Interference, a Threat!?
Chris Rizos
What is Interference?• GPS signal
• Noise
• RF Interference - jamming, unintentional RFI, multipath
GPS Signal
RF Interference Environmental noise
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.
Global IGS Infrastructure… redundancy
Multitude of geoscience apps…but robust & not RT
Global Commercial WADGPS…
Fugro’s Omnistar …Navcom’s Starfire
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
• Interference to one CORSimpacts 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?
Protecting the CORSInfrastructure …
Research Challenge … a project of the CRC for Spatial Information
• 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
Use CORS infrastructure as “sentinels”. Project objectives:
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
Radio Frequency Front End
Antenna
Navigation Data Processing
Output
GPS Signal Acquisition & Tracking
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#pubswww.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 Rxwww.dynamics.co.nz/gpsreceiver
Localisation Using CORS Network?
Interference Source
Receiver_1 (x_1, y_1)
Receiver_2 (x_2, y_2)
Receiver_0 (0,0)
AoA_2 AoA_1
AoA_0
TT
T
ToA_1ToA_2
ToA
_0D
_0
D_2 D_1
Could CORS network be used to localise GPS interference/jamming sources?
Antenna Array
Multi-RF Front-end
A/D Conversion
RFI Source Location
DSP Interference Localiser Test-bed• TOA• AOA• RSS
Detection/Reference Station Hardware
Interference Source
What about synchronised, geographically dispersed detection Rxs ?- either AOA or TOA
Network Configuration…
Base station 1 Base station 2Central station
Receiver Antenna_1 Receiver Antenna_0 Receiver Antenna_2
Synchronizing system
Internet Internet
Data Acquisition
&Processing
Data Acquisition
&Processing
Data Acquisition
&Processing
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…