Reference station network based RTK systems-concepts and progress

The limitation of single base “real-time kinematic” (RTK) techniques is the distance between base receiver and the rover receiver due to distance-dependent biases, namely orbit bias, ionosphere bias and troposphere bias. Techniques have been developed to overcome this distance dependence using a network of GPS reference stations spread over a wide geographic area. Because the measurement biases will be modelled and corrected for, the positioning accuracy will be almost independent of the inter-receiver distance. Since the mid-1990s investigators have been investigating the optimal means of processing reference receiver data, and then providing ‘correction’ information to users, in real-time. This technique is now generally referred to as Network-RTK. In 1993 the International Association of Geodesy (IAG) established a Special Study Group on “Wide Area Modelling for Precise Satellite Positioning” . This paper focusses on the progress made during the last few years in designing Network-RTK architectures and the associated data processing algorithms and issues. Although many university investigators have been researching the fundamental challenges in functional and stochastic modelling, currently there is only one commercially available Network-RTK product, the Trimble VRS. However, with the use of the Internet as the primary data communication link, it is predicted that many more implementations of Network-RTK will come ‘online’, at various sites around the world, over the next few years.