An Overview of Civil GPS Monitoring by warrent


									         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
 Background on civil GPS monitoring
 What has been going on recently
 The new White House policy directive
 Implementation approaches
 Future plans
   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
             What’s missing?
   Signal monitoring
          C/A code not continuously monitored
          Not 100% coverage of signals
          Existing receivers can’t 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
    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
    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
    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
     How can this happen?
   GPS developed for military use
    – Adequate for military operations
          Dropping bombs, search and rescue, landing military
   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
What type of monitoring is
   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
                                           Expected service levels
                                                        GPS SIS User Range Error Trend: 1 January 1997 - 31 December 2002
RMS Estimated Range Deviation (ERD)

                                           1997            1998            1999            2000              2001             2002
                                                                                                              Does not include data from
                                      9                                                                       PRN22 failure on 28 July 2001

                                      8           Constellation User Range Error Specification
                                              Worst Daily SV RMS ERD           Daily Constellation RMS ERD          Best Daily SV RMS ERD
    Civil Monitoring Features
 Monitor all civil signals and data
 Monitoring tailored to GPS failure modes
 Instant reporting of anomalies to satellite
 Instant notification of service failure
  impacts to users
 Ability to archive data
    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
    – Effects-based operations
    – More rapid correction of problems
    – Awareness of problems before the phone rings
       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
         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
         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
    How to implement...
 What architecture?
 Who should do the monitoring?
     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
    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
    Defining Civil Monitoring
   DOT is defining what is meant by civil
    GPS monitoring
    – GPS Civil Service Monitoring Performance
    – To be used when implementing GPS civil
      monitoring capability
          Applies only to core GPS service
          Not application specific
The Future: General Steps
   Consider ways to implement civil
    monitoring into current and future
    – Add capabilities to the Legacy OCS
    – Incorporate monitoring in the new OCX
   Address direction in White House policy
    relative to civil performance monitoring
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
When will this all be done?
      (my view)
   Expanded coverage, improved situational
    – This year
   Formal civil performance monitoring
    – Next 2 to 5 years
   Comprehensive monitoring capability
    – OCX - 2012+
   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
    – Implementation will be incremental
           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: “Archives”

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