Frequency assignment in a SDMA satellite communication system with beam decentring feature

International audienceIn satellite communication, Spatial Division Multiple Access (SDMA) has become one of the most promising techniques that can accommodate continuing increase in the number of users and traffic demands. The technology is based on radio resource sharing that separates communication channels in space. It relies on adaptive and dynamic beam-forming technology and well-designed algorithms for resource allocation among which frequency assignment is considered. This paper studies static Frequency Assignment Problem (FAP) in a satellite communication system involving a satellite and a number of users located in a service area. The objective is to maximize the number of users that the system can serve while maintaining the signal to interference plus noise ratio of each user under a predefined threshold. Traditionally, interference is treated as fixed (binary interferences or fixed minimal required separation between frequencies) . In this paper, the interference is cumulative and variable. To solve the problem, we work on both discrete and continuous optimizations. Integer linear programming formulations and greedy algorithms are proposed for solving the discrete frequency assignment problem. The solution is further improved by beam decentring algorithm which involves continuous adjustment of satellite beams and deals with non-linear change of interference

Allocation de fréquence dans les systèmes de communication par satellites de type SDMA

In this thesis, we consider frequency assignment problems arising from an SDMA satellite communication system which consists of a satellite and a number of users distributed inside a fixed sized service area. The objective is to assign a given number of frequency carriers to as many users as possible. This assignment should not violate the incurred interference constraints. Two types of interference are considered i.e. binary and cumulative interference. For each of them, single carrier and multiple carrier frequency assignment models are taken into account. We also propose an Integer Linear Programming (ILP) formation to deal with 2-dimensional frequency-time assignments which is more complicated and harder to solve. Single carrier FAPs are solved by greedy algorithms and ILP. A Beam Moving algorithm is devised to further improve the solutions by solving a non-linear optimization problem. Multiple carrier FAPs are modeled as scheduling problem and ILPs. We show that the scheduling model solved through constraint programming methods offers superior performance than the proposed ILP. It is worth noting that, by transforming the cumulative interference into binary interference, scheduling method together with clique-induced constraints yields much better results. A frequency assignment problem that incorporates the specifications and constraints provided by the industry is also considered. These requirements render the resource allocation problem highly complex. This complexity and the fact that frequency assignment plans must be recomputed frequently in order to cope for user mobility yield classic optimization tool such as ILP impractical. According to this, two greedy algorithms are devised and tested.Le travail présenté dans cette thèse traite des problèmes d'affectation de fréquences (FAP) qui se produisent dans les systèmes de communication par satellite utilisant la technologie SDMA. Ces systèmes se composent d'un satellite et d'une zone de service de taille fixe dans laquelle sont répartis des utilisateurs. L'objectif est alors de servir un maximum d'utilisateur en fréquence dans cette zone de service. Cependant, l'affectation ne doit pas violer les contraintes d'interférence qui apparaissent lorsque deux utilisateurs utilisent une même fréquence ou lorsqu'ils se partagent une même plage de fréquence. Deux types d'interférences sont considérés dans cette étude : les interférences binaire et cumulative. Pour chacune d'elles, les problèmes d'affectation de fréquence de type mono-porteuse (une fréquence par utilisateur) et multi-porteuses (plusieurs fréquences par utilisateur) sont traités. Le problème de l'affectation bidimensionnelle est aussi abordé et nous proposons des modèles de Programmation Linéaire en Nombre Entiers (PLNE) pour le résoudre. Au niveau des méthodes de résolution, nous utilisons des algorithmes gloutons, des modèles de PLNE pour le problème de type mono-porteuse. En outre, un algorithme de déplacement continu de faisceau est conçu pour améliorer les solutions en résolvant un problème d'optimisation continu non linéaire. Concernant le problème de type multi-porteuses, nous le ramenons à un problème d'ordonnancement et celui-ci est résolu à l'aide de la PLNE et la Programmation Par Contraintes (PPC). Il est par ailleurs montré que les résultats issus de la PPC sont meilleurs que ceux de la PLNE. De plus, en transformant les interférences cumulatives en interférences binaires, la méthode d'ordonnancement avec les contraintes induites par les cliques donne de bien meilleurs résultats. Nous considérons également un problème industriel dans lequel de nombreuses contraintes apparaissent ce qui rend le problème très complexe et insoluble avec des méthodes exactes. Face à ce constat, deux algorithmes gloutons sont réalisés et leurs résultats sont comparés

On scheduling models for the frequency interval assignment problem with cumulative interferences

International audienceIn this paper, models and methods for solving a real-life frequency assignment problem based on scheduling theory are investigated. A realistic frequency assignment problem involving cumulative interference constraints in which the aim is to maximize the number of assigned users is considered. If interferences are assumed to be binary, a multiple carrier frequency assignment problem can be treated as a disjunctive scheduling problem since a user who requests a number of contiguous frequencies can be considered as a non-preemptive task with a processing time and two interfering users can be modeled through a disjunctive constraint on the corresponding tasks. A binary interference version of the problem is constructed and derive a disjunctive scheduling model is derived. Based on the binary representation, two models are proposed. The first one relies on an interference matrix and the second one considers maximal cliques. A third, cumulative, model that yields a new class of scheduling problems is also proposed. Computational experiments show that the case-study frequency assignment problem can be solved efficiently with disjunctive scheduling techniques

Greedy algorithms for time-frequency allocation in a SDMA satellite communication system

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Frequency allocation in a SDMA satellite communication system with beam moving (ICC 2012)

International audienceSpatial Division Multiple Access (SDMA) is a principle of radio resource sharing that separates communication channels in space. It relies on adaptive and dynamic beamforming technology and well-designed algorithms for resource allocation. As satellite communication systems move towards greater capacity in both the number of users and throughput, SDMA becomes one of the most promising techniques that can achieve these two goals. This paper studies static Frequency Assignment Problem (FAP) in a satellite communication system involving a satellite and a number of users located in a service area. The objective is to maximise the number of users that the system can serve while maintaining the signal to interference plus noise ratio of each user under a predefined threshold. Traditionally, interference is binary and fixed. In this paper, the interference is cumulative and variable depending on how the frequency is assigned. To solve the problem, we work on both discrete and continuous optimizations. Integer linear programming formulations and greedy algorithms are proposed for solving the discrete frequency allocation problem. The solution is further improved by beam moving algorithm which involves continuous adjustment of satellite beams and deals with non-linear change of interference

Université Toulouse III Paul Sabatier (UT3 Paul Sabatier)

Allocation de fréquence dans les systèmes de communication par satellites de type SDM