793 research outputs found
Performances of a GNSS receiver for space-based applications
Space Vehicle (SV) life span depends on its station keeping capability. Station keeping is the ability of the vehicle to maintain position and orientation. Due to external perturbations, the trajectory of the SV derives from the ideal orbit. Actual positioning systems for satellites are mainly based on ground equipment, which means heavy infrastructures. Autonomous positioning and navigation systems using Global Navigation Satellite Systems (GNSS) can then represent a great reduction in platform design and operating costs. Studies have been carried out and the first operational systems, based on GPS receivers, become available. But better availability of service could be obtained considering a receiver able to process GPS and Galileo signals. Indeed Galileo system will be compatible with the current and the modernized GPS system in terms of signals representation and navigation data. The greater
availability obtained with such a receiver would allow
significant increase of the number of point solutions and
performance enhancement. For a mid-term perspective Thales Alenia Space finances a PhD to develop the concept of a reconfigurable receiver able to deal with both the GPS system and the future Galileo system. In this context, the aim of this paper is to assess the performances of a receiver designed for Geosynchronous Earth Orbit (GEO) applications. It is shown that high improvements are obtained with a receiver designed to track both GPS and Galileo satellites. The performance assessments have been used to define the specifications of the future satellite GNSS receiver
A null frame for spacetime positioning by means of pulsating sources
We introduce an operational approach to the use of pulsating sources, located
at spatial infinity, for defining a relativistic positioning and navigation
system, based on the use of four-dimensional bases of null four-vectors, in
flat spacetime. As a prototypical case, we show how pulsars can be used to
define such a positioning system. The reception of the pulses for a set of
different sources whose positions in the sky and periods are assumed to be
known allows the determination of the user's coordinates and spacetime
trajectory, in the reference frame where the sources are at rest. We describe
our approach in flat Minkowski spacetime, and discuss the validity of this and
other approximations we have considered.Comment: 19 pages, revised to match the version accepted for publication in
Advances in Space Researc
A relativistic positioning system exploiting pulsating sources for navigation across the Solar System and beyond
We introduce an operational approach to the use of pulsating sources, located at spatial infinity, for defining a relativistic positioning and navigation system, based on the use of null four-vectors in a flatMinkowskian spacetime. We describe our approach and discuss the validity of it and of the other approximations we have considered in actual physical situations. As a prototypical case, we show how pulsars can be used to define such a positioning system: the reception of the pulses for a set of different sources whose positions in the sky and periods are assumed to be known allows the determination of the user's coordinates and spacetime trajectory, in the reference frame where the sources are at rest. In order to confirm the viability of the method, we consider an application example reconstructing the world-line of an idealized Earth in the reference frame of distant pulsars: in particular we have simulated the arrival times of the signals fromfour pulsars at the location of the Parkes radiotelescope in Australia. After pointing out the simplifications we have made, we discuss the accuracy of the method. Eventually, we suggest that the method could actually be used for navigation across the Solar System and be based on artificial sources, rather than pulsar
Autonomous satellite orbit determination during the development phases of the global positioning system
An onboard navigation system was developed to aid the design and evaluation of algorithms used in autonomous satellite navigation with Global Positioning System (GPS) data. The performance of the algorithms designed for a GPS Receiver/Processor Assembly (R/PA) intended for LANDSAT-D was investigated during the development phases of the GPS (four to six satellites in the constellation). This evaluation emphasized the effects on the orbit determination accuracy of the expected user clock errors, GPS satellite visibility, force model approximations, and state and covariance propagation approximations. Results are presented giving the sensitivity of orbit determination accuracy to these constraints
Accuracy Study of a Single Frequency Receiver Using a Combined GPS/GALILEO Constellation
As the date of availability of GALILEO approaches,
more and more interest appears to pre-evaluate the accuracy
of GALILEO and combined GPS+ GALILEO receivers.
The majority of simulations made are based on the
general use of UERE (often presented as a function of the
elevation angle of the satellite) multiplied by the GDOP
(Geometric Dilution Of Precision) matrix. This is a too
approximate approach to state for the real position error
distributions. Therefore, the concept of an Instantaneous
Pseudo Range Error (IPRE) is defined and is implemented
into NAVSIM the DLR’s end to end GNSS simulator. This
new module coupled with the other modules of the simulator
permit to lead complete End-to-End simulations. This
new functionality has the advantage to augment the field of
applications and to couple the generation of errors already
implemented in NAVSIM with error distributions coming
from real measurements. This study is a good first approach
to compare constellations between each other regarding
the accuracy issue. The IPRE concept multiplies
the functionalities thanks to its ability to generate real distributions
of errors. The application to a combined existing
constellation (GPS) for which real measurements can
be used with a not yet existing constellation (GALILEO)
for which only simulated data can be used is an interesting
approach. These results can directly be used to test the
impact of correction models, of filtering techniques, of antenna
types to a combined GPS/GALILEO system thanks
to the time series of IPRE and the instantaneous individual
errors output from NAVSIM. The best strategy of error mitigation
technique can be tested and the result can be used
for receiver design before the launch of GALILEO system
Target Localization Accuracy Gain in MIMO Radar Based Systems
This paper presents an analysis of target localization accuracy, attainable
by the use of MIMO (Multiple-Input Multiple-Output) radar systems, configured
with multiple transmit and receive sensors, widely distributed over a given
area. The Cramer-Rao lower bound (CRLB) for target localization accuracy is
developed for both coherent and non-coherent processing. Coherent processing
requires a common phase reference for all transmit and receive sensors. The
CRLB is shown to be inversely proportional to the signal effective bandwidth in
the non-coherent case, but is approximately inversely proportional to the
carrier frequency in the coherent case. We further prove that optimization over
the sensors' positions lowers the CRLB by a factor equal to the product of the
number of transmitting and receiving sensors. The best linear unbiased
estimator (BLUE) is derived for the MIMO target localization problem. The
BLUE's utility is in providing a closed form localization estimate that
facilitates the analysis of the relations between sensors locations, target
location, and localization accuracy. Geometric dilution of precision (GDOP)
contours are used to map the relative performance accuracy for a given layout
of radars over a given geographic area.Comment: 36 pages, 5 figures, submitted to IEEE Transaction on Information
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