Novel Techniques for Loran-C Skywave Estimation

Abstract

It is conventionally assumed that Loran-C receivers process only samples taken before the first skywave components arrive, 35-60 u s after the groundwave. This technique has significant limitations when implemented in receivers of finite bandwidth, which increase the rise times of the pulses and substantially reduce the amplitudes of the groundwave signals at the 30 KS point. For this reason, many current receivers take samples later in the pulse and so suffer skywave errors. This paper examines the consequences of this practice. It then proposes a new class of techniques to allow the onset of skywave signals to be detected so that the sampling point can be adjusted accordingly. Novel algorithms for distinguishing skywaves from the groundwave are presented. Their benefits, and the computing resources they require, are assessed. The paper includes theoretical analyses, simulations, and Monte Carlo experiments to demonstrate the performance of the techniques proposed.