GPS and GLONASS Vector Tracking for Navigation in Challenging Signal Environments Tanner Watts, Scott Martin, and David Bevly GPS and Vehicle Dynamics Lab – Auburn University October 29, 2019 2 GPS Applications (GAVLAB) Truck Platooning Good GPS Signal Environment Autonomous Vehicles Precise Timing UAVs 3 Challenging Signal Environments • Navigation demand increasing in the following areas: • Cites/Urban Areas • Forests/Dense Canopies • Blockages (signal attenuation) • Reflections (multipath) 4 Contested Signal Environments • Signal environment may experience interference • Jamming . Transmits “noise” signals to receiver . Effectively blocks out GPS • Spoofing . Transmits fake GPS signals to receiver . Tricks or may control the receiver 5 Contested Signal Environments • These interference devices are becoming more accessible GPS Jammers GPS Simulators 6 Traditional GPS Receiver Signals processed individually: • Known as Scalar Tracking • Delay Lock Loop (DLL) for Code • Phase Lock Loop (PLL) for Carrier 7 Traditional GPS Receiver • Feedback loops fail in the presence of significant noise • Especially at high dynamics Attenuated or Distorted Satellite Signal 8 Vector Tracking Receiver • Process signals together through the navigation solution • Channels track each other’s signals together • 2-6 dB improvement • Requires scalar tracking initially 9 Vector Tracking Receiver Vector Delay Lock Loop (VDLL) • Code tracking coupled to position navigation • DLL discriminators inputted into estimator • Code frequencies commanded by predicted pseudoranges 10 Vector Tracking Receiver Vector Frequency Lock Loop (VFLL) • Doppler tracking coupled to velocity navigation • FLL discriminators inputted into estimator • Dopplers commanded by predicted pseudorange- rates 11 James Spilker’s Vector Delay Lock Loop Individual Navigation Tracking Processor Loops Feedback Measurement to Tracking Predictions Loops 12 GLONASS • GNSS owned and operated by Russian Federation • GLONASS L1 Signal: ▫ L1 BPSK modulated satellite signal ▫ 50 kcps PRN code (half of GPS) ▫ 50 bps data message (same as GPS) ▫ FDMA over CDMA • Vector tracking can also be applied to this signal 13 GLONASS Recording Capability IFEN SX3: . Records both GPS and GLONASS L1 . Separate front-ends IFEN SX3 Front-End . 20 MHz sampling rate, 50 MHz bandwidth for each front-end . Same clock (TCXO) . Allows for easy data synchronization 14 GLONASS Recording Capability Time Estimation: TOD = mod TOW, 86400 s + 3 h 18 s TOD = GLONASS Time of Day s − − τ IFEN SX3 Front-End TOW = GPS Time of Week (s) 3-hour difference = GLONASS offset from UTC > 1 s between Greenwich, UK and Moscow, Russia Estimateτ 1 clock bias, 1 clock drift, andμ the time offset 15 GLONASS Recording Capability Time Estimation: TOD = mod TOW, 86400 s + 3 h 18 s TOD = GLONASS Time of Day s − − τ IFEN SX3 Front-End TOW = GPS Time of Week (s) = GLONASS offset from UTC > 1 s Estimateτ 1 clock bias, 1 clock drift, andμ the time GLONASS Time accounts offset for leap seconds, UTC does not 16 GLONASS Recording Capability Time Estimation: TOD = mod TOW, 86400 s + 3 h 18 s TOD = GLONASS Time of Day s − − τ IFEN SX3 Front-End TOW = GPS Time of Week (s) = GLONASS offset from UTC > 1 s Estimateτ 1 clock bias, 1 clock drift, andμ the time offset 17 GPS and GLONASS Positioning 24-hour sky plot over Auburn, AL • Enhanced satellite geometry . Overcome environment blockages . Better estimation of PVT • Frequency diversity . Jamming protection • Constellation diversity . Spoofing protection 18 GPS and GLONASS Positioning 24-hour sky plot over Auburn, AL • Defense sector stays away from combining GPS and GLONASS • Most commercial receivers take advantage of both systems . Scalar processing . Federated estimation 19 GPS and GLONASS Vector Tracking • Vector Delay/Frequency Lock Loop (VDFLL) • Centralized Extended Kalman Filter (EKF) • All tracking commands defined solely by PVT solution 20 Navigation Processor State Vector: • ECEF Position (m) • ECEF Velocity (m/s) • Receiver Clock Bias (m/s) • Time Offset (m) • Receiver Clock Drift (m/s) 0 0 0 0 0 0 0 �+1 0 0 0 0 0 0 0 0 �+1 �̇+1 0 0 0 0 0 0 0 �̇+1 �+1 0 0 0 0 0 0 0 0 �+1 = 0 0 0 0 0 Model: �+1 0 0 �+1 ̇ ̇ +1 0 0 0 0 0 0 0 0 +1 ̂ 0 0 0 0 0 0 0 ̂ ̂̇ +1 0 0 0 0 0 0 0 0 ̂̇ +1 Mitigates noise sharing in VDFLL �+1 0 0 0 0 0 0 0 0 �+1 τ�+1 τ�+1 �̇+1 �̇+1 21 Measurement Observation 0 0 0 0 0 1 δρ 0 0 0 ⋮ 0 0 Δ�+1 ⋮ ⋮ ⋮ ⋮ ⋮ ⋮ δρ 0 0 0 0⋮ 0⋮ ⋮ Δ�̇+1 1 δρ̇ +1 GPS Channels 0 0 0 0 0 Δ� = ⋮ ⋮ ⋮ ⋮ +1 ⋮ 0 ⋮ 0 ⋮ 0 ⋮ ⋮ 0⋮ Δ�̇ GLONASS Channels δρ̇ Δ̂+1 1 0 0 0 0 δρ ̂+1 ⋮ ⋮ ⋮ 0⋮ 0⋮ ⋮ Δ̇ ⋮ 0⋮ 0⋮ 0⋮ +1 Δ� δρ +1 0 0 Δτ� δρ̇ 1 0 0 0 ⋮ ⋮ ⋮ ⋮ ⋮ ⋮ �+1 Δ̇ ⋮ ⋮ ⋮ ⋮ =δρ̇Pseudorange Error (Code Phase Error) , , = Receiver to Satellite Unit Vectors δρ = Doppler Error (Carrier Frequency Error) δρ̇ 22 Vector NCO Commands = ( , ) = ( , ) � Code Frequency: = ρ�+1−ρ� �̇ code chip chip = Chipping Rate (cps) = Predicted− λ Pseudorange (m) = PRN Chip Width (m/chip) Tchip= Integration Period (s) ρ� λchip Carrier Frequency: = ρ�̇ carrier IF 1 = Intermediate Frequency (Hz) [Must− λ account for FMDA in GLONASS] = Predicted Pseudorange Rate (m/s) = Carrier Wavelength (m/cyc) IF ρ�̇ λL1 23 ECEF Transformation Matrix • GPS and GLONASS both use ECEF coordinate frames • GPS uses World Geodetic System 1984 (WGS84) • GLONASS uses Parametry Zemli 1990 (PZ-90) . Have used many versions . Current version: PZ-90.11 • Officially, WGS84 and PZ-90.11 are the same . Within centimeters 24 ECEF Transformation Matrix 25 ECEF Transformation Matrix • PZ-90.11 to WGS84 coordinate transformation developed empirically . Based on static data sets in Alabama and Iowa . Differential corrections not used • Coordinate transformation is applied to GLONASS satellite positions • Helps horizontal positioning 30 = WGS84 Position (m) = + 0 m = PZ90.11 Position (m) −0 26 Heavy Tree Foliage Results Combined and Ublox solutions maintain accurate positions on the bridge Exiting Entering Moving Through GPS VDFLL GLONASS VDFLL Combined VDFLL Ublox 27 Urban Canyon Results Vehicle Lane GPS VDFLL GLONASS VDFLL Combined VDFLL Combined Scalar Ublox 28 Urban Canyon Results Exiting Urban Canyon Open Sky Environment GPS VDFLL GLONASS VDFLL Combined VDFLL Ublox 29 Jamming Experiment Jamming Map • GPS L1 jamming tests performed at Edwards Airforce Base • September 2019 • GLONASS L1 not jammed Receiver Trajectory = ⁄ − 30 Jamming Experiment 10 GPS Satellites 5 GLONASS Satellites 31 Jamming Position Results TURN AROUND END START 32 Jamming Position Results GLONASS Fails GPS Fails 33 Jamming C/No Results 4 of 5 GLONASS channels lose lock 10 of 10 GPS channels lose lock 34 Jamming C/No Results 1 GPS and 1 GLONASS channel lose lock 35 Jamming Scalar Results GPS and GLONASS Scalar Tracking Fails Dead Reckoning by Model 36 Jamming Tracking Results 37 Conclusions • Positioning performance improves when using both GPS and GLONASS ▫ With the PZ90.11 to WGS84 coordinate transformation ▫ Be mindful of GLONASS in bad signal environments • Combining GPS and GLONASS into the VDFLL enhances receiver robustness • Need differential data to improve coordinate transformation • Analyze the algorithm in GPS and/or GLONASS spoofing environments 38 Some Future Work • Characterize the estimated offset between GPS and GLONASS times ▫ Requires significantly longer data sets • Potential for many things: ▫ Integrity checking ▫ Spoofing detection ▫ Receiver clock discipling ▫ Satellite clock analysis ▫ GNSS synchronization 39 References • [1] James J. Spilker. Vector Delay Lock Loop Processing of Radiolocation Transmitter Signals, Stanford, CA, March 1995. US Patent 5,398,034. • [2] J. Sennott and D. Senffner. Navigation Receiver with Coupled Signal-Tracking Channels, Bloomington, IL, August 1994. US Patent 5,343,209. • [3] Kai Borre, Dennis Akos, Nicolaj Bertelsen, Peter Rinder, and Soren Holdt Jensen. A Software-Defined GPS and Galileo Receiver: A Single Frequency Approach. Birkhauser, 2007. • [4] Matthew V. Lashley. Modeling and Performance Analysis of GPS Vector Tracking Algorithms. PhD Dissertation, Auburn University, December 2009. • [5] Dennis M. Akos. A Software Radio Approach to Global Navigation Satellite System Receiver Design. PhD Dissertation, Ohio University, August 1997. • [6] Chao-heh Cheng. Calculations for Positioning with the Global Navigation Satellite System. Master’s Thesis, Ohio University, August 1998. • [7] Pratap Misra. Integrated Use of GPS and GLONASS: Transformation Between WGS84 and PZ-90. In Proceedings of ION GPS 1996, Kansas City, MO, September 1996, pp. 307-314. • [8] Senlin Peng. Implementation of Real-Time Sofware Receiver for GPS or GLONASS L1 Signals. Master’s Thesis, Virginia Polytechnic Institute and State University, January 2010. • [9] M. Zhodzishsky, S. Yudanov, V. Veitsel, and J. Ashjaee. Co-OP Tracking for Carrier Phase. In Proceedings of the 11th International Technical Meeting of the Satellite Division of the Institute of Navigation (ION GPS 1998), Nashville, TN, September 1998, pp. 653-664. 40 Thank You Questions? 41 Fault Detection and Exclusion.