As China's Compass system of positioning satellites rolls out over the next five years, speculation has been rife over how it will interoperate with other systems to improve accuracy. But new research suggests Compass may not need to play well with others
Much has been made of system interoperability among GPS, Galileo, GLONASS, and, most recently, Compass, the Chinese system. A recent study suggests reasons why interoperability may not be high on the Compass wish list, and may foretell some surprises for GNSS receiver manufacturers who anticipate a huge Asian market for interoperable receivers.
A paper presented at September's Institute of Navigation conference in Savannah could lead one to some unexpected conclusions about the coming market for receivers in Asia. 'The Impact of Compass/Beidou-2 on Future GNSS: A Perspective from Asia,' by Huang Yu-sheng and Tsai Meng-lun, two masters students in the Department of Geomatics at National Cheng Kung University in Taiwan, studies the performance of BeiDou-2/Compass compared to GPS, GLONASS, and Galileo in the greater Asia region. The authors also to try to determine whether combining BeiDou-2/Compass with each GNSS would yield performance improvements in the same region.
As China expands its two-satellite prototype, Beidou-1, operating since 2004, from a regional navigation system to a full-constellation global navigation satellite system known as BeiDou-2/Compass, those outside China have speculated on the overlays of planned Chinese signals on frequencies reserved by Galileo and by the US military. The most common inference has been that, well, they'll have to do something about that, won't they, if they want to join the interoperable world‾
Maybe they have no plans to do any such thing.
Compass will consist of 30 orbiting satellites: 27 medium-Earth orbit (MEO) and three inclined geosynchronous (IGSO), and five geostationary (GEO) satellites. Compass could begin operation in 2013 'if all the political statements are brought into reality,' as the authors state.
The multiplicity of satellites will make possible improved performance for all applications, and especially where satellite signals can be obscured, such as in urban canyons, under tree canopies, or in open-cut mines. The benefits of the expected extra satellites and their signals can be in terms of availability, accuracy, continuity, and reliability issues.
Huang and Tsai limited the scope of their study to investigating the impact of current and future GNSS based on the geometrical conditions. They used satellite visibility and DOP values of each system or possible combinations between them as the major indices for the performance evaluation, with emphasis on the addition of Compass. In addition, they further analyzed these indices in terms of their spatial and temporal distributions with the emphasis on the greater Asia region, to illustrate the importance of Compass for the users in that region specifically.
Demand for multiple systems
As satellite navigation becomes a vital technology across a number of critical industrial sectors - a nation's transport infrastructure becoming dependent on this technology, for example - reliance upon one GNSS is a strategic risk that many industrial countries who do not operate their own system are unwilling to accept. These perspectives motivated the Galileo program in Europe, and now Compass in China. China, large and rapidly developing, with an extended geographic domain and sea area, clearly sees this as a high priority. Taiwan in turn is vitally interested in the latest development of Compass/Beidou-2 as well as its performance in the greater Asia region, since its coverage will directly benefit the users in Taiwan, located in the center of East Asia.