Resilient code bias for assured PNT service

As the main means of the Global Navigation Satellite System (GNSS) signal enhancement, the flex power impacts the robustness and availability of the positioning, navigation, and timing (PNT) service. However, routine code bias products provided by the agencies with low temporal resolution often fail to provide accurate values. To overcome the vulnerability of space-based PNT system and enrich resilient PNT theory, a resilient code bias concept is proposed to address limitations of the routine code bias. Firstly, the performance of two categories of routine code products, namely postprocessing code bias product and broadcast ephemeris parameters, is analyzed. Then, the concept of the resilient code bias is presented to solve the code bias problems related to defect prevention and system recovery under uncertainty in the complex environment such as flex power. Subsequently, a method for resilient code bias estimation is developed and four code bias states are defined, that are normal, flex, warning, and exceptional states. A resilient index (RI) is developed and estimated in real-time in the resilient code bias product to characterize the code bias features regarding availability, continuity, integrity, robustness, and accuracy. Resilient code bias is compatible with the characteristics of the routine code bias product in the normal state but switches the flex state in the flex power scenario. The characteristics of the resilient code bias product are analyzed for both normal and flex power scenarios, demonstrating its advantages across different states in the case of flex power for the BDS-2, BDS-3, and GPS systems.