2 What is Interference? GPS signal Noise RF Interference - jamming, unintentional RFI, multipathGPS SignalEnvironmental noiseRF Interference
3 What types of RFI are there? Wideband GaussianIntentional noise jammersWideband FMTelevision transmitter’s harmonicsWideband spread-spectrumIntentional spread spectrum jammersWideband-pulseRadar transmittersNarrowband FMFM stations’ transmittersNarrowband swept CWIntentional CW jammersNarrowband CWAny transmitter’s carrier(s)
4 Why is RFI a Threat? Reduces S/N Degraded (or no) measurements Leads to degraded (or no) positioning accuracyCan have “knock-on” effect (for multiple users) if GNSS CORS receiver(s) is(are) affected
5 GNSS Vulnerability to Interference… Single receiver • low-moderate accuracy applications • denial of service in zone of interference/jamming • geographically isolated consequences • mitigation/augmentation/backup strategies appropriate for user applicationCORS network/infrastructure • high accuracy (&/or high integrity) applications • denial of service to ALL users of differential service • impact over wide area (possibly tens/hundreds of kms) • highest level of mitigation to protect CORS, independent of user requirements/concerns
6 CORS Infrastructure…Permanent high-grade GPS Rx: • low multipath antenna • comms & control box, to NCC • UPS • secure installation • Rx backup?
7 CORS Network Infrastructure Established by civilians beginning in the 1980s.Initially to support high accuracy positioning apps.Also provide enhanced accuracy and integrity for some navigation apps.Established at range of scales … global, national, … and densities … 10s to 1000s km spacing.Trend for all CORS to operate in real-time.Increasingly diverse RTK/DGPS applications.
8 Multitude of geoscience apps…but robust & not RT Global IGS Infrastructure… redundancyMultitude of geoscience apps…but robust & not RT
13 Local Coverage… SydNet Support local RTK operations, expand to other parts of NSW…
14 Precision DGNSS Applications … Machine guidance/ control in mining, construction & agricultureRobotic navigationPorts & logisticsSurveying & mappingScientific applicationsReal-time, high accuracy apps are very vulnerable to interruption of CORS service … not just Rx RFI but wireless comms link interference
15 Protecting the CORS Infrastructure … Interference to one CORS impacts many users in zone of service … 10s-100s kmLittle or no redundancy, especially for RT operations on land, i.e. for RTK-based appsRT ops to support machine guidance/control are most vulnerable … alternatives?How to use CORS network to detect (& localise?) interference/jamming sources?
16 Research Challenge … a project of the CRC for Spatial Information Use CORS infrastructure as “sentinels”. Project objectives:Characterise RFI, using SW Rx, simulated & real-world dataBuild prototype ‘detection’ RxTest on several CORS sitesStudy feasibility of using synchronised network of ‘detection’ Rxs for geo-location of RFI sources
17 What is Affected by RFI? Receiver Operations … AGCLNAFiltersCode Tracking LoopsCarrier Tracking Loops
18 Which Observables are Affected? Signal Quality (C/No)Tracking ErrorCorrelator Output PowerPseudorange MeasurementsPVT Accuracy
19 GPS Receiver and RFI Analysis AntennaOutputNavigation Data ProcessingRadio Frequency Front EndGPS Signal Acquisition & TrackingPre-Correlation RFI DetectionPost-Correlation RFI Detection
20 Progress on Characterisation of RFI… TABATABAEI, A., DEMPSTER, A.G., & BARNES, J., Characterization of interference effects on GPS signal carrier phase error and pseudo-range. Spatial Sciences Conference, Melbourne, Australia, September, , CD-ROM procs.TABATABAEI, A., Statistical inference technique in pre-correlation interference detection in GPS receivers. 19th Int. Tech. Meeting of the Satellite Division of the U.S. Inst. of Navigation, Fort Worth, Texas, September.TABATABAEI, A., & DEMPSTER, A.G., A novel approach in detection and characterization of CW interference of GPS signal using receiver estimation of CNo. IEEE/ION PLANS, San Diego, California, April.TABATABAEI, A., DEMPSTER, A.G., THAN, N.T., & BARNES, J., An application of post-correlation GPS receiver interference detection and characterization. Symp. on GPS/GNSS (IGNSS2006), Surfer’s Paradise, Australia, July.
28 Concluding Remarks…We must assume jamming/interference will happen…just look for it!CORS infrastructure (& the increasing user base) must be protected…use CORS sites to detect/located RFI sources?A number of RFI detection techniques can be refined/developed…just a matter of resources!Ideal solution is RFI localisation using CORS/sentinel network…this is a challenge, but what an achievement!UNSW actively engaged in this work…RFI detection/location, multipath studies, GNSS vulnerabilities, ‘intelligent’ Rx tracking, ultra-tight GNSS/INS integration, multi-sensor integration…