Étude temporelle du couplage d’une onde

This paper deals with a temporal approach of interaction between an external electromagnetic wave and an arbitrary multiconductor transmission lines (Mtl). The loads of the circuits can be linear like resistance elements or non linear as is the case of field effect transistor (Mesfet). The numerical technique used is the finite differences time domain (Fdtd) witch givesMtl temporal responses with good stability. Good agreement between the results obtained by the proposed method and those by literature and Spice model verifies the validity of theFdtd algorithm.     

A MC-CDMA system analysis in a software radio context

This paper presents a Multi-Carrier Code Division Multiple Access (Mc-Cdma) system analysis in a software radio context. Based on a combination of multi-carrier modulation and code division multiple access,Mc-Cdma benefits from the main advantages from both schemes: high spectral efficiency, high flexibility, multiple access capabilities, etc. It is firstly shown why, nowadays,Mc-Cdma is undoubtedly a high potential candidate for the air interface of the 4G cellular networks. TheMc-Cdma concept and the block-diagrams of the transmitter and the receiver are presented first. Afterwards, the technical issues concerning the processing devices for the implementation ofMc-Cdma systems in a software radio context are analysed. The advantages and disadvantages of Digital Signal Processors (Dsps) and Field Programmable Gate Arrays (Fgpas) components are discussed. The implementation ofMc-Cdma systems and the integration of signal processing algorithms as Fast Hadamard Transform (Fht) and Inverse Fast Fourier Transform (Ifft) are considered and analysed for the first time. Finally, implementation results with a mixed prototyping board are presented. Then, it is shown that a new combination of the flow graphs ofFht andIfft leads to interesting computation savings and that hardware structures asFgpas are more adapted thanDsps to those intensive computation functions. Finally, for the completeMc-Cdma modem implementation, the necessity of a Co-Design methodology is highlighted in order to obtain the best matching between algorithms and architecture.     

An evaluation oftcp with explicit congestion notification

We study the effect of Explicit Congestion Notification (ecn) ontcp for relatively large but finite file transfers inip networks, and compare it to other congestion avoidance mechanisms, namely Drop Tail (dt) and Random Early Detection (red). We use simulation to measuretcp performance for transfers initiated by a varying number of end hosts. In contrast to previous work, we focus on situations in which all nodes in the network operate uniformly under the same mechanism (dt orred orecn). Our results show that under such uniform conditionsecn does not necessarily lead to significant improvement intcp goodput, although in no case does it lead to an actual degradation in performance. Our results also show that, withecn, tcp flows benefit from lower overhead for unsuccessful transmissions. Furthermore, lockouts are largely avoided. In other words, in an all-ecn network resources are shared more fairly. Finally, we show that global synchronization is no longer an issue, and argue that currenttcp versions have essentially solved the problem, regardless of the queue management scheme employed.     

Optimizing IP networks in a hybrid IGP/MPLS environment

In this paper, we consider a traffic engineering (te) approach toip networks in a hybridigp/mpls environment. Thoughigp (Interior Gateway Protocol) routing has proven its scalability and reliability, effective traffic engineering has been difficult to achieve in public IP networks because of the limited functional capabilities of conventionalip technologies.mpls (Multi-Protocol Label Switching) on the one hand enhances the possibility to engineer traffic onip networks by allowing explicit routes. But on the other hand it suffers from the scalability (n-square) problem. Hybridigp/mpls approaches rely onip native routing as much as possible and usempls only if necessary. In this work we propose a novel hybrid traffic engineering method based on genetic algorithms, which can be considered as an offlinete approach to handle long or medium-term traffic variations in the range days, weeks or months. In our approach the maximum number of hops anlsp (Label Switched Path) may take and the number oflsps which are applied solely to improve the routing performance, are treated as constraints due to delay considerations and the complexity of management. We apply our method to the German scientific network (b-win) for which a traffic matrix is available and also to some other networks with a simple demand model. We will show results comparing this hybridigp/mpls routing scenario with the result of pureigp routing and that of a full meshmpls with and without traffic splitting.     

Optimisation de la quantification vectorielle codée par treillis: application au codage des paramètres LSF

Speech coders operating at low bit rates necessitate efficient encoding of the linear predictive coding (Lpc) coefficients. Line spectral Frequencies (Lsf) parameters are currently one of the most efficient choices of transmission parameters for theLpc coefficients. In this paper, an optimized trellis coded vector quantization (Tcvq) scheme for encoding theLsf parameters is presented. When the selection of a proper distortion measure is the most important issue in the design and operation of the encoder, an appropriate weighted distance measure has been used during theTcvq construction process. We further applied the optimizedTcvq system for encoding theLsf parameters of the us Federal Standard (Fs1016) 4.8 kbps speech coder. At lower bit rates, objective and subjective evaluation results show that the incorporatedLsf tcvq encoder performs better than the 34 bits/frameLsf scalar quantizer used originally in the fs1016 coder. The subjective tests reveal also that the 27 bit/frame scheme produces equivalent perceptual quality to that when theLsf parameters are unquantized.     

LDPC-based space-time coded OFDM systems: Turbo-EM receiver design with channel state information guessing algorithms

In this paper we study some turbo receiver architectures employing low-density parity check (Ldpc) codes together with orthogonal frequency division multiplexing (Ofdm) for high data rate wireless transmissions. Different demodulation schemes based on expectation-maximization (Em) algorithm are studied along with the channel impulse response (Em) algorithms. We studied differentCir guessing algorithms including the EM-based algorithms such as a space-alternating generalized expectation-maximization algorithm (Sage). It is shown that the proposed turbo-Em receiver employing a soft maximum a posteriori (Map)Em demodulator and a belief propagationLdpc decoder can perform within 1 dB from the ergodic capacity of the studiedMimo ofdm channels. Besides, we find that a suboptimum structure based on a soft interference cancellationMmse filtering demodulator exhibits negligible loss in non-correlated fadingMimo channels but suffer extra performance loss in highly correlatedMimo channels.     

Robust time-frequency distributions based on the robust short time fourier transform

Design of time-frequency distributions (Tfds) that are robust to the impulse noise influence is considered. The robustTfds based on the robust short-time Fourier transform (Stft) are proposed. An efficient procedure to evaluate the robustStft is given. RobustTfds based on the robustStft have better energy concentration around the signal instantaneous frequency (If) than the robustStft itself. Also, theseTfds are more resistant to higher impulse noise than the robustTfds obtained using the local autocorrelation function (Laf) based minimization problem.     

Un environnement de conception de systèmes distribués basé sur UML

This paper introduces a new environment for developing distributed systems. It is based on theTurtle uml profile. Analysis and design phases, described in previous papers, have been extended with an additional deployment phase. In this new step,Turtle components are deployed over hardware execution nodes, and nodes are connected together throughout links,Turtle deployment diagrams are given a formal semantics inRt-lotos, therefore following the approach used forTurtle analysis and design diagrams. Moreover, the paper presents a Java code generator which outputs appropriate Java code forTurtle deployment diagrams. This code is automatically deployable on networks because it implements node communication using network protocols such asUdp orRmi. ttool, the turtle toolkit has been extended to support these new diagrams and code generators. The attack of protected data exchanged throughout securedHttp sessions serves as example.     

Modulation par codage spectral

Using the time-frequency duality principle, the author gives a relation between the so-called Pulse Code Modulation system (Pcm)and a system in which the spectral lines are coded in a similar way (Fcm or Frequency Code Modulation system). The latter appears to be quite comparable to a four phase digital modem, the carrier frequencies of which are multiples of a common basic frequency. It is showed that a Fcm frequency coded multiplexing device may be built, which is quite comparable to a Pcm equipment, as far as the bandwith requirement is concerned. The Fcm terminal equipment is much more expensive and sophisticated than the Pcm one, but the Fcm line amplifiers are simpler than the Pcm regenerative repeaters. The development of the Fcm system relies upon further technical and economical progress of the technology of digital discrete Fourier transformer operating at very high speed.     

Characterization and evaluation of TCP and UDP-based transport on real networks

StandardTcp (RenoTcp) does not perform well on fast long distance networks, due to its AMD congestion control algorithm. In this paper we consider the effectiveness of various alternatives, in particular with respect to their applicability to a production environment. We then characterize and evaluate the achievable throughput, stability and intra-protocol fairness of differentTcp stacks (Scalable,Hstcp,Htcp, FastTcp, Reno,Bictcp, hstcp-lp andLtcp) and aUdp based application level transport protocol (Udtv2) on both production and testbed networks. The characterization is made with respect to both the transient traffic (entry and exit of different streams) and the steady state traffic on production Academic and Research networks, using paths withRtts differing by a factor of 10. We also report on measurements made with 10 Gbit/secNics with and withoutTcp Offload Engines, on 10 Gbit/s dedicated paths set up forSc2004.     

Codage conjoint source-canal des paramètres lsf du codeur FS1016: application de la quantification vectorielle par treillis optimisée pour un canal bruité

In this paper, we present an optimized trellis coded vector quantization (tcvq) coding system designed for the effective and robust coding of lsf spectral parameters at low bit rate. The aim of this system, called at the beginning « lsf-otcvq Encoder », is to achieve a low bit rate transparent quantization of lsf parameters of the us Federal Standard (fs1016) speech coder. Once the effectiveness of our lsf-otcvq encoders (with weighted distance) was proven in the case of ideal transmissions over noiseless channel, we were interested after in the improvement of their robustnesses for real transmissions over noisy channel. To implicitly protect the transmission indices of our lsf-otcvq coders incorporated in the Fsl016, we used a joint source-channel coding carried out by the channel optimized vector quantization (covq) method. In the case of transmissions over noisy channel, we will show that our new encoding system, called “covq-lsf-otcvq Encoder”, would be able to contribute significantly in the improvement of the fs1016 performances by ensuring a good coding robustness of its lsf spectral parameters.     

Use of Gaussian beams to compute antenna pattern

The radiation pattern of the primary feed is developed in a set of elliptical gaussian beams (Egb). Each of them has a limited spatial intersection with the reflector. Under several conditions, any incidentEgb creates a reflected beam which is also anEgb and its parameters can be computed directly. The antenna pattern is achieved by summing all the reflectedEgbS. Such operations require shortCpu time (100 seconds typically on aHa Pa 9000/735 workstation). In the proposed paper, we expose the basic principles and key elements of this method in four points. The first one describes the decomposition of the incident field on a set ofEgb. The second point is the use of improvedEgbS with respect to the paraxial approximation to get stabilized radiation pattern in the far field. The third chapter is related to the interaction of an elementary beam with the reflector. Lastly the radiated field is calculated, at any point of space, as the vectorial superposition of the reflectedEgb. This method allows to obtain the radiated field from the near zone to the remote zone with a similar accuracy in a very short time.     

Méthodes numériques utilisées dans le programme de simulation électrique ELDO

This article describes the original numerical methods introduced in a new circuit simulator named eldo.Its basic algorithm named osr (onestep relaxation) replaces the classical Newton method to solve the implicit schemes with large number of variables. A derived algorithm from osr allows the resolution of very large linear systems,eldo is able to simulate circuits containing 10 000 variables and 15 000 transistors.     

Web-based interorganizational information systems for logistics outsourcing

This article examines how web-based interorganizational information systems(ios)can efficiently support coordination mechanisms between outsourcer and third party logistics (3PL). First, we review the literature on coordination mechanisms andios. Second, we report on the methodology used for gathering information on outsourcers and 3PLs. Third, armed with limited but quality data, we identified two fundamental dimensions: 3PL involvement andios impacts on logistics outsourcing decisions. By combining the two dimensions, we propose a conceptual framework that highlights four main categories ofios that we characterize as neutralios, supply chainios, strategicios and dynamicios. After characterizing and analyzing each category, we discuss how these web basedios support outsourcers and 3PL along the supply chain. Finally, the article discusses the framework’s relevancy and its limits.     

Bandwidth sharing under the assured forwarding Per-Hop behavior

The DiffServ’s Assured Forwarding (af) Per-Hop Behavior (phb) Group defines a differentiated forwarding of packets in four independent classes, each class having three levels of drop precedence. Specific end-to-end services based on thisphb are still being defined. A particular type of service that could assure a given rate to a traffic aggregate has been outlined elsewhere. In such a service, a fair distribution of bandwidth is one of the main concerns. This paper presents experimental work carried out to evaluate howaf distributes bandwidth among flows under different load conditions and traffic patterns. We focused on the effect that marking mechanisms have on bandwidth sharing among flows within a singleaf class. The traffic types we used includeudp flows, individual and aggregatedtcp flows, mix oftcp andudp, tcp sessions with heterogeneous round-trip times, as well as color-blind and color-aware re-marking at the aggregation point fortcp flows. Tests were performed on real and simulated networks. We have found certain conditions under whichaf distributes bandwidth fairly among nonadaptiveudp flows andtcp aggregates. Finally, we evaluate a basic rule for setting the parameters of the two-rate Three-Color Marker conditioning algorithm (trtcm) in order to achieve a better bandwidth distribution fortcp flows.     

WLAN standards and evolutions

Wireless Local Area Networks technologies have known an important technological and commercial development. Multiplicity of standards and variety of domains of use make necessary to compose with different technologies that can be seen either as concurrent or complementary. In this article, after positioning the different types of wireless networks (IEEE 802.11, HomeRF,HIPERLAN/2, Bluetooth) for mass market and professional applications destination, some generalities are briefly reminded such as centralised and ad-hoc architectures, regulatory constraints in the 2.45 and 5GHZ frequency bands used forWLAN, typical ranges, mobility and security features and limitations. Then the differentIEEE (802.11, 802.11a et 802.11b) andETSI (HIPERLAN/2) standards are described in details as well as their foreseen evolutions. It appears that 802.11 family of standards would take benefit of the currently existing products to evolve smoothly while integrating new features (broadband 802.11a physical layer, necessary radio features to meet European regulatory requirements, future introduction of Quality of Service schemes…). In the meantime,HIPERLAN/2 which has been specified as a complete system already supports most of those important features and is able to be adapted to various kinds of higher network layers. Lastly, it is shown that interworking schemes between 3G cellular systems andWLAN currently under investigations in 3GPP andETSI BRAN should permit in the future to easily operate wide area and multi-access technology based mobile networks.     

Measurement-based admission control in UMTS

In this paper, we develop an efficient Call Admission Control (cac) algorithm forumts systems. We first introduce the expressions that we developed for Signal-to-Interference (sir) for both uplink and downlink, to obtain a novelcac algorithm that takes into account, in addition tosir constraints, the effects of mobility, coverage as well as the wired capacity behind the base station, for the uplink, and the maximal transmission power of the base station, for the downlink. As of its implementation, we investigate the measurement-based approach as a means to predict future, both handoff and new, call arrivals and thus manage different priority levels depending on a tunable coefficient. Compared to classicalcac algorithms, ourcac mechanism achieves better performance in terms of outage probability and QoS management.     

TMN implementation strategy based on OSI management standards

In order to facilitate the implementations ofTMN interface protocols/services studied inITU-T, it is very important to define profiles for supportingTMN management service. This paper proposes a concrete method for achieving this based on osi management standards as a promisingTMN implementation method. It proposes an idea of structuring theTMN ISP’S based on the structure of the osi managementISP’S. The paper discusses aTMN based on the osi managementISP’S. Finally the implementation as software is discussed and a software architecture for efficient application development is proposed.     

On the stochastic timed Pétri nets model and its application to the DQDB protocol

The goal of this paper is twofold : at first, to present the stochastic timed Pétri nets model by emphasizing its ability to express the main characteristics of real time distributed systems (parallelism, synchronization by message exchange, time attributes and in particular time constraints) and to allow both qualitative and quantitative analysis (concept of randomized states graph); second, to show a modeling methodology based on this model that allows a rigorous modeling of theDqdb protocol (Qa access, bwb mechanism role,Pa access influence). A new contribution to theQa mechanism has been done (1).     

Mastering quality of service in GPRS/UMTS an overview

Quality of Service (QoS) has become a very important issue in networking, covering many performance aspects and numerous measures. The deployment of next generation wireless system includes 2.5G General Packet Radio Service (Gprs), which is the packet-switched extension of the Global System for Mobile communications (Gsm), and Third-Generation (3G) Universal Mobile Telecommunications System (Umts) to meet the needs of larger capacity and higher bit rates. AnUmts packet core network is an IP-based network. The Internet Engineering Task Force (Ietf) Forum developed several IP QoS related mechanisms available for IP transport networks. Service Quality Management (Sqm), one component of Telecommunication Management Network (Tun), will enable providers to manage QoS against objectives set out in customer Service Level Agreements (Slas) and will enable customers to compare the service offerings of different service providers.