Analysis and Simulation of a Hybrid Filter to Cancel Cross Rate Interference in Loran System

The use of Loran system is a strong defense for navigation due to its immunity against jamming and ability to penetrate indoor locations. This system can be used as a navigation aid system especially in times of crisis and GPS disconnection. One of the most important error sources in Loran navigation system is the Cross Rate Interference (CRI). If such interference is not eliminated, the accuracy of the navigation will considerably be decreased. The aim of this study was to eliminate the CRI in Loran systems using a hybrid filter and loran signal analysis in frequency domain. The results demonstrated that the hybrid filter could eliminate the interference of the irritating chain completely and, therefore, there was not any destructive effect on the desired spectrum signal.  However, the spectral lines located in the frequencies which are equal to reverse of the greatest common divisor between the Phase Code Interval (PCI) of desirable chain and adjacent irritating ones could not be eliminated with the proposed phase coding approach. Spectral lines that  could not be eliminated, are few and do not have significant effects on the system performance. In practice, it is feasible to completely eliminate the remaining spectral lines using two or three of very narrow-band notch filters without causing significant effects on the standard Loran spectrum. Furthermore, Loran system has been analyzed in frequency domain, using the proposed filter in order to discuss the design of the new PCI in eliminating CRI effects caused by Loran irritating chains.