Assessment of Dual-frequency Signal Quality Monitor to Support CAT II/III GBAS
Résumé
This paper assesses the performance of the signal quality monitors for the Ground-Based Augmentation System (GBAS) which supports Category (CAT) II and III precision approach. Three types of monitors are used for signal deformation faults: Honeywell signal quality monitor (SQM), ENAC Code-Carrier Divergence (CCD) monitor and a proposed Divergence-Free (DF)-Innovation monitor. The existing Honeywell SQM and ENAC CCD monitors have some response time due to the smoothing filter used for their metrics. Consequently, the performance of those monitors is limited right after the fault onset. To improve the monitor performance in this time period, the DF-Innovation monitor has been proposed. The performance of the monitors has been assessed by comparing the minimum value of the probabilities of missed detection of three monitors and the required probability of missed detection according to the differential range error, which is defined in the standard document. As a result, for GBAS Approach Service Types (GAST) F, the probability of missed detection of the monitor was compliant with respect to the requirements for all fault cases and receiver configurations, for GPS L1/L5 and Galileo E1/E5. In addition, we observed that the proposed DF-Innovation monitor is effective in reducing time delay, which is the required time at airborne from filter initialization time to the time when the airborne user incorporates the measurement and correction for navigation. To be more specific, the use of the proposed monitor can reduce the time delay by 80% compared to the case without using the proposed monitor, and moreover, it can even reduce the value of time delay below 50 second, which is the recommended value currently.
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