I used the word "interoperability" in my last post. This is an important concept as additional Global Navigation Satellite Systems (GNSS) are built. China is well on the way to having the third system in the form of Compass and the Europeans will be fourth with their Galileo Global Navigation Satellite System. A possibility exists that India may not be willing to rely on other countries providing critical navigation information and build their own system.
As all these systems come on line, increased benefits of better accuracies and integrity will result if all meet interoperability standards. Both Ground Based and Satellite Based Satellite Augmentation Systems (SBAS and GBAS) enhance the GPS signals where both accuracy and integrity are concerned. North America, the USA, Canada and Mexico have joined together to create the Wide Area Augmentation System (WAAS). It has been fully operational for more than 7 years. The European Union has declared their European Geostationary Navigational Overlay Service ( EGNOS) operational on October 1, 2009.
Much of the rest of the world have invested in either Ground Based Augmentation Systems (GBAS) or Satellite Based Augmentation Systems (SBAS) systems. These include India's GPS And Geostationary Augmentation Network (GAGAN), Japan's Multi-transport Satellite Augmentation System (MSAS) and Russia's System of Differential Correction and Monitoring (SDCM). Interoperability between all the augmentation systems is a goal well on the way to being met.