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 a viation and land-mobile receivers in the US and Canada. The designers of Loran-C systems for use in Europe have been obliged to pay consider able attention to CWI in predicting coverage. The paper contains a uni fied analysis of the effects of the phase-decoding and averaging opera tions of receivers on CWI and provides a quantitative assessment of re ceiver performance under CWI conditions. The analysis covers synchrono us, near-synchronous and asynchronous interference. It shows that, in contrast to asynchronous interference, synchronous and near-synchronou s CWI are attenuated by phase decoding and averaging within periods of two group repetition intervals and that longer periods of averaging d o not improve performance. Front-end filtering is incorporated into th e analysis by considering not only the attenuation of interference tha t it provides but also the delay and distortion it causes to Loran-C s ignals. Both the phase-tracking and the cycle-selection functions of r eceivers are examined. The results of the analysis, which are confirme d by computer simulation, are presented in a form that will be of dire ct use to the designers of Loran-C receivers and systems.