Diversity receiver for a serial HF modem

Abstract

Two versions of a high-frequency (HF) diversity combination structure for use with an equalizer were investigated via a modem simulation. The two equalizers differ only in the way the weighting coefficients are generated. The output of each receiver is processed by an automatic gain control circuit. This signal is demodulated and fed into a decision-feedback equalizer. The outputs of the two equalizers are multiplied by a weighting factor before summation. A decision is made on this output. A separate error signal is generated for each equalizer by computing the difference between the final decision and the output of each equalizer. This forms an open looped system with no feedback. The equalizers are made adaptive by use of the stochastic gradient algorithm. Results for the structures are presented which differ from those obtained by P. Monsen (1981) for a troposcatter diversity system. The difference is due to the different channel characteristics for which his work was done.<>