Based on the conception of spectrum sharing, cognitive Radio as a promising technology for optimizing utilization of the radio spectrum has emerged to revolutionize the next generation wireless communications industry. In order to adopt this technology, the current spectrum allocation strategy has to be reformed and the real spectrum occupancy information has to be systemically investigated. To assess the feasibility of cognitive radio technology, the statistical information of the present spectral occupancy needs to be examined thoroughly, which forms the basis of the spectrum occupancy project. We studied the 100-2500 MHz spectrum with the traditional radio monitoring systems whose technical details have been fully recorded in this thesis. In order to detect the frequency agile signals, a channel sounder, which is capable of scanning 300 MHz spectrum within 4 ms with multiple channel inputs, was used as a dedicated radio receiver in our measurements. The conclusion of the statistical information from the spectrum monitoring experiments shows that the spectrum occupancy range from 100-2500 MHz are low indeed in the measuring locations and period. The average occupancies for most bands are less than 20%. Especially, the average occupancies in the 1 GHz to 2.5GHz spectrum are less than 5%. Time series analysis was initially introduced in spectrum occupancy analysis as a tool to model spectrum occupancy variations with time. For instance, the time series Airline model fits well the GSM band occupancy data. In this thesis, generalized linear models were used as complementarily solutions to model occupancy data into other parameters such as signal amplitude. The validation of the direction of arrival algorithms (EM and SAGE) was verified with the anechoic chamber, by which we can determine the spectrum occupancy in space domain.

Extensible Markup Language (XML) is a multi-purpose text-based format, used for storage, transmission and manipulation of data. XML documents are often held in main memory and processed via standard interfaces such as the Document Object Model (DOM). However, XML is inherently verbose, and the in-memory representation of XML documents by existing DOM implementations is up to ten times larger than the file size. This is a problem for machines with limited memory, such as mobile devices, where processing even moderately-sized XML documents requires more memory than is available. We focus on in-memory representations of XML documents for situations where space is limited and where rapid processing time is important. We propose a compact representation of XML documents that uses succinct or highly space-efficient data structures, that allows XML processing to be executed efficiently. Succinct data structures use space that approaches the information-theoretic lower bound on the space that is required to represent the data, and support operations upon the representation in constant time. In the context of XML documents, we study and improve succinct representations for ordinal trees by adding features that make them more suitable for use in XML documents. We explore fast and space-efficient representations of the textual data of XML documents. Our basic approach is to concatenate all the textual data in the XML document into a single string, and extract individual textual values by computing the appropriate substring of the concatenated string. Computing the substring requires us to store offsets into the text. The storage of the offsets is surprisingly expensive, if stored naively (as 32 or 64-bit integer values). We give a succinct representation and provide data-aware representations (adapted from work on inverted indices in information retrieval), and show their close connection. We describe Succinct DOM (SDOM), which is a DOM implementation that has low, stable and predictable memory usage. We show, via an experimental evaluation, that SDOM is extremely fast. A variant, SDOM-CT, applies BZip-based compression to textual and attribute data, and its space usage is comparable with “query-friendly” XML compressors. Some of these compressors support navigation and/or querying (e.g. subpath queries) of the compressed file. SDOM-CT does not support querying directly, but remains extremely fast: it is several orders of magnitude faster for navigation than query-friendly XML compressors that support navigation (and only a few times slower than popular DOM implementations such as the Apache Foundation’s Xerces-C).

Today’s dynamic and scalable collaborative systems demand not only to deal with functional but also some non-functional (e.g., security) requirements. For a secure inter-organisational collaboration scenario, Federated Identity Management systems (FIMs) provide a suitable mechanism to deal with access control. FIMs enable users of an organisation to access resources (or services) of the other trusted organisations in a secure and seamless way. More precisely, FIMs allow cross-domain user authentication to enable access control across organisations under the concept known as Circle of Trust (CoT). Patterns of FIMs emerged as recurring CoT scenarios due to the fact that each of these patterns has different security requirements. More importantly, organisations may join up or leave the CoT during the development life-cycle. Such a change in a FIM system may have an impact on its security requirements. Therefore, it is important to formally describe architectural and reconfiguration aspects of FIMs by considering their patterns. To this purpose, we propose • two UML models for FIMs where one model uses the standard UML notations to describe architectural aspects of FIMs while the other uses the UML profile in [33] to describe those aspects of FIMs together with their reconfigurations • a formal model for FIMs in ADR (Architectural Design Rewriting) to characterise their patterns by describing an architectural style together with style-preserving reconfigurations. We also study the adequacy of UML to describe architectural aspects of systems and compare it with ADR. Our comparison develops through the modelling of architectural and reconfiguration aspects of FIMs. In ADR, these aspects of FIMs are suitably represented through style-consistent (graphical) designs in terms of ADR productions. On the other hand, UML has limitations in expressing constraints over complex associations; also, UML seems to provide unsatisfactory support for presenting architectural styles in a general way. Overall, our investigation shows that UML has some drawbacks due to the complexity of diagrams, their proliferation, and the lack of a precise semantics that consistently relates them. ADR gives precise and simpler specifications for architectural design.

Autonomous instrumentation is used to collect scientific data in very remote locations, especially in the polar regions. Retrieving data from these instruments is often done by the use of satellite communications or by manual retrieval, the latter often requiring the use of an aircraft. This research focussed on the use of HF radio (i.e frequencies of 3-30MHz) as a cheaper technology for data communications in the polar regions and concentrated on three main areas of work: • the development of a channel simulator for high-latitude HF channels based on work by Warrington, Siddle and Stocker (2006) and using it for performance tests of existing HF modems • work on HF modem waveforms, including Polynomial Cancellation Coding OFDM (PCC-OFDM) and conventional OFDM, to try and create waveforms suitable for the more demanding high-latitude channels • an oblique propagation study using an OFDM waveform between Halley and Rothera stations in Antarctica, a 1600km sub-auroral link run for twelve months close to solar minimum. This work has shown that existing military HF modems (MIL-STD-188-110B) perform reasonably well in all but the most demanding high-latitude HF channels simulated. The oblique propagation study showed that a total annual data volume of around 400MB could be transmitted over the Halley-Rothera link, showing that HF can carry sufficient data to be useful for data retrieval. Data volumes were at their highest in the austral summer, but limited communications were possible year-round.

The linguistic annotation' of video sequences is an intellectually challenging task involving the investigation of how images and words are linked .together, a task that is ultimately financially rewarding in that the eventual automatic retrieval of video (sequences) can be much less time consuming, subjective and expensive than when retrieved manually. Much effort has been focused on automatic or semi-automatic annotation. Computational linguistic methods of video annotation rely on collections of collateral text in the form of keywords and proper nouns. Keywords are often used in a particular order indicating an identifiable pattern which is often limited and can subsequently be used to annotate the portion of a video where such a pattern occurred. Once' the relevant keywords and patterns have been stored, they can then be used to annotate the remainder of the video, excluding all collateral text which does not match the keywords or patterns. A new method of video annotation is presented in this thesis. The method facilitates a) annotation extraction of specialist terms within a corpus of collateral text; b) annotation identification of frequently used linguistic patterns to use in repeating key events within the data-set. The use of the method has led to the development of a system that can automatically assign key words and key patterns to a number of frames that are found in the commentary text approximately contemporaneous to the selected number of frames. The system does not perform video analysis; it only analyses the collateral text. The method is based on corpus linguistics and is mainly frequency based - frequency of occurrence of a key word or key pattern is taken as the basis of its representation. No assumptions are made about the grammatical structure of the language used in the collateral text, neither is a lexica of key words refined. Our system has been designed to annotate videos of football matches in English a!ld Arabic, and also cricket videos in English. The system has also been designed to retrieve annotated clips. The system not only provides a simple search method for annotated clips retrieval, it also provides complex, more advanced search methods.

This thesis investigates the application of distributed computing in general and wireless sensor networks in particular to space applications. Particularly, the thesis addresses issues related to the design of "space-based wireless sensor networks" that consist of ultra-small satellite nodes flying together in close formations. The design space of space-based wireless sensor networks is explored. Consequently, a methodology for designing space-based wireless sensor networks is proposed that is based on a modular architecture. The hardware modules take the form of 3-D Multi-Chip Modules (MCM). The design of hardware modules is demonstrated by designing a representative on-board computer module. The onboard computer module contains an FPGA which includes a system-on-chip architecture that is based on soft components and provides a degree of flexibility at the later stages of the design of the mission.

No description available.

No description available.

No description available.

No description available.