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|Title: ||Channel estimators for HF radio links|
|Authors: ||Hariharan, S.|
|Keywords: ||High frequency radio band|
|Issue Date: ||1988|
|Publisher: ||© S. Hariharan|
|Abstract: ||The thesis is concerned with the estimation of the sampled impulse-response (SIR),
of a time-varying HF channel, where the estimators are used in the receiver of a
4800 bits/s, quaternary phase shift keyed (QPSK) system, operating at 2400 bauds
with an 1800 Hz carrier.
FIF modems employing maximum-likelihood detectors at the receiver require
accurate knowledge of the SIR of the channel. With this objective in view, the thesis
considers a number of channel estimation techniques, using an idealised model of
the data transmission system. The thesis briefly describes the ionospheric propagation
medium and the factors affecting the data transmission over BF radio. It then
presents an equivalent baseband model of the I-IF channel, that has three separate
Rayleigh fading paths (sky waves), with a 2Hz frequency spread and transmission
delays of 0,1.1 and 3 milliseconds relative to the first sky wave.
Estimation techniques studied are, the Gradient estimator, the Recursive leastsquares
(RLS) Kalman estimator, the Adaptive channel estimators, the Efficient
channel estimator ( that takes into account prior knowledge of the number of fading
paths in the channel ), and the Fast Transversal Filter (F-FF), estimator (which is a
simplified form of the Kalman estimator). Several new algorithms based on the
above mentioned estimation techniques are also proposed.
Results of the computer simulation tests on the performance of the estimators, over a
typical worst channel, are then presented. The estimators are reasonably optimized to
achieve the minimum mean-square estimation error and adequate allowance has
been made for stabilization before the commencement of actual measurements. The
results, therefore, represent the steady-state performance of the estimators.
The most significant result, obtained in this study, is the performance of the
Adaptive estimator. When the characteristics of the channel are known, the Efficient
estimators have the best performance and the Gradient estimators the poorest.
Kalman estimators are the most complex and Gradient estimators are the simplest.
Kalman estimators have a performance rather similar to that of Gradient estimators.
In terms of both performance and complexity, the Adaptive estimator lies between
the Kalman and Efficient estimators. FTF estimators are known to exhibit numerical
instability, for which an effective stabilization technique is proposed. Simulation
tests have shown that the mean squared estimation error is an adequate measurement
for comparison of the performance of the estimators.|
|Description: ||A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.|
|Appears in Collections:||PhD Theses (Mechanical, Electrical and Manufacturing Engineering)|
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