China is likely to release a document deemed vital for mass application of its Beidou navigation satellite system by the end of the year as it is ready to provide services overseas, according to experts.

"As the Beidou navigation satellite system is to officially provide services to customers in the Asia-Pacific region early next year, its official interface control document, or ICD, will be likely made public around the end of the year, to encourage Beidou's application overseas," Yang Yuanxi, an academician with the Chinese Academy of Sciences and a prominent geodesy scientist, said on the sidelines of the seventh meeting of the International Committee on Global Navigation Satellite Systems. The meeting ended in Beijing on Friday.

China sent the 16th satellite of the Beidou system into space last month, completing its network for the Asia-Pacific region. The plan is for the system to consist of 35 satellites and provide global services by about 2020.

"Releasing ICD is very important as the data it contains is required for the manufacturing, sales and use of terminals," said Yang.

A test version of Beidou's ICD was released at the end of last year, when the system was launched for trial use.

The interface is a communication protocol and works to link navigation satellite signals to the terminals. Although domestic enterprises can obtain the interface for Beidou, it is still inaccessible to overseas manufacturers, according to Cao Chong, director of the Advisory Center of China Association for Global Navigation Satellite Systems.

The Beidou system has been gaining popularity in China and is now ready to provide services to overseas users, Yang said.

"We can produce enough terminals for overseas users," Yang said. "Customers from countries such as Pakistan, Mongolia, South Korea and Australia have expressed a desire for the Beidou services due to its unique advantages."

Because Beidou's interface control document has not been officially released, the satellite system is only in trial use in some countries, a factor that hinders production of Beidou terminals by overseas manufacturers, Yang said.

The interface for the global positioning system, the GPS, has been made public, enabling enterprises all over the world to manufacture GPS-based products.

Larry Hothem, a scientist at the US Geological Survey, said the lack of the document makes manufacturers outside China reluctant to build the equipment used for the Beidou system, as "they are not sure that they get the right information".

"The signal requires a special design in the hardware. They need to know what that is to proceed with the design," he said.

Lu Xiaochun, a professor at the National Time Service Center at the Chinese Academy of Sciences, said the Beidou system is now capable of serving most parts of the Asia-Pacific, but it is still in the trial stage, and its performance is not yet guaranteed.

"The interface should be released before Beidou officially provides services to the Asia-Pacific early next year," she said.

After the interface is released, overseas manufacturers will be able to design and produce terminals based on Beidou, which will greatly promote the application of the system, according to Cao, from the Advisory Center of China Association for Global Navigation Satellite Systems.

The Beidou navigation satellite system will be compatible and interoperable with all other major global navigation satellite systems, such as GPS and GLONASS, to improve service performance, according to Wang Li, director of the International Cooperation Research Center, China Satellite Navigation Office.

"The concept of compatibility and interoperability among global navigation satellite systems has been widely accepted, but some technical difficulties have to be overcome," she said. "Experts from different countries are actively conducting technical research to achieve this goal."

"China is a big country, and opening more technology to the international community will speed up its development, such as the application of Beidou among the international community," said Sompoch Puntavungkoon, an official with the Asia-Pacific Space Cooperation Organization.

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