Received Electric Field Strength-Based Approach for Resolving Loran Positioning Ambiguity and Coverage Area Limitation

The long-range navigation (Loran) system serves as a reliable backup to the global navigation satellite system (GNSS) and holds strategic significance in critical applications. However, the Loran system faces positioning ambiguity and range limitation challenges due to its time difference positioning mechanism and the constraints of the station chain signal in the additional time difference ambiguity discrimination (ATDAD) approach. To address these issues, this paper proposes a received electric field strength ambiguity discrimination (REFSAD) approach based on the electric field strength (EFS) attenuation characteristics of the Loran signal. The research constructs a comprehensive attenuation model applicable to mixed sea-land propagation paths and designs an ambiguity resolution strategy that does not require additional station information, thus enabling reliable identification of the true position. Through comprehensive Monte Carlo simulations and field-based experimental validation, this study demonstrates that the REFSAD approach exhibits statistically significant performance advantages, with 98.5% of positioning results falling within the high success rate interval (80-100%), compared to 97.4% for the ATDAD approach. When the coverage area is expanded by a factor of 3.8, the REFSAD approach maintains robust performance, with 98.2% of results within the high success rate range. Field experiments conducted in the South China Sea further validated the efficacy of REFSAD in regions where ATDAD is inapplicable, yielding a 100% positioning success rate with a root mean square error (RMSE) consistently maintained below 20 meters, thereby satisfying maritime navigation accuracy requirements.