In Network RTK rather than only base station and rover(s), as the name indicates, there are network of reference stations.
In this paper, the BDS fractional cycle biases (FCBs) are estimated with least-squares estimation method using the float undifferenced ambiguity collected from the network of reference stations.
Today, NORMAN is an independent and highly recognized network of reference laboratories, research centers, and related organizations for the monitoring of contaminants of emerging concern.
PPP uses a global network of reference stations to determine the corrections to the GNSS broadcast satellite orbits and clocks with an accuracy of better than 5 cm.
IRC products were generated from a network of reference stations globally distributed, available in real-time and post-processed using final orbits and clocks.
In 2005, the European Commission funded the NORMAN project to promote a permanent network of reference laboratories and research centers, including academia, industry, standardization bodies, and NGOs.
In 2004, NORMAN came into existence following a call by the EU Commission DG Researchh) to create "a permanent network of reference laboratories and related organizations dealing with emerging environmental substances" [7].
However, in the US, where the railway network differs strongly from the European one, some control and command systems are now based on GPS, enhanced by the NDGPS (Nationwide Differential GPS), which is a network of reference stations allowing the receiver to have better performances.
Other important activities include the Centre's involvement in NORMAN, a network of reference laboratories, research centers and related organisations for monitoring of emerging environmental substances, where it participates in working groups on the prioritization of chemicals, the use of bioassays and biomarkers in, and the application of passive samplers to water quality monitoring.
