Interference, a Threat!?

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…