MP-ABT: A Minimal Perturbation Approach for Complex Local Problems

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Modeling Slotted Aloha as a Stochastic Game with Random Discrete Power Selection Algorithms

We consider the uplink case of a cellular system where bufferless mobiles transmit over a common channel to a base station, using the slotted aloha medium access protocol. We study the performance of this system under several power differentiation schemes. Indeed, we consider a random set of selectable transmission powers and further study the impact of priorities given either to new arrival packets or to the backlogged ones. Later, we address a general capture model where a mobile transmits successfully a packet if its instantaneous SINR (signal to interferences plus noise ratio) is lager than some fixed threshold. Under this capture model, we analyze both the cooperative team in which a common goal is jointly optimized as well as the noncooperative game problem where mobiles reach to optimize their own objectives. Furthermore, we derive the throughput and the expected delay and use them as the objectives to optimize and provide a stability analysis as alternative study. Exhaustive performance evaluations were carried out, we show that schemes with power differentiation improve significantly the individual as well as global performances, and could eliminate in some cases the bi-stable nature of slotted aloha

The Uplink Capacity Evaluation of Wireless Networks: Spectral Analysis Approach

In this paper we study the capacity of wireless cellular network, in particular the uplink of WCDMA system by using the two dimensional continuous-time Markov chain (CTMC) technique. Considering two types of calls: real-time (RT) calls that characterized by a quasi fixed transmission rate, and best-effort (BE) calls which do not require strict demand but need some reliability conditions. We develop an approach based on the spectral analysis for evaluating the cell capacity. We explicitly obtain the simultaneous distribution of the number of RT connections and the number of BE connections in the steady-state. This analysis allows us to simplify the computation of the performance measures including expected delay and throughput of BE traffic. These performances are obtained explicitly in both cases (finite and infinite) of BE calls as function of system parameters like arrival rate of BE and RT calls, service rate of BE and RT calls. These results allow the operator to evaluate the cell capacity by varying these parameters independently of the number of BE calls according to its policy to manage the network. Note that this analysis can be applied to various systems such as WiMAX/HSPA, and for both uplink and downlink scenarios, so our spectral analysis approach is not only applicable to the uplink of WCDMA system. We further propose some CAC (Call admission control) policies for BE traffic. We finally conclude this work by some numerical and simulation results. The simulation results obtained by the network simulator (NS2) are closely to the numerical results of our analytical results which validate our theoretical model

Le BackTracklng Intelligent distribué optimal

No Abstract

Algorithmes de résolution et heuristiques d'ordonnancement pour les problèmes de satisfaction de contraintes distribués

Les problèmes de satisfaction de contraintes distribués (DisCSP) permettent de formaliser divers problèmes qui se situent dans l'intelligence artificielle distribuée. Ces problèmes consistent à trouver une combinaison cohérente des actions de plusieurs agents. Durant cette thèse nous avons apporté plusieurs contributions dans le cadre des DisCSPs. Premièrement, nous avons proposé le Nogood-Based Asynchronous Forward-Checking (AFC-ng). Dans AFC-ng, les agents utilisent les nogoods pour justifier chaque suppression d'une valeur du domaine de chaque variable. Outre l'utilisation des nogoods, plusieurs backtracks simultanés venant de différents agents vers différentes destinations sont autorisés. En deuxième lieu, nous exploitons les caractéristiques intrinsèques du réseau de contraintes pour exécuter plusieurs processus de recherche AFC-ng d'une manière asynchrone à travers chaque branche du pseudo-arborescence obtenu à partir du graphe de contraintes dans l'algorithme Asynchronous Forward-Checking Tree (AFC-tree). Puis, nous proposons deux nouveaux algorithmes de recherche synchrones basés sur le même mécanisme que notre AFC-ng. Cependant, au lieu de maintenir le forward checking sur les agents non encore instanciés, nous proposons de maintenir la consistance d'arc. Ensuite, nous proposons Agile Asynchronous Backtracking (Agile-ABT), un algorithme de changement d'ordre asynchrone qui s'affranchit des restrictions habituelles des algorithmes de backtracking asynchrone. Puis, nous avons proposé une nouvelle méthode correcte pour comparer les ordres dans ABT_DO-Retro. Cette méthode détermine l'ordre le plus pertinent en comparant les indices des agents dès que les compteurs d'une position donnée dans le timestamp sont égaux. Finalement, nous présentons une nouvelle version entièrement restructurée de la plateforme DisChoco pour résoudre les problèmes de satisfaction et d'optimisation de contraintes distribués.Distributed Constraint Satisfaction Problems (DisCSP) is a general framework for solving distributed problems. DisCSP have a wide range of applications in multi-agent coordination. In this thesis, we extend the state of the art in solving the DisCSPs by proposing several algorithms. Firstly, we propose the Nogood-Based Asynchronous Forward Checking (AFC-ng), an algorithm based on Asynchronous Forward Checking (AFC). However, instead of using the shortest inconsistent partial assignments, AFC-ng uses nogoods as justifications of value removals. Unlike AFC, AFC-ng allows concurrent backtracks to be performed at the same time coming from different agents having an empty domain to different destinations. Then, we propose the Asynchronous Forward-Checking Tree (AFC- tree). In AFC-tree, agents are prioritized according to a pseudo-tree arrangement of the constraint graph. Using this priority ordering, AFC-tree performs multiple AFC-ng processes on the paths from the root to the leaves of the pseudo-tree. Next, we propose to maintain arc consistency asynchronously on the future agents instead of only maintaining forward checking. Two new synchronous search algorithms that maintain arc consistency asynchronously (MACA) are presented. After that, we developed the Agile Asynchronous Backtracking (Agile-ABT), an asynchronous dynamic ordering algorithm that does not follow the standard restrictions in asynchronous backtracking algorithms. The order of agents appearing before the agent receiving a backtrack message can be changed with a great freedom while ensuring polynomial space complexity. Next, we present a corrigendum of the protocol designed for establishing the priority between orders in the asynchronous backtracking algorithm with dynamic ordering using retroactive heuristics (ABT_DO-Retro). Finally, the new version of the DisChoco open-source platform for solving distributed constraint reasoning problems is described. The new version is a complete redesign of the DisChoco platform. DisChoco 2.0 is an open source Java library which aims at implementing distributed constraint reasoning algorithms.MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF