EARTHQUAKE LED TO ADVANCES IN COMMUNICATION
The Tiantong Project, which was set up in wake of the 2008 Sichuan disaster, has resulted in some smartphones now supporting satellite calls
In 2008, a massive magnitude-8 earthquake hit the southwestern province of Sichuan. More than 80,000 people were killed in a disaster compounded by disruptions to communications in many towns, which hindered rescue efforts.
Following the tragedy, the government launched the Tiantong Project to set up a satellite communication system accessible to everyone, regardless of socio-economic status.
Now, 16 years on, the project has led to major advances in satellite communication and new trends in mobile phone development.
“Tiantong” means “connecting with heaven” and it echoes the biblical story of the Tower of Babel. The first satellite of the Tiantong-1 series was launched on August 6, 2016, with the second and third satellites following in 2020 and 2021. The three form a network in a geosynchronous orbit at an altitude of 36,000km, covering the entire Asia-Pacific region from the Middle East to the Pacific Ocean.
Then in September last year, Huawei Technologies released the world’s first smartphone that supports satellite calls. It can directly connect to the Tiantong satellites. Other Chinese smartphone manufacturers, including Xiaomi, Honor and Oppo, have introduced similar models.
Now, ordinary Chinese mobile phone users can dial any number via the Tiantong satellite in places without signal coverage, such as deserts or isolated islands, by paying an additional 10 yuan (HK$11) per month.
“Direct satellite connectivity for mobile phones has become a new development trend, and satellite communication will gradually become popular among the general public,” wrote a team of Chinese scientists led by Cui Wanzhao, of the China Academy of Space Technology.
Their peer-reviewed paper was published in the Chinese academic journal, Aerospace
Science and Technology, on February 29.
It was previously believed to be impossible for a remote communications satellite to exchange information with a large number of mobile phones on the ground.
To reach a small smartphone the satellite needs to produce a very powerful signal. When a large number of different high-power signals flood the satellite’s transmitting antenna simultaneously, they can interfere with each other, generating new signals.
These randomly occurring signals can degrade the quality of satellite calls and, in severe cases, can cause the entire system to collapse. This issue, known as passive intermodulation (PIM) among telecommunications engineers, has become a bottleneck in the development of satellite communication technology. Although many people are eager to solve this problem, there is currently no universally effective technology to suppress the occurrence of PIM.
According to Cui’s team, China’s Tiantong Project has gathered communication technology experts from across the country to tackle this “technical challenge of common concern in the international aerospace community”.
Different metal components in huge satellite antennas come into contact with each other, leading to the main source of PIM.
Chinese physicists have delved deep into the microscopic physical mechanisms such as quantum tunnelling and thermal emission at the contact interface, discovering a series of new laws of physics that accurately describe silver-plated and gold-plated microwave components.
They have also established a physical model that can predict the occurrence of PIM with unprecedented precision under various contact states, connection pressures, temperatures, vibrations and other external factors.
Based on this work, Chinese scientists have developed the world’s first universal PIM simulation software. This can numerically analyse and evaluate the possibility of PIM generation in microwave components with complex structures under the influence of external factors such as electricity, heat and stress, with very low error rates.
This powerful software has helped engineers develop effective PIM suppression techniques, including dielectric isolation capacitors and optimised mesh antenna wire preparation and weaving methods.
Cui’s team has further developed the world’s most sensitive PIM detection technology, which can instantly locate the site of PIM generation when it occurs at extremely weak levels.
This allows the satellite to achieve unprecedented reception sensitivity, enabling signals from smartphones without external antennas to be captured and identified by antennas tens of thousands of kilometres away.
Each Tiantong satellite is designed to have a lifespan of 12 years, and its antenna undergoes daily temperature changes of up to 160 degrees Celsius while simultaneously transmitting and receiving electromagnetic waves in 800 different frequency bands.
Solving the PIM problem in such harsh working conditions was extremely challenging.
“The development of the Tiantong-1 satellite system is inseparable from multiple key technological breakthroughs. Its success is a testament to the hard work of the project team and marks China’s leading position in this technical field around the globe,” Cui’s team wrote.
[Tiantong’s] success marks China’s leading position in this technical field around the globe CUI WANZHAO, SCIENTIST