Energy Efficient Radio Resource Management for Heterogeneous Networks

In the continuous evolution of mobile communication systems, there are many issues and aspects to be addressed, as well as in their effective implementation and deployment on cellular networks. In a general way, the most outstanding challenge is how to take the most advantage from the available resources, namely RF spectrum, to satisfy the communication requirements associated to a specific service or application offered to an end user. Energy efficiency has also become one important aspect associated to such requirements, since it has a significant practical impact on operators, namely regarding their networks operational expenditure, as well as on UEs, concerning their battery duration and associated autonomy. This thesis addresses and targets contributing to the growing concerns regarding energy efficiency in the ICT industry, specifically focusing on cellular wireless networks. Moreover, taking into account the current panorama and developments in this field, namely concerning the emerging 5G communication systems and networks, the heterogeneous network (HetNet) concept is also at the core of the work that has been carried out and is presented in this thesis. The work takes into consideration the two ends of the considered system of networks. The first are the nomad end users that should be able to roam freely in such system, always with continuous service provided in a seamless way, and the second is the core network managed by the respective telecommunications operator. To achieve this, the work carried out focused in addressing two key challenges in HetNets in general, specifically towards optimizing the energy efficiency associated to vertical handovers (VHO) and to radio resource management (RRM) mechanisms and approaches to allow energy efficient communication in a HetNet. The work addresses energy efficiency in two different perspectives, each using a different solution exploiting distinct available mechanisms specified for cellular wireless networks. One considers UEs integrating multiple RAT interfaces, and involve a VHO-based solution exploiting IEEE 802.21 standard, and the other targets both core and radio access networks, exploiting a RRM-based solution. The first proposed energy efficient solution exploiting features provided by IEEE 802.21 (MIH/MIIS) and VHO, targeting energy saving at modern multi-RAT mobile UEs, can eventually reduce the energy consumption at their RAT interfaces by roughly 30% on average, with a straightforward implementation, according to the attained simulation results. However, the currently proposed scheme presents a trade-off in terms of added packet loss linked to UEs velocity, which is mostly caused by delayed network re-association. In the second solution, for downlink OFDMA HetNet system, the proposed energy efficiency optimization algorithm for radio resource allocation, taking a given data rate requirement into account, associated to QoS, presented fast convergence, which is key in the design of real EE HetNet systems. The algorithm considers not only the radiated power, but also both types of the circuit power. Simulation results can eventually be exploited towards designing optimal energy consumption networks based on QoS-oriented HetNet method, while total power is fixed. As future work it would also be important to take into account the paradigm shift that arise with the emergence of new standards, namely 3GPP Release 15, placing the stepping stones for 5G systems and networks. In this perspective, at a first instance, it is key to go beyond the assumptions made in this work, by considering C-RAN architecture in the addressed challenge for achieving higher EE, which is a prime concern when redesigning existing and future mobile communication systems, namely in sustainable and environmental perspectives.La continua y rápida evolución de los sistemas de comunicación actuales presenta diversas líneas de actuación, con aspectos muy diversos como el despliegue e implementación eficiente de redes celulares. En este ámbito, el mayor desafío se presenta en cómo aprovechar los recursos disponibles, principalmente en cuanto al espectro RF, para satisfacer los requisitos asociados a los servicios o aplicaciones específicas ofrecidas al usuario final. La eficiencia energética también se ha convertido en un aspecto importante, dentro de los mencionados requisitos, debido al impacto que tiene para los operadores con respecto al coste operacional de las redes, y para el usuario final, debido al efecto en la autonomía de los dispositivos móviles. Este trabajo aborda la eficiencia energética en dos perspectivas diferentes, cada una utilizando una solución diferente que explota los distintos mecanismos disponibles especificados de las redes inalámbricas celulares, en particular HetNets. Uno considera que los dispositivos móviles integran múltiples interfaces RAT e involucran una solución basada en VHO que explota el estándar IEEE 802.21, y el otro apunta a las redes de acceso radio y núcleo de red, explotando una solución basada en RRM. La primera solución de eficiencia energética propuesta aprovecha las características proporcionadas por IEEE 802.21 (MIH / MIIS) y VHO para obtener un ahorro de energía en los dispositivos móviles modernos multi-RAT, y puede eventualmente reducir el consumo de energía en sus interfaces RAT en aproximadamente un 30% en promedio, con una sencilla implementación, de acuerdo con los resultados de la simulación. En la segunda solución, para el sistema OFDMA HetNet de enlace descendente, el algoritmo de optimización de eficiencia energética propuesto para la asignación de recursos de radio, teniendo en cuenta un dado requisito de velocidad de datos, asociado a QoS, presentó una convergencia rápida, lo cual es clave en el diseño de sistemas EE HetNet. El algoritmo considera no solo la potencia radiada, sino también los dos tipos de potencia del circuito. Los resultados de la simulación pueden aprovecharse para diseñar redes de consumo de energía óptimas basadas en el método HetNet orientado a QoS con una potencia total fija