BeiDou Performances

COMPASS
Title	BeiDou Performances
Edited by	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. The system is being deployed using an incremental approach and full operational capability is expected to be reached by 2020. The COMPASS System has been designed to reach accuracy levels similar to those of GPS and Galileo Open Service: positioning accuracy within 10 meters, timing accuracy within 20 ns and velocity accuracy within 0.2 meters per second.

COMPASS Performances

The BeiDou-1 system was established in 2003 for the area of the greater China and provided navigation, communication and timing services with performance characteristics as follows::

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

The Initial Operational Service of COMPASS was officially declared in December 2011, for which the initial performances as reported in the Munich Satellite Navigation Summit of 2012 are:

• Service coverage area: regional
• Positioning accuracy: 25 meters horizontally adn 30 meters vertically
• Timing accuracy of 50 ns
• Velocity accuracy of 0.4 m/s

These performances are expected to improve as the number of satellites in orbit increase and the user segment evolves.

The global COMPASS system will be built by 2020 and it is being designed to offer the following performances for each COMPASS Services:

• 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. The Open Service is planned to be available a few years ahead of the system full operational capability;

• 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 COMPASS constellation available at the time (referred to as "3+3", standing for 3 GEO Satellites and 3 IGSO satellites), operational in 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.