250 research outputs found
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
Dimensioning mobile WiMAX in the access and core network : a case study
Existing broadband wireless technologies such as evolving 3G and WiFi have enjoyed widespread adoption but are far from offering the flexibility in deployment and high data rates. Mobile WiMAX, an emerging broadband wireless technology promises to bring a new experience to mobile broadband services by offering users high data rates and efficient network access techniques.
This thesis work provides a technical description of mobile WiMAX and compares its technical capabilities with the existing technologies such as WiFi and 3G. The work continues further on dimensioning mobile WiMAX in the access and core network.
In the access network, we determine the number of base stations required to cover a given metropolitan area, explore their configurations, and perform frequency selection. In the core network we dimension the interfaces, and nodes involved. From the study we will show that WiMAX provides the operator with the antenna configurations options of high capacities, large cell coverage area, and a wide selection of QoS classes. The study will also show that the data density requirements of customers, resulting from the capacity analysis are fulfilled by properly dimensioning the elements in the access and core network
Contribution to resource management in cellular access networks with limited backhaul capacity
La interfaz radio de los sistemas de comunicaciones mĂłviles es normalmente considerada como
la Ășnica limitaciĂłn de capacidad en la red de acceso radio. Sin embargo, a medida que se van
desplegando nuevas y mĂĄs eficientes interfaces radio, y de que el trĂĄfico de datos y multimedia va
en aumento, existe la creciente preocupaciĂłn 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 gestiĂłn de recursos en la interfaz radio y el backhaul. Esto conduce a un nuevo
paradigma donde los recursos del backhaul se consideran no sĂłlo en la etapa de dimensionamiento,
sino que ademĂĄs son incluidos en la problemĂĄtica de gestiĂłn 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 tecnologĂa de transporte, de acuerdo a las
recientes tendencias de la arquitectura de red. En particular, se analiza el impacto que tiene una
soluciĂłn 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 evaluaciĂłn se realiza en el contexto de la
red de acceso radio de UMTS, donde se proporciona una caracterizaciĂłn detallada de la interfaz
Iub. El anĂĄlisis 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 gestiĂłn de recursos. A fin de evaluar los beneficios del marco de
gestiĂłn de recursos propuesto, esta tesis se centra en la evaluaciĂłn del problema de asignaciĂłn de
base, como estrategia para distribuir el trĂĄfico entre las estaciones base en funciĂłn 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 genĂ©rica, mediante la definiciĂłn de un modelo analĂtico
basado en cadenas de Markov. Dicho modelo permite calcular la ganancia de capacidad que puede
alcanzar la estrategia de asignaciĂłn de base propuesta. Posteriormente, el anĂĄlisis de la estrategia
propuesta se extiende considerando tecnologĂas especĂficas de acceso radio. En particular, en el
contexto de redes WCDMA se desarrolla un algoritmo de asignaciĂłn de base basado en simulatedannealing
cuyo objetivo es maximizar una funciĂłn de utilidad que refleja el grado de satisfacciĂłn
de las asignaciones respecto los recursos radio y transporte. Finalmente, esta tesis aborda el diseño
y evaluaciĂłn de un algoritmo de asignaciĂłn de base para los futuros sistemas de banda ancha
basados en OFDMA. En este caso, el problema de asignaciĂłn de base se modela como un problema
de optimizaciĂłn 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 optimizaciĂłn conocido como
Multiple-Choice Multidimensional Knapsack Problem (MMKP). Posteriormente, se desarrolla un
algoritmo de asignaciĂłn de base heurĂstico, el cual es evaluado y comparado con esquemas de
asignaciĂłn basados exclusivamente en criterios radio. El algoritmo concebido se basa en el uso de
los multiplicadores de Lagrange y estå diseñado para aprovechar de manera simultånea el balanceo
de carga en la intefaz radio y el backhaul.Postprint (published version
A Distributed Architecture for Spam Mitigation on 4G Mobile Networks
The 4G of mobile networks is considered a technology-opportunistic and user-centric system combining the economical and technological advantages of
various transmission technologies. Part of its new architecture dubbed as the System Architecture Evolution, 4G mobile networks will implement an evolved packet core. Although this will provide various critical advantages, it will however expose telecom networks to serious IP-based attacks. One often adopted solution by the industry to mitigate such attacks is based on a centralized security architecture. This centralized approach nonetheless, requires large processing resources to handle huge amount of traffic, which results in a significant over dimensioning problem in the centralized nodes causing this approach to fail from achieving its security task.\\
In this thesis, we primarily contribute by highlighting on two Spam flooding attacks, namely RTP VoIP SPIT and SMTP SPAM and demonstrating, through simulations and comparisons, their feasibility and DoS impact on 4G mobile networks and subsequent effects on mobile network operators. We further contribute by proposing a distributed architecture on the mobile architecture that is secure by mitigating those attacks, efficient by solving the over dimensioning problem and cost-effective by utilizing `off the shelf' low-cost hardware in the distributed nodes. Through additional simulation and analysis, we reveal the viability and effectiveness of our approach
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Investigation of efficient resource allocation schemes for WiMAX networks
This thesis was submitted for the degree of Master of Philosophy and was awarded by Brunel University on 9 July 2008.WiMax (Worldwide Interoperability for Microwave Access) is a promising wireless technology with the aim of providing the last mile wireless broadband access designed for both fixed and mobile consumers as an alternative solution to the wired DSL and cable access schemes. The purpose of this research project is to investigate efficient resource allocation algorithms for WiMax. To achieve this goal, we investigate efficient PHY layer Partial Usage of SubCarriers (PUSC) allocation as well as MAC layer piggyback bandwidth request mechanisms. At the PHY layer we proposed improvements on the Uplink and Downlink PUSC subcarrier allocation scheme. For the Uplink PUSC we suggested a method by allocating different frequencies to neighbouring cells in combination with the Integer Frequency Reuse (IFR) and Fractional Frequency Reuse (FFR) in order to reduce interferences and collisions. The simulation results exhibit that collision rates can be reduced to zero for both IFR and FFR patterns with the proposed improvement by assuming that perfect power control is used in the system. In addition, there is no collision at cell edges. The results also show that FFR patterns achieve lower inter-cell interference and higher capacities as compared to the IFR patterns. For the Downlink PUSC we introduced an offset scheme with the purpose of increasing the number of users in the system. At the MAC layer we propose an improvement on the piggyback bandwidth request mechanism by increasing the size of the piggyback bandwidth request in order to reduce the number of bandwidth requests and hence improve the resource utilisation. The simulation results demonstrate that our improved scheme achieves higher throughput, less delay and packet loss rates as compared to the standardised piggyback bandwidth request mechanism
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