Showing papers by "Orange S.A. published in 1995"

Subspace methods for the blind identification of multichannel FIR filters

Abstract: This paper addresses a problem arising in a context of digital communications. A digital source is transmitted through a continuous channel (the propagation medium), and several measurements are performed at the receiver, either by means of several sensors, or by oversampling the received signal compared to the emission rate. Given only these observations, the baseband equivalents of the corresponding channels have to be recovered. An orthogonality property between "signal" and "noise" subspaces is exploited to build some quadratic form whose minimization yields the desired estimates up to a scale factor. This is in the same spirit as recent works by Tong et al. (see Proc. 25th Asilomar Conf., p.856-860, 1991) but requires fewer computations. Numerical simulations demonstrate the performance of the proposed methods in a channel identification context. >

Chiral metal complexes with large octupolar optical nonlinearities

Abstract: OPTICALLY nonlinear organic materials show considerable potential for applications in optical signal processing and telecommunications1,2. Most materials are based on the p-nitro-aniline template, in which the optical nonlinearities are intimately associated with quasi-one-dimensional charge transfer. But there are problems associated with this conventional approach, arising from the strongly dipolar nature of the molecules2. It has recently been recognized3–5 that two- and three-dimensional stereochemistry offers new possibilities for the design and synthesis of optically nonlinear molecules, in which charge transfer is multidirectional rather than dipolar in character; octupolar nonlinearities have now been demonstrated in several molecular systems5–7. Tri-substituted ruthenium complexes6 appear particularly attractive because intense, multidirectional metal-to-ligand charge transfer leads to a significant enhancement of the optical nonlinearity, as quantified by the quadratic hyperpolarizability, β. Here we show that the choice of ligand can further increase β to values in excess of 10-27e.s.u., comparable to the best dipolar optically nonlinear molecules.

A fast single-chip implementation of 8192 complex point FFT

Abstract: Large-scale single-frequency networks are now being considered in Europe as very promising network topologies to achieve drastic savings in spectrum usage for digital terrestrial television transmission. Such networks are possible using the COFDM system, with large guard intervals (more than 200 /spl mu/s) to absorb long echoes. In order to limit the spectral efficiency loss to about 20%, very long size fast Fourier transforms (up to 8 K complex points) have to be performed in real time for the demodulation of every COFDM symbol (every 1 ms). This paper presents the first VLSI single chip dedicated to the computation of direct or inverse fast Fourier transforms of up to 8192 complex points. Due to its pipelined architecture, it can perform an 8 K FFT every 400 /spl mu/s and a 1 K FFT every 50 /spl mu/s. All the storage is onchip, so that no external memories are required. A new internal result scaling technique, called convergent block floating point, has been introduced in order to minimize the required storage for a given quantization noise, The chip, 1 cm/sup 2/ large with 1.5 million transistors, has been designed in a 3.3 V-0.5 /spl mu/m triple-level metal CMOS process and is fully functional. The 8 K complex FFT function could therefore be introduced in the coming years in digital terrestrial TV receivers at low cost. >

Memory device for high-density content adressable memory

Abstract: The invention relates to a memory cell for a static associative memory comprising two arrays of transistors, a first array having a data storage function and a second array having a comparison function between the stored data item and a data item applied to the input of the cell, the comparison result being obtained on a selection line S, in which the second array (T1,T2,T3,T4) of transistors is partly formed by the transistors of the first array (T3,T4,T7,T8,T5,T6). The structure of the cell thus has reduced overall dimensions compared with known structures.

Squarylium Dyes: Structural Factors Pertaining to the Negative Third-Order Nonlinear Optical Response

Abstract: Off-resonant electric field induced second harmonic generation (EFISH) and resonant third harmonic generation (THG) measurements of two squarylium dyes are reported. The magnitude of y is large for both processes. The EFISH measurement clearly shows that the off-resonant third-order polarizability is negative, a consequence of the dominance of a non-two-photon mechanism. This unusual result is in agreement with our earlier reports on two other squarylium dyes. Resonant THG measurements strongly suggest that the two-photon contribution, while smaller than the one-photon contribution, is not negligible and cannot be entirely ignored when defining the overall third- order optical susceptibility. Consequently, the squaryliums are best qualitatively described by a three-level model that truncates to two dominant perturbation terms. Also reported is the isomeric distribution of squaryliums. Proton Nh4R results are interpreted by way of molecular mechanics to show that the squaryliums can readily exist as a mixture of isomers. The possible effects on nonlinear optical (NLO) measurements via an orientational contribution to the EFISH y are discussed. An X-ray structure for the squarylium dye TSQ is presented and interpreted. The X-ray structure clearly suggests that the squarylium dyes are extensively bond delocalized with relatively little bond length alternation.

Process of combined authentication of a telecommunication terminal and of a user module

Abstract: The terminal and the user module are authenticated in a combined manner on the basis of an authentication key calculated on the one hand by the terminal and on the other hand by the network. A session key is firstly calculated by the user module on the basis of a secret user key, of a terminal identification parameter and of a first random number. Calculation of the authentication key by the terminal involves this session key calculated by the user module, a secret terminal identification key and a second random number. The network calculates in the same way the session key and the authentication key by retrieving the secret keys on the basis of the identification parameters transmitted by the terminal. The terminals can then be authenticated by the network independently of the associated user modules.

A finite element method based on Whitney forms to solve Maxwell equations in the time domain

Abstract: A new finite element method in the time domain based on the Whitney forms is presented. Using edge elements and face elements for space discretization of the fields and a leap-frog scheme in time, the algorithm gives a direct way to solve Maxwell equations in general unstructured meshes. >

Modelling of the rainfall rate cumulative distribution for the design of satellite and terrestrial communication systems

Abstract: The design of line of sight (L.O.S.) or satellite links requires annual point rainfall rate statistics for several percentages of time in the locations where the radiocommunication links are planned. Rain rate data within an average year, indeed, allow the estimation of the time percentage during which attenuation due to rain is significant, and consequently the future link margin. To meet ITU Radiocommunication Sector's Recommendations, we propose a probability law model allowing the prediction of the rainfall rate cumulative distribution in temperate and tropical climates. This model, which can be easily used, may serve as a very useful and accurate enough tool for radiocommunication engineers and scientists.

A Decomposition Method for Quadratic Zero-One Programming

Abstract: This paper proposes a decomposition method to compute a lower bound for unconstrained quadratic zero-one minimization. First, we show that any quadratic function can be expressed as a sum of particular quadratic functions whose minima can be computed by a simple branch and bound algorithm. Then, assuming some hypothesis, we prove that, among all possible decompositions, the best one can be found by a Lagrangian decomposition method. Moreover, we show that our algorithm gives at least the roof dual bound and should give better results in practice. Eventually, computational results and comparison with Pardalos and Rodgers' algorithm demonstrate the efficiency of our method for medium size problems up to 100 variables.

Raman Scattering Enhancement by Optical Confinement in a Semiconductor Planar Microcavity

Abstract: We report optical-phonon Raman scattering enhancements of over 4 orders of magnitude in a $\frac{\ensuremath{\lambda}}{2}$ semiconductor planar microcavity. By varying the incidence angle both excitation and Stokes photons can simultaneously resonate with the cavity mode, their fields being strongly amplified. We demonstrate the cavity geometry as a promising tool to study solid state excitations in reduced dimensions with highly increased sensitivity.

Large deviations approximation for fluid queues fed by a large number of on/off sources

Abstract: A general logarithmic equivalent is given for the stationary complementary distribution function of a fluid queue fed by a large number of on/off sources. Close asymptotic approximations are also provided. These approximations are numerically validated and applied to the dimensioning of an ATM multiplexer offered variable bit rate sources of general on/off type. >

Optical packet switching system

Abstract: An optical signal switch identifies the routing of each optical packet, directs each packet arriving at any input to the output corresponding to the routing, and includes delay lines through which the optical signals pass selectively. The switch has three stages: a first stage directing each optical packet received at an input to a chosen delay line, a second stage coupled to the output of the delay lines to direct the optical packets selectively to the output corresponding to the determined routing, and an output third stage.

A set of algorithms linking NLMS and block RLS algorithms

Abstract: This paper describes a set of block processing algorithms which contains as extremal cases the normalized least mean squares (NLMS) and the block recursive least squares (BRLS) algorithms. All these algorithms use small block lengths, thus allowing easy implementation and small input-output delay. It is shown that these algorithms require a lower number of arithmetic operations than the classical least mean squares (LMS) algorithm, while converging much faster. A precise evaluation of the arithmetic complexity is provided, and the adaptive behavior of the algorithm is analyzed. Simulations illustrate that the tracking characteristics of the new algorithm are also improved compared to those of the NLMS algorithm. The conclusions of the theoretical analysis are checked by simulations, illustrating that, even in the case where noise is added to the reference signal, the proposed algorithm allows altogether a faster convergence and a lower residual error than the NLMS algorithm. Finally, a sample-by-sample version of this algorithm is outlined, which is the link between the NLMS and recursive least squares (RLS) algorithms. >

Smart card based system for telephone-securized transactions

Abstract: A Smart Card Based System for telephone-securized transactions. The system includes a telephone terminal (10) connected to a server (30) and a package or unit (40) incorporating a keypad (42), a smart card (48) and sound signal transmission device. The transmission of the information of the card to the server takes place by way of sound signals and the telephone terminal. In the other direction, the information is addressed in vocal manner to the user, who types them on the keypad (42) of the unit (40). Application to securized teletransactions, particularly electronic funds transfer.

Process for the broadcasting of programmes with progressive conditional access and separation of the information flow and the corresponding receiver

Abstract: Process for the broadcasting of programmes with progressive conditional access and separation of the information flow, as well as the corresponding receiver, In order to form the elementary flow, groups of m successive elements of the multiplex are taken and for forming the complimentary flow groups of p successive elements of the multiplex are taken. Application to television with entitlement checking.

Device for rejection of the image signal of a signal converted to an intermediate frequency

Abstract: In a device for rejecting the image signal of a signal converted to a predetermined intermediate frequency, a local oscillator supplies a local signal at a frequency chosen according to the frequency of the signal and the intermediate frequency. A first phase-shifter has two passive phase-shifter cells including resistive and capacitive components and respectively connected to the output of the oscillator to supply two mixer signals in phase quadrature. Two mixers receive an input signal containing a signal and its image signal and a respective mixer signal and supply two intermediate signals at the intermediate frequency. A second phase-shifter comprises two passive phase-shifter cells comprising resistive and capacitive components and respectively connected to the outputs of the two mixers to introduce a further phase quadrature relationship between the two intermediate signals. A summing device connected to the outputs of the two passive phase-shifter cells of the second phase-shifter eliminates the image signal.

Dual-polarization slot-coupled printed antennas fed by stripline

Abstract: This article presents recent techniques in the field of dual-polarization printed antennas for designing shielded radiating structures with high-quality performances in terms of cross-polarization level and input-port isolation. The use of gridded patches provides a natural solution to filtering surface currents and is of key importance in limiting inter-element coupling in arrays. Experimental results obtained on various designs are presented. >

Porous silicon: material processing, properties and applications

Abstract: Porous silicon (PS) is known to form during electrochemical dissolution of silicon in HF-based solutions. This dissolution is obtained by monitoring either the anodic current or potential. In general, constant current is preferable, as it allows a better control of both the porosity and thickness and a good reproducibility from run to run. The simplest cell which can be used to anodize silicon is shown in Figure 1. The silicon wafer serves as the anode. The cathode is made of platinum or any HF-resistant and conducting material. The cell body itself is in general made of highly acid-resistant polymer such as Teflon. Since the entire silicon wafer serves as the anode, PS is formed on any wafer surface in contact with the HF solution, including the cleaved edges. The advantage of such equipment is its simplicity and ability to anodize Silicon-On-Insulator structures. Its drawback is the non uniformity in both the porosity and thickness of the resulting layer. This inhomogeneity is mainly due to a lateral potential drop. In fact, since the current flows laterally along the bulk of the silicon wafer, there is a difference in potential between the top (point A in Fig. 1) and the bottom (point B in Fig. 1). The potential drop across the wafer leads to different values of the local current density which induce porosity and thickness gradients.

Telecommunications network organized in reconfigurable wavelength-division-multiplexed optical loops

Abstract: In a telecommunications network organized in wavelength-division-multiplexed optical loops, each loop has tunable reception means tuned as a function of the density of the network traffic, thus being capable of being reconfigured as a function of requirements. The disclosed system can be applied to public, private and data communication networks.

OFDM signal organized so as to simplify reception

Abstract: The invention relates to a signal intended to be transmitted towards a plurality of receivers, of the type comprising at least two source signals and consisting of a plurality of independently modulated substantially orthogonal carrier frequencies distributed over a predetermined frequency band. According to the invention, said frequency band (12) is divided into at least two frequency sub-bands (131 - 134) each comprising a set of said substantially orthogonal carrier frequencies (11), and to each of said sub-bands is allocated one of said source signals, so that a receiver may retrieve from the transmitted signal, by filtration, at least one of said sub-bands and perform demodulation processing only on the carrier frequencies contained in the retrieved sub-bands. The invention also relates to a transmission process as well as to a receiver of such signal.

System for control of access to computer machines which are connected in a private network

Abstract: A system for control of access by messages to computer machines which are connected in a host private network by at least one private terminal that comprises an access control module interconnected at each input-output point of the host private network, each module allowing the selective transmission by inhibition, free or conditional authorization of the transmission of the messages to the host private network. A centralized supervisor module is associated with the host private network and interconnected by a specialized link to each access control module, allowing thus to control the selective transmission of the messages by each access control module.

Electroabsorption modulators for high-bit-rate optical communications: a comparison of strained InGaAs/InAIAs and InGaAsP/InGaAsP MQW

Abstract: Conventional high-speed (>10 GHz) external modulators at 1.55 mu m exist in various types and on several kinds of substrate material. Only electroabsorption modulators on InP have so far demonstrated polarization-independent operation at high speeds. In this paper, the properties of two strained multiple quantum well (MQW) modulators are reviewed in the context of optical fibre communications in terms of loss, drive voltage, bandwidth (>40 GHz), eye diagram, bit error rate measurements and optical power handling capacity. An effective modulation polarization sensitivity of 0.6 dB is reported. The two components differ mainly in their saturation optical power levels. A new power saturation mechanism is proposed to explain the nonlinearity of the InGaAs/lnAIAs modulator.

Review of the Synthesis Methods for AIN

Abstract: The different routes for the synthesis of aluminum nitride (AIN) powders are reviewed: the different industrial techniques from both the direct nitridation of aluminum metal and the carbothermal nitridation of alumina, and also other synthesis routes not industrially developed up to now. This paper presents a comprehensive presentation of the different chemical systems analyzed from the compilation of more than 70 publications and analysis of 91 patents.

Linearly polarized fiber-optic laser

Abstract: A fiber-optic laser comprising a birefringent optic fiber possessing a Bragg grating at each of its ends,. A light source emits a light beam having two modes of polarization in the fiber. The birefringence of the fiber makes it possible to keep the two polarization modes separate. The two Bragg gratings are photo-recorded in the fiber and are made in such a way that their resonance wavelength is matched for one polarization. The wave emitted by the fiber is then polarized linearly along P1. Applications to linearly polarized lasers for optical transmission, instrumentation, spectroscopy, medicine, the detection of chemical species and telemetry.

Modelling the network component of geographical information systems

Abstract: This paper presents a data model to manage networks with a Geographical Information System with some consideration of the path operator. The data model is based on the merge of graph theory concepts and the object-oriented paradigm. The introduction of the Master_nodes (with respect to Master_edges) allows definition of a node (with respect to an edge) as an abstraction of a sub-network. A network can be defined using several levels of definition (detail) following the importance of the nodes (with respect to the edges) within an application. The object-oriented concepts are applied to both the alphanumerical data part and to the modelling part of the topology of the graph. The data manipulation operators are basic operators. These operators are the union, an intersection and a difference. More elaborated operators, such as under constraints paths, are obtained by combining these basic operators. We present some considerations of the path operator in a GIS context and introduce the concept of the...