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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
Performance of the LHCb muon system
The performance of the LHCb Muon system and its stability across the full
2010 data taking with LHC running at ps = 7 TeV energy is studied. The
optimization of the detector setting and the time calibration performed with
the first collisions delivered by LHC is described. Particle rates, measured
for the wide range of luminosities and beam operation conditions experienced
during the run, are compared with the values expected from simulation. The
space and time alignment of the detectors, chamber efficiency, time resolution
and cluster size are evaluated. The detector performance is found to be as
expected from specifications or better. Notably the overall efficiency is well
above the design requirementsComment: JINST_015P_1112 201
An absolute calibration system for millimeter-accuracy APOLLO measurements
Lunar laser ranging provides a number of leading experimental tests of
gravitation -- important in our quest to unify General Relativity and the
Standard Model of physics. The Apache Point Observatory Lunar Laser-ranging
Operation (APOLLO) has for years achieved median range precision at the ~2 mm
level. Yet residuals in model-measurement comparisons are an order-of-magnitude
larger, raising the question of whether the ranging data are not nearly as
accurate as they are precise, or if the models are incomplete or
ill-conditioned. This paper describes a new absolute calibration system (ACS)
intended both as a tool for exposing and eliminating sources of systematic
error, and also as a means to directly calibrate ranging data in-situ. The
system consists of a high-repetition-rate (80 MHz) laser emitting short (< 10
ps) pulses that are locked to a cesium clock. In essence, the ACS delivers
photons to the APOLLO detector at exquisitely well-defined time intervals as a
"truth" input against which APOLLO's timing performance may be judged and
corrected. Preliminary analysis indicates no inaccuracies in APOLLO data beyond
the ~3 mm level, suggesting that historical APOLLO data are of high quality and
motivating continued work on model capabilities. The ACS provides the means to
deliver APOLLO data both accurate and precise below the 2 mm level.Comment: 21 pages, 10 figures, submitted to Classical and Quantum Gravit
A Code Phase Division Multiple Access (CPDMA) technique for VSAT satellite communications
A reference concept and implementation relevant to the application of Code Phase Division Multiple Access (CPDMA) to a high capacity satellite communication system providing 16 Kbps single hop channels between Very Small Aperture Terminals (VSAT's) is described. The description includes a potential implementation of an onboard CPDMA bulk demodulator/converter utilizing programmable charge coupled device (CCD) technology projected to be available in the early 1990's. A high level description of the system architecture and operations, identification of key functional and performance requirements of the system elements, and analysis results of end-to-end system performance relative to key figures of merit such as spectral efficiency are also provided
Blip glitches in Advanced LIGO data
Blip glitches are short noise transients present in data from ground-based
gravitational-wave observatories. These glitches resemble the
gravitational-wave signature of massive binary black hole mergers. Hence, the
sensitivity of transient gravitational-wave searches to such high-mass systems
and other potential short duration sources is degraded by the presence of blip
glitches. The origin and rate of occurrence of this type of glitch have been
largely unknown. In this paper we explore the population of blip glitches in
Advanced LIGO during its first and second observing runs. On average, we find
that Advanced LIGO data contains approximately two blip glitches per hour of
data. We identify four subsets of blip glitches correlated with detector
auxiliary or environmental sensor channels, however the physical causes of the
majority of blips remain unclear
Digital pulse-shape discrimination of fast neutrons and gamma rays
Discrimination of the detection of fast neutrons and gamma rays in a liquid
scintillator detector has been investigated using digital pulse-processing
techniques. An experimental setup with a 252Cf source, a BC-501 liquid
scintillator detector, and a BaF2 detector was used to collect waveforms with a
100 Ms/s, 14 bit sampling ADC. Three identical ADC's were combined to increase
the sampling frequency to 300 Ms/s. Four different digital pulse-shape analysis
algorithms were developed and compared to each other and to data obtained with
an analogue neutron-gamma discrimination unit. Two of the digital algorithms
were based on the charge comparison method, while the analogue unit and the
other two digital algorithms were based on the zero-crossover method. Two
different figure-of-merit parameters, which quantify the neutron-gamma
discrimination properties, were evaluated for all four digital algorithms and
for the analogue data set. All of the digital algorithms gave similar or better
figure-of-merit values than what was obtained with the analogue setup. A
detailed study of the discrimination properties as a function of sampling
frequency and bit resolution of the ADC was performed. It was shown that a
sampling ADC with a bit resolution of 12 bits and a sampling frequency of 100
Ms/s is adequate for achieving an optimal neutron-gamma discrimination for
pulses having a dynamic range for deposited neutron energies of 0.3-12 MeV. An
investigation of the influence of the sampling frequency on the time resolution
was made. A FWHM of 1.7 ns was obtained at 100 Ms/s.Comment: 26 pages, 14 figures, submitted to Nuclear Instruments and Methods in
Physics Research
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