Network RTK Versus Single Base RTK - Understanding the Error Characteristics

The use of reference station networks has become the ubiquitous solution for high precision satellite positioning applications. The main systematic errors affecting the RTK rover performance are multipath, atmospheric and ephemeris errors. Whereas single base RTK is limited with respect to the distance between reference and rover the network RTK approach offers the possibility to increase the coverage area. It ideally leads to a situation in which the positioning error is independent of the rover position in the area of the network. One technique proven in production systems for network RTK is the Virtual Reference Station paradigm, simulating a local reference station for the user. Ideally, this provides a data quality equivalent to a very close reference station. This paper gives a quantitative assessment of the data characteristics leading to the known rover performance improvements using data from different RTK/VRS networks from Asia, Europe, Australia and the U.S.A. One major effect from the application of VRS can be seen as a significant reduction of the temporal correlation of the ionospheric residual errors. Autocorrelation functions respective the autocorrelation time constants show this clearly. Improvements for multipath, tropospheric delay and ephemeris errors are achieved by VRS techniques, too. Detailed analyses explain the reduction of initialization times, improvement in position accuracy and increase in reliability seen in network RTK systems. This is not only due to the mitigation of systematic errors. It is demonstrated that network RTK does not only reduce the errors but also changes the error characteristics which lead to an additional performance increase in RTK positioning.