59 research outputs found
Final report on the evaluation of RRM/CRRM algorithms
Deliverable public del projecte EVERESTThis deliverable provides a definition and a complete evaluation of the RRM/CRRM algorithms selected in D11 and D15, and evolved and refined on an iterative process. The evaluation will be carried out by means of simulations using the simulators provided at D07, and D14.Preprin
Performance improvement in mobile ad-hoc networks.
The objective of this research is to enhance the network performance under realistic mobile ad-hoc networks environments without modification of the standard. Overview of this research is summarized as follows:
First, a packet-fragmentation technique to improve network throughput under the worst channel
conditions is proposed. While the conventional packet-fragmentation technique research focuses only on random-bit errors, the proposed technique employs both random bit errors and hidden-node collisions. The analytical models based on Markov-chain model shows that the optimal fragmentation technique can effectively reduce the number of retransmissions caused by both collisions from hidden nodes and corrupted packets by random bit errors, and eventually improving throughput in noisy VANETs channels.
As a second contribution, a dynamic service-channel allocation (DSCA) scheme is proposed to maximize the network throughput by dynamically assigning different service channels to the users. The theoretical analysis in this thesis will consider wireless access in the vehicular environment (WAVE) protocol, which is the main characteristic of the vehicular ad-hoc networks standard (the IEEE 802.11p).
To summarize, the main contribution of this research is that two schemes will improve the network throughput significantly without modification of the standard. Therefore, there is no implementation issue to deploy the proposed schemes in real devices.PhDCommittee Chair: Copeland, John; Committee Co-Chair: Chang, Yusun; Committee Member: Ammar, Mostafa; Committee Member: Beyah, Raheem; Committee Member: Owen, Henry; Committee Member: Taylor, Davi
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Dynamic wireless mobile framework for distributed collaborative real-time information generation and control systems
Intelligent Transportation Systems (ITS) have only recently discovered the exciting possibilities in the nomadic and ubiquitous computing space to build a new generation of information systems by allowing the vehicle to act both as a carrier and consumer of wireless (and thus omnipresent) information. Wide deployment of such ITS systems may eventually allow for more dynamic and efficient transportation systems, which can contribute in several ways towards greater economic growth whilst respecting environmental sustainability. A great number of researchers have dedicated considerable time and resources to tackling traffic related issues by utilising the new wireless capabilities enabled by ITS; such initiatives cover a wide range of applications such as safety, knowledge sharing and infotainment. Indicative of the extent of such efforts is the plethora of research projects initiated by many national and multi-national organisations such as the EU Framework Programme for Research and Technological Development. To achieve their goals, proposed solutions from such organisations depend on the development and deployment of intelligent wireless mobile communication systems, where data dissemination issues make the prospect of efficient and effective communication a challenging proposition. Presently, Car-to-Car and Car-to-Infrastructure communications are two distinct avenues that make possible efficient and reliable delivery of messages via direct radio links in traffic areas. In all cases, high quality of communication performance is desirable for a communication system composed mostly of roaming participants; such a system needs to be dynamic, flexible and infrastructure-less. Consequently, Mobile Ad hoc Network (MANET)-based networks are a natural fit to ITS
Efficient Cross Layer Designs for IEEE 802.11 Wireless Networks
Various properties of wireless networks, such as mobility, frequent disconnections and varying
channel conditions, have made it a challenging task to design networking protocols for wireless communications. In this dissertation, we address several problems related to both the routing layer and medium access control (MAC) layer in wireless
networks aiming to enhance the network performance.
First, we study the effect of the channel noise on the network performance. We present mechanisms to compute energy-efficient paths in noisy environments for ad hoc networks by exploiting the IEEE 802.11 fragmentation mechanism. These mechanisms enhance the network performance up to orders of magnitude in terms of energy and throughput. We also enhance the IEEE 802.11 infrastructure networks with a capability to differentiate between different types of unsuccessful transmissions to enhance the network performance.
Second, we study the effects of the physical layer capture phenomena on network performance. We modify the IEEE 802.11 protocol in a way to increase the concurrent transmissions by exploiting the capture phenomena. We analytically study the potential performance enhancement of our mechanism over the original IEEE 802.11. The analysis shows that up to 35% of the IEEE 802.11 blocking decisions are unnecessary. The results are verified by simulation in which we show that our enhanced mechanism can achieve up to 22% more throughput.
Finally, we exploit the spatial reuse of the directional antenna in the IEEE 802.11 standards by developing two novel opportunistic enhancement mechanisms. The first mechanism augments the IEEE 802.11 protocol with additional information that gives a node the flexibility to transmit data while other transmissions are in its vicinity. The second mechanism changes the access routines of the IEEE 802.11 data queue. We show analytically how the IEEE 802.11 protocol using directional antenna is conservative in terms of assessing channel availability, with as much as 60% of unnecessary blocking assessments and up to 90% when we alter the accessing mechanism of the data queue. By simulation, we show an improvement in network throughput of 40% in the case of applying the first mechanism, and up to 60% in the case of applying the second mechanism
Quality aspects of Internet telephony
Internet telephony has had a tremendous impact on how people communicate.
Many now maintain contact using some form of Internet telephony.
Therefore the motivation for this work has been to address the quality aspects
of real-world Internet telephony for both fixed and wireless telecommunication.
The focus has been on the quality aspects of voice communication,
since poor quality leads often to user dissatisfaction. The scope of the work
has been broad in order to address the main factors within IP-based voice
communication.
The first four chapters of this dissertation constitute the background
material. The first chapter outlines where Internet telephony is deployed
today. It also motivates the topics and techniques used in this research.
The second chapter provides the background on Internet telephony including
signalling, speech coding and voice Internetworking. The third chapter
focuses solely on quality measures for packetised voice systems and finally
the fourth chapter is devoted to the history of voice research.
The appendix of this dissertation constitutes the research contributions.
It includes an examination of the access network, focusing on how calls are
multiplexed in wired and wireless systems. Subsequently in the wireless
case, we consider how to handover calls from 802.11 networks to the cellular
infrastructure. We then consider the Internet backbone where most of our
work is devoted to measurements specifically for Internet telephony. The
applications of these measurements have been estimating telephony arrival
processes, measuring call quality, and quantifying the trend in Internet telephony
quality over several years. We also consider the end systems, since
they are responsible for reconstructing a voice stream given loss and delay
constraints. Finally we estimate voice quality using the ITU proposal PESQ
and the packet loss process.
The main contribution of this work is a systematic examination of Internet
telephony. We describe several methods to enable adaptable solutions
for maintaining consistent voice quality. We have also found that relatively
small technical changes can lead to substantial user quality improvements.
A second contribution of this work is a suite of software tools designed to
ascertain voice quality in IP networks. Some of these tools are in use within
commercial systems today
A Mechanism to Improve the Performance of IEEE 802.11 MAC Protocol
Ad hoc networks are gaining popularity due to their less cost and ease deployment. Efficiency of these networks depend on the performance and reliability of the medium access control (MAC) protocol applied in such networks. Since the channel is shared by nodes, an efficient MAC should allow the nodes to access channel without degrading the performance. The performance of IEEE 802.11 gets degraded due to the presence of hidden and exposed terminal. IEEE 802.11 DCF was designed to overcome these problem using a virtual carrier sensing mechanism. Though IEEE 802.11 DCF is able to overcome the hidden and exposed terminal problem, the throughput and channel utilization is lower due to the inability of the hidden and exposed node to either transmit or receive. In this paper we proposed a mechanism that permits the hidden node to transmit and the exposed node to receive. The proposed mechanism also overcome the RTS induced and CTS-induced problem. We performed extensive simulation using NS-2 simulator. It is observed that the proposed scheme outperforms 802.11 DCF in-terms of throughput and packet delivery ratio with marginally increased in control overhead
Comunicações sem-fios de tempo-real para ambientes abertos
Doutoramento em Engenharia InformáticaWireless communication technologies have become widely adopted, appearing
in heterogeneous applications ranging from tracking victims, responders and
equipments in disaster scenarios to machine health monitoring in networked
manufacturing systems. Very often, applications demand a strictly bounded
timing response, which, in distributed systems, is generally highly dependent
on the performance of the underlying communication technology. These
systems are said to have real-time timeliness requirements since data
communication must be conducted within predefined temporal bounds, whose
unfulfillment may compromise the correct behavior of the system and cause
economic losses or endanger human lives.
The potential adoption of wireless technologies for an increasingly broad range
of application scenarios has made the operational requirements more complex
and heterogeneous than before for wired technologies. On par with this trend,
there is an increasing demand for the provision of cost-effective distributed
systems with improved deployment, maintenance and adaptation features.
These systems tend to require operational flexibility, which can only be ensured
if the underlying communication technology provides both time and event
triggered data transmission services while supporting on-line, on-the-fly
parameter modification.
Generally, wireless enabled applications have deployment requirements that
can only be addressed through the use of batteries and/or energy harvesting
mechanisms for power supply. These applications usually have stringent
autonomy requirements and demand a small form factor, which hinders the use
of large batteries. As the communication support may represent a significant
part of the energy requirements of a station, the use of power-hungry
technologies is not adequate. Hence, in such applications, low-range
technologies have been widely adopted. In fact, although low range
technologies provide smaller data rates, they spend just a fraction of the energy
of their higher-power counterparts.
The timeliness requirements of data communications, in general, can be met by
ensuring the availability of the medium for any station initiating a transmission.
In controlled (close) environments this can be guaranteed, as there is a strict
regulation of which stations are installed in the area and for which purpose.
Nevertheless, in open environments, this is hard to control because no a priori
abstract
knowledge is available of which stations and technologies may contend for the
medium at any given instant. Hence, the support of wireless real-time
communications in unmanaged scenarios is a highly challenging task.
Wireless low-power technologies have been the focus of a large research
effort, for example, in the Wireless Sensor Network domain. Although bringing
extended autonomy to battery powered stations, such technologies are known
to be negatively influenced by similar technologies contending for the medium
and, especially, by technologies using higher power transmissions over the
same frequency bands. A frequency band that is becoming increasingly
crowded with competing technologies is the 2.4 GHz Industrial, Scientific and
Medical band, encompassing, for example, Bluetooth and ZigBee, two lowpower
communication standards which are the base of several real-time
protocols. Although these technologies employ mechanisms to improve their
coexistence, they are still vulnerable to transmissions from uncoordinated
stations with similar technologies or to higher power technologies such as Wi-
Fi, which hinders the support of wireless dependable real-time communications
in open environments.
The Wireless Flexible Time-Triggered Protocol (WFTT) is a master/multi-slave
protocol that builds on the flexibility and timeliness provided by the FTT
paradigm and on the deterministic medium capture and maintenance provided
by the bandjacking technique. This dissertation presents the WFTT protocol
and argues that it allows supporting wireless real-time communication services
with high dependability requirements in open environments where multiple
contention-based technologies may dispute the medium access. Besides, it
claims that it is feasible to provide flexible and timely wireless communications
at the same time in open environments. The WFTT protocol was inspired on
the FTT paradigm, from which higher layer services such as, for example,
admission control has been ported. After realizing that bandjacking was an
effective technique to ensure the medium access and maintenance in open
environments crowded with contention-based communication technologies, it
was recognized that the mechanism could be used to devise a wireless
medium access protocol that could bring the features offered by the FTT
paradigm to the wireless domain. The performance of the WFTT protocol is
reported in this dissertation with a description of the implemented devices, the
test-bed and a discussion of the obtained results.As tecnologias de comunicação sem fios tornaram-se amplamente adoptadas,
surgindo em aplicações heterógeneas que vão desde a localização de vítimas,
pessoal médico e equipamentos em cenários de desastre à monitorização da
condição física de máquinas em ambientes industrials. Muito frequentemente,
as aplicações exigem uma resposta limitada no tempo que, geralmente, em
sistemas distribuídos, é substancialmente dependente do desempenho da
tecnologia de comunicação utilizada. Estes sistemas tendem a possuir
requisitos de tempo-real uma vez que a comunicação de dados tem de ser
conduzida dentro de limites temporais pré-definidos que, quando não
cumpridos, podem comprometer o correcto funcionamento do sistema e
resultar em perdas económicas ou colocar em risco vidas humanas.
A potencial adopção de tecnologias sem-fios para um crescente número de
cenários traduz-se num aumento da complexidade e heterogeneidade dos
requisitos operacionais relativamente às tecnologias cabladas. A acompanhar
esta tendência verifica-se uma crescente procura de sistemas distribuídos,
caracterizados quer por uma boa relação custo-eficácia, quer pela simplicidade
de instalação, manutenção e adaptação. Ao mesmo tempo, estes sistemas
tendem a requerer flexibilidade operacional, que apenas pode ser assegurada
se a tecnlogia de comunicação empregue supportar transmissões de dados
dispoletadas quer por eventos (event-triggered), quer por tempo (timetriggered)
e se, ao mesmo tempo, em funcionamento, permitir a alteração dos
parâmetros de comunicação correspondentes.
Frequentemente, as aplicações com comunicações sem fios caracterizam-se
por exigências de instalação que apenas podem ser endereçadas usando
alimentação através de baterias e/ou mecanismos de recolha de energia do
ambiente envolvente. Estas aplicações têm tipicamente requisitos exigentes de
autonomia e de tamanho, impedindo o recurso a baterias de grande dimensão.
Dado que o suporte de comunicações pode representar uma parte significativa
dos requisitos de energia da estação, o uso de tecnologias de comunicação de
elevado consumo não é adequado. Desta forma, nestas aplicações, as
tecnologias de comunicação de curto-alcance tornaram-se amplamente
adoptadas uma vez que, apesar de se caracterizarem por taxas de
transmissão inferiores, consomem apenas uma fracção da energia das
tecnologias de maior alcance.
resumo
Em geral, os requisitos de pontualidade da comunicação de dados podem ser
cumpridos através da garantia da disponibilidade do meio no instante em que
qualquer estação inicie uma transmissão. Em ambientes controlados esta
disponibilidade pode ser garantida, na medida em que existe um controlo de
quais as estações que foram instaladas na área e qual a sua função.
Contrariamente, em ambientes abertos, tal controlo é difícil de garantir uma
vez que não existe conhecimento a priori de que estações ou tecnologias
podem competir pelo meio, tornando o suporte de comunicações de temporeal
um desafio difícil de implementar em cenários com estações de
comunicação não controladas.
As comunicações de baixo consumo têm sido o foco de um esforço de
investigação bastante amplo, por exemplo, no domínio das redes de sensores
sem fios. Embora possam permitir uma maior autonomia a estações baseadas
em baterias, estas tecnologias são reconhecidas como sendo negativamente
influenciadas por tecnologias semelhantes competindo pelo mesmo meio e,
em particular, por tecnologias que utilizem níveis de potência de transmissão
mais elevados em bandas de frequências comuns. De forma cada vez mais
acentuada, a banda industrial, científica e médica (ISM) dos 2.4 GHz tem-se
tornado mais saturada com tecnologias que competem entre si pelo acesso ao
meio tais como, por exemplo, Bluetooth e ZigBee, dois padrões de
comunicação que são a base de vários protocolos de tempo-real. Apesar
destas tecnologias aplicarem mecanismos para melhorar a sua coexistência,
são vulneráveis a transmissões de estações não controladas que usem as
mesmas tecnologias ou que usem tecnologias com níveis de potência de
transmissão mais elevados, impedindo, desta forma, o suporte de
comunicações de tempo-real fiáveis em ambientes abertos.
O protocolo de comunicação sem fios flexível disparado por tempo (WFTT) é
baseado numa arquitectura mestre/múltiplo escravo alavancado na
flexibilidade e pontualidade promovidas pelo paradigma FTT e na captura e
manutenção determinística do meio suportadas pela técnica de bandjacking
(captura de banda). Esta tese apresenta o protocolo WFTT e argumenta que
este permite suportar serviços de comunicação de tempo-real com requisitos
elevados de fiabilidade em ambientes abertos onde várias tecnologias de
comunicação baseadas em contenção disputam o acesso ao meio. Adicionalmente, esta tese reivindica que é possível suportar comunicações
sem-fios simultaneamente flexíveis e pontuais em ambientes abertos. O
protocolo WFTT foi inspirado no paradigma FTT, do qual importa os serviços
de alto nível como, por exemplo, o controlo de admissão. Após a observação
da eficácia da técnica de bandjacking em assegurar o acesso ao meio e a
correspondente manutenção, foi reconhecida a possibilidade de utilização
deste mecanismo para o desenvolvimento de um protocolo de acesso ao meio,
capaz de oferecer as funcionalidades do paradigma FTT em meios de
comunicação sem-fios. O desempenho do protocolo WFTT é reportado nesta
tese com uma descrição dos dispositivos implementados, da bancada de
ensaios desenvolvida e dos resultados obtidos
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Cognitive radio systems in LTE networks
This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University London.The most important fact in the mobile industry at the moment is that demand for wireless services will continue to expand in the coming years. Therefore, it is vital to find more spectrums through cognitive radios for the growing numbers of services and users. However, the spectrum reallocations, enhanced receivers, shared use, or secondary markets-will not likely, by themselves or in combination, meet the real exponential increases in demand for wireless resources. Network operators will also need to re-examine network architecture, and consider integrating the fibre and wireless networks to address this issue. This thesis involves driving fibre deeper into cognitive networks, deploying microcells connected through fibre infrastructure to the backbone LTE networks, and developing the algorithms for diverting calls between the wireless and fibre systems, introducing new coexistence models, and mobility management. This research addresses the network deployment scenarios to a microcell-aided cognitive network, specifically slicing the spectrum spatially and providing reliable coverage at either tier. The goal of this research is to propose new method of decentralized-to-distributed management techniques that overcomes the spectrum unavailability barrier overhead in ongoing and future deployments of multi-tiered cognitive network architectures. Such adjustments will propose new opportunities in cognitive radio-to-fibre systematic investment strategies. Specific contributions include:
1) Identifying the radio access technologies and radio over fibre solution for cognitive network infrastructure to increase the uplink capacity analysis in two-tier networks.
2) Coexistence of macro and microcells are studied to propose a roadmap for optimising the deployment of cognitive microcells inside LTE macrocells in the case of considering radio over fibre access systems.
3) New method for roaming mobiles moving between microcells and macrocell coverage areas is proposed for managing spectrum handover, operator database, authentication and accounting by introducing the channel assigning agent entity. The ultimate goal is to reduce unnecessary channel adaptation
Cluster based jamming and countermeasures for wireless sensor network MAC protocols
A wireless sensor network (WSN) is a collection of wireless nodes, usually with limited computing resources and available energy. The medium access control layer (MAC layer) directly guides the radio hardware and manages access to the radio spectrum in controlled way. A top priority for a WSN MAC protocol is to conserve energy, however tailoring the algorithm for this purpose can create or expose a number of security vulnerabilities. In particular, a regular duty cycle makes a node vulnerable to periodic jamming attacks. This vulnerability limits the use of use of a WSN in applications requiring high levels of security. We present a new WSN MAC protocol, RSMAC (Random Sleep MAC) that is designed to provide resistance to periodic jamming attacks while maintaining elements that are essential to WSN functionality. CPU, memory and especially radio usage are kept to a minimum to conserve energy while maintaining an acceptable level of network performance so that applications can be run transparently on top of the secure MAC layer. We use a coordinated yet pseudo-random duty cycle that is loosely synchronized across the entire network via a distributed algorithm. This thwarts an attacker\u27s ability to predict when nodes will be awake and likewise thwarts energy efficient intelligent jamming attacks by reducing their effectiveness and energy-efficiency to that of non-intelligent attacks. Implementing the random duty cycle requires additional energy usage, but also offers an opportunity to reduce asymmetric energy use and eliminate energy use lost to explicit neighbor discovery. We perform testing of RSMAC against non-secure protocols in a novel simulator that we designed to make prototyping new WSN algorithms efficient, informative and consistent. First we perform tests of the existing SMAC protocol to demonstrate the relevance of the novel simulation for estimating energy usage, data transmission rates, MAC timing and other relevant macro characteristics of wireless sensor networks. Second, we use the simulation to perform detailed testing of RSMAC that demonstrates its performance characteristics with different configurations and its effectiveness in confounding intelligent jammers
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