GPS and GLONASS Vector Tracking for Navigation in Challenging Signal Environments

Tanner Watts, Scott Martin, and David Bevly

GPS and Vehicle Dynamics Lab – Auburn UniversityOctober 29, 2019

GPS Applications (GAVLAB)

2

Autonomous Vehicles

TruckPlatooning

PreciseTiming

UAVs

Good GPS SignalEnvironment

Challenging Signal Environments

• Navigation demand increasing in the following areas:

• Cites/Urban Areas

• Forests/Dense Canopies

• Blockages (signal attenuation)

• Reflections (multipath)

3

Contested Signal Environments

4

• 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

Contested Signal Environments

5

• These interference devices are becoming more accessible GPS Jammers

GPS Simulators

Traditional GPS Receiver

6

Signals processed individually:

• Known as Scalar Tracking

• Delay Lock Loop (DLL) for Code

• Phase Lock Loop (PLL) for Carrier

Traditional GPS Receiver

7

Attenuated or DistortedSatellite Signal

• Feedback loops fail in the presence of significant noise

• Especially at high dynamics

Vector Tracking Receiver

8

• Process signals together through the navigation solution

• Channels track each other’s signals together

• 2-6 dB improvement

• Requires scalar tracking initially

Vector Tracking Receiver

9

Vector Delay Lock Loop (VDLL)

• Code tracking coupled to position navigation

• DLL discriminators inputted into estimator

• Code frequencies commanded by predicted pseudoranges

Vector Tracking Receiver

10

Vector Frequency Lock Loop(VFLL)

• Doppler tracking coupled to velocity navigation

• FLL discriminators inputted into estimator

• Dopplers commanded by predicted pseudorange-rates

James Spilker’s Vector Delay Lock Loop

11

IndividualTracking

LoopsNavigationProcessor

MeasurementPredictions

Feedbackto Tracking

Loops

GLONASS

12

• 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

GLONASS Recording Capability

13

IFEN SX3 Front-End

IFEN SX3: Records both GPS and GLONASS L1

Separate front-ends

20 MHz sampling rate, 50 MHz bandwidth for each front-end

Same clock (TCXO)

Allows for easy data synchronization

GLONASS Recording Capability

14

IFEN SX3 Front-End

Time Estimation:TOD = mod TOW, 86400 s + 3 h − 18 s − τ

TOD = GLONASS Time of Day s

TOW = GPS Time of Week (s)

τ = GLONASS offset from UTC > 1 μs

Estimate 1 clock bias, 1 clock drift, and the time offset

3-hour difference between Greenwich, UK

and Moscow, Russia

GLONASS Recording Capability

15

IFEN SX3 Front-End

GLONASS Time accounts for leap seconds, UTC

does not

Time Estimation:TOD = mod TOW, 86400 s + 3 h − 18 s − τ

TOD = GLONASS Time of Day s

TOW = GPS Time of Week (s)

τ = GLONASS offset from UTC > 1 μs

Estimate 1 clock bias, 1 clock drift, and the time offset

GLONASS Recording Capability

16

IFEN SX3 Front-End

Time Estimation:TOD = mod TOW, 86400 s + 3 h − 18 s − τ

TOD = GLONASS Time of Day s

TOW = GPS Time of Week (s)

τ = GLONASS offset from UTC > 1 μs

Estimate 1 clock bias, 1 clock drift, and the time offset

GPS and GLONASS Positioning

17

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

GPS and GLONASS Positioning

18

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

GPS and GLONASS Vector Tracking

19

• Vector Delay/Frequency Lock Loop (VDFLL)

• Centralized Extended Kalman Filter (EKF)

• All tracking commands defined solely by PVT solution

Navigation Processor

20

State Vector:• ECEF Position (m)• ECEF Velocity (m/s)• Receiver Clock Bias (m/s)• Time Offset (m)• Receiver Clock Drift (m/s)

Model:

�𝑥𝑥𝑘𝑘+1�̇𝑥𝑥𝑘𝑘+1�𝑦𝑦𝑘𝑘+1�̇𝑦𝑦𝑘𝑘+1�̂�𝑧𝑘𝑘+1̂̇𝑧𝑧𝑘𝑘+1�𝑏𝑏𝑘𝑘+1�τ𝑘𝑘+1�̇𝑏𝑏𝑘𝑘+1

=

𝟏𝟏00000000

𝑻𝑻𝟏𝟏0000000

00𝟏𝟏000000

00𝑻𝑻𝟏𝟏00000

0000𝟏𝟏0000

0000𝑻𝑻𝟏𝟏000

000000𝟏𝟏00

0000000𝟏𝟏0

000000𝑻𝑻0𝟏𝟏

�𝑥𝑥𝑘𝑘+1�̇𝑥𝑥𝑘𝑘+1�𝑦𝑦𝑘𝑘+1�̇𝑦𝑦𝑘𝑘+1�̂�𝑧𝑘𝑘+1̂̇𝑧𝑧𝑘𝑘+1�𝑏𝑏𝑘𝑘+1�τ𝑘𝑘+1�̇𝑏𝑏𝑘𝑘+1

Mitigates noise sharing in VDFLL

Measurement Observation

21

δρ1𝐺𝐺𝐺𝐺𝐺𝐺⋮

δρ𝑛𝑛𝐺𝐺𝐺𝐺𝐺𝐺δρ̇1𝐺𝐺𝐺𝐺𝐺𝐺⋮

δρ̇𝑛𝑛𝐺𝐺𝐺𝐺𝐺𝐺δρ1𝐺𝐺𝐿𝐿𝐿𝐿⋮

δρ𝑚𝑚𝐺𝐺𝐿𝐿𝐿𝐿

δρ̇1𝐺𝐺𝐿𝐿𝐿𝐿⋮

δρ̇𝑚𝑚𝐺𝐺𝐿𝐿𝐿𝐿

=

𝒂𝒂𝒙𝒙𝟏𝟏𝑮𝑮𝑮𝑮𝑮𝑮⋮

𝒂𝒂𝒙𝒙𝒏𝒏𝑮𝑮𝑮𝑮𝑮𝑮0⋮0

𝒂𝒂𝒙𝒙𝟏𝟏𝑮𝑮𝑳𝑳𝑳𝑳⋮

𝒂𝒂𝒙𝒙𝒎𝒎𝑮𝑮𝑳𝑳𝑳𝑳0⋮0

0⋮0

𝒂𝒂𝒙𝒙𝟏𝟏𝑮𝑮𝑮𝑮𝑮𝑮⋮

𝒂𝒂𝒙𝒙𝒏𝒏𝑮𝑮𝑮𝑮𝑮𝑮0⋮0

𝒂𝒂𝒙𝒙𝟏𝟏𝑮𝑮𝑳𝑳𝑳𝑳⋮

𝒂𝒂𝒙𝒙𝒎𝒎𝑮𝑮𝑳𝑳𝑳𝑳

𝒂𝒂𝒚𝒚𝟏𝟏𝑮𝑮𝑮𝑮𝑮𝑮⋮

𝒂𝒂𝒚𝒚𝒏𝒏𝑮𝑮𝑮𝑮𝑮𝑮0⋮0

𝒂𝒂𝒚𝒚𝟏𝟏𝑮𝑮𝑳𝑳𝑳𝑳⋮

𝒂𝒂𝒚𝒚𝒎𝒎𝑮𝑮𝑳𝑳𝑳𝑳0⋮0

0⋮0

𝒂𝒂𝒚𝒚𝟏𝟏𝑮𝑮𝑮𝑮𝑮𝑮⋮

𝒂𝒂𝒚𝒚𝒏𝒏𝑮𝑮𝑮𝑮𝑮𝑮0⋮0

𝒂𝒂𝒚𝒚𝟏𝟏𝑮𝑮𝑳𝑳𝑳𝑳⋮

𝒂𝒂𝒚𝒚𝒎𝒎𝑮𝑮𝑳𝑳𝑳𝑳

𝒂𝒂𝒛𝒛𝟏𝟏𝑮𝑮𝑮𝑮𝑮𝑮⋮

𝒂𝒂𝒛𝒛𝒏𝒏𝑮𝑮𝑮𝑮𝑮𝑮0⋮0

𝒂𝒂𝒛𝒛𝟏𝟏𝑮𝑮𝑳𝑳𝑳𝑳⋮

𝒂𝒂𝒛𝒛𝒎𝒎𝑮𝑮𝑳𝑳𝑳𝑳0⋮0

0⋮0

𝒂𝒂𝒛𝒛𝟏𝟏𝑮𝑮𝑮𝑮𝑮𝑮⋮

𝒂𝒂𝒛𝒛𝒏𝒏𝑮𝑮𝑮𝑮𝑮𝑮0⋮0

𝒂𝒂𝒛𝒛𝟏𝟏𝑮𝑮𝑳𝑳𝑳𝑳⋮

𝒂𝒂𝒛𝒛𝒎𝒎𝑮𝑮𝑳𝑳𝑳𝑳

𝟏𝟏⋮𝟏𝟏0⋮0𝟏𝟏⋮𝟏𝟏0⋮0

0⋮00⋮0𝟏𝟏⋮𝟏𝟏0⋮0

0⋮0𝟏𝟏⋮𝟏𝟏0⋮0𝟏𝟏⋮𝟏𝟏

Δ�𝑥𝑥𝑘𝑘+1Δ �̇𝑥𝑥𝑘𝑘+1Δ�𝑦𝑦𝑘𝑘+1Δ �̇𝑦𝑦𝑘𝑘+1Δ�̂�𝑧𝑘𝑘+1Δ ̂̇𝑧𝑧𝑘𝑘+1Δ�𝑏𝑏𝑘𝑘+1Δ�τ𝑘𝑘+1Δ�̇𝑏𝑏𝑘𝑘+1

δρ = Pseudorange Error (Code Phase Error)

δρ̇ = Doppler Error (Carrier Frequency Error)

𝑛𝑛 GPS Channels𝑚𝑚 GLONASS Channels

𝑎𝑎𝑥𝑥, 𝑎𝑎𝑦𝑦, 𝑎𝑎𝑧𝑧 = Receiver to Satellite Unit Vectors

Vector NCO Commands

22

Code Frequency: 𝑓𝑓code = 𝑓𝑓chip −�ρ𝑘𝑘+1−�ρ𝑘𝑘𝑇𝑇λchip

Carrier Frequency: 𝑓𝑓carrier = 𝑓𝑓IF −�̇ρ𝑘𝑘λ𝐿𝐿1

𝑓𝑓chip = Chipping Rate (cps) �ρ = Predicted Pseudorange (m)

T = Integration Period (s) λchip = PRN Chip Width (m/chip)

𝑓𝑓IF = Intermediate Frequency (Hz) [Must account for FMDA in GLONASS]�̇ρ = Predicted Pseudorange Rate (m/s) λL1 = Carrier Wavelength (m/cyc)

�𝛒𝛒 = 𝒇𝒇(𝐏𝐏𝐏𝐏𝐏𝐏𝐏𝐏𝐏𝐏𝐏𝐏𝐏𝐏𝐏𝐏,𝐂𝐂𝐂𝐂𝐏𝐏𝐂𝐂𝐂𝐂 𝐁𝐁𝐏𝐏𝐁𝐁𝐏𝐏)�̇𝛒𝛒 = 𝒇𝒇(𝐕𝐕𝐕𝐕𝐂𝐂𝐏𝐏𝐂𝐂𝐏𝐏𝐏𝐏𝐕𝐕,𝐂𝐂𝐂𝐂𝐏𝐏𝐂𝐂𝐂𝐂 𝐃𝐃𝐃𝐃𝐏𝐏𝐃𝐃𝐏𝐏)

ECEF Transformation Matrix

23

• 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

ECEF Transformation Matrix

24

ECEF Transformation Matrix

25

• 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

𝑥𝑥𝑦𝑦𝑧𝑧

=𝑢𝑢𝑣𝑣𝑤𝑤

+−30

00

m𝑥𝑥 𝑦𝑦 𝑧𝑧 𝑇𝑇 = WGS84 Position (m)

𝑢𝑢 𝑣𝑣 𝑤𝑤 𝑇𝑇 = PZ90.11 Position (m)

Heavy Tree Foliage Results

26

Entering MovingThrough

Exiting

GPS VDFLLGLONASS VDFLLCombined VDFLLUblox

Combined and Ublox solutions maintain accurate positions on the bridge

Urban Canyon Results

27

Vehicle Lane

GPS VDFLLGLONASS VDFLLCombined VDFLLUblox

Combined Scalar

Urban Canyon Results

28

GPS VDFLLGLONASS VDFLLCombined VDFLLUblox

Exiting Urban Canyon Open Sky Environment

Jamming Experiment

29

Jamming Map• GPS L1 jamming tests performed

at Edwards Airforce Base

• September 2019

• GLONASS L1 not jammed

Receiver Trajectory⁄𝑱𝑱 𝑮𝑮 = 𝟒𝟒𝟒𝟒 − 𝟔𝟔𝟒𝟒 𝐝𝐝𝐁𝐁

Jamming Experiment

30

10 GPS Satellites

5 GLONASS Satellites

Jamming Position Results

31

START

TURNAROUND

END

Jamming Position Results

32

GPS Fails

GLONASS Fails

Jamming C/No Results

33

10 of 10 GPS channels lose lock

4 of 5 GLONASS channels lose lock

Jamming C/No Results

34

1 GPS and 1 GLONASS channel lose lock

Jamming Scalar Results

35

GPS and GLONASS Scalar Tracking Fails

Dead Reckoning by Model

Jamming Tracking Results

36

Conclusions

37

• 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

Some Future Work

38

• 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

References

39

• [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.

Thank You

Questions?

40

Fault Detection and Exclusion

41