Radio Frequency Interference Monitoring Research Articles

GNSS Radio Frequency Interference Monitoring from LEO Satellites: An In-Laboratory Prototype.

The disruptive effect of radio frequency interference (RFI) on global navigation satellite system (GNSS) signals is well known, and in the last four decades, many have been investigated as countermeasures. Recently, low-Earth orbit (LEO) satellites have been looked at as a good opportunity for GNSS RFI monitoring, and the last five years have seen the proliferation of many commercial and academic initiatives. In this context, this paper proposes a new spaceborne system to detect, classify, and localize terrestrial GNSS RFI signals, particularly jamming and spoofing, for civil use. This paper presents the implementation of the RFI detection software module to be hosted on a nanosatellite. The whole development work is described, including the selection of both the target platform and the algorithms, the implementation, the detection performance evaluation, and the computational load analysis. Two are the implemented RFI detectors: the chi-square goodness-of-fit (GoF) algorithm for non-GNSS-like interference, e.g., chirp jamming, and the snapshot acquisition for GNSS-like interference, e.g., spoofing. Preliminary testing results in the presence of jamming and spoofing signals reveal promising detection capability in terms of sensitivity and highlight room to optimize the computational load, particularly for the snapshot-acquisition-based RFI detector.

Survey and monitoring of ASKAP’s RFI environment and trends I: Flagging statistics

Abstract We present an initial analysis of Radio Frequency Interference (RFI) flagging statistics from archived Australian SKA Pathfinder (ASKAP) observations for the ‘Survey and Monitoring of ASKAP’s RFI environment and Trends’ (SMART) project. SMART is a two-part observatoryled project combining analysis of archived observations with a dedicated, comprehensive RFI survey. The survey component covers ASKAP’s full 700–1 800 MHz frequency range, including bands not typically used due to severe RFI. Observations are underway to capture a detailed snapshot of the ASKAP RFI environment over representative 24 h periods. In addition to this dedicated survey, we routinely archive and analyse flagging statistics for all scientific observations to monitor the observatory’s RFI environment in near real-time. We use the telescope itself as a very sensitive RFI monitor and directly assess the fraction of scientific observations impacted by RFI. To this end, flag tables are now automatically ingested and aggregated as part of routine ASKAP operations for all science observations, as a function of frequency and time. The data presented in this paper come from processing all archived data for several ASKAP Survey Science Projects (SSPs). We found that the average amount of flagging due to RFI across the routinely used ‘clean’ continuum science bands is 3%. The ‘clean’ mid band from 1 293 to 1 437 MHz (excluding the 144 MHz below 1293 MHz impacted by radionavigation-satellites which is discarded before processing) is the least affected by RFI, followed by the ‘clean’ low band from 742 to 1 085 MHz. ASKAP SSPs lose most of their data to the mobile service in the low band, aeronautical service in the mid band and satellite navigation service in the 1 510–1 797 MHz high band. We also show that for some of these services, the percentage of discarded data has been increasing year-on-year. SMART provides a unique opportunity to study ASKAP’s changing RFI environment, including understanding and updating the default flagging behaviour, inferring the suitability of and calibrating RFI monitoring equipment, monitoring spectrum management compliance in the Australian Radio Quiet Zone – Western Australia (ARQZWA), and informing the implementation of a suite of RFI mitigation techniques.

SMOS ESA RFI Monitoring and Information Tool: Lessons Learned

The issue of Radio Frequency Interference (RFI) is a widespread problem in most microwave Earth observation missions, and passive instruments are particularly sensitive to RFI. This is the case for SMOS, Soil Moisture and Ocean Salinity, a satellite of the European Space Agency, which operates in the 1400–1427 MHz band, where all emissions are prohibited. Notwithstanding this regulatory framework, SMOS has been affected by RFI all around the world since the beginning of operations in 2010. In the first years of operations, manual detection processes and reporting of RFI to National Regulatory Authorities were in place in order to mitigate the detected sources. After 12 years, a tool called ERMIT (ESA RFI Monitoring and Information Tool) has been developed at ESAC (European Space Astronomy Center). This tool helps the SMOS RFI team in its spectrum monitoring tasks (e.g., RFI monitoring, logging, and reporting) thus allowing it to counteract RFI pollution more efficiently, providing external users with detailed and user-friendly information on the L-band RFI observed by SMOS. The ERMIT tool is now publicly available. This document aims at describing the needs that lead to the development of ERMIT and at presenting the information made available by it.

Aerial Locating Method Design for Civil Aviation RFI: UAV Monitoring Platform and Ground Terminal System

A key open question in the aerial locating method is ensure that parameters that identify the location of the radio frequency interference (RFI) are monitored, and to make sure that the locating algorithm is unbiased. Furthermore, the transmission of parameters to the ground for real-time analysis and display of the RFI location is important as it provides insight into the performance advantages of the aerial location method. The main contributions of the article are four points: the first is the introduction of the angle of arrival (AOA) algorithm to civil aviation RFI location, and the integration of algorithm characteristics with unmanned aerial vehicle (UAV) operations proposing an aerial monitoring method for civil aviation RFI. Simulation results show that the two-point cross-location method obtains effective information on the location parameters of the RFI. The second is to build a UAV monitoring platform, which is as light as possible to make sure the direction finding and digital transmission devices meet the airworthiness requirements, so that the UAV can complete the data acquisition task within a safety margin. Thirdly, a ground analysis system was designed to receive information on the UAV’s parameters, enabling software manipulation to ensure safe operation under non-visual conditions. In addition to this, the monitoring data is processed in real time and algorithms are used to resolve the location of interference sources and display them on a map. The fourth one is to verify the implementation of the aerial positioning method by setting up different test scenarios. Compared with portable direction-finding equipment and ground monitoring, the test results show that the UAV-based RFI monitoring method performances better in monitoring radius and positioning accuracy with a small direction-finding error, and the advantages of the ground analysis system are highly integrated and intuitive display.

Satellite RFI mitigation on FAST

As the most sensitive single-dish radio telescope, the Five-hundred Aperture Spherical radio Telescope (FAST) is very susceptive to radio frequency interference (RFI) from active radio services. Moreover, due to the rapid development of space applications and research, satellite interference has become one of the main RFI sources for FAST, particularly at the L band. Therefore, we have developed several measures to mitigate satellite RFI. On the one hand, an antenna with 4.5-meter diameter has been constructed and installed at the FAST site to detect the satellite interference in the frequency band between 1 to 5 GHz. Meanwhile, we have developed a satellite RFI database based on the FAST sky coverage, the observing frequency bands, and known satellite systems. By combining the satellite RFI monitoring antenna and the database, we have established a satellite RFI mitigation system. With this system, we can not only track satellites to collect their characteristics and update the database but also help the observer to program the observing plan by predicting satellite interference. During the practical observation of FAST at the L band, the feasibility of this system to mitigate satellite RFI has been proved. In particular, the system effectively avoids strong satellite interference from entering the main beam of the telescope and causing receiver saturation.

Design and Implementation of Remote RFI Monitoring System for Ghana Radio Telescope Observatory-Nkutunse

Radio telescope receivers are sensitive instruments designed to detect very weak signals radiating from astronomical sources. These signals travel several light years and are sometimes drain by the interference of man-made and terrestrials RFI’s. This work aims at the design of a cost-effective Radio Frequency Interference Monitoring System (RFIMS) for the Ghana Radio Astronomy Observatory at Nkutunse. The design of automated RFIMS was constructed with a log-periodic antenna for receiving the electric field being radiated, Low Noise Amplifier (LNA) to amplify the weak signals for detectability, an attenuator to control the high power interfering signals, a filter to pass frequency of interest and a spectrum analyzer as backend. Ideally, telescopes are supposed to be sited at a radio quiet environment. The implementation is to continually monitor the radio space for potential interference at the telescope site for remedial actions since it has become a global candidate site by location and necessitation.

Design of GPS antijamming algorithm using adaptive array antenna to mitigate the noise and interference

This paper describes the Matlab based simulation of radio frequency interference monitoring and mitigation techniques using adaptive array antenna and null steering algorithm. The proposed research is described to show the design and implementation of the GPS transmitter and receiver system for real time navigation, location based services and last but not least tracking applications. Two interferences arriving at 35° and 55° with power greater than seven times of original GPS signals arriving at 45°. Least mean square (LMS) and recursive least square (RLS) algorithms. The proposed system has been evaluated by conducting experiments by using the simulation tool for AntiJammer. The proposed model is useful for developing the smart health care application. Results showed better performance of RLS over LMS to mitigate the effect of interference as well as noise with a higher signal to noise ratio. This system will be useful for enhancing the communication effectiveness of smarthealth care systems.

A CNN and LSTM-based approach to classifying transient radio frequency interference

Abstract Transient radio frequency interference (RFI) is detrimental to radio astronomy. It is typically broadband, intermittent and particularly difficult to classify by source. RFI of this type can be generated by devices like mechanical relays, fluorescent lights or AC machines. Such sources may be present in the vicinity of a radio telescope array, especially if other new instruments are under construction nearby. One mitigating approach is to deploy independent RFI monitoring stations at radio telescope arrays. Once the sources of RFI signals are identified, they may be removed or replaced where possible. For the first time in the open literature, we demonstrate an approach to classifying the sources of transient RFI (in time domain data) using deep learning techniques. Our proposed model includes a pre-trained CNN followed by a bidirectional LSTM layer. Applied to a previously obtained dataset of experimentally recorded transient RFI signals, our approach offers good results. It shows potential for development into a tool for identifying the sources of transient RFI signals recorded by RFI monitoring stations.

A high‐performance log‐periodic dipole‐antenna for radio frequency interference monitoring system at the Sardinia Radio Telescope

AbstractThe Italian National Institute for Astrophysics (INAF) is currently involved in the construction of the Sardinia Radio Telescope (SRT). The radio observatory will be equipped with an accurate and sensitive Radio Frequency Interference (RFI) monitoring system, aimed to control if the radio bands allocated to the Radio Astronomy Service are actually free of interferences. This article describes a Log‐Periodic Dipole‐Antenna (LPDA) designed for such a system, operating with very high‐performance in L‐band and S‐band. The LPDA, consisting of 38‐elements, achieves a gain higher than 11 dBi with peaks up to 13 dBi and good impedance match in the whole band of interest: 1.2–2.5 GHz. The antenna was designed, manufactured, and finally tested in an anechoic chamber; the results for each step will be described in this article. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 132–136, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23997

RFI Test Observations at a Candidate Ska Site in China

Radio frequency interference (RFI) test observations were carried out at one of the candidate Square Kilometre Array (SKA) sites in Guizhou province, following the “RFI Measurement Protocol for Candidate SKA Sites” (hereafter RFI protocol). All data (raw and calibrated) are preserved in some suitable format, such as that set by the international RFI working group of the Site Evaluation and Selection Committee (SESC). An RFI test in December 2003 was performed according to Mode 1 of the RFI Protocol, in order to identify technical difficulties which might arise during a co-ordinated RFI measurement campaign over a period of 1 year. In this paper we describe the current equipment, observational technique and data presentation. The preliminary results demonstrate that the RFI situation at Dawodang depression in Guizhou province makes it quite a promising location for the proposed SKA. Furthermore, the first session of the RFI monitoring program, whichwas made in May 2004, showed that a complete RFI measurement including both modes 1 and 2 of the RFI Protocol would take about 2 weeks. The possible ways to minimize some limitations of the current equipment are also discussed, which will enable us to meet the RFI protocol. kg]Keywords kw]antenna kw]measurement

A Radio Frequency Interference Survey of Central Ohio

ABSTRACTA long-term radio frequency interference monitoring program is now in progress at the Ohio State University Radio Observatory. Current observations encompass the 1-2 GHz band, measuring the signal strength in each 150 KHz subband. Preliminary results show many strong and persistent signals, and wide bands in which no signals are detected. Daily and weekly variations appear to be correlated with periods of maximum human activity such as “rush hours”. It may be that aircraft reflections are causing many of the signals to be received, and that airline schedules correlate with “rush hours”. The program is being upgraded to automatically measure the direction of arrival of each signal, as an aid to further identify it. This directional information will also be used in designing rolled edges and side shields for the co-located OSU Radio Telescope, to further reduce its vulnerability to RFI.