What will Beidou do after networking? The PNT system takes you to the sky, the ground and the sea

Part 1

Isn’t Beidou enough? What is PNT?

On July 31, 2020, the BeiDou Global Navigation Satellite System (BD-3) was officially launched, marking that my country has built a space-time reference facility with fully autonomous and controllable capabilities.

Although the Beidou satellite navigation system is powerful, like other satellite navigation systems (such as the US GPS), it also inevitably has problems such as weak radio signal landing power and unsuitability for indoor and underwater spaces . This cannot fully meet the needs of various users for spatiotemporal information and cannot provide all-round coverage of spatiotemporal information services. Therefore, the concept of the PNT (navigation, positioning, and timing) system came into being.

PNT is the abbreviation of positioning, navigation and timing system. It is a huge system project involving the integration of land, sea, air and space. The global satellite navigation system is its main component. The PNT system is also a further improvement and deepening of the global satellite navigation system.

PNT is a system engineering that integrates multiple technical means. Its concept was first proposed in the report "National Space-Based Positioning, Navigation and Timing Policy of the United States" issued by the United States in 2004. The report describes in detail the importance of time and space reference services, analyzes the problems of GPS, and elevates PNT to the status of a national strategy. Since then, the concept of PNT has replaced GPS in the official US.

According to relevant reports, my country is also accelerating the construction of a national comprehensive PNT system with the BeiDou system as the core. my country's goal is to provide a safe, reliable, better-performing, ubiquitous and omnipresent space-time infrastructure. The construction of the PNT system can significantly enhance the country's space-time information service capabilities and provide better services to global users, truly achieving "BeiDou of China, BeiDou of the world".

Figure 1. Design of the U.S. PNT architecture

(Image source: U.S. PNT Development Report)

Figure 2 Scope of the U.S. PNT architecture

(Image source: self-made by the author)

Part 2

360° protection of the PNT system

Since the establishment of the BeiDou satellite navigation system, it has been providing time and space information services to the public almost every day. In fact, human production and life are dealing with time and space information almost every day. Relevant research statistics show that nearly 80% of human information interaction is related to PNT (navigation, positioning, and timing).

For example, the navigation function of some map apps we use in our daily lives is a service provided by the satellite navigation system (Beidou or GPS); WeChat uses the positioning service of the satellite navigation system to enable location sharing; shared bicycles also use the positioning service function for docking; the power industry and the financial industry require the synchronization of the entire network system time, and use the Beidou's precise timing function.

In addition to the daily life of firewood, rice, oil and salt, humans have never stopped pursuing the stars and the sea. In the future, the scope of human activities may not be limited to land. The blue deep sea and the vast deep space are both targets of human exploration. At the same time, with the diversification of applications, users have higher and higher requirements for the accuracy and reliability of spatiotemporal information in various complex environments. The shortcomings of the satellite navigation system have begun to emerge. For tasks that the satellite navigation system cannot complete, it is necessary to vigorously carry out relevant explorations, which is also the starting point of the PNT system research.

The biggest feature of the PNT system is its seamless horizontal coverage of indoor areas, vertical expansion to underwater and deep space, and its ability to provide high-precision, continuous and stable space-time information services in complex environments.

The PNT system integrates space-based, air-based, land-based and other types of navigation resources to form a high-precision space-time unified service system that covers the entire land, air, space, underwater, indoor and outdoor areas. The PNT system relies on a variety of information technologies to support the establishment, maintenance and transmission of national space-time benchmarks; the broadcasting and acquisition of space-time information; and the national information infrastructure for positioning, navigation and timing services. It is a national heavyweight!

Figure 3 Schematic diagram of the overall PNT architecture

(Image source: self-made by the author)

Part 3

The future has arrived. It is no longer a dream to explore the sky, the earth and the sea.

Today, China has achieved the brilliant achievements of the Shenzhou manned spacecraft, the Chang'e lunar exploration, and the Jiaolong submersible. Whether in space or in the sea, my country hopes to explore the unknown deeper, farther, and more steadily. Knowing the destination will help us know the way back, and PNT can guide us along the way.

my country has begun to propose the strategic concept of building the next-generation national comprehensive PNT system and has carried out the demonstration work of the national comprehensive PNT system.

So, what key technologies are involved in the PNT system?

First of all, as a global system independently built by the country, the Beidou satellite navigation system is undoubtedly the cornerstone and main body of my country's PNT system. At the same time, it is also necessary to develop deep space navigation technologies such as pulsar navigation, low-orbit satellite enhancement technology, indoor positioning technology, and ground-based/air-based enhancement technology. The underwater part also needs the support of sonar, gravity matching, inertial navigation and other technologies. With the support of the above technologies, a combination, fusion, and networking method can be used to build navigation, positioning and timing services that meet the needs of the ground, underwater, and even deep space.

Figure 4 Beidou Satellite Navigation System

(Image source: Beidou Satellite Navigation System official website)

Today, my country's Beidou system has solved the problem of outdoor navigation and positioning services. In the future, the construction of a comprehensive PNT system will seamlessly cover indoor and outdoor navigation and positioning services, and truly realize the integrated space-time information service of land, sea, air, and land. Whether in the sky or in the sea, PNT will escort you.

References:

[1]Xie Jun, Liu Qingjun, Bian Lang. Development concept of national integrated positioning, navigation and timing (PNT) system based on BeiDou system[J]. Space Electronics Technology, 2017, 14(5):6.

[2] Yang Yuanxi. Integrated PNT system and its key technologies[J]. Acta Geodaetica et Cartographica Sinica, 2016(5):6.

[3] Pursuing the Ultimate Interview with Ran Chengqi, Deputy Chief Designer of Beidou Satellite Navigation System Engineering, China Discipline Inspection and Supervision News 2020.8.1

Produced by: Science Popularization China

Author: Chen Weiyi

Producer: China Science Expo

The article only represents the author's views and does not represent the position of China Science Expo

This article was first published in China Science Expo (kepubolan)

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