Self-Optimization in Mobile Cellular Networks: Power Control and User Association

International audienceIn this work, we develop mathematical and algorithmic tools for the self-optimization of mobile cellular networks. Scalable algorithms which are based on local measurements and do not require heavy coordination among the wireless devices are proposed. We focus on the optimization of transmit power and of user association. The method is applicable to both joint and separate optimizations. The global utility minimized is linked to potential delay fairness. The distributed algorithm adaptively updates the system parameters and achieves global optimality by measuring SINR and interference. It is built on Gibbs' sampler and offers a unified framework that can be easily reused for different purposes. Simulation results demonstrate the effectiveness of the algorithm

User association strategies in HetNets leading to rate balancing under energy constraints

This paper deals with the development of several strategies for associating users to base stations (BSs) in heterogeneous networks. These strategies are able to balance the rate among users and BSs and increase the overall network utility. Constraints related to the energy availability at BSs are considered explicitly in the design, assuming that the BSs are equipped with batteries that are recharged through energy harvesting. We develop a general association strategy, and then we present several suboptimum but less complex solutions suitable for scenarios with high mobility or deployments of BSs with low computational capabilities. We also present an implementation that is to be executed in a distributed way among users and BSs without the need of having a central entity gathering all the information. The performance of the proposed strategies is evaluated through simulations in terms of rate balancing and the effect of the energy harvesting capabilities on the network throughput is shown. We also compare the proposed strategies with the traditional max-SINR user association approach.Peer ReviewedPostprint (published version

Characterizing the orthogonality factor in WCDMA downlinks

Multipath dispersion leads to the loss of orthogonality between signals transmitted simultaneously on a wideband code division multiple access (WCDMA) downlink. The orthogonality factor (OF), which models its impact in the link signal-to-interference-plus-noise ratio (SINR) equation, depends-to a large extent-on the power delay profile of the multipath channel between the mobile and its serving base station. We use the comprehensive and general COST259 channel model for urban cellular environments to evaluate the impact on the OF of multipath clusters and distance-dependence of the multipath delay decay time constant, both of which have been observed in several channel measurements. The observed large standard deviation of the OF indicates that using a single value for all users in downlink capacity analyses and simulations, as has been the practice, may lead to erroneous conclusions. We also propose an empirical model to analytically characterize the observed statistics of the OF

Algoritmos para Sistemas de Comunicaciones Multi-Usuario con Múltiples Antenas

Los sistemas MIMO (Multiple-Input Multiple-Output) multi-usuario multi-celda coordinados se definen como una configuración avanzada y cooperativa de sistema MIMO. En estos sistemas, varias estaciones base cooperan perfectamente en datos a través de un enlace de alta capacidad, y transmiten de forma coordinada a todos los usuarios de una determinada área. Además, cada estación base del sistema está sujeta a una restricción en la potencia total que puede transmitir. El objetivo general de la Tesis es estudiar algoritmos que combinan control de potencia y beamforming óptimo para resolver el problema de minimización de potencia en el enlace downlink de un sistema W-CDMA MIMO multi-usuario multi-celda coordinado. Al mismo tiempo, se propone un modelo de sistema matricial y lineal que caracteriza completamente los procesos que tienen lugar en transmisión y en recepción en este tipo de sistemas. Paralelamente, a lo largo de la Tesis se contemplan soluciones a problemas de tipo práctico, como por ejemplo, limitaciones en el tipo de información que se dispone en transmisión.Botella Mascarell, C. (2008). Algoritmos para Sistemas de Comunicaciones Multi-Usuario con Múltiples Antenas [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/2421Palanci