During the last decade the technique of CORS-based Network RTK has been proven capable of providing cm-level positioning accuracy for rovers receiving GNSS correction data from the CORS network. The technique relies on successful integer carrier-phase ambiguity resolution at both network and user level: at the level of the CORS network, ambiguity
resolution is a prerequisite in order to determine very precise atmospheric corrections for (mobile) users, while these users need to resolve their integer ambiguities (with respect to a certain CORS network master reference station) to obtain precise cm-level positioning accuracy. In case of Network RTK a user thus needs corrections from the network, plus the GNSS data of one of the CORS stations. In practice, there exists a variety of implementations of the Network RTK concept, of which VRS, FKP and MAC are best known [1, 2, 3, 4]. In this contribution we discuss a closely related concept, PPP-RTK, and show its performance on two CORS networks.