The widespread use of radio frequencies of wavelengths small compared with the major terrain irregularities has led to the development of theoretical deterministic models for the prediction of field strengths over paths of given profile. The examination of these models is the main objective of the present thesis. Although present radio links are mainly based on empirical developments, theoretical approaches may offer considerable alternative for the design of future wireless communications systems. It is well known that the methods applied are based on multidimensional integral equations, which only in certain and idealised cases reduce to a practical form suitable for realistic utilisation. The present work attempts to reveal the physical processes that characterise the radio channel and how these are approached by certain models for common engineering applications. Since the major mechanism of propagation in radio environments is diffraction, extensive analysis is performed for this physical process. In particular, a new fast implementation of the Vogler multiple knife-edge diffraction algorithm is described with the additional benefit of improved accuracy at path profile configurations where the original solution fails considerably. An entirely new approach to slope-Uniform Theory of Diffraction is introduced and shown to produce essentially identical results to Vogler within much shorter computation times. This is applied to 3D urban propagation and to terrestrial fixed links and is shown to produce accurate results compared with measurements. Finally, new physical-statistical models are introduced in order to overcome the excessive cost of high resolution building databases. Application to both mobilesatellite and to broadband fixed access systems revealed a high degree of statistical accuracy
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:343526 |
| Date | January 2001 |
| Creators | Tzaras, Constantinos |
| Publisher | University of Surrey |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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