Researchers have developed a low-cost, high-accuracy positioning system for a 380 km tunnel network running beneath the Xiong’an New Area.
The research team at Beijing University of Posts and Telecommunications (BUPT), led by Associate Professor Lu Zhaoming, combines China’s BeiDou technology with a 5G network to create a positioning system for the urban area that will become the largest underground city in the world.
The Xiong’an New Area sits above an underground tunnel network. (Photo: Xinhua).
Xiong’an is a national smart city located in Hebei Province, about 120 km from Beijing. The project was initiated in 2017 to relocate business facilities, government agencies, and research and development organizations from Beijing. From the design phase, an underground maze was planned to be constructed beneath the city. Technical pipelines such as electricity, network transmission, gas, and water will be placed underground. High-speed corridors, 4 meters high and 16 meters wide, will be built to facilitate the transportation of goods. Additionally, there will be a significant amount of underground parking for residential areas and shopping centers.
This will combine to form an underground maze consisting of three main levels, reaching a depth of 22.5 meters. In total, more than 380 km of tunnels and 22 km2 of underground parking are under construction. Above this complex is an underground road network connecting all residential communities above ground and the parking areas. Once completed, this project will break the record for the largest underground city from Montreal. The Canadian super city has only 32 km of tunnels covering 12 km2. In contrast, the underground city in Helsinki, Finland, has about 1 km2 of underground space corresponding to 100 m2 of above-ground area. The ratio in Xiong’an is 1/80.
The scale of this maze presents a unique challenge for positioning, as individuals can easily get lost in the vast space. To address this issue, the School of Information and Communication Engineering at BUPT, with expertise in 5G and signal positioning, has been leading research since 2020. “We can make phone calls and browse a website in the underground space because mobile phones receive signals from signal boosters,” Lu stated.
These boosters receive 5G signals from the surface and transmit them through the nearby space. The BUPT research team uses this equipment as a starting point. If they can transmit BeiDou positioning signals using the existing relay system, they will create an accurate underground positioning system at a low cost. Initially, researchers developed specialized indoor devices to enhance weak signals transmitted from satellites to the ground. According to Chu Xinghe, a postdoctoral researcher at BUPT, the devices can also filter out irrelevant signals while preventing harmful interference.
However, the 10-meter accuracy above ground of the BeiDou system is likely insufficient for underground requirements, as parking areas especially need high precision in positioning. Therefore, the research team developed an algorithm that integrates BeiDou satellite signals, 5G signals, and feedback from the devices. The new algorithm allows for unprecedented vehicle location accuracy within a range of 2-3 meters. The combination of satellite signals and 5G also presents many challenges, including potential interference. Consequently, the research team adjusted filtering capabilities and power parameters to successfully transmit BeiDou signals underground without affecting existing communication channels.
After testing the technology on the BUPT campus, field trials in Xiong’an helped refine the positioning system in complex road segments. A vehicle begins receiving directional guidance from the approach to the parking area, leading to precise parking. The system has been deployed over an area of more than 700,000 m2 underground in Xiong’an.
In comparison to other indoor positioning technologies based on Wi-Fi or Bluetooth, the project’s costs are only about half and have the potential to be expanded to hospitals, commercial complexes, mines, airports, and many other complex environments. Lu hopes that the technology can be implemented in other regions such as Henan, Fujian, and Guangdong.
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