Location Of Radio Sources Research Articles

A hidden semi-Markov model for indoor radio source localization using received signal strength

Multipath propagation makes the use of received signal strength (RSS) unreliable as a signal propagation model for localization of a radio source based on RSS data. An approach to mitigation of this problem is the use of a Hidden Markov model (HMM) to represent the relationship between RSS and the radio source location by incorporating an environment prior and RSS source dynamics. The HMM structure forces a geometric form for the distribution for the sojourn time. This, combined with missing data problems, reduces confidence in location estimation. It is found, in this paper, that Hidden semi-Markov Models (HsMMs), with a more flexible sojourn time distribution are more able to represent source dynamics while retaining the advantages of HMMs for environmental constraints and improving resilience to missing measurements. The performance of the proposed HsMM algorithm is compared with a standard HMM via experiments and simulations involving indoor radio source localization using RSS data. Simulations use a ray tracing software-based simulator and the experiments for transmitter localization with RSS data are collected by software defined radios.

Adaptive Filtration of Radio Source Movement Parameters Based on Sensor Network TDOA Measurements in Presence of Anomalous Measurements

The methods based on TDOA measurements find wide application for localization of radio sources using wireless sensor networks. The need of taking into account the presence of anomalous measurement results often occurs in real conditions. Their appearance means a significant malfunction of sensor network components that results in divergence of traditional algorithms of Kalman filtration of radio source movement parameters. Based on the mathematical tools of mixed Markov processes in discrete time domain, the optimal and quasioptimal algorithms of adaptive filtration of radio source movement parameters were synthesized on the basis of TDOA measurements of sensor network in the presence of anomalous measurements. The optimal algorithm describes the evolution of joint a posteriori probability density of the vector of movement parameters and switching variables determining the type of measurement errors of network sensors. The quasioptimal algorithm obtained by linearization of the measurement equation involves the implementation of sequential technique of incoming data processing and performance of the Gaussian approximation of a posteriori probability density of radio source movement parameters. For the case considered in this paper using the statistical simulation, the developed quasioptimal algorithm makes it possible to recognize the appearance of anomalous errors of measurements with probability close to unity and eliminate their impact on the accuracy of determining the radio source movement parameters.

Methods of determining angular coordinates and location of radio sources in pilotless monitoring systems and experimental estimates of accuracy of these parameters

Methods of determining angular coordinates and location of radio sources in pilotless monitoring systems and experimental estimates of accuracy of these parameters

Radio Source Localization in Multipath Channels Using EM Lens Assisted Massive Antennas Arrays

The focusing ability of the lens antennas can significantly contribute to perform precise radio localization with low complexity in a massive antennas array (MAA) system. Thus, by combining lens antennas with an MAA, we propose an approach for radio source localization through an angle of arrival (AoA) estimation in a multipath propagation scenario. We discuss two simplified antenna selection techniques to select and process the focused subsets of antennas. Then, we implement a low-complexity time of arrival estimation scheme to detect the first arrival path (FAP) that contains the actual AoA information. Finally, the FAP signal is processed to estimate the AoA very efficiently, by applying one of the traditional subspace-based methods. To further simplify the system architecture with only slight degradation in performance, we also propose a mixed analog–digital AoA estimation structure based on the application of the sum–difference signal patterns technique. The simulated root mean squared error performance curves as a function of the signal-to-noise-ratio demonstrate that the proposed approach is capable of providing good AoA estimation results while considerably reducing the overall system complexity compared with the MAA system without the lens.

Оценка точности позиционирования источника радиоизлучения разностно-дальномерным и угломерным методами. Часть 2. 2D-моделирование

This article presents the development of a generalized mathematical model for estimating the limits of positioning accuracy, which was studied in part 1, when determining the radio source location using the difference-range and goniometric methods for particular scenarios on the plane. The results of this study were implemented in 2D models, which is a convenient tool for establishing the positioning accuracy limits and can it be practically used to substantiate the topologies of station placement in modern and advanced radio networks for solving radio communication, radar, and radio navigation problems, including adaptive beamforming for establishing and maintaining communications. Using private scenarios with three radio stations as an example, it is shown that for positioning of neighboring devices under conditions of their ultra dense distribution on the plane during the cooperation of the minimum required receivers number, the goniometer method is preferable.

Optimal Path Planning for Two Unmanned Aerial Vehicles in DRSS Localization

Optimal path planning for three or more unmanned aerial vehicles (UAVs) in radio source localization has been studied extensively; but path planning for two UAVs in signal strength based localization is still a challenge. This paper investigates the autonomous path planning for a pair of UAVs equipped with received signal strength (RSS) sensors applying optimum experimental design criteria based on the fisher information matrix (FIM). The control strategy steers the UAVs along the paths that minimize the emitter location uncertainty. Since there is one differential received signal strength (DRSS) measurement (two RSS sensors) in each time step, the emitter location uncertainty is infinite for a single measurement and the FIM is singular. The FIM is approximated at successive waypoints using the estimated location of the emitter produced by the extended kalman filter (EKF). The objective of this paper is to propose path planning approaches for minimum number of UAVs in DRSS-based localization based on different optimum criteria including D-, E-, A-optimality and sensitivity. Each criterion is related to a different characteristic of the estimation uncertainty ellipsoid and consequently generates different trajectories. The proposed steering algorithms are evaluated through extensive simulations.

DETERMINATION OF RADIO SOURCES LOCATION BY THE METHOD OF "IMAGINARY BASE" WHEN USING THE LINEAR MODEL

This article presents the expressions which allow evaluating the potential accuracy of radio source location by the method of «imaginary base» when using the linear model of changing the bearing on it. The concept of the method of «imaginary base» is to be used in solving the triangulation problem not only of measuring bearing, but also their extrapolated values at a certain time interval. Potential characteristics is determined by accuracy, dynamic and geometrical factors, bearing measurement and extrapolation times. The article shows that when using a linear model, there are limitations both on the time of measuring bearing and on the time of extrapolation. It will be because of the increase in the variance of the error of estimating the distance. Limiting of series decomposition members number of non-linear bearing change dependence from time there are. It depends on the speed of changing bearing (depends on the range and speed) and the initial bearing (depends on the track angle). Extrapolation over long time intervals is possible only at long distances and at relatively low speeds.

Radio bearing of sources with directional antennas in urban environment

AbstractThis paper focuses on assessing the limitations in the direction-finding process of radio sources with directional antennas in an urbanized environment, demonstrating how signal source antenna parameters, such as beamwidth and maximum radiation direction affect bearing accuracy in non-line-of-sight conditions. These evaluations are based on simulation studies, which use measurement-tested signal processing procedures. These procedures are based on a multi-elliptical propagation model, the geometry of which is related to the environment by the power delay profile or spectrum. The probability density function of the angle of arrival for different parameters of the transmitting antenna is the simulation result. This characteristic allows assessing the effect of the signal source antenna parameters on bearing error. The obtained results are the basis for practical correction bearing error and these show the possibility of improving the efficiency of the radio source location in the urbanized environment.

Single-Station Location of Radio Emission Sources in the Decameter Wavelength Range Using a Wide-Aperture Direction Finder and a Chirp Ionosonde–Radio Direction Finder

We present the results of single-station location of radio emission sources on the mid-latitude Vasil’sursk—Rostov-on-Don path using a wide-aperture direction finder and a chirp ionosonde–radio direction finder. Methods for determining the arrival angles under conditions of multipath reception of radio signals are described. It is shown that when single- and double-hop propagation modes are separated by different direction-finding techniques, deviations of the arrival angles reach 5° in the azimuthal plane and up to 10◦ in the elevation plane, which is due to the traveling ionospheric disturbances. It is established that under conditions of a sporadic Es layer, the chirptransmitter azimuth with averaging over frequency and sounding sessions can be determined to an accuracy of 0.1°. When regular 1F and 2F propagation modes are used to estimate the chirptransmitter azimuth, the average errors are 0.5° and 1°–2°, respectively. An algorithm for solving the inverse problem, by which the coordinates of the radio emission sources can be determined from the arrival angles using both the IRI-2012 ionospheric prediction model and correction of the data from the vertical sounding station at the reception point, have been developed. It is shown that the average error in determining the range to radio emission sources is 13%.

A Multi-wavelength Study of the Turbulent Central Engine of the Low-mass AGN Hosted by NGC 404

Abstract The nearby dwarf galaxy NGC 404 harbors a low-luminosity active galactic nucleus powered by the lowest-mass (<150,000 M ⊙) central massive black hole (MBH), with a dynamical mass constraint, currently known, thus providing a rare low-redshift analog to the MBH “seeds” that formed in the early universe. Here, we present new imaging of the nucleus of NGC 404 at 12–18 GHz with the Karl G. Jansky Very Large Array (VLA) and observations of the CO(2–1) line with the Atacama Large Millimeter/Submillimeter Array (ALMA). For the first time, we have successfully resolved the nuclear radio emission, revealing a centrally peaked, extended source spanning 17 pc. Combined with previous VLA observations, our new data place a tight constraint on the radio spectral index and indicate an optically thin synchrotron origin for the emission. The peak of the resolved radio source coincides with the dynamical center of NGC 404, the center of a rotating disk of molecular gas, and the position of a compact, hard X-ray source. We also present evidence for shocks in the NGC 404 nucleus from archival narrowband HST imaging, Chandra X-ray data, and Spitzer mid-infrared spectroscopy, and discuss possible origins for the shock excitation. Given the morphology, location, and steep spectral index of the resolved radio source, as well as constraints on nuclear star formation from the ALMA CO(2–1) data, we find the most likely scenario for the origin of the radio source in the center of NGC 404 to be a radio outflow associated with a confined jet driven by the active nucleus.

Recursive algorithm of the passive location in sensor networks based on measurement of the received signal strength

Introduction. Broad application for monitoring and control of surrounding space is found by sensor networks. For the passive location of radio sources (RS) in the sensor networks uses the method of RSS (received signal strength). It brings together a group of procedures, the hallmark of which is the application to determine the location of RS of the measured strength values of a received signal. In the known RSS algorithms received on the basis of the least squares method, the error of measurement of the ranges, calculated on the measured values of power isn't considered. At the same time definitions of location of RS is performed after receipt of the measurements from all sensors.Statement of the problem. It is believed that during the propagation of the signal from RS to sensor network, its coordinates don’t change. It is required to synthesize an algorithm which after formation of entry conditions on the basis of measurements of power of signals from three sensors, allowed to specify recurrently location of RS in process of receipt of measurements from other sensors in which the error of measurement of power is considered.The main part. The vector of the estimated parameters includes coordinates of position of a RS on the plane. The recurrent algorithm of estimation is received on the basis of the extended Kalman filter and belongs to the class of quasi-optimal algorithms with Gaussian approximation of a posteriori density of probability. The initial vector of an assessment of coordinates of RS and correlation matrix of an error of assessment are defined on the basis of the method of least squares in the presence of three measurements of the signal power.Analysis of the effectiveness of the algorithm. The analysis of efficiency of recurrent algorithm and its comparison with the known algorithms are carried out by means of statistical modeling. Sensor network includes eight sensors. The RS settles down on a circle with a radius of 600 m. Comparison of precision characteristics of the considered algorithms with the lower bound of Rao-Cramer is carried out.Conclusions. The algorithm is developed belongs to the class of RSS algorithms, which after formation of initial conditions on the basis of measurements of power of signals from three sensors, allows recurrently clarify the location of RS in process of receipt of measurements from other sensors. For the considered example, the values of the circular MSD of an error of assessment of location of RS the developed algorithm is close to potentially achievable values of circular MSD of lower limit of the Cramer-Rao, and less than those of known algorithms on 36-44.4 %. The received algorithm can be also easily extended to a case of a trajectory filtration of a RS at which parameters of his movement are estimated.

Path planning for two unmanned aerial vehicles in passive localization of radio sources

This paper studies the trajectory control problem for a pair of unmanned aerial vehicles (UAVs) equipped with time of arrival (TOA) sensors to measure the time difference of arrival (TDOA) of the transmitted radio signal to localize the source. The extended Kalman filter (EKF) is applied to estimate the source's position. The proposed trajectory control strategy encompasses three optimum experimental design criteria based on the position error covariance produced by the EKF. The control strategy steers the UAVs to the positions to minimize the uncertainty about the location of the source. The effectiveness of the proposed approach is illustrated through simulation examples.

Unknown Radio Source Localization Based on a Modified Closed form Solution Using TDOA Measurement Technique

There have been huge advances in the development of positioning applications after the success of GPS. Accurate positioning capability of a radio source is in great demand in the fields of medicine, defence, automation etc. Especially in the Indian subcontinent, localization of an unknown enemy Radio Source such as an enemy radar system, tracking of Unmanned Aerial Vehicle (UAV) etc are essential capabilities for the defence wing. The time difference of arrival (TDOA) technique used for location determination makes use of the method of hyperbolic multilateration. Position accuracy is affected by various factors such as choice of number of sensors, measurement noise, algorithm employed for positioning and sensor geometry. A number of positioning algorithms are available for this purpose. These include iterative algorithms, evolutionary algorithms and many others that are not particularly feasible as the run time of the hardwired code is a major constraint in real time applications. A closed form algorithm proposed in the literature achieves considerable speed in implementation but falters in the resolution of the altitudinal estimate. Hence, a modified algorithm is proposed in this paper that resolves the altitude of the unknown radio source. For better understanding, an example of localizing an unknown radio source using the proposed algorithm is explained.

TDOA Measurement Based GDOP Analysis for Radio Source Localization

The revolution brought by GPS has lead to the development of various positioning applications. These applications use measurements (travel time of signal or time of flight) in determining the position. The time of flight requirement in GPS has restricted its use in positioning of unknown objects. Whereas, localization of an unknown enemy Radio Source (URS) such as enemy radar system, tracking of Unmanned Aerial Vehicle (UAV) etc., have high demand in the field of defence in a country like India, they require a new type of measurement technique called Time difference of Arrival (TDOA). There are various factors that affect the position accuracy including amount of measurement noise, algorithm employed for positioning and sensor URS geometry. The sensor-URS geometry is one of the most predominant factors in determining the accuracy estimate and is referred to as Geometry Dilution of Precision (GDOP). This is a well defined problem in positioning systems that use GPS/Time of arrival (TOA) measurements. However, it needs to be refined for URS localization systems/TDOA measurements. This paper mainly focuses on explaining and deriving the concepts of GDOP in relation to TDOA measurement based URS localization systems. For a comprehensive understanding, an illustrative example of localizing an URS with TDOA measurements is explained and discusses the effect of sensor geometry with the help of GDOP profiles. In addition, this paper explains the process of identifying an optimal sensor configuration for URS localization systems. For the purpose of simulation, five sensors arranged in two different configurations are considered. A target surveillance area of 3600 Sq-Kms with 169 target zones is used in generation of GDOP profiles over the Indian subcontinent.

Multipath propagation of low‐frequency radio waves inferred from high‐resolution array analysis

AbstractThe low‐frequency radio sky shows the locations of electromagnetic radio sources with a characteristic dilution of precision. Here we report a thorough high‐resolution analysis of radio waves from low‐frequency (∼20–150 kHz) radio communication transmitters which are recorded with a small aperture array of radio receivers during the day. It is found that the observed dilution of precision results from the array geometry of the radio receivers, a birefringent wave propagation, and the correlated multipath propagation of low‐frequency radio waves. The influence of the array geometry on the dilution of precision is reduced by taking into account the impulse response of the array. This procedure reveals for the very first time the splitting of one single radio source into two distinct source locations separated by ∼0.2°–1.9° which result from a birefringent wave propagation. The two locations are yet more clearly identified by using the polarity of the modulated wave number vectors of the radio waves. This polarity is also used to quantify the dilution of precision arising from correlated multipath propagation which is discriminated against wave number fluctuations arising from the timing accuracy of the radio receivers. It is found that ∼69% of the wave number variability is of natural origin and ∼31% originates from the timing accuracy of the receivers. The wave number variability from correlated multipath propagation results in a standard deviation ∼2–8% relative to the source location. This compact measurement of correlated multipath propagation is used to characterize the uncertainty of source locations in the radio sky. The identification of correlated multipath propagation strongly suggests the existence of very fast processes acting on time scales <1 ms in the D region ionosphere with physically meaningful effects on low‐frequency radio wave propagation. This important result has implications for practical applications in that the observed multipath propagation enables the determination of natural limits for the accuracy of navigation and lightning location methods using low‐frequency radio waves.

Array analysis of electromagnetic radiation from radio transmitters for submarine communication

AbstractThe array analyses used for seismic and infrasound research are adapted and applied here to the electromagnetic radiation from radio transmitters for submarine communication. It is found that the array analysis enables a determination of the slowness and the arrival azimuth of the wave number vectors associated with the electromagnetic radiation. The array analysis is applied to measurements of ∼20–24 kHz radio waves from transmitters for submarine communication with an array of 10 radio receivers distributed over an area of ∼1 km ×1 km. The observed slowness of the observed wave number vectors range from ∼2.7 ns/m to ∼4.1 ns/m, and the deviations between the expected arrival azimuths and the observed arrival azimuths range from ∼−9.7° to ∼14.5°. The experimental results suggest that it is possible to determine the locations of radio sources from transient luminous events above thunderclouds with an array of radio receivers toward detailed investigations of the electromagnetic radiation from sprites.

Statistical Survey of Type III Radio Bursts at Long Wavelengths Observed by the Solar TErrestrial RElations Observatory (STEREO)/Waves Instruments: Goniopolarimetric Properties and Radio Source Locations

We have performed statistical analysis of a large number of Type III radio bursts observed by STEREO between May 2007 and February 2013. Only intense, simple, and isolated cases have been included in our data set. We have focused on the goniopolarimetric (GP, also referred to as direction-finding) properties at frequencies between $125$ kHz and $2$ MHz. The apparent source size $\gamma$ is very extended ($\approx60^\circ$) for the lowest analyzed frequencies. Observed apparent source sizes $\gamma$ expand linearly with a radial distance from the Sun at frequencies below $1$ MHz. We have shown that Type III radio bursts statistically propagate in the ecliptic plane. Calculated positions of radio sources suggest that scattering of the primary beam pattern plays an important role in the propagation of Type III radio bursts in the IP medium.

Cooperative multi-robot estimation and control for radio source localization

We develop algorithms for estimation and control that allow a team of robots equipped with range sensors to localize an unknown target in a known but complex environment. We present an experimental model for radio-based time-of-flight range sensors. Adopting a Bayesian approach for estimation, we then develop a control law which maximizes the mutual information between the robot’s measurements and their current belief of the target position. We describe experimental results for a robot team localizing a stationary target in several representative indoor environments in which the unknown target is reliably localized with an error well below the typical error for individual measurements.

Variant of more accurate determination of the locations of shortwave radio emission sources

The paper discusses how the trajectory calculation method can be used to solve the problem of locality determination of shortwave (SW) emission sources. The dependence of the electron concentration on the coordinates is specified using the SPIM model; it is corrected using the ionospheric solar activity index, which is specified with the help of maps of total electron content. We suggested a variant of how a regional map of the total electron content can be plotted according to measurements of signals from GLONASS/GPS navigation systems. It is shown that the trajectory calculation method, coupled with an adjustable ionospheric model, allows for a more exact locality determination of SW radio emission sources.

Lightning leader stepping, K changes, and other observations near an intracloud flash

[1] An intracloud lightning flash in central New Mexico began with the initiation of a negative stepped leader at an altitude of 8.2 km above sea level. As this leader propagated eastward and upward, at 9.1 km above sea level it passed about 200 m to the north of a balloon-borne, electric field-change instrument (Esonde). After the first leader stopped, a second negative stepped leader began near the point of origin of the first leader, but it propagated away from the Esonde. From the changes in the electric vectors and the locations of impulsive radio frequency sources detected by a lightning-mapping array (LMA), we conclude the following: (1) The first negative stepped leader was not preceded by any significant charge rearrangement due to positive leaders. (2) Each step of the first negative leader had both a forward-going wave and a step recoil wave that propagated simultaneously backwards away from the leader tip along the existing channel. The presence of a step recoil wave during each step leads to an explanation for the existence of stepping. (3) After the first (nearby) leader stopped, step recoil waves from the second (distant) leader may have found their way onto the channel formed by the first leader. (4) After the second leader stopped, waves carrying negative charge propagated along the channel of the first leader, producing strong K changes in the electric field at the Esonde and providing a good record of the wavefront shapes.