1. Interference, a Threat!?
Chris Rizos

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

3. 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)

4. 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

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 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

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… redundancy
Multitude of geoscience apps…but robust & not RT

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

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

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

12. Regional Coverage… GPSnet

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

14. 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

15. 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?

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 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

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

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

19. 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

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.

21. 1) Experiment Setup 2) Real-World Data

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

24. Next? Building a Detection Rx
Key resource: “Namuru I” FPGA-based Rx

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

26. 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

27. Network Configuration…

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…