improve the achievable clock precision at the optimal dark time compared with unentangled atoms13. Towards overcoming this hurdle, we simultaneously prepare a cascade of varying-size GHZ states to perform unambiguous phase estimation over an extended interval14-17. These results demonstrate key building blocks for approaching Heisenberg-limited scaling of optical atomic clock precision.

К оценке риска негативного воздействия электромагнитных полей сотовой связи на центральную нервную систему детей и подростков (Обзор). Часть 2. Параметры когнитивных процессов

This paper continues the authors’ review that dwells on modeling radiofrequency electromagnetic fields (RF EMF) and results obtained by measuring electroencephalography indicators, sensorimotor reactions, fatigue, work capacity, duration of an individual minute and the reproduction of a given rhythm in children and adolescents. Health risk assessment is always based on data obtained by either laboratory tests or epidemiological studies. This paper analyses publications that describe effects of RF EMF exposure, including Wi-Fi, on cognitive processes in children and adolescents as well as methodical approaches to investigating this exposure. However, there are few such studies; in particular, effects produced by Wi-Fi exposure on cognitive indicators of adolescents aged 14–17 years, were found only in two publications. Literature analysis has established that research findings do not always give an unambiguous estimation of RF EMF effects. The review covers the reasons for ambiguous interpretation of research results: a variable range of test-systems used for investigating indicators of cognitive processes; simultaneous analysis of single exposures including descriptions of ‘effect of improvement’ in indicators; changes in cognitive indicators registered for a group of children and adolescents in a wide age range. Nevertheless, most results give evidence of negative changes in attention and memory of children and adolescents. Given that, longitudinal studies are becoming especially relevant since they estimate changes in various indicators in dynamics, including those induced by changes in mobile phone use. The review highlights the relevance of comprehensive investigations with their focus on health outcomes of RF EMF exposure intrinsic to 5G technologies considering their global implementation.

Assessing the risk of negative effects produced by electromagnetic fields of cellular communication on the central nervous system of children and adolescents (Review). Part 2. Indicators of cognitive processes

This paper continues the authors’ review that dwells on modeling radiofrequency electromagnetic fields (RF EMF) and results obtained by measuring electroencephalography indicators, sensorimotor reactions, fatigue, work capacity, duration of an individual minute and the reproduction of a given rhythm in children and adolescents. Health risk assessment is always based on data obtained by either laboratory tests or epidemiological studies. This paper analyses publications that describe effects of RF EMF exposure, including Wi-Fi, on cognitive processes in children and adolescents as well as methodical approaches to investigating this exposure. However, there are few such studies; in particular, effects produced by Wi-Fi exposure on cognitive indicators of adolescents aged 14–17 years, were found only in two publications. Literature analysis has established that research findings do not always give an unambiguous estimation of RF EMF effects. The review covers the reasons for ambiguous interpretation of research results: a variable range of test-systems used for investigating indicators of cognitive processes; simultaneous analysis of single exposures including descriptions of ‘effect of improvement’ in indicators; changes in cognitive indicators registered for a group of children and adolescents in a wide age range. Nevertheless, most results give evidence of negative changes in attention and memory of children and adolescents. Given that, longitudinal studies are becoming especially relevant since they estimate changes in various indicators in dynamics, including those induced by changes in mobile phone use. The review highlights the relevance of comprehensive investigations with their focus on health outcomes of RF EMF exposure intrinsic to 5G technologies considering their global implementation.

Retrieval of leaf-level fluorescence quantum efficiency and NPQ-related xanthophyll absorption through spectral unmixing strategies for future VIS-NIR imaging spectroscopy

Current and future vegetation imaging spectroscopy satellites will bring a new data stream of information, of high scientific value to refine existing remote sensing products, and develop new ones. The sensors on board ESA's Fluorescence Explorer (FLEX) will cover the entire 500–780 nm range, designed to track the photosynthetic energy partitioning based on the key pigment players in the light reactions. To quantify the actual photosynthetic efficiency unambiguously, the dynamic pigment absorption behavior is crucial to complement the fluorescence information. An important role is given by the xanthophylls, regulating the non-photosynthetic quenching (NPQ) behavior which affects the 500–600 nm range. Therefore, this work focused on the development of a non-negative least squares (NNLS) spectral unmixing algorithm for reflectance (500–780 nm) retrieving the effective absorbance of individual pigments, i.e., Chlorophyll (Chl) a and b, beta-Carotene and xanthophylls. The NNLS fitting was applied to fit the total effective absorbance at leaf level, linearly composed of pigment and background absorption coefficient spectra. The model succeeded to obtain spectral fitting errors generally below 20% across the 500–780 nm range. Further, we focused on the further use of the effective absorbance by Chlorophyll a to calculate the absorbed photosynthetically active radiation or APAR Chl a. This product was combined with the total emitted fluorescence flux (670–780 nm), expressed in photon flux units, to obtain the fluorescence quantum efficiency (FQE), capturing the stress-related fluorescence quenching in the light reactions. Finally, we applied the leaf-based algorithm to foreseen FLEX image products simulated by the FLEX End-to-End Scene Generator. We were able to retrieve APAR Chl a with a RMSE of 85.5 μmol m−2 s−1 (NNLS with additional upper fitting constraints) and 158.2 μmol m−2 s−1 (regular NNLS), and FQE retrievals could be obtained with an R2 of 0.93 and 0.90, respectively. While the subtle xanthophyll absorption could be meaningfully fitted at the leaf scale, further improvements to the algorithms and an understanding of the physiological mechanisms are needed to deal with the complexity at larger scales. Given several challenges to be overcome, the proposed bottom-up strategy using specific pigment absorbance unmixing for (imaging) spectroscopy demonstrates the ongoing developments to complement the fluorescence product, with the aim to provide an unambiguous estimate on the actual carbon sequestration of vegetation.

Dental proteomic analyses and Raman spectroscopy for the estimation of the biological sex and age of human remains from the Greek cemetery of San Giorgio Extra, Reggio Calabria (Italy)

Sex and age estimation is one of the most fundamental steps in mortuary studies and bioarchaeology. It is essential for a deeper understanding of ancient societies, and has wide applications in gender archaeology. The aim of this paper is to create a new and reliable protocol for unambiguous sex estimation of the deceased, comparing proteomic analyses, archaeological evidence, and anthropological data from a Greek cemetery located in Reggio Calabria (or the ancient Rhegion), as well as a first approach to estimate the age of the deceased by Raman spectroscopy in archaeology. Excavations carried out in the San Giorgio Extra district, headed by the Superintendence for the Archaeological Heritage of Calabria during the years 2004 and 2007, led to the discovery of the most significant Hellenistic cemetery in the city. Specifically, archaeological campaigns brought to light thirty Greek inhumation burials and their related funerary objects. Through proteomic analyses, we monitored a total of eight characteristic peptides for the amelogenin isoform variants AMELX and AMELY from the dental enamel of twelve selected adult individuals. The presence or absence of the AMELY variant (exclusively present in male subjects, being encoded by the Y gene) allowed us to estimate the sex of the analyzed individuals with high accuracy. Raman spectroscopy was also applied to study the enamel and dentin crystallinity to determine other environmental and biological parameters. At the same time, archaeological studies based on artifacts discovered inside the graves and double-blind bio-anthropological sex estimation of the twelve subjects were performed in order to compare these evaluations with data from the proteomic analyses. Comparison between these different approaches produced totally congruent results for the majority of individuals. In addition, the proteomic analysis allowed us to estimate the sex of four poorly preserved subjects for whom sex estimation was somewhat doubtful, as well as that of one undetermined individual. Finally, proteomic results were produced here with a faster protocol than those found in the literature and are potentially scalable to much lower sample amounts.

A Multi-Correlation Peak Phase Deblurring Algorithm for BeiDou B1C Signals in Urban Environments

With the widespread global application of BeiDou navigation, BeiDou B1C signaling based on Quadrature Multiplexed Binary Offset Carrier (QMBOC) modulation is expected to be extensively used in urban environments due to its wider signal bandwidth, smaller code pseudorange measurement errors, and stronger multipath capabilities. Despite offering higher positioning accuracy and secondary modulation characteristics of the BeiDou, B1C signals introduce the challenge of multiple peaks in the autocorrelation function. This leads to phase ambiguity during signal acquisition and tracking, resulting in positioning deviations of tens or even hundreds of meters. In urban environments, such deviations give rise to significant practical application issues. To address this problem, we have designed a multi-loop structure for the synchronous tracking of B1C signals and proposed a multi-peak phase-deblurring algorithm specifically tailored for the BeiDou B1C signal in urban environments. This algorithm considers the coupling relationship between the code and the carrier loops, and by matching the structural design of multiple loops, it achieves a precise and unambiguous phase estimation of the pseudocode, enabling the stable tracking of the entire loop for the BeiDou B1C signal. Simulation and actual testing demonstrate that the algorithm exhibits an error less than 0.03 for chip intervals when the signal-to-noise ratio is greater than −20 dB. Additionally, the accuracy can be improved by adjusting the set conditions, making it suitable for urban environments.

An analytical approach for the stability analysis of power networks through Kuramoto oscillators model

In recent years, ensuring stability in power networks has posed a significant challenge for network control engineers, primarily due to the substantial growth in power demand and the complexities involved in integrating renewable energy sources. This study endeavours to augment the existing research by presenting theoretical findings in a practical manner through the introduction of a novel Lyapunov function and the application of LaSalle’s invariance principle to establish an unequivocal and accurate synchronization condition in power networks. The study’s salient contributions include (I) the Fresh approach of utilizing a second-order configuration of asymmetrically networked, dissimilar oscillators; (II) the incorporation of lossy power networks, culminating in non-identical phase delays in the analytical model of the oscillating network; and (III) the introduction of an entirely original Lyapunov function to provide a precise and unambiguous estimation for the region of attraction in power networks. Analytical findings substantiate that network synchronization is assured by the algebraic connectivity of the network graph exceeding a particular threshold value. The study’s transient stability conditions have been authenticated via numerical simulations of the IEEE 39-bus system.

An Unambiguous 2D DOA Estimation Algorithm by a Large-Space L-Shaped Array

An Unambiguous 2D DOA Estimation Algorithm by a Large-Space L-Shaped Array

Quantum Rabi interferometry of motion and radiation

The precise determination of a displacement of a mechanical oscillator or a microwave field in a predetermined direction in phase space can be carried out with trapped ions or superconducting circuits, respectively, by coupling the oscillator with ancilla qubits. Through that coupling, the displacement information is transferred to the qubits which are then subsequently read out. However, unambiguous estimation of displacement in an unknown direction in the phase space has not been attempted in such oscillator-qubit systems. Here, we propose a hybrid oscillator-qubit interferometric setup for the unambiguous estimation of phase space displacements in an arbitrary direction, based on feasible Rabi interactions beyond the rotating-wave approximation. Using such a hybrid Rabi interferometer for quantum sensing, we show that the performance is superior to the ones attained by single-mode estimation schemes and a conventional interferometer based on Jaynes-Cummings interactions. Moreover, we find that the sensitivity of the Rabi interferometer is independent of the thermal occupation of the oscillator mode, and thus cooling it to the ground state before sensing is not required. We also perform a thorough investigation of the effect of qubit dephasing and oscillator thermalization. We find the interferometer to be fairly robust, outperforming different benchmark estimation schemes even for large dephasing and thermalization.

Estimating the magnitude of money laundering in the United Arab Emirates (UAE): evidence from the currency demand approach (CDA)

PurposeDespite the vulnerability of rapidly developing and emerging market economies, researchers have paid less attention to the determination of the size of money laundering (ML) in these economies, including the United Arab Emirates (the UAE). Therefore, this paper aims to estimate the magnitude of ML in the UAE between 1975 and 2020 based on the currency demand approach (CDA).Design/methodology/approachThe study uses the Gregory–Hansen cointegration technique alongside the autoregressive distributed lag bounds testing procedure to estimate the CDA model.FindingsThe results illustrate that an amount equivalent to about 19.034% of the GDP is laundered in the UAE between 1975 and 2020, on average, with the value lying between 15.129% and 23.121%. In addition, the results demonstrate the importance of the real estate market, gold trade, remittance channels and the size of the underground economy in facilitating the laundering of illicit funds in the country.Originality/valueTo the best of the authors’ knowledge, the study is the pioneering attempt at estimating the amount of illicit funds laundered in the UAE. Besides, the adoption of a novel, yet robust, approach based on the modification of the CDA technique also sets the study apart as it ensures a correct, clear, unambiguous and indisputable estimate of the magnitude of ML is obtained. In addition, it is expected that the outcome of the study will expand the frontiers of knowledge among policy makers and relevant agencies and ensure the adoption of the most efficient and effective measures to curb the ML menace in the country.

Improving the beamforming performance of a vector sensor line array with a coprime array configuration

Coprime arrays provide appealing performance in many scenarios. In this paper, we show the benefits of spatially undersampled acoustic vector hydrophone coprime line arrays over traditional uniform hydrophone line arrays for beamforming and direction-of-arrival (DOA) estimation. This paper presents the perceptiveness of the theoretical performance of an underwater vector sensor coprime line array (vCLA) in the physical array domain. Based on the Product and Min methods, an array extending approach for the vCLA has been proposed to reduce the area of grating lobes of beam output leading to unambiguous DOA estimates. To minimize the sidelobe and improve the left–right suppression ability of the array, we present a data-independent weighting design method based on sound pressure and vibration velocity joint processing (PVJP) and evaluate its performance in detail. The results suggest that the proposed method can improve the vCLA beam output directivity, enhance the spatial resolution, benefit the left–right ambiguity rejection capability, and productively mitigate the influence of side and grating lobes, thus promoting the DOA estimation accuracy.

Phase ambiguity resolution and mixed pixel detection in EDM with multiple modulation wavelengths

Distance measurement based on the accumulated phase of intensity-modulated continuous-wave lasers is an established approach for pointwise geometry acquisition in uncontrolled conditions, enabling some of the most accurate Lidar/laser-scanning solutions. Inherently affected by cycle ambiguities due to the modulo 2π phase observations, several modulation wavelengths are typically used in practical implementations to extend the measurement range. One of the main limitations of these systems arises from their inability to decouple mixed signals affected by different delays. This is especially relevant when the laser beam illuminates simultaneously two or more surfaces at significantly different distances, producing mixed-pixel measurements in which the estimated distance does not reliably correspond to any of the involved scatterers. Algorithms for detection and filtering of mixed pixels within point-cloud data have been proposed based on analyzing consistency across local neighborhoods. The resolution of multiple scatterers on individual measurements, however, has not been yet reported nor is provided by undisclosed commercial implementations. In this work, we analyze the problem of signal mixing in multi-wavelength phase-based distance estimation, and propose an algorithm for joint phase ambiguity resolution and mixed pixel detection based on mixed integer linear programming. We first analyze theoretically the performance limits of the proposed solution, demonstrating unbiasedness in the presence of noise and robustness in the presence of multiple scatterers. In addition, we investigate empirically the impact of noise, mixed measurements and choice of modulation wavelengths on the performance of the proposed algorithm. The results demonstrate the capacity of the presented approach, given an adequate wavelength selection, to provide unambiguous distance estimates under realistic noise conditions and to identify measurements affected by mixed pixels while approximating the position of the dominant scatterer. Aside from contributing to improving the reliability and resolution capability of Lidar and laser-scanning data, the proposed solution sets a promising step towards fully resolved multi-target distance measurement.

Nonuniform-Array-Based Integrated MIMO Communication and Positioning in Wireless Local Area Networks

The angle of arrival (AoA) is a vital parameter for geometry-based 3-D indoor positioning. Considering a wireless local area network (WLAN) as an example, a conventional antenna array designed for multiple-input–multiple-output (MIMO) communication is not suitable for AoA estimation due to the angle ambiguity introduced by the large interelement spacing (IES). Consequently, the integration of positioning and communication functions using the same radio frequency (RF) frontend and the array would be highly valuable. A nonuniform array (NUA) is proposed to solve this challenging problem. The NUA is optimized to achieve unambiguous angle estimation while maintaining high-capacity WLAN MIMO communication. Moreover, based on the estimated MIMO channel state information (CSI), an improved trilinear parallel factor (TPF) decomposition method is proposed to accurately estimate AoAs with low complexity. Simulated and experimental results show that the proposed NUA-based scheme can achieve decimeter-level 3-D positioning accuracy.

Application of interval estimations of the total content of antioxidants for the analysis of juice products by the CUPRAC method using the Cu(II) – NC–PMM system

Сu(II) – neocuproinе indicator system (CUPRAC method, R. Apak) was used for spectrophotometric determination of the total content of antioxidant reductants (ΣAO) in juice products. Gallic acid, ascorbic acid, quercetin, luteolin, dihydroquercetin, which are typical for fruit and berry juices, as well as trolox, as a frequently used standard, were used as model compounds of antioxidant-reducing agents (AO). The polymethacrylate matrix (PMM) with immobilized reagents was immersed in the test solution for 20 minutes, and then photometrically measured at 450 nm. The aim of the work was to compare two methods for estimating ΣAO: a) in terms of the content of a standard substance (generally accepted method); b) in the form of an interval calculated taking into account the sensitivity coefficients when determining different AO at a selected wavelength (interval estimate according to V.I. Vershinin). It was established that the analytical signals of the model AO obeyed the Beer-Lambert-Bouguer law in the range of 10–6–2.10–5 mol/l, and were measured with a relative standard deviation not exceeding 10 %; deviations from the light absorption additivity of AO mixtures were statistically insignificant. As in the photometry of solutions, the sensitivity coefficients of different AO were different, and the differences decreased when using «normal» concentrations. The modulus of the relative error in estimating ΣAO in model mixtures, even when using optimal standards (luteolin), reached 17%. The possibility of interval estimation of ΣAO from generalized analytical signals measured by the CUPRAC method using PMM matrices was shown. The boundaries of the intervals practically did not depend on the standards used during the calculation. For all mixtures the actual values of ΣAO were within the boundaries of the corresponding intervals. The results of the group analysis of fruit and berry juices before and after their dilution confirmed the approximate correctness of the results obtained both by method (a), i.e. in terms of luteolin, and by method (b), i.e. in the interval form. Unfortunately, the width of the intervals that take into account the intragroup signal intensity was an order of magnitude larger than the width of the confidence intervals calculated from the results of repeated measurements of generalized signals (Student's test, n = 3, P = 0.95). This indicates the necessity of leveling the sensitivity coefficients for different AO. Thus, both methods of calculation are suitable for the group analysis of juice products, but method (b) leads to more reliable, more metrological correct, but less unambiguous estimates of the total content of the antioxidants.

Unambiguous broadband direction of arrival estimation based on improved extended frequency-difference method.

In this paper, we consider the problem of bearing ambiguity in the direction of arrival (DOA) estimation due to spatial aliasing when the minimum wavelength of the processing broadband signal is less than the element spacing of a uniform linear array (ULA). First, an extended frequency-difference (FD) method is presented. Unlike the existing FD methods, the extended FD signal is constructed by conjugate multiplying a diagonal matrix consisting of steering vectors at high frequency and pre-processing direction with the array sampled signal matrix at low frequency. Then, this paper establishes a decision criterion for distinguishing the aliasing component that varies linearly with frequency in the extended FD space. Finally, an unambiguous broadband DOA estimation method is achieved by suppressing spatial aliasing in the extended FD space. The simulation results show the effectiveness of the proposed method in low signal-to-noise ratio, low signal-to-interference ratio, and multi-interference conditions. The unambiguous processing ability of the proposed method is further verified in the South China Sea using ship signals in the frequency band of 200 to 700 Hz and a 10-element ULA with a 6.25 m spacing deployed on the seabed.

Unambiguous Direction Estimation and Localization of Two Unresolved Targets via Monopulse Radar

Traditional monopulse radar cannot resolve two closely spaced targets present in one resolution cell (range and Doppler) by means of the monopulse ratio. This study presents a closed-form solution to resolve the directions of arrival of two unresolved targets using a single snapshot of four independent channels in phase comparison monopulse radar. If both targets have the same elevation or same azimuth direction, the proposed scheme cannot estimate their directions. To estimate the direction of such targets, an extra antenna is required. The impact of input noise power, the targets’ direction, and phase difference of the targets’ signal on the accuracy of angle estimation are also explained. The numerical simulation result validates the effectiveness of the presented scheme.

Design of a Grating Lobes-Free Architecture for Distributed Sensor System with Arbitrary Element Spacing

Two main difficulties for the accurate direction of arrival (DOA) estimation in a distributed sensor system are grating lobes and system synchronization. Different from the traditional phased array system based on single carrier frequency, this paper designs a novel architecture for distributed sensor system using dual carrier frequency measurements. Both two carrier frequencies are combined and transmitted simultaneously in the proposed architecture. Instead of single carrier frequency f1 in the traditional method, the frequency separation f2−f1 is used in the proposed algorithm to determine a maximum unambiguous DOA estimate. Since f2−f1 is much less than f1 and the choice of f2−f1 is more flexible, the proposed method can provide an unambiguous DOA estimate in the whole field of view (FOV) for arbitrary element spacing and a looser requirement on system synchronization than the traditional method based on single carrier frequency. For a case with f1=3 Ghz, f2−f1=150 Mhz and 10 times element spacing, there is no grating lobe for the proposed method in the whole FOV [−π/2,π/2], whereas the traditional method has many grating lobes and the FOV of the traditional method without grating lobes is only 5.73∘. To obtain the same combining efficiency in this case, the requirement on the positioning error of the proposed method is 0.4 m and the location error of the traditional method must be smaller than 0.02 m. Hence, the proposed method can greatly reduce hardware requirements. The performances of the proposed architecture for the cases with perfect and imperfect system synchronizations are evaluated in terms of the average beampattern and combining efficiency, respectively. Some characteristics of the derived beampattern and combining efficiency are also presented in the paper.

Radar-Based UAV Swarm Surveillance Based on a Two-Stage Wave Path Difference Estimation Method

The numerous applications of unmanned aerial vehicles (UAVs) have caused them to receive growing interest worldwide. However, misused UAVs have caused significant public safety and privacy concerns. Therefore, developing an anti-UAV surveillance system is of paramount importance. In this paper, we propose a radar-based UAV swarm surveillance approach. A frequency estimation-based approach is used to obtain a coarse wave path difference estimate. Then, by combining the coarse estimate from the first stage with an estimate from the phase comparison method, a fine and unambiguous estimate of the wave path difference is derived. Through the solution of a system of nonlinear equations regarding the measured range and wave path difference, the proposed method is able to provide an unambiguous three-dimensional (3D) position estimate for a given UAV swarm. Once such 3D positions have been collected throughout an observation period, system tracks of the UAV swarm can be formed. With these tracks, a target object map (TOM) can be generated and handed over to an interceptor to counter the UAV swarm. Theoretical analyses of the accuracy of the estimation results and the restrictions of the proposed method are presented in detail. Several simulations are also carried out to evaluate the performance of the proposed method.

DOA estimation based on density-tapered thinned array

In this paper, several classical DOA estimation methods are applied to density-tapered thinned array. The density-tapered thinned array has the advantage that there is no grating lobe in the whole angle scanning range, and the unambiguous angle estimation of the target is obtained. The experimental results show that the classical DOA estimation method can be applied directly to the density-tapered thinned array to obtain satisfactory results, which lays a foundation for the practical application of the density-tapered thinned array. In addition, the effects of sparsity and number of elements on DOA estimation are analyzed, and the advantages of density-tapered thinned array over uniform arrays are verified.