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Tightly-Coupled Opportunistic Navigation for Deep Urban and Indoor Positioning
Ken Pesyna, Zak Kassas, Jahshan Bhatti, and Todd Humphreys
Presentation at ION 2011|September 23, 2011
Outline
I. Motivate & define Tightly-Coupled Opportunistic Navigation (TCON)
II. Explore “signals of opportunity” for TCON
III. Discuss the central estimator to optimally fuse signals together
IV. Present experimental results
Goal
Optimally extract navigation and timing information from ambient radio signals
Tightly-Coupled Opportunistic Navigation is a framework to achieve this goal
TCON is an optimal generalization of specific hybrid navigation technologies
Generalize Optimize
Tightly-Coupled Opportunistic Navigation
Cellular [1]
HDTV [2]
GNSS
Iridium [3]
TCON
[1] R. Rowe, P. Duffett-Smith, et. al., “Enhanced GPS: The tight integration of received cellular timing signals and GNSS receivers for ubiquitous positioning,” in Position, Location, and Navigation Symposium, IEEE/ION, 2008.
[2] J. Do, M. Rabinowitz, and P. Enge, “Performance of hybrid positioning system combining GPS and television signals,” in Position, Location, And Navigation Symposium, IEEE/ION, 2006.
[3] M. Joerger, et. al., “Iridium/gps carrier phase positioning and fault detection over wide areas,” ION GNSS 2009.
TCON: Breaking it Down
Tightly-Coupled
Signals downmixed and sampled with the same clock
Absolute time correspondence at the nanosecond level
Opportunistic Navigation
Receiver continuously searches for signals from which to extract navigation and timing information
Receiver employs on-the-fly signal characterization: Clock stability Clock offset Carrier-to-noise ratio Transmitter location
Tightly-Coupled Opportunistic Navigation
Signals of Opportunity
TCON treats all RF signals as potential signals of opportunity GNSS signals: GPS, Galileo, Glonass Cellular signals: CDMA, GSM, 4G LTE, & WiMAX Other satellite signals: Iridium Other ground-based signals: HDTV, Wi-Fi
What SOP characteristics are desirable?
1. High received carrier-to-noise ratio
2. Good frequency stability
3. Known location/timing offset
Unfortunately, we almost never get all three properties if we are not working with dedicated
navigation signals
Freestyle Navigation CDMA Cellular
Carrier-to-noise is high, penetrates well Towers do not move Only roughly synchronized to GPS Carrier stability varies from provider to provider
Iridium Carrier-to-noise ratio is higher than GNSS Global coverage Not continuous – “Bursty” TDMA structure Ambiguous in carrier phase from burst to burst
Centralized Estimator
Optimally combines observables from all SOPs
Our preferred implementation is an extended Kalman filter:
Base State: SOP state:
Full State:
Centralized Estimator
GPS carrier phase measurement model:
CDMA carrier phase measurement model:
Iridium carrier phase measurement model:
Carrier Phase Measurement Models
Dynamics dependent on current state and process noise:
Process noise covariance formed by models of clock dynamics:
Dynamics Model
Adaptive Dynamics Model
Run Kalman FilterUpdate SOP Clock Model
old new
Iterate
Output *
* Can only be done when is observable (to within a constant offset)
Simple TCON Demo: Experiment Setup
GRID Software Receiver
MATLAB EKFNational Instruments RFSA
Storage
Simple TCON Demo: SOP Wardriving
A Simple Demonstration of TCON
Run Kalman Filter
old new
Iterate
Update SOP Clock Model
6x 2x
(1) Obtaining Truth
(2) Characterizing CDMA SOP (3) Demonstrate post-characterization CDMA SOP only estimate of
Truth Estimate CDMA-based estimate vs.
So What?
Achieve our estimate error of by differencing the CDMA-only estimate from the truth variations:
The stability of will affect the length of achievable GNSS coherent integration in weak signal conditions
In this experiment, CDMA-only TCON (after-characterization) could supply coherent integration times beyond 100 seconds
100+ sec. coherent integration allows GNSS acquisition of signals below 0 dB-Hz assuming all else ideal
-
Mean squared coherence of
Conclusions
TCON is a framework to optimally extract navigation and timing information from ambient radio signals
Tight-coupling at the carrier-phase level and SOP characterization are essential to TCON
A simple TCON demonstration on timing showed a TCON-enabled receiver can coherently integrate beyond 100 seconds using characterized CDMA signals
Questions?