Direction Finding Method Research Articles

Real-time source localization using phase and amplitude gradient estimator for acoustic intensity

Recent demonstrations of real-time source localization systems have used a variety of direction-finding methods. One such system uses a multi-microphone probe to estimate acoustic intensity [Inoue et al., Proc. Meetings Acoust. 29, 025001 (2016)], although the bandwidth of intensity estimates are traditionally limited by the microphone spacing. The Phase and Amplitude Gradient Estimator (PAGE) method [Thomas et al., J. Acoust. Soc. Am. 137, 3366–3376 (2015)] greatly extends the bandwidth of active intensity, providing an accurate method of source localization for a wide bandwidth. An initial system implemented in LabVIEW estimates active intensity using the PAGE method to identify the direction of the source location in real time. Using a paired webcam, the program then overlays the direction as a three-dimensional arrow onto a webcam image. A demonstration will be provided. Initial quantitative results show the accuracy of the system and limitations of the device. [Sponsored by the NSF REU program.]

Validation of Sensing Ocean Surface Currents Using Multi-Frequency HF Radar Based on a Circular Receiving Array

To reduce the floor space of receiving antenna arrays, the Radio Ocean Remote SEnsing (RORSE) laboratory of Wuhan University developed a circular receiving array for a multi-frequency high frequency (MHF) radar system in 2014, consisting of seven uniformly spaced antenna elements positioned on a circle with a diameter of 5 m. The new system, which is abbreviated MHF-C radar, adopts frequency modulated interrupted continuous wave (FMICW) chirps and is capable of simultaneously operating at a maximum of four frequencies in the band of 7.5–25 MHz, and providing current, wave and wind maps every ten minutes. The phase direction-finding method is utilized to estimate the directions of the current signals, and array phase uncertainties are also taken into consideration in the signal model. This paper introduces the system in detail and investigates the performance of current measurements using MHF-C radars installed at Shengshan and Zhujiajian along the coast of the East China Sea. Radial current measurements derived from 8.27 MHz and 19.20 MHz at the same range are compared. Observations and comparisons between MHF-C radars and acoustic Doppler current profilers (ADCPs) are also presented in this paper. The results preliminarily demonstrate that the MHF-C radar system is capable of maintaining the same performance for current measurements whenever it steers to any other azimuth in the coverage and has a good ability to measure currents.

Acoustic direction finding using single acoustic vector sensor under high reverberation

We propose a novel and robust method for acoustic direction finding, which is solely based on acoustic pressure and pressure gradient measurements from single Acoustic Vector Sensor (AVS). We do not make any stochastic and sparseness assumptions regarding the signal source and the environmental characteristics. Hence, our method can be applied to a wide range of wideband acoustic signals including the speech and noise-like signals in various environments. Our method identifies the “clean” time frequency bins that are not distorted by multipath signals and noise, and estimates the 2D-DOA angles at only those identified bins. Moreover, the identification of the clean bins and the corresponding DOA estimation are performed jointly in one framework in a computationally highly efficient manner. We mathematically and experimentally show that the false detection rate of the proposed method is zero, i.e., none of the time-frequency bins with multiple sources are wrongly labeled as single-source, when the source directions do not coincide. Therefore, our method is significantly more reliable and robust compared to the competing state-of-the-art methods that perform the time-frequency bin selection and the DOA estimation separately. The proposed method, for performed simulations, estimates the source direction with high accuracy (less than 1 degree error) even under significantly high reverberation conditions.

A Direction Finding Method with A 3-D Array Based on Aperture Synthesis

Direction finding for electronic warfare application should provide a wider field of view as possible. But the maximum unambiguous field of view for conventional direction finding methods is a hemisphere. It cannot distinguish the direction of arrival of the signals from the back lobe of the array. In this paper, a full 3-D direction finding method based on aperture synthesis radiometry is proposed. The model of the direction finding system is illustrated, and the fundamentals are presented. The relationship between the outputs of the measurements of a 3-D array and the 3-D power distribution of the point sources can be represented by a 3-D Fourier transform, and then the 3-D power distribution of the point sources can be reconstructed by an inverse 3-D Fourier transform. And in order to display the 3-D power distribution of the point sources conveniently, the whole spherical distribution is represented by two 2-D circular distribution images, one of which is for the upper hemisphere, and the other is for the lower hemisphere. Then a numeric simulation is designed and conducted to demonstrate the feasibility of the method. The results show that the method can estimate the arbitrary direction of arrival of the signals in the 3-D space correctly.

Interferometric Direction Finding by a Vector-Scalar Receiver

A method for interferometric direction finding of a broadband sound source in an oceanic waveguide by a single vector-scalar receiver is presented. The method is based on the double Fourier transform of the interference pattern formed during motion. The efficiencies of the proposed direction finding method and the method based on measuring the delay times of signals arriving at spaced scalar receivers are compared based on the natural experiment results. The noise immunity of the interferometric direction finding method is considered.

Methods for spatial direction finding of geoacoustic signals at Mikizha Lake in Kamchatka

In the framework of the work, a spatial analysis of geoacoustic emissions properties recorded by a hydroacoustic receiver in a shallow Mikizha Lake, Kamchatkskiy kray, is carried out. The features of geoacoustic pulse registration are considered, methods to determine the directions of their arrival and to locate the sources are proposed. Examples of geoacoustic signals during background periods and seismic event preparation periods are presented.

Subspace‐Based Method for Direction Finding of Multiple Partially Polarized Signals

We investigate the problem of direction finding for multiple Partially polarized (PP) electromagnetic signals, each of which possesses two spatial degrees of freedom. We use a uniform linear array of L sensors, where each consists of two co-located single-polarized elements. By exploiting the array geometry and its shift invariance property, we construct a set of data correlation sequences using the array output and its conjugate to transform the problem of direction finding to that of the estimation of complex sinusoid frequencies. The rank-2 signal correlation matrices of the PP signals become real-valued amplitudes of complex sinusoids, and thus, the rank-2K signal subspace of the array output transforms to the rank-K signal subspace of the constructed correlation sequences. We show that only L=K+1 sensors are needed to resolve K PP signals by solving the problem of estimation of sinusoid frequencies using subspace-based methods. The proposed method is also applicable to the scenario, where both Completely polarized (CP) and PP signals coexist, without the need of any prior information on the degree of polarization of the signal.

Efficient sparse representation method for wideband DOA estimation using focusing operation

The computational complexity of wideband sparse representation (SR) greatly restricts the application of SR-based wideband direction-of-arrival (DOA) estimation in practical system. Here, an efficient method for wideband direction finding based on SR is proposed. This method combines the focusing operation with weighted subspace fitting (WSF) to not only decrease the computational complexity but also improve the performance of DOA estimation. Exploiting the result of the focusing operation, the covariance matrix at the focusing frequency can be obtained and used as the data for sparse recovery to get wideband DOA estimates. The WSF is employed to reduce the sensitivity to the noise and the regularisation parameter is given by the asymptotic distribution of the WSF cost function. Simulations are provided to show the efficiency and performance of the proposed method.

The scheme of automatic pseudo Doppler software defined radio direction finder

The research describes the implementation approaches of a pseudo Doppler radio direction finding method based on software defined radio technology. A block diagram of an automatic pseudo Doppler software defined radio direction finder is proposed. A hardware functional diagram of specialized software architecture is offered. New schematic solution for antenna commutator and beating software synchronization is realized. For smoothing the bearing measurement of an aperiodic cyclic field based filtering procedure is proposed. By mathematical and experimental modeling a key features of a pseudo Doppler software defined radio direction finder are proved in comparison with the classical implementation: short signals bearing ability, statistical smoothing algorithms implementation convenience, simultaneous multiple frequency channels direction finding possibility, processing information simplification, flexibility and reconfigurability of radio direction finding systems. A prototype that implements the proposed approaches, circuitry design, software and algorithmic solutions is developed.

APPLICATION OF DISTRIBUTED ANTENNA SYSTEMS FOR DETERMINATION OF RADIATION SOURCE COORDINATES WITH USE OF PHASE METHOD IN FRESNEL ZONE

Background. Talking about evolution of passive radar systems and multifunction antenna systems, it is necessary to acknowledge that distributed antenna systems (DAS) are supposed to be widely spread in the very near future in many areas of human activity, such as organization of high-quality mobile communication in large offices, shopping centers, fitness buildings and so on. Structurally, DAS consist of different groups of antennas and base stations with active and passive repeaters of radio signals. Generally, mutual location of such antennas and base stations can be chosen experimentally according to the criterion of service area maximization. For the further quality of service improvement, it is necessary to use smart antennas in DAS as basic structure elements. The use of smart antennas will allow tracking the subscriber`s (or SOR – source of radiation) location by means of direction-finding (DF) and to increase radiation power of radio signal towards SOR thus decreasing interference to other subscribers. It is important to note that amplitude methods of DF are unacceptable in this case because base stations have antenna beam patterns which are rather wide. Use of phase methods for direction finding is actual but constrained because of electromagnetic waves (EMW) multipath propagation and large DF errors caused by the following reason – it happens that SOR is located in Fresnel zone of direction-finder antenna system. So, consideration of the phenomenon of EMW front curvature in DAS is very important in order to construct direction-finders. Objective. Consideration of EMW phase front sphericity (curvature) and its influence on the accuracy of SOR coordinates determination measured by DAS phase methods. Scheme technical decisions of phase direction-finders (PDF) based on this process are also represented. Methods. To study the effect of the EMW phase front curvature on the accuracy of determining the coordinates of the SOR analytical dependencies are synthesized. Calculations of the direction characteristics, errors in determining the phase shifts between the antenna elements of the phase direction-finder, as well as the error in determining the distance to SOR in the Fresnel zone as a function of the range to SOR and its bearing were made based on MathCad 14 program. Results. During the process of SOR angular coordinates determination in Fresnel zone with use of EMW phase front curvature оn the basis of planar antenna array, it is necessary to execute consistently two operations: 1) to define the fact of presence of EMW phase front curvature; 2) to switch PDF from the mode of bearing and tilt angles estimation (when it is in plane phase front) to the mode of bearing and tilt angles estimation (and also distance to SOR if needed) with phase front curvature of EMW. Taking into account the analysis relating to errors of bearing angle measurements in Fresnel zone (depending on the location of rough, but exact bases, for three-element sparse LAA) it is possible to conclude that their position doesn’t impact on exactness of bearing angle measuring in PDF. But to support more exact determination of SOR distance they must be placed in the center of exact, but ambiguous bases of PDF. Conclusions. Failure to take into account EMW phase front curvature from SOR harmonic signal leads to errors of SOR coordinate calculation under conditions of its location in Fresnel zone and absence of other SORs. Knowledge of distance to SOR can be used in passive radar systems, in radio monitoring systems of radio interference sources which have bearing angles equal with useful SOR ones, but located on different distances from useful SOR. This knowledge can also be used in mobile communication networks to strengthen signal level on certain distance with EMW energy focusing, in vehicle control systems on the basis of the satellite navigation systems etc.

Robust time delay estimation based direction finding in lp-space

ABSTRACTA robust time delay estimation (TDE)-based direction-finding method for multipath signals in the presence of impulsive noise is proposed in this paper. Compared to traditional algorithms, developed for Gaussian distribution, this method performs more robust in the presence of non-Gaussian noise. The robust TDE is first obtained by utilising the matched filtering in -space which is less sensitive to outliers. Then direction-of-arrival (DOA) is estimated by ‘steering vector fitting’ approach based on the delay estimates. An iterative approach is employed to estimate each multipath component separately and improve the estimation accuracy. The method is developed in -space, which minimises the -norm of residual fitting error vector instead of the Frobenius norm. The number of antennas required can be less than that of the sources. Simulation results show that the method outperforms several outliers-resistant algorithms both in cases of impulsive noise and Gaussian distribution noise.

Analysis of interference immunity of the searchless method of correlation-interferometric direction finding with recostruction of the spatial analytical signal

An analysis of noise immunity of the searchless digital method of correlation-interferometric direction finding with reconstruction of the spatial analytical signal has been carried out. An analytical estimate of the direction finding error variance consisting of the noise and interference components was obtained. It was shown that the main controllable factors affecting the noise component of the direction finding error variance are as follows: the number of direction-finding channels, the amount of separation between the selected elements of the antenna array, the type of the weight function in spatial spectral analysis and the time of emission analysis. The interference component of the direction finding error variance, unlike the noise component, does not depend on the analysis time but is determined, first of all, by the quality of frequency-spatial selection. In simulation, a family of dependencies of the root mean square deviation of the bearing estimate on the signal-to-noise ratio and the type of the weight function of the spectral analysis window was obtained. Possibility of direction finding with a value of the root mean square deviation of the bearing estimate of 0.03 degrees at an input signal-to-noise ratio of 0 dB has been shown. The estimates of the direction finding error variance obtained analytically and by software simulation practically coincided which confirms the analysis correctness. As a result of simulation, a family of dependences of root-mean square deviation of the bearing estimation on the separation of direction to the signal and interference sources at different signal frequencies was also obtained. It was determined that when the 64-element linear array is used, the resolution of the direction finder depends on the signal frequency. It varies between 6–15 degrees in the range of the direction finder operating frequencies at a signal/interference ratio of 0 dB. The resolution of the direction finder which was found to be high compared to the annular antenna array is an important advantage in conditions of a complex electromagnetic situation.

Motion-Extended Array Synthesis—Part I: Theory and Method

We consider the realization of motion-extended array synthesis (MXAS), in the RF and acoustic sensing domains, for the purpose of achieving high resolution in imaging, direction finding (DF), and geolocation applications. The focus is on a method in which, like synthetic aperture radar (SAR), the aperture synthesized is much larger than any aspect of the physical system, but, unlike SAR, in which there is no reference waveform available to exploit. We show that arbitrarily large virtual arrays, limited only by antenna element field of view, can be created by moving one collection system away from another, sweeping out a 1-D or 2-D area. The virtual array so created is suitable for use in general signal environments, including complex scenarios with cochannel and/or ultraweak sources. In the MXAS processing construct, the temporally distributed array formation is cast into a form resembling standard array processing and affording the same degrees of freedom as a real array of the same size. A performance assessment comparing an MXAS implementation to a leading method for DF and geolocation shows orders of magnitude improvement for MXAS, and conformance to the Cramer–Rao lower bound for DF for an array, under the correct interpretation of motion extension. Finally, we discuss candidate application areas.

Energy direction finding method taking into account the curvature of the Earth and interference

This paper presents a method using a two-position system to determine the spatial coordinates of a moving radiation source from one bearing measurement and relative energy measurements of the received signal taking into account the effect of its reflection from the Earth surface. The passive location problem is solved for low elevation angles taking into account the curvature of the Earth and using a polynomial model of source motion. An algorithm for the parametric identification of this model using a measurement sample of increasing size in a regularized formulation is developed, and the accuracy characteristics of the method are analyzed.

Development of direct method of direction finding with two-dimensional correlative processing of spatial signal

The development of the direct digital method of correlative-interferometric direction finding with two-dimensional correlative processing of the reconstructed complex spatial signal in the aperture of linear antenna array was conducted. The estimations of directions towards the radio sources are obtained through the use of a two-dimensional frequency domain of determination and a two-stage processing, which enables the direct correlative analysis with minimal computing expense. At this point, the direct estimation of directions towards the sources of casual radio emissions, which spectra are fully overlapped by frequency, is performed in real time by reconstructing of the complex spatial analytical signals, their spatial selection and dispersive-correlative processing. As a result of simulation, the dependence family of mean square deviation of estimation of direction from the direction of the source of radio radiation for different signal/noise ratios is obtained. The analysis showed that the examined method provides a higher accuracy of direction finding in comparison with the known method in a wide sector of directions, but it has lower computation costs and provides a significant speed increase of direction finding. It is shown that the direction finding in the sector 360 degrees with an error of less than 0.04 degrees, when the input signal/noise ratio of 0 dB, is possible by using two antenna arrays. The possibility to ensure the resolution of 8 degrees or less at a signal/noise ratio of 0 dB, which is an important advantage in a complex electromagnetic environment is also shown.

The application of the on-board devices radio direction-finding in the navigation systems of drones

Problems of the solving the tasks of navigation in the conditions of use by the enemy jammers radio signals from global navigation satellite systems is actual for small military drones during the fighting. Without navigation information unmanned aerial vehicle strays off course and lose the ability to perform combat missions. When you try to control the aircraft by active radio then the stealth mode is broken. This gives the opponent the opportunity to destroy the not hidden aircraft and ground control station.Construction of autonomous navigation systems based on MEMS gyroscopes and accelerometers is difficult due to the fact that they quickly accumulate measurement errors and therefore are not able to provide a reliable solution to problems of navigation. More perfect laser and fiber optic gyros have unacceptable size, weight and cost.The using the passive radio direction finding method is rational for automatically solving navigation tasks. Elements of the spatial antennas arrays of direction finder can be combined with elements of the primary structure of the aircraft. In the zones of local military conflicts usually work continues stationary sources of radio signals civilian use. Such sources can be be used as of radio beacons. The coordinates and characteristics of potential radio beacons must to be stored in the database of the on-board computer of aircraft.The accuracy of navigation by radio beacons depends on the angular error of direction finding and distance to beacon. In most cases, it is sufficient for the automatic flight on a given route and aerial photography.

Joint direction finding and array calibration method for MIMO radar with unknown gain phase errors

A novel method for joint direction finding and array calibration in multiple-input multiple-output (MIMO) radar with unknown array gain phase errors is proposed. The transmit array and receive array are innovatively arranged along different axes, which are orthogonal to each other. After the trilinear decomposition, the influenced transmit direction matrix and receive direction matrix are combined to estimate the angles, and the gain phase errors can be calculated subsequently. The proposed algorithm is suitable for both uniform linear array (ULA) and non-ULA, and it can achieve favourable angle and gain phase errors estimation without any auxiliary sensors and any information of the gain phase errors. Furthermore, it has better estimation performance and lower complexity than the eigenstructure method. Simulation results verify the usefulness of the approach.

Higher order direction finding from rectangular cumulant matrices: The rectangular [formula omitted]-MUSIC algorithms

Fourth-order (FO) high resolution direction finding methods such as 4-MUSIC have been developed for more than two decades for non-Gaussian sources mainly to overcome the limitations of second order (SO) high resolution methods such as MUSIC. In order to increase the performance of 4-MUSIC in the context of multiple sources, the MUSIC method has recently been extended to an arbitrary even order 2q (q≥2), for square arrangements of the 2qth-order data statistics, giving rise to the 2q-MUSIC algorithm. To further improve the performance of 2q-MUSIC, the purpose of this paper is to extend the latter to rectangular arrangements of the data statistics, giving rise to rectangular 2q-MUSIC algorithms. Two kinds of rectangular arrangements, corresponding to redundant and non-redundant arrangements are considered. In particular, it is shown that rectangular arrangements of the higher order (HO) data statistics achieve a trade-off between performance and maximal number of sources to be estimated. These rectangular arrangements also lead to a complexity reduction for a given level of performance, which is still increased by non-redundant arrangements of the statistics. These results, completely new, open new perspectives in HO array processing.

Adaptive methods for signal detection and direction finding

Adaptive methods for signal detection and direction finding are considered in the framework of the maximum likelihood method. The possibility of application of adaptive methods for solution of the problem of coherent passive radar is shown.

A direction finding method for spatial optical beam-forming network based on sparse Bayesian learning

This paper addresses the problem of direction-of-arrival (DOA) estimation of multiple sources for spatial optical beam forming network (SOBFN). A method which utilizes sparse Bayesian learning techniques to reconstruct the spatial power spectrum of the signals is proposed. The reconstruction procedure takes advantage of the amplitude distribution of the fiber-array output and the spatial sparsity of the incident signals. The reconstructed spectrum contains some evident peaks that indicate the coarse directions of the radiation sources. Then, a linear interpolation procedure is applied to make the DOA estimation results more precise. Sufficient numerical simulations are carried out to verify the performance of the proposed algorithm. Simulation results show that the proposed method fits well with the signal model of SOBFN and has favorable DOA estimation performance.