Étude de la précision de l’estimation de la densité spectrale de puissance croisée,obtenue par transformation de fourier de la fonction de corrélation

The authors compare two different estimators of the crosscorrelation function and show that they give equivalent estimators in the frequency domain. They calculate the first and second order moments of the estimator of the cross-spectral-density (DSPC)due to the statistical errors and the quantification of inputs. From these general formulas, they perform numerical calculations for a particular case and they compare them to practical measurements. They show the interesting fact, that the variance of the statistical errors on the dspc is inferior by estimating its phase than by estimating its module. Furthermore, the quantification of the inputs may influence the variance of the phase of the DSPC estimated.     

Une nouvelle approche pour la gestion de la qualité de service dans les réseaux UMTS

The fast expansion of the applications and services in the 3G mobile networks and the competition between the operators have increased the need to improve the QoS either for the subscribers or for the service providers. The umts operators’ principal goal is to guarantee their maximal benefit and offer the best QoS to the subscribers. Our work is funded on the optimisation of the network parameters, especially bit-rate. Our proposal’s goal is to offer the best rate distribution between the subscribers (bit-rate balancing) and to guarantee the load balancing between the network cells. It is based on network and radio engineering concepts. We used the genetic algorithm for the optimisation of the bit-rate allocation and we proposed a new process for the bit-rate and load balancing. The differentiation of the services treatment has been done by the definition of a priority based on each service requirements in QoS. To show the contribution of this approach in the practice, we simulated it on a Tunisian operator’s test platform model. The gotten results showed an increase of the connected users, some very weak blocking and call-drop rates and a better load balancing between the cells.     

Investigation de la gestion de qualité de service dans le réseau UMTS

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 inUmts network. More specifically, we explore the main challenge of quality of service management to dynamically optimize the distribution of load inUmts networks. Our investigation is organized in the following way. We formalize the optimization problem which is based on the graph theory and modellingUmts 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 anUmts user in terms of bit rate, blocking and connection drop.     

Modélisation de la technique temporelle asynchrone

The evolution towards the integrated broadband communication network is undertaken by several countries. In France, system designers ofCnet in Lannion have assembled an experimental integrated broadband communication network (Ibcn)called Prelude based upon a 4.5 Gbit/s switching matrix and a new and promising transfer mode called the asynchronous time-division technique (Atd).During the project, performance evaluation studies have been carried through, aiming to validate the Atd concepts and to dimension the switching matrix. This paper reviews the Ibcn lab experiments in the world, with operational characteristics;Atd concepts are detailed and the most important features of Ibcn modelling are given. Finally, the network dimensioning is carried through giving packet size, buffers length, loss probabilities and waiting times.     

Utilisation d’un analyseur syntaxique pour la reconnaissance de la parole continue

The author describes the syntactic analyzer which is used in the system keal for continuous speech recognition. After detection of the words in an utterance by a lexical analyzer, the syntactic analyzer builds all the possible syntactic structures according to a context free grammar previously defined by means of a compiled metalanguage. This analyzer allows, in some cases, to correct some errors such as omission and insertion of phonemes by the phonemic analyzer, or non-detection of short words by the lexical analyzer. This program enables presently the recognition of 65 % of utterances in simple dialogs. A few seconds are enough to recognize a sentence.