Multi-GNSS Precise Point Positioning Software Architecture and Analysis of GLONASS Pseudorange Biases

With expanding satellite-based navigation systems, multi-Global Navigation Satellite System (GNSS) Precise Point Positioning (PPP) presents an advantage over a single navigation system, which improves position accuracy and enhances availability of satellites and signals. The York GNSS PPP software was developed using C++ in the Microsoft.Net platform to utilize the existing multi-GNSS satellite constellations based on the software processor used by the Natural Resources Canada (NRCan) PPP online service. The software was built as a robust, scalable, modular tool that meets the highest of scientific standards compared to existing online PPP engines.There exists a correlation between receiver stations from heterogeneous networks, such as the IGS, in GNSS PPP processing and the increase in magnitude of the pseudorange and carrier-phase biases in both GPS + GLONASS and GLONASS-only PPP solutions. The correlation is due to mixed receiver and antenna hardware as well as firmware versions. Unlike GPS, GLONASS observations are affected by the Frequency Division Multiple Access (FDMA) satellite signal structure, which introduces inter-frequency channel biases and other system biases. The GLONASS pseudorange inter-channel frequency biases show a strong correlation with different receiver types, firmware versions and antenna types. This research estimated the GLONASS pseudorange inter-frequency channel biases using 350 IGS stations, based on 32 receiver types and 4 antenna types over a period of one week. An improvement of 19% was observed after calibrating for the pseudorange ICBs, in the horizontal components respectively, considering 20 minutes convergence period.