According to statistics, more than 80% of peopleTime spent in buildings, mobile vehicles, underground and other non exposed spaces.As a typical scene of non exposed space, urban rail transit (hereinafter referred to as "urban rail") is not only the artery and the core public area of the city, but also the key construction field of "new infrastructure".For a long time, positioning, navigation, timing and communication in non exposed space has been a worldwide technical problem and a bottleneck restricting the development of smart city rail.

 

As a global system providing time and space information, Beidou satellite navigation system (hereinafter referred to as "Beidou system") is an important space infrastructure independently constructed and operated by China. At present, the system construction has been completed and is being applied and popularized in various industries. By applying Beidou system and building its based high-precision positioning network, high-precision time synchronization network, high-throughput communication network and spatial digitization platform, it can play a basic supporting role in the construction of smart city rail.

Because the application of Beidou system is basic, innovative, penetrating and driving, it can have a significant impact on the development form, development concept, development mode and operation mode of urban rail transit, so as to promoteNew operation and management mode of "Beidou urban rail"To meet the various needs of passengers, enterprises, governments and other multiple subjects, and build a more safe, reliable, convenient, comfortable, cost-effective, green and energy-saving smart city rail system.

#01

Beidou system and smart city rail

At present, Beidou system has been widely used in the fields of national defense and security, transportation, marine fisheries, meteorology and hydrology, power dispatching, disaster relief and disaster reduction, and has produced remarkable social and economic benefits; Especially in transportation, it has been widely used in vehicle positioning, transportation process monitoring and management, infrastructure safety monitoring and other fields.

 

On this basis, the application of Beidou system still has room for further expansion. For example, from the perspective of the space environment of the application, in the outdoor exposed space environment (hereinafter referred to as "exposed space") that can directly receive satellite navigation system signals, users can directly use the space-time information provided by Beidou system; However,In a non exposed space environment that cannot receive satellite navigation system signals(hereinafter referred to as "non exposed space"), such as subway, underground parking lot, commercial complex and under viaduct, due to the influence of building shielding and multipath effect, the satellite positioning accuracy decreases sharply, which can not meet the needs of non exposed space location service.

becausePeople spend 80% of their time in non exposed spaces such as buildings and mobile vehiclesTherefore,Solving the problem of navigation and positioning in non exposed space is an important direction of the application and development of Beidou system。

 

At present, the country is building a comprehensive positioning, navigation and timing (pnt) system based on Beidou system. The system can use a variety of PNT information sources based on different principles to generate a unified spatio-temporal benchmark through cloud platform control, multi-sensor high integration and multi-source data fusion Pnt service information with the advantages of continuity and reliability can cover indoor, underwater, deep space and other fields.

In recent years, with the acceleration of construction speed and the continuous growth of operation mileage, urban rail is facing a series of challenges such as network operation, cost reduction and efficiency increase, fast service, low-carbon environmental protection and sustainable development. The concept of smart urban rail has emerged.

 

The essence of transportation is to provide displacement, that is, to realize the position movement of personnel and materials by means of transportation according to needs. As a public transport system, the core goal of smart city rail development is to achieve the location movement with the lowest cost and maximum coverage on the premise of ensuring safety. Its means is to realize the intellectualization of all links in the process of urban rail service, that is, "displacement", with the support of information technology. Therefore, it is necessary to make full use of advanced information communication, artificial intelligence, Internet of things, big data Robot and other technologies, with autonomous perception, autonomous learning, autonomous decision-making and autonomous control as the core processing process, provide passengers with efficient, accurate and personalized displacement services on the basis of optimal control of equipment and facilities, so as to build a safer, efficient, comfortable and green new generation urban rail system.

Time and space location information is the basis for realizing the independent operation, accurate management and full-time personalized service of smart city rail systemTherefore, the construction of smart city rail needs to be integrated with the Beidou system that provides space-time information.

The future development trend of urban rail transit is to promote safe, convenient, economic, efficient and green intelligent transportation in the way of "displacement"; The development trend of Beidou system is to empower the rail transit industry in the way of "Beidou" (that is, taking Beidou technology as the enabling means, using space-time information as the application mode, combining with the original technology and business of other industries or replacing the traditional application scheme), so as to promote its transformation and upgrading. "Displacement Beidou", as the core concept of the integrated development of Beidou system and smart city rail, will further enrich the technical application and industrial ecosystem of urban rail and Beidou system, promote their all-round development, and promote the implementation of the national strategy.

 

Integrated development of Beidou system and smart subway

#02

Requirements of smart city rail for Beidou System

As a typical complex information physical system, smart city rail involves a wide variety of information systems, such as automatic train control (ATC), automatic fare collection (AFC), power supply system management automation (SCADA), environmental monitoring (BAS), fire alarm (FAS). In order to realize its independent operation, these complex information systems must be integrated for the perception, processing, decision-making and control of massive time and space information. Therefore, it is more necessary to establish a unified spatio-temporal benchmark to avoid the risk of spatio-temporal information conflict and endanger the safe operation of urban rail transit.Using Beidou system and CGCS2000 coordinate system (the latest national geodetic coordinate system in China), the urban rail transit system can obtain a unified, autonomous and controllable space-time benchmark.

 

In addition, the space environment of urban rail transit is very complex. Exposed space and non exposed space coexist. Relying solely on satellite navigation system can not meet the current application requirements. By introducing the absolute time-space benchmark of Beidou system into the non exposed space of urban rail and maintaining it dynamically, on the one hand, it can realize the unity of the relative position of non exposed space and the absolute position of exposed space, and display and apply the position of non exposed space in urban rail in the form of absolute coordinate system; On the other hand, it can unify time and realize time synchronization in non exposed space.

Due to the complex spatial environment of urban rail transit, mastering rich and accurate geographic information is the basis for the construction and operation of smart urban rail transit. Spatial digitization, i.eBuilding digital geographic data framework (dsdf)It is the product of the development and integration of Surveying and mapping technology, geographic information technology and other modern information technologies.

 

With the progress of technical means, surveying and mapping technology is developing towards three-dimensional digitization, networking, real-time and visualization of information collection, data processing and achievement application. There is a demand for spatial digitization application with three-dimensional real scene modeling as the core. In the construction of smart city rail, based on the time-space benchmark of Beidou system, it is necessary to use station mounted, push broom, backpack, handheld and other surveying and mapping tools and geographic information data acquisition equipment to focus on the spatial structure, equipment and facilities, consumables and other elements of the machine room, station hall, section, depot, warehouse and other places in the underground and aboveground space of urban rail, Collect 3D laser point cloud data, supplemented by on-site photography, texture and other data information, and create a set of fine real scene 3D model of all elements to realize the spatial digitization of urban rail transit.

Using the above data, relevant staff can generate high-precision maps, sort out spatial resources, master the spatial structure, facilities and equipment of urban rail, provide accurate and comprehensive geographic information for the planning, construction, transformation and maintenance of smart urban rail, and provide important basic data and technical support for space utilization and refined management. As a new scene application of Beidou technology in the space-time system, spatial digitization has injected new vitality into the development of smart city rail.

High precision space and time information is the basis for the construction of smart city rail. Traffic data is a typical spatiotemporal data, which not only has the attribute of time dimension, but also has a strong dependence on spatial structure.

 

• It is difficult to receive satellite signals.In the non exposed space of urban rail transit, due to the shielding of the wall (especially reinforced concrete), the satellite positioning signal will obviously weaken after passing through the building, the positioning accuracy will be greatly reduced, and even the signal can not be received.
• Multiple obstacles and multiple interference sources.There are columns, elevators, escalators, equipment, screen doors, pedestrians and other obstacles in the urban rail, and the layout is different. In addition, pedestrians and vehicles are moving all the time, and the signal will be reflected many times. These many uncertain disturbances make the urban rail environment extremely complex. This situation is particularly prominent in the subway, because the subway environment is relatively closed, and the complex environmental interference such as radio signal, sound, light and temperature will have a negative impact on the accuracy of positioning equipment sensors.
  
• Elevation positioning is difficult.In the subway environment, we should not only consider the location of two-dimensional plane, but also consider the location and height of above ground and underground floors for multi-storey buildings.
  
• It is difficult to develop application terminals.Urban rail transit needs miniaturized, personalized and combined application terminals, and solves the problems of component optimization design, material optimization, precision manufacturing, component deep integration, sensor real-time calibration, sensor output information adaptive fusion and so on. Researchers should conduct targeted research from the above four aspects to solve the above problems, so as to provide high-precision space and time information for the construction and operation of smart city rail and ensure its smooth progress.

#03

Application prospect of Beidou System in smart city rail

Smart city rail must build an independent and controllable space-time system network.

In view of the problems that Beidou navigation and positioning system cannot be used in non exposed space, lack of high-throughput communication means, lack of all factor geographic information and so on, the "Beidou 5g spatial digitization" technology should be comprehensively applied to build a "three networks and one platform" space-time system network composed of high-precision positioning network, high-precision time synchronization network, high-throughput communication network and spatial digitization platform, Form the urban rail space-time benchmark information network and use it as the infrastructure for the construction and operation of smart urban rail to provide unified and continuous space and time information, positioning, timing and communication services for urban rail, so as to supplement, enhance and backup the application of Beidou System in non exposed space, so as to break the barrier between exposed space and non exposed space of urban rail.

 

Construction of smart city rail space-time system network

To build a smart city rail space-time system network, we need to focus on breaking through key technologies such as indoor and outdoor integrated high-precision continuous positioning, large-scale high-precision time-frequency transmission based on general network protocol, 5g based high-throughput wireless communication application and so on.

 

In terms of positioning, it is necessary to realize continuous positioning in exposed space and non exposed space on a unified spatial benchmark, dominated by ultra wide band (UWB) positioning technology, supplemented and enhanced by a variety of positioning technologies, and through the integration of navigation and positioning software and algorithms; Through the comprehensive pnt system invested and constructed by the state and the micro pnt system developed by miniaturized, personalized and combined service terminals, high-precision location services are provided.

In terms of time, based on the precise clock synchronization protocol (also known as precise time synchronization protocol (PTP)) of IEEE 1588v2 network measurement and control system, it is necessary to combine synchronous Ethernet (synce) technology and white rabbit (WR) time synchronization method on a unified time benchmark, Realize the dynamic time synchronization of the whole network node in the intercity range to provide high-precision time service.

In the aspect of communication, it is necessary to develop the urban rail indoor distribution system and the time slicing algorithm for metro service in order to realize the application of high-throughput communication. In addition, with the development of system construction, we must also break through a series of key technologies applied by Beidou System in smart city rail.

 

• In terms of intelligent operation, the Beidou system can obtain the real-time and high-precision location information of station affairs, management and construction personnel. On this basis, the urban rail workers can be accurately managed by building an electronic fence, electronic roll call sign in, performance evaluation analysis and other methods; Train positioning is the guarantee for the safe and efficient operation of urban rail trains. The use of Beidou system can make the train positioning more accurate, more redundant, more autonomous, deeper integration and more efficient linkage.

• In terms of intelligent maintenance, urban rail facilities and equipment are complex, highly automated and large-scale assets. Their maintenance and management are directly related to the safety and reliability of urban rail operation. Obtaining the accurate location of facilities and equipment through Beidou system can realize the automatic inventory of assets and equipment based on the accurate location in the asset management system, and create a closed-loop chain of condition monitoring, fault diagnosis, risk early warning, maintenance evaluation and asset management.

• In terms of intelligent customer service, using Beidou system, passengers can quickly find and plan the route of self-service ticket machines, self-service vending machines, toilets and other service facilities inside and outside the urban rail station; It can also realize functions such as self-service navigation, intelligent mobile terminal and robot guidance service based on multi-dimensional and multi-level digital map, so as to provide full-time and personalized travel services for passengers with passengers' travel needs as the core

#04

epilogue

Time and space information has become the basic information in modern production and life. The development of satellite navigation and positioning system has completely changed people's lifestyle and the management mode of society and enterprises. With the completion and application of Beidou system, the construction and development of smart city rail in China put forward higher requirements for space-time benchmark, spatial digitization, high-precision positioning and timing.

In the future, Beidou system and smart city rail have broad integration space and potential. Its core is to define its pnt system according to the application scenarios of urban rail, break through key technologies and build a "three networks and one platform" space-time system network. The application and promotion of Beidou system will create the best basic conditions for the intelligent transformation of urban rail transit.

reference:

Lin Luzhou, Li Yujie, Deng pingke, et al Application and Prospect of Beidou System in smart city rail [J] Modern urban rail transit, 2021 (4):6-10.


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