Future Directions in GNSS Research

Todd Humphreys | Aerospace EngineeringThe University of Texas at Austin

GPS World Webinar | November 15, 2012

• University of Texas Radionavigation Lab graduate students Jahshan Bhatti, Kyle Wesson, Ken Pesyna, Zak Kassas, Daniel Shepard, and Andrew Kerns

Acknowledgements

PNT DesiderataAvailable Everywhere

Instantaneous Fix

Secure & RobustLow Power

Cost Effective

Precise and Accurate

Kanwar Chadha, Texas Wireless Summit, Oct. 26, 2012

State of Art: uBlox UC530MAvailable Everywhere

-148 dBm acq, -165 dBm trk

Instantaneous Fix

1 second hot TTFF

Secure & Robust

CW interference removal

Low Power

66 mW continuous

Cost Effective

~$30 - $50

Precise and Accurate

2.0 m CEP with SBAS

Promising Directions for University Research

Available Everywhere

-148 dBm acq, -165 dBm trk

Instantaneous Fix

1 second hot TTFF

Secure & Robust

CW interference removal

Low Power

66 mW continuous

Cost Effective

~$30 - $50

Precise and Accurate

2.0 m CEB with SBAS

(Practically) Closed Problems

Available Everywhere

Instantaneous Fix

Secure & Robust

Low Power

Precise and Accurate 2-meter insecure rural outdoor location Elimination of ionospheric delay

– Multi-frequency open civil signals eliminate 1st-order effects

– 2nd-order effects at mm level– Ray-tracing models available for single-freq.

networked RX– Broadcast model obsolete

Data-aided carrier tracking– Half-cycle carrier tracking (e.g. Costas-loop

tracking) is outmoded– GPS L1 C/A is >99% predictable – build on-the-

fly database or get one over network – Other GNSS signals have pilot channels– One remaining open problem: Exploit coding

on L2 CM to improve L2C carrier tracking

Open Problems (1 of 4)

Available Everywhere

Instantaneous Fix

Secure & Robust

Low Power

Precise and Accurate Move sub-centimeter positioning into the mainstream– Precise positioning applications are much

bigger than surveying, mining, and geodesy – there are myriad consumer applications

– Precise positioning is not intrinsically expensive – primary cost is in non-recurring engineering

– Mainstreaming of cm-positioning will be enormously disruptive for established precise positioning providers

CDGNSS-EnabledPrecise Augmented Reality

AR Video

Open Problems (1 of 4)

Available Everywhere

Instantaneous Fix

Secure & Robust

Low Power

Precise and Accurate Move sub-centimeter positioning into the mainstream– Robustify and increase sensitivity of carrier-phase

differential GNSS (current state of art can’t handle even heavy foliage)• Overlay CDGPS engine on vectorized tracking (VDLL/VFLL

+ phase recovery), or, better yet … • Integrate CDGPS engine within vector tracking

architecture• Difference correlators offer improved robustness and

greater sensitivity. See T. Pany et al. “Difference Correlators,” May/June 2012.

– Exploit non-RF sensors to move indoors• IMUs• Cameras are cheap, pervasive. Camera central to precise

augmented reality, for which IMUs may be unnecessary.

– “Green” carrier-phase recovery – low power will enable consumer applications

Open Problems (2 of 4)

Available Everywhere

Instantaneous Fix

Secure & Robust

Low Power

Precise and Accurate Move toward cooperative signal-opportunistic PNT– Indoor problem won’t be solved by GNSS signals

alone– Might as well assume all future PNT devices will

be networked– Natural evolution of processing platform:

• Navigation processing on chip • Navigation processing on host processor • Navigation processing on cloud

– Natural evolution of tracking architecture: • Single-channel scalar tracking • Single-receiver vector tracking• Multi-receiver vector tracking

Cooperative Opportunistic Vectorized Tracking for Robust PNT

Open Problems (3 of 4)

Available Everywhere

Instantaneous Fix

Secure & Robust

Low Power

Precise and Accurate Civil GNSS receivers insecure– No commercial GNSS receiver has yet

been built with security in mind– Open GNSS signals are predictable

spoofable– Vast majority of receivers in critical

national infrastructure are GPS L1 C/A receivers

– Securing GNSS across a wide variety of application domains (e.g., low-power, low-cost, space-constrained) will remain a challenge for years to come

GNSS Spoofing

UT June 2012 Spoofing Demo

Spoofing DefensesCryptographic Non-Cryptographic

Stan

d-Al

one

Net

wor

ked

J/N Sensing(Ward, Scott, Calgary)

SSSC or NMA on WAAS(Scott, UT)

Single-Antenna Spatial Correlation(Cornell, Calgary)

SSSC on L1C(Scott)

Correlation Anomaly Defense(TENCAP, Ledvina, Torino, UT)

Sensor Diversity Defense(DARPA, BAE, UT)

NMA on L2C, L5, or L1C(MITRE, Scott, UT)

P(Y) Cross-Correlation(Stanford, Cornell)

Multi-Element Antenna Defense(Keys, Montgomery, DLR, Stanford)

Open Problems (4 of 4)

Available Everywhere

Instantaneous Fix

Secure & Robust

Low Power

Precise and Accurate Move GPS dot from fiction to non-fiction– Dime-sized tracking device accurate to two feet

anywhere on the globe

The GPS Dot

Open Problems (4 of 4)

Available Everywhere

Instantaneous Fix

Secure & Robust

Low Power

Precise and Accurate Move GPS dot from fiction to non-fiction– Dime-sized tracking device accurate to two feet

anywhere on the globe– Competing goals ensure that dots will offer

interesting research challenges for years to come:• High sensitivity vs. small size• High sensitivity vs. low-power

– Dots could cooperate in a wireless sensor network

radionavlab.ae.utexas.edu