Interference, a Threat!? Chris Rizos

What is Interference? GPS signal Noise RF Interference - jamming, unintentional RFI, multipath GPS Signal Environmental noise RF Interference

What types of RFI are there? Wideband Gaussian Intentional noise jammers Wideband FM Television transmitter’s harmonics Wideband spread-spectrum Intentional spread spectrum jammers Wideband-pulse Radar transmitters Narrowband FM FM stations’ transmitters Narrowband swept CW Intentional CW jammers Narrowband CW Any transmitter’s carrier(s)

Why is RFI a Threat? Reduces S/N Degraded (or no) measurements Leads to degraded (or no) positioning accuracy Can have “knock-on” effect (for multiple users) if GNSS CORS receiver(s) is(are) affected

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 application CORS 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

CORS Infrastructure… Permanent high-grade GPS Rx: • low multipath antenna • comms & control box, to NCC • UPS • secure installation • Rx backup?

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.

Multitude of geoscience apps…but robust & not RT Global IGS Infrastructure… redundancy Multitude of geoscience apps…but robust & not RT

Fugro’s Omnistar … Navcom’s Starfire Global Commercial WADGPS… Fugro’s Omnistar … Navcom’s Starfire

Plus stns in SW Pacific, Antarctica, Macquarie Is., etc National CORS … geodesy Plus stns in SW Pacific, Antarctica, Macquarie Is., etc

National CORS… navigation Part of global free-to-air DGPS network…

Regional Coverage… GPSnet

Local Coverage… SydNet Support local RTK operations, expand to other parts of NSW…

Precision DGNSS Applications … Machine guidance/ control in mining, construction & agriculture Robotic navigation Ports & logistics Surveying & mapping Scientific applications Real-time, high accuracy apps are very vulnerable to interruption of CORS service … not just Rx RFI but wireless comms link interference

Protecting the CORS Infrastructure … Interference to one CORS impacts many users in zone of service … 10s-100s km Little or no redundancy, especially for RT operations on land, i.e. for RTK-based apps RT ops to support machine guidance/control are most vulnerable … alternatives? How to use CORS network to detect (& localise?) interference/jamming sources?

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 data Build prototype ‘detection’ Rx Test on several CORS sites Study feasibility of using synchronised network of ‘detection’ Rxs for geo-location of RFI sources

What is Affected by RFI? Receiver Operations … AGC LNA Filters Code Tracking Loops Carrier Tracking Loops

Which Observables are Affected? Signal Quality (C/No) Tracking Error Correlator Output Power Pseudorange Measurements PVT Accuracy

GPS Receiver and RFI Analysis Antenna Output Navigation Data Processing Radio Frequency Front End GPS Signal Acquisition & Tracking Pre-Correlation RFI Detection Post-Correlation RFI Detection

Progress on Characterisation of RFI… TABATABAEI, A., DEMPSTER, A.G., & BARNES, J., 2005. Characterization of interference effects on GPS signal carrier phase error and pseudo-range. Spatial Sciences Conference, Melbourne, Australia, 12-16 September, 1323-1331, CD-ROM procs. TABATABAEI, A., 2006. 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, 26-29 September. TABATABAEI, A., & DEMPSTER, A.G., 2006. A novel approach in detection and characterization of CW interference of GPS signal using receiver estimation of CNo. IEEE/ION PLANS, San Diego, California, 25-27 April. TABATABAEI, A., DEMPSTER, A.G., THAN, N.T., & BARNES, J., 2006. An application of post-correlation GPS receiver interference detection and characterization. Symp. on GPS/GNSS (IGNSS2006), Surfer’s Paradise, Australia, 17-21 July. www.gmat.unsw.edu.au/snap/new/news2006.htm#pubs www.gmat.unsw.edu.au/snap/about/publications_year.htm

1) Experiment Setup 2) Real-World Data

RFI in Sydney … last week SBS TV Tx NordNav frontend sampling (spectrum)

Next? Building a Detection Rx Key resource: “Namuru I” FPGA-based Rx www.dynamics.co.nz/gpsreceiver

Localisation Using CORS Network? Could CORS network be used to localise GPS interference/jamming sources?

Detection/Reference Station Hardware Antenna Array Interference Source Multi-RF Front-end What about synchronised, geographically dispersed detection Rxs ? - either AOA or TOA A/D Conversion DSP Interference Localiser Test-bed TOA AOA RSS RFI Source Location

Network Configuration…

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…