Open Topics

Vol. 61, n° 5-6, May-June 2006
Content available on Springerlink

Integration of the digital signature in the protocol SSL/TLS


GET/Télécom Paris, LTCI-UMR 5141 CNRS – 46, Rue Barrault, 75013 Paris, France

Abstract SSL/TLS is currently the most deployed security protocol on the Internet. SSL/TLS provides end-to-end secure communications between two entities with authentication and data protection. However, what is missing from the protocol is a way to provide the non-repudiation service. In this paper, we describe a generic implementation of the non-repudiation service as an optional module in the SSL/TLS protocol. This approach provides both parties with evidence that the transaction has taken place and a clear separation with application design and development. We discuss the motivation for our approach and our proposed architecture.

Keywords: Internet security, Transmission protocol, Electronic signature, Computing transaction, e-business, Client-server architecture, Standardization.

Quality of service management investigation in UMTS network


École Supérieure des communications de Tunis – Route Raoued Km 3.5, 2083 Ariana, Tunis, Tunisie

Abstract Bit rate announced for the future standards of telecommunication, as well as the level of integration reached are, as many factors, determining for the establishment of new applications in mobile terminals. Nowadays, mobile video streaming services are possible. Mobile users expect to receive multimedia traffic with some performance guarantees, so we must ensure the necessary quality of service during the video transmission. This paper aims at investigating quality of service issue in UMTS network. More specifically, we explore the main challenge of quality of service management to dynamically optimize the distribution of load in UMTS networks. Our investigation is organized in the following way. We formalize the optimization problem which is based on the graph theory and modelling UMTS network as well as mobile users and applications to be used. The simulation of our optimization model show a clear improvement of the quality of service perceived by an UMTS user in terms of bit rate, blocking and connection drop.

Keywords: Mobile radiocommunication, UMTS, Quality of Service, Optimization, Graph theory, Videocommunication service, Streaming, Simplex method, Simulation.

Improvement of the sensitivity detection and quality of radargram for a GPR by a micro-wave modulation

Jamal BELKADID*, Saad Dosse BENNANI**, Mounir RIFI***

* Dépt. Génie Industriel, Univ Ibn Zohr, ENSA-Agadir – BP 1136, 80 000 Agadir, Maroc
** LT, École Nationale des Sciences Appliquées – BP 696, Oujda, Maroc
*** École Supérieure de Technologie – BP. 8012 Oasis Rte d’El Jadida Casablanca, Maroc

Abstract The primary effect of the field continuously capted by a GPR is the production of a class which limits the contrast of the reflections on the targets. The target response becomes illegible sight the influence of certain disturbances which are due to the reflections caused by certain parasitic elements which are randomly distributed in the soil and the dispersion phenomenon. We present in this paper an approach based on a m-wave modulation which allowed stage this problem. The technique suggested makes it possible to do a classification of capted signals. It will be shown that the frequency of modulation fm must be higher than a cut-off frequency fc which depends on the electric parameters of the ground. In a second part of this paper, we show how to improve quality of the radargram of a system GPR by a simple convolution between the collected signal and a wavelet with a defined parameters.

Keywords Radar, Geophysical prospecting, Sol, Electrical characteristic, Microwave, Electromagnetic wave propagation, Classification, Wavelets.

Simple iterative receivers for MIMO LP-OFDM systems

Pierre-Jean BOUVET*, Maryline HÉLARD**, Vincent LE NIR***

* P.J. Bouvet is now with Philips Semiconductors, Home Innovation Center (HIC) – 2, rue de la girafe, 14079 Caen cedex 5, France
** France Telecom R&D, RESA/BWA Laboratory – 4, rue du Clos Courtel, BP 91226, 35512 Cesson Sévigné Cedex, France;
*** V. Le Nir is now with the Katholieke Universiteit Leuven, Departement Elektrotechniek (ESAT) – Kasteelpark Arenberg 10 B-3001 Leuven-Heverlee, Belgium

Abstract In this paper, LP-OFDM is combined with different MIMO schemes in order to improve performance in terms of diversity gain and to exploit capacity brought by the MIMO channel. The original contribution is the development of a generic iterative receiver designed for LP MIMO transmission able to work whatever the antenna configuration and the spatial coding scheme. By using a global MMSE criterion, interference terms coming from space-time coding and linear precoding are jointly treated leading to a very good trade-off between performance and complexity compared to trellis based detectors particularly for high order modulations, high number of antennas and/or large size of precoding matrices.

Keywords Radiocommunication, Space diversity, OFDM, Jeu signal, Itération, Transformation linéaire, Récepteur, Simulation.

Strategy oriented topology control based on mobile dedicated routers


GET/Télécom Paris (ENST) – LTCI-UMR 5141 CNRS, Computer Science and Networks Department, 46 rue Barrault, 75634 Paris Cedex, France

Abstract Due to the inherent mobility within the ad hoc environment, network topology plays a key role on routing and network performance. In this paper we propose to control the ad hoc network morphology using a set of dedicated routers. The idea is to use positively the mobility, in order to enhance ad hoc network performance. Two deployment policies are studied for a global network connectivity or a limited network diameter. We describe the Mixed Integer Linear Programming (MILP) models for these deployment policies with respect to the constraints, and show the efficiency, of the described approach through simulations (NS-2).

Keywords Radiocommunication, Ad hoc network, Topology, Network routing, Quality of Service, Linear programming, Integer programming, Graph connectivity, Mixed programming, Graph diameter, Cluster analysis.

Accurate characterization of intermodulation noise in multi carrier wide band power amplifiers based on a digital synthesis of pseudo noise gaussian stimuli

Tibault REVEYRAND*, Denis BARATAUD*, Jean-Michel NEBUS*, Alain MALLET**, Francis GIZARD**, Luc LAPIERRE**, Jacques SOMBRIN **

* IRCOM, CNRS UMR 6615, University of Limoges – 87000 Limoges, France
** Centre National d’Études Spatiales (CNES) – Centre spatial de Toulouse, 18 avenue Edouard Belin, 31401 Toulouse cedex 9, France

Abstract This paper presents an accurate technique for the characterization of intermodulation noise in wide band multi carrier power amplifiers. Band limited pseudo noise stimuli which are generated by using a computer controlled arbitrary waveform generator (AWG) connected to an I/Q modulator drive the input of the amplifier under test (AUT). The complex envelopes of the pseudo noises are measured using a sampling scope. A vector error correction is applied in order to remove systematic errors due to the imperfections of the measurement channels. Using this technique, the linearity of L and Ka band amplifiers was characterized by the noise power ratio criterion (NPR). This paper focuses also on the particular attention that must be paid to the statistical properties and peak to average ratio (PAR) of pseudo noise test signals which significantly impact the NPR measurement accuracy.

Keywords Power amplifier, Intermodulation, Wide band, Gaussian noise, Non linear amplification, Pseudo random signal, Signal envelope, Measurement method, Calibration, Time domain method.

Parallel interference cancellation efficiency for noisy signals in O-CDMA system


Université de Limoges, École Nationale Supérieure d’Ingénieurs de Limoges (ENSIL), Groupe d’Étude des Systèmes de Télécommunications de l’ENSIL (UMOP/GESTE CNRS FRE 2701) – 16, rue Atlantis – Parc ESTER – BP 6804- 87068 Limoges cedex, France.

Abstract The aim of this paper is to evaluate the robustness of Parallel Interference Cancellation (PIC) to noise contribution for an optical Code Division Multiple Access system. The theoretical expression of the PIC error probability is developed in the case of white additive Gaussian noise. From theoretical analysis, we show that, even with noise contribution, the PIC receiver outperforms the Conventional Correlation Receiver (CCR). Moreover, the results highlight that, for a given performance, the PIC receiver relaxes not only the constraint on the code length, but also the Signal to Noise Ratio compared to CCR. Particularly, this is proofed in access network context, i.e. 30 users with BER < 10-9.

Keywords CDMA, Optical telecommunication, Signal interference, Additive white Gaussian noise, Signal cancellation, Parallel system.

Secure time-stamping schemes: a distributed point of view

Alexis BONNECAZE*, Pierre LIARDET**, Alban GABILLON***, Kaouther BLIBECH***

* LIF; ESIL, département Réseaux et Multimédia, Luminy case 925, 13288 Marseille cedex 09, France ; alexis.bonnecaze  at
** LATP; UMR CNRS 6632, Université de Provence, 39 rue F Joliot-Curie, 13453 Marseille cedex 13, France
*** CSySEC/LIUPPA, Université de Pau, IUT de Mont de Marsan, Département GTR 371, rue du Ruisseau, BP 201, 40004 Mont de Marsan Cedex, France

Abstract Time-stamping is a technique used to prove the existence of a digital document prior to a specific point in time. Today, implemented schemes rely on a centralized server model that has to be trusted. We point out the drawbacks of these schemes, showing that the unique serveur represent a weak point for the system. We propose an alternative scheme which is based on a network of servers managed by administratively independent entities. This scheme appears to be a trusted and reliable distributed time-stamping scheme.

Keywords: Internet security, Distributed system, Time stamping, Digital document, Hashing.

WebAnalyzer: accurate detection of HTTP attack traces in web server logs


France Télécom R&D – 42 rue des Coutures, F-14000 Caen, France

Abstract  This paper presents a tool for detecting attacks against web server, using the analysis of web server log files. The main characteristic of this tool is its accuracy, being able to carefully graduate its analysis according to the actual success of the attacker. This capability is based on the design of a simple yet powerful signature definition language. We demonstrate the accuracy of the tool using a set of log lines representing several attack conditions and attack results.

Keywords Internet security, Web server, Intrusion detection, Data analysis.

On the effect of a spherical shield on the radiation Q and efficiency of ideal dipole antennas

Johan C.-E. STEN, Arto HUJANEN

Technical Research Centre of Finland VTT, P. O. Box 1000, FI-02044 VTT, Finland

Abstract A method is developed for calculating the radiation efficiency and quality factor, Q, for azimuthally symmetric electric (TM) and magnetic (TE) multipole fields surrounded by a semitransparent spherical shield of variable thickness, dielectric and magnetic constants involving losses. A matrix method is used to connect the transverse field components at adjacent interfaces. The Q and efficiency are determined by computing the energy stored in the near field of the multipole as well as the power radiated and dissipated in the shield. A numerical comparison of the performance of electric and magnetic dipole radiators is given as a function of frequency. An expression is derived for the permittivity of the shield which optimisés the Q.

Keywords: Dipole, Electric dipole, Magnetic dipole, Spherical configuration, Quality factor, Energetic efficiency, Near field, Stratified medium, Electromagnetic field, Matrix method, Dielectric loss.

Illumination of lines or cables network by a lightning wave modeling by current generators

Sabrina MEZOUED*, Senaa KAOUCHE*, Bachir NEKHOUL*, Kamal KERROUM**, Khalil EL KHAMLICHI DRISSI**, Françoise PALADIAN**

* Université de Jijel, BP N° 98 Ouled Aissa, Jijel 18 000, Algeria
**LASMEA, Université Blaise Pascal, 63177 Aubière, France

Abstract In this paper we propose a new formalism for the analysis of electromagnetic coupling between the lightning wave and a network of lines or cables. This approach allows obtaining currents and induced voltages directly on the set of lines or cables extremities. For this objective we use the current generators representation of the lightning wave. Then by a mathematical formulation based on the topological analysis of the network, we deduce a linear equation system which resolution leads directly to the currents and induced voltages. In order to confirm our theoretical work, we present a set of applications that allows validating this formalism.

Keywords Lightning, Transmission line, Cable, Electromagnetic coupling, Modeling, Meshed network, Induced voltage, Current source.