A 2008 earthquake in China has brought about technological advances, some smartphones can now support satellite calls, and Chinese scientists have created the world's first simulation software to solve the problem of passive intermodulation.
South China Morning Post's March 12 report by Stephen Chen
In 2008, a magnitude 8 earthquake struck the southwestern Chinese province of Sichuan.
More than 80,000 people were killed in the disaster, and communications in many towns and cities were disrupted, hampering relief efforts.
In the aftermath of the tragedy, the Chinese government quietly launched the "Tiantong Project" to build a satellite communications system that could be used by everyone, regardless of socioeconomic status.
Now, 16 years later, the project has made significant progress in the field of satellite communications and has led to a new trend in the development of mobile telephony.
"Tiantong" means "connected to the sky", echoing the story of the Tower of Babel in the Bible.
The first satellite of the Tiantong-1 series was launched on August 6, 2016, and the second and third satellites will be launched in 2020 and 2021, respectively. The three satellites form a network in geosynchronous orbit at an altitude of 36,000 kilometers, covering the entire Asia-Pacific region, from the Middle East to the Pacific Ocean.
In September last year, Huawei Technologies released the world's first smartphone that supports satellite calling, which can be directly connected to Tiantong satellite. Other Chinese smartphone makers, including Xiaomi, Honor and OPPO, have launched similar models.
The products have been popular with Chinese consumers, with industry estimates that Huawei alone has sold tens of millions of units, surpassing SpaceX's Starlink satellite service, which has more than 2 million users worldwide.
Now, for an additional 10 yuan a month, the average mobile phone user in China can call any number via Tiantong satellite in places where there is no coverage, such as deserts or isolated islands.
The direct connection of mobile phones to satellites has become a new development trend, and satellite communication will gradually become popular among the public, and it has also begun to bear fruit. On December 18, a magnitude 6.2 earthquake struck northwestern Gansu Province, again causing widespread communication disruptions. This time, however, many of the affected people were able to get in touch with the outside world through the satellite phone function on their smartphones. The death toll from the earthquake is about 150.
In a peer-reviewed paper published February 29 in the Chinese academic journal Aerospace Science and Technology, a team of Chinese scientists led by Cui Wanzhao of the China Academy of Space Technology wrote: "The direct connection of mobile phones to satellites has become a new development trend, and satellite communications will gradually become popular among the public."
Previously, it was believed that it was impossible for long-range communication satellites to exchange information with a large number of mobile phones on the ground. In the biblical story, the reason for the failure of the Tower of Babel is that the workers began to speak different languages and confused each other. Satellite communications are subject to similar interference.
The satellite needs to produce a very powerful signal to reach a small smartphone. When a large number of different high-power signals flood into a satellite's transmitting antenna at the same time, they interfere with each other, generating new signals.
These random signals can degrade the quality of satellite calls and, in severe cases, crash the entire system.
Since the 70s of the 20th century, almost all commercial communication satellite networks operated by the United States, Europe, and international organizations have experienced major failures due to these signals falling into the receiving frequency band.
This problem, known as passive intermodulation (PIM) among telecommunications engineers, has become a bottleneck for the further development of satellite communication technology. Although many people are eager to solve this problem, there is currently no universally effective technology to inhibit the occurrence of PIM.
According to Cui Wanzhao's team, China's "Tiantong Plan" has gathered communication technology elites from all over the country to jointly overcome this "technical problem of common concern to the international aerospace community".
The contact between different metal parts in a huge satellite dish is the main reason for the occurrence of passive intermodulation. Chinese physicists have delved into microscopic physical mechanisms such as quantum tunneling and thermal emission at contact interfaces, and have discovered a series of new physical laws that can accurately describe silver- and gold-plated microwave components.
They also built a physical model that was able to predict the occurrence of PIM effects under various contact states, connection pressures, temperatures, vibrations, and other external factors with unprecedented accuracy.
On this basis, Chinese scientists have developed the world's first universal passive intermodulation simulation software. The software can numerically analyze and evaluate the possibility of PIM generation of complex microwave components under the influence of external factors such as electricity, heat, and stress, with a very low error rate.
This powerful software has enabled Chinese engineers to develop effective passive intermodulation suppression techniques, including dielectric isolation capacitors and optimized mesh antenna wire fabrication and braiding methods.
Cui's team has further developed the world's most sensitive passive intermodulation detection technology, which can immediately locate the location of the passive intermodulation when it is generated at very weak levels.
This allows the satellite to achieve unprecedented reception sensitivity, allowing signals from smartphones without external antennas to be captured and recognized by antennas tens of thousands of kilometers away.
Each Tiantong satellite is designed to last 12 years, and its antennas are subjected to temperature changes of up to 160 degrees Celsius per day, while also transmitting and receiving electromagnetic waves in 800 different frequency bands.
Solving the problem of passive intermodulation under such harsh operating conditions is extremely challenging. "The development of the Tiantong-1 satellite system is inseparable from a number of breakthroughs in key technologies. Its success is a testament to the hard work of the project team and a sign of China's global leadership in this technology field," Cui Wanzhao's team wrote in the paper.
China has filed a large number of patents for the Tiantong satellite, which means that Chinese high-tech companies do not have to worry about patent barriers or sanctions from the West when using this revolutionary technology.
Earlier this year, SpaceX launched the first of several Starlink satellites, which can be connected to smartphones and plans to begin commercial service next year.
These satellites operate in low-Earth orbit at an altitude of several hundred kilometers and have a small antenna area, which can reduce passive intermodulation interference. However, since satellites can only stay over a certain area for a short period of time, a large number of satellites must be deployed to achieve large-area, full-time coverage.
Currently, most of the more than 5,000 Starlink satellites launched by SpaceX do not have the ability to connect to mobile phones.
However, the new Starlink satellites have a significant advantage: they can connect to older 4G phones.
As Starlink technology matures, the launch speed of Starlink satellites is likely to increase dramatically, while China has yet to develop a full-fledged recyclable rocket technology to compete with it.