Affectation heuristique de cellules à des commutateurs dans les réseaux cellulaires pour mobiles

The problem of assigning of cells to switches in a cellular network is a NP-hard problem which cannot be solved in an exact way in reasonable calculating times. In this article, we propose a compromise based on the tabu search heuristics to obtain acceptable solutions with little processing effort. The method essentially consists in modifying in an iterative way an initial solution while hoping to reach a final solution which respects the constraints of the problem. The results obtained confirm the effectiveness and the robustness of the tabu search method particularly to solve problems with a certain number of cells and switches.     

Minimisation de la consommation d’Énergie dans les réseaux ad hoc

An ad hoc network is a collection of wireless devices forming a temporary network independently of any administration or fixed infrastructure. The main benefits of this new generation of mobile networks are flexibility and their low cost. Wireless devices have maximum utility when they can be used “anywhere at anytime “. However, one of the greatest limitations to that goal is the finite power supplies. Since batteries provide limited power, a general constraint of wireless communication is the short continuous operation time of mobile terminals. This constraint is more important for the ad hoc networks, since every terminal has to perform the functions of a router. Therefore, energy consumption should be a crucial issue while designing new communication protocols and particularly ad hoc routing protocols. We propose, in this paper, some extensions to the most important on-demand routing algorithm,Aodv (Ad hoc On demand Distance Vector). The discovery mechanism in these extensions uses energy as a routing metric. These algorithms improve the network survivability by maintaining the network connectivity, which is the strong requirement for a high-quality communication. They carry out this objective with low message overhead for computing routes and without affecting the other network protocol layers.     

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.     

Contrôle de topologie orienté stratégie basé sur des routeurs mobiles dédiés

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).     

Décodage à sortie souple des réseaux de points

We present a universalmse algorithm for lattice decoding in dimensions up to 1024 for both Gaussian and Rayleigh fading channels. This algorithm can be applied to decode high diversity multidimensional rotations. The decoding is performed by a decision feedback equalizer and provides soft output which allows a concatenation of the lattice codes with other type of error-correcting codes. The problem of selecting a good rotation is also considered, and we show that a high dimensional random rotation exhibits very good performance on a Rayleigh fading channel.     

Recherche locale à voisinage variable pour le routage optique dans des réseaux utilisant des routeurs latins

This paper proposes an approach based on Variable Neighbourhood Search (vns) to solve the Routing and Wavelength Assignment (rwa) problem in optical networks including latin routers. It can be summed up as establishing routing (finding intermediate routers on optical paths between each origin/destination pair) and wavelength assignment of these optical paths in such networks. The problem will be tackled according to two scenarii: to optimize the number of established connections (scenario 1) or to answer as well as possible an accurate traffic array (scenario 2). In traditional optical networks (without latin routers), one often separates routing and wavelength assignment because of the general problem complexity (each of the two sub-problems isnp-hard). However, latin routers introduce constraints connecting routing and assignment, this requires a simultaneous treatment of the two problems. A local search heuristic,vnsfor, based on the definition of different neighbourhoods (with simple and double moves) is proposed in this paper to provide us with solutions close to the optimum. Experimental results show howvnsfor leads to better solutions, according to both scenarii, in comparison with the reference algorithmlonca.     

Modèles de télétrafic pour le réseau à intégration de services du satellite TELECOM 1

The author discusses models of multiservice circuit switched communications systems where, in particular, the amount of transmission capacity (e.g. bit rate) depends on the call type. Two modes of call set up are considered: «on demand» with blocked calls cleared and «reservation» where capacity is previously reserved for planned calls. The latter mode is described generally and, for particular cases, we suggest interpretations leading to birth process and multiservice queue models. The models have been studied for evaluating the performance of the telecom 1business communication network but derived exact and approximate results should be useful in other applications.     

Prise en compte de la dépendance spatiale du trafic dans un modèle hiérarchique stochastique de réseau

A study of the traffic flow in a network, based on stochastic geometry considerations, is presented. The network is modelled by a spatially homogeneous hierarchical structure, of any number of levels. The spatial dependence of the offered traffic is taken into account in the computation of the quantity of traffic seen by the stations of a given level.