1,654 research outputs found
Interference-aware adaptive spectrum management for wireless networks using unlicensed frequency bands
The growing demand for ubiquitous broadband network connectivity and continuously
falling prices in hardware operating on the unlicensed bands have put Wi-Fi
technology in a position to lead the way in rapid innovation towards high performance
wireless for the future. The success story of Wi-Fi contributed to the development of
widespread variety of options for unlicensed access (e.g., Bluetooth, Zigbee) and has
even sparked regulatory bodies in several countries to permit access to unlicensed devices
in portions of the spectrum initially licensed to TV services. In this thesis we
present novel spectrum management algorithms for networks employing 802.11 and
TV white spaces broadly aimed at efficient use of spectrum under consideration, lower
contention (interference) and high performance.
One of the target scenarios of this thesis is neighbourhood or citywide wireless
access. For this, we propose the use of IEEE 802.11-based multi-radio wireless mesh
network using omnidirectional antennae. We develop a novel scalable protocol termed
LCAP for efficient and adaptive distributed multi-radio channel allocation. In LCAP,
nodes autonomously learn their channel allocation based on neighbourhood and channel
usage information. This information is obtained via a novel neighbour discovery
protocol, which is effective even when nodes do not share a common channel. Extensive
simulation-based evaluation of LCAP relative to the state-of-the-art Asynchronous
Distributed Colouring (ADC) protocol demonstrates that LCAP is able to achieve its
stated objectives. These objectives include efficient channel utilisation across diverse
traffic patterns, protocol scalability and adaptivity to factors such as external interference.
Motivated by the non-stationary nature of the network scenario and the resulting
difficulty of establishing convergence of LCAP, we consider a deterministic alternative.
This approach employs a novel distributed priority-based mechanism where nodes decide
on their channel allocations based on only local information. Key enabler of this
approach is our neighbour discovery mechanism. We show via simulations that this
mechanism exhibits similar performance to LCAP.
Another application scenario considered in this thesis is broadband access to rural
areas. For such scenarios, we consider the use of long-distance 802.11 mesh networks
and present a novel mechanism to address the channel allocation problem in a
traffic-aware manner. The proposed approach employs a multi-radio architecture using
directional antennae. Under this architecture, we exploit the capability of the 802.11
hardware to use different channel widths and assign widths to links based on their relative
traffic volume such that side-lobe interference is mitigated. We show that this
problem is NP-complete and propose a polynomial time, greedy channel allocation
algorithm that guarantees valid channel allocations for each node. Evaluation of the
proposed algorithm via simulations of real network topologies shows that it consistently
outperforms fixed width allocation due to its ability to adapt to spatio-temporal
variations in traffic demands.
Finally, we consider the use of TV-white-spaces to increase throughput for in-home
wireless networking and relieve the already congested unlicensed bands. To the best
of our knowledge, our work is the first to develop a scalable micro auctioning mechanism
for sharing of TV white space spectrum through a geolocation database. The goal
of our approach is to minimise contention among secondary users, while not interfering
with primary users of TV white space spectrum (TV receivers and microphone
users). It enables interference-free and dynamic sharing of TVWS among home networks
with heterogeneous spectrum demands, while resulting in revenue generation
for database and broadband providers. Using white space availability maps from the
UK, we validate our approach in real rural, urban and dense-urban residential scenarios.
Our results show that our mechanism is able to achieve its stated objectives of
attractiveness to both the database provider and spectrum requesters, scalability and
efficiency for dynamic spectrum distribution in an interference-free manner
Recommended from our members
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
Spectrum handoff management in cognitive hetnet systems overlaid with femtocells
Cognitive radio networks can facilitate seamless mobility to users considering their effective use of the dynamic spectrum access. This is performed by proactive/reactive adaptation of transmission operations in response to the wireless environment changes. One of these operations includes handoff between various wireless domains. The handoff here is not just a registration with a new base station, but it is also a negotiation to get access to the available channels locally in coexistence with the primary users.
This dynamic adaptation between channels, known as spectrum handoff (SH), significantly impacts the time of handoff reconnection, which raises many questions about the functioning of the cognitive radio solution in the next generation of network
systems. Therefore, it is necessary to develop a new method for roaming mobile users, particularly networks that employ small cells such as femtocells in order to reduce the unnecessary channel adaptations. This paper proposes a new entity, namely,
channel assigning agent for managing SH, operator database, and channel access authentication. The goal of this mechanism is to retain the same channel used by a mobile user whenever possible to improve network performance by reducing the unnecessary SHs. The modeling and efficiency of the proposed scheme are validated through simulation results. The proposed solution improves the accessibility of resources and stability ofmobile radio connections that benefits mobile users as well as operators
Channel Allocation in An Overlaid Mesh Network
In spite of recent advancement of Wireless Mesh Technology, a lot of research challenges remained to be solved to extract the full capacity of this modern technology. As 802.11a/b/g standards make available the use of multi radio multi channel in a wireless node, a lot of research activities are going on to efficiently allocate the channel of a Mesh Network to boost its overall performances. In this research, the prospect of dividing the total network area into two non-overlapping channels of a given Mesh Network is investigated and analyzed numerically. It is found that the throughput is doubled as well as the fairness improves considerably if we deploy two channels instead of single channel backbone. An extensive simulation study has been carried out to find the optimum coverage area between two channels. The study shows that at a particular point of allocation, the network gives the optimum response.fi=OpinnÀytetyö kokotekstinÀ PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=LÀrdomsprov tillgÀngligt som fulltext i PDF-format
Recommended from our members
Design of interface selection protocols for multi-homed wireless networks
This thesis was submitted for the degree of Doctor of Philosophy and was awarded by Brunel University on 10 December 2010.The IEEE 802.11/802.16 standards conformant wireless communication stations have multi-homing transmission capability. To achieve greater communication efficiency, multi-homing capable stations use handover mechanism to select appropriate transmission channel according to variations in the channel quality. This thesis presents three internal-linked handover schemes, (1) Interface Selection Protocol (ISP), belonging to Wireless Local Area Network (WLAN)- Worldwide Interoperability for Microwave Access (WiMAX) environment (2) Fast Channel Scanning (FCS) and (3) Traffic Manager (TM), (2) and (3) belonging to WiMAX Environment. The proposed schemes in this thesis use a novel mechanism of providing a reliable communication route. This solution is based on a cross-layer communication framework, where the interface selection module uses various network related parameters from Medium Access Control (MAC) sub-layer/Physical Layer (PHY) across the protocol suite for decision making at the Network layer. The proposed solutions are highly responsive when compared with existing multi-homed schemes; responsiveness is one of the key factors in the design of such protocols. Selected route under these schemes is based on the most up to date link-layer information. Therefore, such a route is not only reliable in terms of route optimization but it also fulfils the application demands in terms of throughput and delay. Design of ISP protocol use probing frames during the route discovery process. The 802.11 mandates the use of different rates for data transmission frames. The ISP-metric can be incorporated into various routing aspects and its applicability is determined by the possibility of provision of MAC dependent parameters that are used to determine the best path metric values. In many cases, higher device density, interference and mobility cause variable medium access delays. It causes creation of âunreachable zonesâ, where destination is marked as unreachable. However, by use of the best path metric, the destination has been made reachable, anytime and anywhere, because of the intelligent use of the probing frames and interface selection algorithm implemented. The IEEE 802.16e introduces several MAC level queues for different access categories, maintaining service requirement within these queues; which imply that frames from a higher priority queue, i.e. video frames, are serviced more frequently than those belonging to lower priority queues. Such an enhancement at the MAC sub-layer introduces uneven queuing delays. Conventional routing protocols are unaware of such MAC specific constraints and as a result, these factors are not considered which result in channel performance degradation. To meet such challenges, the thesis presents FCS and TM schemes for WiMAX. For FCS, Its solution is to improve the mobile WiMAX handover and address the scanning latency. Since minimum scanning time is the most important issue in the handover process. This handover scheme aims to utilize the channel efficiently and apply such a procedure to reduce the time it takes to scan the neighboring access stations. TM uses MAC and physical layer (PHY) specific information in the interface metric and maintains a separate path to destination by applying an alternative interface operation. Simulation tests and comparisons with existing multi-homed protocols and handover schemes demonstrate the effectiveness of incorporating the medium dependent parameters. Moreover, show that suggested schemes, have shown better performance in terms of end-to-end delay and throughput, with efficiency up to 40% in specific test scenarios
Secure Communication in Disaster Scenarios
WĂ€hrend Naturkatastrophen oder terroristischer AnschlĂ€ge ist die bestehende Kommunikationsinfrastruktur hĂ€ufig ĂŒberlastet oder fĂ€llt komplett aus. In diesen Situationen können mobile GerĂ€te mithilfe von drahtloser ad-hoc- und unterbrechungstoleranter Vernetzung miteinander verbunden werden, um ein Notfall-Kommunikationssystem fĂŒr Zivilisten und Rettungsdienste einzurichten. Falls verfĂŒgbar, kann eine Verbindung zu Cloud-Diensten im Internet eine wertvolle Hilfe im Krisen- und Katastrophenmanagement sein.
Solche Kommunikationssysteme bergen jedoch ernsthafte Sicherheitsrisiken, da Angreifer versuchen könnten, vertrauliche Daten zu stehlen, gefĂ€lschte Benachrichtigungen von Notfalldiensten einzuspeisen oder Denial-of-Service (DoS) Angriffe durchzufĂŒhren. Diese Dissertation schlĂ€gt neue AnsĂ€tze zur Kommunikation in Notfallnetzen von mobilen GerĂ€ten vor, die von der Kommunikation zwischen MobilfunkgerĂ€ten bis zu Cloud-Diensten auf Servern im Internet reichen. Durch die Nutzung dieser AnsĂ€tze werden die Sicherheit der GerĂ€te-zu-GerĂ€te-Kommunikation, die Sicherheit von Notfall-Apps auf mobilen GerĂ€ten und die Sicherheit von Server-Systemen fĂŒr Cloud-Dienste verbessert
Mobile Ad-Hoc Networks
Being infrastructure-less and without central administration control, wireless ad-hoc networking is playing a more and more important role in extending the coverage of traditional wireless infrastructure (cellular networks, wireless LAN, etc). This book includes state-of-the-art techniques and solutions for wireless ad-hoc networks. It focuses on the following topics in ad-hoc networks: quality-of-service and video communication, routing protocol and cross-layer design. A few interesting problems about security and delay-tolerant networks are also discussed. This book is targeted to provide network engineers and researchers with design guidelines for large scale wireless ad hoc networks
- âŠ