Adaptive channel estimator for an HF radio link

A simple estimator designed for a 2400-b/s modem is a development of the conventional gradient estimator and uses a polynomial filter that gives a prediction of the channel response. A description is given of new estimators that are developments of the simple estimator but make no use of any knowledge of the number of different paths. The new estimators have performances intermediate between those of the simple and improved estimators, but are only a little more complex than the simple estimator. The new estimators are studied for a particular QPSK modem that operates at 4800 b/s over voiceband HF radio links. Results of computer simulation tests are presented, comparing the accuracies of the channel estimates given by different estimators, and hence suggesting the most suitable of these