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Xiaodai Dong - One of the best experts on this subject based on the ideXlab platform.
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Near-Optimal Hybrid Processing for Massive MIMO Systems via Matrix Decomposition
IEEE Transactions on Signal Processing, 2017Co-Authors: Xiaodai DongAbstract:For practical implementation of massive multiple-input multiple-output (MIMO) systems, the hybrid processing (precoding/combining) structure is promising to reduce the high implementation cost and power consumption rendered by large number of radio frequency (RF) chains of the traditional processing structure. The hybrid processing is realized through low-dimensional digital baseband processing combined with analog RF processing enabled by phase shifters. We propose to design hybrid RF and baseband precoders/Combiners for multistream transmission in massive MIMO systems, by directly decomposing the predesigned unconstrained digital precoder/Combiner of a large dimension. This approach is fundamental and general in the sense that any conventional full RF chain precoding solution of a MIMO system configuration can be converted to a hybrid processing structure by matrix decomposition. The constant amplitude constraint of analog RF processing results in the matrix decomposition problem nonconvex. Based on an alternate optimization technique, the nonconvex matrix decomposition problem can be decoupled into a series of convex subproblems and effectively solved by restricting the phase increment of each entry in the RF precoder/Combiner within a small vicinity of its preceding iterate. A singular value decomposition-based technique is proposed to secure an initial point sufficiently close to the global solution of the original nonconvex problem. Through simulation, the convergence of the alternate optimization for such a matrix decomposition-based hybrid processing (MD-HP) scheme is examined, and the performance of the MD-HP scheme is demonstrated to be near-optimal.
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Near-Optimal Hybrid Processing for Massive MIMO Systems via Matrix Decomposition
arXiv: Information Theory, 2015Co-Authors: Xiaodai DongAbstract:For the practical implementation of massive multiple-input multiple-output (MIMO) systems, the hybrid processing (precoding/combining) structure is promising to reduce the high cost rendered by large number of RF chains of the traditional processing structure. The hybrid processing is performed through low-dimensional digital baseband processing combined with analog RF processing enabled by phase shifters. We propose to design hybrid RF and baseband precoders/Combiners for multi-stream transmission in point-to-point massive MIMO systems, by directly decomposing the pre-designed unconstrained digital precoder/Combiner of a large dimension. The constant amplitude constraint of analog RF processing results in the matrix decomposition problem non-convex. Based on an alternate optimization technique, the non-convex matrix decomposition problem can be decoupled into a series of convex sub-problems and effectively solved by restricting the phase increment of each entry in the RF precoder/Combiner within a small vicinity of its preceding iterate. A singular value decomposition based technique is proposed to secure an initial point sufficiently close to the global solution of the original non-convex problem. Through simulation, the convergence of the alternate optimization for such a matrix decomposition based hybrid processing (MD-HP) scheme is examined, and the performance of the MD-HP scheme is demonstrated to be near-optimal.
Arno Mittelbach - One of the best experts on this subject based on the ideXlab platform.
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Hash Combiners for Second Pre-Image Resistance, Target Collision Resistance and Pre-Image Resistance have Long Output.
IACR Cryptology ePrint Archive, 2012Co-Authors: Arno MittelbachAbstract:A (k;l) hash-function Combiner for property P is a construction that, given access to l hash functions, yields a single cryptographic hash function which has property P as long as at least k out of the l hash functions have that property. Hash function Combiners are used to hedge against the failure of one or more of the individual components. One example of the application of hash function Combiners are the previous versions of the TLS and SSL protocols (10, 8). The concatenation Combiner which simply concatenates the outputs of all hash functions is an example of a robust Combiner for collision resistance. However, its output length is, naturally, signicantly longer than each individual hash-function output, while the security bounds are not necessarily stronger than that of the strongest input hash-function. In 2006 Boneh and Boyen asked whether a robust black-box Combiner for collision resistance can exist that has an output length which is signicantly less than that of the concatenation Combiner (4). Regrettably, this question has since been answered in the negative for fully black-box constructions (where hash function and adversary access is being treated as black- box), that is, Combiners (in this setting) for collision resistance roughly need at least the length of the concatenation Combiner to be robust (4, 5, 16, 17). In this paper we examine weaker notions of collision resistance, namely: second pre-image resistance and target collision resistance (20) and pre-image resistance. As a generic brute-force attack against any of these would take roughly 2 n queries to an n-bit hash function, in contrast to only 2 n=2 queries it would take to break collision resistance (due to the birthday bound), this might indicate that Combiners for weaker notions of collision resistance can exist which have a signicantly shorter output than the concatenation Combiner (which is, naturally, also robust for these properties). Regrettably, this is not the case.
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SCN - Hash Combiners for second pre-image resistance, target collision resistance and pre-image resistance have long output
Lecture Notes in Computer Science, 2012Co-Authors: Arno MittelbachAbstract:A (k,l) hash-function Combiner for property P is a construction that, given access to l hash functions, yields a single cryptographic hash function which has property P as long as at least k out of the l hash functions have that property. Hash function Combiners are used to hedge against the failure of one or more of the individual components. One example of the application of hash function Combiners are the previous versions of the TLS and SSL protocols [7,6]. The concatenation Combiner which simply concatenates the outputs of all hash functions is an example of a robust Combiner for collision resistance. However, its output length is, naturally, significantly longer than each individual hash-function output, while the security bounds are not necessarily stronger than that of the strongest input hash-function. In 2006 Boneh and Boyen asked whether a robust black-box Combiner for collision resistance can exist that has an output length which is significantly less than that of the concatenation Combiner [2]. Regrettably, this question has since been answered in the negative for fully black-box constructions (where hash function and adversary access is being treated as black-box), that is, Combiners (in this setting) for collision resistance roughly need at least the length of the concatenation Combiner to be robust [2,3,11,12]. In this paper we examine weaker notions of collision resistance, namely: second pre-image resistance and target collision resistance [15] and pre-image resistance. As a generic brute-force attack against any of these would take roughly 2n queries to an n-bit hash function, in contrast to only 2n/2 queries it would take to break collision resistance (due to the birthday bound), this might indicate that Combiners for weaker notions of collision resistance can exist which have a significantly shorter output than the concatenation Combiner (which is, naturally, also robust for these properties). Regrettably, this is not the case.
K Perraut - One of the best experts on this subject based on the ideXlab platform.
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single mode waveguides for gravity i the cryogenic 4 telescope integrated optics beam Combiner
Astronomy and Astrophysics, 2018Co-Authors: K Perraut, L Jocou, F Eisenhauer, J. Berger, A. Chabli, V. Cardin, A. Delboulbé, Y. Gambérini, G Chamiotmaitral, S. GillessenAbstract:Context. Within the framework of the second-generation instrumentation of the Very Large Telescope Interferometer of the European Southern Observatory we have developed the four-telescope beam Combiner in integrated optics.Aims. We optimized the performance of such beam Combiners, for the first time in the near-infrared K band, for the GRAVITY instrument dedicated to the study of the close environment of the galactic centre black hole by precision narrow-angle astrometry and interferometric imaging.Methods. We optimized the design of the integrated optics chip and the manufacturing technology as well, to fulfil the very demanding throughput specification. We also designed an integrated optics assembly able to operate at 200 K in the GRAVITY cryostat to reduce thermal emission.Results. We manufactured about 50 beam Combiners by silica-on-silicon etching technology. We glued the best Combiners to single-mode fluoride fibre arrays that inject the VLTI light into the integrated optics beam Combiners. The final integrated optics assemblies have been fully characterized in the laboratory and through on-site calibrations: their global throughput over the K band is higher than 55% and the instrumental contrast reaches more than 95% in polarized light, which is well within the GRAVITY specifications.Conclusions. While integrated optics technology is known to be mature enough to provide efficient and reliable beam Combiners for astronomical interferometry in the H band, we managed to successfully extend it to the longest wavelengths of the K band and to manufacture the most complex integrated optics beam Combiner in this specific spectral band.
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Single-mode waveguides for GRAVITY
Astronomy and Astrophysics - A&A, 2018Co-Authors: K Perraut, L Jocou, F Eisenhauer, J. Berger, A. Chabli, V. Cardin, G. Chamiot-maitral, A. Delboulbé, Y. Gambérini, S. GillessenAbstract:Context. Within the framework of the second-generation instrumentation of the Very Large Telescope Interferometer of the European Southern Observatory we have developed the four-telescope beam Combiner in integrated optics.Aims. We optimized the performance of such beam Combiners, for the first time in the near-infrared K band, for the GRAVITY instrument dedicated to the study of the close environment of the galactic centre black hole by precision narrow-angle astrometry and interferometric imaging.Methods. We optimized the design of the integrated optics chip and the manufacturing technology as well, to fulfil the very demanding throughput specification. We also designed an integrated optics assembly able to operate at 200 K in the GRAVITY cryostat to reduce thermal emission.Results. We manufactured about 50 beam Combiners by silica-on-silicon etching technology. We glued the best Combiners to single-mode fluoride fibre arrays that inject the VLTI light into the integrated optics beam Combiners. The final integrated optics assemblies have been fully characterized in the laboratory and through on-site calibrations: their global throughput over the K band is higher than 55% and the instrumental contrast reaches more than 95% in polarized light, which is well within the GRAVITY specifications.Conclusions. While integrated optics technology is known to be mature enough to provide efficient and reliable beam Combiners for astronomical interferometry in the H band, we managed to successfully extend it to the longest wavelengths of the K band and to manufacture the most complex integrated optics beam Combiner in this specific spectral band.
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the integrated optics beam Combiner assembly of the gravity vlti instrument
Proceedings of SPIE, 2012Co-Authors: L Jocou, K Perraut, A Nolot, Thibaut Moulin, Yves Magnard, P Labeye, V Lapras, F Eisenhauer, G Perrin, A AmorimAbstract:Gravity aims at enhancing infrared imaging at VLTI to significantly improve our understanding of the physical processes related to gravitation and accretion within compact objects. With its fiber-fed integrated optics, infrared wavefront sensors, fringe tracker, beam stabilization and a novel metrology concept, GRAVITY will push the sensitivity and accuracy of astrometry and interferometric imaging far beyond what is offered today. Four telescopes will be combined in dual feed in the K band providing precision astrometry of order 10 micro-arcseconds, and imaging with 4- milliarcsecond resolution. The fringe tracker and the scientific instrument host an identical integrated optics beam Combiner made by silica-on-silicon etching technology that is put inside a cryogenic vessel and cooled down to 200K to reduce thermal background and increase sensitivity. This paper gives the design of the integrated beam Combiner and of its fibered array that allows feeding the Combiner with stellar light. Lab measurement of spectral throughput and interferometric performance for beam Combiners made by Flame Hydrolysis Deposition and by Plasma-Enhanced Chemical Vapor Deposition (PECVD) are given. The procedure to glue together the beam Combiner and its fibered array is described as well as the tests to validate the performance and the ageing effects at low temperature. Finally the thermal analysis and the eigen-frequency study of the whole device are presented.
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an integrated optics beam Combiner for the second generation vlti instruments
Astronomy and Astrophysics, 2009Co-Authors: M Benisty, L Jocou, K Perraut, P Labeye, J. Berger, F Malbet, P KernAbstract:Context. Recently, an increasing number of scientific publications making use of images obtained with near-infrared long-baseline interferometry have been produced. The technique has reached, at last, a technical maturity level that opens new avenues for numerous astrophysical topics requiring milli-arc-second model-independent imaging. The Very Large Telescope Interferometer (VLTI) will soon be equipped with instruments able to combine between four and six telescopes. Aims. In the framework of the VLTI second generation instruments Gravity and VSI, we propose a new beam combining concept using integrated optics (IO) technologies with a novel ABCD-like fringe encoding scheme. Our goal is to demonstrate that IO-based combinations bring considerable advantages in terms of instrumental design and performance. We therefore aim at giving a full characterization of an IO beam Combiner in order to establish its performance and check its compliance with the specifications of an imaging instrument. Methods. For this purpose, prototype IO beam Combiners have been manufactured and laboratory measurements were made in the H band with a dedicated testbed, simulating a four-telescope interferometer. We studied the beam Combiners through the analysis of throughput, instrumental visibilities, phases and closure phases in wide band as well as with spectral dispersion. Study of the polarization properties was also carried out. Results. We obtain competitive throughput (65%), high and stable instrumental contrasts (from 80% in wide band up to 100% ± 1% with spectral dispersion), stable but non-zero closure phases (e.g. 115° ± 2°) which we attribute to internal optical path differences (OPD) that can be calibrated. We validate a new static and an achromatic phase shifting IO function close to the nominal 90° value (e.g. 80° ± 1°). All these observables show limited chromaticity over the H band range. Conclusions. Our results demonstrate that such ABCD-like beam Combiners are particularly well suited for interferometric combination of multiple beams to achieve aperture synthesis imaging. This opens the way to extending this technique to all near infrared wavelengths and in particular, the K band.
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an integrated optics beam Combiner for the second generation vlti instruments
arXiv: Instrumentation and Methods for Astrophysics, 2009Co-Authors: M Benisty, L Jocou, K Perraut, P Labeye, J. Berger, F Malbet, P KernAbstract:The very recent years have seen a promising start in scientific publications making use of images produced by near-infrared long-baseline interferometry. The technique has reached, at last, a technical maturity level that opens new avenues for numerous astrophysical topics requiring milli-arcsecond model-independent imaging. The Very Large Telescope Interferometer (VLTI) is on the path to be equipped with instruments capable to combine between four to six telescopes. In the framework of the VLTI second generation instruments Gravity and VSI, we propose a new beam combining concept using Integrated Optics (IO) technologies with a novel ABCD-like fringe encoding scheme. Our goal is to demonstrate that IO-based combination brings considerable advantages in terms of instrumental design and performance. We therefore aim at giving a full characterization of an IO beam Combiner to establish its performances and check its compliance with the specifications of an imaging instrument. Laboratory measurements were made in the H band with a dedicated testbed. We studied the beam Combiners through the analysis of throughput, instrumental visibilities, phases and closure phases in wide band as well as with spectral dispersion. Study of the polarization properties is also done. We obtain competitive throughput, high and stable instrumental contrasts, stable but non-zero closure phases which we attribute to internal well calibrable optical path differences. We validate a new static and achromatic phase shifting IO function close to the nominal 90deg value. All these observables show limited chromaticity over the H band range. Our results demonstrate that such ABCD-like beam Combiners are particularly well suited to achieve aperture synthesis imaging. This opens the way to extend to all near infrared wavelengths and in particular, the K band.
Lin Gao - One of the best experts on this subject based on the ideXlab platform.
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parametric analysis and optimization for a combined power and refrigeration cycle
Applied Energy, 2008Co-Authors: Jiangfeng Wang, Yiping Dai, Lin GaoAbstract:Abstract A combined power and refrigeration cycle is proposed, which combines the Rankine cycle and the absorption refrigeration cycle. This combined cycle uses a binary ammonia–water mixture as the working fluid and produces both power output and refrigeration output simultaneously with only one heat source. A parametric analysis is conducted to evaluate the effects of thermodynamic parameters on the performance of the combined cycle. It is shown that heat source temperature, environment temperature, refrigeration temperature, turbine inlet pressure, turbine inlet temperature, and basic solution ammonia concentration have significant effects on the net power output, refrigeration output and exergy efficiency of the combined cycle. A parameter optimization is achieved by means of genetic algorithm to reach the maximum exergy efficiency. The optimized exergy efficiency is 43.06% under the given condition.
S. Gillessen - One of the best experts on this subject based on the ideXlab platform.
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single mode waveguides for gravity i the cryogenic 4 telescope integrated optics beam Combiner
Astronomy and Astrophysics, 2018Co-Authors: K Perraut, L Jocou, F Eisenhauer, J. Berger, A. Chabli, V. Cardin, A. Delboulbé, Y. Gambérini, G Chamiotmaitral, S. GillessenAbstract:Context. Within the framework of the second-generation instrumentation of the Very Large Telescope Interferometer of the European Southern Observatory we have developed the four-telescope beam Combiner in integrated optics.Aims. We optimized the performance of such beam Combiners, for the first time in the near-infrared K band, for the GRAVITY instrument dedicated to the study of the close environment of the galactic centre black hole by precision narrow-angle astrometry and interferometric imaging.Methods. We optimized the design of the integrated optics chip and the manufacturing technology as well, to fulfil the very demanding throughput specification. We also designed an integrated optics assembly able to operate at 200 K in the GRAVITY cryostat to reduce thermal emission.Results. We manufactured about 50 beam Combiners by silica-on-silicon etching technology. We glued the best Combiners to single-mode fluoride fibre arrays that inject the VLTI light into the integrated optics beam Combiners. The final integrated optics assemblies have been fully characterized in the laboratory and through on-site calibrations: their global throughput over the K band is higher than 55% and the instrumental contrast reaches more than 95% in polarized light, which is well within the GRAVITY specifications.Conclusions. While integrated optics technology is known to be mature enough to provide efficient and reliable beam Combiners for astronomical interferometry in the H band, we managed to successfully extend it to the longest wavelengths of the K band and to manufacture the most complex integrated optics beam Combiner in this specific spectral band.
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Single-mode waveguides for GRAVITY
Astronomy and Astrophysics - A&A, 2018Co-Authors: K Perraut, L Jocou, F Eisenhauer, J. Berger, A. Chabli, V. Cardin, G. Chamiot-maitral, A. Delboulbé, Y. Gambérini, S. GillessenAbstract:Context. Within the framework of the second-generation instrumentation of the Very Large Telescope Interferometer of the European Southern Observatory we have developed the four-telescope beam Combiner in integrated optics.Aims. We optimized the performance of such beam Combiners, for the first time in the near-infrared K band, for the GRAVITY instrument dedicated to the study of the close environment of the galactic centre black hole by precision narrow-angle astrometry and interferometric imaging.Methods. We optimized the design of the integrated optics chip and the manufacturing technology as well, to fulfil the very demanding throughput specification. We also designed an integrated optics assembly able to operate at 200 K in the GRAVITY cryostat to reduce thermal emission.Results. We manufactured about 50 beam Combiners by silica-on-silicon etching technology. We glued the best Combiners to single-mode fluoride fibre arrays that inject the VLTI light into the integrated optics beam Combiners. The final integrated optics assemblies have been fully characterized in the laboratory and through on-site calibrations: their global throughput over the K band is higher than 55% and the instrumental contrast reaches more than 95% in polarized light, which is well within the GRAVITY specifications.Conclusions. While integrated optics technology is known to be mature enough to provide efficient and reliable beam Combiners for astronomical interferometry in the H band, we managed to successfully extend it to the longest wavelengths of the K band and to manufacture the most complex integrated optics beam Combiner in this specific spectral band.
