Theoretical and experimental study of LOS refractive multipath at 18 GHz.
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