# An Improved RAIM Availability Assessment Method Based on the Characteristic Slope

## TL;DR

This paper introduces a new method for assessing RAIM availability that reduces on-board computation while maintaining accuracy.

## Contribution

The novel slope-based RAIM availability assessment method matches ideal PL-based accuracy with reduced on-board computation.

## Key findings

- The slope-based method achieves the same RAIM availability assessment as the ideal-PL-based method.
- The slope threshold can be calculated offline, reducing on-board computational burden.
- Simulations confirm the improved method's performance compared to existing PL-based approaches.

## Abstract

The availability assessment is an important step for onboard application in Receiver Autonomous Integrity Monitoring (RAIM)s. It is commonly implemented using the protection level (PL)-based method. This paper analyzes the deficiencies of three kinds of PL-based methods: RAIM availability might be optimistically or conservatively assessed using the classic-PL-base method; might be conservatively assessed using the enhanced-PL-based method, and neither be optimistically nor conservatively assessed using the ideal-PL-based method with the cost of large calculation amount on-board. An improved slope-based RAIM availability assessment method is proposed, in which the characteristic slope is designed as the assessment basis, and its threshold that can exactly match the integrity risk requirement is derived. The slope-based method has the same RAIM availability assessment result as the ideal-PL-based method. Moreover, because the slope threshold can be calculated offline and searched online, the on-board calculation burden can be reduced using the slope-based method. Simulation is presented to verify the theoretical analysis of the RAIM availability assessment performances for the three PL-based and the slope-based methods.