Orange S.A.

About: Orange S.A. is a company organization based out in Paris, France. It is known for research contribution in the topics: Terminal (electronics) & Signal. The organization has 6735 authors who have published 9190 publications receiving 156440 citations. The organization is also known as: Orange SA & France Télécom.

Turbo channel estimation for OFDM systems on highly time and frequency selective channels

Abstract: We propose an optimum turbo channel estimation algorithm for OFDM systems on highly selective fading channels. This algorithm performs an iterative estimation of the multiplicative fading channel according to the maximum a posteriori criterion. It requires a convenient representation of the highly time and frequency selective fading channel based on the Karhunen-Loeve expansion theorem. It also optimally takes into account the coded structure of the data symbols in the estimation process thanks to the Bahl (1974) algorithm.

Boiling local heat transfer enhancement in minichannels using nanofluids

Abstract: This paper reports an experimental study on nanofluid convective boiling heat transfer in parallel rectangular minichannels of 800 μm hydraulic diameter. Experiments are conducted with pure water and silver nanoparticles suspended in water base fluid. Two small volume fractions of silver nanoparticles suspended in water are tested: 0.000237% and 0.000475%. The experimental results show that the local heat transfer coefficient, local heat flux, and local wall temperature are affected by silver nanoparticle concentration in water base fluid. In addition, different correlations established for boiling flow heat transfer in minichannels or macrochannels are evaluated. It is found that the correlation of Kandlikar and Balasubramanian is the closest to the water boiling heat transfer results. The boiling local heat transfer enhancement by adding silver nanoparticles in base fluid is not uniform along the channel flow. Better performances and highest effect of nanoparticle concentration on the heat transfer are obtained at the minichannels entrance.

Perfect reconstruction conditions and design of oversampled DFT-modulated transmultiplexers

Abstract: This paper presents a theoretical analysis of oversampled complex modulated transmultiplexers. The perfect reconstruction (PR) conditions are established in the polyphase domain for a pair of biorthogonal prototype filters. A decomposition theorem is proposed that allows it to split the initial system of PR equations, that can be huge, into small independent subsystems of equations. In the orthogonal case, it is shown that these subsystems can be solved thanks to an appropriate angular parametrization. This parametrization is efficiently exploited afterwards, using the compact representation we recently introduced for critically decimated modulated filter banks. Two design criteria, the out-of-band energy minimization and the time-frequency localization maximization, are examined. It is shown, with various design examples, that this approach allows the design of oversampled modulated transmultiplexers, or filter banks with a thousand carriers, or subbands, for rational oversampling ratios corresponding to low redundancies. Some simulation results, obtained for a transmission over a flat fading channel, also show that, compared to the conventional OFDM, these designs may reduce the mean square error.

Noiseless optical amplification in quasi-phase-matched bulk lithium niobate

Abstract: An optical parametric amplifier (OPA) has been demonstrated in bulk, periodically poled lithium niobate and is shown to operate with a noise figure well below the classical limit. In contrast to conventional OPA's, this device uses quasi-phase matching to provide the coupling between the pump and the signal. Comparison of the measured performance with that of a theoretical model reveals that the main intrinsic contribution to the output noise is due to spatial and temporal mode mixing, which arises as a consequence of tight focusing of the incident beams. Factors that affect the performance of this amplifier are identified theoretically and their relative importance investigated for both amplification and squeezing.

Dynamics of microcavity polaritons in the presence of an electron gas

Abstract: The dynamics of microcavity polaritons in the presence of an electron gas is experimentally studied through time-resolved photoluminescence under nonresonant excitation. Electrons are shown to accelerate the emission dynamics of the whole system, both in the polariton trap close to the center of the Brillouin zone $(k=0)$ and in the reservoir of large in-plane wave-vector excitonic states. By studying both the bare quantum well and the microcavity sample, the observed features are explained by the interplay between the physics of excitons and that of polariton relaxation.