A Study of the Distortion and Propagation Time-Delay of Loran-C Pulse Wave Based on a Model of the Propagation Path.

The main cause of the absolute positioning error in the Loran-C system is in the occurrence of the propagation time delay error caused by the fact that the propagation speed of the pulse signal on the actual propagation path is different from that assumed in the formation of the Loran-C maritime chart. The propagation path characteristics not only cause the propagation time delay of each received pulse signal but also generates waveform distortion in the received pulse. Hence, it is possible to estimate the propagation delay time by means of this waveform distortion. At present, a measure of the distortion of the pulse waveform distortion of the Loran-C is envelope to cycle difference (ECD). In this paper, as a new measure for the pulse-wave distortion to estimate the propagation time delay, CHACLE, or change of half-cycle length, is proposed. A method for correction of the absolute positioning error is provided based on the estimation of the propagation time delay from the measures of the waveform distortion (CHACLE end ECD) by means of the simplified propagation path for an easy analysis and of the general propagation path. It is demonstrated that CHACLE is superior to ECD in terms of the effect of correction. Further, to confirm the validity of the correction method proposed in this paper, the present method is applied to a propagation path model resembling the mixed propagation path used in the United States to estimate the pulse time delay. It is confirmed that the absolute positioning error can be reduced to less than about 20 percent. [ABSTRACT FROM AUTHOR]