27 June 2000IAIN/ION Meeting1 Practical Implementation Considerations in the Detection of GPS Satellite Signal Failure A. J. Van Dierendonck, AJ Systems Dennis Akos, Sam Pullen, Eric Phelts and Per Enge Stanford University

27 June 2000IAIN/ION Meeting2 Topics Paper Objective Satellite Failure Threat Models Airborne Receiver Design Constraints Detection Metric Definitions/Implementation Detection Metric Performance Requirements Detection Metric Performance Some Simulation Results Noise/Interference Considerations Scan Peak Requirements Summary & Conclusions

27 June 2000IAIN/ION Meeting3 Paper Objectives Provide summary and update of SQM requirements Present practical implementation of SQM detection metrics Reason why detection is not as complex as it may seem Provide an update on metric performance Justification for changes to airborne receiver requirements

27 June 2000IAIN/ION Meeting4 Satellite Failure Thread Models

27 June 2000IAIN/ION Meeting5 Undistorted Correlation Function

27 June 2000IAIN/ION Meeting6 Distorted Correlation Function

27 June 2000IAIN/ION Meeting7 Satellite Failure Threat Models Threat A Lead/Lag chips    0.12 chips Threat B Ringing 4 MHz  f d  17 MHz 0.8    8.8 Threat C Combination chips    0.12 chips 4 MHz  f d  17 MHz 0.8    8.8

27 June 2000IAIN/ION Meeting8 Threat Model A

27 June 2000IAIN/ION Meeting9 Threat Model B

27 June 2000IAIN/ION Meeting10 Threat Model C

27 June 2000IAIN/ION Meeting11 Airborne Receiver Design Constraints

27 June 2000IAIN/ION Meeting12 Airborne E-L Discriminator Constraint Space Region 3 dB Precorrelation bandwidth (MHz) Average Correlator Spacing (Chips) Instantaneous Correlator Spacing (Chips) Differential Group Delay (nsec) 1 2 < BW   < BW   < BW   < BW  – – 0.13  150

27 June 2000IAIN/ION Meeting13 Airborne  Discriminator Constraint Space Region3 dB Precorrelation bandwidth (MHz) Average Correlator Spacing (Chips) Instantaneous Correlator Spacing (Chips) Differential Group Delay (nsec) 1 2 < BW  – – 0.65  < BW   < BW   150

27 June 2000IAIN/ION Meeting14 SQM Detection Metric Definitions/Implementation Don’t require pseudoranges Don’t need a “picket fence”

27 June 2000IAIN/ION Meeting15 Close-in Correlation Function Values

27 June 2000IAIN/ION Meeting16 SQM2b Test Metrics Can use more ratios

27 June 2000IAIN/ION Meeting17 Detection Thresholds, Mean Values, MDEs and MDRs Real World Thresholds, Mean Values Used for Simulations (Include missed detection probability)

27 June 2000IAIN/ION Meeting18 Fault-Free Probability Densities

27 June 2000IAIN/ION Meeting19 Metric Statistics Based upon Stanford and NovAtel Roof Tests Two environmental extremes Multipath dominates noise and interference

27 June 2000IAIN/ION Meeting20 Difference Metric Performance Comparisons

27 June 2000IAIN/ION Meeting21 Ratio Metric Performance Comparisons

27 June 2000IAIN/ION Meeting22 Some Simulation Results Justify simple metric definition Justify change in airborne receiver design constraints Additional constraints on  discriminator receivers Smaller constraint space Reduction of constraints on E – L discriminator receivers Larger constraint space No “Scan Peak” requirement

27 June 2000IAIN/ION Meeting23  Discriminator Error Performance – SQM3

27 June 2000IAIN/ION Meeting24  Discriminator Error Performance – SQM2b

27 June 2000IAIN/ION Meeting25 Threat Model C E-L Discriminator Protection Results

27 June 2000IAIN/ION Meeting26 Summary & Conclusions SQM doesn’t have to be exceeding complex Use correlation function amplitude measurements instead of PRs Performance is dominated by multipath Performance varies widely with environment Performance simulations are useful to define airborne receiver design constraints  constraint space E – L scan peak requirement DoD receiver accommodation