Novel Multi-Chain-Based Loran Positioning Algorithm for Resilient Navigation

Intentional high-power GPS 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, 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 (TOF)-based ASF correction is not applicable in Northeast Asia because several transmitters are not synchronized to Universal Time Coordinated (UTC). Thus, we propose a time difference of arrival (TDOA)-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 multi-chain-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.