BeiDou Performances

COMPASS
Title	BeiDou Performances
Author(s)	GMV
Level	Basic
Year of Publication	2011

The Compass Navigation Satellite System (CNSS), also named BeiDou-2, is China’s second-generation satellite navigation system that will be capable of providing positioning, navigation, and timing services to users on a continuous worldwide basis.

Although the upgrade of its regional navigation system towards a global solution started in 1997, the formal approval by the Government of the development and deployment of BeiDou-2/CNSS was done in 2004. The system is currently under development evolving from a regional system called BeiDou-1, and in the first phase will provide high-accuracy positioning services for users in China and its neighboring regions by 2012. In a second stage, the system will evolve to provide global navigation services by 2020, similarly to the GPS, GLONASS or Galileo systems.

As of August 2011, nine satellites for Compass have been launched, the first eight of which completed the deployment foreseen for the first phase of BeiDou-2.

COMPASS Performances

In May 2003, the successful launch of BeiDou-1C also meant the establishment of the BeiDou-1 navigation system, providing navigation, communication and timing services for the greater China area. The system services and performance characteristics at this time (2003) were:

• Positioning: 100m (1σ); 20m (1σ, with reference stations).
• Regional Service short message service (SMS): up to 120 Chinese characters.
• Timing: 20 ns.

On November 2, 2006, China announced the second generation Chinese navigation system, COMPASS, that in the completion of its first phase by 2012 would offer an open service with an accuracy of 10 meters, timing of 0.2 nanoseconds, speed of 0.2 meter/second. As of April 2011, eight satellites for COMPASS have been launched, and another 3 more satellites will be put in orbit in 2011, expecting by 2012 to complete the first phase of the system and then, the open service performances reached the levels described before. The global COMPASS system will be built by 2020.

The performances for COMPASS Services would be:

• Open service: a free service for civilian users with positioning accuracy of within 10 meters, velocity accuracy of within 0.2 m/s and timing accuracy of within 20 nanoseconds;

• Authorized service: a licensed service with higher accuracy even in complex situations for authorized and military users only.

• Wide area differential positioning service: with positioning accuracy of 1 m.

• Short message service (SMS): up to 120 Chinese characters.

Table 1: COMPASS Signals Characteristics

Preliminary performance figures were presented in the COMPASS Workshop, integrated in the ION GNSS 2011 Conference. The current COMPASS constellation (referred to as "3+3", standing for 3 GEO Satellites and 3 IGSO satellites), operational since July 2011, includes the signals depicted in Table 1.

These results show that a combined COMPASS("3+3")+GPS constellation provides:

• higher availability: up to 14 satellites were visible in the test conditions (compared to up to 9 with GPS only);
• better geometry: the PDOP for the combined constellation was lower than the PDOP for each individual constellation.

The results show that the accuracy of the combined solution (GPS and current COMPASS) is in general worse than the single GPS Solution - even though in the same order of magnitude. This was explained by the differences between systems and the preliminary status of the COMPASS constellation which is still expected to improve their satellite clocks and orbits accuracy as it reaches full operational capability.