Integrity Support Message Generation Algorithm Prototype

Advanced RAIM service relies on the provision of an Integrity Support Message (ISM) containing information on the Constellation Service Provider (CSP) performance and provided by an external entity, the so called ISM Generator (ISMG). This paper describes the design and optimization of the ISM generation algorithms performed in the framework of the development of an ARAIM demonstrator (ARTEX). The design started with a critical review of the method to identify the worst Signal In Space Ranging Error (SISRE): an alternative to the Worst User Location approach was developed to avoid the generation of not unimodal SISRE distributions and to optimize the user availability by reducing the ISM parameters. Besides the accurate representation from a statistical point of view of the SISRE distribution was investigated developing a concept to assess sampling rate and number of effective samples. The method to derive consistent set of ISM parameters, ensuring the identification of a continuous bounding curve is also described in this work. Finally the ARAIM single frequency case was investigated and a methodology to monitor instantaneous BGD residuals and their contribution to the satellite fault probabilities was developed. The paper provides a description of these design choices together with the justifications based on real measurements.