Wireless communication networks are traditionally designed to operate at high spectral e ciency with less emphasis on power consumption as it is assumed that endless power supply is available through the power grid where the cells are connected to. As new generations of mobile networks exhibit decreasing gains in spectral e ciency, the mobile industry is forced to consider energy reform policies in order to sustain the economic growth of itself and other industries relying on it. Consequently, the energy e ciency of conventional direct transmission cellular networks is being examined while alternative green network architectures are also explored. The relay-aided cellular network is being considered as one of the potential network architecture for energy e cient transmission. However, relaying transmission incurs multiplexing loss due to its multi-hop protocol. This, in turn, reduces network spectral e ciency. Furthermore, interference is also expected to increase with the deployment of Relay Stations (RSs) in the network. This thesis examines the power consumption of the conventional direct transmission cellular network and contributes to the development of the relay-aided cellular network. Firstly, the power consumption of the direct transmission cellular network is investigated. While most work considered transmitter side strategies, the impact of the receiver on the Base Station (BS) total power consumption is investigated here. Both the zero-forcing and minimum mean square error weight optimisation approaches are considered for both the conventional linear and successive interference cancellation receivers. The power consumption model which includes both the radio frequency transmit power and circuit power is described. The in uence of the receiver interference cancellation techniques, the number of transceiver antennas, circuit power consumption and inter-cell interference on the BS total power consumption is investigated. Secondly, the spectral-energy e ciency trade-o in the relay-aided cellular network is investigated. The signal forwarding and interference forwarding relaying paradigms are considered with the direct transmission cellular network taken as the baseline. This investigation serves to understand the dynamics in the performance trade-o . To select a suitable balance point in the trade-o , the economic e ciency metric is proposed whereby the spectral-energy e ciency pair which maximises the economic pro tability is found. Thus, the economic e ciency metric can be utilised as an alternative means to optimise the relay-aided cellular network while taking into account the inherent spectral-energy e ciency trade-o . Finally, the method of mitigating interference in the relay-aided cellular network is demonstrated by means of the proposed relay cooperation scheme. In the proposed scheme, both joint RS decoding and independent RS decoding approaches are considered during the broadcast phase while joint relay transmission is employed in the relay phase. Two user selection schemes requiring global Channel State Information (CSI) are considered. The partial semi-orthogonal user selection method with reduced CSI requirement is then proposed. As the cooperative cost limits the practicality of cooperative schemes, the cost incurred at the cooperative links between the RSs is investigated for varying degrees of RS cooperation. The performance of the relay cooperation scheme with di erent relay frequency reuse patterns is considered as well. In a nutshell, the research presented in this thesis reveals the impact of the receiver on the BS total power consumption in direct transmission cellular networks. The relayaided cellular network is then presented as an alternative architecture for energy e cient transmission. The economic e ciency metric is proposed to maximise the economic pro tability of the relay network while taking into account the existing spectral-energy e ciency trade-o . To mitigate the interference from the RSs, the relay cooperation scheme for advanced relay-aided cellular networks is proposed.

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Communication systems at microwave and millimetre wave regimes require compact broadband high gain antenna devices for a variety of applications, ranging from simple telemetry antennas to sophisticated radar systems. High performance can usually be achieved by fabricating the antenna device onto a substrate with low dielectric constant or recently through micromachining techniques. This thesis presents the design, fabrication, assembly and characterisation of microstrip and CPW fed micromachined aperture coupled single and stacked patch antenna devices. It was found that the micromachining approach can be employed to achieve a low dielectric constant region under the patch which results in suppression of surface waves and hence increasing radiation efficiency and bandwidth. A micromachining method that employs photolithography and metal deposition techniques was developed to produce high efficiency antenna devices. The method is compatible with integration of CMOS chips and filters onto a common substrate. Micromachined polymer rims (SU8 photoresist) was used to create millimetre thick air gaps between the patch and the substrate. The effect of the substrate materials and the dimensions of the SU8 polymer rims on the performance of the antenna devices were studied by numerical simulation using Ansoft HFSS electromagnetic field simulation package. The antenna structures were fabricated in layers and assembled by bonding the micromachined polymer spacers together. Low cost materials like SU8, polyimide and liquid crystal polymer films were used for fabrication and assembly of the antenna devices. A perfect patch antenna device is introduced by replacing the substrate of a conventional patch antenna device with air in order to compare with the micromachined antenna devices. The best antenna parameters for a perfect patch antenna device with air as a substrate medium are ~20% for bandwidth and 9.75 dBi for antenna gain with a radiation efficiency of 99.8%. In comparison, the best antenna gain for the simple micromachined patch antenna device was determined to be ~8.6 dBi. The bandwidth was ~20 % for a microstrip fed device with a single patch; it was ~40 % for stacked patch devices. The best bandwidth and gain of 6.58 GHz (50.5%) and 11.2 dBi were obtained for a micromachined sub-array antenna device. The simulation results show that the efficiency of the antenna devices is above 95 %. Finally, a novel high gain planar antenna using a frequency selective surface (FSS) was studied for operation at ~60 GHz frequency. The simulation results show that the novel antenna device has a substantial directivity of around 25 dBi that is required for the emerging WLAN communications at the 60 GHz frequency band.

The aim of this work is the design and analysis of novel antennas realised with electromagnetic bandgap (EBG) structures based on simple two-dimensional cylindrical, triangular and square lattices of dielectric rods. In particular, we focused our attention on designing antennas with high directivity and front-to-back-ratio (FTBR) on the azimuthal plane. Several EBG structures have been investigated, divided in two main categories: multilayer EBG structures with an angular defect window and EBG corner reflectors. The former are based on a feeding source excited within a cavity: fields at badgap frequencies are trapped inside the cavity and opening an angular defect window allows propagation in that privileged directions leading to directive radiation patterns. The latter are based on a source placed in front of an EBG corner reflector: at bandgap frequencies, the excited fields are reflected toward the corner aperture (in a similar fashion to metallic corners of analogous dimensions) enhancing radiation patterns’ directivity. The analysed structures have been also modified to host multiple sources to create multiple-feed antenna structures with the ability of rotating the radiation patterns on the azimuthal plane. Antennas have been modelled using an in-house developed Finite-Difference Time- Domain solver and the commercial Finite Element Method solver Ansoft HFSS, focusing on structures designed to operate in the X-band frequency region (8.2GHz-12.4GHz) in order to take advantage of the available equipment and facilities at Heriot-Watt University for prototypes testing. The proposed structures can be nevertheless scaled up or down in size in order to respectively scale down or up of the same factor the frequency of operation. The main achievements of the analysed multilayer EBG structures and corner EBG reflectors are the large impedance bandwidth (greater than 30%) with stable radiation patterns within, high gain (>12dBi) and high FTBR (greater than 25dB) accomplished using EBG structures made with a small number (10-20) of low-loss ceramic rods arranged in very simple two-dimensional crystals. EBG corner reflectors have been also found basically equivalent (at badgap frequencies) to metal reflectors in terms of achieved gain and radiation patterns, suggesting them as possible substitutes for high frequencies applications where dielectric losses would be smaller than metal losses.

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In order to securely monitor user or system activities and detect malicious attempts across a distributed system, provision of trustworthy audit and logging services is necessary. Existing audit-based monitoring services, however, are often prone to compromise due to the lack of guarantees of log integrity, confidentiality, and availability. This thesis presents several use cases where these properties are essential, conducts a threat analysis on these use cases, and identifies key security requirements from the threats and their risks. Then, this thesis proposes a log generation and reconciliation infrastructure in which the requirements are satisfied and threats are mitigated. Applications usually expose a weak link in the way logs are generated and protected. In the proposed logging system, important application events are involuntarily recorded through a trustworthy logging component operating inside a privileged virtual machine. Virtual machine isolation makes it infeasible for applications to bypass the logging component. Trusted Computing attestation allows users to verify the logging properties of remote systems, and ensure that the collected logs are trustworthy. Despite ongoing research in the area of usable security for distributed systems, there remains a `trust gap' between the users' requirements and current technological capabilities. To bridge this `trust gap', this thesis also proposes two different types of distributed systems, one applicable for a computational system and the other for a distributed data system. Central to these systems is the configuration resolver which maintains a list of trustworthy participants available in the virtual organisation. Users submit their jobs to the configuration resolver, knowing that their jobs will be dispatched to trustworthy participants and executed in protected environments. As a form of evaluation, this thesis suggests how these ideas could be integrated with existing systems, and highlights the potential security enhancements.

Photo sharing on camera phones is becoming a common way of maintaining closeness and relationships with friends and family and can evoke pleasurable, enjoyable or exciting experiences. People have fun when sharing photos containing amusing scenes or friends being caught doing something 'naughty'. Recent research has seen an increase in studies that focus on the use of camera phones, remote sharing using online services or sharing in a home environment using different digital technology. However, studies that extend this focus to the equally important issues of how co-located sharing using camera phones occurs and what influences it are less common. In addition, there is a dearth of research that links photo sharing with user experience (e.g. pleasure, fun, excitement collectively called hedonic experience; HE). The experience of photo sharing, however, does not exist in a vacuum but in a dynamic relationship with other people, places and objects and photo sharing is a social experience. This thesis explores the relationship between sharing practices within different groups of people and the various settings where sharing occurs. It investigates the situations when people experience pleasure, excitement or fun during the photo sharing activity. However, to understand the nature of HE using mobile interactive technology (digital cameras, PDAs, mobile phones) and what influences experiences a prerequisite is an investigation of photo sharing experiences using mobile phones. The HCI contributions of this thesis include dentification of different types of HE and their characteristics; provides factors influencing such experience and the vocabulary to help communicating issues related to HE when using technology. In addition, it proposes an empirically based Photo Sharing Components Model that captures the contributors of the photo sharing experience (Value of Photos, Social Affordances, Place Affordances and Technology Affordances) and the photo sharing scenario notations, which account for the different sharing behavioural phenomena occurring between different groups of people (e.g. family, friends, others) in different settings (e.g. private, public, work). Finally, an account of how this model might be developed by further research is detailed.

Mobile Ad-hoc networks extend communications beyond the limit of infrastructure based networks. Future wireless applications will take advantage of rapidly deployable, self-configuring multi-hop mobile Ad-hoc networks. In order to provide robust performance in mobile Ad-hoc networks and hence cope with dynamic path loss conditions, it is apparent that research and development of energy efficient geographic routing protocols is of great importance. Therefore various mobile Ad-hoc routing protocols have been studied for their different approaches. Forwarding strategies for geographic routing protocols are discussed and there is a particular focus on the pass loss model used by those routing protocols, the restriction and disadvantage of using such path loss model is then discussed. A novel geographic routing protocol which incorporates both the link quality and relay node location information has been developed to determine an energy efficient route from source to destination. The concepts of a gain region and a relay region to minimize the energy consumption have been proposed to define the area in where the candidate relay nodes will be selected with the minimized hop count. The signalling overhead required by the protocol has been analyzed in various scenarios with different traffic load, node densities and network sizes. Discrete event simulation models are therefore developed to capture the behaviour and characteristics of the operation of the developed routing protocol under different path loss conditions and network scenarios. A non-free space path loss model has been developed with a random loss between the nodes to simulate a realistic path loss scenario in the network. An enhanced signalling process has been designed in order to achieve advanced routing information exchange and assist routing determination. Comparison of simulated characteristics demonstrates the significant improvement of the new routing protocol because of its novel features, the gain region to ensure the deductiono f the energyc onsumptiont,h e relay region to ensuret he forward progress to the destination and hence maintain an optimised hop count. The simulation results showed that the energy consumption under the operation of the developed protocol is 30% of that with a conventionagl eographicarl outing protocol.

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