Evaluation of Tropospheric and Mixed Single - Dual Frequency Error Models in Advanced RAIM

Abstract

Advanced Receiver Autonomous Integrity Monitoring is a proposed evolution of RAIM to multi-constellation and dual frequency that is being standardized. Enabling dual frequency will have at least two effects. First, the error bounds on the pseudorange will be decreased substantially. As a result, the tropospheric residual error, which had very little effect in the user Protection Level in RAIM, will be more critical in ARAIM. Second, not all satellites will be dual frequency capable (at least initially for GPS). Only using the dual frequency satellites could result in a performance degradation compared to single frequency. To start addressing these points, in this work we: 1) evaluate the effect of tropospheric error models with correlation on ARAIM protection levels, 2) propose an implementation of mixed single frequency - dual frequency measurements and evaluate the potential performance improvements. For the first point, we find that introducing a tropospheric model with perfect correlation causes the HPL to slightly decrease in a Horizontal-ARAIM scenario and the VPL to increase by 10% in a Vertical-ARAIM scenario. For the second point, we find that introducing a mixed mode would allow users to benefit from dual frequency well before a full and redundant L1-L5 GPS constellation is available.