Bell Labs

About: Bell Labs is a based out in . It is known for research contribution in the topics: Laser & Optical fiber. The organization has 36499 authors who have published 59862 publications receiving 3190823 citations. The organization is also known as: Bell Laboratories & AT&T Bell Laboratories.

Indefinite-quadratic estimation and control: a unified approach to H 2 and H ∞ theories

Abstract: This monograph presents a unified mathematical framework for a wide range of problems in estimation and control. The authors discuss the two most commonly used methodologies: the stochastic H^2 approach and the deterministic (worst-case) H∞ approach. Despite the fundamental differences in the philosophies of these two approaches, the authors have discovered that, if indefinite metric spaces are considered, they can be treated in the same way and are essentially the same. The benefits and consequences of this unification are pursued in detail, with discussions of how to generalize well-known results from H^2 theory to H∞ setting, as well as new results and insight, the development of new algorithms, and applications to adaptive signal processing.

Infrared Lattice Bands of Quartz

Abstract: The infrared lattice bands of $\ensuremath{\alpha}$ quartz have been investigated at 297\ifmmode^\circ\else\textdegree\fi{}K from 5 to 37\ensuremath{\mu} in reflection and transmission with polarized light. Previously published measurements of the optical constants do not agree in this spectral range. It is shown that dispersion theory can fit the data within experimental error throughout the range, and accurate values of the dispersion parameters and the optical constants are obtained. This is the first accurate dispersion analysis of a complex spectrum. A study was made of the accuracy of the Kramers-Kronig method of analysis on this spectrum. The strength, width, and frequency of 14 optically active lattice vibrations are given, 4 of which have not previously been established. From a consideration of published Raman data, 10 of the resonances are assigned according to symmetry type as fundamental vibrations.

Raman response function of silica-core fibers

Abstract: For analyzing the propagation of ultrashort optical pulses, Raman gain is conveniently described as a response function in the time domain. In this paper we develop the Raman response function for silica-core fibers and use it to study the effect of Raman gain in regimes of normal and anomalous dispersion.

How Much Training is Required for Multiuser Mimo

Abstract: An M-element antenna array (the base station) transmits, on the downlink, K les M sequences of QAM symbols selectively and simultaneously to K autonomous single-antenna terminals through a linear pre-coder that is the pseudo-inverse of an estimate of the forward channel matrix. We assume time-division duplex (TDD) operation, so the base station derives its channel estimate from taurp pilot symbols which the terminals transmit on the reverse link. A coherence interval of T symbols is expended as follows: taurp reverse pilot symbols, one symbol for computations, and (T-l-taurp) forward QAM symbols for each terminal For a given coherence interval, number of base station antennas, and forward- and reverse-SINR's we determine the optimum number of terminals to serve simultaneously and the optimum number of reverse pilot symbols to employ by choosing these parameters to maximize a lower bound on the net sum-throughput. The lower bound rigorously accounts for channel estimation error, and is valid for all SINR's. Surprisingly it is always advantageous to increase the number of base station antennas, even when the reverse SINR is low and the channel estimate poor: greater numbers of antennas enable us to climb out of the noise and to serve more terminals. Even within short coherence intervals (T= 10 symbols) and with low SINR's (-10.0 dB reverse, 0.0 dB forward) given large numbers of base station antennas (M ges 16 ) it is both feasible and advantageous to learn the channel and to serve a multiplicity of terminals simultaneously as well.

Efficient Pattern Recognition Using a New Transformation Distance

Abstract: Memory-based classification algorithms such as radial basis functions or K-nearest neighbors typically rely on simple distances (Euclidean, dot product...), which are not particularly meaningful on pattern vectors. More complex, better suited distance measures are often expensive and rather ad-hoc (elastic matching, deformable templates). We propose a new distance measure which (a) can be made locally invariant to any set of transformations of the input and (b) can be computed efficiently. We tested the method on large handwritten character databases provided by the Post Office and the NIST. Using invariances with respect to translation, rotation, scaling, shearing and line thickness, the method consistently outperformed all other systems tested on the same databases.