295 research outputs found
Frequency Rendezvous and Physical Layer Network Coding for Distributed Wireless Networks
In this thesis, a transmission frequency rendezvous approach for secondary users deployed in decentralized dynamic spectrum access networks is proposed. Frequency rendezvous is a critical step in bootstrapping a wireless network that does not possess centralized control. Current techniques for enabling frequency rendezvous in decentralized dynamic spectrum access networks either require pre-existing infrastructure or use one of several simplifying assumptions regarding the architecture, such as the use of regularly spaced frequency channels for communications. Our proposed approach is designed to be operated in a strictly decentralized wireless networking environment, where no centralized control is present and the spectrum does not possess pre-defined channels. In our proposed rendezvous algorithm, the most important step is pilot tone detection and receiver query. In order to realize a shortest search time for the target receiver, an efficient scanning rule should be employed. In this thesis, three scanning rules are proposed and evaluated, namely: frequency sequence scanning, pilot tone strength scanning, and cluster scanning. To validate our result, we test our scanning rules with actual paging band spectrum measurements. Previous research on security of network coding focuses on the protection of data dissemination procedures and the detection of malicious activities such as pollusion attacks. The capabilities of network coding to detect other attacks has not been fully explored. In this thesis, a new mechanism based on physical layer network coding to detect wormhole attacks is proposed. When two signal sequences collide at the receiver, the difference between the two received sequences is determined by its distances to the senders. Therefore, by comparing the differences between the received sequences at two nodes, we can estimate the distance between them and detect those fake neighbor connections through wormholes. While the basic idea is clear, we design many schemes at both physical and network layers to turn the idea into a practical approach. Simulations using BPSK modulation at the physical layer show that the wireless nodes can effectively detect fake neighbor connections without the adoption of any special hardware on them
New Approaches in Cognitive Radios using Evolutionary Algorithms
Cognitive radio has claimed a promising technology to exploit the spectrum in an ad hoc network. Due many techniques have become a topic of discussion on cognitive radios, the aim of this paper was developed a contemporary survey of evolutionary algorithms in Cognitive Radio. According to the art state, this work had been collected the essential contributions of cognitive radios with the particularity of base they research in evolutionary algorithms. The main idea was classified the evolutionary algorithms and showed their fundamental approaches. Moreover, this research will be exposed some of the current issues in cognitive radios and how the evolutionary algorithms will have been contributed. Therefore, current technologies have matters presented in optimization, learning, and classification over cognitive radios where evolutionary algorithms can be presented big approaches. With a more comprehensive and systematic understanding of evolutionary algorithms in cognitive radios, more research in this direction may be motivated and refined
Facilitating Flexible Link Layer Protocols for Future Wireless Communication Systems
This dissertation addresses the problem of designing link layer protocols
which are flexible enough to accommodate the demands offuture wireless
communication systems (FWCS).We show that entire link layer protocols with
diverse requirements and responsibilities can be composed out of
reconfigurable and reusable components.We demonstrate this by designing and
implementinga novel concept termed Flexible Link Layer (FLL)
architecture.Through extensive simulations and practical experiments, we
evaluate a prototype of the suggested architecture in both
fixed-spectrumand dynamic spectrum access (DSA) networks.
FWCS are expected to overcome diverse challenges including the continual
growthin traffic volume and number of connected devices.Furthermore, they
are envisioned to support a widerange of new application requirements and
operating conditions.Technology trends, including smart homes,
communicating machines, and vehicularnetworks, will not only grow on a
scale that once was unimaginable, they will also become the predominant
communication paradigm, eventually surpassing today's human-produced
network traffic.
In order for this to become reality, today's systems have to evolve in many
ways.They have to exploit allocated resources in a more efficient and
energy-conscious manner.In addition to that, new methods for spectrum
access and resource sharingneed to be deployed.Having the diversification
of applications and network conditions in mind, flexibility at all layers
of a communication system is of paramount importance in order to meet the
desired goals.
However, traditional communication systems are often designed with specific
and distinct applications in mind. Therefore, system designers can tailor
communication systems according to fixedrequirements and operating
conditions, often resulting in highly optimized but inflexible
systems.Among the core problems of such design is the mix of data transfer
and management aspects.Such a combination of concerns clearly hinders the
reuse and extension of existing protocols.
To overcome this problem, the key idea explored in this dissertation is a
component-based design to facilitate the development of more flexible and
versatile link layer protocols.Specifically, the FLL architecture,
suggested in this dissertation, employs a generic, reconfigurable data
transfer protocol around which one or more complementary protocols, called
link layer applications, are responsible for management-related aspects of
the layer.
To demonstrate the feasibility of the proposed approach, we have designed
andimplemented a prototype of the FLL architecture on the basis ofa
reconfigurable software defined radio (SDR) testbed.Employing the SDR
prototype as well as computer simulations, thisdissertation describes
various experiments used to examine a range of link layerprotocols for both
fixed-spectrum and DSA networks.
This dissertation firstly outlines the challenges faced by FWCSand
describes DSA as a possible technology component for their construction.It
then specifies the requirements for future DSA systemsthat provide the
basis for our further considerations.We then review the background on link
layer protocols, surveyrelated work on the construction of flexible
protocol frameworks,and compare a range of actual link layer protocols and
algorithms.Based on the results of this analysis, we design, implement, and
evaluatethe FLL architecture and a selection of actual link layer
protocols.
We believe the findings of this dissertation add substantively to the
existing literature on link layer protocol design and are valuable for
theoreticians and experimentalists alike
Survey of Inter-satellite Communication for Small Satellite Systems: Physical Layer to Network Layer View
Small satellite systems enable whole new class of missions for navigation,
communications, remote sensing and scientific research for both civilian and
military purposes. As individual spacecraft are limited by the size, mass and
power constraints, mass-produced small satellites in large constellations or
clusters could be useful in many science missions such as gravity mapping,
tracking of forest fires, finding water resources, etc. Constellation of
satellites provide improved spatial and temporal resolution of the target.
Small satellite constellations contribute innovative applications by replacing
a single asset with several very capable spacecraft which opens the door to new
applications. With increasing levels of autonomy, there will be a need for
remote communication networks to enable communication between spacecraft. These
space based networks will need to configure and maintain dynamic routes, manage
intermediate nodes, and reconfigure themselves to achieve mission objectives.
Hence, inter-satellite communication is a key aspect when satellites fly in
formation. In this paper, we present the various researches being conducted in
the small satellite community for implementing inter-satellite communications
based on the Open System Interconnection (OSI) model. This paper also reviews
the various design parameters applicable to the first three layers of the OSI
model, i.e., physical, data link and network layer. Based on the survey, we
also present a comprehensive list of design parameters useful for achieving
inter-satellite communications for multiple small satellite missions. Specific
topics include proposed solutions for some of the challenges faced by small
satellite systems, enabling operations using a network of small satellites, and
some examples of small satellite missions involving formation flying aspects.Comment: 51 pages, 21 Figures, 11 Tables, accepted in IEEE Communications
Surveys and Tutorial
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