I've done a ton of research into precision positioning with GPS (centimeter resolution). Have you investigated using NOAA CORS data in your project? http://geodesy.noaa.gov/CORS/
Disclaimer: GPS is one of those parts of science that gives me the nerd chills.
Cors data is limited to the USA, we used RGP data, a network of ground stations maintained by the IGN which is analogous to Cors. The IGS gathers data throughout the world to enable global applications but it looks like the data is more complete when accessed through national networks.
I worked a few years ago on precision guidance. I was supposed to assess the performance of automatically guided tractors. Sub centimetric guidance on 4 tons huge tractors was pretty tricky to test. On what exactly did you work?
Disclaimer: GPS is one of those parts of science that gives me the nerd chills.