676 research outputs found
On teaching always evolving wireless technologies
Teaching on wireless telecommunication networks faces a number of challenges, such as the
fact that contents are dynamic in nature, the resulting framework is complex and
heterogeneous, design principles can largely vary from one system to another, etc. In order to
cope with these challenges, novel and advanced methodologies have to be implemented so
that the expectations placed by students and industry are met. In this context, this paper will
stress the relevance of exploiting the always-evolving wireless technologies to introduce
concepts to students in a non-disruptive way, so that novel concepts associated to newly
introduced technologies can be presented on top of previous concepts associated to
previously existing technologies. In addition, the integration of theoretical contents and
practical experience as key enablers of the learning process will also be stressed.Postprint (published version
MOBILITY SUPPORT ARCHITECTURES FOR NEXT-GENERATION WIRELESS NETWORKS
With the convergence of the wireless networks and the Internet and the booming
demand for multimedia applications, the next-generation (beyond the third generation, or
B3G) wireless systems are expected to be all IP-based and provide real-time and non-real-time
mobile services anywhere and anytime. Powerful and efficient mobility support is
thus the key enabler to fulfil such an attractive vision by supporting various mobility
scenarios. This thesis contributes to this interesting while challenging topic.
After a literature review on mobility support architectures and protocols, the thesis
starts presenting our contributions with a generic multi-layer mobility support framework,
which provides a general approach to meet the challenges of handling comprehensive
mobility issues. The cross-layer design methodology is introduced to coordinate the
protocol layers for optimised system design. Particularly, a flexible and efficient cross-layer
signalling scheme is proposed for interlayer interactions. The proposed generic
framework is then narrowed down with several fundamental building blocks identified to
be focused on as follows.
As widely adopted, we assume that the IP-based access networks are organised into
administrative domains, which are inter-connected through a global IP-based wired core
network. For a mobile user who roams from one domain to another, macro (inter-domain)
mobility management should be in place for global location tracking and effective handoff
support for both real-time and non-real-lime applications. Mobile IP (MIP) and the Session
Initiation Protocol (SIP) are being adopted as the two dominant standard-based macro-mobility
architectures, each of which has mobility entities and messages in its own right.
The work explores the joint optimisations and interactions of MIP and SIP when utilising
the complementary power of both protocols. Two distinctive integrated MIP-SIP
architectures are designed and evaluated, compared with their hybrid alternatives and other
approaches. The overall analytical and simulation results shown significant performance
improvements in terms of cost-efficiency, among other metrics.
Subsequently, for the micro (intra-domain) mobility scenario where a mobile user
moves across IP subnets within a domain, a micro mobility management architecture is
needed to support fast handoffs and constrain signalling messaging loads incurred by intra-domain
movements within the domain. The Hierarchical MIPv6 (HMIPv6) and the Fast
Handovers for MIPv6 (FMIPv6) protocols are selected to fulfil the design requirements.
The work proposes enhancements to these protocols and combines them in an optimised
way. resulting in notably improved performances in contrast to a number of alternative
approaches
Artificial neural networks for location estimation and co-cannel interference suppression in cellular networks
This thesis reports on the application of artificial neural networks to two important problems encountered in cellular communications, namely, location estimation and co-channel interference suppression. The prediction of a mobile location using propagation path loss (signal strength) is a very difficult and complex task. Several techniques have been proposed recently mostly based on linearized, geometrical and maximum likelihood methods. An alternative approach based on artificial neural networks is proposed in this thesis which offers the advantages of increased flexibility to adapt to different environments and high speed parallel processing. Location estimation provides users of cellular telephones with information about their location. Some of the existing location estimation techniques such as those used in GPS satellite navigation systems require non-standard features, either from the cellular phone or the cellular network. However, it is possible to use the existing GSM technology for location estimation by taking advantage of the signals transmitted between the phone and the network. This thesis proposes the application of neural networks to predict the location coordinates from signal strength data. New multi-layered perceptron and radial basis function based neural networks are employed for the prediction of mobile locations using signal strength measurements in a simulated COST-231 metropolitan environment. In addition, initial preliminary results using limited available real signal-strength measurements in a metropolitan environment are also reported comparing the performance of the neural predictors with a conventional linear technique. The results indicate that the neural predictors can be trained to provide a near perfect mapping using signal strength measurements from two or more base stations.
The second application of neural networks addressed in this thesis, is concerned with adaptive equalization, which is known to be an important technique for combating distortion and Inter-Symbol Interference (ISI) in digital communication channels. However, many communication systems are also impaired by what is known as co-channel interference (CCI). Many digital communications systems such as digital cellular radio (DCR) and dual polarized micro-wave radio, for example, employ frequency re-usage and often exhibit performance limitation due to co-channel interference. The degradation in performance due to CCI is more severe than due to ISI. Therefore, simple and effective interference suppression techniques are required to mitigate the interference for a high-quality signal reception. The current work briefly reviews the application of neural network based non-linear adaptive equalizers to the problem of combating co-channel interference, without a priori knowledge of the channel or co-channel orders. A realistic co-channel system is used as a case study to demonstrate the superior equalization capability of the functional-link neural network based Decision Feedback Equalizer (DFE) compared to other conventional linear and neural network based non-linear adaptive equalizers.This project was funded by Solectron (Scotland) Ltd
Paging and Location Management in IEEE 802.16j Multihop Relay Network
IEEE 802.16j is an emerging wireless broadband
networking standard that integrates infrastructure base stations
with multihop relay technology. Based on the idle mode operation
in IEEE 802.16j, we propose a novel location management and
paging scheme. It integrates the paging area-based and the
timer-based location update mechanism. In paging area-based
scheme, an idle mode mobile station updates when it moves to
a new paging area. In timer-based scheme, an idle mode MS
updates when the location update timer expires. In this work, we
formulate the mathematical model to evaluate the performance of
the proposed paging scheme. A new random walk mobility model
that is suitable for modeling in multihop relay network is created.
Optimization of location update timer is also investigated
End to end architecture and mechanisms for mobile and wireless communications in the Internet
Architecture et mécanismes de bout en bout pour les communications mobiles et sans fil dans l'Internet. La gestion performante de la mobilité et l'amélioration des performances des couches basses sont deux enjeux fondamentaux dans le contexte des réseaux sans fil. Cette thèse apporte des solutions originales et innovantes qui visent à répondre à ces deux problématiques empêchant à ce jour d'offrir des possibilités de communication performantes et sans couture aux usagers mobiles accédant à l'Internet via des réseaux d'accès locaux sans fil (WLAN). Ces solutions se distinguent en particulier par l'impact minimum qu'elles ont sur les protocoles standards de l'Internet (niveaux transport et réseau) ou de l'IEEE (niveaux physique et liaison de données). S'inscrivant dans les paradigmes de "bout en bout" et "cross-layer", notre architecture permet d'offrir des solutions efficaces pour la gestion de la mobilité : gestion de la localisation et des handover en particulier. En outre, nous montrons que notre approche permet également d'améliorer l'efficacité des transmissions ainsi que de résoudre efficacement plusieurs syndromes identifiés au sein de 802.11 tels que les anomalies de performance, l'iniquité entre les flux et l'absence de contrôle de débit entre la couche MAC et les couches supérieures. Cette thèse résout ces problèmes en combinant des modèles analytiques, des simulations et de réelles expérimentations. Ces mécanismes adaptatifs ont été développés et intégrés dans une architecture de communication qui fournit des services de communication à haute performance pour réseaux sans fils tels que WIFI et WIMAX. ABSTRACT : Wireless networks, because of the potential pervasive and mobile communication services they offer, are becoming the dominant Internet access networks. However, the legacy Internet protocols, still dominant at that time, have not been designed with mobility and wireless in mind. Therefore, numerous maladjustments and “defaults of impedance” can be observed when combining wireless physical and MAC layers with the traditional upper layers. This thesis proposes several solutions for a pacific coexistence between these communication layers that have been defined and designed independently. Reliable mobility management and Low layer performance enhancements are two main challenging issues in the context of wireless networks. Mobility management (which is mostly based on mobile IP architecture nowadays) aims to continuously assign and control the wireless connections of mobile nodes amongst a space of wireless access networks. Low layer performance enhancements mainly focus on the transmission efficiency such as higher rate, lower loss, interference avoidance. This thesis addresses these two important issues from an original and innovative approach that, conversely to the traditional contributions, entails a minimum impact on the legacy protocols and internet infrastructure. Following the “end to end” and “cross layer” paradigms, we address and offer efficient and light solutions to fast handover, location management and continuous connection support through a space of wireless networks. Moreover, we show that such an approach makes it possible to enhance transmission efficiency and solve efficiently several syndromes that plague the performances of current wireless networks such as performance anomaly, unfairness issues and maladjustment between MAC layer and upper layers. This thesis tackles these issues by combining analytical models, simulations and real experiments. The resulting mechanisms have been developed and integrated into adaptive mobility management communication architecture that delivers high performing communication services to mobile wireless systems, with a focus on WIFI and WIMAX access networks
Femtocell deployment; next generation in cellular systems
The final Bachelor’s Thesis that is shown below has such a final purpose of
giving an overview of the inclusion of the so-called Femtocells (or Home Node
B) in the current cellular systems. The main objective is to give a clear but
simple idea about the concepts of Femtocells, as well as to explain the
benefits and disadvantages of the mass uses of these services both for
consumers and associated companies with this phenomenon.
In this text it is also possible to find a brief review of wireless technologies
throughout the history of telecommunications, as well as an introduction to the
more current wireless technologies, with a special interest in the concept of
cellular systems.
In the last chapter a simple mathematical explanation of the key issue of
interference between Femtocells and macrocellular networks is presented,
with a brief argument about possible solutions
Multi-server collaboration system for disaster relief mission planning
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2001.Includes bibliographical references (p. 123-125).by Chang Kuang.S.M
Mobile Networks
The growth in the use of mobile networks has come mainly with the third generation systems and voice traffic. With the current third generation and the arrival of the 4G, the number of mobile users in the world will exceed the number of landlines users. Audio and video streaming have had a significant increase, parallel to the requirements of bandwidth and quality of service demanded by those applications. Mobile networks require that the applications and protocols that have worked successfully in fixed networks can be used with the same level of quality in mobile scenarios. Until the third generation of mobile networks, the need to ensure reliable handovers was still an important issue. On the eve of a new generation of access networks (4G) and increased connectivity between networks of different characteristics commonly called hybrid (satellite, ad-hoc, sensors, wired, WIMAX, LAN, etc.), it is necessary to transfer mechanisms of mobility to future generations of networks. In order to achieve this, it is essential to carry out a comprehensive evaluation of the performance of current protocols and the diverse topologies to suit the new mobility conditions
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