Comparing the 'Big 4' - A User's View on GNSS Performance

Abstract

With BeiDou-3 and Galileo complementing the legacy systems GPS and GLONASS, a total of four global navigation satellite systems (GNSS) has now become available that offer free and ubiquitous access to accurate positioning, navigation, and timing (PNT). Following an overview of the system status and capabilities, we compare the "Big 4" GNSSs in terms of signal and clock characteristics. The signal-in-space range error (SISRE) are assessed and related to the achievable single-point positioning accuracy. Furthermore, service stability and availability aspects are adressed. With respect to geodetic users, we discuss the determination and prediction of GNSS satellite orbits and clocks from measurements of global receiver networks, which forms the basis for precise point positioning applications. Within the International GNSS Service (IGS) various analysis centers independently provide such products based on data of the IGS multi-GNSS network. The challenges in generating precise orbit and clock solutions for the individual constellations are discussed, and the significance of satellite metadata knowledge is highlighted.