An Overview of Civil GPS Monitoring

1
An Overview of Civil GPS Monitoring

• John W. Lavrakas
• ION Western Regional Vice President
• Presented to the So. California Section ION
• March 31, 2005
• Aerospace Corp. El Segundo, CA

The opinions expressed in this briefing are those
of the author and do not represent the views of
the U.S. Government, the ION, or Overlook Systems
2
Overview

• Background on civil GPS monitoring
• What has been going on recently
• The new White House policy directive
• Implementation approaches
• Future plans

3
Background

• GPS has extensive monitoring of the signal and
  the service
  
• Worldwide network of monitor stations
• 24-hour crews
• Automated and manual checks of data
• Is it adequate? Not really

4
Whats missing?

• Signal monitoring
• C/A code not continuously monitored
• Not 100 coverage of signals
• Existing receivers cant track large clock
  runoffs
  
• Navigation message monitoring
• Nav message send/receive checked but not content
• Service monitoring
• Only range errors, signal availability checked
• No formal checks of position and time accuracy,
  service availability

5
What has gone wrong?

• Single Frequency Iono Coefficients
• 28 May - 02 Jun 2002, single frequency iono
  coefficients incorrect
  
• Partition reconciliation anomaly
• 12 Mar - 22 Mar 1993, time transfer error, 15 ns
  over six days
  
• SVN19/PRN19 evil waveform
• 1993 - 2-8 meter vertical position errors

6
What has gone wrong?

• Invalid almanac
• 28 Mar 2000 GPS almanac contained incorrect
  information
  
• When used in GPS modeling tools, resulted in
  generation of incorrect PDOP and SEP values
  

7
What has gone wrong?

• Clock failure
• 28 Jul 2001 SVN22 clock failure
• Range errors in excess of 200,000 meters
• Occurred over southern Pacific Ocean
• For about a half an hour not in view of any OCS
  monitor stations
  
• Clock failure
• 1 Jan 2004 SVN23 clock failure
• Transmission of ranging errors up to 280,000
  meters with duration of 2.75 hours

8
How can this happen?

• GPS developed for military use
• Adequate for military operations
• Dropping bombs, search and rescue, landing
  military planes
  
• Not built for high integrity applications
• Not adequate for civilian operations involving
  safety of life and large-scale economics
  
• Landing commercial airliners, navigating in
  harbors and inter-coastal waterways
  
• Using GPS for time synchronization of networks

9
What type of monitoring is needed?

• Expected service levels
• No worse than current performance
• Find and fix problems promptly
• Specified service levels
• GPS System Specification
• Service commitments
• GPS Standard Positioning Service (SPS)
  Performance Standard

10
Expected service levels
11
Civil Monitoring Features

• Monitor all civil signals and data
• Monitoring tailored to GPS failure modes
• Instant reporting of anomalies to satellite
  operators
  
• Instant notification of service failure impacts
  to users
  
• Ability to archive data

12
Civil Monitoring Benefits

• Adding new measuring capability means we can
  measure things we could not previously
  
• more robust tracking
• position domain assessments
• and use these new capabilities to our
  advantage
  
• Effects-based operations
• More rapid correction of problems
• Awareness of problems before the phone rings

13
White House Policy

• U.S. Space-Based Positioning, Navigation, and
  Timing Policy
  
• Authorized by the President
• Authorized December 8, 2004
• GPS civil performance monitoring funded by
  agencies requiring these capabilities
  
• Secretary of Transportation to ensure the
  performance monitoring of U.S. civil space-based
  PNT services

14
White House Policy

• The continuing growth of services based on the
  GPS presents opportunities, risks, and threats to
  U.S. national, homeland, and economic security.
  The widespread and growing dependence on the GPS
  of military, civil, and commercial systems and
  infrastructures has made many of these systems
  inherently vulnerable to unexpected interruption
  in positioning, navigation, and/or timing
  services. Page 2 para 4
• The US must continue to improve and maintain the
  GPS, augmentations, and backup capabilities to
  meet growing national, homeland, and economic
  security requirements, for civil requirements,
  and to meet commercial and scientific demands.
  In addition, the diverse requirements for and
  multiple applications of space-based positioning,
  navigation, and timing services, require stable
  yet adaptable policies and management
  mechanisms. Page 2, para 5

15
White House Policy

• GPS civil signal performance monitoring will be
  funded by the agency or agencies requiring those
  services or capabilities, including out-year
  procurement and operations costs. Page 5, para
  6
• The SECTRANS shall ensure, in cooperation with
  the Secretary of Defense and Secretary of
  Homeland Security, the performance monitoring of
  U.S. civil space-based positioning, navigation,
  and timing services. Page 8, para 5

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How to implement...

• What architecture?
• Who should do the monitoring?

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Architecture (my view)

• Real time monitoring done by OCS
• Range and position domain assessments
• Non-real time monitoring done by external
  agencies
  
• Signal waveform and power levels

18
Agency roles (my view)

• Office Secretary of Transportation (DOT)
• coordinate establish MOUs
• US Air Force (DoD)
• Operate real-time monitoring services
• Respond to anomalies
• US Coast Guard (DHS) and FAA (DOT)
• Respond to civilian complaints
• Coordinate non-real-time monitoring
• Coordinate with USAF when non-compliant

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Defining Civil Monitoring

• DOT is defining what is meant by civil GPS
  monitoring
  
• GPS Civil Service Monitoring Performance
  Specification
  
• To be used when implementing GPS civil monitoring
  capability
  
• Applies only to core GPS service
• Not application specific

20
The Future General Steps

• Consider ways to implement civil monitoring into
  current and future infrastructure
  
• Add capabilities to the Legacy OCS
• Incorporate monitoring in the new OCX
• Address direction in White House policy relative
  to civil performance monitoring

21
The Future Specific Steps

• GPS Operations Center
• New vision for GPS operations in 2 SOPS
• 24 hour operation begun in Feb 2005
• Focused on effects-based operation
• Legacy Accuracy Improvement Initiative
• Addition of six NGA monitor stations
• 100 redundant coverage of all signals
• C/A code tracking

22
When will this all be done? (my view)

• Expanded coverage, improved situational
  awareness
  
• This year
• Formal civil performance monitoring
• Next 2 to 5 years
• Comprehensive monitoring capability
• OCX - 2012

23
Summary

• Civil monitoring is important
• Satellite operators need it
• Users need it
• GPS needs it to stay competitive
• Steps are being taken
• Capabilities are being defined and incorporated
• Implementation will be incremental

24
Further Reading

• ION GPS 1993, GPS Integrity An MCS
  Perspective
  
• GPS World, GPS for the Rest of Us Monitoring
  the Civil Signals, 1 Sep 2003
  
• ION National Technical Meeting 2003, Defining
  the Elements of a Civil GPS Monitoring Service
  
• ION National Technical Meeting 2005, Development
  of a Performance Specification for Civil
  Monitoring
  
• GPS Operations Center Web Site
  www.schriever.af.mil/GpsSupportCenter Archives