Distributed, computer based communication is becoming established within many working environments. Furthermore, the near future is likely to see an increase in the scale, complexity and usage of telecommunications services and distributed applications. As a result, there is a critical need for a global Directory service to store and manage communication information and therefore support the emerging world-wide telecommunications environment. This thesis describes research into the design of distributed Directory services. It addresses a number of Directory issues ranging from the abstract structure of information to the concrete implementation of a prototype system. In particular, it examines a number of management related issues concerning the management of communication information and the management of the Directory service itself. The following work develops models describing different aspects of Directory services. These include data access control and data integrity control models concerning the abstract structure and management of information as well as knowledge management, distributed operation and replication models concerning the realisation of the Directory as a distributed system. In order to clarify the relationships between these models, a layered directory architecture is proposed. This architecture provides a framework for the discussion of directory issues and defines the overall structure of this thesis. This thesis also describes the implementation of a prototype Directory service, supported by software tools typical of those currently available within many environments. It should be noted that, although this thesis emphasises the design of abstract directory models, development of the prototype consumed a large amount of time and effort and prototyping activities accounted for a substantial portion of this research. Finally, this thesis reaches a number of conclusions which are applied to the emerging ISO/CCITT X. 500 standard for Directory services, resulting in possible input for the 1988-92 study period.

The result of many years of international co-operation in video coding has been the development of algorithms that remove interframe redundancy, such that only changes in the image that occur over a given time are encoded for transmission to the recipient. The primary process used here is the derivation of pixel differences, encoded in a method referred to as Differential Pulse-Coded Modulation (DPCM)and this has provided the basis of contemporary research into low-bit rate hybrid codec schemes. There are, however, instances when the DPCM technique cannot successfully code a segment of the image sequence because motion is a major cause of interframe differences. Motion Compensation (MC) can be used to improve the efficiency of the predictive coding algorithm. This thesis examines current thinking in the area of motion-compensated video compression and contrasts the application of differing algorithms to the general requirements of interframe coding. A novel technique is proposed, where the constituent features in an image are segmented, classified and their motion tracked by a local search algorithm. Although originally intended to complement the DPCM method in a predictive hybrid codec, it will be demonstrated that the evaluation of feature displacement can, in its own right, form the basis of a low bitrate video codec of low complexity. After an extensive discussion of the issues involved, a description of laboratory simulations shows how the postulated technique is applied to standard test sequences. Measurements of image quality and the efficiency of compression are made and compared with a contemporary standard method of low bitrate video coding.

This thesis discusses the issues involving the support of Living Ontologies: collaborating in the construction and maintenance of ontologies using the Internet. Ontologies define the concepts used in describing a domain: they are used by knowledge engineers as reusable components of knowledge-based systems. Knowledge engineers create ontologies by eliciting information from domain experts. However, experts often have different conceptualisations of a domain and knowledge engineers often have different ways of formalising their conceptualisations. Taking a constructivist perspective, constructing ontologies from multiple conflicting conceptualisations can be seen as a design activity, in which knowledge engineers make choices according to the context in which the representation will be used. Based on this theory, a methodology for collaboratively constructing ontologies might involve comparing differing conceptualisations and using these comparisons to initiate discussion, changes to the conceptualisations and the development of criteria against which they can be evaluated. APECKS (Adaptive Presentation Environment for Collaborative Knowledge Structuring) is designed to support this methodology. APECKS aims not only to support the collaborative construction of ontologies but also to use ontologies to present information to its users adaptively within a virtual environment. It demonstrates a number of innovations over conventional ontology servers, such as prompted knowledge elicitation from domain experts, automated comparisons between ontologies, the creation of design rationales and change tracking. A small evaluation of APECKS has shown that it is usable by domain experts and that automated comparisons between ontologies can be used to initiate alterations, investigations of others' conceptualisations and as a basis for discussion. Possible future development of APECKS includes tighter integration with a virtual environment and with other networked knowledge-based tools. Further research is also needed to develop the methodology on which APECKS is based, by investigating ways of comparing, combining and discussing ontologies.

This thesis investigates the performance of free-space optical (FSO) communication systems in a turbulent atmosphere employing optical amplifiers (OAs) to extend transmission reach and wavelength-division multiplexing (WDM) to improve capacity. This system performance is considered in the presence of amplified spontaneous emission (ASE) noise, scintillation, beam spreading, atmospheric attenuation and interchannel crosstalk. In this work, the modulation scheme used is the on-off keying non-return-to-zero and the main performance metric employed is the average bit error rate (BER). Various performance evaluation methods are used to estimate system performance. Analysis of single link, cascaded OA and WDM FSO communication systems are given and the implications of using both adaptive (to channel state) and non-adaptive decision threshold schemes are analysed. The benefits of amplifier saturation, for example in the form of effective scintillation reduction when a non-adaptive decision threshold scheme is utilised at the receiver for different atmospheric turbulence regimes, are presented. Monte Carlo simulation techniques are used to model the probability distributions of system parameters such as the optical signal power, amplified spontaneous emission noise, optical signal to noise ratio and the average bit error rate due to scintillation. It is found that the performance of an adaptive decision threshold is superior to a non-adaptive decision threshold for both saturated and fixed gain preamplified receivers and the ability of a saturated gain OA to suppress scintillation is only meaningful for system performance when a non-adaptive decision threshold is used at the receiver. In a saturated gain preamplified system, the optimum non-adaptive decision threshold is investigated. An OA cascade can be successfully used to extend reach in FSO communication systems and specific system implementations are presented. The optimal cascade scheme with a non-adaptive receiver would use frequent low gain saturated amplification although this has a cost implication. Furthermore, a saturated gain amplified WDM FSO system with a non-adaptive decision threshold is superior to a non-amplified WDM FSO system with an adaptive decision threshold.

Device to device (D2D) links density is expected to increase dramatically in future networks. The D2D user equipments (DUEs) reuse frequency resources to cover the next generation D2D-enabled cellular network requirements. The cellular user equipments (CUEs) and DUEs experience in-band emission interference (IEI) from DUEs that use adjacent frequencies. In this thesis, the IEI impact in D2D-enabled cellular network is investigated comprehensively. In the first part, the IEI from the DUEs to cellular links is initially mitigated for all time slots. An open loop power control (OLPC)-based scheme is introduced for the D2D discovery scenario to mitigate the IEI and compared with recent proposed methods. The scheme defines time slots to boost the DUEs transmission power, where the IEI is mitigated and the D2D link performance is improved. A simulation system is used to evaluate the IEI impact. The IEI from DUEs to cellular links is mitigated without taking into account the proposed power control can affect the DUEs that use the same frequency resource and the constraints can affect the D2D link performance. Therefore, the second part expands the IEI investigation, where the D2D-enabled cellular network is modelled by taking into account the IEI interferers using the stochastic geometry tool. The IEI impact is analysed and mitigated for all time slots by taking into account the D2D links performance. The IEI impact is evaluated theoretically in terms of coverage probability and data rate for cellular link side, successful probability and data rate for D2D link side. The IEI intra-cell and IEI inter-cell are investigated separately to detect the dominant part of IEI. The expected reuse factor of the D2D resource blocks (DRBs) is derived to examing the number of DUEs that can be served when the IEI is or is not taken into account. Following, a power-density based (PDB) strategy is proposed to mitigate the IEI by controlling the number of DUEs that use each DRB, and by allocating predefined DRBs to the DUEs that cause lowest interference power at the serving BS. The thinning process and Poisson hole process (PHP) are employed to remodel the network. The performance improvement can be achieved by employing this strategy is evaluated. The optimal DRBs setting is found that mitigates the IEI and improves the cellular link performance. Furthermore, the optimal power allocation (OPA) algorithm is proposed to mitigate the IEI by calculating the optimal DUEs transmission power profile that maximizes the DUEs sum rate and maintains the interference level at the BS below a predefined threshold. The performance improvement that can be achieved by employing this algorithm is also evaluated. It is concluded that, in a D2D-enabled cellular network, the IEI impact is significant and needs to be considered to evaluate the performance of the future network accurately. Thus, the proposed model can be used to represent and evaluate the future network. Also, by employing the PDB strategy, the IEI can be mitigated effectively if the D2D links performance has higher priority than the number of DUEs required to be served for D2D discovery and transmission data scenarios. In case the required number of served DUEs in one time slot cannot be covered by PDB, the OPA algorithm and the OLPC-based strategy can be used for D2D data transmission and D2D discovery scenarios, respectively.

The landscape of television is changing. Modern Internet enabled sets are now capable computing devices offering new forms of connectivity and interaction to viewers. One development enabled by this transition is the distribution of auxiliary content to a portable computing device, such as a mobile phone or tablet, working in concert with the television. These configurations are enabled by second screen applications that provide relevant content in synchronisation with the programme on a nearby television set. This thesis extends the notion of second screen to arrangements that incorporate multiple mobile devices working with the television, utilised by collocated groups of participants. Herein these arrangements are referred to as ‘many-screen’ television. Two many-screen applications were developed for the augmentation of sports programming in preparation of this thesis; the Olympic Companion and MarathOn Multiscreen Applications. Both of these applications were informed by background literature on second screen television and wider issues in HCI multiscreen research. In addition, the design of both applications was inspired by the needs of traditional and online broadcasters, through an internship with BBC Research and Development and involvement in a YouTube sponsored project. Both the applications were evaluated by collocated groups of users in formative user studies. These studies centred on how users share and organise what to watch, incorporate activity within the traditionally passive television viewing experience and the integration of user-generated video content in a many-screen system. The primary contribution of this thesis is a series of industry validated guidelines for the design of many-screen applications. The guidelines highlight issues around user awareness devices, content and other user’s actions, the balance between communal and private viewing and the appropriation of user-generated content in many-screen watching.

With recent developments in the Global Satellite Navigation Systems (GNSS), the applications and services of positioning and navigation have developed rapidly worldwide. Location-based services (LBS) have become a big application which provide position related services to the mass market. As LBS applications become more popular, positioning services and capacity are demanded to cover all types of environment with improved accuracy and reliability. While GNSS can provide promising positioning and navigation solutions in open outdoor environments, it does not work well when inside buildings, in tunnels or under canopy. Positioning in such difficult environments have been known as the indoor positioning problem. Although the problem has been looked into for more than a decade, there currently no solution that can compare to the performance of GNSS in outdoor environments. This thesis introduces a collaborative indoor positioning solution based on particle filtering which integrates multiple sensors, e.g. inertial sensors, Wi-Fi signals, map information etc., and multiple local users which provide peer-to-peer (P2P) relative ranging measurements. This solution addresses three current problems of indoor positioning. First of all is the positioning accuracy, which is limited by the availability of sensors and the quality of their signals in the environment. The collaborative positioning solution integrates a number of sensors and users to provide better measurements and restrict measurement error from growing. Secondly, the reliability of the positioning solutions, which is also affected by the signal quality. The unpredictable behaviour of positioning signals and data could lead to many uncertainties in the final positioning result. A successful positioning system should be able to deal with changes in the signal and provide reliable positioning results using different data processing strategies. Thirdly, the continuity and robustness of positioning solutions. While the indoor environment can be very different from one another, hence applicable signals are also different, the positioning solution should take into account the uniqueness of different situations and provide continuous positioning result regardless of the changing datWith recent developments in the Global Satellite Navigation Systems (GNSS), the applications and services of positioning and navigation have developed rapidly worldwide. Location based services (LBS) have become a big application which provide position related services to the mass market. As LBS applications become more popular, positioning services and capacity are demanded to cover all types of environment with improved accuracy and reliability. While GNSS can provide promising positioning and navigation solutions in open outdoor environments, it does not work well when inside buildings, in tunnels or under canopy. Positioning in such difficult environments have been known as the indoor positioning problem. Although the problem has been looked into for more than a decade, there currently no solution that can compare to the performance of GNSS in outdoor environments. This thesis introduces a collaborative indoor positioning solution based on particle filtering which integrates multiple sensors, e.g. inertial sensors, Wi-Fi signals, map information etc., and multiple local users which provide peer-to-peer (P2P) relative ranging measurements. This solution addresses three current problems of indoor positioning. First of all is the positioning accuracy, which is limited by the availability of sensors and the quality of their signals in the environment. The collaborative positioning solution integrates a number of sensors and users to provide better measurements and restrict measurement error from growing. Secondly, the reliability of the positioning solutions, which is also affected by the signal quality. The unpredictable behaviour of positioning signals and data could lead to many uncertainties in the final positioning result. A successful positioning system should be able to deal with changes in the signal and provide reliable positioning results using different data processing strategies. Thirdly, the continuity and robustness of positioning solutions. While the indoor environment can be very different from one another, hence applicable signals are also different, the positioning solution should take into account the uniqueness of different situations and provide continuous positioning result regardless of the changing data. The collaborative positioning aspect is examined from three aspects, the network geometry, the network size and the P2P ranging measurement accuracy. Both theoretical and experimental results indicate that a collaborative network with a low dilution of precision (DOP) value could achieve better positioning accuracy. While increasing sensors and users will reduce DOP, it will also increase computation load which is already a disadvantage of particle filters. The most effective collaborative positioning network size is thus identified and applied. While the positioning system measurement error is constrained by the accuracy of the P2P ranging constraint, the work in this thesis shows that even low accuracy measurements can provide effective constraint as long as the system is able to identify the different qualities of the measurements. The proposed collaborative positioning algorithm constrains both inertial measurements and Wi-Fi fingerprinting to enhance the stability and accuracy of positioning result, achieving metre-level accuracy. The application of collaborative constraints also eliminate the requirement for indoor map matching which had been a very useful tool in particle filters for indoor positioning purposes. The wall constraint can be replaced flexibly and easily with relative constraint. Simulations and indoor trials are carried out to evaluate the algorithms. Results indicate that metre-level positioning accuracy could be achieved and collaborative positioning also gives the system more flexibility to adapt to different situations when Wi-Fi or collaborative ranging is unavailable. The collaborative positioning aspect is examined from three aspects, the network geometry, the network size and the P2P ranging measurement accuracy. Both theoretical and experimental results indicate that a collaborative network with a low dilution of precision (DOP) value could achieve better positioning accuracy. While increasing sensors and users will reduce DOP, it will also increase computation load which is already a disadvantage of particle filters. The most effective collaborative positioning network size is thus identified and applied. While the positioning system measurement error is constrained by the accuracy of the P2P ranging constraint, the work in this thesis shows that even low accuracy measurements can provide effective constraint as long as the system is able to identify the different qualities of the measurements. The proposed collaborative positioning algorithm constrains both inertial measurements and Wi-Fi fingerprinting to enhance the stability and accuracy of positioning result, achieving metre-level accuracy. The application of collaborative constraints also eliminate the requirement for indoor map matching which had been a very useful tool in particle filters for indoor positioning purposes. The wall constraint can be replaced flexibly and easily with relative constraint. Simulations and indoor trials are carried out to evaluate the algorithms. Results indicate that metre-level positioning accuracy could be achieved and collaborative positioning also gives the system more flexibility to adapt to different situations when Wi-Fi or collaborative ranging is unavailable.

This thesis evaluates the potentials of hybrid fibre and free space optical (FSO) communications access networks in providing a possible solution to an all optical access network. In such network architectures, the FSO link can extend the system to areas where an optical fibre link is not feasible, and/or provide limited mobility for indoor coverage. The performance of hybrid fibre and FSO (HFFSO) networks based on digital pulse position modulation (DPPM), for both the indoor and outdoor environments of the optical access network, are compared with the performance of such a network that is based on conventional on-off keying non-return-to-zero (OOK NRZ) modulation using results obtained through computational and analytical modelling. Wavelength division multiplexing (WDM) and/or code division multiple access (CDMA) are incorporated into the network for high speed transmission and/or network scalability. The impacts of optical scintillation, beam spreading and coupling losses, multiple access interference (MAI), linear optical crosstalk and amplified spontaneous emission noise (ASE) on the performance of hybrid fibre and FSO (HFFSO) access networks are analysed, using performance evaluation methods based on simple Gaussian approximation (GA) and more complex techniques based on moment generating function (MGF), including the Chernoff bound (CB), modified Chernoff bound (MCB) and saddlepoint approximation (SPA). Results in the form of bit error rate (BER), power penalty, required optical power and outage probability are presented, and both the CB and MCB, which are upper bounds, are suggested as safer methods of assessing the performance of practical systems. The possibility of using a CDMA-based HFFSO network to provide high speed optical transmission coverage in an indoor environment is investigated. The results show a reduction in transmit power of mobile devices of about 9 – 20 dB (depending on number of active users) when an optical amplifier is used in the system compared to a non-amplified system, and up to 2.8 dB improvement over OOK NRZ receiver sensitivity is provided by a DPPM system using integrate and compare circuitry for maximum likelihood detection, and at coding level of two, for minimum bandwidth utilization. Outdoor HFFSO networks using only WDM, and incorporating CDMA with WDM, are also investigated. In the presence of atmospheric scintillations, an OOK system is required (for optimum performance) to continuously adapt its decision threshold to the fluctuating instantaneous irradiance. This challenge is overcome by using the maximum likelihood detection DPPM system, and necessitated the derivation of an interchannel crosstalk model for WDM DPPM systems. It is found that optical scintillation worsens the effect of interchannel crosstalk in outdoor HFFSO WDM systems, and results in error floors particularly in the upstream transmission, which are raised when CDMA is incorporated into the system, because of MAI. In both outdoor HFFSO networks (with WDM only and with WDM incorporating CDMA), the optical amplifier is found necessary in achieving acceptable BER, and with a feeder fibre of 20 km and distributive FSO link length of 1500 m, high speed broadband services can be provided to users at safe transmit power at all turbulence levels in clear air atmosphere.

Mental health has long been a neglected problem in global healthcare. The social and economic impacts of conditions affecting the mind are still underestimated. However, in recent years it is becoming more apparent that mental disorders are a growing global concern that is not to be trivialised. Considering the rising burden of psychiatric illnesses, there is a necessity of developing novel services and researching effective means of providing interventions to sufferers. Such novel services could include technology-based solutions already used in other healthcare applications but are yet to make their way into standard psychiatric practice. This thesis presents a study on how pervasive technology can be utilised to devise an “early warning” system for patients with bipolar disorder. The system, containing wearable and environmental sensors, would collect behavioural data and use it to inform the user about subtle changes that might indicate an upcoming episode. To test the feasibility of the concept a prototype system was devised, which was followed by trials including four healthy volunteers as well as a bipolar patient. The system included a number of sensory inputs including: accelerometer, light sensors, microphones, GPS tracking and motion detectors. The experiences from the trials led to a conclusion that a large number of sensors may result in incompliance from the users. Therefore, a separate investigation was launched into developing a methodology for detecting behavioural patterns in inputs possible to collect from a mobile phone alone. The premise being that a phone is an everyday use appliance and is likely to be carried and accepted by the patient. The trial revealed that monitoring GPS tracks and Bluetooth encounters has the potential of gaining an insight into a person’s social and behavioural patterns, which usually are strongly influenced by the course of bipolar disorder. Lessons learned during these proceedings amounted to a clearer concept of how a future personalised ambient monitoring system could improve the outcome of treatment of bipolar disorder as well as other psychiatric conditions.

In this thesis, some of the functions of punctuation marks in digital discourse are explored. A theoretical model of punctuation mark function was generated specifically for this project and is based in rhetorical theory. According to this model, punctuation marks can function in three ways: First, they can build or damage the credibility of the writer; second, they can clarify the meanings of texts in a number of ways; and third, they can convey emotional and relational meaning. Two empirical studies are presented in this thesis. The first uses data from text-messages and the second uses data from message boards. For the text-message study, a new method of data collection was employed: Respondents were given Discourse Completion Tasks that asked what text-message they would send in a series of four respective hypothetical contexts; they were then asked to type out and send their responses, in text-messages, to email addresses. For the second study, data was taken from Reddit message boards on the Internet. In the analysis sections of the thesis, punctuation marks are examined in the collected data according to the rhetorical model with special attention being paid to how punctuation marks can convey emotional and relational meaning; and they are also examined according to how they influence speech acts. It is concluded that different punctuation marks can function in a variety of ways, and that punctuation marks can exert a powerful influence on speech acts. It is furthermore concluded that the thesis’s rhetorical model is effective both as a description of the ways punctuation marks can function and as a guide for analysis.