Точность местоопределения наземных источников, использующих геостационарные ретрансляторы

Introduction. Currently, there is a significant increase in the number of relay satellites in geostationary orbit. However, frequent incidents of illegal use of the satellites frequency resource, as well as unintentional and deliberate interference with other users are fixed. In this regard, it becomes necessary to evaluate accuracy and applicability of various methods for determining the location of sources of illegal and interfering radio emission with different signal parameters and with different levels of uncertainty for relay satellite coordinates and velocities.Aim. To study and to evaluate the accuracy of methods of geolocation of radio emission sources operating through geostationary relay satellites, with different signal parameters and with different levels of uncertainty for relay satellite coordinates and velocities.Materials and methods. Imitation modeling and the theory of digital signal processing were used.Results. Factors influencing the accuracy of the estimation of TDOA and FDOA parameters when determining the position of radio emission sources, which operate via relay satellites located in geostationary orbit, were considered. As a result of simulation, the estimate of the accuracy of the considered geolocation methods was obtained. It depends on the bandwidth of radio emission source signal, on the recording duration and on the level of a priori uncertainty relatively the relay satellites coordinates and velocities. Recommendations for the application of the considered methods in various conditions were formulated.Conclusions. Conclusions and recommendations formulated as a result of the study, will allow one to choose the most appropriate geolocation method to improve the accuracy of radio emission sources locating depending on conditions and signal parameters.Введение. В настоящее время наблюдается значительное увеличение количества спутников-ретрансляторов на геостационарной орбите, при этом часто фиксируются случаи незаконного использования частотного ресурса таких спутников, а также непреднамеренного и преднамеренного создания помех другим пользователям. В связи с этим возникает необходимость оценки точности и применимости различных методов определения местоположения источников нелегального и помехового радиоизлучения при различных параметрах сигналов и различной степени неопределенности относительно координат и векторов скорости спутников-ретрансляторов.Цель работы. Исследование и оценка точности методов геолокации источников радиоизлучения (ИРИ), работающих через геостационарные спутники-ретрансляторы, при различных параметрах сигналов геолоцируемых ИРИ и различной степени априорной неопределенности относительно координат и векторов скорости спутников-ретрансляторов.Материалы и методы. Используются метод имитационного моделирования и теория цифровой обработки сигналов.Результаты. Рассмотрены факторы, влияющие на точность оценки параметров TDOA (Тime Difference of Arrival) и FDOA (Frequency Difference of Arrival) при определении местоположения (ОМП) ИРИ, работающих через спутники-ретрансляторы, расположенные на геостационарной орбите. В результате имитационного моделирования получена оценка точности рассмотренных методов геолокации в зависимости от ширины полосы сигнала ИРИ, длительности записи и степени априорной неопределенности относительно координат и векторов скорости спутников-ретрансляторов. Сформулированы рекомендации по применению рассмотренных методов в различных условиях.Заключение. Выводы и рекомендации, сформулированные в результате исследования, позволят в зависимости от конкретных условий и параметров сигналов выбирать наиболее подходящий метод геолокации для повышения точности ОМП ИРИ

Passive Geolocation of Low Power Emitters in Urban Environments using TDOA

Low-power devices are commonly used by the enemy to control Improvised Explosive Devices (IEDs), and as communications nodes for command and control. Quickly locating the source of these signals is difficult, especially in an urban environment where buildings and towers can cause interference. This research presents a geolocation system that combines several geolocation and error mitigation methods to locate an emitter in an urban environment. The proposed geolocation system uses a Time Difference of Arrival (TDOA) technique to estimate the location of the emitter of interest. Using sensors at known locations, TDOA estimates are obtained by cross-correlating the signal received at all the sensors. A Weighted Least Squares (WLS) solution is used to estimate the emitter\u27s location. If the variance of the location estimate is too high, a sensor is detected as having a Non-Line of Sight (NLOS) path from the emitter, and is removed from the geolocation system and a new position estimate is calculated with the remaining sensor TDOA information. The performance of the system is assessed through modeling and simulations. The test results confirm the feasibility of identifying a NLOS sensor, thereby improving the geolocation system\u27s accuracy in an urban environment

Совместное использование станции активного подсвета и опорных источников сигналов при местоопределении наземных радиопередающих устройств, работающих через геостационарные ретрансляторы

Introduction.  There  are  incidences  of  jamming  the  users  of  satellite  communication  systems,  who  apply  e.g. geostationary relay satellites, and the illegal use of such satellite resources. These actions can be both intentional and unintentional, and, among other things, be caused by non-compliance with electromagnetic compatibility standards on part of other users of satellite communication systems. For a prompt and high -quality response of radio monitoring services and satellite operators to these illegal  actions, it seems urgent to develop methods for accurate determination of the geolocation of radio emission sources.Aim.  To develop a method for improving the accuracy of determining the coordinates of ground-based radio emission sources operating via geostationary relay satellites based on shared operation of a barrage jammer and reference signal sources.Materials and methods.  The research was conducted using the statistical theory of radio engineering systems, the theory of digital signal processing and the method of simulation.Results.  A  method  was  developed  for  improving  the  geolocation  accuracy  of  ground-based  radio  emission sources operating via geostationary relay satellites based on shared operation of a barrage jammer and reference signal sources. A method for resolving ambiguity regarding the true correlation peak of a reference source signal using a signal from a barrage jammer was described. An expression was obtained for the probability of a correct  solution  when  resolving  such  ambiguity.  As  a  result,  the  estimates  of  geolocation  accuracy  obtained using the developed method were compared with those obtained by a conventional method relying on the usage of 3 different reference stations.Conclusions. The method proposed in this paper makes it possible to achieve a relatively high accuracy when determining the geolocation of ground-based radio emission sources in the Earth’s regions of interest, at the same time as involving no organizational and financial costs for the installation of a large number of reference stations.Введение.  В настоящее время часто наблюдаются случаи постановки  помех пользователям спутниковых систем связи, использующих, в частности, космические аппараты-ретрансляторы, расположенные на геостационарной орбите, а также нелегального использования ресурса таких космических аппаратов. Подобные действия могут быть как непреднамеренными, так и  целенаправленными, и, в частности, приводят к несоблюдению  норм электромагнитной совместимости  с  другими пользователями спутниковой системы связи. Для оперативного и качественного реагирования служб радиоконтроля и операторов космических аппаратов на нелегальные действия актуальна  разработка  методов, позволяющих с  необходимой  точностью определять местоположение источника помехового радиоизлучения.Цель  работы.  Разработка  метода  повышения  точности  определения  координат  наземных  источников радиоизлучения,  работающих  через  геостационарные  спутники-ретрансляторы,  за  счет  совместного использования станции активного подсвета и опорных источников сигналов.Материалы и методы.  Используются статистическая теория радиотехнических систем, теория  цифровой обработки сигналов и метод имитационного моделирования.Результаты.  Разработан метод повышения точности местоопределения наземных источников радиоизлучения, работающих через геостационарные ретрансляторы, за счет совместного использования станции  активного подсвета и опорных источников сигналов. Описан метод разрешения неоднозначности относительно истинного корреляционного пика опорного источника сигнала с помощью сигнала станции активного подсвета. Получено выражение для вероятности правильного решения при разрешении неоднозначности. В результате имитационного моделирования получена оценка точности геолокации при  использовании  разработанного  метода  в  сравнении  с  известным  методом,  предполагающим  использование трех реперных станций.Заключение.  Метод,  описываемый в данной статье, позволяет достичь относительно высокой точности определения местоположения наземных источников радиоизлучения в интересующих регионах Земли, не требуя организационных и финансовых затрат по установке большого количества реперных станций

Multi-Satellite Orbit Determination Using Interferometric Observables with RF Localization Applications

Very long baseline interferometry (VLBI) specifically same-beam interferometry (SBI), and dual-satellite geolocation are two fields of research not previously connected. This is due to the different application of each field, SBI is used for relative interplanetary navigation of two satellites while dual-satellite geolocation is used to locate the source of a radio frequency (RF) signal. In this dissertation however, we leverage both fields to create a novel method for multi-satellite orbit determination (OD) using time difference of arrival (TDOA) and frequency difference of arrival (FDOA) measurements. The measurements are double differenced between the satellites and the stations, in so doing, many of the common errors are canceled which can significantly improve measurement precision. Provided with this novel OD technique, the observability is first analyzed to determine the benefits and limitations of this method. In all but a few scenarios the measurements successfully reduce the covariance when examining the Cramér-Rao Lower Bound (CRLB). Reduced observability is encountered with geostationary satellites as their motion with respect to the stations is limited, especially when only one baseline is used. However, when using satellite pairs with greater relative motion with respect to the stations, even satellites that are close to, but not exactly in a geostationary orbit can be estimated accurately. We find that in a strong majority of cases the OD technique provides lower uncertainties and solutions far more accurate than using conventional OD observables such as range and range-rate while also not being affected by common errors and biases. We specifically examine GEO-GEO, GEO-MEO, and GEO-LEO dual-satellite estimation cases. The work is further extended by developing a relative navigation scenario where the chief satellite is assumed to have perfect knowledge, or some small amount of uncertainty considered but not estimated, while estimating the deputy satellite state with respect to the chief. Once again the results demonstrate that the TDOA and FDOA OD results are favorable with faster dynamics over classical measurements. This dissertation not only explores the OD side, but also gaps in geolocation research. First the mapping of ephemeris uncertainty to the geolocation covariance to provide a more realistic covariance was implemented. Furthermore, the geolocation solution was improved by appending a probabilistic altitude constraint to the posterior covariance, significantly reducing the projected geolocation uncertainty ellipse. The feasibility of using the geolocation setup to passively locate a LEO satellite was also considered. Finally the simulated results were verified using a long-arc of real data. The use of FDOA for small-body navigation and gravity recovery was also examined as an extended application

Advanced Wireless Localisation Methods Dealing with Incomplete Measurements

Positioning techniques have become an essential part of modern engineering, and the improvement in computing devices brings great potential for more advanced and complicated algorithms. This thesis first studies the existing radio signal based positioning techniques and then presents three developed methods in the sense of dealing with incomplete data. Firstly, on the basis of received signal strength (RSS) location fingerprinting techniques, the Kriging interpolation methods are applied to generate complete fingerprint databases of denser reference locations from sparse or incomplete data sets, as a solution of reducing the workload and cost of offline data collection. Secondly, with incomplete knowledge of shadowing correlation, a new approach of Bayesian inference on RSS based multiple target localisation is proposed taking advantage of the inverse Wishart conjugate prior. The MCMC method (Metropolis-within-Gibbs) and the maximum a posterior (MAP) / maximum likelihood (ML) method are then considered to produce target location estimates. Thirdly, a new information fusion approach is developed for the time difference of arrival (TDOF) and frequency difference of arrival (FDOA) based dual-satellite geolocation system, as a solution to the unknown time and frequency offsets. All proposed methods are studied and validated through simulations. Result analyses and future work directions are discussed

Performance Evaluation of Hyperbolic Position Location Technique in Cellular Wireless Networks

This study addresses the wireless geolocation problem that has been an attractive subject for the last few years after Federal Communications Commission (FCC) mandate for wireless service providers to locate emergency 911 users with a high degree of accuracy -within a radius of 125 meters, 67 percent of the time by October 2001. There are a number of different geolocation technologies that have been proposed. These include, Assisted GPS (A-GPS), network-based technologies such as Enhanced Observed Time Difference (E-OTD), Time Difference of Arrival (TDOA), Angle of Arrival (AOA), and Cell of Origin (COO). This research focuses on network based techniques, namely the more prominent TDOA which is also called hyperbolic position location technique. The main problem in time-based positioning systems is solving nonlinear hyperbolic equations derived from set of TDOA estimates. Two algorithms are implemented as a solution to this problem: A closed form solution and a Least Squares (LS) algorithm. Accuracy and computational efficiency performances are compared in a wireless system established using DGPS measurements in Dayton, OH area

Interference Mitigation and Localization Based on Time-Frequency Analysis for Navigation Satellite Systems

Interference Mitigation and Localization Based on Time-Frequency Analysis for Navigation Satellite SystemsNowadays, the operation of global navigation satellite systems (GNSS) is imperative across a multitude of applications worldwide. The increasing reliance on accurate positioning and timing information has made more serious than ever the consequences of possible service outages in the satellite navigation systems. Among others, interference is regarded as the primary threat to their operation. Due the recent proliferation of portable interferers, notably jammers, it has now become common for GNSS receivers to endure simultaneous attacks from multiple sources of interference, which are likely spatially distributed and transmit different modulations. To the best knowledge of the author, the present dissertation is the first publication to investigate the use of the S-transform (ST) to devise countermeasures to interference. The original contributions in this context are mainly: • the formulation of a complexity-scalable ST implementable in real time as a bank of filters; • a method for characterizing and localizing multiple in-car jammers through interference snapshots that are collected by separate receivers and analysed with a clever use of the ST; • a preliminary assessment of novel methods for mitigating generic interference at the receiver end by means the ST and more computationally efficient variants of the transform. Besides GNSSs, the countermeasures to interference proposed are equivalently applicable to protect any direct-sequence spread spectrum (DS-SS) communication

RF signal sensing and source localisation systems using Software Defined Radios

Radio frequency (RF) source localisation is a critical technology in numerous location-based military and civilian applications. In this thesis, the problem of RF source localisation has been studied from the perspective of the system implementation for real-world applications. Commercial off-the-shelf Software Defined Radio (SDR) devices are used to demonstrate the practical RF source localisation systems. Compared to the conventional localisation systems, which rely on dedicated hardware, the SDR-based system is developed using general-purpose hardware and software-defined components, offering great flexibility and cost efficiency in system design and implementation. In this thesis, the theoretical results of source localisation are evaluated and put into practice. To be specific, the practical localisation systems using different measurement techniques, including received-signal-strength-indication (RSSI) measurements, time-difference-of-arrival (TDOA) measurements and joint TDOA and frequency-difference-of-arrival (FDOA) measurements, are demonstrated to localise the stationary RF signal sources using the SDRs. The RSSI-based localisation system is demonstrated in small indoor and outdoor areas with a range of several metres using the SDR-based transceivers. Furthermore, interests from the defence area motivated us to implement the time-based localisation systems. The TDOA-based source localisation system is implemented using multiple spatially distributed SDRs in a large outdoor area with the sensor-target range of several kilometres. Moreover, they are implemented in a fully passive way without prior knowledge of the signal emitter, so the solutions can be applied in the localisation of non-cooperative signal sources provided that emitters are distant. To further reduce the system cost, and more importantly, to deal with the situation when the deployment of multiple SDRs, due to geographical restrictions, is not feasible, a joint TDOA and FDOA-based localisation system is also demonstrated using only one stationary SDR and one mobile SDR. To improve the localisation accuracy, the methods that can reduce measurement error and obtain accurate location estimates are studied. Firstly, to obtain a better understanding of the measurement error, the error sources that affect the measurement accuracy are systematically analysed from three aspects: the hardware precision, the accuracy of signal processing methods, and the environmental impact. Furthermore, the approaches to reduce the measurement error are proposed and verified in the experiments. Secondly, during the process of the location estimation, the theoretical results on the pre-existing localisation algorithms which can achieve a good trade-off between the accuracy of location estimation and the computational cost are evaluated, including the weight least-squares (WLS)-based solution and the Extended Kalman Filter (EKF)-based solution. In order to use the pre-existing algorithms in the practical source localisation, the proper adjustments are implemented. Overall, the SDR-based platforms are able to achieve low-cost and universal localisation solutions in the real-world environment. The RSSI-based localisation system shows tens of centimetres of accuracy in a range of several metres, which provides a useful tool for the verification of the range-based localisation algorithms. The localisation accuracy of the TDOA-based localisation system and the joint TDOA and FDOA-based localisation system is several tens of metres in a range of several kilometres, which offers potential in the low-cost localisation solutions in the defence area

Cooperative Interference Detection, Localization, and Mitigation in GNSS

Due to the low cost of GNSS receivers and their consequent diffusion, a wide range of location-aware applications are arising. Some of these applications are critical and have strict requirements in terms of availability, integrity and reliability. Examples of critical applications are precision landing and en-route navigation in air transportations; automated highways and mileage-based toll in road transportations; search and rescue in safety of life applications. A failure in fulfilling one or more requirements of a critical application may have dramatic consequences and cause serious damage. One of the most challenging threats for critical GNSS application, is represented by interference. In particular, jamming devices, operating inside GNSS bands, are easily and cheaply purchasable on the Internet. These devices transmit disturbing signals with the aim of preventing the correct operations of GNSS receivers. In order to satisfy the requirements of critical applications, it is necessary to promptly detect, localize and remove such interfering sources. Moreover, it is important to characterize the interfering signals in order to develop interference avoidance and mitigation techniques that ensure robustness of GNSS receivers to interference. This thesis studies the problem of interference in GNSS, from a cooperative perspective