After the 2008 Wenchuan earthquake destroyed the communication system and many people were unable to contact the outside world with their mobile phones, the mainland began to build the Tiantong satellite mobile communication system.
On August 6, 2016, the first satellite of the Tiantong-1 satellite mobile communication system was successfully launched, and the second and third satellites were launched in 2020 and 2021. The three satellites operate in tandem and fly in a geosynchronous orbit 36,000 kilometers above the ground, covering the Asia-Pacific region, the Middle East and other regions.
In 2023, Huawei released the first smartphone to support satellite calls, the Mate 60, which can directly connect to Tiantong satellite, and then Xiaomi, Honor, and OPPO have followed. Industry insiders estimate that Huawei has sold nearly 10 million satellite smartphones, far more users than SpaceX Starlink, which has just over 2 million customers.
Even in areas where there is no mobile coverage, users can make calls via satellite for a monthly fee of only 10 yuan. In the event of an earthquake and communication is interrupted, users with satellite smartphones can make normal calls.
Cui Wanzhao, a scientist at the China Academy of Space Technology, said in a February article: "It has become a new trend for mobile phones to connect directly to satellites, and satellite communications will gradually become popular among the public. ”
Previously, it was generally accepted that it was unlikely that a large number of users on the ground would process information via distant satellites. In order to connect to a small number of mobile phones, satellites need to send extremely strong signals. If a large number of mobile phones are connected, many signals of different strengths will pour into the satellite transmission antenna at the same time, and the signals will interfere with each other and generate new signals. Random signals can degrade the quality of satellite calls, which in turn can cause the entire system to crash.
Since the 1970s, the United States, Europe, and other international organizations have deployed commercial communications satellite networks, but almost all of them have failed. The main reason for the failure is that the problem of passive intermodulation interference is difficult to solve. When two or more wireless signals are present simultaneously on nonlinear devices (e.g., antennas, connectors, feeders, etc.), they may produce nonlinear intermodulation products, which are passive intermodulation products. Passive intermodulation jamming has become a major obstacle to the development of satellite communication technology.
The problem of passive intermodulation interference has also attracted the attention of the international aerospace industry, and the Tiantong project has organized a large number of communication elites to concentrate on solving this problem. Satellites have components made of different metals that are in close proximity, which is the main cause of passive intermodulation interference. Scientists are looking for new solutions to the microscopic physical mechanisms of the interface, such as quantum tunneling and thermal radiation. Eventually, Chinese scientists developed a physical model that could accurately predict the occurrence of passive intermodulation interference.
Scientists have developed the world's first universal PIM interference simulation software, which can analyze and evaluate the possibility of passive IMM interference when microwave components are exposed to external interference, such as external factors such as current, heat, and pressure. Cui's team has also developed the world's most sensitive PIM detection technology, which can locate the location of PIM interference in the most extreme environments.
With the support of new technologies, the reception sensitivity of satellites has been greatly improved, and even without external antennas, the signals emitted by smartphones can be captured by satellites thousands of kilometers away.
The design life of each Tiantong satellite is about 12 years, and the satellite antenna will operate in a high temperature environment of 160 degrees Celsius every day, and need to transmit and receive electromagnetic signals in about 800 different frequency bands at the same time. Cui Wanzhao's team pointed out in the report: "The development of Tiantong-1 system is inseparable from a number of breakthroughs in key technologies. ”
SpaceX has already launched satellites that can connect to smartphones, and it is expected to provide commercial services next year. SpaceX satellites are a little different, they operate in low orbit and do not require too large antennas, which can reduce passive intermodulation interference. There are pros and cons, and due to the low orbit, SpaceX will have to launch a large number of satellites if it wants to expand its coverage. Although SpaceX has launched more than 5,000 satellites, these satellites are basically unable to provide satellite call services, and only recently launched satellites that support mobile phone calls.
In terms of satellite communication technology, Huawei has not stopped, and the newly released Pura 70 series mobile phones are equipped with dual-satellite satellite communication, supporting Tiantong satellite communication and Beidou satellite messaging. The Beidou satellite message function has also been upgraded, supporting the sending of satellite picture messages, the free editing of satellite messages, and the generation of trajectory maps, etc., bringing more practical functional support to outdoor scenes. (Knife)