2,013 research outputs found
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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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The GPS Assimilator: a Method for Upgrading Existing GPS User Equipment to Improve Accuracy, Robustness, and Resistance to Spoofing
Preprint of the 2010 ION GNSS Conference
Portland, OR, September 21–24, 2010A conceptual method is presented for upgrading existing GPS user equipment, without requiring hardware or software modifications to the equipment, to improve the equipment’s position, velocity, and time (PVT) accuracy, to increase its PVT robustness in weak-signal or jammed environments, and to protect the equipment from counterfeit GPS signals (GPS spoofing). The method is embodied in a device called the GPS Assimilator that couples to the radio frequency (RF) input of an existing GPS receiver. The Assimilator extracts navigation and timing information from RF signals in its environment—including non-GNSS signals—and from direct baseband aiding provided, for example, by an inertial navigation system, a
frequency reference, or the GPS user. The Assimilator optimally fuses the collective navigation and timing information to produce a PVT solution which, by virtue of the diverse navigation and timing sources on which it is based, is highly accurate and inherently robust to GPS signal obstruction and jamming. The Assimilator embeds the PVT solution in a synthesized set of GPS signals and injects
these into the RF input of a target GPS receiver for which an accurate and robust PVT solution is desired. A prototype software-defined Assimilator device is presented with three example applications.Aerospace Engineerin
GNSS Signal Authentication via Power and Distortion Monitoring
We propose a simple low-cost technique that enables
civil Global Positioning System (GPS) receivers and other civil
global navigation satellite system (GNSS) receivers to reliably
detect carry-off spoofing and jamming. The technique, which
we call the Power-Distortion detector, classifies received signals
as interference-free, multipath-afflicted, spoofed, or jammed
according to observations of received power and correlatio
n
function distortion. It does not depend on external hardware or
a network connection and can be readily implemented on many
receivers via a firmware update. Crucially, the detector can with
high probability distinguish low-power spoofing from ordinary
multipath. In testing against over 25 high-quality empirical data
sets yielding over 900,000 separate detection tests, the detector
correctly alarms on all malicious spoofing or jamming attack
s
while maintaining a
<0.5% single-channel false alarm rate.Aerospace Engineering and Engineering Mechanic
Robust Positioning in the Presence of Multipath and NLOS GNSS Signals
GNSS signals can be blocked and reflected by nearby objects, such as buildings, walls, and vehicles. They can also be reflected by the ground and by water. These effects are the dominant source of GNSS positioning errors in dense urban environments, though they can have an impact almost anywhere. Non- line-of-sight (NLOS) reception occurs when the direct path from the transmitter to the receiver is blocked and signals are received only via a reflected path. Multipath interference occurs, as the name suggests, when a signal is received via multiple paths. This can be via the direct path and one or more reflected paths, or it can be via multiple reflected paths. As their error characteristics are different, NLOS and multipath interference typically require different mitigation techniques, though some techniques are applicable to both. Antenna design and advanced receiver signal processing techniques can substantially reduce multipath errors. Unless an antenna array is used, NLOS reception has to be detected using the receiver's ranging and carrier-power-to-noise-density ratio (C/N0) measurements and mitigated within the positioning algorithm. Some NLOS mitigation techniques can also be used to combat severe multipath interference. Multipath interference, but not NLOS reception, can also be mitigated by comparing or combining code and carrier measurements, comparing ranging and C/N0 measurements from signals on different frequencies, and analyzing the time evolution of the ranging and C/N0 measurements
Mass-Market Receiver for Static Positioning: Tests and Statistical Analyses
Nowadays, there are several low cost GPS receivers able to provide both pseudorange and carrier phase measurements in the L1band, that allow to have good realtime performances in outdoor condition. The present paper describes a set of dedicated tests in order to evaluate the positioning accuracy in static conditions. The quality of the pseudorange and the carrier phase measurements let hope for interesting results. The use of such kind of receiver could be extended to a large number of professional applications, like engineering fields: survey, georeferencing, monitoring, cadastral mapping and cadastral road. In this work, the receivers performance is verified considering a single frequency solution trying to fix the phase ambiguity, when possible. Different solutions are defined: code, float and fix solutions. In order to solve the phase ambiguities different methods are considered. Each test performed is statistically analyzed, highlighting the effects of different factors on precision and accurac
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Receiver-Autonomous Spoofing Detection: Experimental Results of a Multi-antenna Receiver Defense Against a Portable Civil GPS Spoofer
In this work we demonstrate the use of a dual antenna
receiver that employs a receiver-autonomous angle-ofarrival
spoofing countermeasure. This defense is
conjectured to be effective against all but the most sophisticated spoofing attempts. The technique is based
on observation of L1 carrier differences between multiple
antennas referenced to a common oscillator.
We first employ a moderately sophisticated spoofer to
"fool" a single-antenna civil receiver. We then deploy the
same attack after augmenting the receiver with an
additional antenna and with receiver-autonomous spoofdetection
software. The work discusses the experimental
results together with various issues related to sensitivity,
probability of false alarm, impact of carrier multipath,
line-bias-calibration, and physical setup and security.
We suggest that this work is important to the community
as it provides experimental validation of a low-cost
technique for receiver-autonomous spoofing detection.
Furthermore, the technique, when combined with physical
security of the antenna installation, provides a strong
defense against even a sophisticated attack.
The receiver employed is an L1-only civil GPS receiver
with multiple antenna capability. The GPS chipset
employed is the venerable GP2015/GP2021 that has been
freely available for over a decade. As such, this receiver is
representative of many civil receivers in use today for a
variety of applications. Multiple antennas are enabled
either through multiple independent RF front ends and
correlators or via antenna multiplexing into a single RF
front end and correlator bank.Aerospace Engineering and Engineering Mechanic
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A Technique for Determining the Carrier Phase Differences between Independent GPS Receivers during Scintillation
A method for recovering the carrier phase differences between
pairs of independent GPS receivers has been developed
and demonstrated in truth-model simulations. This
effort is in support of a project that intends to image the disturbed
ionosphere with diffraction tomography techniques
using GPS measurements from large arrays of receivers.
Carrier phase differential GPS techniques, common in surveying
and relative navigation, are employed to determine
the phase relationships between the receivers in the imaging array. Strategies for estimating the absolute carrier phase
disturbances at each receiver are discussed. Simulation results
demonstrate that the system can rapidly detect the onset
of scintillation, identify one non-scintillating reference
signal, and recover the carrier phase differences accurate to
0.1 cycles.Aerospace Engineering and Engineering Mechanic
Unambiguous Acquisition and Tracking Technique for General BOC Signals
This article presents a new unambiguous acquisition and tracking technique for general Binary Offset Carrier (BOC) ranging signals, which will be used in modern GPS, European Galileo system and Chinese BeiDou system. The test criterion employed in this technique is based on a synthesized correlation function which completely removes positive side peaks while keeping the sharp main peak. Simulation results indicate that the proposed technique completely removes the ambiguity threat in the acquisition process while maintaining relatively higher acquisition performance for low order BOC signals. The potential false lock points in the tracking phase for any order BOC signals are avoided by using the proposed method. Impacts of thermal noise and multipath on the proposed technique are investigated; the simulation results show that the new method allows the removal of false lock points with slightly degraded tracking performance. In addition, this method is convenient to implement via logic circuits
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