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Title: Theoretical and experimental study of LOS refractive multipath at 18 GHz.
Author: Hewitt, A.
ISNI:       0000 0001 3555 508X
Awarding Body: Portsmouth Polytechnic
Current Institution: University of Portsmouth
Date of Award: 1986
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This thesis describes research into multipath frequency-selective fading over a wide bandwidth (100's of MHz). In particular it focuses on the use of wideband fade measurements f0r the study of the underlying multipath propagation. The early chapters are concerned with a survey of the 0verall topic of multipath and of the physical processes involved, including the geometrical optics model of propagation. The thesis then discusses wideband channel measurement techniques such as the popular frequencysweep method. It also describes in some detail the "wideband experimental system" developed by Portsmouth Polytechnic and Rutherford Appleton Laboratory. This system uses a PRES cross-correlation approach rather than a frequency-sweep, and it is the equipment that has been used in this research. The central interest of the research is the estimation of multipath "ray" delays and amplitudes using wideband fade measurements. Because of its inherent limitations of resolution and sidelobes, the Fourier transform is rejected in favour of modern "parametric" spectral methods. These are discussed, and one in particular, the modified Prony algorithm, is selected. It is applied to a database of 250 MHzbandwidth measurements made in the laboratory using the wideband system and a "multipath simulator" network to simulate real operational situations. The results obtained demonstrate the algorithm's ability to resolve rays closer than the Fourier limit and to assign amplitudes which enable accurate reconstruction of the original measurement. Statistical analysis of the results also reveals a de~~ee of systematic bias in the delay and amplitude estimators. As well as the laboratory measurements, the algorithm is applied to a selection of "in-the-field" multipath measurements obtained in the UK and in France. These illustrate the applicability of the method and they also highlight certain limitations. Appendices to the main thesis include a study on the use of a simple 2-ray propagation model to facilitate the interpretation of the delays and amplitudes obtained. There is also a detailed mathematical analysis of the PRBS technique as used in the wideband system which indicates the system-dependent nature of the transfer-function estimates generated.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Communication systems & telecommunications