Radio Frequency Interference Events Research Articles

Characterization of the GNSS RFI Threat to DFMC GBAS Signal Bands.

This article presents analysis results from a long-term multi-site Global Navigation Satellite System (GNSS) Radio Frequency Interference (RFI) monitoring campaign in the context of Ground Based Augmentation System (GBAS) Dual Frequency Multi Constellation (DFMC) concept operation. GBAS resilience against unintentional RFI is an important area for investigation as the ground station receivers often must operate adjacent to high-traffic roads where chances of being affected by RFI are high. To be able to develop algorithms and reaction strategies necessary to ensure continuity and availability of service, knowledge of interference signal characteristics and frequency band/bands affected, as well as relative occurrence rates between the considered frequencies and frequency combinations, is necessary. The analysis presented in the article covers the prevalence and properties of the RFI events observed on the GPSs L1 and L5 and the Galileo E1 and E5a frequency bands that are considered by the on-going DFMC GBAS concept development initiatives. Due to being spectrally adjacent, the observed event analysis is also carried out for the Galileo E5b and GLONASS G1 frequency bands. The article also addresses the issue of spectral occupancy distribution of the observed events and presents new interesting RFI event types captured during the considered monitoring period.

Spectral Characteristics of GEO Satellite Arcing \u2013 300 To 350\xa0MHz

In a series of previous papers, the detection of arcing on GPS, Van Allen Probe, and GEO satellites with the Arecibo Observatory Wm. E. Gordon 305 m radiotelescope has been reported and elaborated. In this paper, characteristics of the radiofrequency spectra of two true GEO satellites are reported as they were measured with the Arecibo Mock spectrometer every 9.6 microseconds, and are contrasted with spectra of impulsive RFI (RadioFrequency Interference) events. It is shown that the arc spectra in the 300–350 MHz range are not continuous, but consist of a number of narrow spectral lines. These lines are consistent within the duration of single arcs, but change between arcs, so that when averaged over many arcs, the appearance of a continuous spectrum is approximated. This behavior is replicated in the laboratory within charging-induced vacuum arcing on small solar array samples. In contrast, the spectrum of impulsive RFI (including, but not limited to lightning strokes) is essentially random from one 9.6 microsecond sampling interval to the next. Since the spectrum of a true arc changes little throughout many samples, it cannot be due to the risetime of the arc current, which is much less than one sampling interval. Furthermore, in laboratory experiments done at very high time resolution (< 1 ns), there is little correlation between the arc current spectra and the arcing RFI spectra, indicating that even arc current fluctuations within each arc can have little to do with the UHF spectra observed.

A survey of spatially and temporally resolved radio frequency interference in the FM band at the Murchison Radio-astronomy Observatory

AbstractWe present the first survey of radio frequency interference (RFI) at the future site of the low frequency Square Kilometre Array (SKA), the Murchison Radio-astronomy Observatory (MRO), that both temporally and spatially resolves the RFI. The survey is conducted in a 1 MHz frequency range within the FM band, designed to encompass the closest and strongest FM transmitters to the MRO (located in Geraldton, approximately 300 km distant). Conducted over approximately three days using the second iteration of the Engineering Development Array in an all-sky imaging mode, we find a range of RFI signals. We are able to categorise the signals into: those received directly from the transmitters, from their horizon locations; reflections from aircraft (occupying approximately 13% of the observation duration); reflections from objects in Earth orbit; and reflections from meteor ionisation trails. In total, we analyse 33 994 images at 7.92 s time resolution in both polarisations with angular resolution of approximately 3.5$^{\circ}$, detecting approximately forty thousand RFI events. This detailed breakdown of RFI in the MRO environment will enable future detailed analyses of the likely impacts of RFI on key science at low radio frequencies with the SKA.

Design of a Multiband Global Navigation Satellite System Radio Frequency Interference Monitoring Front-End with Synchronized Secondary Sensors.

This paper investigates the challenges of developing a multi-frequency radio frequency interference (RFI) monitoring and characterization system that is optimized for ease of deployment and operation as well as low per unit cost. To achieve this, we explore the design and development of a multiband global navigation satellite system (GNSS) front-end which is intrinsically capable of synchronizing side channel information from non-RF sensors, such as inertial measurement units and integrated power meters, to allow the simultaneous production of substantial amounts of sampled spectrum while also allowing low-cost, real-time monitoring and logging of detected RFI events. While the inertial measurement unit and barometer are not used in the RFI investigation discussed, the design features that provide for their precise synchronization with the RF sample stream are presented as design elements worth consideration. The designed system, referred to as Four Independent Tuners with Data-packing (FITWD), was utilized in a data collection campaign over multiple European and Scandinavian countries in support of the determination of the relative occurrence rates of L1/E1 and L5/E5a interference events and intensities where it proved itself a successful alternative to larger and more expensive commercial solutions. The dual conclusions reached were that it was possible to develop a compact low-cost, multi-channel radio frequency (RF) front-end that implicitly supported external data source synchronization, and that such monitoring systems or similar capabilities integrated within receivers are likely to be needed in the future due to the increasing occurrence rates of GNSS RFI events.

A Dictionary Approach to Identifying Transient RFI

AbstractAs radio telescopes become more sensitive, the damaging effects of radio frequency interference (RFI) become more apparent. One particular approach to mitigating RFI is to deploy independent, omnidirectional wideband monitoring systems at radio telescope arrays. Near such radio telescopes, detected RFI sources are often easily removed or replaced; the challenge lies in identifying them. Transient (impulsive) RFI is particularly difficult to identify. We propose a novel dictionary‐based approach to transient RFI identification. RFI events are treated as sequences of subevents, drawn from particular labeled classes. We demonstrate an automated method of extracting and labeling subevents using a data set of transient RFI. A dictionary of labels may be used in conjunction with hidden Markov models to identify the sources of RFI events reliably. We attain improved classification accuracy over traditional approaches such as support vector machines or a naïve k‐Nearest Neighbor classifier. Finally, we investigate why transient RFI is difficult to classify. We show that cluster separation in the principal components domain is influenced by the alternating current supply phase for certain sources.

A regional scale performance evaluation of SMOS and ESA-CCI soil moisture products over India with simulated soil moisture from MERRA-Land

Abstract Three multi-decadal satellite soil moisture (SM) products, obtained by merging two active and six passive, all-active-merged (CCI-ACT), all-passive-merged (CCI-PAS) and all-active-passive-merged (CCI-COMBINED), and Level-3 SM retrieved from Soil Moisture Ocean Salinity (SMOS) mission were evaluated over India. The evaluation strategy employed is twofold: (a) time series and correlation analysis of SM datasets with respect to the Modern Era Retrospective-analysis for Research and Applications-Land (MERRA-L) SM simulation and the India Meteorological Department (IMD) gridded rainfall; (b) investigate the spatial distribution of random error of the satellite products using Triple Collocation (TC) approach. The Pearson's correlation analysis showed that the performance of CCI-ACT and CCI-COMBINED are comparable to each other and they agree well with the MERRA-L simulated SM time series. They also had a good rank correlation with rainfall. The random error from TC is represented in terms of fractional Root Mean Square Error ( fRMSE TC ). It also represents the sensitivity of satellite retrievals to changes in true state. The analysis of fRMSE TC showed that descending swath of SMOS SM has a lower error than ascending for 71% of the pixels over India. CCI-ACT was found to have the most number of pixels with the lowest errors, having a mean fRMSE TC of 0.7188, compared to 0.7705 for CCI-COMBINED, 0.7828 for CCI-PAS and 0.8308 for SMOS-D. However, the error in CCI-ACT was highest in arid desert regions of western India. The error in CCI-COMBINED, CCI-PAS and SMOS-D grew with an increase in vegetation density. The fRMSE TC maps were analysed against the maps of the probability of occurrence of Radio Frequency Interference (RFI), Normalized Difference Vegetation Index (NDVI), soil texture (percentage of clay, sand, and silt) and modified Koppen-Geiger climate classification. The climate classification map was used to classify fRMSE TC against the different homogeneous climate classes. The analysis of the maps revealed that the inconsistency in SMOS is because of the RFI events over India. However, a multiple linear regression based attribution study showed that SMOS-D is the least affected by vegetation (4%) and the spatial distribution of CCI-ACT and CCI-COMBINED error showed more affinity towards soil texture than vegetation density.

Radio Frequency Interference messages during breath testing of suspected impaired drivers using the Intoxilyzer® 5000C: A 13-year retrospective analysis

ABSTRACTRetrospective analysis of the incidence of Radio Frequency Interference (RFI) exception messages obtained during testing of suspected impaired drivers on the Intoxilyzer® 5000C over a 13-year period (1997 to 2009) was examined in order to address concerns on the hypothetical impact of RFI on breath alcohol testing. RFI messages were rare, occurring in less than 0.48% (n = 128) of the 26,939 drivers tested. Multiple RFI messages were even more infrequent, occurring in only 10.2% of RFI-positive cases (n = 13). There was no significant effect of the incidence of RFI messages attributable to a particular testing location (p = 0.98), a specific instrument (p = 0.98), or year of testing (p = 0.99). In addition, the data show no evidence that hypothetical “undetected” RFI events, in addition to those already detected by the instrument, affected either the calibration check results or the subject breath tests in this study. Instruments are designed with an RFI detection system and shielding to protect the internal electronics against RFI. The breath testing procedure requiring two tests in good agreement (within 20 mg/100 mL truncated) is an additional safeguard against “undetected” RFI impacting the tests, and serves to increase the scientific confidence in the results obtained.

RFI detection by automated feature extraction and statistical analysis

AbstractIn this paper we present an interference detection toolbox consisting of a high dynamic range Digital Fast‐Fourier‐Transform spectrometer (DFFT, based on FPGA‐technology) and data analysis software for automated radio frequency interference (RFI) detection. The DFFT spectrometer allows high speed data storage of spectra on time scales of less than a second. The high dynamic range of the device assures constant calibration even during extremely powerful RFI events. The software uses an algorithm which performs a two‐dimensional baseline fit in the time‐frequency domain, searching automatically for RFI signals superposed on the spectral data. We demonstrate, that the software operates successfully on computer‐generated RFI data as well as on real DFFT data recorded at the Effelsberg 100‐m telescope. At 21‐cm wavelength RFI signals can be identified down to the 4σ rms level. A statistical analysis of all RFI events detected in our observational data revealed that: (1) mean signal strength is comparable to the astronomical line emission of the Milky Way, (2) interferences are polarised, (3) electronic devices in the neighbourhood of the telescope contribute significantly to the RFI radiation. We also show that the radiometer equation is no longer fulfilled in presence of RFI signals. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Technique for correlating radiated noise with individual spark events in an automotive ignition system

A technique is described for obtaining synchronization signals from an engine's ignition system without significantly modifying the far field radio frequency interference (RFI) produced by the engine. These signals are used to view the output of an RFI receiver as a function of time, allowing for a correlation between RFI and individual arcing events in the ignition sequence. Examples of real time and statistical data obtained with the technique are given.