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The last few years, much research is aimed at using light as an information carrier in systems. Photonic crystals are materials with varying dielectric properties, designed to interact with photons. If these crystals are arranged in a periodic structure they can control the propagation of electromagnetic waves through the structure. Photonic Band Gap (PBG) crystal is a periodic structure that prohibits propagation of all electromagnetic waves within a particular frequency band. Original PBG research was done in the optical region, but PBG properties are scaleable and applicable to a wide range of frequencies. In recent years, there has been increasing interest in microwave and millimeter-wave applications of PBG structures. Currently, research has also extended to Metallodielectric Electromagnetic Band Gap structures (MEBG), which are replacing the photonic crystals. MEBG structures are composed of periodic metallic elements usually printed in a dielectric region. The research effort in this thesis concentrates on the analysis, modelling and practical implementation of a novel concept called CCMEBG.

The need for higher data rates in wireless communication systems and the lack of available frequency space has led the researchers in developing new technologies, such as UWB. Ultra-wideband systems utilise signals with very short duration and very large bandwidth, from which the benefits are twofold; more information can be exchanged and coexistence with narrowband technologies is possible, as such systems perceive UWB as noise and interference is thus avoided. The increased bandwidth offers multipath resolution, which when properly treated can enhance system's performance and reliability. Signal distortion however, may prohibit system's optimum performance. It is more efficiently treated directly into the time-domain. The lack of information on the propagation of UWB signals in a complex environment, other than single reflected and diffracted waves, was tackled in this work. Easy-to-use and accurate reflection and transmission coefficients for a wave impinging on a dielectric slab were deduced. An algorithm for the prediction of a signal, which is multiply diffracted waves on an number of absorbing knife-edges and/or imperfect conducting wedges was also implemented. The algorithm accurately took into account the arisen higher-order fields, that are created in such cases, according to the Uniform Theory of Diffraction. A tool for signal prediction in a complex environment was constructed, based on the environment discretisation into tiles and segments. Its validity was initially tested for the narrowband case, by comparing its predictions with measurement, with a quite good agreement. Then, it was modified, so as to incorporate the dispersive nature of the channel. This was accomplished in the time-domain, where the TD ray-trace model not only predicts the arrival times of the multipaths but also their shape. The results were compared with measurement data collected with a VNA.

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Communication systems are susceptible to degradation in performance because of interference received through their side lobes. The interference may be deliberate electronic counter measure (ECM), Accidental RF Interference (RFI) or natural noise. The growth of interference communication systems have given rise to different algorithms, Adaptive array techniques offer a possible solution to this problem of interference received through side lobes because of their automatic null steering in both spatial and frequency domains. Key requirement for space-time architecture is to use robust adaptive algorithms to ensure reliable operation of the smart antenna. Space division multiple access (SDMA) involves the use of adaptive nulling to allow two or more users (mobiles) in the same cell to share same frequency and time slot. One beam is formed for each user with nulls in the direction of other users. Different approaches have been used to identify the interferer from desired user. Thus a basic model for determining the angle of arrival of incoming signals, an appropriate antenna beam forming and adaptive algorithms are used for array processing. There is an insatiable demand for capacity in wireless data networks and cellular radio communication systems. However the RF environment that these systems operate in is harsh and severely limits the capacity of traditional digital wireless networks. With normal wireless systems this limits the data rate in cellular radio environments to approximately 200 kbps whereas much higher data rates in excess of 25Mbps are required. A common wireless channel problem is that of frequency selective multi-path fading. To combat this problem, new types of wireless interface are being developed which utilise space, time and frequency diversity to provide increasing resilience to the channel imperfections. At any instant in time, the channel conditions may be such that one or more of these diversity methods may offer a superior performance to the other diversity methods. The overall aim of the research is to develop new systems that use a novel combination of smart antenna MIMO techniques and an advanced communication system based on advanced system configuration that could be exploited by IEEE 802.20 user specification approach for broadband wireless networking. The new system combines the Multi-input Multi-output communication system with frequency diversity in the form of an OFDM modulator. The benefits of each approach are examined under similar channel conditions and results presented.

Wireless technology constitutes the basis of the majority of modem communication systems. The deployment of wireless systems mainly concerns data services such as mobile and broadcasting applications, or target identification and military services. The key element for the successful planning of any kind of wireless network is the detailed and in depth knowledge of the propagation channel. The mobility of the user and the physical obstructions that may intervene in the propagation path between the communication points cause distortion to the transmitted information. The understanding of the propagation conditions and the channel characterisation is achieved either by extensive measurement campaigns or by employing sophisticated propagation algorithms. Since the measurement campaign is an expensive and time consuming task, contemporary research is focused on the development of deterministic models that can accurately predict the channel behaviour in real environments. The demand for high data delivery services in modem communication systems requires the utilisation of large bandwidth at high frequency regions of the available spectrum. Therefore, asymptotic high frequency modelling techniques and relevant algorithms have emerged as the major propagation modelling tools for modern radio systems analysis and design. In this thesis, we address the problem of high frequency diffraction over complex structures and scenarios that incorporate a cascade of physical canonical obstructions in the propagation path between the two ends. New formulations are derived for field predictions over rounded surfaces and a cascade of multi-shape structures. The Uniform Theory of Diffraction (UTD) is applied in all the work and it is further extended to account for transition zone diffraction over scenarios that incorporate arbitrary multiple canonical objects being multi-shaped in nature. The concept of continuity equations and slope diffraction are also emphasized. The simulation results show uniform and accurate field predictions and extensive comparison tests are performed with other diffraction theories and measurements. The developed formulations are incorporated in a propagation tool for irregular terrain channel modelling. An unambiguous terrain modelling algorithm is synthesized and used to assign optimum fitted canonical shapes to the terrain irregularities. The results of the simulations are compared with real measurements over irregular scenarios and a very good fit is observed. The importance of the choice of the used canonical shape to the terrain modelling is also highlighted.

In this thesis, we investigate the frequency division duplex (FDD) mode of the downlink of UMTS terrestrial radio access (UTRA) focusing on the signal to interference ratio (SIR) estimation for the closed loop power control (CLPC), diversity exploitation in both spatial and temporal domains and the suppression of multi-access interference that is encountered in handover regions, with the aid of a calibrated link-level simulator. Firstly, SIR estimation methods are studied for single and two-antenna transmissions and it is shown that when the common pilot channel (CPICH) is available, SIR could be estimated on that and related to the SIR for the dedicated physical channel (DPCH) through a simple relation. This way, a reduction in the overhead of the slot formats specified by the 3GPP, could be obtained. Secondly, factors influencing the handover performance such as the multipath fading correlation between radio channels of the two links, limited number of Rake fingers in a UE and imperfect channel estimation that cannot be modeled adequately at the system-level are investigated via link-level simulations. It is shown that the geometry factor has an influence on the handover performance and exhibits a threshold value (which depends on the correlation of the two links) above which the capacity starts degrading. The variation of the handover gain with the CLPC step-size, space-time transmit diversity (STTD) and receive antenna diversity is also quantified. Thirdly, blind interference suppression techniques are studied for the rejection of multi-access interference in handover regions. It is shown that the CLPC acts as an effective solution to the mismatch problem associated with the minimum output energy (MOE) detector. Furthermore, two methods are proposed for increasing the convergence speed of the MOE detector. Finally, chip-interleaved induced time diversity is investigated for multimedia broadcast / multicast services (MBMS) in UMTS, as a method of enhancing the downlink capacity. It is shown that the chip block interleaving with a block length of half the spreading factor provides similar diversity gain (by using only one transmit antenna) as that provided by STTD, but at the cost of an additional delay that is equal to the interleaving depth. Simulation results are presented for both the terrestrial and satellite modes of MBMS delivery for a range of mobile velocities.

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Radio communication systems operating at microwave frequencies are strongly attenuated by hydrometeors such as rain and wet snow (sleet). Hydrometeor attenuation dominates the dynamic fading of most types of radio links operating above 10 GHz, especially high capacity, fixed, terrestrial and Earth-Space links. The International Telecommunication Unions – Radio Section (ITU-R) provides a set of internationally recognized models to predict annual fade distributions for a wide variety of individual radio link. However, these models are not sufficient for the design and optimisation of networks, even as simple as two links. There are considerable potential gains to be achieved from the optimized design of real-time or predictive Dynamic Resource Management systems. The development of these systems requires a joint channel simulation tool applicable to arbitrary, heterogeneous networks. This thesis describes the development of a network fade simulation tool, known as GINSIM, which can simulate joint dynamic fade time-series on heterogeneous networks of arbitrary geometry, spanning Europe. GINSIM uses as input meteorological and topological data from a variety of sources and numerically calculates the joint effects on fading on all links in a specified network. ITU-R models are used to transform rain rate into specific attenuation and to estimate the specific attenuation amplification due to non-liquid hydrometeors. The resulting simulation tool has been verified against ITU-R models of average annual fade distributions, fade slope and fade duration distributions, in the southern UK. Validation has also been performed against measured terrestrial and Earth-space link data, acquired in the Southern UK and Scotland.

The overall growth in cellular, fixed and satellite communications markets, has exceeded many expectations and there is a widespread anticipation that the demand for wireless telecommunication systems will continue to expand in the foreseeable future. Such systems rely in their planning, design and implementation on the availability of radiowave propagation models. In the particular case of land mobile radio systems and wireless fixed access systems, obstacles in the form of vegetation volumes, e.g formations of trees, are likely to influence radio propagation, giving rise to absorption and scattering of radio signals. In this context, this thesis investigates suitable techniques to characterise and model the effects of inhomogeneous volumes of vegetation on the propagation modes of radiowaves. The thesis proposes an enhanced model based on the Radiative Energy Transfer theory (RET) which was discretised to accommodate forests formed by different vegetation species with their distinct propagation characteristics. The discretised model computational structure, comprises several element cells, whose characteristic propagation parameters may be assigned independently. The discretised RET (dRET), is therefore capable of gathering the interactive responses between the element cells comprising the computational structure, leading to the determination of the received signal inside or around a given illuminated vegetation medium. The performance of the proposed model, was assessed utilising results from an extended range of measurements, carried out in different environments. Such measurements comprised those necessary for the model input parameters extraction. Others enabled the model assessment through comparison between the model predictions and the actual directional profile of the measured received signal results. An initial assessment of the model was carried out in the laboratory, using an idealised test forest formation placed inside an anechoic chamber, whereas the final model assessment was performed in an outdoor tree groupings formed by several different full size trees. Both indoor and outdoor measurements, confirmed good overall model performance and predictions of both absorption and scattering propagation modes caused by the presence of vegetation in the radio path. This was demonstrated at micro- and millimetre wave frequency bands, centered at 11.2, 20, 40 and 62.4 GHz frequencies. The thesis provides a valid tested method to evaluate the dRET propagation parameters for various isolated volumes of vegetation. Such parameters, may subsequently be utilized into the proposed propagation model, which is shown to be capable of dealing with typical and non homogeneous forests thereby effectively predicting the received signal directional profile at several locations inside and around the inhomogeneous forest. The thesis has many novel features. These include the development and extension of the basic dRET model removing many limitations. The parameter extraction including the effects of the receive antenna radiation pattern is another novel contribution. Further novelty lies in the application of the dRET model to mixed, finite and inhomogeneous vegetation formations. As a result of these refinements and extensions, the dRET propagation model has been shown to yield predicted results which agree well with measurements.