There are a lot of satellite navigation systems for Earth. Some are regional others are global. Some are composed by only one satellite and multiple earth-based stations, and other with hundred of satellites.
This post will be an overview of the actual satellite systems. Some are in development but all are operational in some degree. Have fun.
Global Navigation Satellite System (GNSS)
This is the only system that offers a global coverage. That means that the constellation needs to be enough to be visible from any point of Earth in any moment, with at least four satellites (3 for position and 1 for time correction).
Global Positioning System (GPS)
It is the United States of America’s system operated by the United States Air Force. Provides geolocation and time information and military critical positioning capabilities. The civilian radio is freely accessible but the US government can selectively deny access to the system. It is the most used system.
Global Navigation Satellite System (GLONASS)
It is the Russian Federation’s system operated by by the Russian Aerospace Defence Forces. Provides the same services and capabilities of the GPS system.
It is the European Union’s system operated by the European GNSS Agency (GSA) it is the full civilian oriented version. The basic (low precision) services will be free and open, and the higher precision (equivalent of the military capabilities) will be available for payin commercial users like airlines. It will have a availability certification and it will be used in critical operation like aircraft operations with safety.
It is the People’s Republic of China’s system operated by the China National Space Administration (CNSA). It is in development.
GNSS augmentation is a method to provide a better accuracy, reliability and availability of a current satellite system providing an external source of information that corrects the errors of the main system.
They usually have a satellite in geostationary position and a network of receivers and monitoring system to ensure the seasonal changes and the satellite systems malfunctions.
Non-global satellite navigation systems
It is the Chinese regional (Asia-Pacific) network that expanded into a global one with the BeiDou-2 and BeiDou-3 satellite generations.
It is the Republic of India’s system operated by the Indian Space Research organisation (ISRO). The coverage is like this:
It is the proposed three-satellite system for time transfer and GPS enhancement (augmentation system) for Japan. It is in development.