This thesis explores a novel technique for transceiver design in future wireless systems, which is cloud radio access networks (CRANs) with single radio frequency (RF) chain antennas at each remote radio head (RRH). This thesis seeks to make three contributions. Firstly, it proposes a novel algorithm to solve the oscillatory/unstable behaviour of electronically steerable parasitic array radiators (ESPAR) when it provides multi-antenna functionality with a single RF chain. This thesis formulates an optimization problem and derives closed-form expressions when calculating the configuration of an ESPAR antenna (EA) for arbitrary signals transmission. This results in simplified processing at the transmitter. The results illustrate that the EA transmitter, when utilizing novel closed-form expressions, shows significant improvement over the performance of the EA transmitter without any pre-processing. It performs at nearly the same symbol error rate (SER) as standard multiple antenna systems. Secondly, this thesis illustrates how a practical peak power constraint can be put into an EA transceiver design. In an EA, all the antenna elements are fed centrally by a single power amplifier. This makes it more probable that during use, the power amplifier reaches maximum power during transmission. Considering limited power availability, this thesis proposes a new algorithm to achieve stable signal transmission. Thirdly, this thesis shows that an energy efficiency (EE) optimization problem can be formulated and solved in CRANs that deploy single RF chain antennas at RRHs. The closed-form expressions of the precoder and power allocation schemes to transmit desired signals are obtained to maximise EE for both single-user and multi-user systems. The results show that the CRANs with single RF chain antennas provide superior EE performance compared to the standard multiple antenna based systems.

La interfaz radio de los sistemas de comunicaciones móviles es normalmente considerada como la única limitación de capacidad en la red de acceso radio. Sin embargo, a medida que se van desplegando nuevas y más eficientes interfaces radio, y de que el tráfico de datos y multimedia va en aumento, existe la creciente preocupación de que la infraestructura de transporte (backhaul) de la red celular pueda convertirse en el cuello de botella en algunos escenarios. En este contexto, la tesis se centra en el desarrollo de técnicas de gestión de recursos que consideran de manera conjunta la gestión de recursos en la interfaz radio y el backhaul. Esto conduce a un nuevo paradigma donde los recursos del backhaul se consideran no sólo en la etapa de dimensionamiento, sino que además son incluidos en la problemática de gestión de recursos. Sobre esta base, el primer objetivo de la tesis consiste en evaluar los requerimientos de capacidad en las redes de acceso radio que usan IP como tecnología de transporte, de acuerdo a las recientes tendencias de la arquitectura de red. En particular, se analiza el impacto que tiene una solución de transporte basada en IP sobre la capacidad de transporte necesaria para satisfacer los requisitos de calidad de servicio en la red de acceso. La evaluación se realiza en el contexto de la red de acceso radio de UMTS, donde se proporciona una caracterización detallada de la interfaz Iub. El análisis de requerimientos de capacidad se lleva a cabo para dos diferentes escenarios: canales dedicados y canales de alta velocidad. Posteriormente, con el objetivo de aprovechar totalmente los recursos disponibles en el acceso radio y el backhaul, esta tesis propone un marco de gestión conjunta de recursos donde la idea principal consiste en incorporar las métricas de la red de transporte dentro del problema de gestión de recursos. A fin de evaluar los beneficios del marco de gestión de recursos propuesto, esta tesis se centra en la evaluación del problema de asignación de base, como estrategia para distribuir el tráfico entre las estaciones base en función de los niveles de carga tanto en la interfaz radio como en el backhaul. Este problema se analiza inicialmente considerando una red de acceso radio genérica, mediante la definición de un modelo analítico basado en cadenas de Markov. Dicho modelo permite calcular la ganancia de capacidad que puede alcanzar la estrategia de asignación de base propuesta. Posteriormente, el análisis de la estrategia propuesta se extiende considerando tecnologías específicas de acceso radio. En particular, en el contexto de redes WCDMA se desarrolla un algoritmo de asignación de base basado en simulatedannealing cuyo objetivo es maximizar una función de utilidad que refleja el grado de satisfacción de las asignaciones respecto los recursos radio y transporte. Finalmente, esta tesis aborda el diseño y evaluación de un algoritmo de asignación de base para los futuros sistemas de banda ancha basados en OFDMA. En este caso, el problema de asignación de base se modela como un problema de optimización mediante el uso de un marco de funciones de utilidad y funciones de coste de recursos. El problema planteado, que considera que existen restricciones de recursos tanto en la interfaz radio como en el backhaul, es mapeado a un problema de optimización conocido como Multiple-Choice Multidimensional Knapsack Problem (MMKP). Posteriormente, se desarrolla un algoritmo de asignación de base heurístico, el cual es evaluado y comparado con esquemas de asignación basados exclusivamente en criterios radio. El algoritmo concebido se basa en el uso de los multiplicadores de Lagrange y está diseñado para aprovechar de manera simultánea el balanceo de carga en la intefaz radio y el backhaul.

An unprecedented era of “connected vehicles” is becoming an imminent reality. This is driven by advances in vehicular communications, and the development of in-vehicle telematics systems supporting a plethora of applications. The diversity and multitude of such developments will, however, introduce excessive congestion across wireless infrastructure, compelling operators to expand their networks. An alternative to network expansions is to develop more efficient content delivery paradigms. In particular, alleviating Radio Access Network (RAN) congestion is important to operators as it postpones costly investments in radio equipment installations and new spectrum. Efficient RAN frameworks are therefore paramount to expediting this realm of vehicular connectivity. Fortunately, the predictability of human mobility patterns, particularly that of vehicles traversing road networks, offers unique opportunities to pursue proactive RAN transmission schemes. Knowing the routes vehicles are going to traverse enables the network to forecast spatio-temporal demands and predict service outages that specific users may face. This can be accomplished by coupling the mobility trajectories with network coverage maps to provide estimates of the future rates users will encounter along a trip. In this thesis, we investigate how this valuable contextual information can enable RANs to improve both service quality and operational efficiency. We develop a collection of methods that leverage mobility predictions to jointly optimize 1) long-term wireless resource allocation, 2) adaptive video streaming delivery, and 3) energy efficiency in RANs. Extensive simulation results indicate that our approaches provide significant user experience gains in addition to large energy savings. We emphasize the applicability of such predictive RAN mechanisms to video streaming delivery, as it is the predominant source of traffic in mobile networks, with projections of further growth. Although we focus on exploiting mobility information at the radio access level, our framework is a direction towards pursuing a predictive end-to-end content delivery architecture. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2014-04-30 06:15:34.31

When it comes to their Radio Access Network (RAN) infrastructure, no two Mobile Operators, serving remote service areas, are alike. Despite situations and technologies being diverse, a well designed optimized RAN solution must adapt itself to the existing networking technologies, both with regard to legacy core networks and modern telecommunication networks in order to produce the best network which is possible subject to many constraints. There is a misconception in technical circles that an optimized internet protocol (IP) enabled RAN architecture is more theoretical than practical. On the contrary, the aforesaid is highly dependent on the technology used. Packet optimized IP- GSM Radio Access Network (GRAN) architecture is proposed in this thesis, it uses Internet Protocol (IP) rather than proprietary protocols for communication between Base Transceiver Stations (BTS), Base Station Controllers (BSC), and the Network Switching Subsystem (NSS). This architecture must deliver carrier-grade mobility, scalability, and reliability; while being optimized for efficient roaming, routing and backhauling from remote service areas. In a geographic arena that spans across the globe, classical circuit-switched networks are not cost efficient due to their integrated call control (signaling) and switching architecture. A solution to this may be soft-switching which separates the call control (Media Gateway Controller (MGC)) and switching (Media Gateway (MG)) into separate nodes. This methodology would fundamentally change the way circuit-switched services, such as traditional voice telephony, are handled. For a service provider this enables a much more efficient network, because it allows optimized equipment location for voice termination into other carrier networks. Co-location of media gateways with satellite ground stations enables local termination to the public switched telephone network (PSTN), thus offloading a great deal of the traffic from the backhaul transmission network of the mobile operator. This thesis adopts soft-switching as part of the call routing processes. The thesis considers the problem of transporting voice and signaling from-to the remote service areas, efficient routing and backhaul to the location of most suitable operator’s point of presence. The thesis explores an alternative which uses a packet switched backbone (e.g. IP based) to transport the media as close (geographically) to the dialed party as possible before terminating it at the PSTN network, thus achieving optimal routing of voice and signaling. Considering the aforesaid, the thesis describes a detailed network architecture and an operational system prototype for maritime GSM network deployment, as a befitting and challenging example of remote service area. / När det gäller deras Radio access nät, finns det inte två Mobiloperatörer, som betjänar avlägsna områden, som är lika. Trots olika omständigheter och teknologier, ett väl designat optimerat RAN måste anpassa sig till den existerande nätverks teknologin, både med avseende på äldre befintlig teknologi och på moderna telekomnät, för att kunna skapa bästa möjliga nätverk givet många begränsningar. Det är en missuppfattning i tekniska kretsar att en optimerad IP anpassad RAN arkitektur är mer teoretisk än praktisk. Å andra sidan så är det ovan sagda väldigt beroende på vilken teknologi som har använts. En paket optimerad IP-GSM Radio Access Nätverks (IPGRAN) arkitektur är föreslagen i denna masters uppsats, den baseras på Internet Protokollet (IP) snarare än något egenutvecklat proprietärt protokol för komunikation mellan Basstation (BTS), Basstationscontroller (BSC), och nätets switchade subsystem (NSS). Denna arkitektur måste leverera carrier-grade (operatörs klassad) mobilitet, skalbarhet och tillgänglighet och samtidigt vara optimerat för effektiv roaming, routing och anslutning från avlägsna områden. På ett geografiskt område som sträcker sig runt hela jordklotet är inte klassiska kretskopplade nätverk kostnadseffektiva beroende på deras integrerade signallerings och samtals arkitektur. En bättre arkitektur kan vara en sk “softswitch” lösning som separerar samtalet i en (Media Gateway Controller (MGC)) och signaleringen (Media Gateway (MG)) i separata noder. Denna metod skulle på ett fundamentalt vis ändra det sätt på vilket traditionella kretskopplade tjänster som traditionell telefoni hanteras. För en tjänsteleverantör möjliggör detta ett mycket effektivare nätverk då det möjliggör optimerad utplacering av utrustning för terminering av rösttrafik in i andra operatörers nät. Samlokalisering av media gateways (MG:s) med jordstationer för satellitkommunikation möjliggör lokal anslutning till det allmänna telenätet (PSTN), vilket kraftigt minskar den trafik som behöver transporteras genom operatörens stomnät. Denna mastersuppsats behandlar “softswitching” som en del av metoden att växla och transportera samtalstrafik. Uppsatsen behandlar problemet med att skicka samtalstrafik och signalering från avlägsna områden, effektiv routing och transport av trafiken till den operatör som har den närmaste(alt. mest optimala) anslutningspunkten. Uppsatsen undersöker ett alternativ som använder ett paketförmedlat (IP baserat) transportsätt för att transportera trafiken geografiskt sett så nära den uppringda parten som möjligt innan den termineras i det allmänna telenätet (PSTN) varvid man uppnår optimal växling (alt. routing) av rösttrafik och signalering. I beaktande av ovanstående beskriver uppsatsen en detaljerad nätverksarkitektur och en funktionsduglig systemprototyp för ett maritimt GSM nät som ett utmanande exempel på ett avlägset beläget nät.

As 5G becomes more established and faces widespread roll-out, energy consumption of radio access networks around the globe will increase. Since the high-frequency radio waves used in 5G communication has a shorter effective range compared to the waves used in previous generations, 5G networks will require a higher number of radio units to compensate for their reduced range. Since the transmission of radio waves is a costly procedure in terms of energy consumption, this further increases the relevancy of radio equipment when considering solutions for increasing radio access networks' energy efficiency. This thesis has therefore provided a possible solution for increasing the energy efficiency of an O-RAN compliant radio access network by decreasing the energy consumption of its radio units. If a network's radio units are capable of entering a low-power sleep mode whenever they are left idle, i.e. not handling any traffic, the energy efficiency of a network can thus be increased by forcing its radio units to enter sleep mode as often as possible. This can be done by offloading traffic from radio units with little traffic onto other nearby radio units. The handovers required to perform such offloading, however, need to be predicted on the fly somewhere within the network. The solution proposed within this thesis therefore utilizes a component indigenous to the O-RAN architecture called RIC and its functionality-defining xApps which are capable of automatically detecting situations where radio units can be put to sleep as well as handling the offloading procedures. Through testing inside a simulated network, the set of xApps designed as a solution resulted in a potential 20-35% decrease in energy consumption among a radio access network's radio units.

The 5G Radio Access Network (RAN) is a critical system that must be secured against potential attacks, particularly its Base-Band Unit (BBU), which is a common target for intrusions. Ericsson, which is a big provider of such systems, has placed significant emphasis on implementing Intrusion Detection Systems (IDS) to detect threats. However, the attention given to Intrusion Response Systems (IRS) in general is limited, with current challenges including false alarms, response cost, response time and reliability. Also, the hardware limitations of the BBU present difficulties in designing an effective IRS. To address these challenges, a semi-automated IRS was implemented with a dynamic and cost-based response selection approach. Open Source SECurity (OSSEC), which is a free, open-source endpoint detection and response tool, was employed to execute the selected responses. The effectiveness of the IRS was assessed based on Ericsson's requirements, reliability, response time, response cost and false alarms. The results obtained show that the proposed IRS is reliable as it can handle a huge number of intrusions and has negligible performance overhead in less extreme attack cases. These findings offer valuable insights into addressing intrusions within a system with constrained hardware resources.

The increasing demand on user rates in the fifth generation (5G) requires network architectures that can support high data rates with acceptable reliability. In order to increase the data rates in the presence of the current spectrum crisis, shrinking cells and reusing the spectrum is a proposed solution. Conventional implementation of dense cells requires a large number of expensive BSs to locally process and decode users’ signals. Another limiting factor that degrades the performance in a dense network is the inter-cell interference. A cloud radio access network (CRAN) is a promising solution to those cost, complexity, and interference challenges. A typical CRAN architecture consists of simplified low-cost base stations (BSs), termed radio units (RUs), that collect the radio frequency (RF) user equipments’ (UEs) signals and forward them over the fronthaul links to the central office (CO) where signal processing is done over shared resources. Besides the reduced cost and complexity of a CRAN, the joint processing at the CO enables joint interference mitigation techniques. However, the performance of CRANs depends critically on the availability of reliable fronthaul links with large bandwidth that may be expensive. Analog optical fronthaul links provide high data rates at lower cost and complexity since UEs’ signals are optically analog-modulated without digitalization, however, they suffer from other channel impairments and nonlinearities. In this thesis, analog optical fronthaul topologies are considered in which radio signals are forwarded over free-space optical (FSO) links, termed radio-over-free-space optical (RoFSO) links, and optical fiber (OF) links, termed radio-over-fiber (RoF) links. Firstly, a CRAN with mixed RF/RoFSO fronthaul is considered to investigate the performance improvement when RF fronthaul links are replaced one-by-one by RoFSO links. A novel joint optimization problem is introduced for the given architecture in which the weighted sum of UEs’ rates is maximized by jointly designing RF and RoFSO links. The optimization problem is solved over different numbers of RF and RoFSO links and under various weather conditions. Under favorable weather conditions, the replacement of 1 RF link by a RoFSO link is shown to increase the 50th percentile of UEs’ rates by 7 times. Secondly, the reliability of a CRAN with two-hop RoFSO/RoF fronthaul links is derived along with other performance metrics such as the average bit-error rate and the cumulative distribution function of UEs’ rates. For the given architecture, the Gaussian noise model of fiber nonlinearity is applied and an optimal OF average optical power is derived to minimize the outage probability. Using the optimal power, and under favorable weather conditions, the 50th percentile of user rate exceeds 1:5 Gbps. Finally, a CRAN with passive all-optical two-hop fronthaul links is considered where optical signals from the first RoFSO fronthaul hop are passively coupled into the RoF fronthaul link. The fronthaul outage probability is derived in the context of network planning to provide guidance on designing a set of system parameters. Those parameters include coverage area radius, density of RUs, RoFSO gain, RoFSO optical power and RoF length. / Thesis / Doctor of Philosophy (PhD) / The upcoming generation of wireless communications, termed fifth generation (5G), promises faster data rates and lower latency. In order to achieve this, more base stations (BSs) have to be deployed which increases the cost and complexity of the network. A solution to this challenge is to install simple BSs, i.e. radio units (RUs), that collect signals from users and forward them to a central office (CO) for joint processing which is referred to as a cloud radio access network (CRAN). The fronthaul network in a CRAN connects the RUs to the CO and it can be implemented using different kinds of links. While there are several fronthaul media (e.g., radio frequency (RF), free-space optical (FSO) links, copper lines, satellite communications, and optical fiber (OF)), optical links provide high data rates that are promising to achieve the 5G requirements. In this thesis, a novel architecture of a CRAN is considered in which analog optical links, namely FSO links and OF links, are used for fronthauling. Performance improvement in terms of rate and reliability is investigated and optimized through different design tools. In response to the challenges introduced by the proposed architecture, such as the nonlinearities of analog FSO and OF links, various design parameters are proposed in the optimization problems to tackle those challenges. Furthermore, a network planning framework is introduced to provide guidance and insights on designing the network.

Yes / Fifth generation (5G) cellular networks will be comprised of millions of connected devices like wearable devices, Androids, iPhones, tablets and the Internet of Things (IoT) with a plethora of applications generating requests to the network. The 5G cellular networks need to cope with such sky-rocketing tra c requests from these devices to avoid network congestion. As such, cloud radio access networks (C-RAN) has been considered as a paradigm shift for 5G in which requests from mobile devices are processed in the cloud with shared baseband processing. Despite call admission control (CAC) being one of radio resource management techniques to avoid the network congestion, it has recently been overlooked by the community. The CAC technique in 5G C-RAN has a direct impact on the quality of service (QoS) for individual connections and overall system e ciency. In this paper, a novel Fuzzy-Logic based CAC scheme with pre-emption in C-RAN is proposed. In this scheme, cloud bursting technique is proposed to be used during congestion, where some delay tolerant low-priority connections are pre-empted and outsourced to a public cloud with a penalty charge. Simulation results show that the proposed scheme has low blocking probability below 5%, high throughput, low energy consumption and up to 95% of return on revenue.

Submitted by JOSIANE SANTOS DE OLIVEIRA (josianeso) on 2018-05-11T12:40:43Z No. of bitstreams: 1 Felipe Rabuske Costa_.pdf: 3408830 bytes, checksum: 25a67ecb02629c811b5f305a1f2e3d27 (MD5) / Made available in DSpace on 2018-05-11T12:40:43Z (GMT). No. of bitstreams: 1 Felipe Rabuske Costa_.pdf: 3408830 bytes, checksum: 25a67ecb02629c811b5f305a1f2e3d27 (MD5) Previous issue date: 2018-02-28 / Nenhuma / Estima-se que até o ano de 2020, cerca de 50 bilhões de dispositivos móveis estarão conectados a redes sem fio e que 78% de todo o tráfego de dados gerado por esse tipo de dispositivos será conteúdo multimídia. Essas estimativas fomentam o desenvolvimento da quinta geração de redes móveis (5G). Uma das arquiteturas mais recentemente proposta, chamada de Fog Radio Access Networks (F-RAN), dá aos componentes localizados na borda da rede poder de processamento e armazenamento endereçados às atividades da rede. Um dos principais problemas dessa arquitetura é o intenso tráfego de dados no seu canal de comunicação centralizado chamado fronthaul, utilizado para conectar as antenas (F-APs) à rede externa. Dado esse contexto, esse trabalho apresenta o Nuoxus, um modelo de caching de conteúdo multimídia voltado para F-RANs que visa amenizar esse problema. Ao armazenar esse tipo de conteúdo nos nós de rede mais próximos ao usuário, o número de acessos concorrentes ao fronthaul é reduzido, sendo esse um dos fatores agravantes na latência de comunicação na rede. O Nuoxus pode ser executado em qualquer nó da rede que possua capacidade de armazenamento e processamento, ficando responsável por gerenciar o caching de conteúdo desse nó. Sua política de substituição de conteúdo utiliza a similaridade de requisições entre os nós filhos e o restante da rede como um fator para definir a relevância de armazenar o conteúdo requisitado em cache. Além disso, utilizando esse mesmo processo, o Nuoxus sugere, de forma proativa, aos demais nós filhos que apresentam um alto grau de similaridade que façam o caching desse conteúdo, visando um possível futuro acesso. A análise do estado da arte demonstra que até o momento não existe nenhum outro trabalho que explore o histórico de requisições para fazer caching de conteúdo em arquiteturas multicamadas para redes sem fio de forma proativa e sem utilizar algum componente centralizado para fazer coordenação e predição de caching. A fim de comprovar a eficiência do modelo, foi desenvolvido um protótipo utilizando o simulador ns-3. Os resultados obtidos demostram que a utilização do Nuoxus foi capaz de reduzir a latência de rede em cerca de 29.75%. Além disso, quando comparado com outras estratégias de caching, o número de acesso à cache dos componentes de rede aumentou em 53.16% em relação à estratégia que obteve o segundo melhor resultado. / It is estimated that by the year 2020, about 50 billion mobile devices will be connected to wireless networks and 78% of the data traffic of this kind of device will be multimedia content. These estimates foster the development of the 5th generation of mobile networks (5G). One of the most recently proposed architectures, named Fog Radio Access Networks or F-RAN, gives the components located at the edge of the network the processing power and storage capacity to address network activities. One of the main problems of this architecture is the intense data traffic in its centralized component named fronthaul, which is used to connect the antennas (FAPs) to the external network. Given this context, we propose Nuoxus, a multimedia content caching model for F-RANs that aims to mitigate this problem. By storing the content in the nodes closest to the user, the number of concurrent accesses to the fronthaul is reduced, which decreases the communication latency of the network. Nuoxus can run on any network node that has storage and processing capacity, becoming the responsible for managing the cache of that node. Its content replacement policy uses the similarity of requests between the child nodes and the rest of the network as a factor to decide the relevance of storing the requested content in the cache. Furthermore, by using this same process, Nuoxus proactively suggests to the child nodes whose degree of similarity is high to perform the caching of the content, assuming they will access the content at a future time. The State-of-the-art analysis shows that there is no other work that explores the history of requests to cache content in multi-layer architectures for wireless networks in a proactive manner, without using some centralized component to do coordination and prediction of caching. To demonstrate the efficiency of the model, a prototype was developed using the ns 3 simulator. The results obtained demonstrate that the use of Nuoxus reduced network latency in 29.75%. In addition, when compared to other caching strategies, the cache hit increased by 53.16% when compared to the strategy that obtained the second-best result.

De nos jours, la demande en trafic mobile a considérablement augmenté. Face à cette croissance, plusieurs propositions font l'objet d'étude pour remédier à un tel défi. L’architecture des réseaux d’accès de type Cloud (C-RAN) est l’une des propositions pour faire face à cette demande croissante, et constitue une solution candidate potentielle pour les réseaux futurs 5G. L'architecture C-RAN dissocie deux éléments principaux de la station de base: La BBU ou ``Baseband Unit", qui constitue une unité intelligente pour le traitement des données en bande de base, et le RRH ou ``Remote Radio Head", constituant en une antenne passive pour fournir l'accès aux utilisateurs (UEs). Grâce à l’architecture C-RAN, les BBUs sont centralement regroupées, alors que les RRHs sont distribués sur plusieurs sites. Plusieurs avantages sont ainsi dérivés, tels que le gain en multiplexage statistique, l’efficacité d’utilisation des ressources, et l’économie de puissance. Contrairement à l’architecture conventionnelle où chaque RRH est exclusivement associé à une BBU, dans l’architecture C-RAN, plusieurs RRHs sont regroupés en une seule BBU lorsque les conditions de charge sont faibles. Ceci présente plusieurs avantages, tel que l’amélioration en efficacité énergétique et la minimisation en consommation de puissance. Dans cette thèse, nous adressons le problème d’optimisation des associations BBU-RRH. Nous nous intéressons à l’optimisation des regroupements des RRHs aux BBUs en tenant compte de critères multiples. Plusieurs contraintes sont ainsi envisagées, tel que la réduction de la consommation d'énergie sous garantie de Qualité de Service (QoS) minimale. En outre, la prise en compte du changement du niveau d’interférence en activant/désactivant les BBUs est primordiale pour l’amélioration de l’efficacité spectrale. En plus, décider dynamiquement de la réassociation des RRHs aux BBUs sous des conditions de charges variables représente un défi, vu que les UEs connectés aux RRHs changeant leurs associations font face à des ``handovers" (HOs). / The demand on mobile traffic has been largely increasing nowadays. Facing such growth, several propositions are being studied to cope with this challenge. Cloud-Radio Access Networks Architecture (C-RAN) is one of the proposed solutions to address the increased demand, and is a potential candidate for future 5G networks. The C-RAN architecture dissociates two main elements composing the base station: The Baseband Unit (BBU), consisting in an intelligent element to perform baseband tasks functionalities, and the Remote Radio Head (RRH), that consists in a passive antenna element to provide access for serviced User Equipments (UEs). In C-RAN architecture, the BBUs migrate to a Cloud data center, while RRHs remain distributed across multiple sites. Several advantages are derived, such as statistical multiplexing gain, efficiency in resource utilization and power saving. Contrarily to conventional architecture, where each RRH is associated to one BBU, in C-RAN architecture, multiple RRHs can be embraced by one single BBU when network load conditions are low, bringing along several benefits, such as enhanced energy efficiency, and power consumption minimization. In this thesis, the BBU-RRH association optimization problem is addressed. Our aim is to optimize the BBU-RRH association schemes, taking into consideration several criteria. The problem presents many constraints: For example, achieving minimized power consumption while guaranteeing a minimum level of Quality of Service (QoS) is a challenging task. Further, taking into account the interference level variation while turning ON/OFF BBUs is paramount to achieve enhanced spectral efficiency. Moreover, deciding how to re-associate RRHs to BBUs under dynamic load conditions is also a challenge, since connected UEs face handovers (HOs) when RRHs change their associations.