1. Riding out the Rough Spots: Scintillation-Robust GNSS Carrier Tracking Dr. Todd E. Humphreys Radionavigation Laboratory University of Texas at Austin

2.  UT Radionavigation Laboratory UT Radionavigation Lab Research Agenda  GNSS Spoofing  Characterize spoofing signatures  Develop receiver-autonomous defenses  Develop augmentation-based defenses (GPS + eLORAN + Iridium + …)  GPS Jamming  Develop augmentation-based defenses  Locate jamming sources by combining data from a network of receivers  Indoor Navigation  Pioneer collaborative navigation  Develop augmentation-based indoor nav techniques (GPS + eLORAN + Iridium + …)  Natural GNSS Interference  Improve tracking loop robustness to scintillation

3.  UT Radionavigation Laboratory Ionospheric Diagnosis via Arrays of GPS Receivers  Ionospheric Monitoring (sparse array)  Ionospheric Tomography (dense array) Incident plane wave Disturbed ionosphere Diffracted wavefront Linear array of GRID receivers Nominal magnetic field direction CASES Connected Autonomous Space Environment Sensors Cornell University, UT Austin, ASTRA LLC AFOSR STTR Proposal, 2008 CASES Connected Autonomous Space Environment Sensors Cornell University, UT Austin, ASTRA LLC AFOSR STTR Proposal, 2008

4.  UT Radionavigation Laboratory CASES Sensor Evolution

5.  UT Radionavigation Laboratory Carrier Tracking Goals  Receiver noise and  scintillation-induced  phase errors Cycle slips (phase unlock) Total loss of carrier lock (frequency unlock) Analyze scintillation effects on GPS receivers; isolate cause of phase unlock Model scintillation well enough to generate realistic synthetic scintillation Synthesize scintillation to test tracking loop strategies Design phase tracking loops for operation in scintillation  Strategy  Long-term Goals Eliminate frequency unlock Minimize cycle slips and generally reduce phase errors

6.  UT Radionavigation Laboratory Carrier Tracking Goals Analyze scintillation effects on GPS receivers; isolate cause of phase unlock Model scintillation well enough to generate realistic synthetic scintillation Synthesize scintillation to test tracking loop strategies Design phase tracking loops for operation in scintillation  Long-term Goals Eliminate frequency unlock Minimize cycle slips and generally reduce phase errors  Strategy

7.  UT Radionavigation Laboratory Analyze: The Empirical Scintillation Library  Canonical fades

8.  UT Radionavigation Laboratory Fading Interpreted on the Complex Plane

9.  UT Radionavigation Laboratory Model: Distill Scintillation Down to Essential Characteristics for Carrier Tracking Standard statistical analysis techniques Standard statistical analysis techniques DPSK bit error prediction with Rice and 2 nd -order Butterworth models

10.  UT Radionavigation Laboratory Synthesize: Turn the Model Around

11.  UT Radionavigation Laboratory Scintillation Simulator Implementation

12.  UT Radionavigation Laboratory Hardware-in-the-loop Scintillation Robustness Evaluation  Scintillation SimulatorSimulated time history GNSS Signal Simulator GNSS Receiver  Phase difference time history

13.  UT Radionavigation Laboratory Design: Scintillation-hardened Tracking Loops Straightforward approach: navigation data bit prediction Incorporate the observed second-order dynamics into a Kalman filter whose state includes the complex components of z(t) Combine this with a Bayesian multiple-model filter that spawns a new tracking loop whenever a data bit is uncertain. Prune loops at parity check. GOAL: Ts > 240 seconds for {S 4 = 0.8,  0 = 0.8 sec., C/N0 = 43 dB-Hz} (a factor of 10 longer than current best) GOAL: Ts > 240 seconds for {S 4 = 0.8,  0 = 0.8 sec., C/N0 = 43 dB-Hz} (a factor of 10 longer than current best)

14.  UT Radionavigation Laboratory Traditional Approach to Carrier Modeling

15.  UT Radionavigation Laboratory A New Approach to Carrier Modeling

16.  UT Radionavigation Laboratory A Multiple-Model Approach to Data Bit Estimation

17.  UT Radionavigation Laboratory The GPS Assimilator The GPS Assimilator modernizes and makes existing GPS equipment resistant to jamming, spoofing, and scintillation without requiring hardware or software changes to the equipment  A Backward-Compatible Way to Harden Existing UE Against Scintillation

18.  UT Radionavigation Laboratory  All digital signal processing implemented in C++ on a high-end DSP  Marginal computational demands:  Tracking: ~1.2% of DSP per channel  Simulation: ~4% of DSP per channel  Full capability:  12 L1 C/A & 10 L2C tracking channels  8 L1 C/A simulation channels  1 Hz navigation solution  Acquisition in background GPS Assimilator Prototype

19.  UT Radionavigation Laboratory Summary  Models of scintillation effects on phase tracking loops must faithfully capture deep fades  The mean time between differentially-detected navigation bit errors is a good lumped indicator of scintillation severity  The triple accurately predicts  For carrier tracking, scintillation modeling & simulation can be boiled down to two parameters: S 4 & τ 0  A hardware-in-the-loop scintillation testbed has been built and validated  Carrier tracking techniques inspired by the proposed model promises to extend

20.  UT Radionavigation Laboratory Acknowledgements  CASES sensor development funded by STTR grant through AFOSR via ASTRA LLC  Adaptation of CASES sensor for Antarctic deployment funded by ASTRA LLC

21.  UT Radionavigation Laboratory Model: Link Cycle Slips to Differentially-Detected Bit Errors

22.  UT Radionavigation Laboratory Amplitude Distribution: Rice distribution applies p(|z(t)|) can be summarized by the S 4 index Rice distribution applies p(|z(t)|) can be summarized by the S 4 index

23.  UT Radionavigation Laboratory Autocorrelation Function: Empirical Spectrum vs. Models 2 nd -order Butterworth autocorrelation model applies R  (  ) can be summarized by  0 2 nd -order Butterworth autocorrelation model applies R  (  ) can be summarized by  0