36 research outputs found
Downlink Cellular Interference Alignment
Cellular networks have been notoriously interference-limited systems in dense urban areas, where base stations are deployed in close proximity to one-another. Recently, a signal processing method called Interference Alignment has emerged, making use of the increasing signal dimensions available in the system through multiple-input multiple output (MIMO) and Orthogonal Frequency Division Multiplexing (OFDM) technologies. In this report, we review the state of the art of interference alignment since its foundation, and we detail algorithms and baseline comparisons to make when applying interference alignment schemes to downlink cellular networks. We also propose a number of research directions of interest which are not yet answered in the current literature.Les rĂ©seaux cellulaires ont Ă©tĂ© l'exemple typique de rĂ©seaux dont les performances sont limitĂ©s par les interfĂ©rences, particuliĂšrement dans les rĂ©gions urbaines. RĂ©cemment, une nouvelle technique de traitement du signal appelĂ©e "alignement d'interfĂ©rences" a Ă©tĂ© dĂ©velopĂ©e, et permet d'utiliser les dimensions du signal reçu Ă travers les technologies MIMO (multiple input multiple output) et OFDM (orthogonal frequency division multiplexing) pour annuler tout ou partie de l'interfĂ©rence reçue par les mobiles. Dans ce rapport, nous Ă©valuons la littĂ©rature liĂ©e Ă l'alignement d'interfĂ©rence et nous dĂ©taillons les algorithmes existants et leur application aux rĂ©seaux cellulaires en voie descendante. Nous proposons ensuite un ensemble de directions de recherche d'intĂ©rĂȘt par rapport Ă l'Ă©tat de l'art actuel
Review on Radio Resource Allocation Optimization in LTE/LTE-Advanced using Game Theory
Recently, there has been a growing trend toward ap-plying game theory (GT) to various engineering fields in order to solve optimization problems with different competing entities/con-tributors/players. Researches in the fourth generation (4G) wireless network field also exploited this advanced theory to overcome long term evolution (LTE) challenges such as resource allocation, which is one of the most important research topics. In fact, an efficient de-sign of resource allocation schemes is the key to higher performance. However, the standard does not specify the optimization approach to execute the radio resource management and therefore it was left open for studies. This paper presents a survey of the existing game theory based solution for 4G-LTE radio resource allocation problem and its optimization
D13.1 Fundamental issues on energy- and bandwidth-efficient communications and networking
Deliverable D13.1 del projecte europeu NEWCOM#The report presents the current status in the research area of energy- and bandwidth-efficient communications and networking and highlights the fundamental issues still open for further investigation. Furthermore, the report presents the Joint Research Activities (JRAs) which will be performed within WP1.3. For each activity there is the description, the identification of the adherence with the identified fundamental open issues, a presentation of the initial results, and a roadmap for the planned joint research work in each topic.Preprin
D13.2 Techniques and performance analysis on energy- and bandwidth-efficient communications and networking
Deliverable D13.2 del projecte europeu NEWCOM#The report presents the status of the research work of the
various Joint Research Activities (JRA) in WP1.3 and the results
that were developed up to the second year of the project. For
each activity there is a description, an illustration of the
adherence to and relevance with the identified fundamental
open issues, a short presentation of the main results, and a
roadmap for the future joint research. In the Annex, for each
JRA, the main technical details on specific scientific activities
are described in detail.Peer ReviewedPostprint (published version
Enhancing physical layer security in wireless networks with cooperative approaches
Motivated by recent developments in wireless communication, this thesis aims to
characterize the secrecy performance in several types of typical wireless networks.
Advanced techniques are designed and evaluated to enhance physical layer security in
these networks with realistic assumptions, such as signal propagation loss, random node
distribution and non-instantaneous channel state information (CSI).
The first part of the thesis investigates secret communication through relay-assisted
cognitive interference channel. The primary and secondary base stations (PBS and SBS)
communicate with the primary and secondary receivers (PR and SR) respectively in the
presence of multiple eavesdroppers. The SBS is allowed to transmit simultaneously with
the PBS over the same spectrum instead of waiting for an idle channel. To improve
security, cognitive relays transmit cooperative jamming (CJ) signals to create additional
interferences in the direction of the eavesdroppers. Two CJ schemes are proposed to
improve the secrecy rate of cognitive interference channels depending on the structure of
cooperative relays. In the scheme where the multiple-antenna relay transmits weighted
jamming signals, the combined approach of CJ and beamforming is investigated. In
the scheme with multiple relays transmitting weighted jamming signals, the combined
approach of CJ and relay selection is analyzed. Numerical results show that both these
two schemes are effective in improving physical layer security of cognitive interference
channel.
In the second part, the focus is shifted to physical layer security in a random wireless
network where both legitimate and eavesdropping nodes are randomly distributed. Three
scenarios are analyzed to investigate the impact of various factors on security. In
scenario one, the basic scheme is studied without a protected zone and interference. The
probability distribution function (PDF) of channel gain with both fading and path loss
has been derived and further applied to derive secrecy connectivity and ergodic secrecy
capacity. In the second scenario, we studied using a protected zone surrounding the source
node to enhance security where interference is absent. Both the cases that eavesdroppers
are aware and unaware of the protected zone boundary are investigated. Based on the
above scenarios, further deployment of the protected zones at legitimate receivers is
designed to convert detrimental interference into a beneficial factor. Numerical results
are investigated to check the reliability of the PDF for reciprocal of channel gain and to
analyze the impact of protected zones on secrecy performance.
In the third part, physical layer security in the downlink transmission of cellular network
is studied. To model the repulsive property of the cellular network planning, we assume
that the base stations (BSs) follow the MatÂŽern hard-core point process (HCPP), while
the eavesdroppers are deployed as an independent Poisson point process (PPP). The
distribution function of the distances from a typical point to the nodes of the HCPP is
derived. The noise-limited and interference-limited cellular networks are investigated
by applying the fractional frequency reuse (FFR) in the system. For the noise-limited
network, we derive the secrecy outage probability with two different strategies, i.e. the
best BS serve and the nearest BS serve, by analyzing the statistics of channel gains. For
the interference-limited network with the nearest BS serve, two transmission schemes are
analyzed, i.e., transmission with and without the FFR. Numerical results reveal that both
the schemes of transmitting with the best BS and the application of the FFR are beneficial
for physical layer security in the downlink cellular networks, while the improvement du
Recommended from our members
Hybrid Radio Resource Management with Limited Channel Feedback Information in Relay enhanced OFDMA Networks
In orthogonal frequency division multiple access based mobile networks buffer aided nontransparent in-band half duplex decode-and-forward relay nodes aim to improve coverage and capacity under fairness considerations. The existing centralized radio resource management and inter-cell interference coordination schemes can achieve this goals, although at the cost of a heavy signalling overhead. This cost is a critical issue, particularly for the frequency division duplex downlink transmission. On the other hand, the fully decentralized schemes often focus on different types of frequency reuse schemes with smaller amount of necessary feedback. Here, it is often overseen that in a practical deployment, the backhaul link quality is the bottleneck of the two-hop transmission, and the backhaul link is often modelled way too optimistically. Moreover, it is necessary to allocate radio resources to single hop mobile stations as well, which further limits the possible data rates of the relay-attached users. The research presented in this Thesis aims to improve the backhaul link quality in relay-assisted cellular networks under full consideration of practical constraints. In order to minimize the required channel feedback overhead this work proposes a hybrid radio resource management scheme consisting of three adapted procedures. The hybrid radio resource management scheme includes an adapted decentralized cell selection metric which improves the possibility to gain from the relays in the system for each user. A macro cell-centralized synchronous procedure is proposed, which is responsible to allocate the radio resources in each transmission time interval. Furthermore, an asynchronous network-centralized subband power allocation scheme with very limited feedback is proposed to maximize the wireless backhaul link quality with no losses for single-hop Mobile Station (MS)s. Comprehensive system level simulation results show stable fairness and improved throughput of the proposed hybrid radio resource management scheme. In addition possible energy savings for the shared channel are presented
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
Efficient resource allocation algorithm for dense femtocell networks
La couverture d'intĂ©rieur pauvre et la basse capacitĂ© d'utilisateur reprĂ©sentent deux dĂ©fis importants pour les opĂ©rateurs cellulaires. Plusieurs solutions (telles que les antennes distribuĂ©es) ont Ă©tĂ© proposĂ©es pour rĂ©soudre ces problĂšmes. Cependant, aucune de ces solutions ne fournit le niveau dĂ©sirĂ© de l'Ă©volutivitĂ© et elles manquent l'aspect pratique. Pour ces raisons, une solution attrayante caractĂ©risĂ©e par sa faible puissance et son prix faible connue sous le nom de femto-cellule a Ă©tĂ© introduite pour offrir une meilleure capacitĂ© et couverture d'utilisateur. MalgrĂ© tous les avantages provoquĂ©s par l'intĂ©gration de cette nouvelle technologie femto-cellule, plusieurs nouveaux dĂ©fis ont Ă©mergĂ©. Ces dĂ©fis sont principalement prĂ©sentĂ©s dans deux genres d'interfĂ©rences ; connu comme interfĂ©rence cross-tier et interfĂ©rence co-tier. Tandis que l'impact d'interfĂ©rence cross-tier (provoquĂ© en partageant le spectre de frĂ©quence) peut ĂȘtre rĂ©duit en mettant en application des algorithmes efficaces de rĂ©utilisation de frĂ©quence, l'interfĂ©rence co-tier continue Ă prĂ©senter un dĂ©fi difficile pour les opĂ©rateurs et les chercheurs dans le domaine de rĂ©seaux cellulaires. Le dĂ©ploiement non planifiĂ© et mal organisĂ© des stations de base femto-cellule a comme consĂ©quence une rĂ©duction radicale de la capacitĂ© d'utilisateur qui peut mener Ă une dĂ©connexion des utilisateurs. L'impact de l'interfĂ©rence co-tier devient plus provocant dans un dĂ©ploiement dense des femto-cellule oĂč les utilisateurs demandent des services en temps rĂ©el (par exemple, taux de donnĂ©es constant). Afin de rĂ©duire l'interfĂ©rence co-tier, plusieurs solutions ont Ă©tĂ© proposĂ©es dans la littĂ©rature comprenant des algorithmes de contrĂŽle de puissance, des techniques de dĂ©tection avancĂ©es et des schĂ©mas d'allocation de ressources intelligentes. Dans ce projet, nous proposons une stratĂ©gie intelligente d'attribution des frĂ©quences avec une stratĂ©gie avancĂ©e d'association de station de base femto-cellule pour les rĂ©seaux femto-cellule basĂ©s sur LTE. L'objectif des deux stratĂ©gies proposĂ©es est d'attĂ©nuer l'interfĂ©rence co-tier et de rĂ©duire la probabilitĂ© de panne des utilisateurs en augmentant le nombre d'utilisateurs actifs par station de base femto-cellule. Nous montrons par simulations l'efficacitĂ© de notre solution proposĂ©e.\ud
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MOTS-CLĂS DE LâAUTEUR : femtocell base station, interference management, resource block assignment, base station assignment, outage probability