Benchmarking a wide spectrum of metaheuristic techniques for the radio network design problem

The radio network design (RND) is an NP-hard optimization problem which consists of the maximization of the coverage of a given area while minimizing the base station deployment. Solving RND problems efficiently is relevant to many fields of application and has a direct impact in the engineering, telecommunication, scientific, and industrial areas. Numerous works can be found in the literature dealing with the RND problem, although they all suffer from the same shortfall: a noncomparable efficiency. Therefore, the aim of this paper is twofold: first, to offer a reliable RND comparison base reference in order to cover a wide algorithmic spectrum, and, second, to offer a comprehensible insight into accurate comparisons of efficiency, reliability, and swiftness of the different techniques applied to solve the RND problem. In order to achieve the first aim we propose a canonical RND problem formulation driven by two main directives: technology independence and a normalized comparison criterion. Following this, we have included an exhaustive behavior comparison between 14 different techniques. Finally, this paper indicates algorithmic trends and different patterns that can be observed through this analysis.Publicad

Identification of femtocells in mobile networks

The evolving mobile networks are requested to convey increasing data traffic as popularity of online services together with affordability of mobile devices is growing. One solution to mobile carriers, which can help them quickly deploy small base stations (BS) ensuring great indoor coverage with minimum costs, and high data rate capability, is femtocell technology. However, standard deployment techniques are unsatisfactory for these type of BSs. There are two main reasons for that. Firstly, femtocells will be deployed in great numbers. Secondly, they are deployed by users and are portable. It means their position is not known in advance, and can vary in time. Therefore, femtocells have to implement self-configuration principles. Physical Cell Identity is one of the most important parameters to be chosen automatically under defined conditions. It is crucial parameter, which allows them to convey a communication between a user equipment and a core network. A study on Physical Cell Identity issues in mobile networks with femtocells is presented in my thesis. For this purpose, I created two different models of femtocells deployment and deal with a collision and a confusion. They are two main problems, which threaten proper Physical Cell Identity assignment in mobile networks. Outputs of the thesis serves for better understanding of interrelations between differently placed femtocells in term of collision and confusion issue and as the basis to design the framework handling Physical Cell Identity allocation. The simulations conducted on proposed models were utilized to obtain probability characteristics and indicators based on graph theory. In the evaluation section, I appoint several characteristics as probability of collision, probability of confusion and maximal number of neighbourhood cells and some others to support solution of collision and confusion issue. I use results of evaluation and layout the framework for automated Physical Cell Identity assignment with two different approaches, the distributed one, and the centralized one. Since, femtocells are subcategory of small cells so findings, mentioned in this thesis, can also be used for other types of small cells.Katedra telekomunikační technik

Exploring Hidden Networks Yields Important Insights in Disparate Fields of Study

Network science captures a broad range of problems related to things (nodes) and relationships between them (edges). This dissertation explores real-world network problems in disparate domain applications where exploring less obvious hidden networks reveals important dynamics of the original network. The power grid is an explicit network of buses (e.g., generators) connected by branches (e.g., transmission lines). In rare cases, if k branches (a k-set) fail simultaneously, a cascading blackout may ensue; we refer to such k-sets as defective . We calculate system risk of cascading failure due to defective 2-sets and 3-sets in synthetic test cases of the Polish and Western US power grids. A stochastic group testing algorithm (Random Chemistry) is used to efficiently sample defective k-sets in the hidden network of all possible k-sets, and new methods are proposed to derive bounds on the total number of defective sets from the obtained sample. We use copula analysis, with a custom distance metric, to estimate risk when the k initiating outages are spatially correlated and show that this realistic assumption increases the relative contribution to risk of 3-sets over 2-sets. In the power systems application, among others, computational costs vary when testing defective vs. non-defective k-sets, a consideration that has not previously been made when evaluating group testing algorithms. We develop a domain-independent test problem generator that enables us to vary the number of defective k-sets, with a tunable parameter to control the cost ratio of testing defective vs. non-defective k-sets. We introduce a deterministic group-testing algorithm (SIGHT) capable of sampling from this space, and show that both the number of defective sets and the test cost ratio affect the relative efficiency of Random Chemistry vs. SIGHT. We discuss various applications where each algorithm is expected to outperform the other. Conversations can also be viewed as explicit networks of dialog (edges) between speakers (nodes). We propose using second and third order Markov models based on the sequence of speaker turn lengths to elucidate hidden networks of information flow and reveal patterns of information sharing between participants. The proposed method is demonstrated on a corpus of conversations between patients with advanced cancer and palliative care clinicians. We demonstrate the efficacy of the model by confirming known patterns of conversational discourse, identifying normative patterns of information flow in serious illness conversation, and showing how these patterns differ under a variety of contexts, including the expression of distressing emotion

Planificación automática de parámetros en redes LTE mediante teoría de grafos

El método se prueba con una instancia del problema construida a partir de datos de la red real. Los resultados muestran que el método es capaz de eliminar completamente los problemas de colisión y confusión, a la vez que reduce las colisiones de señales de referencia del enlace ascendente y descendente, respecto a la solución actualmente implementada en la red. Por otra parte, se propone un método de asignación de celdas pequeñas (small cells) a emplazamientos para reducir los costes de despliegue en redes celulares heterogéneas. Para ello, se desarrolla un modelo analítico del problema, basado en programación lineal entera, que establece los costes de implementación tras el agrupamiento de equipos en función de la distancia entre celdas. Con este modelo, se resuelve el problema de asignación de emplazamiento con un método exacto mediante una herramienta de optimización entera. Como alternativa, se propone un método heurístico de agrupamiento de celdas pequeñas, que, por su simplicidad, puede integrarse en algoritmos de selección de emplazamientos de interior. Los métodos propuestos se evalúan con simulaciones realizadas sobre instancias del problema construidas con datos de una red real. Los resultados muestran que, cuando se consideran criterios de cobertura, capacidad y coste monetario al seleccionar los nuevos emplazamientos de interior, la inclusión del método propuesto reduce enormemente el coste total de la red. Los métodos desarrollados en esta tesis han sido concebidos para su integración en una herramienta de planificación comercial. Por ello, en su desarrollo, se presta especial atención a los requisitos de los operadores y a la eficiencia computacional de los algoritmos de resolución.En las redes de comunicaciones móviles, las tareas de planificación son de vital importancia, ya que permiten aprovechar al máximo la capacidad de los equipos de los que se dispone mediante una configuración inicial óptima de sus parámetros. Lamentablemente, el aumento de la complejidad de las redes móviles en los últimos años dificulta enormemente estas tareas de planificación. Por ello, operadores y fabricantes vienen buscando la forma de automatizar los procesos de planificación, empleando técnicas de redes autoorganizadas (Self-Organizing Networks, SON). En esta tesis, se proponen dos métodos de planificación automática de parámetros para la red de acceso radio del sistema Long Term Evolution (LTE). Como nexo de unión, ambos métodos formulan y resuelven el problema mediante teoría de grafos. Por un lado, se propone un método de planificación de identificadores físicos de celda (Physical Cell Identifier, PCI). A diferencia de trabajos anteriores, el método propuesto optimiza el rendimiento tanto del enlace ascendente como descendente de LTE, además de resolver los problemas clásicos de colisión y confusión de identificadores. Como punto de partida, se realiza un estudio preliminar para cuantificar el impacto de la planificación de PCIs en ambos enlaces, mediante sendos modelos analíticos de rendimiento del canal de acceso compartido del enlace descendente (Physical Downlink Shared CHannel, PDSCH) y del canal de control del enlace ascendente (Physical Uplink Control CHannel, PUCCH). De los resultados obtenidos al integrar estos modelos en herramientas de simulación, se extraen los requisitos que debe cumplir un buen plan de PCI. Tras formular el problema, se propone un nuevo método de resolución heurístico basado en técnicas de partición de grafos, que tiene en cuenta tanto los problemas de colisión-confusión de identificadores de celda, como las colisiones de señales de referencia del enlace descendente y ascendente