Presentation on theme: "Advancement of GPS for AR&C"— Presentation transcript:
1 Advancement of GPS for AR&C Janet W. BellNASA / JSCMay 23, 2002
2 Contributors NASA-JSC UT @ Austin / Center for Space Research: Aeroscience & Flight Mechanics DivisonBoeingTitan-LinCom (Dr. Kevin Key)GeoControlsAustin / Center for Space Research:Dr. Glenn LightseyTexas A&M Commercial Space Center for Engineering:Dr. John CrassidisUniversity of Houston Applied Electromagnetics Laboratory :Dr. Jeffery WilliamsDr. L. S. ShiehDr. G. Ron ChenSteve ProvenceCSDL
3 JSC GPS Navigation Experience Includes:MAGR Flight Test ProgramGANE (GPS Attitude Navigation Experiment)STS-80 SPAS relative navigation RMEFirst GPS/INS space-flights (for RLV Program)Litton LN-100G on STS-81Honeywell H764-G on STS-84SIGI Series of Flight Tests, starting with STS-86SOAR (SIGI Operational Attitude Readiness) STS-106X-38 SIGI flight tests (STS-100, -108, ’01)Operational ISS SIGI, STS-110, 04/02
4 Some LessonsComplex / costly DDT&E & SE&I with use of proprietary commercial GPS receivers targeted to military vs. spaceMust have Open Systems ArchitecturePerform precision (few-m/cm) navigation and attitude determination investigations in ground / spaceAlgorithms must be designed for space vs. retrofitSupport integration with other sensors (INS, optics,etc.)Mitigate signal blockage, reflection multi-path, etc.GPS & INS are complementary technologiesLow power / size / weight mandatoryMiniaturization / MEMs a primary goal
5 Key GPS Technology Areas for AR&C Open Architecture GPS Receiver (X-GPSR: Experimental GPS Receiver)GPS Augmentation (INS, VisNAV etc.)Reduced Surface Wave AntennaMultipath Mitigation
6 X-GPSR Status To-Date1997, developed open architecture Plessey chipset GPS receiver for Houston Ship Channel Authority heading determination (SCR)Modified SCR firmware to conduct GPS pseudolite precision relative navigation investigationsCross-strapped 2 SCR’s to evaluate attitude capabilityConducted periodic trades of GPS chipsets, chipset-based receivers available worldwideChipset-based GPS receiver benchmark underway, 5/02 – 9/02 (SCR, Zarlink Orion, GSFC PiVoT, JPL BlackJack, SSTL SGR, Trimble Force 19, Novatel Millenium, etc.)Initiated X-GPSR development
7 X-GPSR Components Open architecture L1 frequency PVT / Attitude capableIntegrate with INS and other sensorsKalman filter designed for space vs. retrofitOrbital dynamics model, including fast gravity model (vs aircraft dynamics)Maneuver detection & measurementMultipath Mitigation MethodsGPS antenna technology (RSW)
8 GPS / INS IntegrationPursue techniques with high probability to maximize performance:Tracking loop & filtering algorithms for rapid acquisition & measurement of GPS signals Austin)CSDL “Deep Integration”When GPS signals are blocked, INS data actively controls GPS correlators to account for frequency uncertainty and changing pseudoranges. When GPS returns, the GPS correlators are already positioned to detect lock. Reacquisition is rapid and INS realigns.Select INS to optimize cost & requirementsSeveral CSDL candidates, including MEMS
9 X-GPSR Multipath Mitigation Generic GPS Receiver ComponentsRF Down Conversion: GHz to Intermediate Frequency ~1 MHzIF Tracking Loops: Maintain lock on incoming GPS SignalsNavigation Algorithms: Generate Receiver’s PVT solutionMultipath Mitigation ConceptsNew Hardware: Feedback error estimates of multipath to hardware that compensates incoming signal for multipathTracking Loop Modifications: Use multiple correlators for multipath estimation or new state space approach to tracking loopsNavigation Estimation Strategies: Estimate multipath error as part of the Kalman filter approach to navigation
10 Adaptive Self-tuning GPS Filter (UH/Shieh/Chen) FocusMinimize the effects of noise, particularly multipath, on the pseudorange measurementsProvide accurate and rapid pseudorange solutions in poor environments, using:Adaptive controlUncertain noise estimationNonlinear system modelChaotic System ModelAdaptive System BlockNonwhite bounded noise
11 Adaptive Self-tuning GPS filter ObjectivesPseudorange measurement results resistant to nonwhite noiseFast and accurate pseudorange solution with a small number of GPS satellites, pseudolites or combinationMinimal computational processor loadApproachAdaptive controller & nonlinear modelMultipath mitigation with uncertain noise analysis implementationReal-time parameter identification of nonlinear system modelDigital Redesign techniques to reduce model complexity
12 Reduced Surface Wave (RSW)Antennas Due to surface and lateral waves, conventional patch designs are sensitive to their support structure and low angle multipath signals.Shorted Annular Ring (SAR) RSW antennaOuter radius designed to eliminate surface and lateral wavesInner radius designed to resonant at the design frequency.
14 Areas of Continuing Work Multipath rejectionImproved feed and fabrication techniques to enhance pattern performance.Stable phase centerStudy the general phase center characteristics of microstrip patch antennas.Measurement of phase center for RSW antennas.Improved feed techniques.Dual band (L1 & L2) operationDevelopment of dual band RHCP RSW designs.
15 Navigation Systems & Technology Lab Resources NSTL16A/1004GPS Receivers / NavSensors / RSW AntennasGPS PseudolitesMotionPlatformRoof-top2-AxisPositionerESD Certified Laboratory1553, 422, 488EthernetRFVME’s, SUN’s,Power HawkRapid Development Lab 16A/1169GPS Signal Generator3-Axis Rate TableReal TimeSimulation PlatformRapid Development Lab16A/2115
16 JSC Navigation Systems & Technology Lab - To develop, test & evaluate advanced space navigation systems and technologies- Evaluate GPS stand-alone and by fusing with multiple sensor technologies ( RF, INS, optics, Magnetometers, etc.)- Current Technology Investigations:Pseudolite-Enhanced Relative Position & Attitude Det.Investigates use of a localized GPS-like satellite constellation for GPS applications where signal blockage is an issueExperimental GPS Receiver (X-GPSR)Reduced Surface Wave (RSW) Antenna for GPSMini-Aercam (ISS co-orbiting vehicle)FIRE precision relative navigation filterVisNAV optical sensor for precision relative navigation
18 Experimental GPS Receiver (X-GPSR) For Advancement of SLI Navigation SystemsProducts/BenefitsProductsA non-proprietary, configurable, modifiable GPS receiver capable of performing precision navigation and attitude determination investigations in ground and space applications (X-GPSR)BenefitsOvercomes proprietary issues prevalent throughout industryGrowth path to integrate with different bus architectures (PCI, VME, 1553, etc.)Benchmark for nav systems & GPS/INS filters in MSFC RITAT TestbedGrowth path to SLI flight navigation system & MEMS scaleCustomersMSFC RITAT Testbed, SLI Contractors , Nav Sys Designers, NASA Centers, U.S. Labs, Universities, multiple ground/space applicationsX-cutting/Unique to ProjectOvercomes proprietary limitations; GPS & pseudolite modesImplementation/MetricsFY0203040506TotalCurrent State of the ArtComplex and costly development and integration due to proprietary receivers; vendor receivers targeted to military vs. space.Performance MetricsMeets SLI navigation requirements; supports GPS and pseudolite modes; cost reduction in development turn-around time by providing for open evaluation of multiple nav systems; cost reduction by providing path to SLI flight system.RisksContinuation of funding and availability of key personnel.ParticipantsJSC, U of Texas Austin, Texas A&M, U of Houston.2Prototype Evaluation3Breadboard EvaluationTRL4Flight Version, Testing & Ground Demo56Ground FEU, Testing & DemoSpace Demo7
19 Possible Multipath Mitigation Schemes RF Down Conversion: Take GHz down to Intermediate Frequency (IF)IF Tracking Loops: Maintain lock on incoming GPS SignalsLocal Oscillator: Used to generate a reference signalsNavigation Algorithms: Generate Receiver’s PVT solution for users
20 New Hardware for Multipath Mitigation Takes input from tracking loop estimates of multipath and navigation estimate of multipathUse Xt-1 estimate of multipath to compensate signal at XtUse loop error & covariance to determine amplitude and direction of compensationMultipathCompensatorTrackingLoopsNavigation SystemReceivedSignalNavigation errorTracking error
21 Tracking Loop Modifications Digital Signal Processing of Uncertain Noise ParametersMultipath fits in the category of uncertain noiseUse novel state space techniques to estimate multipathUse of several correlators to estimate multipath effectsA 4 RF receiver with 4 x 12 channels could be designed to track 1 sv 4 timesTrack early and late with variable chip sizes for correlation peak estimation (and therefore, multipath estimation)Use FIRs to estimate/compensate multipathUse knowledge of navigation message to determine error between received signal and expected signal
22 Navigation Estimate of Multipath Estimate the multipath as part of the Navigation solutionUse phase along with the pseudorange in filterPhase has small multipathPhase has ambiguityPossibly use the “Code Minus Carrier” observable to estimate multipathInclude channel multipath in a Kalman filter implementation of PVATDerive a multipath mapping algorithmThe algorithm should be computational efficientThe algorithm could be applied to any large space structureApply a multipath mapping algorithm to space based platformsUse “in situ” data to refine the mapping algorithm for a particular space based vehicle
23 Some notes on Digital Redesign & the Nonlinear Model Digital Redisgn is a technique for converting a continuous time control system into adigital system. Industry primarily uses the Bilinear transform method, but often with poorresults. Dr. Shieh developed the adaptive, self-tuning approach in 1981 (see below).The method is very well received in the controls community.Overall approach:The foundation is from a system Dr. Shieh worked onin 1981 for the Red Stone Arsenal in Huntsville Alabama.At that time, it was the very first parameter identificationtechniques of it’s kind. He revised it over the years. In 1999,he and Dr. Chen began seeing if the systemcould track and control a chaotic system. With slightmodifications / improvements they’ve been able to achievetheir goal of chaotic system tracking.The system has a strong history of working (1981 version still in use today in military),with new adaptations (chaos analysis) that improve the scheme.
24 CSDL CSDL Deep Integration Details GPS tracking loop is built into the Nav filter. Filter accepts I & Q signals from correlator and then drives GPS oscillator.Kalman filter replaced by non-linear estimator with adaptive gain as a function of measured S/N ratio.Longer coherent integration period obtained by using knowledge of the bits associated with data messageDraper's Deep Integration techniqueNot dependent on proprietary GPS designs. Open architectures will work.Not dependent on specific INS devices. MEMS, IFOGsGPS need only be a "component" chipset capable of I/O outputs and control of correlators.
25 CSDL Integrated INS/GPS Deep Integration Provides:Code tracking: 15 to 20 db anti-jam performance improvement against Gaussian jammers. Hangs on to signal longer at onset of GPS blockageRe-acquisition: 2 to 3 times better error tracking range vs. tightly-coupled systems. Increasing parallelism of correlators further improves re-acquisitionOverall, shortens the no-GPS period, shortens INS-only flight
26 MEMS & Alternates MEMS Draper is a world leader in MEMS technology Draper MEMS devices are used in a 9 in3, 3 watt package fired from a 5" Naval gunWhere MEMS devices meet performance requirements, MEMS provides an extremely robust, low cost/volume/power INS solution