arXiv subjects

Gregory Hellbourg

Publications and source records attributed to Gregory Hellbourg.

15 recordsLinked to original sources

arXiv2026

A measurement-based approach to EPFD calculation, to quantify the impact of satellite mega-constellations on low-frequency radio astronomy

Context: Satellite mega-constellations generate Unintended Electro-Magnetic Radiation (UEMR) impacting low frequency radio astronomy. The Radio Regulations of the International Telecommunications Union Radiocommunication Sector (ITU-R) contain the basis for addressing UEMR, but enforcement mechanisms are absent. Aims: To adapt compatibility study methods based on satellite constellation simulations, in particular the Equivalent Power Flux-Density (EPFD) framework, to radio telescope measurements. Methods: We adapt the ITU-R EPFD calculation framework to measurement data obtained from all-sky interferometric imaging. We address the conceptual differences between forward-model EPFD calculations and measurement-based approaches. In particular, we consider low frequency systems, which are typically wide field-of-view and interferometric instruments. Results: For the first time, we demonstrate that all-sky interferometric observations enable a direct adaptation of the EPFD formalism to measurement data. We thus confirm previous estimations (Di Vruno et al. 2023) that the resulting measurement-based EPFD distributions exceed the radio astronomy interference threshold levels defined in Recommendation ITU-R RA.769-2 in 50-70% of samples. These exceedance fractions are well above the 2% single-system data-loss criterion in Recommendation ITU-R RA.1513-2. Expressed using the conventional 2% compatibility margin, the corresponding margins are negative, ranging from -18.6 to -16.3 dB, equivalent to a required uniform attenuation of 16.3-18.6 dB. Conclusions: Measurement-based implementations provide a practical pathway toward verification and long-term monitoring at low radio frequencies, which could form an important component of enforceability. We suggest instrumentation approaches to support measurement.

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arXiv2026

Towards Genuine Coexistence: Per-Satellite Emission and Radiation Limits to Protect Radio Astronomy and Geodetic VLBI at 1-14 GHz from Satellite Constellations

Geodetic very long baseline interferometry (VLBI) is a vulnerable application of the radio astronomy service (RAS): it provides the fundamental link between the celestial and terrestrial reference frames, and is the only technique that uniquely determines UT1-UTC. The next-generation geodetic VLBI Global Observing System (VGOS) achieves millimetre accuracy by synthesising group delay across 3-14 GHz using 32x32 MHz channels, most of which lie outside RAS primary allocations. The SNIFFLES-I survey (Indermuehle et al 2026) measured intended emissions, unwanted emissions (spurious emissions, notably harmonics), and unintended electromagnetic radiation (UEMR) of NGSO systems from 1-26 GHz. On this basis we model the equivalent power flux density (EPFD) of current and future constellations and compare against protection criteria of ITU-R RA.769. The analysis extends to frequencies without radio astronomy allocations where SNIFFLES-I made detections. For geodetic VLBI, we run a Monte-Carlo EPFD model at the AuScope VGOS stations and scale the aggregate from the present catalogued fleet (~12000 satellites) to the hundreds of thousands on file with a validated method. Inverting the EPFD analysis against the interpolated RA.769 thresholds yields maximum tolerable per-satellite levels for spurious emissions and for UEMR, expressed as a field-strength limit in dB(uV/m) at 10 m for standard-setting bodies. We treat proposed orbital-data-centres in Sun-synchronous orbit as a distinctively UEMR-dominated case. We find that already today the single-dish protection criteria are exceeded in two primary RAS bands. For geodetic VLBI, the dominant threat is spurious emission from the 2620 MHz Direct-to-device (DTD) downlink, whose second harmonic at 5240 MHz already causes at least 59% data loss today. (Abstract modified for arxiv limits)

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arXiv2026

Can Dynamic Spectrum Sharing Protect Passive Radio Sciences?

Dynamic Spectrum Sharing (DSS) is increasingly promoted as a key element of modern spectrum policy, driven by the rising demand from commercial wireless systems and advances in spectrum access technologies. Passive radio sciences, including radio astronomy, Earth remote sensing, and meteorology, operate under fundamentally different constraints. They rely on exceptionally low interference spectrum and are highly vulnerable to even brief radio frequency interference. We examine whether DSS can benefit passive services or whether it introduces new failure modes and enforcement challenges. We propose just-in-time quiet zones (JITQZ) as a mechanism for protecting high value observations and assess hybrid frameworks that preserve static protection for core passive bands while allowing constrained dynamic access in adjacent frequencies. We analyze the roles of propagation uncertainty, electromagnetic compatibility constraints, and limited spectrum awareness. Using a game theoretic framework, we show why non-cooperative sharing fails, identify conditions for sustained cooperation, and examine incentive mechanisms including pseudonymetry-enabled attribution that promote compliance. We conclude that DSS can support passive radio sciences only as a high-reliability, safety-critical system. Static allocations remain essential, and dynamic access is viable only with conservative safeguards and enforceable accountability.

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arXiv2025

Real-time RFI Mitigation Techniques in Radio Astronomy and Their Practical Limitations

Radio astronomy is facing critical challenges due to an ever-increasing human-made signal density filling up the radio spectrum. With the rise of satellites, mobile networks, and other wireless technologies, radio telescopes are struggling with radio frequency interference (RFI), which can masquerade, block or distort astronomical signals. In this chapter, we explain where RFI comes from, how it affects observations, and discuss different ways to reduce or remove interference. The techniques presented here reflect the state of the art in real-time RFI mitigation at the time of publication and include methods such as filtering, digital processing, and optimal scheduling. The proposed catalogue also explores new ideas like satellite avoidance through scheduling, the use of intelligent surfaces to block interference, and advanced computer algorithms to clean up data. The chapter also highlights the need for strong cooperation between astronomers and spectrum regulators to protect radio frequencies for future discoveries. By combining technical solutions and better policies, we can help ensure that radio astronomy continues to provide important insights into the universe.

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arXiv2025

Quiet Skies Report: A Primer on Protecting Radio Astronomy in the Age of Satellite Mega-Constellations

The rapid expansion of satellite constellations is transforming the radio-frequency environment around the Earth. At the same time, radio astronomy is entering a new era of sensitivity and survey capability, requiring unprecedented control of interference. This primer introduces satellite operators, engineers, spectrum managers and policy makers to the basic concepts of radio astronomy, explains why the discipline is uniquely vulnerable to interference, and outlines the regulatory and practical tools available to manage coexistence.

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arXiv2025

Real-time RFI Excision Techniques and their Limitations

Contemporary real-time RFI mitigation is carried out at different stages primarily using regulatory and technical approaches. Regulatory approaches include spectrum management, radio quiet zones, and ensuring protection from self-generated RFI. The technical approaches include mitigation RFI in the analog and RF frontend systems, digital signal processing systems, and offline systems. As is known, the signal received by a radio telescope is a combination of the contributions from the astronomical signal and a combination of system and sky background noise. RFI has an additive effect on the signal received by the radio telescope. The key distinguishing properties of RFI are that it is generally stronger than the signal and non-Gaussian. The capability of signal processing receiver systems has grown manifold with the advent of high-speed signal processing platforms like Field Programmable Gate Arrays (FPGA)and Graphics Processing Unit (GPU). This has enabled the development of different signal-processing techniques for real-time RFI mitigation algorithms. This document provides an overview of contemporary techniques while focusing on the implementation of the same in specific radio telescopes.

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arXiv2023

Cellular Wireless Networks in the Upper Mid-Band

The upper mid-band - roughly from 7 to 24 GHz - has attracted considerable recent interest for new cellular services. This frequency range has vastly more spectrum than the highly congested bands below 7 GHz while offering more favorable propagation and coverage than the millimeter wave (mmWave) frequencies. The upper mid-band can thus provide a powerful and complementary frequency range to balance coverage and capacity. Realizing the full potential of these bands, however, will require fundamental changes to the design of cellular systems. Most importantly, spectrum will likely need to be shared with incumbents including communication satellites, military RADAR, and radio astronomy. Also, the upper mid-band is simply a vast frequency range. Due to this wide bandwidth, combined with the directional nature of transmission and intermittent occupancy of incumbents, cellular systems will need to be agile to sense and intelligently use large spatial and frequency degrees of freedom. This paper attempts to provide an initial assessment of the feasibility and potential gains of wideband cellular systems operating in the upper mid-band. The study includes: (1) a system study to assess potential gains of multi-band systems in a representative dense urban environment and illustrate the value of wide band system with dynamic frequency selectivity; (2) an evaluation of potential cross interference between satellites and terrestrial cellular services and interference nulling to reduce that interference; and (3) design and evaluation of a compact multi-band antenna array structure. Leveraging these preliminary results, we identify potential future research directions to realize next-generation systems in these frequencies.

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arXiv2022

Collaboration with Cellular Networks for RFI Cancellation at Radio Telescope

The growing need for electromagnetic spectrum to support the next generation (xG) communication networks increasingly generate unwanted radio frequency interference (RFI) in protected bands for radio astronomy. RFI is commonly mitigated at the Radio Telescope without any active collaboration with the interfering sources. In this work, we provide a method of signal characterization and its use in subsequent cancellation, that uses Eigenspaces derived from the telescope and the transmitter signals. This is different from conventional time-frequency domain analysis, which is limited to fixed characterizations (e.g., complex exponential in Fourier methods) that cannot adapt to the changing statistics (e.g., autocorrelation) of the RFI, typically observed in communication systems. We have presented effectiveness of this collaborative method using real-world astronomical signals and practical simulated LTE signals (downlink and uplink) as source of RFI along with propagation conditions based on preset benchmarks and standards. Through our analysis and simulation using these signals, we are able to remove 89.04% of the RFI from cellular networks, which reduces excision at the Telescope and capable of significantly improving throughput as corrupted time frequency bins data becomes usable.

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arXiv2020

Cyclic Imaging for All-Sky Interference Forecasting with Array Radio Telescopes

Radio Frequency Interference (RFI) is threatening modern radio astronomy. A classic approach to mitigate its impact on astronomical data involves discarding the corrupted time and frequency data samples through a process called flagging and blanking. We propose the exploitation of the cyclostationary properties of the RFI signals to reliably detect and predict their locations within an array radio telescope field-of-view, and dynamically schedule the astronomical observations such as to minimize the probability of RFI data corruption.

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arXiv2020

Machine Learning in Heliophysics and Space Weather Forecasting: A White Paper of Findings and Recommendations

The authors of this white paper met on 16-17 January 2020 at the New Jersey Institute of Technology, Newark, NJ, for a 2-day workshop that brought together a group of heliophysicists, data providers, expert modelers, and computer/data scientists. Their objective was to discuss critical developments and prospects of the application of machine and/or deep learning techniques for data analysis, modeling and forecasting in Heliophysics, and to shape a strategy for further developments in the field. The workshop combined a set of plenary sessions featuring invited introductory talks interleaved with a set of open discussion sessions. The outcome of the discussion is encapsulated in this white paper that also features a top-level list of recommendations agreed by participants.

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arXiv2020

Performance analysis of the Karhunen-Loève Transform for artificial and astrophysical transmissions: denoising and detection

In this work, we propose a new method of computing the Karhunen-Loève Transform (KLT) applied to complex voltage data for the detection and noise level reduction in astronomical signals. We compared this method with the standard KLT techniques based on the Toeplitz correlation matrix and we conducted a performance analysis for the detection and extraction of astrophysical and artificial signals via Monte Carlo simulations. We applied our novel method to a real data study-case: the Voyager 1 telemetry signal. We evaluated the KLT performance in an astrophysical context: our technique provides a remarkable improvement in computation time and Monte-Carlo simulations show significant reconstruction results for signal-to-noise ratio (SNR) down to -10 dB and comparable results with standard signal detection techniques. The application to artificial signals, such as the Voyager 1 data, shows a notable gain in SNR after the KLT.

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arXiv2018

Comparison of signal detectors for time domain radio SETI

The radio Search for Extra Terrestrial Intelligence (SETI) aims at identifying intelligent and communicative civilizations in the Universe through the detection of engineered transmissions. In the absence of prior knowledge concerning the expected signal, SETI detection pipelines necessitate high sensitivity, versatility, and limited computational complexity to maximize the search parameter space and minimize the probability of misses. This paper addresses the SETI detection problem as a binary hypothesis testing problem, and compares four detection schemes exploiting artificial features of the data collected by a single receiver radio telescope. After a theoretical comparison, those detectors are applied to real data collected with the Green Bank Telescope in West Virginia (USA).

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arXiv2018

RFI subspace smearing and projection for array radio telescopes

Active Radio Frequency Interference (RFI) mitigation becomes a necessity for radio astronomy. The solution commonly applied by the community consists in monitoring the statistics of the received signal, and flag out the detected corrupted data. Subspace projection with array radio telescopes has been suggested as an alternative to data excision to avoid important losses of data and overcome its inherent ineffectiveness with continuous interference. Spatial filtering relies on the estimation of the RFI spatial contribution, and the projection of the subspace spanned by the RFI out of the observed data vector space. To perform well, the dimensionality of the RFI subspace is constrained. RFI subspace estimation techniques assume the source of RFI to be spatially stationary over the sample covariance matrix evaluation. When the relative movement between the telescope and the interferer becomes significant, the RFI subspace gets smeared over the whole data vector space. The subspace projection can then no longer be applied without affecting the source of interest recovery. This paper addresses the effect of RFI subspace smearing on the subspace projection approach, and suggests an alternative technique based on a covariance matrix subtraction, improving the performance of spatial filtering in the case of high subspace smearing.

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arXiv2018

SETI Detection Strategies for Single Dish Radio Telescopes

Radio Searches for Extra Terrestrial Intelligence aim at detecting artificial transmissions from extra terrestrial communicative civilizations. The lack of prior knowledge concerning these potential transmissions increase the search parameter space. Ground-based single dish radio telescopes offer high sensitivity, but standard data products are limited to power spectral density estimates. To overcome important classical energy detector limitations, two detection strategies based on asynchronous ON and OFF astronomical target observations are proposed. Statistical models are described to enable threshold selection and detection performance assessment.

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arXiv2017

The Breakthrough Listen Search for Intelligent Life: A Wideband Data Recorder System for the Robert C. Byrd Green Bank Telescope

The Breakthrough Listen Initiative is undertaking a comprehensive search for radio and optical signatures from extraterrestrial civilizations. An integral component of the project is the design and implementation of wide-bandwidth data recorder and signal processing systems. The capabilities of these systems, particularly at radio frequencies, directly determine survey speed; further, given a fixed observing time and spectral coverage, they determine sensitivity as well. Here, we detail the Breakthrough Listen wide-bandwidth data recording system deployed at the 100-m aperture Robert C. Byrd Green Bank Telescope. The system digitizes up to 6 GHz of bandwidth at 8 bits for both polarizations, storing the resultant 24 GB/s of data to disk. This system is among the highest data rate baseband recording systems in use in radio astronomy. A future system expansion will double recording capacity, to achieve a total Nyquist bandwidth of 12 GHz in two polarizations. In this paper, we present details of the system architecture, along with salient configuration and disk-write optimizations used to achieve high-throughput data capture on commodity compute servers and consumer-class hard disk drives.

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