Assessment of Network-based Positioning Performance Using GPS Alone versus GPS and GLONASS Combined

As it is anticipated that the full operational capability of GLONASS will be achieved in the very near future, GLONASS is now attracting surveyors' attention, with questions being asked on how much improved accuracy can be obtained if GPS and GLONASS were used together. Such a performance assessment has been undertaken in the past; however, most of the tests were conducted with a limited number of available (at the time) GLONASS satellites. It is timely to re-assess the performance because most networks of continuously operating reference stations (CORS) are now equipped with receivers that can track both GPS and GLONASS satellites, and therefore network-based positioning with combined GPS and GLONASS observations is possible. This paper compares the network-based positioning results with GPS measurements only versus the use of combined GPS and GLONASS measurements, under various sky view conditions. The benefit of adding GLONASS measurements to GPS measurements is more obvious when a limited number of satellites are available due to the fact that sky view is partially blocked. Comparing the GPS-only solution with the GPS+GLONASS solution, the accuracy improves by approximately 2mm and 3mm in the 2-dimensional and 3-dimensional coordinates, respectively. However, the combined solution shows its clear advantage when GLONASS-only solutions are considered.