The demand for high data rate and high user mobility has driven modern wireless communications into a new era, in which advanced technologies are developed to facilitate the fulfilment of such demands, as well as to guarantee the quality of service of transmissions under adverse channel conditions. OFDM has become a popular choice for wideband high data rate communication systems due to its strength in mitigating frequency selective fading as well as inter-symbol interference. However, OFDM operation faces a number of challenges, such as high channel estimation complexity and sensitivity to Doppler shift. In this thesis, we investigate channel estimation techniques for OFDM systems, especially with a view to the optimisation of estimation accuracy at low complexity, so as to maximise the practicability and minimise the cost of user terminals. Firstly, we investigate channel estimation techniques for an OFDM based satellite mobile broadcast system DVB-SH. The main difficulty DVB-SH faces is its large frame size that drastically increases the channel estimation complexity. We have proposed an optimised estimation scheme that has much lower complexity, whilst minimising performance degradation. Secondly, we investigate the impact of severe inter-carrier interference caused by large Doppler shift. Inter-carrier interference damages the orthogonality between subcarriers and leads to performance degradation. In order to optimise the existing interference cancellation techniques, we have proposed an adaptive cancellation scheme that achieves a significant performance improvement over existing technique whilst the computational complexity is maintained at the same level. Finally, we consider channel estimation in the time-domain in the presence of synchronisation errors. We have proposed a low-complexity time-domain scheme that compensates performance degradation due to synchronisation errors. The proposed scheme achieves near-ideal accuracy at low speed while it can be widely applicable to many existing systems.

The thesis focuses on the industrial design role against a backdrop of the technological and business development of advanced personal telecommunication products - defined within this thesis as System Orientated Products (SOPs) - and systems. SOPs are becoming functionally and visually sophisticated but offer less physical feedback to users in relation to purpose, operation and value. The thesis argues that if designers are involved early during development they may enhance commercial success, help teams to explore user issues, and strengthen user empathy with individual devices and task environments. The literature review explored industrial design, models of product development, and user issues associated with SOP development (SOPD). Findings suggest that industrial design is characterised by lateral and experience-based problem solving activities that can expand understanding of design opportunity and end-user knowledge. Product development teams, in contrast, support different specialist interests, and therefore, it is harder to maintain a collective user focus. This is illustrated within linear models of the design process, defined by the Design Methods Movement in the 1960s, and early generations of the innovation process described by Rothwell (Dogdson and Rothwell, 1994), where the introduction of expertise is staged according to development activities. Since the 1970s more integrated and user-centred models (e. g. Quality Function Deployment or integrated New Product Development) have supported collaboration during development. The review concluded that it would be positive to organise SOPD around collaborative, user-centred goals. A qualitative case analysis of industrial design activity during SOPD added to the literature review and the development of guidelines that outline a designer's optimal involvement during SOPD. Five case interviews were conducted with development specialists in the UK to compare development activity. Participants included engineering manager Larkin, and industrial design specialists Berry, Desbarats, Hohl, and McBrien. It was concluded that designers rarely adopt specific SOPD strategies, but support development teams with wide-ranging experience and problem solving abilities, and help to focus user requirements. A design process model is proposed that positions the Industrial designer as an integrator of design knowledge within development teams when clarifying design briefs. Implemented as a web-based design tool and co-ordinated by the designer, it supports an evolving knowledge base for development teams. Evaluation of the tool involved implementing a simplified e-mail version with development specialists. An industrial designer was asked to explore a specified design opportunity, then an engineer and an ergonomist responded to the emerging data. The exercise was repeated with a similar sample of specialists to compare data entry patterns. Data analysis suggested that the tool would offer an open and unrestricted platform for developing a brief, and encourage broader exploration of user requirements. The research conclusions highlight the exponential development of SOPs over the last decade, and the rapid response made by the industry to new and emerging technologies. This made it difficult to prove objectively the research hypothesis. However, conclusions suggested that opportunities exist for broadening industrial design contribution within SOPD in light of the clear shift from a technologically led, to a user- experience- and context-driven approach, reinforced by collaborative and multidisciplinary practice.

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The Gigahertz Transverse Electromagnetic (GTEM) cell was developed about 20 years ago and the applications using GTEM cells for electromagnetic compatibility (EMC) measurements are continuously increasing. The research described in this Thesis proposes a new method for characterizing emissions from electrical appliances using a GTEM cell. The research adapts the method used in the Transverse Electromagnetic (TEM) cell where the measurements are done by using a two-port system which includes a phase measurement. This is a restriction in GTEM cells because only one port exists and normally only the magnitude reading can be performed. This requires the development and application of new techniques, which allow the description of emitters in terms of equivalent electric and magnetic dipoles measured using a GTEM cell with phase measurement. A full field 3D Transmission Line Model (TLM) model of a GTEM cell is generated. Further simulations based on this model were performed to assess the behaviour of the emitters and when the GTEM cell is under actual working conditions. The model is also used to validate results obtained from measurements. The assumption that the dipole moments from a general emitter are in phase is also studied and evidence is presented to assess the validity of this assumption. The impact of the phase variations within an EUT towards the total radiated power estimated according to IEC 61000-4-20 is discussed and a technique to measure phase using a GTEM cell is introduced.

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One of the airborne radar antenna problems is the integration of microwave circuits with waveguide components. As part of this research, an optimum transition from a waveguide to a microstrip using the short transformer technique is proposed. A layer of dielectric substrate is employed as a matching structure between the waveguide and microstrip line structure, which is optimised using the direct search method. It is shown that the transition has an average return loss value of -19.2 dB throughout the X band (8 - 12.5 GHz) with the best predicted return loss value of - 64 dB. Another issue of airborne radar antennas investigated is the high impedance surface (HIS) structure which could be employed to suppress surface effect usually encountered in conventional low profile antennas so that their efficiency such as radiation pattern and gain can be greatly improved. A 3x3 cells simulation model is proposed to investigate performance of high impedance surface (HIS) structure. This simulation model is used to determine resonant frequencies of the test HIS structure. The obtained actual and additional resonant frequencies are 5 GHz and 3.65 GHz respectively. The additional resonant frequency can be used to determine the start of the band gap frequency. Empirical equations for the additional resonant frequency have been successfully derived based on the behaviour ofthe current distribution along the surface ofthe HIS structure. A suspended microstrip fed slot antenna (MSA) on HIS structure is suggested to overcome bidirectional radiation behaviour exhibited in MSA and at the same time improving the gain, radiation pattern and return loss performance. This proposed antenna offers low side lobe, a maximum gain of 10 dB in the desired direction and a maximum gain ofless than -3 dB in the undesired direction. Radiations in both the E and H planes are symmetrical. The accuracy of the effective medium method is enhanced by applying proper boundary conditions. These rules and limits are derived based on the parametric study. A test structure is designed and created to validate the method. A close agreement b~tween the values of reflection phase angle (-90 to 90 degree) and surface impedance from 4.5 to 8 GHz is obtained by using this proposed improved method and numerical simulation. S21 graph and dispersion diagram are plotted to further confirm validity ofthe proposed method. A new improved enhanced effective medium is proposed to evaluate performance ofthe HIS structure with different patch shapes. This method is a combination of the enhanced effective medium method and the Guass' law. To validate the proposed method, the surface impedance values of the circular and octagonal patch HIS structures obtained from both HFSS simulation tool and the presented theory are compared. Close agreement between the results is observed. An industry standard full wave simulation tool (HFSS) is used to optimise the band gap bandwidth of the mushroom-like HIS structure under limited space condition. The optimisation approach is based on the variation of the patch width. It is shown that a fractional bandwidth of 110% can be achieved using our optimum patch width.

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