2,252 research outputs found
GPS Multipath Detection in the Frequency Domain
Multipath is among the major sources of errors in precise positioning using
GPS and continues to be extensively studied. Two Fast Fourier Transform
(FFT)-based detectors are presented in this paper as GPS multipath detection
techniques. The detectors are formulated as binary hypothesis tests under the
assumption that the multipath exists for a sufficient time frame that allows
its detection based on the quadrature arm of the coherent Early-minus-Late
discriminator (Q EmL) for a scalar tracking loop (STL) or on the quadrature (Q
EmL) and/or in-phase arm (I EmL) for a vector tracking loop (VTL), using an
observation window of N samples. Performance analysis of the suggested
detectors is done on multipath signal data acquired from the multipath
environment simulator developed by the German Aerospace Centre (DLR) as well as
on multipath data from real GPS signals. Application of the detection tests to
correlator outputs of scalar and vector tracking loops shows that they may be
used to exclude multipath contaminated satellites from the navigation solution.
These detection techniques can be extended to other Global Navigation Satellite
Systems (GNSS) such as GLONASS, Galileo and Beidou.Comment: 2016 European Navigation Conference (ENC 2016), May 2016, Helsinki,
Finland. Proceedings of the 2016 European Navigation Conference (ENC 2016
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A Testbed for Developing and Evaluating GNSS Signal Authentication Techniques
An experimental testbed has been created for developing
and evaluating Global Navigation Satellite System (GNSS)
signal authentication techniques. The testbed advances the state
of the art in GNSS signal authentication by subjecting candidate
techniques to the strongest publicly-acknowledged GNSS spoofing
attacks. The testbed consists of a real-time phase-coherent GNSS
signal simulator that acts as spoofer, a real-time softwaredefined
GNSS receiver that plays the role of defender, and
post-processing versions of both the spoofer and defender. Two
recently-proposed authentication techniques are analytically and
experimentally evaluated: (1) a defense based on anomalous
received power in a GNSS band, and (2) a cryptographic
defense against estimation-and-replay-type spoofing attacks. The
evaluation reveals weaknesses in both techniques; nonetheless,
both significantly complicate a successful GNSS spoofing attackAerospace Engineering and Engineering Mechanic
An autonomous GNSS anti-spoofing technique
open3siIn recent years, the problem of Position, Navigation and Timing (PNT) resiliency has received significant attention due to an increasing awareness on threats and the vulnerability of the current GNSS signals. Several proposed solutions make uses of cryptography to protect against spoofing. A limitation of cryptographic techniques is that they introduce a communication and processing computation overhead and may impact the performance in terms of availability and continuity for GNSS users. This paper introduces autonomous non cryptographic antispoofing mechanisms, that exploit semi-codeless receiver techniques to detect spoofing for signals with a component making use of spreading code encryption.openCaparra, Gianluca; Wullems, Christian; Ioannides, Rigas T.Caparra, Gianluca; Wullems, Christian; Ioannides, Rigas T
A New System Noise Measurement Method Using a 2-bit Analog-To-Digital Converter
We propose a new method to measure the system noise temperature, , using a 2-bit analog-to-digital converter (ADC). The statistics of the
digitized signal in a four-level quantization brings us information about the
bias voltage and the variance, which reflects the power of the input signal.
Comparison of the variances in {\it hot} and {\it sky} circumstances yields
without a power meter. We performed test experiments using the
Kagoshima 6-m radio telescope and a 2-bit ADC to verify this method. Linearity
in the power-variance relation was better than 99% within the dynamic range of
10 dB. Digitally measured coincided with that of conventional
measurement with a power meter in 1.8-% difference or less for elevations of
. No significant impact was found by the bias voltages
within the range between -3.7 and +12.8% with respect to the threshold voltage.
The proposed method is available for existing interferometers that have a
multi-level ADC, and release us from troubles caused by power meters.Comment: to appear in the Publications of the Astronomical Society of Japan,
Vol.62, No.5; 12 pages, 6 figure
Multi Detector Fusion of Dynamic TOA Estimation using Kalman Filter
In this paper, we propose fusion of dynamic TOA (time of arrival) from
multiple non-coherent detectors like energy detectors operating at sub-Nyquist
rate through Kalman filtering. We also show that by using multiple of these
energy detectors, we can achieve the performance of a digital matched filter
implementation in the AWGN (additive white Gaussian noise) setting. We derive
analytical expression for number of energy detectors needed to achieve the
matched filter performance. We demonstrate in simulation the validity of our
analytical approach. Results indicate that number of energy detectors needed
will be high at low SNRs and converge to a constant number as the SNR
increases. We also study the performance of the strategy proposed using IEEE
802.15.4a CM1 channel model and show in simulation that two sub-Nyquist
detectors are sufficient to match the performance of digital matched filter
High dynamic global positioning system receiver
A Global Positioning System (GPS) receiver having a number of channels, receives an aggregate of pseudorange code time division modulated signals. The aggregate is converted to baseband and then to digital form for separate processing in the separate channels. A fast fourier transform processor computes the signal energy as a function of Doppler frequency for each correlation lag, and a range and frequency estimator computes estimates of pseudorange, and frequency. Raw estimates from all channels are used to estimate receiver position, velocity, clock offset and clock rate offset in a conventional navigation and control unit, and based on the unit that computes smoothed estimates for the next measurement interval
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