2,216 research outputs found
A Stochastic Geometry Approach to Doppler Characterization in a LEO Satellite Network
A Non-terrestrial Network (NTN) comprising Low Earth Orbit (LEO) satellites
can enable connectivity to underserved areas, thus complementing existing
telecom networks. The high-speed satellite motion poses several challenges at
the physical layer such as large Doppler frequency shifts. In this paper, an
analytical framework is developed for statistical characterization of Doppler
shift in an NTN where LEO satellites provide communication services to
terrestrial users. Using tools from stochastic geometry, the users within a
cell are grouped into disjoint clusters to limit the differential Doppler
across users. Under some simplifying assumptions, the cumulative distribution
function (CDF) and the probability density function are derived for the Doppler
shift magnitude at a random user within a cluster. The CDFs are also provided
for the minimum and the maximum Doppler shift magnitude within a cluster.
Leveraging the analytical results, the interplay between key system parameters
such as the cluster size and satellite altitude is examined. Numerical results
validate the insights obtained from the analysis.Comment: Accepted in IEEE International Conference on Communications (ICC)
202
Architectures and Key Technical Challenges for 5G Systems Incorporating Satellites
Satellite Communication systems are a promising solution to extend and
complement terrestrial networks in unserved or under-served areas. This aspect
is reflected by recent commercial and standardisation endeavours. In
particular, 3GPP recently initiated a Study Item for New Radio-based, i.e., 5G,
Non-Terrestrial Networks aimed at deploying satellite systems either as a
stand-alone solution or as an integration to terrestrial networks in mobile
broadband and machine-type communication scenarios. However, typical satellite
channel impairments, as large path losses, delays, and Doppler shifts, pose
severe challenges to the realisation of a satellite-based NR network. In this
paper, based on the architecture options currently being discussed in the
standardisation fora, we discuss and assess the impact of the satellite channel
characteristics on the physical and Medium Access Control layers, both in terms
of transmitted waveforms and procedures for enhanced Mobile BroadBand (eMBB)
and NarrowBand-Internet of Things (NB-IoT) applications. The proposed analysis
shows that the main technical challenges are related to the PHY/MAC procedures,
in particular Random Access (RA), Timing Advance (TA), and Hybrid Automatic
Repeat reQuest (HARQ) and, depending on the considered service and
architecture, different solutions are proposed.Comment: Submitted to Transactions on Vehicular Technologies, April 201
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
Experimental single photon exchange along a space link of 7000 km
Extending the single photon transmission distance is a basic requirement for
the implementation of quantum communication on a global scale. In this work we
report the single photon exchange from a medium Earth orbit satellite (MEO) at
more than 7000 km of slanted distance to the ground station at the Matera Laser
Ranging Observatory. The single photon transmitter was realized by exploiting
the corner cube retro-reflectors mounted on the LAGEOS-2 satellite. Long
duration of data collection is possible with such altitude, up to 43 minutes in
a single passage. The mean number of photons per pulse ({\mu}sat) has been
limited to 1 for 200 seconds, resulting in an average detection rate of 3.0 cps
and a signal to noise ratio of 1.5. The feasibility of single photon exchange
from MEO satellites paves the way to tests of Quantum Mechanics in moving
frames and to global Quantum Information.Comment: 5 pages, updated versio
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