349394.pdf (13.6 MB)
Techniques of estimation for HF radio links
thesis
posted on 2010-11-29, 11:26 authored by R. HarunThe thesis is concerned with the estimation of the sampled
impulse-response of time-varying voiceband channels, and in particular
with the proposed synchronous serial transmission of 16-level quadrature
amplitude modulated digital data signals at 9600 bit/s over HF
radio links. With such a system, the optimum detector at the receiver
is a maximum likelihood detector implemented, for example, using the
Viterbi algorithm. In this case, the detector requires knowledge of
the sampled impulse-response of the channel. Channel estimators can
also be used for estimating the response of any time-varying linear
bandpass channel and need not be restricted in use only with a
maximum likelihood detector. They may be employed in any such
application where a time-varying channel must be tracked to ensure
the correct operation of the detector.
The thesis includes a description of the ionospheric propagation
medium, with particular emphasis on the nature of the impairments that
are likely to be encountered by the data signal. An appropriate model
of the HF channel is simulated for subsequent use in testing the
channel estimators. A summary is also given of the more important
forms of channel estimators that are used for time-invariant or
slowly time-varying channels.
The characteristics of the HF radio medium may vary rapidly
with time, so an estimator based on the Kalman filter is investigated
in order to exploit the fast tracking capability of the filter. It is shown that inadequate modelling of the channel by the Kalman
filter results in suboptimum performance (in the minimum mean square
error sense) of the estimator, however, this can be improved by
including a suitable predictor. The performance of the Kalman
filter estimator, with and without the predictor, is then compared
with the corresponding estimator which uses a feedforward transversal
filter.
The recently developed HF channel estimator based on the
feedforward transversal-filter estimator is also investigated, but
it is tested here over the simulated HF radio links with three
independent Rayleigh fading sky waves, which represent typical
poor conditions over actual links. Various degrees of prediction
are also studied and based on the results, a change in the degree
of prediction from that previously proposed is suggested as a
better arrangement for use with the estimator when there are three
sky waves. Finally, it is shown that a considerable reduction in
the equipment complexity can be achieved by exploiting a selfcorrecting
property of the estimator that has been discovered.
History
School
- Mechanical, Electrical and Manufacturing Engineering
Publisher
© R. HarunPublication date
1984Notes
A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.EThOS Persistent ID
uk.bl.ethos.349394Language
- en