Carrier wave interference and Loran-C receiver performance

Carrier wave interference (CWI) has been shown to be a serious problem which affects the operation of all Loran-C receivers in Europe, and aviation and land-mobile receivers in the US and Canada. The designers of Loran-C systems for use in Europe have been obliged to pay considerable attention to CWI in predicting coverage. The paper contains a unified analysis of the effects of the phase-decoding and averaging operations of receivers on CWI and provides a quantitative assessment of receiver performance under CWI conditions. The analysis covers synchronous, near-synchronous and asynchronous interference. It shows that, in contrast to asynchronous interference, synchronous and near-synchronous CWI are attenuated by phase decoding and averaging within periods of two group repetition intervals and that longer periods of averaging do not improve performance. Front-end filtering is incorporated into the analysis by considering not only the attenuation of interference that it provides but also the delay and distortion it causes to Loran-C signals. Both the phase-tracking and the cycle-selection functions of receivers are examined. The results of the analysis, which are confirmed by computer simulation, are presented in a form that will be of direct use to the designers of Loran-C receivers and systems