The world’s first! Xiongan ＂Dungeon＂ is used

Start, speed up, park…

Lu Zhaoming, an associate professor at Beijing University of Posts and Telecommunications, was sitting in a test vehicle in a parking lot 12 meters underground in the Xiongan New Area. He kept an eye on the position cursor on his mobile phone.

The test vehicle uses "5G + Beidou" positioning and navigation technology.At present, this technology has been demonstrated in Xiongan underground for more than 500,000 square meters, with a positioning accuracy of 2 meters, and the construction cost is only half of the traditional underground navigation technology.

Inspired to channel signals from the sky into the ground

Today, ever-advancing navigation technology makes people’s lives more and more convenient. But many people also have the experience that once they enter a building below the ground, the reinforced concrete will block the navigation signals such as Beidou "clean".

At the beginning of the planning of Xiongan New Area, it was proposed to build "an underground city".This includes about 380 kilometers of underground integrated pipe corridors and over 22 million square meters of underground parking. The precise management of the "underground city" requires high-precision positioning and navigation, and requires new technology and low cost, which can provide replicable samples for other urban construction.

"We compared all kinds of existing technical solutions, and the investment cost became an insurmountable’roadblock ‘," Zhang Qiang, secretary general of the Xiongan New Area Smart City Innovation Federation (hereinafter referred to as the "Innovation Federation"), told the Science and Technology Daily reporter. At the beginning of research and development, as the lead organizational unit for the research and development of underground navigation technology, the Innovation Federation tried almost all mature technical means –

Deploying Bluetooth point beacons in the basement has high construction costs and high operation and maintenance costs;

The addition of Beidou navigation base station indoors cannot afford the high cost of equipment.

Using WiFi positioning requires not only deploying WiFi access points, but also investing in a new network…

Is there a low-cost and effective technical route? Zhang Qiang and the project team members sat around and kept "brainstorming". Proposals, discussions, collisions… More than a week has passed, and there is still no solution.

One evening, the three members of the project team who had discussed nothing stood on the side of the road unhappily. Suddenly, an idea came to Zhang Qiang’s mind: Why can’t we "use local materials" and borrow existing communication facilities – 5G indoor distribution system?

The indoor distribution system is not mysterious, it is a small antenna that looks like a "small mushroom head" that people often see in the corridor or at the door of the house. In 2020, the Ministry of Industry and Information Technology made it clear that 5G indoor signals should be jointly built and shared. Telecom operators uniformly "mix" various signals into the key equipment – the combiner, and the standard 5G indoor signal is then distributed to each "small mushroom head" by the combiner. However, these "small mushroom heads" can only provide communication protection, not positioning and navigation.

"By the way, receive the Beidou signal and forward it with the help of the’little mushroom head ‘!"

This idea made everyone suddenly enlightened. Lu Zhaoming, who was invited to participate in the project team, recalled that in the past, everyone just made a fuss about communication, and no one thought of it.The combination of Beidou signal and 5G indoor distribution system has opened a new door for underground high-precision positioning and navigation.

"That night, I looked at the night sky, and the shadowy Big Dipper was particularly charming." Zhang Qiang said.

Breakthrough algorithms to achieve accurate underground positioning

Walking into the corridor on the sixth floor of the third teaching building of Beijing University of Posts and Telecommunications, Lu Zhaoming pointed to the line above his head and told reporters: "The experimental demonstration of ‘5G + Beidou ‘is carried out here."

The idea of fusing Beidou signals into a 5G indoor distribution system sounds simple, but the implementation process is full of challenges.

The first challenge is how to introduce the Beidou signal underground.In the 5G indoor distribution system, the three telecom operators’ respective 3G/4G/5G and other multi-channel communication signals are transmitted. If a Beidou signal is added, the original communication signal may be interfered, causing the mobile phone to be unable to talk and surf the Internet normally.

"At the beginning, there was nothing I could do. I could only start by analyzing the intermodulation interference model of the two signals and find the fusion algorithm of the signals." Lu Zhaoming said,Communication and Beidou are two types of signals, but they are not mutually incompatible "enemies".The team members calculated the filtering and power parameters required for the Beidou signal to be imported into the 5G indoor distribution system, and then successfully introduced the Beidou signal into the underground through the shared link transmission of broadband multi-channel signals.

The problem of Beidou signal introduction is solved, and the problem of navigation and positioning accuracy emerges.The accuracy of using Beidou signals for positioning outdoors is about 10 meters, but this accuracy is far from enough in the underground environment. Because the distance between two adjacent intersections in the underground parking lot is often less than 10 meters, if the accuracy is not improved, the positioning and navigation will inevitably be wrong.

"This problem has puzzled us for more than a year. During that time, we tried more than 100 different types of algorithms, but the positioning accuracy was not ideal." Lu Zhaoming said that one day, during testing, he accidentally discovered that the wireless reflection environment of Beidou signals in space has static characteristics, which can be used to build data models and provide more location observation sources.

Although the single information of each end point in the parking lot is not accurate, the multi-party information is collected together, and the positioning results will become more and more accurate through the continuous collaborative calibration of the data model.The positioning and navigation strategy was upgraded from "individual combat" to "multi-end point cooperative combat", and a set of positioning algorithms with independent intellectual property rights was born.

In June 2022, in the underground parking lot of Xiongan New District, when Lu Zhaoming saw the positioning cursor move step by step on his mobile phone screen for the first time, he jumped up excitedly.

"This proves that our positioning algorithm and scheme works in actual scenarios!" Lu Zhaoming said.

Pioneering equipment, twisting the "bull’s nose" of independent innovation

In Xiongan New Area, the reporter took a car through a downhill "entrance" and "plunged" into the underground parking lot of Xingqiuyuan in Rongdong District. The navigation map on the mobile phone switched instantaneously, and the arrow guided the vehicle to find the parking space accurately.

In the parking lot, there was neither intricate wiring nor communication equipment crawling all over the wall. There was only a computer room less than 10 square meters at the corner of the passage, and a large amount of equipment was "hidden" here.

"We are’underground workers’," Chu Xinghe, a postdoctoral fellow at Beijing University of Posts and Telecommunications and a member of the project team, told reporters with a smile. Since the experimental verification, the R & D team has spent more than a year debugging and improving equipment underground.

"Here, you must not’judge things by their appearance ‘." Chu Xinghe introduced,Although only a few small boxes are placed on the wall of the computer room, they are like the "heart" of the underground navigation system.The combiner, 5G indoor distribution unit, and Beidou indoor distribution unit rely on these core devices to successfully import Beidou signals and send out positioning signals.

Among these devices, the Beidou indoor distribution unit is the first in the world.The Beidou satellite signal comes to the ground from an altitude of more than 20,000 kilometers, and the signal strength is extremely weak. If it is introduced into the underground computer room, the signal strength will be further attenuated. The project team innovatively developed the receiving module of the Beidou indoor distribution unit, which can amplify the Beidou signal, support feeder transmission up to 1 kilometer, and introduce high-quality signals into the ground.

"The core components in the unit have completely independent intellectual property rights. It can filter the complex signals received layer by layer, remove useless signals, enhance useful signals, and block malicious attack signals to ensure navigation safety." Chu Xinghe said.

In May this year, the Supreme Leader General Secretary pointed out during his inspection of Xiongan New Area that efforts should be made to build a three-dimensional comprehensive transportation network, make full use of underground space, and strive to create a future city without "urban diseases", and truly turn a high-standard urban planning blueprint into a high-quality urban development reality picture.

"In 2025, the ‘5G + Beidou ‘navigation will cover all the built underground parking lots in Xiongan New Area, truly realizing the navigation of’an underground city’."Looking to the future, Lu Zhaoming was full of expectations, "We hope that this technology will be applied to more scenarios such as mining areas, transportation hubs, terminals, etc., and play a greater role in making full use of underground space!"