Preliminary Study of Multichain-Based Loran Positioning Accuracy for Dynamic Users in South Korea
Pyo-Woong Son and Jiwon Seo, Yonsei University, Republic of Korea
Global navigation satellite systems (GNSS) have been used in wide areas and become the primary source for navigation. However, GNSS is vulnerable to intentional or unintentional radio frequency interference (RFI) due to its weak signal strength. Because it is important to provide resilient position, navigation, and timing (PNT) services, the necessity of a complementary PNT system has been emphasized.
The Long Range Navigation (Loran) system is a terrestrial high-power radionavigation system using 100 kHz signals and it can be a complementary PNT system for maritime users because of its robustness to RFI even though its positioning accuracy is low comparing to GNSS. The U.S. Federal Radionavigation Plan considered the enhanced Loran (eLoran) as a potential complementary PNT system to GPS, and the General Lighthouse Authorities of the U.K. and Ireland (GLA) has established a prototype eLoran system and declared the Initial Operational Capability (IOC) of eLoran in 2014. South Korea has suffered from GPS jamming attacks from the North and decided to deploy a nationwide eLoran system. However, the Korean eLoran project has been delayed several times due to contractual problems and other issues. Thus, we have developed a multichain-based Loran positioning method to improve the current Loran positioning performance, which does not require the hardware upgrade of Loran transmitters to eLoran transmitters.
Conventional Loran transmitters are time-synchronized only within the same Loran chain, and thus the transmitters from different chains cannot be utilized together to form a time difference of arrival (TDOA) value. If we can form a TDOA value between transmitters from different chains, the navigation performance of Loran can be significantly improved and its performance would be similar to the performance of the “all-in-view” positioning of eLoran.
We have demonstrated about a 15-m (95%) accuracy for a static user by applying our multichain-based Loran positioning algorithm and TDOA-based additional secondary factor (ASF) correction method when the user is at about 12 km distance from a differential correction station. However, experimental validation for a dynamic user has not been performed in the previous study. In this paper, we study the improved Loran positioning performance for a dynamic user based on the multichain-based positioning algorithm and the existing Loran infrastructure in the Northeast Asia.
TDOA-based ASF maps, which are different from the conventional TOA-based ASF maps for eLoran, were generated to compensate for the spatial ASF errors. When we produced the spatial ASF maps, a grid size of 500 m was used and we drove the data collection vehicle at a low speed. Considering the speed of a typical passenger ship, we studied the positioning performance for dynamic land users with a speed of 40 km/h. The differential correction station for the experiment is within a 30-km distance from the dynamic users. In general, the performance of the temporal ASF correction depends on the update interval and the averaging time to generate the corrections. In order to suggest optimal values for these parameters for dynamic users, we analyzed the field test data with various averaging times and update intervals.