Enhancing Availability of SS-RAIM Based CDGNSS Using Integer Aperture Bootstrapping

Carrier-phase Differential Global Navigation Satellite System (CDGNSS) is gaining prominence in autonomous vehicles that require precise and reliable navigation. Our team proposed an integrity architecture based on Solution Separation Receiver Autonomous Integrity Monitoring (SS-RAIM) for CDGNSS. In this previous work, precise fixed position solutions are employed only when the incorrect fix probability, computed from filter covariance matrices, falls below a predefined level depending on integrity risk requirements. However, this approach may unnecessarily restrict users to float position solutions since covariance matrices do not reflect the quality of current ambiguity estimates calculated from actual measurements. This paper proposes a method to utilize the Integer Aperture Bootstrapping (IAB) test within the SS-RAIM architecture to determine fixed position solution usage. The IAB test directly evaluates measurement quality using estimated float and fixed ambiguity solutions. For ambiguities passing the IAB test, the incorrect fix probability can be controlled by adjusting the test parameter. The IAB test provides a closed-form analytical expression for this incorrect probability, enabling precise integrity risk evaluation and Protection Level (PL) computation. We set the IAB test parameter to ensure that ambiguities passing the test meet specified incorrect fix probability constraints. Furthermore, this paper examines how IAB test results affect the Probability Density Functions (PDFs) of float and fixed position solutions for exact PL computation. Since the IAB test directly assesses current measurement quality, the available measurement space depends on test results, leading to changes in position solution PDFs. We derive these changes in PDFs depending on IAB test results and incorporate them into PL computation. Simulation results demonstrate that PLs are reduced by using the IAB test when compared to previous approaches.