gps and future directions in positioning

GPS and Future Directions in PositioningDennis D. McCarthy U. S. Naval Observatory

UNCLASSIFIED//FOR OFFICIAL USE ONLY

Briefing Overview

GPS SystemGPS AugmentationsThe Future


Critical component of the infrastructure Global utility providing positioning, navigation and timing (PNT) Owned by the U.S. Government Operated by the U.S. Air Force Unlimited number of users Free of direct user charges Public domain Performance improved by augmentations


ApplicationsSatellite OperationsCommunicationsNetwork SynchronizationSurveying & MappingFishing & BoatingOffshore DrillingRecreationTrucking & ShippingPersonal NavigationAviationRailroadsPower GridManagement


How It Works

Each satellite has a clockEach satellite broadcasts where it isEach satellite sends timing signalReceiver has clockReceiver determines distance to each satelliteReceiver determines position and clock correction


GPS SegmentsMonitor StationsGroundAntennasMaster Control StationSpace SegmentUser SegmentControl SegmentSatellite Constellation


GPS Space Segment6 orbital planesOrbiting at approximate altitude of 20200 km every 12 hours. L1 channel produces a Carrier signal at 1575.42 MHz with C/A and P CodeL2 channel produces a Carrier signal of 1227.6 MHz, but only P Code.Codes are modulated on the carrier signal. The C/A or Coarse/Acquisition Code (also known as the civilian code), is modulated and repeated every millisecond; P-Code, or Precise Code, is repeated every seven days.14 Block IIA satellites12 Block IIR satellites5 Block IIR-M satellitesTransmitting new second civil signal (L2C)Transmitting new military signal (M code)


GPS Signals


GPS Constellation StatusSatellite Age as of March 2008246810YearsSatellite3935343633403038434651441241545614451647596061532526273237525824235557BLOCK IIABLOCK IIRBLOCK IIR-M


GPS Ground Control SegmentGenerate navigation message Satellite Position dataClock dataAdjust as neededCommand & Control satellitesPerform maneuversMonitor satellite healthThe control segment keeps the GPS system operational and performing within specification


GPS User Segment18UnlimitedBroadcast systemMore users can join system U.S. & InternationalMulti purpose CivilMilitaryCommercial


Continuous Performance ImprovementAccuracyAssured AvailabilityIntegrityResistance to RF Interference/Jamming


GPS ModernizationNew GPS Operational Control Segment -- September 20075 new monitor stations integrated into network6 more in 2008Upgrading GPS ground segment OCX 2012 - 2016Will implement full functionality for L2C and L5Acquiring next generation of GPS satellites GPS IIIA


Modernized GPS Civil SignalsSecond civil signal (L2C)Designed to meet commercial needsHigher accuracy through ionospheric correctionHigher effective power and improved data structure reduce interference, speed up signal acquisition, enable miniaturization of receivers, may enable indoor useBegan with GPS Block IIR-M in Sep 2005; 24 satellites: ~2014Third civil signal (L5)Designed to meet demanding requirements for transportation safety (safety-of-life)Uses highly protected Aeronautical Radio Navigation Service (ARNS) bandBegins with GPS Block IIFFirst launch: ~2008 (GPS IIR-M Demo); ~2009 (GPS IIF); 24 satellites: ~2016Fourth civil signal (L1C)Designed with international partners to enable GNSS interoperabilityBegins with GPS Block IIIFirst launch: ~2014; 24 satellites: ~2021


GPS Modernization ProgramBlock IIA/IIRBlock IIIBlock IIFBackward compatibility4th civil signal (L1C)Increased accuracyAssured availabilityIncreased securitySystem survivabilityBegin launch ~2014IIR-M: IIA/IIR capabilities plus2nd civil signal (L2C)M-Code (L1M and L2M)Currently being launched

IIF: IIR-M capability plus3rd civil signal (L5)Begin launch 2009Basic GPSStandard ServiceSingle frequency (L1)Coarse acquisition (C/A) code navigationPrecise ServiceY-Code (L1Y and L2Y)Y-Code navigationBlock IIR-M


Benefits of GPS ModernizationSystem-wide improvements in accuracy, availability, integrity, and reliability to meet US Space-Based PNT PolicyHigher standalone accuracy More robust against interference Provides separate, more secure military signalCapability for second (L2C) and third (L5) civil signalsDelivers L1C for interoperability with other GNSSImproved indoor, mobile, and urban use


U.S. Policy PrinciplesProvide civil GPS and augmentations free of direct user fees on a continuous, worldwide basisProvide open, free access to information needed to develop equipmentImprove performance of civil GPS and augmentations to meet or exceed that of international systemsEncourage international development of PNT systems based on GPSSeek to ensure international systems are interoperable with civil GPS and augmentationsAddress mutual security concerns with international providers to prevent hostile useOutlined in 2004 Presidential Policy on Space-Based Positioning, Navigation, and Timing (PNT)


National Space-Based PNT Organization StructureWHITE HOUSEAd Hoc Working Groups


Key Executive Committee ActionsFive-Year National Space-Based PNT PlanSummarizes EXCOM Departments/Agencies planning for development, acquisition, sustainment, and modernization of U.S. space-based PNT systems Interference Detection and Mitigation PlanDepartment of Homeland Security coordinating USG capabilities to detect and mitigate sources of interference to GPS and its augmentationsNational PNT ArchitectureProvide national PNT framework/investment strategy to help guide future PNT system-of-systems investment 2025 timeframeInternational Cooperation and ConsultationCompatibility and Interoperability with other foreign systems


ProblemsOrbitsClocksAtmosphereIonosphereMultipathLow number of visible satellitesHigh PDOP (position dilution of precision- a measure of the current satellite geometry)Low signal to noise ratioLow satellite elevationReceiver


Space-based Augmentation SystemsWAAS Wide Area Augmentation SystemiGPS Commercial Services: OmniSTAR, STARFIREGround-based Augmentation SystemsLAAS - Local Area Augmentation SystemNDGPS-National Differential GPSUSCG U. S. Coast GuardCORS-Continuously Operating Reference StationsNOAA/NGS National Geodetic SurveyJPL Real-Time NetworkCarrier phase IGS e-LORAN


Space-Based Augmentations


WAAS38 Wide-area Reference Stations2 geostationary satellitesTwo or three master stationsprovide fast and slow GPS signal correctionsaccuracy of better than three meters 95 percent of the timeFederal Aviation Administration (FAA) developing for use in precision flight approachesaccounts for GPS satellite orbit and clock drift plus signal delays caused by the atmosphere and ionosphereDetects errors in GPS and notify users within 5.2 seconds (integrity)Transparent - no post processing


iGPSProposed 66 low Earth orbiting Iridium satellite systemEarth stationsOperations centerProvides correction message for GPS signalsRequires new equipment but can use GPS antennaAccuracy ????Constellation will need replenishment in 2014


Commercial ServicesOmnistar, STARFIRE, SynchroneticsL-Band communication satellitesmonitor sitesProcessing and upload centerRequires special receiver equipmentDecimeter accuracyNo post-processing


Ground-Based Augmentations


Local Area Augmentation System (LAAS)Aircraft landing system based on real-time differential correction of GPS. Local reference receivers at precisely surveyed locations send data to a central location at airport.Signal is compared to the surveyed location and correction message transmitted to users via a VHF data link.

A receiver on the aircraft uses this information to correct GPS signal.Designed exclusively for aircraft Intended for use within 20 to 30 miles of installed airfield location.No consumer-grade LAAS-capable GPS receiversAccuracy better than 1 meter


Nationwide Differential GPSFunded by DOT (Research and Innovative Technology Administration)Maintained by Coast GuardNeeds special low-frequency receiving equipmentAccuracy0.5 meter near the reference stationCan degrade up to 1 meter/150 kmTypical accuracy is 1 to 3 meters2 to 5cm accuracy with Post ProcessingHigh Accuracy NDGPS


Continuously Operating Reference StationsNational Continuously Operating Reference Stations (CORS) networkOnline Positioning User Service (OPUS)Atmospheric modelsTroposphereIonosphereCooperative CORS provides access to GPS data disseminated by organizations other than the National Geodetic Survey (NGS). Links to the web sites of cooperating organizations where users can download pertinent GPS data, positional coordinates, and related information.


JPL Real-Time NetworkGlobal GPS Network20% of International GNSS ServiceInternet data deliveryAccuracy10 cm horizontal25 cm vertical


Carrier PhaseStaticHigh accuracy (about 5mm + 1ppm)Long distances. Data collected for several hours Rapid StaticForm of static GPS Special ambiguity resolution techniques which use extra informationRequires minutes instead of hours for observation Accuracy can reach the centimeter level on baselines less than 20km. Real Time KinematicUses a radio to link so that the reference station broadcasts the data obtained from the satellites to the rover instantaneouslyLimits baseline lengthsaccuracy will be in the range of 1-5cm. results are fast and co-ordinates are displayed in real time.bit rate about 1 MHz


Real Time KineticComponentsBase StationGPS receiverRTK radioStable mounting structure12 volt power sourceRoverGPS receiverRTK radio


Comparisons


e-LORANFebruary 7, 2008 DHS announced adoption of eLoran as a national backup to the GPS to mitigate any safety, security, or economic effects of a GPS outage or disruptionPresidents Fiscal Year 2009 Budget Request:Migrate administration of LORAN-C from USCG to DHS National Protection and Programs Directorate (NPPD), includes transfer of budget authority for funding and personnelPrepare for conversion of Loran-C operations to eLoranNPPD to oversee development of eLoran to provide national backup capabilities for positioning, navigation, and timing.Coast Guard will continue operation of the system in 2009 on a reimbursable basis


Fundamental FindingsNational PNT Architectures main task is to generate PNT information and move it to the usersCurrent Architecture depends mostly on radio frequency-based operationsMultilateration (e.g., Global Positioning System, LORAN)Beacons (e.g., Instrument Landing Systems)Distributing augmentation data (e.g., National Differential GPS)Most PNT challenges result from the inherent weaknesses of an RF-based architectureImpedance and interferenceLimits on accuracy and precision due to physics


Fundamental FindingsMany user needs are common across domains, but specialized needs still require specialized solutionsApplication-centric and system-specific approaches have bred inefficienciesIncreasing demands will be placed upon the enterprise in the future Expectations change faster than capabilities can keep up, so must design architecture for flexibility and adaptabilityCurrent organizational constructs are not structured to ensure cooperation and information sharingMany users accept reduced performance or increased risk over more burden, (size, weight, power, and cost)Users are willing to accept marginally more burden when commensurate benefits are available


Fundamental FindingsDependent PNT technologies offer significant capabilitiesUser bears marginal cost of accessing performance designed to meet the needs of the most demanding customers Autonomous PNT technologies offer significant capabilitiesUser burden is based on required performanceReliance on diverse PNT sources increases robustness and availabilityDiversity within a phenomenology (e.g. GPS L1-L2C-L5 or Multi-GNSS)Use of multiple phenomenologies (e.g. GPS-CSAC-INS or image-aided INS)High levels of interoperability enable efficiency and source diversityInterchangeability, (e.g. 2 GNSS + 1 LF + 1 Clock = 4D solution)Communications capabilities offer potential for addition of PNT informationTiming synchronization, ranging, augmentation or integrity information


National PNT Architecture StrategyGreater Common Denominator approachSpecialized needs still require specialized solutions Divest US GNSS augmentations that are duplicative after capability is available from US GNSS modernizationPromote low-burden autonomous capabilities for special needsSpecialized capabilities are still needed in some applications and when cost per capability precludes a common solution


Use Multiple Phenomenologies to the Maximum Extent PracticableEncourage development and employment of equipment that integrates information from diverse sources and information pathsShould develop clear standards for use of foreign PNT systems for safety-of-life and critical infrastructure usersEstablish standards for pseudolites and beacons to promote interchangeability and avoid interferencePursue diverse space- and terrestrially-based PNT capabilities to support diversity in PNT sources and information pathsRationaleDiverse PNT sources and data paths will be needed since no one method will meet any customers needs in all circumstancesDiverse PNT sources and data paths are inherently robust against single point failures


Interchangeable SolutionsEnhance efficiency and exploit source diversityUse participation in international PNT-related activities to promote the interchangeability of PNT sourcesEvolve standards, calibration techniques, and reference frames to support future accuracy and integrity needsIdentify and develop standards for PNT information exchange, assurance, and protectionEstablish standards for the depiction of position information in local and regional operationsCombine information from GNSS, RF network, and precision clocksFuse data from GNSS, gyroscopes, and active/passive sensorsUse or discard PNT information from different sources as customers traverse impeded environments and environmental boundariesRationaleDiverse sources must be synchronized, coordinated, and calibrated to allow user equipment to integrate their information more readilyThe architecture must enable flexibility and adaptability to allow capabilities to keep up with improving expectations


Fusion of PNT with New and Evolving Communications CapabilitiesStudy methods, standards, and potential capabilities for fusion of PNT and communicationsLeverage/adapt RF broadcast and communication Ranging information to known locationsPNT-related information (integrity, etc.)May include SATCOM, cell phones, TV, AM/FM/satellite radio, etc.RationaleRF imposes least user burden in communicating PNT information to mobile and remote users, but RF spectrum is limitedPotential for low-impact addition of PNT information to new and evolving communications systems for synergy with civilian emergency (911) service, and first responders


Interagency Cooperation to Ensure Necessary Levels of Information SharingEstablish a National PNT Coordination Function Establish champions within the National PNT Coordination Function Define, develop, sustain, and manage a PNT modeling and simulation core analytical frameworkRationaleCurrent interagency organizational constructs do not ensure the necessary levels of cooperation and information sharing


Standards and Reference FramesRationaleStandards are fundamental to ensuring interchangeabilityAnticipated future measurement accuracy needs will be more demanding than they are today; reference infrastructures must be an order of magnitude better than required measurement accuracyMajor improvements to reference frame definitions will be needed for the reference frame accuracies needed to support centimeter-level accuracyEvolve standards, calibration techniques, and reference frames to support future accuracy and integrity needsProposed Transition TasksDetermine accuracy of standards, calibration techniques, and reference frames needed to support projected real-time absolute positioning accuracy and integrity needs. Include: earth-fixed and celestial reference frames, earth orientation, grids, timing, frequency, physical models, and data transfer


Web-based InformationPNT.gov established to distribute information on the U.S. National Executive CommitteeInformation on U.S. policy, Executive Committee membership, Advisory Board and frequently asked questionsAll recent public presentationGPS.gov established for public information about GPS applications


APPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSThis slide contains key language from the Coast Guard Posture Statement on Loran. It is drawn from page 501 of the FY09 Presidents Budget request which named DHS as Executive Agent for development of a national backup for critical systems used in position, navigation, and timing.

As indicated, administration of the Loran program is slated to migrate from the Coast Guard to the National Protection and Programs Directorate to prepare for conversion of Loran-C to Enhanced Loran (eLoran).

Budget authority at the level of $34.5M will be transferred to NPPD, and the Coast Guard, as the servicing agency, will continue operation under a reimbursable agreement.

The DHS National Communications System (NCS) is tasked to oversee Loran-C modernization as a first step toward providing back-up capability for critical infrastructure that depends on GPS for position, navigation, and time. The Coast Guard has been working with NCS to carry out the FY09 Presidents Budget Request.APPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGSA Mission statement: tells you what the company is now. It concentrates on present; it defines the customer(s), critical processes and it informs you about the desired level of performance. A Vision statement: outlines what a company wants to be. It concentrates on future; it is a source of inspiration; it provides clear decision-making criteria.

APPROPRIATE CLASSIFICATION MARKINGSAPPROPRIATE CLASSIFICATION MARKINGS(F) Routine refinements to reference frames can support frame accuracies down to 1cm (or user accuracies down to ~10cm)(F) Accuracy with integrity drives a tighter requirement (as a protection limit) than position accuracy alone(F) For very high absolute accuracy applications like ITS (

gps and future directions in positioning

Documents

carrier signal

signal acquisition

gps system operational

gps ground segment ocx

workseach satellite

iseach satellite

precise code

millisecond pcode