Tunis, Tunisia
Tunis, Tunisia

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Cherif R.,CirtaCom Laboratory | Zghal M.,CirtaCom Laboratory | Nikolov I.,Elettra - Sincrotrone Trieste | Danailov M.,Elettra - Sincrotrone Trieste
Optics Communications | Year: 2010

A large mode area photonic crystal fiber (LMA PCF) with an effective area of 180 μm2 is used to generate a high energy, micro-joule range, flat, octave spanning supercontinuum (SC) extending from ~ 600 nm to ~ 1720 nm. A train of femtosecond pulses from a widely-tunable parametric amplifier pumped by a Ti:Sapphire regenerative amplifier system are coupled into a 20 cm length of LMA PCF generating a SC of 1.4 μJ energy. We present an experimental study of the high energy SC as a function of the input power and the pumping wavelength. The spectrum obtained at a pump wavelength of 1260 nm presents spectral flatness variation less than 12 dB over more than 1.1 octave bandwidth. The physical processes behind the SC formation are described in the normal and the anomalous dispersion regions. Our experimental results are successfully compared with the numerical solution of the nonlinear Schrödinger equation. © 2010 Elsevier B.V. All rights reserved.

Mlayeh Y.,CirtaCom Laboratory | Tlili F.,CirtaCom Laboratory | Ghazel A.,CirtaCom Laboratory | Nafkha A.,Supelec
2010 2nd International Conference on Communications and Networking, ComNet 2010 | Year: 2010

Performances and capacity of MIMO-OFDM systems are enhanced with adaptive MIMO techniques such as Demmel condition number based switching algorithm. In this paper we show that the complexity of this algorithm can be reduced by using the 2-norm condition number of the channel matrix as the selection metric. Simulation results show that using this selection criterion, the switching algorithm offers the same performances obtained when using the Demmel condition number.

Grati K.,Cirtacom Laboratory | Khouja N.,Cirtacom Laboratory | Le Gal B.,University of Bordeaux 1 | Ghazel A.,Cirtacom Laboratory
VLSI Design | Year: 2012

Decimation filters are widely used in communication-embedded systems. In fact, decimation filters are useful for implementing channel filtering or selection with low-computation complexity requirements. Many multistandard receiver designs that are required in ubiquitous embedded systems are based on a cascade of decimation filter processing. Filter number and implementation architectures have a significant impact on system performances, such as computation complexity, area, throughput, and power consumption. In this work, we present filter power consumption estimation models for FIR filters. Power consumption models were obtained from a large number of FIR filter syntheses using a direct form. Several curves that estimate power consumption were extracted from these synthesis results. Then, we have evaluated the impact of polyphase decomposition on power consumption of FIR filter and compared it with the direct form results. Some tips regarding power consumption were deduced for the polyphase implementation form. The aim of this work is to help a system designer to select an efficient implementation for FIR in terms of power consumption without having to implement and synthesize the different possible solutions. The proposed method is applied for STMicroelectronics libraries 90nm and 65nm low power then validated with a use case of multistandard receiver designing. Copyright 2012 Khaled Grati et al.

Khouja N.,CirtaCom Laboratory | Grati K.,CirtaCom Laboratory | Le Gal B.,University of Bordeaux 1 | Ghazel A.,CirtaCom Laboratory
2011 IEEE GCC Conference and Exhibition, GCC 2011 | Year: 2011

Many communications embedded systems implement decimation filters. In particular, base-band stage in multistandard receivers is composed of cascade of decimation filters performing channel selection. The number of used filter and the kind of these filters can have a significant impact on the computation complexity and power consumption of multistandard receivers. In This work we present FIR filters' power consumption estimation models. Models were obtained from a large number of FIR filter syntheses using direct and polyphase forms. Several curves that estimate power consumption were extracted from these experimental results. The idea behind this work is to use the obtained models and curves to help filter designer to make the right choice regarding decimation factor versus power consumption. © 2011 IEEE.

Cherif R.,CirtaCom Laboratory | Zghal M.,CirtaCom Laboratory | Tartara L.,University of Pavia | Degiorgio V.,University of Pavia
NATO Science for Peace and Security Series B: Physics and Biophysics | Year: 2010

We report on the influence of the cut-off wavelength on the super-continuum generation in which the spectral broadening occurs only on the blue side of the pump wavelength. As a consequence a limit to the extent of the super-contiuum is set and thus a way for tailoring the broadened spectrum according to a peculiar application is provided. The experiment consists of launching a train of femtosecond pulses into a 45-cm-long span of a photonic crystal fiber (PCF) by means of an offset pumping technique that can selectively excite higher-order modes. The PCF presents a wide range of wavelengths in which the fundamental mode experiences normal dispersion, whereas higher-order modes, LP11 and LP21 propagate in the anomalous dispersion regime, generating a supercontinuum based on the soliton fission mechanism. When exciting LP 21 we are able to generate an almost purely visible supercontinuum even with pulse energies below 100 pJ. Our experimental results are compared with the numerical solutions of the nonlinear Schrödinger equation. © 2010 Springer Science+Business Media B.V.

Mlayeh Y.,CIRTACOM Laboratory | Rouissi F.,CIRTACOM Laboratory | Tlili F.,CIRTACOM Laboratory | Ghazel A.,CIRTACOM Laboratory
2011 18th IEEE International Conference on Electronics, Circuits, and Systems, ICECS 2011 | Year: 2011

In this paper, we propose two methods to perform a switching between spatial multiplexing and MIMO diversity in order to improve performances of a 2x2 OFDM-MIMO system. Each method is defined depending on the granularity of the spatial processing. The comparison of BER performances of the two schemes leads to the choice of the sub-carrier based switching processing which gives the most significant improvement. © 2011 IEEE.

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