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Automatic equalisation of TV telephone channels

Lee, TT 1975 , 'Automatic equalisation of TV telephone channels', Unspecified thesis, University of Tasmania.

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One possible way of implementing the TV telephone system
is by transmitting the video signal over existing telephone
cables. Not only is this attractive from an economical standpoint,
it also appears to be technically reasonable. However, there are
certain basic problems to be considered, particularly in reference
to baseband analogue transmission over the local subscriber
For a start, it is expected that fixed equalisers will
be required at regular intervals along the line to compensate
for attenuation losses. These equalisers will have to be
designed on the basis of some average channel characteristic.
As a result, there will be uncorrected losses owing to deviations
from the average characteristic for the different TV telephone
connections. These and other channel imperfections will have
to be compensated automatically.
This thesis is concerned with the design and testing of
an automatic equaliser to serve the above-mentioned purpose.
Chapter One outlines the basic principles of operation, together
with the performance criterion used to assess the degree of
optimality achieved. The mode of operation is discussed, as
well as the different possible choices and arrangements of the
basic equaliser function.
To provide further insight into the process, a mathematical
study is given in Chapter Two. This includes considering the
control algorithm for tap adjustments, the conditions for
convergence, and the choice of step size to be used. The analysis
is extended to cover adaptive operations, where the information
for updating the tap settings is not exactly available but must
be estimated on-line. In addition, ways of improving performance
through modifying the basic equaliser structure (such as using
a feedback configuration instead of the conventional feedforward
arrangement) are also considered.
The theoretical investigation is carried further in
Chapter Three. The effect of noise on equaliser capability and performance is discussed, along with the need for a
defined standard of signal-to-noise ratio for acceptable
transmission. This is followed by an evaluation of the
effect of having a non-linearity in the feedback loop.
The resulting system is studied, using some form of linearised
analysis. Some reference to stability requirements is also
In order to confirm some of the theoretical findings
of the previous chapters, and to demonstrate the potential
of automatic equalisation in practice, a real-time
experimental system was designed and assembled. Chapter
Four outlines the work involved and the problems encountered.
The choice of suitable test signals and their method of
generation are discussed in some detail.
After the experimental equaliser had been built,
various tests were conducted, using 500 yards of 4 lb P.I.U.T.
cable to represent the TV telephone channel. The tests
were designed to provide an estimate of some of the critical
parameters and an assessment of system capability. The
nature of the tests, with the results obtained, are given
in Chapter Five.
The implications of the test results are discussed in
Chapter Six. The areas requiring further investigation
are identified. A preliminary discussion of the problems
involved in integrating the system into the existing
telephone network is also included.
The conclusion summarises the state of progress in
evaluating the practicability of the automatic mean square
equaliser for TV telephone applications.

Item Type: Thesis - Unspecified
Authors/Creators:Lee, TT
Keywords: Automatic control, Telephone communication channels
Copyright Holders: The Author
Copyright Information:

Copyright 1975 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (M.Eng.Sc.)--University of Tasmania, 1976. Includes bibliography

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