PPP/PPP-RTK open formats: Overview, comparison, and proposal for an interoperable message

This paper presents and reviews the main existing open specifications for PPP/PPP-RTK services, including satellite navigation providers (QZSS, Galileo, BeiDou, GLONASS) and other industrial or scientific initiatives (RTCM, SAPCORDA, 3GPP, IGS). To structure the comparison, we adapted PPP/PPP-RTK services to the well-known OSI model and defined them according to their properties in the OSI communication layers. We show how the proposed formats relate to the current standards, mainly RTCM SSR and CSSR, and what their differences and similarities are in terms of transmitted corrections and bandwidth. We compare the efficiency of the existing formats in two scenarios: a global PPP scenario with multi-GNSS corrections, and a regional PPP-RTK scenario, also multi-GNSS and including ionospheric corrections. We propose an interoperable format that can be an extension to CSSR and allows efficient transmission of corrections for both global-scale MEO-based PPP as well as nationwide IGSO/GEO-based PPP-RTK.