Optimisation of Mobile Communication Networks - OMCO NET

The mini conference “Optimisation of Mobile Communication Networks” focuses on advanced methods for search and optimisation applied to wireless communication networks. It is sponsored by Research & Enterprise Fund Southampton Solent University. The conference strives to widen knowledge on advanced search methods capable of optimisation of wireless communications networks. The aim is to provide a forum for exchange of recent knowledge, new ideas and trends in this progressive and challenging area. The conference will popularise new successful approaches on resolving hard tasks such as minimisation of transmit power, cooperative and optimal routing

Networking - A Statistical Physics Perspective

Efficient networking has a substantial economic and societal impact in a broad range of areas including transportation systems, wired and wireless communications and a range of Internet applications. As transportation and communication networks become increasingly more complex, the ever increasing demand for congestion control, higher traffic capacity, quality of service, robustness and reduced energy consumption require new tools and methods to meet these conflicting requirements. The new methodology should serve for gaining better understanding of the properties of networking systems at the macroscopic level, as well as for the development of new principled optimization and management algorithms at the microscopic level. Methods of statistical physics seem best placed to provide new approaches as they have been developed specifically to deal with non-linear large scale systems. This paper aims at presenting an overview of tools and methods that have been developed within the statistical physics community and that can be readily applied to address the emerging problems in networking. These include diffusion processes, methods from disordered systems and polymer physics, probabilistic inference, which have direct relevance to network routing, file and frequency distribution, the exploration of network structures and vulnerability, and various other practical networking applications.Comment: (Review article) 71 pages, 14 figure

A Branch-and-Cut based Pricer for the Capacitated Vehicle Routing Problem

openIl Capacitated Vehicle Routing Problem, abbreviato come CVRP, è un problema di ottimizzazione combinatoria d'instradamento nel quale, un insieme geograficamente sparso di clienti con richieste note deve essere servito da una flotta di veicoli stazionati in una struttura centrale. Negli ultimi due decenni, tecniche di Column generation incorporate all'interno di frameworks branch-price-and-cut sono state infatti l'approccio stato dell'arte dominante per la costruzione di algoritmi esatti per il CVRP. Il pricer, un componente critico nella column generation, deve risolvere il Pricing Problem (PP) che richiede la risoluzione di un Elementary Shortest Path Problem with Resource Constraints (ESPPRC) in una rete di costo ridotto. Pochi sforzi scientifici sono stati dedicati allo studio di approcci branch-and-cut per affrontare il PP. L'ESPPRC è stato tradizionalmente rilassato e risolto attraverso algoritmi di programmazione dinamica. Questo approccio, tuttavia, ha due principali svantaggi. Per cominciare, peggiora i dual bounds ottenuti. Inoltre, il tempo di esecuzione diminuisce all'aumentare della lunghezza dei percorsi generati. Per valutare la performance dei loro contributi, la comunità di ricerca operativa ha tradizionalmente utilizzato una serie d'istanze di test storiche e artificiali. Tuttavia, queste istanze di benchmark non catturano le caratteristiche chiave dei moderni problemi di distribuzione del mondo reale, che sono tipicamente caratterizzati da lunghi percorsi. In questa tesi sviluppiamo uno schema basato su un approccio branch-and-cut per risolvere il pricing problem. Studiamo il comportamento e l'efficacia della nostra implementazione nel produrre percorsi più lunghi comparandola con soluzioni all'avanguardia basate su programmazione dinamica. I nostri risultati suggeriscono che gli approcci branch-and-cut possono supplementare il tradizionale algoritmo di etichettatura, indicando che ulteriore ricerca in quest'area possa portare benefici ai risolutori CVRP.The Capacitated Vehicle Routing Problem, CVRP for short, is a combinatorial optimization routing problem in which, a geographically dispersed set of customers with known demands must be served by a fleet of vehicles stationed at a central facility. Column generation techniques embedded within branch-price-and-cut frameworks have been the de facto state-of-the-art dominant approach for building exact algorithms for the CVRP over the last two decades. The pricer, a critical component in column generation, must solve the Pricing Problem (PP), which asks for an Elementary Shortest Path Problem with Resource Constraints (ESPPRC) in a reduced-cost network. Little scientific efforts have been dedicated to studying branch-and-cut based approaches for tackling the PP. The ESPPRC has been traditionally relaxed and solved through dynamic programming algorithms. This approach, however, has two major drawbacks. For starters, it worsens the obtained dual bounds. Furthermore, the running time degrades as the length of the generated routes increases. To evaluate the performance of their contributions, the operations research community has traditionally used a set of historical and artificial test instances. However, these benchmark instances do not capture the key characteristics of modern real-world distribution problems, which are usually characterized by longer routes. In this thesis, we develop a scheme based on a branch-and-cut approach for solving the pricing problem. We study the behavior and effectiveness of our implementation in producing longer routes by comparing it with state-of-the-art solutions based on dynamic programming. Our results suggest that branch-and-cut approaches may supplement the traditional labeling algorithm, indicating that further research in this area may bring benefits to CVRP solvers

Operational research:methods and applications

Throughout its history, Operational Research has evolved to include a variety of methods, models and algorithms that have been applied to a diverse and wide range of contexts. This encyclopedic article consists of two main sections: methods and applications. The first aims to summarise the up-to-date knowledge and provide an overview of the state-of-the-art methods and key developments in the various subdomains of the field. The second offers a wide-ranging list of areas where Operational Research has been applied. The article is meant to be read in a nonlinear fashion. It should be used as a point of reference or first-port-of-call for a diverse pool of readers: academics, researchers, students, and practitioners. The entries within the methods and applications sections are presented in alphabetical order

Efficient Algorithms for Infrastructure Networks: Planning Issues and Economic Impact

Mei, R.D. van der [Promotor]Bhulai, S. [Copromotor

Topological optimization of fault-tolerant networks meeting reliability constraints.

The relevant entities in a network are its nodes, and the links between them. In general, the goal is to achieve a reliable communication between dierent pairs of nodes. Examples of applications are telephonic services, data communication, transportation systems, computer systems, electric networks and control systems. The predominant criterion for the design of a reliable and survivable system is the minimum-cost in most contexts. An attractive topic for research is to consider a minimum-cost topological optimization design meeting a reliability threshold. Even though the cost has been the primary factor in the network design, recently, the network reliability has grown in relevance. With the progress of Fiber-To-the-Home (FTTH) services for the backbone design in most current networks, combined with the rapid development of network communication technologies, and the explosive increase of applications over the Internet infrastructure, the network reliability has supreme importance, for traditional communication systems but for the defense, business and energy, and emergent elds such as trusted computing, cloud computing, Internet of Things (IoT) and Next Generation Networks (NGN), the fault tolerance is critical. We can distinguish two main problems to address in the analysis and design of network topologies. First, the robustness is usually met under multi-path generation. Therefore, we require certain number of node-disjoint paths between distinguished nodes, called terminals. The second problem is to meet a minimum-reliability requirement in a hostile environment, using the fact that both nodes and links may fail. Both problems are strongly related, where sometimes the minimum-cost topology already meets the reliability threshold, or it should be discarded, and the design is challenging. This thesis deals with a topological optimization problem meeting reliability constraints. The Generalized Steiner Problem with Node-Connectivity Constraints and Hostile Reliability (GSP-NCHR) is introduced, and it is an extension of the well-known Generalized Steiner Problem (GSP). Since GSP-NCHR subsumes the GSP, it belongs to the class of N P-Hard problems. A full chapter is dedicated to the hardness of the GSP-NCHR, and an analysis of particular sub-problems. Here, the GSP-NCHR is addressed approximately. Our goal is to meet the topological x requirements intrinsically considered in the GSP-NCHR, and then test if the resulting topology meets a minimum reliability constraint. As a consequence a hybrid heuristic is proposed, that considers a Greedy Randomized construction phase followed by a Variable Neighborhood Search (VNS) in a second phase. VNS is a powerful method that combines local searches that consider dierent neighborhood structures, and it was used to provide good solutions in several hard combinatorial optimization problems. Since the reliability evaluation in the hostile model belongs to the class of N P-Hard problems, a pointwise reliability estimation was adopted. Here we considered Recursive Variance Reduction method (RVR), since an exact reliability evaluation is prohibitive for large-sized networks. The experimental analysis was carried out on a wide family of instances adapted from travel salesman problem library (TSPLIB), for heterogeneous networks with dierent characteristics and topologies, including up to 400 nodes. The numerical results show acceptable CPU-times and locally-optimum solutions with good quality, meeting network reliability constraints as well.En una red las entidades relevantes son nodos y conexiones entre nodos, y en general el principal objetivo buscado es lograr una comunicación segura entre nodos de esta red, ya sea para redes telefónicas y de comunicación de datos, de transporte, arquitectura de computadores, redes de energía eléctrica o sistemas de comando y control. La optimización relativa al costo de una red y la contabilidad de la misma, relacionada con la supervivencia de esta, son los criterios predominantes en la selección de una solución para la mayor parte de los contextos. Un tema interesante que ha atraído un gran esfuerzo es cómo diseñar topologías de red, con un uso mínimo de recursos de red en términos de costo que brinde una garantía de contabilidad. A pesar que por años el costo ha sido el factor primario, la contabilidad ha ganado rápidamente en relevancia. Con sistemas de transmisión de fibra óptica de alta capacidad formando la columna vertebral de la mayoría de las redes actuales y junto con el rápido desarrollo de la tecnología de comunicación de redes y el crecimiento explosivo de las aplicaciones de Internet, la contabilidad de la red parece cada vez más importante, tanto para áreas tradicionales como la industria de defensa, finanzas y energía, y áreas emergentes como la computación contable, la computación en la nube, internet de las cosas (IoT) y la próxima generación de Internet, la supervivencia del tráfico por sobre los fallos de red se ha convertido aún en más crítica. En ese sentido podemos diferenciar, a grandes rasgos, dos de los principales problemas a resolver en el análisis y diseño de topologías de red. Primeramente la obtención de una red óptima en algún sentido, siendo este definido por ejemplo mediante la obtención de la máxima cantidad posible de caminos disjuntos entre pares de nodos, esto sujeto a determinadas restricciones definidas según el contexto. El segundo problema es la evaluación de la contabilidad de la red en función de las contabilidades elementales de los nodos y conexiones entre nodos que componen la red. Estas contabilidades elementales son probabilidades de operación asociadas a los nodos y conexiones entre nodos. Ambos problemas están fuertemente relacionados, pudiendo tener que comparar en el proceso de búsqueda de redes óptimas la contabilidad entre soluciones candidatas, o luego de obtener una solución candidata tener que evaluar la contabilidad de la misma y de esta forma descartarla o no. El presente trabajo se centra en la resolución del problema enfocado en ambos puntos planteados. Para ello modelamos el problema de diseño de la topología de red sobre la base de un modelo de nido como Generalized Steiner Problem with Node-Connectivity Constraints and Hostile Reliability (GSP-NCHR) extensión del más conocido Generalized Steiner Problem (GSP). El presente problema es NP-duro, dedicamos un capítulo para presentar resultados teóricos que lo demuestran. Nuestro objetivo es atacar de forma aproximada el modelo GSP-NCHR de tal modo de poder resolver la optimización de la red y luego medir la contabilidad de la solución obtenida. Para ello optamos por desarrollar la metaheurística Variable Neighborhood Search (VNS). VNS es un método potente que combina el uso de búsquedas locales basadas en distintas definiciones de vecindad, el cual ha sido utilizado para obtener soluciones de buena calidad en distintos problemas de optimización combinatoria. En lo referente al cálculo de contabilidad de la red, nuestro modelo GSP-NCHR pertenece a la clase NP-duro, por eso desarrollamos Recursive Variance Reduction (RVR) como método de simulación, ya que la evaluación exacta de esta medida para redes de tamaño considerable es impracticable. Las pruebas experimentales fueron realizadas utilizando un conjunto amplio de casos de prueba adaptados de la librería travel salesman problem (TSPLIB), de heterogéneas topologías con diferentes características, incluyendo instancias de hasta 400 nodos. Los resultados obtenidos indican tiempos de cómputo altamente aceptables acompañados de óptimos locales de buena calidad

OPTIMISATION TECHNIQUES FOR TELECOMMUNICATION NETWORKS

This thesis deals with various facets of the optimisation problem for telecommunication networks and proposes a number of new techniques for their solution. The necessary essentials, Graph Theory, Complexity Theory and Telecommunication Principles, are investigated. The relevant graphs are enumerated and the requirements of suitable optimisation algorithms for certain graphical problems are established. The Private Automatic Branch Exchange (PABX) is introduced. the variety of telecommunications traffic as well as the practical requirements of a connection topology are discussed. The fundamental Network Optimisation Problem (NJP) is defined and analysed. Simple exhaustive methods of solution are considered together with partial solution algorithms and simplification methods. Centralised networks with and without concentrators are introduced. Extensions and modifications are proposed for some techniques and existing practical methods of dealing with the NOP are investigated. A number of new ideas are proposed for the practical solution of the NOP. Reduction methods are presented for replacing large unmanageable networks with smaller ones, on which optimisation can take place. Fixed topology techniques are introduced for initial tandem switch selection purposes and perturbation methods are considered which can be applied to such an initial solution. Lookahead methods of link removal are introduced for the purposes of determining the tandem interconnection network together with the traffic routeing strategy. A composite method is proposed incorporating all of these concepts and the results of a number of numerical experiments upon actual network problem; are presented. the extension of the proposed techniques to other areas of problem solving and optimisation is considered. In particular, a new method for the solution of the Euclidean Travelling Salesman Problem (ETSP) is presented. A brief discussion is undertaken, in conclusion, concerning the practical difficulties of the NOP and The restrictions this placed upon solution algorithms of various types.Brit1sh Telecom, Ta1lis Consultancy, Londo