60 research outputs found
On the Design of Irregular HetNets with Flow-Level Traffic Dynamics
The application of stochastic geometry theory for the study of cellular networks has gained huge popularity recently. Most existing works however rely on unrealistic assumptions concerning the underlying user traffic model. This paper aims to make a step in this direction by devising a new model for the performance analysis and optimization of heterogeneous cellular networks (HetNets) with irregular BS deployment and flow- level traffic dynamics. We provide a unified methodology for the evaluation of the flow rate with closed-form expressions of the useful signal power and aggregate network interference over Nakagami-m fading channels. The problem of computing the optimal loading factors which result in the greatest sustainable traffic whilst the system remains stable is formulated and tackled
A cell outage management framework for dense heterogeneous networks
In this paper, we present a novel cell outage management (COM) framework for heterogeneous networks with split control and data planes-a candidate architecture for meeting future capacity, quality-of-service, and energy efficiency demands. In such an architecture, the control and data functionalities are not necessarily handled by the same node. The control base stations (BSs) manage the transmission of control information and user equipment (UE) mobility, whereas the data BSs handle UE data. An implication of this split architecture is that an outage to a BS in one plane has to be compensated by other BSs in the same plane. Our COM framework addresses this challenge by incorporating two distinct cell outage detection (COD) algorithms to cope with the idiosyncrasies of both data and control planes. The COD algorithm for control cells leverages the relatively larger number of UEs in the control cell to gather large-scale minimization-of-drive-test report data and detects an outage by applying machine learning and anomaly detection techniques. To improve outage detection accuracy, we also investigate and compare the performance of two anomaly-detecting algorithms, i.e., k-nearest-neighbor- and local-outlier-factor-based anomaly detectors, within the control COD. On the other hand, for data cell COD, we propose a heuristic Grey-prediction-based approach, which can work with the small number of UE in the data cell, by exploiting the fact that the control BS manages UE-data BS connectivity and by receiving a periodic update of the received signal reference power statistic between the UEs and data BSs in its coverage. The detection accuracy of the heuristic data COD algorithm is further improved by exploiting the Fourier series of the residual error that is inherent to a Grey prediction model. Our COM framework integrates these two COD algorithms with a cell outage compensation (COC) algorithm that can be applied to both planes. Our COC solution utilizes an actor-critic-based reinforcement learning algorithm, which optimizes the capacity and coverage of the identified outage zone in a plane, by adjusting the antenna gain and transmission power of the surrounding BSs in that plane. The simulation results show that the proposed framework can detect both data and control cell outage and compensate for the detected outage in a reliable manner
Learning and Reasoning Strategies for User Association in Ultra-dense Small Cell Vehicular Networks
Recent vehicular ad hoc networks research has been focusing on providing intelligent transportation services by employing information and communication technologies on road transport. It has been understood that advanced demands such as reliable connectivity, high user throughput, and ultra-low latency required by these services cannot be met using traditional communication technologies.
Consequently, this thesis reports on the application of artificial intelligence to user association as a technology enabler in ultra-dense small cell vehicular networks. In particular, the work focuses on mitigating mobility-related concerns and networking issues at different mobility levels by employing diverse heuristic as well as reinforcement learning (RL) methods.
Firstly, driven by rapid fluctuations in the network topology and the radio environment, a conventional, three-step sequence user association policy is designed to highlight and explore the impact of vehicle speed and different performance indicators on network quality of service (QoS) and user experience. Secondly, inspired by control-theoretic models and dynamic programming, a real-time controlled feedback user association approach is proposed. The algorithm adapts to the changing vehicular environment by employing derived network performance information as a heuristic, resulting in improved network performance. Thirdly, a sequence of novel RL based user association algorithms are developed that employ variable learning rate, variable rewards function and adaptation of the control feedback framework to improve the initial and steady-state learning performance. Furthermore, to accelerate the learning process and enhance the adaptability and robustness of the developed RL algorithms, heuristically accelerated RL and case-based transfer learning methods are employed.
A comprehensive, two-tier, event-based, system level simulator which is an integration of a dynamic vehicular network, a highway, and an ultra-dense small cell network is developed. The model has enabled the analysis of user mobility effects on the network performance across different mobility levels as well as served as a firm foundation for the evaluation of the empirical properties of the investigated approaches
A comprehensive survey on radio resource management in 5G HetNets: current solutions, future trends and open issues
The 5G network technologies are intended to accommodate innovative services with a large influx of data traffic with lower energy consumption and increased quality of service and user quality of experience levels. In order to meet 5G expectations, heterogeneous networks (HetNets) have been introduced. They involve deployment of additional low power nodes within the coverage area of conventional high power nodes and their placement closer to user underlay HetNets. Due to the increased density of small-cell networks and radio access technologies, radio resource management (RRM) for potential 5G HetNets has emerged as a critical avenue. It plays a pivotal role in enhancing spectrum utilization, load balancing, and network energy efficiency. In this paper, we summarize the key challenges i.e., cross-tier interference, co-tier interference, and
user association-resource-power allocation (UA-RA-PA) emerging in 5G HetNets and highlight their significance. In addition, we present a comprehensive survey of RRM schemes based on interference management (IM), UA-RA-PA and combined approaches (UA-RA-PA + IM). We introduce a taxonomy for individual (IM, UA-RA-PA) and combined approaches as a framework for systematically studying the existing schemes. These schemes are also qualitatively analyzed and compared to each other. Finally, challenges and opportunities for RRM in 5G are outlined, and design guidelines along with possible solutions
for advanced mechanisms are presented
Eficiência energética avançada para sistema OFDMA CoMP coordenação multiponto
Doutoramento em Engenharia EletrotécnicaThe ever-growing energy consumption in mobile networks stimulated by
the expected growth in data tra ffic has provided the impetus for mobile
operators to refocus network design, planning and deployment towards reducing
the cost per bit, whilst at the same time providing a signifi cant step
towards reducing their operational expenditure. As a step towards incorporating
cost-eff ective mobile system, 3GPP LTE-Advanced has adopted the
coordinated multi-point (CoMP) transmission technique due to its ability
to mitigate and manage inter-cell interference (ICI). Using CoMP the cell
average and cell edge throughput are boosted. However, there is room for
reducing energy consumption further by exploiting the inherent
exibility of
dynamic resource allocation protocols. To this end packet scheduler plays
the central role in determining the overall performance of the 3GPP longterm
evolution (LTE) based on packet-switching operation and provide a
potential research playground for optimizing energy consumption in future
networks. In this thesis we investigate the baseline performance for down
link CoMP using traditional scheduling approaches, and subsequently go
beyond and propose novel energy e fficient scheduling (EES) strategies that
can achieve power-e fficient transmission to the UEs whilst enabling both
system energy effi ciency gain and fairness improvement. However, ICI can
still be prominent when multiple nodes use common resources with di fferent
power levels inside the cell, as in the so called heterogeneous networks (Het-
Net) environment. HetNets are comprised of two or more tiers of cells. The
rst, or higher tier, is a traditional deployment of cell sites, often referred
to in this context as macrocells. The lower tiers are termed small cells, and
can appear as microcell, picocells or femtocells. The HetNet has attracted
signiffi cant interest by key manufacturers as one of the enablers for high
speed data at low cost. Research until now has revealed several key hurdles
that must be overcome before HetNets can achieve their full potential:
bottlenecks in the backhaul must be alleviated, as well as their seamless
interworking with CoMP. In this thesis we explore exactly the latter hurdle,
and present innovative ideas on advancing CoMP to work in synergy with
HetNet deployment, complemented by a novel resource allocation policy
for HetNet tighter interference management. As system level simulator has
been used to analyze the proposed algorithm/protocols, and results have
concluded that up to 20% energy gain can be observed.O aumento do consumo de energia nas TICs e em particular nas redes de
comunicação móveis, estimulado por um crescimento esperado do tráfego de
dados, tem servido de impulso aos operadores m oveis para reorientarem os
seus projectos de rede, planeamento e implementa ção no sentido de reduzir
o custo por bit, o que ao mesmo tempo possibilita um passo signicativo no
sentido de reduzir as despesas operacionais. Como um passo no sentido de
uma incorporação eficaz em termos destes custos, o sistema móvel 3GPP
LTE-Advanced adoptou a técnica de transmissão Coordenação Multi-Ponto
(identificada na literatura com a sigla CoMP) devido à sua capacidade de
mitigar e gerir Interferência entre Células (sigla ICI na literatura). No entanto
a ICI pode ainda ser mais proeminente quando v arios n os no interior
da célula utilizam recursos comuns com diferentes níveis de energia,
como acontece nos chamados ambientes de redes heterogéneas (sigla Het-
Net na literatura). As HetNets são constituídas por duas ou mais camadas
de células. A primeira, ou camada superiora, constitui uma implantação
tradicional de sítios de célula, muitas vezes referidas neste contexto como
macrocells. Os níveis mais baixos são designados por células pequenas, e
podem aparecer como microcells, picocells ou femtocells. A HetNet tem
atra do grande interesse por parte dos principais fabricantes como sendo
facilitador para transmissões de dados de alta velocidade a baixo custo. A
investigação tem revelado at e a data, vários dos principais obstáculos que
devem ser superados para que as HetNets possam atingir todo o seu potencial:
(i) os estrangulamentos no backhaul devem ser aliviados; (ii) bem
como sua perfeita interoperabilidade com CoMP. Nesta tese exploramos
este ultimo constrangimento e apresentamos ideias inovadoras em como a
t ecnica CoMP poder a ser aperfeiçoada por forma a trabalhar em sinergia
com a implementação da HetNet, complementado ainda com uma nova
perspectiva na alocação de recursos rádio para um controlo e gestão mais
apertado de interferência nas HetNets. Com recurso a simulação a níível de
sistema para analisar o desempenho dos algoritmos e protocolos propostos,
os resultados obtidos concluíram que ganhos at e a ordem dos 20% poderão
ser atingidos em termos de eficiência energética
On three use cases of multi-connectivity paradigm in emerging wireless networks
As envisioned by global network operators, the increasing trend of data traffic demand is expected to continue with exponential growth in the coming years. To cope with this rapid increase, significant efforts from the research community, industry and even regulators have been focused towards improving two main aspects of the wireless spectrum: (i) spectrum capacity and (ii) spectral efficiency. Concerning the spectrum capacity enhancement, the multi-connectivity paradigm has been seen to be fundamentally important to solve the capacity problem in the next generation networks. Multi-connectivity is a feature that allows wireless devices to establish and maintain multiple simultaneous connections across homogeneous or heterogeneous technologies. In this thesis, we focus on identifying the core issues in applying the multi-connectivity paradigm for different use cases and propose novel solutions to address them.
Specifically, this thesis studies three use cases of the multi-connectivity paradigm. First, we study the uplink/downlink decoupling problem in 4G networks. More specifically, we focus on the user association problem in the decoupling context, which is considered challenging due to the conflicting objectives of different entities (e.g., mobile users and base stations) in the system. We use a combination of matching theory and stochastic geometry to reconcile competing objectives between users in the uplink/downlink directions and also from the perspective of base stations.
Second, we tackle the spectrum aggregation problem for wireless backhauling links in unlicensed opportunistic shared spectrum bands, specifically, TV White Space (TVWS) spectrum. In relation to this, we present a DIY mobile network deployment model to accelerate the roll-out of high-end mobile services in rural and developing regions. As part of this model, we highlight the importance of low-cost and high-capacity backhaul infrastructure for which TVWS spectrum can be exploited. Building on that, we conduct a thorough analytical study to identify the characteristics of TVWS in rural areas. Our study sheds light on the nature of TVWS spectrum fragmentation for the backhauling use case, which in turn poses requirements for the design of spectrum aggregation systems for TVWS backhaul. Motivated by these findings, we design and implement WhiteHaul, a flexible platform for spectrum aggregation in TVWS. Three challenges have been tackled in this work. First, TVWS spectrum is fragmented in that the spectrum is available in non-contiguous manner. To fully utilize the available spectrum, multiple radios should be enabled to work simultaneously. However, all the radios have to share only a single antenna. The key challenge is to design a system architecture that is capable of achieving different aggregation configurations while avoiding the interference. Second, the heterogeneous nature of the available spectrum (i.e., in terms of bandwidth and link characteristics) requires a design of efficient traffic distribution algorithm that takes into account these factors. Third, TVWS is unlicensed opportunistic shared spectrum. Thus, the coordination mechanism between the two nodes of backhauling link is essential to enable seamless channel switching.
Third, we study the integration of multiple radio access technologies (RATs) in the context of 4G/5G networks. More specifically, we study the potential gain of enabling the Multi-RAT integration at the Packet Data Convergence Protocol (PDCP) layer compared with doing it at the transport layer. In this work, we consider ultra-reliable low-latency communication (URLLC) as one of the motivating services. This work tackles the different challenges that arise from enabling the Multi-RAT integration at the PDCP layer, including, packet reordering and traffic scheduling
Internet of Things and Sensors Networks in 5G Wireless Communications
This book is a printed edition of the Special Issue Internet of Things and Sensors Networks in 5G Wireless Communications that was published in Sensors
Design of static intercell interference coordination schemes for realistic lte-based cellular networks
Today, 3.5 and 4G systems including Long Term Evolution (LTE) and LTE-Advanced
(LTE-A) support packet-based services and provide mobile broadband access for
bandwidth-hungry applications. In this context of fast evolution, new and challenging
technical issues must be e ectively addressed. The nal target is to achieve a
signi cant step forward toward the improvement of the Quality of Experience (QoE).
To that end, interference management has been recognized by the industry as a key
enabler for cellular technologies based on OFDMA. Indeed, with a low frequency
reuse factor, intercell interference (ICI) becomes a major concern since the Quality of
Service (QoS) is not uniformly delivered across the network, it remarkably depends on
user position. Hence, cell edge performance is an important issue in LTE and LTE-A.
Intercell Interference Coordination (ICIC) encompasses strategies whose goal
is to keep ICI at cell edges as low as possible. This alleviates the aforementioned
situation. For this reason, the novelties presented in this Ph.D. thesis include not
only developments of static ICIC mechanisms for data and control channels, but
also e orts towards further improvements of the energy e ciency perspective.
Based on a comprehensive review of the state of the art, a set of research
opportunities were identi ed. To be precise, the need for
exible performance
evaluation methods and optimization frameworks for static ICIC strategies. These
mechanisms are grouped in two families: the schemes that de ne constraints on the
frequency domain and the ones that propose adjustments on the power levels. Thus,
Soft- and Fractional Frequency Reuse (SFR and FFR, respectively) are identi ed as
the base of the vast majority of static ICIC proposals.
Consequently, during the rst part of this Ph.D. thesis, interesting insights into
the operation of SFR and FFR were identi ed beyond well-known facts. These
studies allow for the development of a novel statistical framework to evaluate the
performance of these schemes in realistic deployments. As a result of the analysis, the
poor performance of classic con gurations of SFR and FFR in real-world contexts
is shown, and hence, the need for optimization is established. In addition, the
importance of the interworking between static ICIC schemes and other network
functionalities such as CSI feedback has also been identi ed. Therefore, novel CSI
feedback schemes, suitable to operate in conjunction with SFR and FFR, have been
developed. These mechanisms exploit the resource allocation pattern of these static
ICIC techniques in order to improve the accuracy of the CSI feedback process. The second part is focused on the optimization of SFR and FFR. The use of
multiobjective techniques is investigated as a tool to achieve e ective network-speci c
optimization. The approach o ers interesting advantages. On the one hand, it allows
for simultaneous optimization of several con
icting criteria. On the other hand, the
multiobjective nature results in outputs composed of several high quality (Pareto
e cient) network con gurations, all of them featuring a near-optimal tradeo
between the performance criteria. Multiobjective evolutionary algorithms allow
employing complex mathematical structures without the need for relaxation, thus
capturing accurately the system behavior in terms of ICI. The multiobjective
optimization formulation of the problem aims at achieving e ective adjustment of
the operational parameters of SFR and FFR both at cell level and network-wide.
Moreover, the research was successfully extended to the control channels, both the
PDCCH and ePDCCH.
Finally, in an e ort to further improve the network energy e ciency (an aspect
always considered throughout the thesis), the framework of Cell Switch O (CSO),
having close connections with ICIC, is also introduced. By means of the proposed
method, signi cant improvements with respect to traditional approaches, baseline
con gurations, and previous proposals can be achieved. The gains are obtained in
terms of energy consumption, network capacity, and cell edge performance.Actualmente los sistemas 3.5 y 4G tales como Long Term Evolution (LTE) y
LTE-Advanced (LTE-A) soportan servicios basados en paquetes y proporcionan
acceso de banda ancha m ovil para aplicaciones que requieren elevadas tasas de
transmisi on. En este contexto de r apida evoluci on, aparecen nuevos retos t ecnicos
que deben ser resueltos e cientemente. El objetivo ultimo es conseguir un salto
cualitativo importante en la experiencia de usuario (QoE). Con tal n, un factor
clave que ha sido reconocido en las redes celulares basadas en Orthogonal Frequency-
Division Multiple Access (OFDMA) es la gesti on de interferencias. De hecho, la
utilizaci on de un factor de reuso bajo permite una elevada e ciencia espectral pero
a costa de una distribuci on de la calidad de servicio (QoS) que no es uniforme en la
red, depende de la posici on del usuario. Por lo tanto, el rendimiento en los l mites
de la celda se ve muy penalizado y es un problema importante a resolver en LTE
y LTE-A.
La coordinaci on de interferencias entre celdas (ICIC, del ingl es Intercell Interfe-
rence Coordination) engloba las estrategias cuyo objetivo es mantener la interferencia
intercelular (ICI) lo m as baja posible en los bordes de celda. Esto permite aliviar
la situaci on antes mencionada. La contribuci on presentada en esta tesis doctoral
incluye el dise~no de nuevos mecanismos de ICIC est atica para los canales de datos y
control, as como tambi en mejoras desde el punto de vista de e ciencia energ etica.
A partir de una revisi on completa del estado del arte, se identi caron una serie
de retos abiertos que requer an esfuerzos de investigaci on. En concreto, la necesidad
de m etodos de evaluaci on
exibles y marcos de optimizaci on de las estrategias de
ICIC est aticas. Estos mecanismos se agrupan en dos familias: los esquemas que
de nen restricciones sobre el dominio de la frecuencia y los que proponen ajustes
en los niveles de potencia. Es decir, la base de la gran mayor a de propuestas ICIC
est aticas son la reutilizaci on de frecuencias de tipo soft y fraccional (SFR y FFR,
respectivamente).
De este modo, durante la primera parte de esta tesis doctoral, se han estudiado
los aspectos m as importantes del funcionamiento de SFR y FFR, haciendo especial
enfasis en las conclusiones que van m as all a de las bien conocidas. Ello ha permitido
introducir un nuevo marco estad stico para evaluar el funcionamiento de estos
sistemas en condiciones de despliegue reales. Como resultado de estos an alisis, se
muestra el pobre desempe~no de SFR y FFR en despliegues reales cuando funcionan con sus con guraciones cl asicas y se establece la necesidad de optimizaci on. Tambi en
se pone de mani esto la importancia del funcionamiento conjunto entre esquemas
ICIC est aticos y otras funcionalidades de la red radio, tales como la informaci on que
env an los usuarios sobre el estado de su canal downlink (feedback del CSI, del ingl es
Channel State Information). De este modo, se han propuesto diferentes esquemas de
feedback apropiados para trabajar conjuntamente con SFR y FFR. Estos mecanismos
explotan el patr on de asignaci on de recursos que se utiliza en ICIC est atico para
mejorar la precisi on del proceso.
La segunda parte se centra en la optimizaci on de SFR y FFR. Se ha investigado el
uso de t ecnicas multiobjetivo como herramienta para lograr una optimizaci on e caz,
que es espec ca para cada red. El enfoque ofrece ventajas interesantes, por un lado, se
permite la optimizaci on simult anea de varios criterios contradictorios. Por otro lado,
la naturaleza multiobjetivo implica obtener como resultado con guraciones de red
de elevada calidad (Pareto e cientes), todas ellas con un equilibrio casi- optimo entre
las diferentes m etricas de rendimiento. Los algoritmos evolucionarios multiobjetivo
permiten la utilizaci on de estructuras matem aticas complejas sin necesidad de relajar
el problema, de este modo capturan adecuadamente su comportamiento en t erminos
de ICI. La formulaci on multiobjetivo consigue un ajuste efectivo de los par ametros
operacionales de SFR y FFR, tanto a nivel de celda como a nivel de red. Adem as,
la investigaci on se extiende con resultados satisfactorios a los canales de control,
PDCCH y ePDCCH.
Finalmente, en un esfuerzo por mejorar la e ciencia energ etica de la red (un
aspecto siempre considerado a lo largo de la tesis), se introduce en el an alisis global
el apagado inteligente de celdas, estrategia con estrechos v nculos con ICIC. A trav es
del m etodo propuesto, se obtienen mejoras signi cativas con respecto a los enfoques
tradicionales y propuestas previas. Las ganancias se obtienen en t erminos de consumo
energ etico, capacidad de la red, y rendimiento en el l mite de las celdas.Actualment els sistemes 3.5 i 4G tals com Long Term Evolution (LTE) i LTE-
Advanced (LTE-A) suporten serveis basats en paquets i proporcionen acc es de
banda ampla m obil per a aplicacions que requereixen elevades taxes de transmissi
o. En aquest context de r apida evoluci o, apareixen nous reptes t ecnics que
han de ser resolts e cientment. L'objectiu ultim es aconseguir un salt qualitatiu
important en l'experi encia d'usuari (QoE). Amb tal , un factor clau que ha estat
reconegut a les xarxes cel lulars basades en Orthogonal Frequency-Division Multiple
Access (OFDMA) es la gesti o d'interfer encies. De fet, la utilizaci o d'un factor de
re us baix permet una elevada e ci encia espectral per o a costa d'una distribuci o de
la qualitat de servei (QoS) que no es uniforme a la xarxa, dep en de la posici o de
l'usuari. Per tant, el rendiment en els l mits de la cel la es veu molt penalitzat i es
un problema important a resoldre en LTE i LTE-A.
La coordinaci o d'interfer encies entre cel les (ICIC, de l'angl es Intercell Interfe-
rence Coordination) engloba les estrat egies que tenen com a objectiu mantenir la
interfer encia intercel lular (ICI) el m es baixa possible en les vores de la cel la. Aix o
permet alleujar la situaci o abans esmentada. La contribuci o presentada en aquesta
tesi doctoral inclou el disseny de nous mecanismes de ICIC est atica per als canals de
dades i control, aix com tamb e millores des del punt de vista d'e ci encia energ etica.
A partir d'una revisi o completa de l'estat de l'art, es van identi car una s erie de
reptes oberts que requerien esfor cos de recerca. En concret, la necessitat de m etodes
d'avaluaci o
exibles i marcs d'optimitzaci o de les estrat egies de ICIC est atiques.
Aquests mecanismes s'agrupen en dues fam lies: els esquemes que de neixen restriccions
sobre el domini de la freq u encia i els que proposen ajustos en els nivells de
pot encia. Es a dir, la base de la gran majoria de propostes ICIC est atiques s on la
reutilitzaci o de freq u encies de tipus soft i fraccional (SFR i FFR, respectivament).
D'aquesta manera, durant la primera part d'aquesta tesi doctoral, s'han estudiat
els aspectes m es importants del funcionament de SFR i FFR, fent especial emfasi en
les conclusions que van m es enll a de les ben conegudes. Aix o ha perm es introduir un
nou marc estad stic per avaluar el funcionament d'aquests sistemes en condicions
de desplegament reals. Com a resultat d'aquestes an alisis, es mostra el pobre
acompliment de SFR i FFR en desplegaments reals quan funcionen amb les seves
con guracions cl assiques i s'estableix la necessitat d'optimitzaci o. Tamb e es posa de
manifest la import ancia del funcionament conjunt entre esquemes ICIC est atics i altres funcionalitats de la xarxa radio, tals com la informaci o que envien els usuaris
sobre l'estat del seu canal downlink (feedback del CSI, de l'angl es Channel State
Information). D'aquesta manera, s'han proposat diferents esquemes de feedback
apropiats per treballar conjuntament amb SFR i FFR. Aquests mecanismes exploten
el patr o d'assignaci o de recursos que s'utilitza en ICIC est atic per millorar la precisi o
del proc es.
La segona part se centra en l'optimitzaci o de SFR i FFR. S'ha investigat l' us
de t ecniques multiobjectiu com a eina per aconseguir una optimitzaci o e ca c, que
es espec ca per a cada xarxa. L'enfocament ofereix avantatges interessants, d'una
banda, es permet l'optimitzaci o simult ania de diversos criteris contradictoris. D'altra
banda, la naturalesa multiobjectiu implica obtenir com resultat con guracions de
xarxa d'elevada qualitat (Pareto e cients), totes elles amb un equilibri gaireb e optim
entre les diferents m etriques de rendiment. Els algorismes evolucionaris multiobjectiu
permeten la utilitzaci o d'estructures matem atiques complexes sense necessitat de
relaxar el problema, d'aquesta manera capturen adequadament el seu comportament
en termes de ICI. La formulaci o multiobjectiu aconsegueix un ajust efectiu dels
par ametres operacionals de SFR i FFR, tant a nivell de cel la com a nivell de xarxa.
A m es, la recerca s'est en amb resultats satisfactoris als canals de control, PDCCH
i ePDCCH.
Finalment, en un esfor c per millorar l'e ci encia energ etica de la xarxa (un
aspecte sempre considerat al llarg de la tesi), s'introdueix en l'an alisi global l'apagat
intel ligent de cel les, estrat egia amb estrets vincles amb ICIC. Mitjan cant el m etode
proposat, s'obtenen millores signi catives pel que fa als enfocaments tradicionals i
propostes pr evies. Els guanys s'obtenen en termes de consum energ etic, capacitat de
la xarxa, i rendiment en el l mit de les cel les
A Stochastic Geometry approach towards Green Communications in 5G
In this dissertation, we investigate two main research directions towards net- work efficiency and green communications in heterogeneous cellular networks (HetNets) as a promising network structure for the fifth generation of mobile systems. In order to analyze the networks, we use a powerful mathematical tool, named stochastic geometry. In our research, first we study the performance of MIMO technology in single-tier and two-tier HetNets. In this work, we apply a more realistic network model in which the correlation between tiers is taken into account. Comparing the obtained results with the commonly used model shows performance enhancement and greater efficiencies in cellular networks. As the second part of our research, we apply two Cell Zooming (CZ) techniques to HetNets. With focus on green communications, we present a K−tier HetNet in which BSs are only powered by energy har- vesting. Despite the uncertain nature of energy arrivals, combining two CZ techniques, namely telescopic and ON/OFF scenarios, enables us to achieve higher network performance in terms of the coverage and blocking probabilities while reducing the total power consumption and increasing the energy and spectral efficiencies
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