Development and Demonstration of a TDOA-Based GNSS Interference Signal Localization System

Background theory, a reference design, and demonstration results are given for a Global Navigation Satellite System (GNSS) interference localization system comprising a distributed radio-frequency sensor network that simultaneously locates multiple interference sources by measuring their signals’ time difference of arrival (TDOA) between pairs of nodes in the network. The end-to-end solution offered here draws from previous work in single-emitter group delay estimation, very long baseline interferometry, subspace-based estimation, radar, and passive geolocation. Synchronization and automatic localization of sensor nodes is achieved through a tightly-coupled receiver architecture that enables phase-coherent and synchronous sampling of the interference signals and so-called reference signals which carry timing and positioning information. Signal and crosscorrelation models are developed and implemented in a simulator. Multiple-emitter subspace-based TDOA estimation techniques are developed as well as emitter identification and localization algorithms. Simulator performance is compared to the CramérRao lower bound for single-emitter TDOA precision. Results are given for a test exercise in which the system accurately locates emitters broadcasting in the amateur radio band in Austin, TX.Aerospace Engineering and Engineering Mechanic

Effects of rotor blade modulation on GNSS anti-jamming algorithms

In hostile environment, Global Navigation Satellite System (GNSS) could be disturbed by intentional jamming. Many adaptive algorithms have been developed to deal with these threats, among which use of antenna arrays is one of the most efficient. However, most of them have been designed under stationary hypothesis and their performances in harsher environments are questionable. For instance, when a GNSS receiver is placed near rotating bodies, the signal undergo complex and non-stationary effects called Rotor Blade Modulation (RBM). These variations can degrade significantly anti-jamming performance. This paper investigates the impact of the RBM on three conventional space-time adaptive processing (STAP). First, to simulate the RBM, the signal received by an antenna mounted on a helicopter is computed thanks to electromagnetic (EM) asymptotic methods. Then, to quantify precisely the loss in performance of each algorithm, we compare post correlation carrier to noise ratio (post - C/N0) and covariance matrix estimation with respect of the time. Finally, the simulation results are confirmed by experiments conducted on an EC-120 helicopter with an L-band Continuous Wave (CW) jammer

Effective GPS jamming techniques for UAVs using low-cost SDR platforms

Lately, a rising number of incidents between unmanned aerial vehicles (UAVs) and airplanes have been reported in airports and airfields. In order to help cope with the problem of unauthorized UAV operations, in this paper we evaluate the use of low cost SDR platforms (software defined radio) for the implementation of a jammer able to generate an effective interfering signal aimed at the GPS navigation system. Using a programmable BladeRF x40 platform from Nuand and the GNU radio software development toolkit, several interference techniques were studied and evaluated, considering the spectral efficiency, energy efficiency and complexity. It was shown that the tested approaches are capable of stopping the reliable reception of the radionavigation signal in real-life scenarios, neutralizing the capacity for autonomous operation of the vehicle.info:eu-repo/semantics/acceptedVersio

Radio frequency interference detection and mitigation techniques for navigation and Earth observation

Radio-Frequency Interference (RFI) signals are undesired signals that degrade or disrupt the performance of a wireless receiver. RFI signals can be troublesome for any receiver, but they are especially threatening for applications that use very low power signals. This is the case of applications that rely on the Global Navigation Satellite Systems (GNSS), or passive microwave remote sensing applications such as Microwave Radiometry (MWR) and GNSS-Reflectometry (GNSS-R). In order to solve the problem of RFI, RFI-countermeasures are under development. This PhD thesis is devoted to the design, implementation and test of innovative RFI-countermeasures in the fields of MWR and GNSS. In the part devoted to RFI-countermeasures for MWR applications, first, this PhD thesis completes the development of the MERITXELL instrument. The MERITXELL is a multi-frequency total-power radiometer conceived to be an outstanding platform to perform detection, characterization, and localization of RFI signals at the most common MWR imaging bands up to 92 GHz. Moreover, a novel RFI mitigation technique is proposed for MWR: the Multiresolution Fourier Transform (MFT). An assessment of the performance of the MFT has been carried out by comparison with other time-frequency mitigation techniques. According to the results, the MFT technique is a good trade-off solution among all other techniques since it can mitigate efficiently all kinds of RFI signals under evaluation. In the part devoted to RFI-countermeasures for GNSS and GNSS-R applications, first, a system for RFI detection and localization at GNSS bands is proposed. This system is able to detect RFI signals at the L1 band with a sensitivity of -108 dBm at full-band, and of -135 dBm for continuous wave and chirp-like signals when using the averaged spectrum technique. Besides, the Generalized Spectral Separation Coefficient (GSSC) is proposed as a figure of merit to evaluate the Signal-to-Noise Ratio (SNR) degradation in the Delay-Doppler Maps (DDMs) due to the external RFI effect. Furthermore, the FENIX system has been conceived as an innovative system for RFI detection and mitigation and anti-jamming for GNSS and GNSS-R applications. FENIX uses the MFT blanking as a pre-correlation excision tool to perform the mitigation. In addition, FENIX has been designed to be cross-GNSS compatible and RFI-independent. The principles of operation of the MFT blanking algorithm are assessed and compared with other techniques for GNSS signals. Its performance as a mitigation tool is proven using GNSS-R data samples from a real airborne campaign. After that, the main building blocks of the patented architecture of FENIX have been described. The FENIX architecture has been implemented in three real-time prototypes. Moreover, a simulator named FENIX-Sim allows for testing its performance under different jamming scenarios. The real-time performance of FENIX prototype has been tested using different setups. First, a customized VNA has been built in order to measure the transfer function of FENIX in the presence of several representative RFI/jamming signals. The results show how the power transfer function adapts itself to mitigate the RFI/jamming signal. Moreover, several real-time tests with GNSS receivers have been performed using GPS L1 C/A, GPS L2C, and Galileo E1OS. The results show that FENIX provides an extra resilience against RFI and jamming signals up to 30 dB. Furthermore, FENIX is tested using a real GNSS timing setup. Under nominal conditions, when no RFI/jamming signal is present, a small additional jitter on the order of 2-4 ns is introduced in the system. Besides, a maximum bias of 45 ns has been measured under strong jamming conditions (-30 dBm), which is acceptable for current timing systems requiring accuracy levels of 100 ns. Finally, the design of a backup system for GNSS in tracking applications that require high reliability against RFI and jamming attacks is proposed.Les interferències de radiofreqüència (RFI) són senyals no desitjades que degraden o interrompen el funcionament dels receptors sense fils. Les RFI poden suposar un problema per qualsevol receptor, però són especialment amenaçadores per les a aplicacions que fan servir senyals de molt baixa potència. Aquest és el cas de les aplicacions que depenen dels sistemes mundials de navegació per satèl·lit (GNSS) o de les aplicacions de teledetecció passiva de microones, com la radiometria de microones (MWR) i la reflectometria GNSS (GNSS-R). Per combatre aquest problema, sistemes anti-RFI s'estan desenvolupament actualment. Aquesta tesi doctoral està dedicada al disseny, la implementació i el test de sistemes anti-RFI innovadors en els camps de MWR i GNSS. A la part dedicada als sistemes anti-RFI en MWR, aquesta tesi doctoral completa el desenvolupament de l'instrument MERITXELL. El MERITXELL és un radiòmetre multifreqüència concebut com una plataforma excepcional per la detecció, caracterització i localització de RFI a les bandes de MWR més utilitzades per sota dels 92 GHz. A més a més, es proposa una nova tècnica de mitigació de RFI per MWR: la Transformada de Fourier amb Multiresolució (MFT). El funcionament de la MFT s'ha comparat amb el d'altres tècniques de mitigació en els dominis del temps i la freqüència. D'acord amb els resultats obtinguts, la MFT és una bona solució de compromís entre les altres tècniques, ja que pot mitigar de manera eficient tots els tipus de senyals RFI considerats. A la part dedicada als sistemes anti-RFI en GNSS i GNSS-R, primer es proposa un sistema per a la detecció i localització de RFI a les bandes GNSS. Aquest sistema és capaç de detectar senyals RFI a la banda L1 amb una sensibilitat de -108 dBm a tota la banda, i de -135 dBm per a senyals d'ona contínua i chirp fen un mitjana de l'espectre. A més a més, el Coeficient de Separació Espectral Generalitzada (GSSC) es proposa com una mesura per avaluar la degradació de la relació senyal a soroll (SNR) en els Mapes de Delay-Doppler (DDM) a causa del impacte de les RFI. La major contribució d'aquesta tesi doctoral és el sistema FENIX. FENIX és un sistema innovador de detecció i mitigació de RFI i inhibidors de freqüència per aplicacions GNSS i GNSS-R. FENIX utilitza la MFT per eliminar la interferència abans del procés de correlació amb el codi GNSS independentment del tipus de RFI. L'algoritme de mitigació de FENIX s'ha avaluat i comparat amb altres tècniques i els principals components de la seva arquitectura patentada es descriuen. Finalment, un simulador anomenat FENIX-Sim permet avaluar el seu rendiment en diferents escenaris d'interferència. El funcionament en temps real del prototip FENIX ha estat provat utilitzant diferents mètodes. En primer lloc, s'ha creat un analitzador de xarxes per a mesurar la funció de transferència del FENIX en presència de diverses RFI representatives. Els resultats mostren com la funció de transferència s'adapta per mitigar el senyal interferent. A més a més, s'han realitzat diferents proves en temps real amb receptors GNSS compatibles amb els senyals GPS L1 C/A, GPS L2C i Galileo E1OS. Els resultats mostren que FENIX proporciona una resistència addicional contra les RFI i els senyals dels inhibidors de freqüència de fins a 30 dB. A més a més, FENIX s'ha provat amb un sistema comercial de temporització basat en GNSS. En condicions nominals, sense RFI, FENIX introdueix un petit error addicional de tan sols 2-4 ns. Per contra, el biaix màxim mesurat en condicions d'alta interferència (-30 dBm) és de 45 ns, el qual és acceptable per als sistemes de temporització actuals que requereixen nivells de precisió d'uns 100 ns. Finalment, es proposa el disseny d'un sistema robust de seguiment, complementari als GNSS, per a aplicacions que requereixen alta fiabilitat contra RFI.Postprint (published version

Advanced Integration of GNSS and External Sensors for Autonomous Mobility Applications

L'abstract è presente nell'allegato / the abstract is in the attachmen

A Robust Method to Suppress Jamming for GNSS Array Antenna Based on Reconstruction of Sample Covariance Matrix

The Global Navigation Satellite System (GNSS) receiver is vulnerable to active jamming, which results in imprecise positioning. Therefore, antijamming performance of the receiver is always the key to studies of satellite navigation system. In antijamming application of satellite navigation system, if active jamming is received from array antenna main-lobe, main-lobe distortion happens when the adaptive filtering algorithm forms main-lobe nulling. A robust method to suppress jamming for satellite navigation by reconstructing sample covariance matrix without main-lobe nulling is proposed in this paper. No nulling is formed while suppressing the main-lobe jamming, which avoids main-lobe direction distortion. Meanwhile, along with adaptive pattern control (APC), the adaptive pattern of array antenna approaches the pattern without jamming so as to receive the matching navigation signal. Theoretical analysis and numerical simulation prove that this method suppresses jamming without main-beam distortion. Furthermore, the output SINR will not decrease with the main-lobe distortion by this method, which improves the antijamming performance

Exploring the Limits of Multi-Antenna Signal-Rejection for GNSS Receivers

This paper presents experimental results exploring the performance of GNSS receivers equipped with controlled radiation pattern antennas. Experiments focus on identifying those features and characteristics of their implementation that may limit the achievable performance of signal-rejection techniques. The study describes both conductive and broadcast experiments conducted in a large anechoic chamber and computer-based Monte-Carlo simulations. Results include a precise gain pattern measurement of a typical antenna array, an investigation and comparison of both analogue RF and digital IF null steering along with some novel theoretical results.JRC.G.5-Security technology assessmen

Estimation Techniques and Mitigation Tools for Ionospheric effects on GNSS Receivers

Navigation is defined as the science of getting a craft or person from one place to another. The development of radio in the past century brought fort new navigation aids that enabled users, or rather their receivers, to compute their position with the help of signals from one or more radio-navigation system . The U.S. Global Positioning System (GPS) was envisioned as a satellite system for three-dimensional position and velocity determination fulfilling the following key attributes: global coverage, continuous/all weather operation, ability to serve high-dynamic platforms, and high accuracy. It represents the fruition of several technologies, which matured and came together in the second half of the 20th century. In particular, stable space-born platforms, ultra-stable atomic frequency standards, spread spectrum signaling, and microelectronics are the key developments in the realization and success of GPS. While GPS was under development, the Soviet Union undertook to develop a similar system called GLObalnaya NAvigatsionnaya Sputnikovaya Sistema (GLONASS). Both GLONASS and GPS were designed primarily for the military, but have transitioned in the past decades towards providing civilian and Safety-of-Life services as well. Other Global Navigation Satellite Systems (GNSS) are now being developed and deployed by governments, international consortia, and commercial interests. Among these are the European system Galileo and the Chinese system Beidou. Other regional systems are the Japanese Quasi-Zenith Satellite System and the Indian Gagan. GNSS have become a crucial component in countless modern systems, e.g. in telecommunication, navigation, remote sensing, precise agriculture, aviation and timing. One of the main threats to the reliable and safe operation of GNSS are the variable propagation conditions encountered by GNSS signals as they pass through the upper atmosphere of the Earth. In particular, irregular concentration of electrons in the ionosphere induce fast fluctuations in the amplitude and phase of GNSS signals called scintillations. The latter can greatly degrade the performance of GNSS receivers, with consequent economical impacts on service providers and users of high performance applications. New GNSS navigation signals and codes are expected to help mitigate such effects, although to what degree is still unknown. Furthermore, these new technologies will only come on line incrementally over the next decade as new GNSS satellites become operational. In the meantime, GPS users who need high performance navigation solution, e.g., offshore drilling companies, might be forced to postpone operations for which precision position knowledge is required until the ionospheric disturbances are over. For this reason continuous monitoring of scintillations has become a priority in order to try to predict its occurrence. Indeed, it is a growing scientific and industrial activity. However, Radio Frequency (RF) Interference from other telecommunication systems might threaten the monitoring of scintillation activity. Currently, the majority of the GNSS based application are highly exposed to unintentional or intentional interference issues. The extremely weak power of the GNSS signals, which is actually completely buried in the noise floor at the user receiver antenna level, puts interference among the external error contributions that most degrade GNSS performance. It is then of interest to study the effects these external systems may have on the estimation of ionosphere activity with GNSS. In this dissertation, we investigate the effect of propagation issues in GNSS, focusing on scintillations, interference and the joint effect of the two phenomena

A Portfolio Approach to NLOS and Multipath Mitigation in Dense Urban Areas

Non-line-of-sight (NLOS) reception and multipath interference are major causes of poor GNSS positioning accuracy in dense urban environments. They are commonly grouped together. However, both the mechanisms by which they cause position errors and many of the techniques for mitigating those errors are quite different [1]. For example, correlation-based multipath mitigation has no effect on the errors caused by NLOS reception. University College London (UCL) has investigated the performance of a number of multipath and/or NLOS mitigation techniques in dense urban areas, including C/N0-based solution weighting [2], advanced consistency checking [3], dual-polarization NLOS detection [4] and vector tracking [5]. In this paper, we present a new multipath detection technique based on comparing the measured C/N0 on multiple frequencies and also new dual-polarization results. Meanwhile, other researchers have demonstrated NLOS detection using a panoramic camera [6, 7] or 3D city model [8, 9] and detection of NLOS and multipath using an antenna array [10]. All of these techniques bring some improvement in positioning performance in urban environments, but none of them eliminate the effects of both NLOS reception and multipath interference completely. As the different techniques are largely complementary, best performance is obtained by using several of them in combination, a portfolio approach. This paper comprises three parts. The first presents a feasibility study on a new multipath detection technique using multi-frequency C/N0 measurements. Constructive multipath interference results in an increase in the measured C/N0, whereas destructive multipath interference results in a decrease. As the phase of a reflected signal with respect to its directly received counterpart depends on the wavelength, the multipath interference may be constructive on one frequency and destructive on another. Thus, by comparing the difference in measured C/N0 between two frequencies with what would normally be expected for that signal at that elevation angle, strong multipath interference may be detected. However, the converse is not true because, depending on the path delay, the phase of the multipath interference may also be consistent across the two frequencies. Consistency across three frequencies in the presence of multipath interference is much less likely than consistency across two. Therefore, by comparing C/N0 measured across three (or more) frequencies, the chance of detection is improved substantially, noting that reliability is less critical as part of a portfolio approach to multipath detection than for a stand-alone technique. Experimental results are presented demonstrating the potential of this approach using GPS and GLONASS data collected in Central London. The second part of the paper presents the results of the first multi-constellation test of the dual-polarization NLOS detection technique pioneered at UCL [4]. This separately correlates the right hand circularly polarized (RHCP) and left hand circularly polarized (LHCP) outputs of a dual-polarization antenna and differences the resulting C/N0 measurements, producing a result that is positive for directly received signals and negative for most NLOS signals. Data was collected at six different sites in Central London and NLOS reception of both GPS and GLONASS signals was detected. Position solutions with the NLOS signals removed are compared with the corresponding all-satellite solutions. The final part of the paper addresses the portfolio approach to NLOS and multipath mitigation. Each technique is assessed qualitatively for its ease of implementation and its efficiency at detecting or directly mitigating both NLOS reception and multipath mitigation. A compatibility matrix is then presented showing which techniques may be combined without conflict. Suitable portfolios are then proposed both for professional-grade and for consumer-grade user equipment. References [1] Groves, P. D., Principles of GNSS, inertial, and multi-sensor integrated navigation systems, Second Edition, Artech House, 2013. [2] Jiang, Z., P. Groves, W. Y. Ochieng, S. Feng, C. D. Milner, and P. G. Mattos, “Multi-Constellation GNSS Multipath Mitigation Using Consistency Checking,” Proc. ION GNSS 2011. [3] Jiang, Z., and P. Groves, “GNSS NLOS and Multipath Error Mitigation using Advanced Multi-Constellation Consistency Checking with Height Aiding,” Proc. ION GNSS 2012. [4] Jiang, Z., and P. D. Groves, “NLOS GPS Signal Detection Using A Dual-Polarisation Antenna,” GPS Solutions, 2012, DOI: 10.1007/s10291-012-0305-5. [5] Hsu, L.-T., P. D. Groves, and S.-S. Jan, “Assessment of the Multipath Mitigation Effect of Vector Tracking in an Urban Environment,” Proc ION Pacific PNT, 2013. [6] Marais, J., M. Berbineau, and M. Heddebaut, “Land Mobile GNSS Availability and Multipath Evaluation Tool,” IEEE Transactions on Vehicular Technology, Vol. 54, No. 5, 2005, pp. 1697-1704. [7] Meguro, J., et al., “GPS Multipath Mitigation for Urban Area Using Omnidirectional Infrared Camera,” IEEE Transactions on Intelligent Transportation Systems, Vol. 10, No. 1, 2009, pp. 22-30. [8] Obst, M., S. Bauer, and G. Wanielik, “Urban Multipath Detection and mitigation with Dynamic 3D Maps for Reliable Land Vehicle Localization,” Proc. IEEE/ION PLANS 2012. [9] Peyraud, S., et al., “About Non-Line-Of-Sight Satellite Detection and Exclusion in a 3D Map-Aided Localization Algorithm,” Sensors, Vol. 13, 2013, pp. 829-847. [10] Keshvadi, M. H., A. Broumandan, and G. Lachapelle, “Analysis of GNSS Beamforming and Angle of Arrival Estimation in Multipath Environments," Proc ION ITM, San Diego, CA, January 2011, pp. 427-435