Bi-Directional DGPS for Range Safety Applications

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Evelyn Manning
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1 Bi-Directional DGPS for Range Safety Applications Ranjeet Shetty 234-A, Avionics Engineering Center, Russ College of Engineering and Technology, Ohio University Advisor: Dr. Chris Bartone

2 Outline Background DGPS Remote Positioning Bi-Directional DGPS System Instantaneous Impact Point Conclusion Overflight Exclusion Zone Flight Corridor

3 Differential GPS DGPS requires a Reference Station (surveyed location) that processes the GPS signals, derives the pseudo-range corrections with respect to its known location and transmits them to the mobile users in the area. Common error sources are either corrected or eliminated Accuracy can range from sub-meter to 10 meters

its known location and transmits them to the mobile users in the area.

4 Errors Eliminated by DGPS Ionospheric Delay: m during the afternoon and 1 6 m at night. Dependent on latitude and time of day, solar cycle. Tropospheric Delay: Up to 30 m for a low elevation satellite. Dependent on Elevation Angle. Ephemeris Errors: Typically 1 3 m Satellite Clock Error

Tropospheric Delay: Up to 30 m for a low elevation satellite.

5 Errors not eliminated by DGPS Receiver Noise Uncorrelated Multipath Spatial Decorrelation : Changes with distance in Ionosphere and Troposphere Temporal Decorrelation : Changes with time

6 DGPS Illustration GPS Space Segment Navigation Signals Mobile User Data Link Antenna Differential Pseudo-range Corrections Data Link Antenna Navigation Signals Differential Reference Station

7 DGPS at Ground Station Data Link Antenna Freewave Radio GPS Receiver PC with QNX operating system Measured Pseudo-range Ephemeris SV Time Position SV Clock Corrections Smoothing Filter Measured Integrated Doppler Reference Position - Range - Clock Bias Estimation - Pseudo-range Corrections

Position SV Clock Corrections Smoothing Filter Measured Integrated

8 DGPS at Mobile User Data Link Antenna GPS Receiver Freewave Radio PC with QNX operating system SV Clock Corrections Tropospheric Corrections Measured Pseudo-range Smoothing Filter Measured Integrated Doppler High Accuracy Position Solution Pseudo-range Corrections

Corrections Measured Pseudo-range Smoothing Filter Measured

9 Remote-Positioning (stand-alone) System GPS Space Segment Navigation Signals Unmanned Airborne Vehicle (UAV) Data Link Antenna Measurement and Position Data Link Antenna Remote Positioning Ground Station (GPS stand-alone)

(UAV) Data Link Antenna Measurement and Position Data

10 Remote-Positioning DGPS System GPS Space Segment Navigation Signals Navigation Signals Unmanned Airborne Vehicle (UAV) Data Link Antenna Measurement and Position Data Link Antenna Remote Positioning Ground Station (DGPS)

Airborne Vehicle (UAV) Data Link Antenna Measurement

11 Remote-Positioning DGPS at Mobile User Data Link Antenna Freewave Radio GPS Receiver PC with QNX operating system Measured Pseudo-range Measured Integrated Doppler

12 Remote-Positioning at Ground Station Data Link Antenna Freewave Radio GPS Receiver PC with QNX operating system Measured Pseudo-range Ephemeris SV Time Position SV Clock Corrections Smoothing Filter Measured Integrated Doppler Reference Position - Range - Clock Bias Estimation Pseudo-range Corrections - User s Pseudo-range User s Integrated Doppler Tropospheric Corrections Smoothing Filter SV Clock Corrections High Accuracy Position Solution

Doppler Reference Position - Range - Clock Bias Estimation Pseudo-range Corrections - User s Pseudo-range User

13 Positioning Requirements Uplink Differential Pseudo-range Corrections Enables high accuracy position solution at the user end Enables auto pilot, precision landing, etc Downlink Measurement and Position Enables high accuracy position solution of the remote user at the ground station Can track the UAV from a remote position We want both - Simultaneously

Downlink Measurement and Position Enables high accuracy position solution of the remote

14 Bi-directional DGPS System GPS Space Segment Unmanned Airborne Vehicle (UAV) Navigation Signals Data Link Antenna Differential Pseudorange Corrections Measurement and Position Data Link Antenna Navigation Signals Remote Positioning Ground Station (DGPS)

Pseudorange Corrections Measurement and Position Data Link

15 Bi-directional DGPS Mobile User Data Link Antenna GPS Receiver Freewave Radio PC with QNX operating system SV Clock Corrections Tropospheric Corrections Measured Pseudo-range Smoothing Filter Measured Integrated Doppler High Accuracy Position Solution Pseudo-range Corrections

Tropospheric Corrections Measured Pseudo-range Smoothing Filter

16 Bi-Directional DGPS Ground Station Data Link Antenna Freewave Radio GPS Receiver PC with QNX operating system User s Pseudo-range User s Integrated Doppler Ephemeris SV Time Position Reference Position Range Clock Bias Estimation SV Clock Corrections Measured Pseudo-range - - Smoothing - Filter Measured Integrated Doppler Pseudo-range Corrections Tropospheric Corrections Smoothing Filter SV Clock Corrections Calculated High Accuracy Position Solution Transmitted High Accuracy Position Solution - Integrity Threshold Use/Don t Use

Pseudo-range - - Smoothing - Filter Measured Integrated Doppler Pseudo-range Corrections Tropospheric Corrections Smoothing Filter SV

17 Instantaneous Impact Point Instantaneous Impact Point (IIP) - Continuous plot on the ground of where the vehicle would impact. Computed from the vehicles instantaneous velocity, current position and time to impact Displayed in real time during the flight IIP uncertainties Less than 100 ft for the Eastern Range Less than 1000 ft for the Western Range Impact Limit Lines (ILL) - Defined boundaries beyond which significant pieces of debris should not penetrate.

Computed from the vehicles instantaneous velocity, current position and time to impact Displayed in real time

18 IIP Illustration t = t2 t = t1 Projection ILL X t = t1 X t = t2 IIP ILL

19 Launch Parameters Debris Dispersion Radius(D max ): Radius of a circular area indicating limits for flight control and explosive containment. Overflight Exclusion Zone: Area in close priximity to a launch point where mission risk is high. Should be clear of public. Flight Corridor: Area on the earth s surface estimate to contain majority of the hazardous debris from nominal flight.

Overflight Exclusion Zone: Area in close priximity to a launch point where mission risk is high.

20 Overflight Exclusion Zone Flight Azimuth D max D oez D max Launch Point

21 Flight Corridor D Left Boundary C H Uprange Boundary B Launch Point Nominal Trajectory G F 10 NMi 100 NMi Launch Area E Downrange Area 5000 NMi Right Boundary I Downrange Boundary

22 Flight Corridor - Guided Launch Vehicles Uprange Boundary C D Left Boundary Downrange Boundary B Launch Point Nominal Trajectory Final Stage Impact Dispersion Area G Impact Range (D) R F 10 NMi 100 NMi Launch Area E Right Boundary Downrange Area

23 Conclusion DGPS historically used to provide high accuracy position solution at mobile user for their use. DGPS Remote Positioning is applied to autonomous determination of a vehicle position at a remote location. Application of DGPS for IIP application is new. Bi-Directional DGPS System will provide high accuracy position solution at the mobile user as well as autonomous determination of vehicle position at a remote location for IIP applications.

GENERAL INFORMATION ON GNSS AUGMENTATION SYSTEMS

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