87 research outputs found
Energy and Spectral Efficient Inter Base Station Relaying in Cellular Systems
This paper considers a classic relay channel which consists of a source, a relay and a destination node and investigates the energy-spectral efficiency tradeoff under three different relay protocols: amplify-and-forward; decode-and-forward; and compress-and-forward. We focus on a cellular scenario where a neighbour base station can potentially act as the relay node to help on the transmissions of the source base station to its assigned mobile device. We employ a realistic power model and introduce a framework to evaluate the performance of different communication schemes for various deployments in a practical macrocell scenario. The results of this paper demonstrate that the proposed framework can be applied flexibly in practical scenarios to identify the pragmatic energy-spectral efficiency tradeoffs and choose the most appropriate scheme optimising the overall performance of inter base station relaying communications
Practical design of optimal wireless metropolitan area networks: model and algorithms for OFDMA networks
A thesis submitted to the University of Bedfordshire, in partial fulfilment of the requirements for the degree of Ph.D.This thesis contributes to the study of the planning and optimisation of wireless metropolitan area networks, in particular to the access network design of OFDMAbased systems, where different parameters like base station position, antenna tilt and azimuth need to be configured during the early stages of the network life. A practical
view for the solution of this problem is presented by means of the development of a
novel design framework and the use of multicriteria optimisation. A further consideration of relaying and cooperative communications in the context of the design
of this kind of networks is done, an area little researched.
With the emergence of new technologies and services, it is very important to accurately identify the factors that affect the design of the wireless access network and define how to take them into account to achieve optimally performing and cost-efficient networks. The new features and flexibility of OFDMA networks seem particularly suited to the provision of different broadband services to metropolitan areas. However, until now, most existing efforts have been focused on the basic access capability networks. This thesis presents a way to deal with the trade-offs generated during the
OFDMA access network design, and presents a service-oriented optimization framework that offers a new perspective for this process with consideration of the technical and economic factors.
The introduction of relay stations in wireless metropolitan area networks will bring numerous advantages such as coverage extension and capacity enhancement due to the
deployment of new cells and the reduction of distance between transmitter and receiver.
However, the network designers will also face new challenges with the use of relay
stations, since they involve a new source of interference and a complicated air interface;
and this need to be carefully evaluated during the network design process.
Contrary to the well known procedure of cellular network design over regular or
hexagonal scenarios, the wireless network planning and optimization process aims to
deal with the non-uniform characteristics of realistic scenarios, where the existence of
hotspots, different channel characteristics for the users, or different service requirements will determine the final design of the wireless network. This thesis is structured in three main blocks covering important gaps in the existing literature in planning (efficient simulation) and optimisation. The formulation and ideas proposed in the former case can still be evaluated over regular scenarios, for the sake of simplicity, while the study of latter case needs to be done over specific scenarios that will be described when
appropriate. Nevertheless, comments and conclusions are extrapolated to more general
cases throughout this work.
After an introduction and a description of the related work, this thesis first focuses
on the study of models and algorithms for classical point-to-multipoint networks on
Chapter 3, where the optimisation framework is proposed. Based on the framework, this
work:
- Identifies the technology-specific physical factors that affect most importantly
the network system level simulation, planning and optimization process.
- It demonstrates how to simplify the problem and translate it into a formal optimization routine with consideration of economic factors.
- It provides the network provider, a detailed and clear description of different
scenarios during the design process so that the most suitable solution can be found. Existing works on this area do not provide such a comprehensive framework.
In Chapter 4:
- The impact of the relay configuration on the network planning process is analysed.
- A new simple and flexible scheme to integrate multihop communications in the
Mobile WiMAX frame structure is proposed and evaluated.
- Efficient capacity calculations that allow intensive system level simulations in a multihop environment are introduced.
In Chapter 5:
- An analysis of the optimisation procedure with the addition of relay stations and the derived higher complexity of the process is done.
- A frequency plan procedure not found in the existing literature is proposed, which combines it with the use of the necessary frame fragmentation of in-band relay communications and cooperative procedures.
- A novel joint two-step process for network planning and optimisation is proposed.
Finally, conclusions and open issues are exposed
Tutorial on LTE/LTE-A Cellular Network Dimensioning Using Iterative Statistical Analysis
LTE is the fastest growing cellular technology and is expected to increase its footprint in the coming years, as well as progress toward LTE-A. The race among operators to deliver the expected quality of experience to their users is tight and demands sophisticated skills in network planning. Radio network dimensioning (RND) is an essential step in the process of network planning and has been used as a fast, but indicative, approximation of radio site count. RND is a prerequisite to the lengthy process of thorough planning. Moreover, results from RND are used by players in the industry to estimate preplanning costs of deploying and running a network; thus, RND is, as well, a key tool in cellular business modelling. In this work, we present a tutorial on radio network dimensioning, focused on LTE/LTE-A, using an iterative approach to find a balanced design that mediates among the three design requirements: coverage, capacity, and quality. This approach uses a statistical link budget analysis methodology, which jointly accounts for small and large scale fading in the channel, as well as loading due to traffic demand, in the interference calculation. A complete RND manual is thus presented, which is of key importance to operators deploying or upgrading LTE/LTE-A networks for two reasons. It is purely analytical, hence it enables fast results, a prime factor in the race undertaken. Moreover, it captures essential variables affecting network dimensions and manages conflicting targets to ensure user quality of experience, another major criterion in the competition. The described approach is compared to the traditional RND using a commercial LTE network planning tool. The outcome further dismisses the traditional RND for LTE due to unjustified increase in number of radio sites and related cost, and motivates further research in developing more effective and novel RND procedures
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
Energy-efficient LTE transmission techniques : introducing Green Radio from resource allocation perspective
Energy consumption has recently become a key issue from both environmental and economic
considerations. A typical mobile phone network in the UK may consume approximately 40-
50 MW, contributing a significant proportion of the total energy consumed by the information
technology industry. With the worldwide growth in the number of mobile subscribers, the
associated carbon emissions and growing energy costs are becoming a significant operational
expense, leading to the need for energy reduction. The Mobile VCE Green Radio Project has
been launched, which targets to achieve 100x energy reduction of the current wireless networks
by 2020. In this thesis, energy-efficient resource allocation strategies have been investigated
taking the LTE system as an example.
Firstly, theoretical analysis of energy-efficient design in cellular environments is provided according
to the Shannon Theory. Based on a two-link scenario the performance of simultaneous
transmission and orthogonal transmission for network power minimization under the specified
rate constraints is investigated. It is found that simultaneous transmission consumes less
power than orthogonal transmission close to the base station, but much more power in the cell-edge
area. Also, simulation results suggest that the energy-efficient switching margins between
these two schemes are dominated by the sum total of their required data rates. New definitions
of power-utility and fairness metrics are further proposed, following by the design of weighted
resource allocation approaches based on efficiency-fairness trade-offs.
Apart from energy-efficient multiple access between different links, the energy used by individual
base stations can also be reduced. For example, deploying sleep modes is an effective
approach to reduce radio base station operational energy consumption. By periodically switching
off the base station transmission, or using fewer transmit antennas, the energy consumption
of base station hardware may decrease. By delivering less control signalling overhead, the
radio frequency energy consumption can also be reduced. Simulation results suggest that up
to 90% energy reduction can be obtained in low traffic conditions by employing time-domain
optimization in each radio frame. The optimum on/off duty cycle is derived, enabling the
energy consumption of the base station to scale with traffic loads. In the spatial-domain, an
antenna selection criterion is proposed, indicating the most energy-efficient antenna configuration
with the knowledge of users’ locations and quality of service requirements. Without
time-domain sleep modes, using fewer transmit antennas could outperform full antenna transmission.
However, with time-domain sleep modes, using all available antennas is generally the
most energy-efficient choice
PV-Powered CoMP-Based Green Cellular Networks with a Standby Grid Supply
This paper proposes a novel framework for PV-powered cellular networks with a
standby grid supply and an essential energy management technique for achieving
envisaged green networks. The proposal considers an emerging cellular network
architecture employing two types of coordinated multipoint (CoMP) transmission
techniques for serving the subscribers. Under the proposed framework, each base
station (BS) is powered by an individual PV solar energy module having an
independent storage device. BSs are also connected to the conventional grid
supply for meeting additional energy demand. We also propose a dynamic inter-BS
solar energy sharing policy through a transmission line for further greening
the proposed network by minimizing the consumption from the grid supply. An
extensive simulation-based study in the downlink of a Long-Term Evolution (LTE)
cellular system is carried out for evaluating the energy efficiency performance
of the proposed framework. System performance is also investigated for
identifying the impact of various system parameters including storage factor,
storage capacity, solar generation capacity, transmission line loss, and
different CoMP techniques.Comment: 14 pages, International Journal of Photoenergy, 6189468, 201
Spectrally and Energy Efficient Radio Resource Management for Multi-Operator Shared Networks
Commercial mobile communication systems are mainly based on licensed frequency spectrum, and the license is very expensive as the spectrum is a sparse wireless resource. Therefore, sharing this wireless resource is an essential requirement not only at the present but also in the future considering trends like connectivity for everybody and everything. In this thesis, we study the sharing of wireless resources with different approaches for realizing fair, efficient, and predictable sharing solutions in a controlled manner.
The efficient use of wireless channel resources is an important target to reduce the costs of network operation and deployment. To achieve this, we need practical scheduling algorithms for wireless resources, out of which several of them will be presented and analyzed in this work. Different optimization frameworks for the spectral efficiency utility are presented, with an individual focus on guaranteeing resource or rate fairness among the operators in a network with shared radio resources. Thus, the presented proposals will help the mobile network operators to overcome the issues of losing network control and traceability of used wireless resources in a shared environment.
Besides this, emerging vertical industries, such as automotive, healthcare, industry 4.0, internet of things (IoT) industries will put a certain burden on the wireless networks asking for guaranteed service level requirement from the mobile network operators. In this regard, this thesis provides the necessary methods addressing these challenges with the help of scheduling methods which are based on the joint optimization of spectral and energy efficiency. Thus, wireless networks will be enabled as a service function in a controlled and scalable way for new emerging markets. Furthermore, the presented solutions t well with the requirements of fifth generation (5G) network slicing
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