Preliminary Exploration and Verification of Timing Advanced RAIM

This study conducted a preliminary exploration of the timing advanced receiver autonomous integrity monitoring (T-ARAIM) algorithm, which enables receivers to detect and exclude faults locally, thereby enhancing the reliability of timing solutions. The T-ARAIM algorithm builds upon the baseline ARAIM algorithm, incorporating modifications in three critical aspects: risk budget allocation, timing solution estimation, and timing protection level (TPL) calculation. These modifications enable the T-ARAIM algorithm to focus solely on timing solutions rather than positioning solutions. T-ARAIM can either estimate the receiver coordinates and intersystem bias (ISB) or fix them as constants. Fixing the receiver coordinates and ISB significantly increases redundancy in observations, greatly improving the availability of T-ARAIM. A ten-day simulation experiment indicates that with fixed receiver coordinates, T-ARAIM can achieve global availability even using a single constellation. Experiments using actual observations indicate that TPL can fully bind timing errors of all experimental stations. Fixing receiver coordinates improves timing accuracy and reduces TPL by approximately 12 ns, significantly enhancing the availability of T-ARAIM. Fixing the ISB reduces TPL by approximately 2 ns with almost no impact on the accuracy of timing solutions. Results from both simulation experiments and experiments using actual observations demonstrate good consistency.