Integrity Monitoring for Network RTK Systems

Ali Karimidoona, M. Sc. 

Main Supervisor: S. Schön

From the advent of the satellite positioning techniques, civil users have always been trying to find a way to have more accurate and precise coordinates of their position. Differential concepts, from early days of GPS, have been considered. Applying the RTCM format, made the transmission of corrections possible from reference stations to the users. At the first stage the corrections were cast to the users from one single station which was limited in some ways; degrading by increasing distance from CORS (Continuously Operating Reference Station) needed the same signals at reference and rover and remaining the reference station errors. In the next stage the Network RTK concept appeared. The concept of precise point positioning (PPP) is currently associated with global networks. Precise orbit and clock solutions are used to enable absolute positioning of a single receiver. However, it is restricted in ambiguity resolution, in convergence time and in accuracy. Precise point positioning based on RTK networks (PPP-RTK) overcomes these limitations and gives centimeter-accuracy in a few seconds.

Nowadays, the use of automatic applications of navigation is increasing rapidly. Autonomous moving objects (car, UAV, UMV, . . . ) are examples of these kinds of applications. The main navigation engine in these examples is GNSS positioning and the best performance which can be delivered is based on Network RTK solution. The performance of the navigation system depends on accuracy, continuity (temporal), availability (spatial) and integrity (reliability). Because of the complicated moving environment for these autonomous objects and the importance of safety issues especially in urban areas, integrity monitoring is of great importance in navigation systems. Up to now, the integrity definition and standards have been well established for aviation applications especially around airports which are mostly based on SBAS systems. But there is a lack of standard for integrity in the realm of RTK (PPP-RTK) positioning which can be useful in autonomous applications where high-precision GNSS positioning (carrier phase measurement) must be used.