RFI Mitigation & GNSS Security | Dr. Jorge Querol

Protocol-Aware Jamming and Self-Play Defense for Active RIS-Assisted UAV Communications

Tue, 01 Sep 2026 00:00:00 +0000

Abstract & Overview

This research contribution by Selma Yahia, Ildi Alla, Hossien B. Eldeeb, Marcele O. K. Mendonça et al. (2026), published in IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC), investigates “Protocol-Aware Jamming and Self-Play Defense for Active RIS-Assisted UAV Communications” within the domains of RFI Mitigation & GNSS Security. The work is part of Dr. Jorge Querol’s research portfolio in advanced satellite communications, non-terrestrial networks (NTN), and radio-frequency signal processing at SnT (University of Luxembourg) and UPC-BarcelonaTech.

Publication Metadata

Authors: Selma Yahia, Ildi Alla, Hossien B. Eldeeb, Marcele O. K. Mendonça, Carla E. García, Jorge Querol, Symeon Chatzinotas
Venue: IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (PIMRC) (2026)
Research Areas: RFI Mitigation & GNSS Security
DOI: 10.1109/pimrc69400.2026.11711848
Open Access Repository: ORBiLu – University of Luxembourg

High-Accuracy Ranging in 5G Non-Terrestrial Networks: Receiver Architectures and Interference Analysis

Fri, 01 May 2026 00:00:00 +0000

Abstract & Overview

This research contribution by Idir Edjekouane, Alejandro González-Garrido, Jorge Querol, José A. del Peral-Rosado et al. (2026), published in IEEE Transactions on Vehicular Technology, investigates “High-Accuracy Ranging in 5G Non-Terrestrial Networks: Receiver Architectures and Interference Analysis” within the domains of 6G-NTN, RFI Mitigation & GNSS Security, GNSS & Positioning. The work is part of Dr. Jorge Querol’s research portfolio in advanced satellite communications, non-terrestrial networks (NTN), and radio-frequency signal processing at SnT (University of Luxembourg) and UPC-BarcelonaTech.

Publication Metadata

Authors: Idir Edjekouane, Alejandro González-Garrido, Jorge Querol, José A. del Peral-Rosado, Ivan Lapin
Venue: IEEE Transactions on Vehicular Technology (2026)
Research Areas: 6G-NTN, RFI Mitigation & GNSS Security, GNSS & Positioning
DOI: 10.1109/navitec202669090.2026.11692531

Automatic RFI Detection, Location, and Classification System in GNSS Bands

Thu, 01 Jan 2026 00:00:00 +0000

Abstract & Overview

Global Navigation Satellite Systems (GNSS) are critical infrastructure components in modern Positioning, Navigation, and Timing (PNT) services, playing a vital role in both civilian and defense applications. These systems operate in specific frequency bands that are also utilized by other Earth Observation technologies, such as GNSS-Radio Occultations and GNSS-Reflectometry. Other passive microwave remote sensing techniques such as microwave radiometers, work with very faint signals in nearby frequency bands within the L-Band. However, the increasing prevalence of Radio-Frequency Interferences (RFI) poses a significant threat, potentially compromising the integrity and reliability of PNT services, and corrupting geophysical observations. Effective RFI mitigation relies on accurate detection and classification of interference sources, a task that becomes increasingly challenging due to the complexity and diversity of RFI signals. This work presents an automated classification system for RFI detection and characterization in GNSS bands. The methodology employs advanced digital signal processing techniques and statistical algorithms to improve RFI detection and classification. RFI events are then stored in a long-term database to provide insights into the local spectrum, and to aid in mitigation and law enforcement efforts. This study provides a description of the classification system, including its architecture, implementation, and performance analysis. The results highlight the potential of this system to enhance the resilience of GNSS PNT services against RFI.

Publication Metadata

Authors: Adrián Pérez-Portero, Jorge Querol, Adriano Camps
Venue: IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing (2026)
Research Areas: RFI Mitigation & GNSS Security, GNSS & Positioning
DOI: 10.1109/jstars.2025.3647776
Open Access Repository: ORBiLu – University of Luxembourg

Resource-Efficient FPGA Architecture for Real-Time RFI Mitigation in Interferometric Radiometers

Sat, 14 Dec 2024 00:00:00 +0000

Abstract & Overview

Interferometric radiometers operating at L-band, such as ESA’s SMOS mission, enable crucial Earth observations providing high-resolution measurements of soil moisture, ocean salinity, and other geophysical parameters. However, the increasing electromagnetic spectrum utilization has led to significant Radio Frequency Interference (RFI) challenges, particularly critical given the sensors’ fine temperature resolution requirements of less than 1 K. This work presents the hardware implementation of an advanced RFI detection and mitigation algorithm specifically designed for interferometric radiometers, targeting future L-band missions. The implementation processes 1-bit quantized signals at 57.69375 MHz from multiple receivers, employing time-frequency analysis and polarimetric detection techniques while optimizing Field Programmable Gate Array (FPGA) resource utilization. Novel optimization strategies include overclocked processing cores operating at 230.775 MHz, efficient resource sharing through operation serialization, and strategic memory management. The system achieves real-time processing capabilities while maintaining detection probabilities above 63% with false alarm rates below 1% for typical interference scenarios. Performance validation using synthetic datasets demonstrates robust operation across various RFI conditions, making this implementation suitable as part of the RFI detection and mitigation efforts for future interferometric radiometer missions beyond SMOS.

Publication Metadata

Authors: Adrián Pérez-Portero, Jorge Querol, Adriano Camps
Venue: Sensors (2024)
Research Areas: JCAS & Earth Observation, RFI Mitigation & GNSS Security, SDR & Experimental Testbeds
DOI: 10.3390/s24248001
Open Access Repository: ORBiLu – University of Luxembourg

Development of a Dynamically Re-Configurable Radio-Frequency Interference Detection System for L-Band Microwave Radiometers

Fri, 21 Jun 2024 00:00:00 +0000

Abstract & Overview

Real-Time RFI Detection and Flagging (RT-RDF) for microwave radiometers is a versatile new FPGA algorithm designed to detect and flag Radio-Frequency Interference (RFI) in microwave radiometers. This block utilizes computationally-efficient techniques to identify and analyze RF signals, allowing the system to take appropriate measures to mitigate interference and maintain reliable performance. With L-Band microwave radiometry as the main application, this RFI detection algorithm focuses on the Kurtogram and Spectrogram to detect non-Gaussian behavior. To gain further modularity, an FFT-based filter bank is used to divide the receiver’s bandwidth into several sub-bands within the band of interest of the instrument, depending on the application. Multiple blanking strategies can then be applied in each band using the provided detection flags. The algorithm can be re-configured in the field, for example with dynamic integration times to support operation in different environments, or configurable thresholds to account for variable RFI environments. A validation and testing campaign has been performed on multiple scenarios with the ARIEL commercial microwave radiometer, and the results confirm the excellent performance of the system.

Publication Metadata

Authors: Adrián Pérez-Portero, Jorge Querol, Andreu Mas-Viñolas, A. Amézaga, R. Jove‐Casulleras, Adriano Camps
Venue: Sensors (2024)
Research Areas: JCAS & Earth Observation, RFI Mitigation & GNSS Security
DOI: 10.3390/s24134034
Open Access Repository: ORBiLu – University of Luxembourg

Classification and Characterization of RFI Events for Passive Earth Observation Bands

Mon, 01 Jan 2024 00:00:00 +0000

Abstract & Overview

Passive Microwave remote sensing is a very energy-efficient and time-proven technology for remote sensing. Microwave Radiometry and Global Navigation Satellite System (GNSS)-Reflectometry are two widely-used examples. The increasing effects of Radio-Frequency Interferences (RFI) on the performance of these receivers have sparked serious concerns due to their proliferation. Detection and mitigation of RFI heavily rely on the identification and location of the interference sources. Due to the vast amount of degrees of freedom found in these RFIs, classification using classical signal processing techniques becomes problematic, especially if combined RFIs are found within the same bandwidth. In this work, continuous recordings of real RFI events from a real-time system to detect and locate RFI sources are used as training data for an automated classification system, the description and performance of which are presented and analyzed.

Publication Metadata

Authors: Adrian Perez-Portero, Jorge Querol, Adriano Camps
Venue: IGARSS 2024-2024 IEEE International Geoscience and Remote Sensing Symposium (2024)
Research Areas: RFI Mitigation & GNSS Security
DOI: 10.1109/igarss53475.2024.10641435
Open Access Repository: ORBiLu – University of Luxembourg

Interference Analysis and Modeling of Positioning Reference Signals in 5G NTN

Mon, 01 Jan 2024 00:00:00 +0000

Abstract & Overview

The integration of Positioning, Navigation, and Timing (PNT) services within the 5G non-terrestrial networks (NTN) infrastructure is necessary to eliminate the need for a GNSS receiver in the user terminal. Using the positioning reference signal (PRS) in an NTN scenario presents significant challenges, such as interference analysis from the transmission of multiple PRS signals. This study provides a stochastic model for the interference generated by PRS transmissions in a 5G NTN scenario. This model has been derived empirically from a Monte Carlo simulator designed specifically for this purpose, showing that the distribution that best fits the interference is a Generalized Extreme Value (GEV) distribution. The parameters of this distribution are also modeled based on the PRS configuration. Therefore, a designer can use this model to evaluate the probability of encountering certain levels of interference.

Publication Metadata

Authors: Alejandro Gonzalez-Garrido, Jorge Querol, Henk Wymeersch, Symeon Chatzinotas
Venue: IEEE Open Journal of the Communications Society (2024)
Research Areas: 6G-NTN, RFI Mitigation & GNSS Security, GNSS & Positioning
DOI: 10.1109/ojcoms.2024.3503692
Open Access Repository: ORBiLu – University of Luxembourg

Interference analysis of Positioning Reference Signals in 5G NTN

Mon, 01 Jan 2024 00:00:00 +0000

Abstract & Overview

Accurate asset localization holds paramount importance across various industries, ranging from transportation management to search and rescue operations. In scenarios where traditional positioning equations cannot be adequately solved due to limited measurements obtained by the receiver, the utilization of Non-Terrestrial Networks (NTN) based on Low Earth Orbit (LEO) satellites can prove pivotal for precise positioning. The decision to employ NTN in lieu of conventional Global Navigation Satellite Systems (GNSS) is rooted in two key factors. Firstly, GNSS systems are susceptible to jamming and spoofing attacks, thereby compromising their reliability, where LEO satellites link budgets can benefit from a closer distances and the new mega constellations could offer more satellites in view than GNSS. Secondly, 5G service providers seek to reduce dependence on third-party services. Presently, the NTN operation necessitates a GNSS receiver within the User Equipment (UE), placing the service provider at the mercy of GNSS reliability. Consequently, when GNSS signals are unavailable in certain regions, NTN services are also rendered inaccessible.

Publication Metadata

Authors: Alejandro Gonzalez-Garrido, Jorge Querol, Henk Wymeersch, Symeon Chatzinotas
Venue: arXiv preprint arXiv:2401.09157 (2024)
Research Areas: 6G-NTN, RFI Mitigation & GNSS Security, GNSS & Positioning
DOI: 10.48550/arxiv.2401.09157

Doppler effect mitigation in LEO-based 5G non-terrestrial networks

Sun, 01 Jan 2023 00:00:00 +0000

Abstract & Overview

In recent years, integrating Non-Terrestrial Networks (NTN) components with 5G Terrestrial Networks (TN) has led to considerable attention from academia and industry, leading to the standardization of 5G-NTN in 3GPP. Among the various NTN solutions, a notable one is the Low Earth Orbit (LEO)-based 5G-NTN with a regenerative payload. This system stands out because it can provide latency and throughput levels similar to terrestrial 5G networks. However, a significant challenge in this integration arises from the substantial Doppler effect caused by the rapid movement of LEO satellites. This effect must be effectively addressed to establish a successful data link between the User Equipment (UE) and the gNodeB (gNB). This study proposes a simple yet efficient method to tackle this issue. The method involves using a regenerative LEO satellite-based 5G gNB, which pre-compensates the Doppler frequency with respect to its beam center before initiating any data transmission. Subsequently, the UE performs post-compensation to handle residual Doppler frequency and achieve accurate initial synchronization. We evaluated the performance through simulations and demonstrated the effectiveness of the proposed system. The results indicate successful mitigation of Doppler effects, facilitating seamless communication between LEO satellite-based 5G NTN.

Publication Metadata

Authors: Ashish Kumar Meshram, Sumit Kumar, Jorge Querol, Symeon Chatzinotas
Venue: 2023 IEEE Globecom Workshops (GC Wkshps) (2023)
Research Areas: 6G-NTN, Satellite Communications, RFI Mitigation & GNSS Security, GNSS & Positioning
DOI: 10.1109/gcwkshps58843.2023.10464931
Open Access Repository: ORBiLu – University of Luxembourg

Radio Communication Blackout Mitigation: Ray Tracing Analysis and Signal Characterization Including Experimental Validation for Non-magnetized Plasmas

Sun, 01 Jan 2023 00:00:00 +0000

Abstract & Overview

Atmospheric entries and hypersonic flights are challenging. The bow shock in front of the vehicle and friction heat the gas flow around the vehicle and result in the ionization of molecules and atoms. This plasma surrounding the spacecraft leads to a total or partial cut-off of radio communication for telecommand, telemetry, and navigation if the plasma frequency is near or exceeds the radio frequency of the communication system. Recent improvements in high-temperature superconducting materials brought back the focus on the magnetic windowing radio communication blackout mitigation method. Within the Horizon 2020 MEESST (Magnetohydrodynamic Enhanced Entry System for Space Transportation) project the effect of an applied magnetic field using a superconductive magnet with a sufficiently strong magnetic field is analyzed. The BlackOut Ray-Tracer (BORAT) was further developed to predict the wave propagation in the plasma in two dimensions for magnetized plasma using the Eikonal solver. A signal characterization model was added for a better understanding of the physics of wave propagation. The latest results for non-magnetized plasma show a good agreement between the numerical solutions and the experiment. The signal characterization allows us to further define brownout scenarios with partially disrupted communication. The effect of a weak applied magnetic field on the ray propagation path and the signal characteristics are discussed leading to the conclusion that the magnetic windowing method is promising to mitigate radio blackout when strong magnetic fields are applied.

Publication Metadata

Authors: Johannes Laur, Diana Luis, Alan Viladegut, Vincent F Giangaspero, Andrea Lani, Jorge Luis González Rios, Jorge Querol, J Peralvo, J Merlano Duncan, AM Hein
Venue: AEC 2023-10th EUCASS-9th CEAS (2023)
Research Areas: RFI Mitigation & GNSS Security, SDR & Experimental Testbeds
DOI: 10.2514/6.2024-1821
Open Access Repository: ORBiLu – University of Luxembourg

RFI detection and mitigation for advanced correlators in interferometric radiometers

Sat, 01 Jan 2022 00:00:00 +0000

Abstract & Overview

This work presents the first RFI detection and mitigation algorithm for the interferometric radiometers that will be implemented in its correlator unit. The algorithm operates in the time and frequency domains, applying polarimetric and statistical tests in both domains, and exhibiting a tunable and arbitrary low probability of false alarm. It is scalable to a configurable number of receivers, and it is optimized in terms of quantization bits and the implementation of the cross-correlations in the time or frequency domains for hardware resource saving. New features of this algorithm are the computation of the Stokes parameters per frequency bin in the Short-Time Fourier Transform and a new parameter called Polarimetric Kurtosis. If RFI is detected in one domain or in both, it is removed using the calculated blanking masks. The optimum algorithm parameters are computed, such as length of the FFTs, the threshold selection for a given probability of false alarm, and the selection of the blanking masks. Last, an important result refers to the application of Parseval’s theorem for the computation of the cross-correlations in the frequency domain, instead of in the time domain, which is more efficient and leads to smaller errors even when using moderate quantization levels. The algorithm has been developed in the framework of the ESA’s technology preparation for a potential L-band radiometer mission beyond SMOS. However, it is also applicable to (polarimetric) real aperture radiometers, and its performance would improve if more than one bit is used in the signal quantization.

Publication Metadata

Authors: Adrián Pérez-Portero, Jorge Querol, Adriano Camps, Manuel Martín‐Neira, Martin Süess, Juan Ignacio Ramirez, Alberto Zurita, Joséep Closa, Roger Oliva, R. Onrubia
Venue: Remote Sensing (2022)
Research Areas: JCAS & Earth Observation, RFI Mitigation & GNSS Security
DOI: 10.3390/rs14184672

A pre-correlation RFI mitigation algorithm for L-band interferometric radiometers

Fri, 01 Jan 2021 00:00:00 +0000

Abstract & Overview

Radio Frequency Interference (RFI) is a major concern for both real and synthetic aperture radiometers. After the lessons learnt from SMOS, ESA is preparing the next generation of L-band interferometric radiometers with RFI mitigation integrated into the cross-correlators. This work presents a preliminary design and results of a pre-correlation RFI mitigation algorithm tailored for interferometric radiometers. The results show that the correlation error introduced by the RFI is reduced on average to the half, with peaks of 20 dB of mitigation.

Publication Metadata

Authors: Jorge Querol, A. Camps, A. Perez, R. Oliva, R. Onrubia, J. I. Ramirez-Martinez, A. Zurita, M. Suess, M. Martin-Neira
Venue: 2021 IEEE International Geoscience and Remote Sensing Symposium IGARSS (2021)
Research Areas: JCAS & Earth Observation, RFI Mitigation & GNSS Security
DOI: 10.1109/igarss47720.2021.9553195

Radio-frequency interference location, detection and classification using deep neural networks

Wed, 01 Jan 2020 00:00:00 +0000

Abstract & Overview

Global Navigation Satellite System (GNSS) signals are used in Earth Observation for Radio Occultation and Reflectometry. The increasing effects of Radio-Frequency Interferences (RFI) on the performance of these receivers and navigation have suddenly sparked serious concerns due to their proliferation. Detection and mitigation of RFI heavily relies on the nature and location of the interfering sources. In some cases, null-steering or shielding can be used to mitigate RFI effects. In this work, a system to detect and locate RFI sources is presented, including signal classification and recording for countermeasure-related decision-making.

Publication Metadata

Authors: A. Perez, Jorge Querol, H. Park, A. Camps
Venue: IGARSS 2020-2020 IEEE International Geoscience and Remote Sensing Symposium (2020)
Research Areas: RFI Mitigation & GNSS Security, AI & Neuromorphic SatCom
DOI: 10.1109/igarss39084.2020.9324532

Real-time Radio Frequency Interference Detection and Mitigation with the Front-End GNSS Interference eXcisor (FENIX)

Mon, 23 Sep 2019 00:00:00 +0000

Abstract & Overview

This paper presents the real-time hardware architecture and experimental evaluation of the Front-End GNSS Interference eXcisor (FENIX), demonstrating standalone pre-correlation time-frequency excision of continuous-wave, chirp, and pulsed jamming signals across civilian GNSS bands.

Publication Metadata

Authors: Jorge Querol, Adrián Pérez-Portero, Joan Francesc Muñoz-Martín, Adriano Camps
Venue: RFI 2019 - Coexisting with Radio Frequency Interference (2019)
Research Areas: RFI Mitigation & GNSS Security, GNSS & Positioning
DOI: 10.1109/RFI48793.2019.9111819
Open Access Repository: ORBiLu

A review of RFI mitigation techniques in microwave radiometry

Tue, 01 Jan 2019 00:00:00 +0000

Abstract & Overview

Radio frequency interference (RFI) is a well-known problem in microwave radiometry (MWR). Any undesired signal overlapping the MWR protected frequency bands introduces a bias in the measurements, which can corrupt the retrieved geophysical parameters. This paper presents a literature review of RFI detection and mitigation techniques for microwave radiometry from space. The reviewed techniques are divided between real aperture and aperture synthesis. A discussion and assessment of the application of RFI mitigation techniques is presented for each type of radiometer.

Publication Metadata

Authors: Jorge Querol, Adrián Pérez-Portero, Adriano Camps
Venue: Remote Sensing (2019)
Research Areas: JCAS & Earth Observation, RFI Mitigation & GNSS Security
DOI: 10.3390/rs11243042
Open Access Repository: ORBiLu – University of Luxembourg

On the new architecture and capabilities of the front-end GNSS interference excisor (FENIX)

Tue, 01 Jan 2019 00:00:00 +0000

Abstract & Overview

The number of applications based on Global Navigation Satellite Systems (GNSS) has been increasing in the last years. With its proliferation, Radio-Frequency Interference (RFI) has become one of the most concerning topics on GNSS-based devices for navigation, positioning and timing, but also for Earth Observation purposes such as GNSS-Reflectometry and Radio Occultations due to the corruption of the received signal and the corresponding geophysical measurements. The Front-End GNSS Interference eXcisor (FENIX) mitigates the problem of RFI by providing a plug and play solution to excise interferences out of virtually any system. The new version of FENIX is also capable of operating with large signal bandwidths (~50 MHz) and dual-frequency applications. This paper shows the performance of the system for commercial GNSS receivers and GNSS-reflectometry applications. A discussion of the impact of the new architecture on its future capabilities is presented as well.

Publication Metadata

Authors: Adrián Pérez, Adriano Camps, Jorge Querol
Venue: IGARSS 2019-2019 IEEE International Geoscience and Remote Sensing Symposium (2019)
Research Areas: RFI Mitigation & GNSS Security, GNSS & Positioning
DOI: 10.1109/igarss.2019.8900263

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

Fri, 09 Nov 2018 00:00:00 +0000

Abstract & Overview

This PhD thesis is devoted to the design, implementation, and experimental validation of innovative Radio-Frequency Interference (RFI) detection, localization, and mitigation countermeasures in the fields of Microwave Radiometry (MWR), Global Navigation Satellite Systems (GNSS), and GNSS-Reflectometry (GNSS-R). It completes the development of the MERITXELL multi-frequency radiometer, introduces the Multiresolution Fourier Transform (MFT) mitigation algorithm, proposes the Generalized Spectral Separation Coefficient (GSSC) metric for GNSS-R under interference, and presents the patented FENIX real-time pre-correlation anti-jamming architecture (US Patent US9596610B1), demonstrating up to 30 dB of jamming resilience across GPS L1 C/A, GPS L2C, and Galileo E1OS signals. Awarded Best PhD Thesis 2018 by the IEEE Geoscience and Remote Sensing Society (GRSS) Spanish Chapter.

Publication Metadata

Author: Jorge Querol (Supervised by Prof. Adriano Camps)
Venue: PhD Thesis, Universitat Politècnica de Catalunya (UPC-BarcelonaTech) (2018)
Research Areas: RFI Mitigation & GNSS Security, GNSS & Positioning, JCAS & Earth Observation
DOI: 10.5821/dissertation-2117-125028
Open Access Repository: UPCommons Full Text PDF · ORBiLu

An anti-jamming system for GNSS timing applications

Mon, 01 Jan 2018 00:00:00 +0000

Abstract & Overview

Radio-Frequency Interference (RFI) and jamming are increasing problems for timing applications based on Global Navigation Satellite Systems (GNSS). FENIX-lite is a real-time pre-correlation anti-jamming system designed to provide increased resilience against RFI/jamming in critical GNSS-enabled applications. This work aims to evaluate the combined performance of FENIX-lite and a timing setup composed by two GNSS disciplined oscillators named DOWR. The results show that FENIX provides an anti-jamming resilience of 10-30 dB, at the expense of introducing a small bias and an additional jitter of 2-4 ns.

Publication Metadata

Authors: Jorge Querol, Adriano Camps, Esteban Garbin Manfredini, Ricardo Piriz
Venue: 2018 European Frequency and Time Forum (EFTF) (2018)
Research Areas: RFI Mitigation & GNSS Security, GNSS & Positioning
DOI: 10.1109/eftf.2018.8409021

RFI analysis and mitigation in airborne GNSS-R campaign

Mon, 01 Jan 2018 00:00:00 +0000

Abstract & Overview

Radio-Frequency Interference (RFI) is one of the most concerning topics in Global Navigation Satellite Systems (GNSS) and GNSS - Reflectometry (GNSS-R) because any undesired signal present at the antenna can corrupt the received signal and the eventual geophysical measurements. The purpose of this paper is two-fold. First, an RFI analysis is performed to the raw data obtained from an airborne dual-band GNSS reflectometer. Finally, the Front-End GNSS Interference eXcisor (FENIX) mitigation algorithm is applied to the raw data, and then the Signal-to-Noise Ratio (SNR) improvement at the Delay-Doppler Map (DDM) is obtained. From the analysis of one of the datasets, two RFI signals were detected and characterized. Moreover, FENIX output signal was revealed to be much cleaner than before. The mean SNR improvement with coherent DDMs of 1 ms is 0.72 dB, whereas the SNR improvement increases to 1.49 dB when considering 50 incoherent averages. This improvement represents a reduction in the geophysical parameter estimation uncertainty.

Publication Metadata

Authors: Jorge Querol, R. Onrubia, D. Pascual, J. Castellvi-Esturi, H. Park, A. Camps
Venue: IGARSS 2018-2018 IEEE International Geoscience and Remote Sensing Symposium (2018)
Research Areas: JCAS & Earth Observation, RFI Mitigation & GNSS Security, GNSS & Positioning, AI & Neuromorphic SatCom
DOI: 10.1109/igarss.2018.8518827

A radio-frequency interference detector for GNSS navigation and GNSS-reflectometry applications

Sun, 23 Jul 2017 00:00:00 +0000

Abstract & Overview

This paper presents a real-time Radio-Frequency Interference (RFI) detection and monitoring system designed for Global Navigation Satellite Systems (GNSS) navigation and GNSS-Reflectometry (GNSS-R) receivers operating at L-band, evaluating detection sensitivity against continuous-wave, swept-chirp, and pulsed interference sources.

Publication Metadata

Authors: Jorge Querol, Raul Onrubia, Daniel Pascual, Hyuk Park, Adriano Camps
Venue: 2017 IEEE International Geoscience and Remote Sensing Symposium (IGARSS) (2017)
Research Areas: JCAS & Earth Observation, RFI Mitigation & GNSS Security, GNSS & Positioning
DOI: 10.1109/IGARSS.2017.8127965

System and method for detecting and eliminating radio frequency interferences in real time

Wed, 01 Mar 2017 00:00:00 +0000

Abstract & Overview

This research contribution by Jorge Querol, Adriano Joséé Camps Carmona (2017), published in international conference proceedings, investigates “System and method for detecting and eliminating radio frequency interferences in real time” within the domains of RFI Mitigation & GNSS Security. The work is part of Dr. Jorge Querol’s research portfolio in advanced satellite communications, non-terrestrial networks (NTN), and radio-frequency signal processing at SnT (University of Luxembourg) and UPC-BarcelonaTech.

Publication Metadata

Authors: Jorge Querol, Adriano Joséé Camps Carmona
Venue: Conference Paper (2017)
Research Areas: RFI Mitigation & GNSS Security

MERITXELL: the Multifrequency Experimental Radiometer with Interference Tracking for Experiments over Land and Littoral—instrument description, calibration and performance

Sun, 01 Jan 2017 00:00:00 +0000

Abstract & Overview

MERITXELL is a ground-based multisensor instrument that includes a multiband dual-polarization radiometer, a GNSS reflectometer, and several optical sensors. Its main goals are twofold: to test data fusion techniques, and to develop Radio-Frequency Interference (RFI) detection, localization and mitigation techniques. The former is necessary to retrieve complementary data useful to develop geophysical models with improved accuracy, whereas the latter aims at solving one of the most important problems of microwave radiometry. This paper describes the hardware design, the instrument control architecture, the calibration of the radiometer, and several captures of RFI signals taken with MERITXELL in urban environment. The multiband radiometer has a dual linear polarization total-power radiometer topology, and it covers the L-, S-, C-, X-, K-, Ka-, and W-band. Its back-end stage is based on a spectrum analyzer structure which allows to perform real-time signal processing, while the rest of the sensors are controlled by a host computer where the off-line processing takes place. The calibration of the radiometer is performed using the hot-cold load procedure, together with the tipping curves technique in the case of the five upper frequency bands. Finally, some captures of RFI signals are shown for most of the radiometric bands under analysis, which evidence the problem of RFI in microwave radiometry, and the limitations they impose in external calibration.

Publication Metadata

Authors: Jorge Querol, J. M. Tarongíi, Giuseppe Forte, Joséé Luís Eguia Gómez, Adriano Camps
Venue: Sensors (2017)
Research Areas: JCAS & Earth Observation, RFI Mitigation & GNSS Security, SDR & Experimental Testbeds
DOI: 10.3390/s17051081

Performance assessment of time--frequency RFI mitigation techniques in microwave radiometry

Sun, 01 Jan 2017 00:00:00 +0000

Abstract & Overview

Radio-frequency interference (RFI) signals are a well-known threat for microwave radiometry (MWR) applications. In order to alleviate this problem, different approaches for RFI detection and mitigation are currently under development. Since RFI signals are man made, they tend to have their power more concentrated in the time-frequency (TF) space as compared to naturally emitted noise. The aim of this paper is to perform an assessment of different TF RFI mitigation techniques in terms of probability of detection, resolution loss (RL), and mitigation performance. In this assessment, six different kinds of RFI signals have been considered: a glitch, a burst of pulses, a wide-band chirp, a narrow-band chirp, a continuous wave, and a wide-band modulation. The results show that the best performance occurs when the transform basis has a similar shape as compared to the RFI signal. For the best case performance, the maximum residual RFI temperature is 14.8 K, and the worst RL is 8.4%. Moreover, the multiresolution Fourier transform technique appears as a good tradeoff solution among all other techniques since it can mitigate all RFI signals under evaluation with a maximum residual RFI temperature of 21 K, and a worst RL of 26.3%. Although the obtained results are still far from an acceptable bias <; 1 K for MWR applications, there is still work to do in a combined test using the information gathered simultaneously by all mitigation techniques, which could improve the overall performance of RFI mitigation.

Publication Metadata

Authors: Jorge Querol, R. Onrubia, A. Alonso-Arroyo, Daniel Pascual, Hyuk Park, Adriano Camps
Venue: IEEE Journal of Selected Topics in Applied Earth Observations and Remote (2017)
Research Areas: JCAS & Earth Observation, RFI Mitigation & GNSS Security
DOI: 10.1109/jstars.2017.2654541

Real-time Pre-correlation Anti-jamming System for Civilian GNSS Receivers

Sun, 01 Jan 2017 00:00:00 +0000

Abstract & Overview

Global Navigation Satellite Systems (GNSS) have become a key technology that enables numerous location and navigation applications, thanks to the 24/7 worldwide availability of their signals, and the positioning accuracy that can be reached with them. However, GNSS have also some weaknesses, and the most relevant is that their signals reach the Earth’s surface with very low power. This makes them quite vulnerable to the effect of Radio-Frequency Interference (RFI), and particularly to intentional jamming, which degrades, or even disrupts, the performance of the receivers. This problem is particularly threatening for those critical GNSS-enabled applications that trust on the integrity and continuity of GNSS signals, whose reliability may be committed. Such liability/security-critical civilian applications include autonomous aerial/terrestrial navigation, automatic rail signaling, geo-localized toll/insurance payments, or network synchronization among others. Moreover, RFI is also troublesome for derived GNSS applications such as GNSS-Reflectometry (GNSS-R) where GNSS signals are used as signals of opportunity in a multi-static radar configuration for Earth observation purposes. A number of mitigation solutions have been proposed to increase the continuity of GNSS signals in the presence of jamming signals. Regarding the structure of a GNSS system, the mitigation process can be performed at different stages: antenna, front-end, pre-correlation, post-correlation, or measurement. Common antenna solutions can provide spatiotemporal selectivity, which can reach interference rejection ration higher than 40 dB, but this is only achieved in static scenarios. On the contrary, pre-correlation techniques work at signal level, between antenna and GNSS correlators, providing interference selectivity in time, frequency, statistical, or other sub-space signal domains, which can mitigate jamming signals regardless the scenario dynamics. Moreover, pre-correlation techniques usually have a high computational burden in order to achieve high performance with interference rejection ratios higher than 30 dB. However, last generation Field Programmable Gate Arrays (FPGA) can overcome this drawback, and they even enable real-time pre-correlation anti-jamming solutions. The Front-End GNSS Interference eXcisor (FENIX) is a GNSS anti-jamming technology based on the patented combination of statistical interference detection, and a multiresolution time-frequency blanking algorithm for jamming mitigation in DSSS-based multi-constellation GNSS receivers [1]. The main goal of FENIX is to increase the C/N0 in the presence of interference signals, thus improving the continuity of GNSS services. Moreover, the mitigation algorithm has been designed to be DSSS-based multi-constellation, frequency independent (i.e. it works at L1 and L2, L5…), and it is capable of mitigating almost all kinds of jamming signals. A general description of the major building blocks of FENIX was first presented in [2]. This work aims at showing the implementation and first results of a real-time L1/L2 GPS/Galileo lite version of FENIX (FENIX-lite) tested using commercial jammers and GNSS receivers. The FENIX-lite demonstrator has been implemented using a two Software Defined Radio (SDR) model USRP B200mini, the first covers the GPS L1 C/A and Galileo E1 OS services, whereas the second does the same with the GPS L2C signal. The SDR front-ends are tuned to the L1 and L2 bands, and the FENIX interference detection and mitigation algorithm is running in real-time in both FPGA. The FENIX algorithm detects the interference signal using a statistical domain analysis based on normality tests, while the samples containing most part of interference power signal are excised in the time-frequency space computed using the Multiresolution Fourier Transform (MFT). The use of the MFT allows to mitigate almost of kinds of jamming signals since it maximized the projection of the interference signal in the transformed domain as demonstrated in [3]. In order to evaluate the improvement in the continuity of the GNSS signals, the degradation of the SNR with and without the FENIX-lite is compared using jammers at different bands and commercial GNSS receivers. [1] J. Querol, and A. Camps, “System and method for detecting and eliminating radio frequency interferences in real time,” U.S. Patent Application 15 222 036, issued date July 28, 2016. [2] J. Querol, E. M. Julian, R. Onrubia, A. Alonso-Arroyo, D. Pascual and A. Camps, “Preliminary results of FENIX: Front-End GNSS Interference eXcisor,” 2016 IEEE International Geoscience and Remote Sensing Symposium (IGARSS), Beijing, 2016, pp. 5627-5630. [3] J. Querol; R. Onrubia; A. Alonso-Arroyo; D. Pascual; H. Park; A. Camps, “Performance Assessment of Time-Frequency RFI Mitigation Techniques in Microwave Radiometry,” in IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, in press.

Publication Metadata

Authors: Jorge Querol, Adriano Camps
Venue: Proceedings of the 30th International Technical Meeting of The Satellite (2017)
Research Areas: RFI Mitigation & GNSS Security, GNSS & Positioning
DOI: 10.33012/2017.15304

Assessment of DME/TACAN RFI mitigation techniques in GNSS-R

Fri, 01 Jan 2016 00:00:00 +0000

Abstract & Overview

Global Navigation Satellite Systems Reflectometry (GNSSR) is now being recognized as a powerfull tool for remote sensing. With the addition of new frequency bands and codes, it is possible to increase the resolution and accuracy of the measurements. GPS L5 and Galileo E5 bands are becoming popular because of the open codes, with wider bandwidths than the L1 band ones. However, these bands are shared with two radio navigation systems (DME and TACAN) that transmit with high powers and might interfere them. The use of mitigation techniques may affect the power of the received signal, which will affect the GNSS-R observables. This work presents several the mitigation techniques, and evaluates the performance and impact of the selected ones for ESA’s GEROS experiment onboard the International Space Station.

Publication Metadata

Authors: R. Onrubia, Jorge Querol, D. Pascual, H. Park, A. Alonso-Arroyo, A. Camps
Venue: 2016 IEEE International Geoscience and Remote Sensing Symposium (IGARSS) (2016)
Research Areas: JCAS & Earth Observation, RFI Mitigation & GNSS Security, GNSS & Positioning
DOI: 10.1109/igarss.2016.7730255

Comparison of real-time time-frequency RFI mitigation techniques in microwave radiometry

Fri, 01 Jan 2016 00:00:00 +0000

Abstract & Overview

Radio-Frequency Interference (RFI) is a well-known problem for Microwave Radiometers (MWR). A number of RFI mitigation techniques have been studied to deal with RFI from the receiver’s side. In this study, a comparison in terms of performance among several real-time time-frequency RFI mitigation techniques is presented. Time-frequency techniques are of high importance because the vast majority of RFI signals are well-localized in the time-frequency space. The five techniques compared under study are: Pulse Blanking (PB), Frequency Blanking (FB), Spectrogram Blanking (SB), Wavelet Denoising (WD), and Multiresolution Fourier Transform (MFT). Results show that the best performance depends on the particular type of RFI, and occurs when the transform basis is similar to the RFI, that is, the projection on that particular basis is maximized. However, there is not a single technique that is effective for all RFI signals, and future approaches may be based on a combination of several techniques.

Publication Metadata

Authors: Jorge Querol, R. Onrubia, D. Pascual, A. Alonso-Arroyo, H. Park, A. Camps
Venue: 2016 14th Specialist Meeting on Microwave Radiometry and Remote Sensing (2016)
Research Areas: JCAS & Earth Observation, RFI Mitigation & GNSS Security
DOI: 10.1109/microrad.2016.7530506

Preliminary results of FENIX: front-end GNSS interference eXcisor

Fri, 01 Jan 2016 00:00:00 +0000

Abstract & Overview

The number of applications based on Global Navigation Satellite Systems (GNSS) has been increasing in last years. In the passive remote sensing field, GNSS-Reflectometry (GNSS-R) systems have been revealed as cost-effective solutions to retrieve a number of geophysical parameters. However, GNSS-based devices are prone to suffer from Radio-Frequency Interference (RFI) effects due to the extreme low power of involved signals. This paper shows the preliminary results of the Front-End GNSS Interference eXcisor (FENIX), a system designed to mitigate the RFI problem in GNSS-based systems. FENIX is composed by two stages: the RF stage and the SP stage. The former conditions the signal from the antenna, throw the SP stage, and to the receiver; and the latter excises the RFI from the GNSS signal combining thresholding with the Multiresolution Fourier Transform (MFT). Preliminary results show that FENIX can mitigate up to 30 dB a chirp RFI signal generated from commercial jammers.

Publication Metadata

Authors: Jorge Querol, E. M. Julian, R. Onrubia, A. Alonso-Arroyo, D. Pascual, A. Camps
Venue: 2016 IEEE International Geoscience and Remote Sensing Symposium (IGARSS) (2016)
Research Areas: RFI Mitigation & GNSS Security, GNSS & Positioning
DOI: 10.1109/igarss.2016.7730470

SNR degradation in GNSS-R measurements under the effects of radio-frequency interference

Fri, 01 Jan 2016 00:00:00 +0000

Abstract & Overview

Radio-frequency interference (RFI) is a serious threat for systems working with low power signals such as those coming from the global navigation satellite systems (GNSS). The spectral separation coefficient (SSC) is the standard figure of merit to evaluate the signal-to-noise ratio (SNR) degradation due to the RFI. However, an in-depth assessment in the field of GNSS-Reflectometry (GNSS-R) has not been performed yet, and particularly, about which is the influence of the RFI on the so-called delay-Doppler map (DDM). This paper develops a model that evaluates the contribution of intra-/inter-GNSS and external RFI effects to the degradation of the SNR in the DDM for both conventional and interferometric GNSS-R techniques. Moreover, a generalized SSC is defined to account for the effects of nonstationary RFI signals. The results show that highly directive antennas are necessary to avoid interference from other GNSS satellites, whereas mitigation techniques are essential to keep GNSS-R instruments working under external RFI degradation.

Publication Metadata

Authors: Jorge Querol, A. Alonso-Arroyo, R. Onrubia, Daniel Pascual, Hyuk Park, Adriano Camps
Venue: IEEE Journal of Selected Topics in Applied Earth Observations and Remote (2016)
Research Areas: JCAS & Earth Observation, RFI Mitigation & GNSS Security, GNSS & Positioning
DOI: 10.1109/jstars.2016.2597438

Assessment of back-end RFI mitigation techniques in passive remote sensing

Thu, 01 Jan 2015 00:00:00 +0000

Abstract & Overview

Radio-Frequency Interference (RFI) is a growing problem specially for those systems that work with low power signals such as passive remote sensing instruments. Consequently, RFI mitigation techniques are currently under development. This works aims at evaluating back-end mitigation algorithms in terms of their probability of detection and mitigation performance. Results show that Wavelet Denoising (WD), and Multiresolution Fourier Transform (MFT) are the best techniques in most scenarios, specially for GNSS-based instruments.

Publication Metadata

Authors: Jorge Querol, A. Alonso-Arroyo, R. Onrubia, D. Pascual, A. Camps
Venue: 2015 IEEE International Geoscience and Remote Sensing Symposium (IGARSS) (2015)
Research Areas: JCAS & Earth Observation, RFI Mitigation & GNSS Security
DOI: 10.1109/igarss.2015.7326890

Study of RFI signals in protected GNSS bands generated by common electronic devices: Effects on GNSS-R measurements

Wed, 01 Jan 2014 00:00:00 +0000

Abstract & Overview

RFI (Radio Frequency Interference) signals are a threat for GNSS-R (Global Navigation Satellite Systems - Reflectometry) due to the very low power of the navigation signals. Interference signals coming from computers or high-speed buses may affect GNSS-R measurements introducing a bias or even corrupting them completely. These RFI may be in-band or near-band and can desensitize GNSS and GNSS-R receivers. A number of techniques are currently under development to mitigate the effect of RFI signals.

Publication Metadata

Authors: Jorge Querol, G. F. Forte, A. Camps
Venue: 2014 IEEE Geoscience and Remote Sensing Symposium (2014)
Research Areas: JCAS & Earth Observation, RFI Mitigation & GNSS Security, GNSS & Positioning
DOI: 10.1109/igarss.2014.6947375

Digital back-end for RFI detection and mitigation in earth observation

Tue, 01 Jan 2013 00:00:00 +0000

Abstract & Overview

A powerful real time Radio-frequency interference (RFI) mitigation back-end system is presented in this work. The interfering signals are estimated by using the wavelet transform to utilize its effective denoising capability. The estimated RFI signals are then subtracted from the total received signal, and ultimately the RFI-mitigated signal is obtained. Here, the hardware implementation and the system tests are demonstrated, showing sinusoid, chirp, and PRN interference mitigation under different Interference to Noise Ratios (INRs).

Publication Metadata

Authors: G.F. Forte, Jorge Querol, H. Park, A. Camps
Venue: 2013 IEEE International Geoscience and Remote Sensing Symposium-IGARSS (2013)
Research Areas: RFI Mitigation & GNSS Security
DOI: 10.1109/igarss.2013.6723177

Implementation of Radio-Frequency Interference Detection and Mitigation Algorithms for Communications and Navigation

Tue, 01 Jan 2013 00:00:00 +0000

Abstract & Overview

Radio-Frequency Interference (RFI) signals are undesired signals that degrade or disrupt the performance of wireless communications and satellite navigation receivers. This Master Thesis presents the design, real-time FPGA hardware implementation, and experimental validation of digital signal processing algorithms for the detection and mitigation of continuous-wave, chirp, and pulsed radio-frequency interference in Global Navigation Satellite Systems (GNSS) and passive microwave remote sensing receivers.

Publication Metadata

Authors: Jorge Querol
Venue: Master Thesis, Universitat Politècnica de Catalunya (UPC-BarcelonaTech) (2013)
Research Areas: RFI Mitigation & GNSS Security, GNSS & Positioning
Repository: UPCommons (hdl.handle.net/2099.1/18739)

Real-time RFI detection and mitigation system for microwave radiometers

Tue, 01 Jan 2013 00:00:00 +0000

Abstract & Overview

Microwave radiometers are very sensitive passive sensors that measure the power of the thermal noise within a determined bandwidth. Therefore, any other signal present in the band modifies the value of the measured power, and the corresponding estimated antenna temperature, from which the geophysical parameters are retrieved. Due to the high sensitivity and accuracy required for these instruments, radio frequency interference (RFI) is becoming more and more a serious problem. On one hand, ground-based or global RFI surveys are helping to understand the occurrence and types of RFI sources. If RFI does not necessarily affect the whole bandwidth, or it is not present during the whole integration time, the application of either frequency blanking, time blanking or signal spectrogram techniques can be applied. However, it would be desirable to apply techniques to estimate the RFI signal so that it can be subtracted from the received signal itself so that some useful measurements are still possible. Such a real-time system is currently being developed for RFI detection and mitigation. This work focuses however in the description and performance of a wavelet-based RFI-mitigation technique implemented in a FPGA hardware back-end. The interfering signal is estimated by using the powerful denoising capabilities of the wavelet transform, and it is then subtracted from the total received signal to obtain a RFI-mitigated noise signal.

Publication Metadata

Authors: Giuseppe F. Forte, Jorge Querol, Adriano Camps, Merce Vall-llossera
Venue: IEEE transactions on geoscience and remote sensing (2013)
Research Areas: JCAS & Earth Observation, RFI Mitigation & GNSS Security
DOI: 10.1109/tgrs.2013.2267595