Novel Multichain-Based Loran Positioning Algorithm for Resilient Navigation

Intentional high-power global positioning system jamming is a significant threat for ships in the South Korean waters and has occurred multiple times in recent years. The South Korean government intends to utilize the existing long-range navigation (Loran) infrastructure to provide a backup navigation capability to maritime users. However, the observed accuracy of a conventional Loran positioning fix during a field test in Incheon, South Korea, was 592.88 m, far from the 20-m accuracy that the South Korean government tries to provide. The largest error source for Loran is the additional secondary factor (ASF) delay. A conventional time of flight based ASF correction is not applicable in Northeast Asia because several transmitters are not synchronized to universal time coordinated. Thus, we propose a time difference of arrival based ASF correction method that is applicable to the existing Loran signals in Northeast Asia. The demonstrated accuracy with this correction was 32.12 m when using a single Loran chain for positioning. In order to utilize the full capability of the observed signals from the five transmitters of two Loran chains in the region, we further propose a novel multichain-based Loran positioning algorithm. By applying this algorithm together with the ASF correction method, we achieved a 15.32-m accuracy with 100% position availability. This result shows the potential of the existing Loran transmitters in Northeast Asia to provide a reliable and accurate backup maritime navigation service.