Search results for "Constellation"
showing 10 items of 25 documents
Reducing the peak and average power for OFDM systems using QAM by constellation shaping
2009
In this paper, we present a shell mapping scheme to reduce the peak and average power of orthogonal frequency division multiplexing (OFDM) signals using quadrature amplitude modulation (QAM) by constellation shaping. Our approach can be considered as an extension of the shell mapping technique introduced originally in the V.34 recommendation of ITU-T. The shell mapping method uses multiple cost functions, each having the OFDM block length N as a parameter. The cost functions are presented in closed form for any N. The main advantage of the proposed scheme is that the peak and average power can be reduced without sacrificing the data rate, and no side information is needed at the receive sid…
Unitary Space–Time Constellation Design Based on the Chernoff Bound of the Pairwise Error Probability
2008
Unitary space-time constellation design is considered for noncoherent multiple-antenna communications, where neither the transmitter nor the receiver knows the fading coefficients of the channel. By employing the Clarke's subdifferential theorem of the sum of the kappa largest singular values of a unitary matrix, we present a numerical optimization procedure for finding unitary space-time signal constellations of any dimension. The Chernoff bound of the pairwise error probability is used directly as a design criterion. The constellations are found by performing gradient descent search on a family ldquosurrogaterdquo functions that converge to the maximum pairwise error probability. The comp…
Locating Objects Away from Earth Surface: Positioning Accuracy
2013
The motion of the Galileo and GPS satellite constellations is simulated in Schwarzschild space-time, whereas photons travel in Minkowski space-time. This is a good enough approach to deal with the main goal of this paper: the study of positioning accuracy in the framework of the so-called relativistic positioning. Our study is based on numerical 4D simulations. In this meeting, the contribution of J.A. Morales-Lladosa contains some basic ideas which have been important to perform our numerical calculations. For four chosen emitters (satellites) of a certain constellation, many receivers located at different distances from Earth surface and in distinct directions are considered. Thus, we ver…
Reframing the systemic approach to complex organizations as intangible portfolios
2012
The aim of this paper is to pave the way towards the inclusion of mainstream sociological approaches (based on Luhmann’s approach) for the studies of firms-organizations. In social sciences we can observe that the theoretic consequences of a paradigm shift is signiicantly represented by the evolution of systemic thinking from Parsons to Luhmann. This shift implies the change from the vision of systemic organizations as “structures” to that of systemic organizations as “communication flows”. The milestone of systemic approach in management maybe found in the research and applied works of Anthony Staford Beer with his Viable System Model (VSM) that today faced a relevant reconiguration by Gol…
Relativistic positioning: errors due to uncertainties in the satellite world lines
2014
Global navigation satellite systems use appropriate satellite constellations to get the coordinates of an user -close to Earth- in an almost inertial reference system. We have simulated both GPS and GALILEO constellations. Uncertainties in the satellite world lines lead to dominant positioning errors. In this paper, a detailed analysis of these errors is developed inside a great region surrounding Earth. This analysis is performed in the framework of the so-called relativistic positioning systems. Our study is based on the Jacobian, J, of the transformation giving the emission coordinates in terms of the inertial ones. Around points of vanishing J, positioning errors are too large. We show …
Phytochemical and anti-staphylococcal biofilm assessment of Dracaena draco L. Spp. draco resin
2013
Background: Dracaena draco L. ssp. draco is known as the “dragon's blood tree” and it is endemic from the Canary Islands and Morocco. Objective: Carry out phytochemical investigation of acetonic extracts of red resin obtained from the trunk of D. draco, to obtain to the isolation of the most abundant resin constituents, belonging to the class of flavonoids: flavans, along with homoisoflavans and homoisoflavanones. Materials and Methods: The structures of the isolated compounds were established by Nuclear Magnetic Resonance (NMR) and mass spectrometry data and comparison with literature data. The acetonic extract was evaluated for its anti-staphylococcal properties against two reference stra…
Combining super-orthogonal space-frequency trellis coding, constellation shaping by shell mapping, and OFDM for high data rate broadband mobile commu…
2014
In this paper, we seamlessly combine three transmission techniques to design an improved performance broadband mobile communication system with two transmit antennas. In so doing, we took inspiration from the V.34 data modem toolbox designed for public switched telephone network. We modified the constellation shaping by shell mapping algorithm to apply it only to the orthogonal frequency division multiplexing (OFDM) frame sent by the first antenna, in such a way that the peak-to-average power ratio (PAPR) is also reduced for the second antenna. We use a 24-point quadrature amplitude modulation (QAM) signal constellation on each subcarrier, while the reference system employs 16 QAM for the s…
GrailQuest: hunting for atoms of space and time hidden in the wrinkle of Space-Time: A swarm of nano/micro/small-satellites to probe the ultimate str…
2021
AbstractGrailQuest(Gamma Ray Astronomy International Laboratory for QUantum Exploration of Space-Time) is a mission concept based on a constellation (hundreds/thousands) of nano/micro/small-satellites in low (or near) Earth orbits. Each satellite hosts a non-collimated array of scintillator crystals coupled with Silicon Drift Detectors with broad energy band coverage (keV-MeV range) and excellent temporal resolution (≤ 100 nanoseconds) each with effective area$\sim 100 \text {cm}^{2}$∼100cm2. This simple and robust design allows for mass-production of the satellites of the fleet. This revolutionary approach implies a huge reduction of costs, flexibility in the segmented launching strategy, …
The HERMES-Technologic and Scientific Pathfinder
2020
HERMES-TP/SP (High Energy Rapid Modular Ensemble of Satellites Technologic and Scientific Pathfinder) is a constellation of six 3U nano-satellites hosting simple but innovative X-ray detectors, characterized by a large energy band and excellent temporal resolution, and thus optimized for the monitoring of Cosmic High Energy transients such as Gamma Ray Bursts and the electromagnetic counterparts of Gravitational Wave Events, and for the determination of their positions. The projects are funded by the Italian Ministry of University and Research and by the Italian Space Agency, and by the European Union Horizon 2020 Research and Innovation Program under Grant Agreement No. 821896. HERMES-TP/S…