1. The US Global Positioning System (GPS) : wins in maturity

　　Layout: 28 satellites (four of which are spare) have already been launched (deployed in 1994), distributed in six intersecting points 60 degrees apart in the orbital plane, about 20,000 kilometers above the ground. The navigation accuracy of a single machine is about 10 meters, and the accuracy of comprehensive positioning can reach the centimeter level and the millimeter level. However, the accuracy of the civilian field is open to about 10 meters.

　　Features: Three-star positioning, military and civilian dual use. Due to the military use of GPS positioning technology, the United States restricts the use of GPS positioning accuracy by unlicensed users. GPS system in addition to the design of many confidentiality measures, but also to different users to provide different ways of service.

　　Progress: In December 1973, the U.S. Department of Defense approved the joint development of the Global Positioning System (GPS) by the Army, navy and air Force, which covered the world and was widely used in 1993. The next generation of satellite navigation systems is currently being tested.

　　2. Russian "GLONASS" system (GLONASS) : strong anti-interference ability

　　Layout: There are 28 satellites (4 of which are spare) with a navigation accuracy of about 5 to 6 meters, and it is expected that the navigation accuracy can reach about 1 meter in 2015. However, the accuracy of the civilian field is open to about 10 meters.

　　Features: Samsung positioning, lower accuracy than GPS, dual-use military and civilian, using two frequency signals. The work is unstable and the satellite's working life is short.

　　Progress: The Soviet Ministry of Defense began building a global navigation satellite system in the early 1980s. It was commissioned in 1995 and is now managed by the Russian Federal Space Agency. The satellite design has undergone numerous improvements, and Glonass K service has been extended worldwide since 2011. Glonass is the second dual-use global satellite navigation system after GPS. The Russian Federation claims that Glonass is a dual-use system with no restrictions, no SA mechanism, and no plans to charge users.

　　3. European "GALILEO" system: purely civilian

　　Layout: Planned 30 satellites (including 3 spare), satellite orbital position is slightly higher than the GPS, 24126 km above the ground. The positioning error does not exceed 1 meter. Currently, only 26 are operational, and four more in-orbit Verification (IOV) satellites are in production and will be launched into orbit in the near future. The positioning accuracy of the public services provided by Galileo is usually 15-20 meters and 5-10 meters. It can reach 1 meter with local enhancement for publicly licensed services and 10 cm with local enhancement for commercial services.

　　Features: Samsung positioning, specifically for civilian use. A new generation of fully open positioning system with the highest accuracy in the future. Ground users can choose from three types of signals, including free signals, encrypted signals that require a fee to use, and encrypted signals that can meet higher requirements.

　　Progress: ESA and the European Union launched in cooperation in 1999, the first test satellite was successfully launched in 2005, and positioning services were launched in 2008.

　　4. China's Beidou System (COMPASS) : interactive and open

　　Layout: consists of 5 geostationary orbit satellites and 30 non-geostationary orbit satellites, positioning accuracy of 10 meters. At present, 10 satellites have been applied, and the positioning accuracy is only 25 meters. All 35 Beidou satellites will be launched in 2020 to provide navigation services for the world. So far, 17 Beidou navigation satellites have been successfully launched.

　　Features: Dual-star positioning, civilian-oriented, limited military capability. Can at any time, any place for the user to determine its geographical latitude and altitude. Innovative positioning performance, not only allows users to know where they are, but also to tell others where they are, especially for places that need navigation and mobile data communication. In addition, China is committed to improving the compatibility of the Beidou navigation satellite System with other global navigation satellite systems, and promoting the application of satellite positioning, navigation and timing service functions. The Beidou navigation satellite system provides free services to the world.

　　Progress: The first step is the test phase, with a small number of satellites using geosynchronous geostationary orbit to complete the test task; The second step is to launch more than 10 satellites by 2012 and build the Beidou satellite navigation and positioning system covering the Asia-Pacific region. The third step is to build a network of five geostationary and 30 non-geostationary satellites by 2020

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