A US Program to Identify, Geolocate, and Mitigate

Sources of GPS Interference

But are we serious?

Terry McGurn/ConsultantPresented to the EXEC PNT Advisory BoardMeeting of 5-6 November 2009

Background & Motivation

• Motivation: NSPD-39, Dec 2004– Maintain Continuity of GPS service in an

interference environment– Deny hostile exploitation of this service.

• NSPD-39 Actions (From Fact Sheet)– Establish a PNT EXCOM to address these issues,

among others– Establish the EXCOM Advisory Board– Establish Agency Roles

CONCLUSIONS

• Language of the NSPD-39 Fact Sheet is vague.

• Open to Various Interpretations of Assignments.

• NSPD-39 Muddies the Issues (friendly protection & hostile denial).

• I Believe The Program is Headed in the Wrong Direction.

• But I believe we can get back on track.

DHS: The Action Agency• DHS has taken action on this program.

– DHS developed an IDM paper to address

this issue, published in 2007. Largely reflects NSPD-39

– The DHS, as well as its contractors, have been very forthcoming when I’ve contacted them to obtain information on their program. But we differ greatly on the proper approach.

So What’s Wrong?

• No one is tasked to develop and array sensors to detect/geolocate interferers.

• The fact sheet, as well as responses to it, reflect a belief that we have these assets already in place, and the task is primarily to coordinate these assets.

• There are assets available that could be netted to support the program, but these are only mentioned in passing.

So What’s Wrong? (Cont,d)• The responsible DHS body for this program

appears to be the Office of Infrastructure Protection within the Directorate for National Protection & Programs, and several of its high level appointees are not yet in place.

• I believe the present DHS approach puts the cart before the horse. (i.e., developing the “data repository” before developing the sensors that will provide the “reposing” data.)

• In fact, the sensors should dictate the degree of processing to be done at the repository vice in the field.

So: What Can We Do Now?• DHS should address the pieces of the issue.

The “one size fits all” approach not practical• Intentional jamming, spoofing, unintentional

interference are different problems. • But, at present, unintentional jamming

appears to be the most frequent source of signal loss.

So• Let’s develop a capability to minimize the

occurrence of unintentional jamming? • You don’t get partial credit if you lose a

critical function unintentionally.

Recommendations• Define Specific Responsibilities for the

Various Components of the Network. (An EXCOM role?)

• Suggest Several Small Funded Efforts. (Requires more selective expertise/less PPT.)

• Responsible Dept/Agency should have System Engineering Support.

• Let’s Get a Significant Start. First Address

the Unintentional Jamming Issue.

Examples of Unintentional Jamming

• Rome, NY, ADC (3 days/5 watts/ several hundred kilometers) (1997-1998)

• St. Louis Airport (1990s)• Butte, Montana (? days, spurious

harmonics)• Monterey Bay (many months/ VHF/UHF

TV antenna radiating above the L-band noise floor) (~2001)

• San Diego Navy Test Center (4 hrs, 500 mw) (2004)

DGPS SiteInoperative

2 Hours

AIS Display ConsoleAnomaly

Cell Provider Network150 sites detected error

2 sites inoperative

Medical Services Paging Provider Network

Inoperative

1.5 Hours – 20 sites

General AviationPilot Report GPS

Malfunction

Potential for First Responder Impacts

Interference Case Study

Introduction - Typical digital GNSS receiver block diagram

RF

Antenna

LOs

Digital IF

Analog IF

N2

Regulated DC power

Unregulated input power

Navigation processing

User interface

Power supply

Receiver processing

AGC

Frequency synthesizer

Reference oscillator

1 Digital receiver

channel

A/D converter

Down converter

Pre amp

RF front end

Introduction - GNSS receiver front end with Digital Gain Control

ADC

Digital Gain

Control

Analog IF

J/N Meter

Digital IF

DownConverter

Antenna

PreampDigital

Attenuator

Gain Controlled Analog IF

Final Thoughts

• Mitigation:– Where possible, geolocate and prosecute– Otherwise:

• Back-up Systems– Inertial (short term only. Present inertial trends

are for poorer performance, low-cost systems.– eLoran: Provides high availability, good anti-

jam, and good timing performance (sigma about 30 nsec).

– Smart receivers, for situational awareness.

Final Thoughts (Continued)

• “When everyone’s in charge, no one’s in charge”.

(A retired Russian Colonel, in discussing the problems in the GLONASS program)

• This is a hard problem. But a challenging one. Tackle it bit by bit.