Context-Aware Handover Policies in HetNets

Next generation cellular systems are expected to entail a wide variety of wireless coverage zones, with cells of different sizes and capacities that can overlap in space and share the transmission resources. In this scenario, which is referred to as Heterogeneous Networks (HetNets), a fundamental challenge is the management of the handover process between macro, femto and pico cells. To limit the number of handovers and the signaling between the cells, it will hence be crucial to manage the user's mobility considering the context parameters, such as cells size, traffic loads, and user velocity. In this paper, we propose a theoretical model to characterize the performance of a mobile user in a HetNet scenario as a function of the user's mobility, the power profile of the neighboring cells, the handover parameters, and the traffic load of the different cells. We propose a Markov-based framework to model the handover process for the mobile user, and derive an optimal context-dependent handover criterion. The mathematical model is validated by means of simulations, comparing the performance of our strategy with conventional handover optimization techniques in different scenarios. Finally, we show the impact of the handover regulation on the users performance and how it is possible to improve the users capacity exploiting context information

A statistical algorithm for multi-objective handover optimization under uncertainties

The mobility robustness optimization (MRO) problem in LTE self-organizing networks (SON) is a multi-objective optimization problem; it involves a set of non-convex contradicting objective functions that depend on multiple variables such as handover (HO) parameters and user mobility classes. This paper exploits the framework of stochastic processes to develop a novel method of successively choosing a sequence of multi-variate training points for multi-objective optimization. Combined with the collected statistics and a priori knowledge, the proposed method is used in the design of an efficient MRO algorithm. The performance of the algorithm is evaluated by simulations to illustrate significant improvements with respect to both HO-related ratio link failures (RLFs) and unnecessary HOs

Contribución al estudio de técnicas Self Organizing & Self Optimizing Networks para redes de comunicaciones móviles LTE

La aparición continua de nuevos servicios que consumen grandes anchos de banda, unida a la creciente demanda de acceso a Internet por parte de los usuarios en cualquier lugar en el que se encuentren, está aumentando considerablemente la complejidad de las redes de telefonía móvil. Los mecanismos actuales permiten gestionar los limitados recursos radioeléctricos en redes heterogéneas GSM/UMTS/LTE. Mediante el establecimiento de una estructura jerárquica celular, y unas funcionalidades de gestión multicapa, se puede distribuir el tráfico de voz y datos para ofrecer el mejor servicio a los clientes. Por otro lado, la movilidad de los usuarios y su distribución geográfica es muy variable dentro de un mismo territorio, por lo que las redes deben también adaptarse a este escenario. En los entornos urbanos se requiere un diseño de red con muchos elementos, en el que coexistirán células de diferentes tipos (macro, micro, pico, etc.) según la demanda de servicio, concentración de clientes y su movilidad.Además, estas redes han ido evolucionando tecnológicamente, encontrándonos en este momento en España con sistemas GSM 900, DCS 1800, UMTS 2100, UMTS 900 y LTE 1800 (a corto plazo LTE 800), que están en servicio simultáneamente, con un alto grado de relación y traspasos entre ellos. Para ofrecer continuidad del servicio entre todas las redes, y con el objeto de obtener la máxima rentabilidad aprovechando las inversiones realizadas en la infraestructura actual (GSM, UMTS R99, HSPA), la definición de la norma LTE contempla el mecanismo de ¿interworking¿, que consiste en un conjunto de funciones para permitir la interacción entre todas la redes que ofrecen el servicio de telefonía móvil. Este aumento de la complejidad requerirá nuevas inversiones con el objeto de gestionar de forma adecuada las labores de optimización, operación y mantenimiento de las redes, y en consecuencia, poder adaptarse a un mercado tan cambiante en el que constantemente están apareciendo nuevos servicios, terminales y modelos de negocio. En este sentido, aparece el concepto SON, que significa Self Organizing Networks, y tiene como objetivo la automatización de arduas tareas en la configuración, puesta en servicio, y optimización de parámetros de red, así como la de responder adecuadamente a eventualidades, consiguiendo con todo ello una reducción en los costes de operación y una mejora sustancial de la calidad de la red. La movilidad de los usuarios es una de las principales características del servicio de telefonía móvil, por lo que uno de los métodos para garantizar la Calidad consiste en un correcto diseño de relación de colindancias entre células cercanas, de tal manera que el terminal pueda disponer siempre de una célula a la que asociarse mientras se desplaza, dando así continuidad al servicio. En este trabajo de tesis se pretende diseñar un algoritmo de optimización automática que genere una relación de colindancias entre células para ofrecer la mejor calidad posible de la red.In this work we present theoretical studies on the characteristics of the cellular structures employed in the mobile communications networks, where there is a special emphasis on the interference and over reach like main limiting element of coverage, capacity and data rate. It also details the current trends of the different methods of optimization and shown a series of case studies carried out in the UMTS network of Telefónica, the results can be extrapolated to the LTE system. As a solution to the constraints of a real network compared to the theoretical designs, it is proposed in this thesis an ANR algorithm (Automatic Neighbour Relation) for the generation of neighbour lists which optimize the transfer between cells, achieving an increase in the number of completed calls and reduce the dropped calls or interrupted in the link radio Propagation models show the differences in free space loss with respect to complex urban environments, as well as the effects that produces the mobility of terminals in the characterization of the mobile channel. This feature is especially relevant in the heterogeneous scenarios with users where the communication is done through almost free spread, against others where the signal reaches them very attenuated and distorted after multiple reflections. The search for an optimal solution that offers good coverage, quality and capacity at the lowest cost, it is in this case a very complex task, so it is necessary to study the different lines of research in this area. In addition, the arrival of the LTE brings with it a cheaper and simplification of network structure, which includes the automation of the tasks of optimization. Consensus in different international forums and projector, described in this thesis the use cases and the most common algorithms and methods from several authors. To evaluate the characteristics of the test scenarios, measurements analysis and simulations were realized using innovative methods in order to obtain a characterization of the system in situations of high interference. In a first phase were implemented changes to the configuration of isolated cells, with the purpose of checking the mutual dependence that exists between all cells. With this procedure it was demonstrated that in dense scenarios, it is not possible to optimize the performance of a cell or base station without produce effects on the environment cells. With the conclusions of the previous tests there was designed a novel ANR algorithm that proposes different neighbor lists according to a set of constrains. Power measurements and interference obtained by a call traced tool, showed values very scattered and sometimes opposite. This makes difficult the selection of the best adjacent cell to complete a handover when the subscribers move. The algorithm is capable of combining the best option for a very wide area of the network with high interference, which represents a considerable improvement over the usual methods of neighbor list definition. Designed algorithm applied in the UMTS network of Telefónica, which is located in the Valle de la Orotava, and includes the towns of Puerto de la Cruz, La Orotava and Los Realejos. By the topography of the valley and the dispersion of the population, levels of interference and overreach are greater than in a normal urban scenario, so the net performance are lower. With the proposed method was obtained an increase in the total number of successfully calls, and reduced the number of dropped or interrupted calls