Abstract
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.
Highlights
When radio frequency interference (RFI) events were detected, an indicator light illuminated green, which subsequently turned red days, weeks, or months later depending on when the disk had filled to capacity
The adjacent band interference was thought to be due to one or more satellite uplinks located in the same complex that periodically transmitted at relatively high power levels in an azimuth that intersected the roof mounted global navigation satellite system (GNSS) antenna or had a reflection that did so. These types of events were characterized by rapid power level excursions as measured by the integrated radio frequency (RF) power meter, but there was a complete absence of disturbance in the produced waterfall plots of the GNSS L1/E1 and L5/E5a spectra that were produced by post processing of the captured data
RFI source that detectable jamming, indicating that6bthe blockingbythe reception of of satellites targetted experienced power level variation as it moved through the local environment
Summary
This study has focused on the twin objectives of sensor system development in pursuit of producing a GNSS front-end or bit grabber that solves the problems of accurately synchronizing the collected data at the sample level with other navigation sensors, while providing for a cost-effective means of detecting and characterizing RFI events in the GNSS spectrum.The existing strike undertaking (www.gnss-strike3.eu) is a European Horizon 2020 project directed at the standardization of GNSS threat reporting and receiver testing, running from 2016 through 2019, that has some overlap with the goals of this study, but has a stronger focus on the creation of a centralized database of searchable metrics of the detected interference events [1].While the production of this very high-quality data in the sense of it utilizing multi-bit quantization and automated characterization and finger printing worked as expected, one area of weakness in the STRIKE3 effort is that its minimum criteria for interference monitoring covers only a Sensors 2018, 18, 2594; doi:10.3390/s18082594 www.mdpi.com/journal/sensorsSensors 2018, 18, 2594 small subsection of the L1 band, not even ensuring that the wider Galileo binary offset carrier (BOC)components are covered, nor the public regulated service (PRS) on E1. While the production of this very high-quality data in the sense of it utilizing multi-bit quantization and automated characterization and finger printing worked as expected, one area of weakness in the STRIKE3 effort is that its minimum criteria for interference monitoring covers only a Sensors 2018, 18, 2594; doi:10.3390/s18082594 www.mdpi.com/journal/sensors. System (GPS) L1 and 9 MHz around the GLObal NAvigation Satellite System (GLONASS) L1, the vast majority of GNSS signals are unmonitored by many STRIKE3 installations, despite the monitor being a large and expensive piece of rackmount equipment. On this hardware, jam and spoofing alerts are apparently not supported per SPIRENT datasheets
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