378 research outputs found
Dish networks: Protocols, strategies, analysis, and implementation
Ph.DDOCTOR OF PHILOSOPH
Analysis and Ad-hoc Networking Solutions for Cooperative Relaying Systems
Users of mobile networks are increasingly demanding higher data rates from
their service providers. To cater to this demand, various signal processing
and networking algorithms have been proposed. Amongst them the multiple
input multiple output (MIMO) scheme of wireless communications is one of
the most promising options. However, due to certain physical restrictions,
e.g., size, it is not possible for many devices to have multiple antennas
on them. Also, most of the devices currently in use are single-antenna
devices. Such devices can make use of the MIMO scheme by employing
cooperative MIMO methods. This involves nearby nodes utilizing the antennas
of each other to form virtual antenna arrays (VAAs). Nodes with limited
communication ranges can further employ multi-hopping to be able to
communicate with far away nodes. However, an ad-hoc communications scheme
with cooperative MIMO multi-hopping can be challenging to implement because
of its de-centralized nature and lack of a centralized controling entity
such as a base-station. This thesis looks at methods to alleviate the
problems faced by such networks.In the first part of this thesis, we look,
analytically, at the relaying scheme under consideration and derive closed
form expressions for certain performance measures (signal to noise ratio
(SNR), symbol error rate (SER), bit error rate (BER), and capacity) for the
co-located and cooperative multiple antenna schemes in different relaying
configurations (amplify-and-forward and decode-and-forward) and different
antenna configurations (single input single output (SISO), single input
multiple output (SIMO) and MIMO). These expressions show the importance of
reducing the number of hops in multi-hop communications to achieve a better
performance. We can also see the impact of different antenna configurations
and different transmit powers on the number of hops through these
simplified expressions.We also look at the impact of synchronization errors
on the cooperative MIMO communications scheme and derive a lower bound of
the SINR and an expression for the BER in the high SNR regime. These
expressions can help the network designers to ensure that the quality of
service (QoS) is satisfied even in the worst-case scenarios. In the second
part of the thesis we present some algorithms developed by us to help the
set-up and functioning of cluster-based ad-hoc networks that employ
cooperative relaying. We present a clustering algorithm that takes into
account the battery status of nodes in order to ensure a longer network
life-time. We also present a routing mechanism that is tailored for use in
cooperative MIMO multi-hop relaying. The benefits of both schemes are shown
through simulations.A method to handle data in ad-hoc networks using
distributed hash tables (DHTs) is also presented. Moreover, we also present
a physical layer security mechanism for multi-hop relaying. We also analyze
the physical layer security mechanism for the cooperative MIMO scheme. This
analysis shows that the cooperative MIMO scheme is more beneficial than
co-located MIMO in terms of the information theoretic limits of the
physical layer security.Nutzer mobiler Netzwerke fordern zunehmend höhere Datenraten von ihren
Dienstleistern. Um diesem Bedarf gerecht zu werden, wurden verschiedene
Signalverarbeitungsalgorithmen entwickelt. Dabei ist das "Multiple input
multiple output" (MIMO)-Verfahren für die drahtlose Kommunikation eine der
vielversprechendsten Techniken. Jedoch ist aufgrund bestimmter
physikalischer Beschränkungen, wie zum Beispiel die Baugröße, die
Verwendung von mehreren Antennen für viele Endgeräte nicht möglich. Dennoch
können solche Ein-Antennen-Geräte durch den Einsatz kooperativer
MIMO-Verfahren von den Vorteilen des MIMO-Prinzips profitieren.
Dabei schließen sich naheliegende Knoten zusammen um ein sogenanntes
virtuelles Antennen-Array zu bilden. Weiterhin können Knoten mit
beschränktem Kommunikationsbereich durch mehrere Hops mit weiter
entfernten Knoten kommunizieren. Allerdings stellt der Aufbau eines solchen
Ad-hoc-Netzwerks mit kooperativen MIMO-Fähigkeiten aufgrund der dezentralen
Natur und das Fehlen einer zentral-steuernden Einheit, wie einer
Basisstation, eine große Herausforderung dar. Diese Arbeit befasst sich mit
den Problemstellungen dieser Netzwerke und bietet verschiedene
Lösungsansätze.Im ersten Teil dieser Arbeit werden analytisch in
sich geschlossene Ausdrücke für ein kooperatives
Relaying-System bezüglicher verschiedener Metriken, wie das
Signal-Rausch-Verhältnis, die Symbolfehlerrate, die Bitfehlerrate und die
Kapazität, hergeleitet. Dabei werden die "Amplify-and forward" und
"Decode-and-forward" Relaying-Protokolle, sowie unterschiedliche
Mehrantennen-Konfigurationen, wie "Single input single output" (SISO),
"Single input multiple output" (SIMO) und MIMO betrachtet. Diese Ausdrücke
zeigen die Bedeutung der Reduzierung der Hop-Anzahl in Mehr-Hop-Systemen,
um eine höhere Leistung zu erzielen. Zudem werden die Auswirkungen
verschiedener Antennen-Konfigurationen und Sendeleistungen auf die Anzahl
der Hops analysiert. Weiterhin wird der Einfluss von
Synchronisationsfehlern auf das kooperative MIMO-Verfahren herausgestellt
und daraus eine untere Grenze für das
Signal-zu-Interferenz-und-Rausch-Verhältnis, sowie ein Ausdruck für die
Bitfehlerrate bei hohem Signal-Rausch-Verhältnis entwickelt.
Diese Zusammenhänge sollen Netzwerk-Designern helfen die Qualität des
Services auch in den Worst-Case-Szenarien sicherzustellen.
Im zweiten Teil der Arbeit werden einige innovative
Algorithmen vorgestellt, die die Einrichtung und die Funktionsweise von
Cluster-basierten Ad-hoc-Netzwerken, die kooperative Relays verwenden,
erleichtern und verbessern. Darunter befinden sich ein
Clustering-Algorithmus, der den Batteriestatus der Knoten berücksichtigt,
um eine längere Lebensdauer des Netzwerks zu gewährleisten und ein
Routing-Mechanismus, der auf den Einsatz in kooperativen MIMO
Mehr-Hop-Systemen zugeschnitten ist. Die Vorteile beider Algorithmen werden
durch Simulationen veranschaulicht.
Eine Methode, die Daten in Ad-hoc-Netzwerken mit verteilten Hash-Tabellen
behandelt wird ebenfalls vorgestellt. Darüber hinaus wird auch
ein Sicherheitsmechanismus für die physikalische Schicht in
Multi-Hop-Systemen und kooperativen MIMO-Systemen präsentiert. Eine Analyse
zeigt, dass das kooperative MIMO-Verfahren deutliche Vorteile gegenüber dem
konventionellen MIMO-Verfahren hinsichtlich der informationstheoretischen
Grenzen der Sicherheit auf der physikalischen Schicht aufweist
Cooperative communications in wireless networks.
Zhang Jun.Thesis (M.Phil.)--Chinese University of Hong Kong, 2006.Includes bibliographical references (leaves 82-92).Abstracts in English and Chinese.Chapter 1 --- Introduction --- p.1Chapter 1.1 --- Multipath Fading Channels --- p.1Chapter 1.2 --- Diversity --- p.3Chapter 1.3 --- Outline of the Thesis --- p.6Chapter 2 --- Background and Related Work --- p.8Chapter 2.1 --- Cooperative Diversity --- p.8Chapter 2.1.1 --- User Cooperation --- p.9Chapter 2.1.2 --- Cooperative Diversity --- p.10Chapter 2.1.3 --- Coded Cooperation --- p.12Chapter 2.2 --- Information-Theoretic Studies --- p.13Chapter 2.3 --- Multihop Cellular Networks --- p.15Chapter 2.3.1 --- MCN: Multihop Cellular Network --- p.15Chapter 2.3.2 --- iCAR: Integrated Cellular and Ad Hoc Relaying Systems --- p.17Chapter 2.3.3 --- UCAN: Unified Cellular and Ad Hoc Network Architecture --- p.17Chapter 2.4 --- Wireless Ad Hoc Networks --- p.18Chapter 2.5 --- Space-Time Processing --- p.20Chapter 3 --- Single-Source Multiple-Relay Cooperation System --- p.23Chapter 3.1 --- System Model --- p.23Chapter 3.2 --- Fixed Decode-and-Forward Cooperation System --- p.26Chapter 3.2.1 --- BER for system with errors at the relay --- p.28Chapter 3.2.2 --- General BER formula for single-source nr-relay cooperation system --- p.30Chapter 3.2.3 --- Discussion of Interuser Channels --- p.31Chapter 3.3 --- Relay Selection Protocol --- p.33Chapter 3.3.1 --- Transmission Protocol --- p.34Chapter 3.3.2 --- BER Analysis for Relay Selection Protocol --- p.34Chapter 4 --- Multiple-Source Multiple-Relay Cooperation System --- p.40Chapter 4.1 --- Transmission Protocol --- p.41Chapter 4.2 --- Fixed Cooperative Coding System --- p.43Chapter 4.2.1 --- Performance Analysis --- p.43Chapter 4.2.2 --- Numerical Results and Discussion --- p.48Chapter 4.3 --- Adaptive Cooperative Coding --- p.49Chapter 4.3.1 --- Performance Analysis of Adaptive Cooperative Coding System --- p.50Chapter 4.3.2 --- Analysis of p2(2) --- p.52Chapter 4.3.3 --- Numerical Results and Discussion --- p.53Chapter 5 --- Cooperative Multihop Transmission --- p.56Chapter 5.1 --- System Model --- p.57Chapter 5.1.1 --- Conventional Multihop Transmission --- p.58Chapter 5.1.2 --- Cooperative Multihop Transmission --- p.59Chapter 5.2 --- Performance Evaluation --- p.59Chapter 5.2.1 --- Conventional Multihop Transmission --- p.60Chapter 5.2.2 --- Cooperative Multihop Transmission --- p.60Chapter 5.2.3 --- Numerical Results --- p.64Chapter 5.3 --- Discussion --- p.64Chapter 5.3.1 --- Cooperative Range --- p.64Chapter 5.3.2 --- Relay Node Distribution --- p.67Chapter 5.3.3 --- Power Allocation and Distance Distribution (2-hop Case) --- p.68Chapter 5.4 --- Cooperation in General Wireless Ad Hoc Networks --- p.70Chapter 5.4.1 --- Cooperation Using Linear Network Codes --- p.71Chapter 5.4.2 --- Single-Source Single-Destination Systems --- p.74Chapter 5.4.3 --- Multiple-Source Single-Destination Systems --- p.75Chapter 6 --- Conclusion --- p.80Bibliography --- p.82Chapter A --- Proof of Proposition 1-4 --- p.93Chapter A.1 --- Proof of Proposition 1 --- p.93Chapter A.2 --- Proof of Proposition 2 --- p.95Chapter A.3 --- Proof of Proposition 3 --- p.95Chapter A.4 --- Proof of Proposition 4 --- p.9
A Gossip-based optimistic replication for efficient delay-sensitive streaming using an interactive middleware support system
While sharing resources the efficiency is substantially degraded as a result
of the scarceness of availability of the requested resources in a multiclient
support manner. These resources are often aggravated by many factors like the
temporal constraints for availability or node flooding by the requested
replicated file chunks. Thus replicated file chunks should be efficiently
disseminated in order to enable resource availability on-demand by the mobile
users. This work considers a cross layered middleware support system for
efficient delay-sensitive streaming by using each device's connectivity and
social interactions in a cross layered manner. The collaborative streaming is
achieved through the epidemically replicated file chunk policy which uses a
transition-based approach of a chained model of an infectious disease with
susceptible, infected, recovered and death states. The Gossip-based stateful
model enforces the mobile nodes whether to host a file chunk or not or, when no
longer a chunk is needed, to purge it. The proposed model is thoroughly
evaluated through experimental simulation taking measures for the effective
throughput Eff as a function of the packet loss parameter in contrast with the
effectiveness of the replication Gossip-based policy.Comment: IEEE Systems Journal 201
Performance analysis for network coding using ant colony routing
This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The aim of this thesis is to conduct performance investigation of a combined system of Network Coding (NC) technique with Ant-Colony (ACO) routing protocol. This research analyses the impact of several workload characteristics, on system performance.
Network coding is a significant key development of information transmission and processing. Network coding enhances the performance of multicast by employing encoding operations at intermediate nodes. Two steps should realize while using network coding in multicast communication: determining appropriate transmission paths from source to multi-receivers and using the suitable coding scheme.
Intermediate nodes would combine several packets and relay them as a single packet. Although network coding can make a network achieve the maximum multicast rate, it always brings additional overheads. It is necessary to minimize unneeded overhead by using an optimization technique.
On other hand, Ant Colony Optimization can be transformed into useful technique that seeks imitate the ant’s behaviour in finding the shortest path to its destination using quantities of pheromone that is left by former ants as guidance, so by using the same concept of the communication network environment, shorter paths can be formulated.
The simulation results show that the resultant system considerably improves the performance of the network, by combining Ant Colony Optimization with network coding. 25% improvement in the bandwidth consumption can be achieved in comparison with conventional routing protocols. Additionally simulation results indicate that the proposed algorithm can decrease the computation time of system by a factor of 20%
Cross-layer Peer-to-Peer Computing in Mobile Ad Hoc Networks
The future information society is expected to rely heavily on wireless technology. Mobile access to the Internet is steadily gaining ground, and could easily end up exceeding the number of connections from the fixed infrastructure. Picking just one example, ad hoc networking is a new paradigm of wireless communication for mobile devices. Initially, ad hoc networking targeted at military applications as well as stretching the access to the Internet beyond one wireless hop. As a matter of fact, it is now expected to be employed in a variety of civilian applications. For this reason, the issue of how to make these systems working efficiently keeps the ad hoc research community active on topics ranging from wireless technologies to networking and application systems.
In contrast to traditional wire-line and wireless networks, ad hoc networks are expected to operate in an environment in which some or all the nodes are mobile, and might suddenly disappear from, or show up in, the network. The lack of any centralized point, leads to the necessity of distributing application services and responsibilities to all available nodes in the network, making the task of developing and deploying application a hard task, and highlighting the necessity of suitable middleware platforms.
This thesis studies the properties and performance of peer-to-peer overlay management algorithms, employing them as communication layers in data sharing oriented middleware platforms. The work primarily develops from the observation that efficient overlays have to be aware of the physical network topology, in order to reduce (or avoid) negative impacts of application layer traffic on the network functioning. We argue that cross-layer cooperation between overlay management algorithms and the underlying layer-3 status and protocols, represents a viable alternative to engineer effective decentralized communication layers, or eventually re-engineer existing ones to foster the interconnection of ad hoc networks with Internet infrastructures. The presented approach is twofold. Firstly, we present an innovative network stack component that supports, at an OS level, the realization of cross-layer protocol interactions. Secondly, we exploit cross-layering to optimize overlay management algorithms in unstructured, structured, and publish/subscribe platforms
Routing Security Issues in Wireless Sensor Networks: Attacks and Defenses
Wireless Sensor Networks (WSNs) are rapidly emerging as an important new area
in wireless and mobile computing research. Applications of WSNs are numerous
and growing, and range from indoor deployment scenarios in the home and office
to outdoor deployment scenarios in adversary's territory in a tactical
battleground (Akyildiz et al., 2002). For military environment, dispersal of
WSNs into an adversary's territory enables the detection and tracking of enemy
soldiers and vehicles. For home/office environments, indoor sensor networks
offer the ability to monitor the health of the elderly and to detect intruders
via a wireless home security system. In each of these scenarios, lives and
livelihoods may depend on the timeliness and correctness of the sensor data
obtained from dispersed sensor nodes. As a result, such WSNs must be secured to
prevent an intruder from obstructing the delivery of correct sensor data and
from forging sensor data. To address the latter problem, end-to-end data
integrity checksums and post-processing of senor data can be used to identify
forged sensor data (Estrin et al., 1999; Hu et al., 2003a; Ye et al., 2004).
The focus of this chapter is on routing security in WSNs. Most of the currently
existing routing protocols for WSNs make an optimization on the limited
capabilities of the nodes and the application-specific nature of the network,
but do not any the security aspects of the protocols. Although these protocols
have not been designed with security as a goal, it is extremely important to
analyze their security properties. When the defender has the liabilities of
insecure wireless communication, limited node capabilities, and possible
insider threats, and the adversaries can use powerful laptops with high energy
and long range communication to attack the network, designing a secure routing
protocol for WSNs is obviously a non-trivial task.Comment: 32 pages, 5 figures, 4 tables 4. arXiv admin note: substantial text
overlap with arXiv:1011.152
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: vehicular ad-hoc networks, security and caching, TCP in ad-hoc networks and emerging applications. It is targeted to provide network engineers and researchers with design guidelines for large scale wireless ad hoc networks
Energy efficient organization and modeling of wireless sensor networks
With their focus on applications requiring tight coupling with the physical world, as opposed to the personal communication focus of conventional wireless networks, wireless sensor networks pose significantly different design, implementation and deployment challenges. Wireless sensor networks can be used for environmental parameter monitoring, boundary surveillance, target detection and classification, and the facilitation of the decision making process. Multiple sensors provide better monitoring capabilities about parameters that present both spatial and temporal variances, and can deliver valuable inferences about the physical world to the end user.
In this dissertation, the problem of the energy efficient organization and modeling of dynamic wireless sensor networks is investigated and analyzed. First, a connectivity distribution model that characterizes the corresponding sensor connectivity distribution for a multi-hop sensor networking system is introduced. Based on this model, the impact of node connectivity on system reliability is analyzed, and several tradeoffs among various sleeping strategies, node connectivity and power consumption, are evaluated. Motivated by the commonality encountered in the mobile sensor wireless networks, their self-organizing and random nature, and some concepts developed by the continuum theory, a model is introduced that gives a more realistic description of the various processes and their effects on a large-scale topology as the mobile wireless sensor network evolves. Furthermore, the issue of developing an energy-efficient organization and operation of a randomly deployed multi-hop sensor network, by extending the lifetime of the communication critical nodes and as a result the overall network\u27s operation, is considered and studied.
Based on the data-centric characteristic of wireless sensor networks, an efficient Quality of Service (QoS)-constrained data aggregation and processing approach for distributed wireless sensor networks is investigated and analyzed. One of the key features of the proposed approach is that the task QoS requirements are taken into account to determine when and where to perform the aggregation in a distributed fashion, based on the availability of local only information. Data aggregation is performed on the fly at intermediate sensor nodes, while at the same time the end-to-end latency constraints are satisfied. An analytical model to represent the data aggregation and report delivery process in sensor networks, with specific delivery quality requirements in terms of the achievable end-to-end delay and the successful report delivery probability, is also presented. Based on this model, some insights about the impact on the achievable system performance, of the various designs parameters and the tradeoffs involved in the process of data aggregation and the proposed strategy, are gained. Furthermore, a localized adaptive data collection algorithm performed at the source nodes is developed that balances the design tradeoffs of delay, measurement accuracy and buffer overflow, for given QoS requirements. The performance of the proposed approach is analyzed and evaluated, through modeling and simulation, under different data aggregation scenarios and traffic loads. The impact of several design parameters and tradeoffs on various critical network and application related performance metrics, such as energy efficiency, network lifetime, end-to-end latency, and data loss are also evaluated and discussed
- …