7 research outputs found
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Collaborative Opportunistic Navigation
Aerospace Engineering and Engineering Mechanic
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Tightly-Coupled Opportunistic Navigation for Deep Urban and Indoor Positioning
A strategy is presented for exploiting the frequency stability,
transmit location, and timing information of ambient radio-frequency “signals of opportunity” for the purpose of
navigating in deep urban and indoor environments. The
strategy, referred to as tightly-coupled opportunistic navigation
(TCON), involves a receiver continually searching
for signals from which to extract navigation and timing
information. The receiver begins by characterizing these
signals, whether downloading characterizations from a collaborative
online database or performing characterizations
on-the-fly. Signal observables are subsequently combined
within a central estimator to produce an optimal estimate
of position and time. A simple demonstration of the
TCON strategy focused on timing shows that a TCONenabled
receiver can characterize and use CDMA cellular
signals to correct its local clock variations, allowing it to
coherently integrate GNSS signals beyond 100 seconds.Aerospace Engineering and Engineering Mechanic
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Centimeter Positioning with a Smartphone-Quality GNSS Antenna
This paper demonstrates for the first time that centimeteraccurate
positioning is possible based on data sampled
from a smartphone-quality Global Navigation Satellite
System (GNSS) antenna. Centimeter-accurate smartphone
positioning will enable a host of new applications
such as globally-registered fiduciary-marker-free augmented
reality and location-based contextual advertising,
both of which have been hampered by the several-meterlevel
errors in traditional GNSS positioning. An empirical
analysis of data collected from a smartphone-grade GNSS
antenna reveals the antenna to be the primary impediment
to fast and reliable resolution of the integer ambiguities
which arise when solving for a centimeter-accurate carrierphase
differential position. The antenna’s poor multipath
suppression and irregular gain pattern result in large timecorrelated
phase errors which significantly increase the
time to integer ambiguity resolution as compared to even a low-quality stand-alone patch antenna. The time to integer
resolution—and to a centimeter-accurate fix—is significantly
reduced when more GNSS signals are tracked or
when the smartphone experiences gentle wavelength-scale
random motion.Aerospace Engineering and Engineering Mechanic
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Precision Limits of Low-Energy GNSS Receivers
Limitations on position-time precision are analyzed in
energy-constrained GNSS receivers. The goal of this work
is to determine the combination of sampling rate, number
of quantization bits, number of satellites tracked, and coherent
integration time that maximizes the position-time
precision under a fixed low-energy constraint. In this paper,
only the measurement errors due to spectrally flat
Gaussian thermal noise are considered. Analytical expressions
relating the foregoing parameters to precision and
energy consumption are developed. Based on these expressions,
a constrained optimization problem is formulated.
Optimal solutions indicate that under a tight energy
constraint energy should be allocated toward increasing the sampling rate at the expense of the other parameters.
Moreover, the quantization resolution should be set
above 1-bit only under an energy surplus. Interestingly,
optimum settings under tight energy constraints approximately
match those chosen by the designers of energyefficient
commercial GNSS receivers.Aerospace Engineering and Engineering Mechanic
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Precise Augmented Reality Enabled by Carrier-Phase Differential GPS
A prototype precise augmented reality (PAR) system
that uses carrier phase differential GPS (CDGPS)
and an inertial measurement unit (IMU) to obtain
sub-centimeter level accurate positioning and degree
level accurate attitude is presented. Several current
augmented reality systems and applications are discussed
and distinguished from a PAR system. The
distinction centers around the PAR system’s highly
accurate position estimate, which enables tight registration,
or alignment of the virtual renderings and the
real world. Results from static and dynamic tests of
the PAR system are given. These tests demonstrate
the positioning and orientation accuracy obtained by
the system and how this accuracy translates to remarkably
low registration errors, even at short distances
from the virtual objects. A list of areas for
improvement necessary to create a fully capable PAR
system is presented.Aerospace Engineering and Engineering Mechanic
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Opportunistic Frequency Stability Transfer for Extending the Coherence Time of GNSS Receiver Clocks
Preprint of the 2010 ION GNSS Conference
Portland, OR, September 22–25, 2010A framework is presented for exploiting the frequency stability
of non-GNSS signals to extend the coherence time
of inexpensive GNSS receiver clocks. This is accomplished
by leveraging stable ambient radio frequency signals, called
“signals of opportunity,” to compensate for the frequency
instability of the reference oscillators typically used in inexpensive
handheld GNSS receivers. Adequate compensation
for this frequency instability permits the long coherent
integration intervals required to acquire and track GNSS
signals with low carrier-to-noise ratios. The goal of this
work is to push the use of GNSS deeper indoors or into
environments where GNSS may be subject to interference.Aerospace Engineerin
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On the Feasibility of cm-Accurate Positioning via a Smartphone’s Antenna and GNSS Chip
The feasibility of centimeter-accurate carrier-phase
differential GNSS (CDGNSS) positioning using a smartphone’s
internal GNSS antenna and GNSS chip is investigated. Precise positioning
on a mass-market platform would significantly influence
the world economy, ushering in a host of consumer-focused applications
that have so far been hampered by the several-meter-level
errors in traditional GNSS positioning. Previous work has shown
that GNSS signals received through a mass-market smartphone’s
GNSS antenna can be processed to yield a centimeter-accurate
CDGNSS position solution, but this earlier work processed all
GNSS signals externally to the smartphone. The question remains
whether a smartphone’s internal oscillator and GNSS chip can
produce observables of sufficient quality to support centimeteraccurate
carrier-phase-based positioning. This paper answers the
question by accessing and processing the raw code- and carrierphase
observables produced by a mass-market smartphone GNSS
chip—observables that have heretofore been unavailable to the
research community. The phone’s carrier phase measurements
are shown to suffer from five anomalies compared to those
from a survey-grade GNSS receiver, four of which are readily
fixed in post-processing. The remaining anomaly, an error in the
phase measurement that grows approximately linearly with time,
currently prevents the phone’s phase measurements from satisfying
the conditions for CDGNSS positioning. But the phone’s
measurements seem otherwise fully capable of supporting cmaccurate
carrier-phase differential GNSS positioning. A separate
analysis of a smartphone’s GNSS signal strength dependency
on azimuth and elevation reveals that multipath-induced deep
fading and large phase errors remain a significant challenge for
centimeter-accurate smartphone positioning.Aerospace Engineering and Engineering Mechanic