Alcatel-Lucent

About: Alcatel-Lucent is a based out in Stuttgart, Germany. It is known for research contribution in the topics: Signal & Network packet. The organization has 37003 authors who have published 53332 publications receiving 1430547 citations. The organization is also known as: Alcatel-Lucent S.A. & Alcatel.

Time-Varying Network Tomography: Router Link Data

Abstract: The origin-destination (OD) traffic matrix of a computer network is useful for solving problems in design, routing, configuration debugging, monitoring, and pricing. Directly measuring this matrix is not usually feasible, but less informative link measurements are easy to obtain. This work studies the inference of OD byte counts from link byte counts measured at router interfaces under a fixed routing scheme. A basic model of the OD counts assumes that they are independent normal over OD pairs and iid over successive measurement periods. The normal means and variances are functionally related through a power law. We deal with the time-varying nature of the counts by fitting the basic iid model locally using a moving data window. Identifiability of the model is proved for router link data and maximum likelihood is used for parameter estimation. The OD counts are estimated by their conditional expectations given the link counts and estimated parameters. Thus, OD estimates are forced to be positive ...

Network MIMO With Linear Zero-Forcing Beamforming: Large System Analysis, Impact of Channel Estimation, and Reduced-Complexity Scheduling

Abstract: We consider the downlink of a multicell system with multiantenna base stations and single-antenna user terminals, arbitrary base station cooperation clusters, distance-dependent propagation pathloss, and general “fairness” requirements. Base stations in the same cooperation cluster employ joint transmission with linear zero-forcing beamforming, subject to sum or per-base station power constraints. Intercluster interference is treated as noise at the user terminals. Analytic expressions for the system spectral efficiency are found in the large-system limit where both the numbers of users and antennas per base station tend to infinity with a given ratio. In particular, for the per-base station power constraint, we find new results in random matrix theory, yielding the squared Frobenius norm of submatrices of the Moore-Penrose pseudo-inverse for the structured non-i.i.d. channel matrix resulting from the cooperation cluster, user distribution, and path-loss coefficients. The analysis is extended to the case of nonideal Channel State Information at the Transmitters obtained through explicit downlink channel training and uplink feedback. Specifically, our results illuminate the trade-off between the benefit of a larger number of cooperating antennas and the cost of estimating higher-dimensional channel vectors. Furthermore, our analysis leads to a new simplified downlink scheduling scheme that preselects the users according to probabilities obtained from the large-system results, depending on the desired fairness criterion. The proposed scheme performs close to the optimal (finite-dimensional) opportunistic user selection while requiring significantly less channel state feedback, since only a small fraction of preselected users must feed back their channel state information.

Large Synoptic Survey Telescope: Overview

Abstract: A large wide-field telescope and camera with optical throughput over 200 m2 deg2 -- a factor of 50 beyond what we currently have -- would enable the detection of faint moving or bursting optical objects: from Earth threatening asteroids to energetic events at the edge of the optical universe. An optimized design for LSST is a 8.4 m telescope with a 3 degree field of view and an optical throughput of 260 m2 deg2. With its large throughput and dedicated all-sky monitoring mode, the LSST will reach 24th magnitude in a single 10 second exposure, opening unexplored regions of astronomical parameter space. The heart of the 2.3 Gpixel camera will be an array of imager modules with 10 μm pixels. Once each month LSST will survey up to 14,000 deg2 of the sky with many ~10 second exposures. Over time LSST will survey 30,000 deg2 deeply in multiple bandpasses, enabling innovative investigations ranging from galactic structure to cosmology. This is a shift in paradigm for optical astronomy: from "survey follow-up" to "survey direct science." The resulting real-time data products and fifteen petabyte time-tagged imaging database and photometric catalog will provide a unique resource. A collaboration of ~80 engineers and scientists are gearing up to confront this exciting challenge.

Electronic states of semiconductor clusters: Homogeneous and inhomogeneous broadening of the optical spectrum

Abstract: The homogeneous (single‐cluster) and inhomogeneous contributions to the low temperature electronic absorption spectrum of 35–50 A diameter CdSe clusters are separated using transient photophysical hole burning. The clusters have the cubic bulk crystal structure, but their electronic states are strongly quantum confined. The inhomogeneous broadening of these features arises because the spectrum depends upon cluster size and shape, and the samples contain similar, but not identical, clusters. The homogeneous spectrum, which consists of a peak 140 cm−1 (17 meV) wide, with a phonon sideband and continuum absorption to higher energy, is compared to a simple molecular orbital model. Electron–vibration coupling, which is enhanced in small clusters, contributes to the substantial broadening of the homogeneous spectrum. The inhomogeneous width of the lowest allowed optical transition was found to be 940 cm−1, or seven times the homogeneous width, in the most monodisperse sample.