Using Subsequent Mask Information for SBAS and SLAS

Abstract

The SBAS (Satellite-Based Augmentation System) is the standard system augmenting GNSS, while QZSS (Quasi-Zenith Satellite System) offers SLAS (Submeter-Level Augmentation Service) service. Both SBAS and SLAS transmit the mask information indicating which GNSS satellites or ionospheric grids are being augmented, thus corrections and integrity information must be interpreted through the associate masks. Because a mask comes with identifier, messages referencing a mask could refer to not only preceding masks but also subsequent masks with the corresponding identifier. TTFF (Time to First Fix) of the SBAS and SLAS, determined as the time to receive navigation messages of at least four GNSS satellite and the associate augmentation information, could be shortened in case that the set of augmentation information is collected earlier by using subsequent masks. Here the author explains usage of subsequent masks in addition to preceding masks and reports its effect to shorten TTFF up to 110 seconds and 8 seconds for MSAS, Japanese SBAS, and SLAS, respectively, near Tokyo, Japan.