Beidou/Compass Declared Operational, Test ICD Released

A press conference on the Beidou/Compass navigation system was held at the State Council Information Office in Beijing December 27 to announce the official start of operational positioning, navigation, and timing services to China and surrounding areas and the public release of a “beta” or test version of the Beidou/Compass Interface Control Document.

Ran Chengqi, the director of the management office of the China Satellite Navigation System, said that the main service area is currently 84 degrees to 160 degrees east longitude and 55 degrees south latitude to 55 degrees north latitude with horizontal position accuracy of up to 25 metres, height to 30 metres, velocity accuracy of 0.4 metres per second, and a timing accuracy of 50 nanoseconds.

It is not clear how many satellites are actually providing this initial service. Although 10 satellites in the second generation Beidou-2/Compass system have been launched since 2007 (a medium Earth orbit (MEO) test satellite, four geostationary Earth orbit (GEO) satellites, and five inclined geosynchronous orbit satellites (IGSO) grouped into two planes), one of the GEO satellites is drifting uncontrolled in orbit. The current operational constellation possibly consists of three GEO satellites and five IGSO satellites. One or two of the IGSO satellites may be considered as in-orbit spares.

The ground tracks of the Beidou-2/Compass satellites are depicted here.

“The Beidou system is not yet fully completed,” Chengqi said. “In October next year, we want to complete the second step in the three-step program to carry out Beidou’s commissioning services.” According to published reports, the second step or phase of Beidou-2/Compass development, expands the service area to cover most parts of the Asia-Pacific region with 14 satellites: 5 GEOs, 5 IGSOs in two orbit planes, and 4 MEOs in two orbit planes. To accomplish this, Ran Chengqi said, six more satellites would be launched in 2012. According to the NASA Forum website, two GEOs and four MEOs are scheduled to be launched in 2012.

Chengqi further said that the current 25-metre location service accuracy would reach 10 metres by the end of next year.

One key feature of the Beidou/Compass system that distinguishes it from the other satellite navigation systems was highlighted during the press conference and that is the provision of a short messaging communication service. That service was inaugurated with the Beidou-1 demonstration satellite constellation and was used, in part, in disaster management in China.

Also announced at the press conference was the public release of a “beta” or test version of the Beidou-2/Compass Interface Control Document (ICD). It is available in both Chinese and English in PDF format from the official government Beidou/Compass website. Direct link to the English version. It is also available here.

The test version is somewhat incomplete. Running to just 9 pages, it only describes the basics of the coordinate and time systems and the basic characteristics of the open service B1 signal transmitted as the in-phase component on the 1561.098 MHz carrier frequency, including the ranging codes assigned to different satellites. There is no discussion whatsoever of the details of the navigation message or associated algorithms.

Chengqi addressed the limited nature of the test version ICD during the press conference. He stated that the test version is being released to stimulate research and development work and promote applications as soon as possible. He also indicated that some aspects of the transmitted signals are not yet finalized or “cured” and that is why they are not discussed in the test ICD. He said with the further constellation development next year, “we will timely announce the official version of the ICD file, updated according to the further improved situation.”

An unedited automated translation of the transcript of the press conference is available here.

Video item in English on the press conference as aired by China Network Television (CNTV) and China Central Television (CCTV) News.

CCTV video preview for news agencies.

Langley, R. (2011, December 17). Beidou/Compass Declared Operational, Test ICD Released. GPS World Online. Retrieved January 3, 2012, from