Method for applying space-time positioning and three-dimensional communication to rail transit by near-earth satellite

Abstract

According to the method for applying the space-time positioning and the three-dimensional communication to the rail transit through the near-earth satellites, the positioning precision is improved and the initial positioning time is shortened by transmitting navigation enhancement information through a near-earth satellite constellation communication navigation time service function or a transmission channel, or / and the navigation signal strength is enhanced through the positioning satellite function of the near-earth satellites, and the positioning accuracy is improved. Reliable train-ground communication, train-train communication, train head-tail communication, trackside equipment and stations and inter-station communication of a train in a satellite communication section are achieved by providing a switching method between near-earth satellite constellation satellites or wave beams, and the satellite communication section can be obtained through train positioning or prompted by a ground transponder through marking in line data by dividing the satellite communication section. Switching between a satellite communication section and other communication sections can be realized, and the transportation efficiency is improved.

Description

Technical Field

[0001] This invention belongs to the field of rail transit. It utilizes the communication, navigation, and timing functions or transmission channels of near-Earth satellite constellations to transmit navigation enhancement information, thereby improving positioning accuracy and shortening initial positioning time. Alternatively, it utilizes the positioning satellite functions of near-Earth satellites to enhance navigation signal strength. By providing a switching method between near-Earth satellite constellations or beams, it enables reliable train-to-ground, train-to-train, train-to-train, trackside equipment and station, and station-to-station communication within satellite communication sections. By dividing satellite communication sections and marking them in the line data, the satellite communication sections can be obtained through train positioning or prompted by ground transponders. This allows for switching between satellite communication sections and other communication sections, improving transportation efficiency. Background Technology

[0002] With the deployment of near-Earth satellite constellations, the reliability and wide coverage of satellite communication technology are suitable for the communication needs of rail transit. At the same time, with the country deploying ultra-low orbit satellite constellations, the navigation function of ultra-low orbit satellites can improve the positioning accuracy and availability of trains, railcars and locomotives, and can be used for track occupancy checks and train integrity checks.

[0003] Existing rail transit, especially railways, mainly uses track circuits and transponders to provide vehicle-to-ground data interaction. Only passenger dedicated lines, urban rail, and some heavy-haul railways use CBTC. However, the cost of deploying wireless communication base stations along the track is high, especially in remote areas such as mountainous regions, which increases construction and maintenance costs.

[0004] The current status of rail transit positioning and speed measurement, system clock synchronization, track occupancy checks, and train integrity checks has the following problems: Train positioning technology based on track circuits has low positioning accuracy and requires a lot of trackside equipment, which is easily affected by the electrical characteristics of the rails and the environment. Track circuit-based section occupancy and train integrity checks require the rails as a carrier and are easily affected by the environment and electromagnetic fields. Train positioning, occupancy checks, and train integrity checks based on axle counting track circuits are easily interfered with and cannot transmit information. Train positioning technologies based solely on interrogation transponders or beacons require numerous trackside devices, resulting in high positioning costs and difficult maintenance. In most cases, they are only used for positioning calibration. Speed ​​measurement and positioning methods, such as wheel and axle speed measurement, suffer from problems like wheel slippage and error accumulation. Doppler radar velocity measurement is subject to environmental interference and error accumulation; Therefore, it is necessary to further improve the accuracy, reliability, and availability of train positioning and speed measurement, while reducing the maintenance work of trackside or ground equipment.

[0005] According to patent searches, the following patents are mainly related to this invention: Chinese invention patent application number "201910881644.9", application date "2019-09-18", publication number "CN112526570A", publication date "2021-03-19", titled "Train Positioning Method and Device", with CRRC Zhuzhou Electric Locomotive Research Institute Co., Ltd. as the applicant, discloses a train positioning method and device. The train positioning method includes: acquiring differential position information of the train from a satellite receiver and acquiring the train's travel information from an inertial navigation unit; and performing positioning calculations based on the differential position information and the travel information to output the train's positioning information. This invention improves positioning accuracy, reduces errors, and is easy to implement and deploy with low construction costs.

[0006] Chinese invention patent application number "202110597668.9", application date "2021-05-31", publication number "CN113335341A", publication date "2021-09-03", titled "Train Positioning System and Method Based on GNSS and Electronic Map Topology", applicant "CASCO Signal Co., Ltd.", relates to a train positioning system and method based on GNSS and electronic map topology. The system includes a GNSS satellite positioning receiver module, a Kalman filter module, a map matching algorithm module, and an onboard electronic map module. The GNSS satellite positioning receiver module is connected to the map matching algorithm module via the Kalman filter module, and the map matching algorithm module is connected to the onboard electronic map module. The map matching algorithm module accurately matches the train positioning data output by the Kalman filter module to a specific track segment on the electronic map of the onboard electronic map module, thereby achieving precise train positioning. Compared with existing technologies, this invention has advantages such as reducing the dependence of the positioning algorithm on ground equipment and reducing the construction and maintenance costs of local railways.

[0007] Chinese invention patent application number "202111458086.9", application date "2021.12.02", publication number "CN114039653A", publication date "2022.02.11", titled "Method, Device, Ground Terminal, Satellite and Gateway Station for Switching Medium and Low Earth Orbit Satellites", with applicant "Beijing Jiutian Microstar Technology Development Co., Ltd.", discloses a method, device, ground terminal, satellite and gateway station for switching medium and low Earth orbit satellites. The method includes: acquiring pre-switching information, which includes at least one target satellite information and a switching trigger condition; and switching to the service link of the target satellite corresponding to the switching trigger condition when the switching trigger condition is met.

[0008] The train positioning methods proposed in the aforementioned patents and documents employ satellite positioning alone, or satellite positioning combined with traditional positioning methods. Although some of them propose to improve positioning accuracy through differential satellite positioning or auxiliary base station positioning, the railway spans a large area, and considering the cost and maintenance, it is not suitable to set up reference stations or mobile base stations along the entire railway line. Meanwhile, this patent proposes a satellite switching method suitable for trains, which improves the reliability of satellite communication and improves train operation efficiency. Summary of the Invention

[0009] This invention belongs to the field of rail transit. The technical problem it aims to solve is to address the shortcomings of existing technologies by proposing a solution that integrates the communication, navigation, and timing functions of near-Earth orbit satellite (low-Earth orbit and very low-Earth orbit satellite) constellations. This solution transmits enhanced navigation information and / or enhanced navigation signals, improving the accuracy, availability, and continuity of satellite positioning. It also avoids the disadvantages of medium- and high-Earth orbit navigation satellites, reducing or eliminating the need for ground reference stations and mobile base stations. Furthermore, it combines single or combined technologies such as inertial navigation, wheel and axle speed measurement or radar speed measurement, active or passive beacons (including transponders, graphics such as QR codes), track circuit positioning, and railway line feature identification positioning. By leveraging the strengths of each technology and incorporating onboard electronic maps, it achieves precise train positioning and speed measurement, and can be used for shunting, railcars, locomotives, etc.

[0010] Low-Earth orbit satellite positioning refers to patent CN2022102349721.

[0011] Near-Earth satellites can include low-Earth orbit satellites and very low-Earth orbit satellites. Ground communication networks can be WLAN, GSM-R, LTE-R, etc. Communication channels can be vehicle-to-ground communication (communication between the head and tail of the train and ground equipment), vehicle-to-vehicle communication, communication between the head and tail of the train, communication between trackside equipment and the control center, etc.

[0012] When a terrestrial network exists for trains and trackside equipment, the terrestrial communication network can be prioritized as the data transmission channel, with near-Earth satellite communication serving as a backup. The train terminal switches between the terrestrial and near-Earth satellite communication networks based on beacons or track data location coordinates. The division of the train's satellite communication area, the area for terrestrial wireless communication, and other vehicle-to-ground communication methods such as track circuits is determined by setting up ground transponders or beacons, or by setting switching points in the track data and reading them based on the train's positioning, prompting the train to switch.

[0013] Data interaction between trackside equipment and ground control center and on-board equipment can be achieved through mobile communication provided by near-Earth satellites, as well as between train tail equipment and ground equipment, and between adjacent trains.

[0014] The station uses a near-Earth satellite constellation for external communication and adopts a gateway approach to unify with low-Earth orbit satellite communication. Internal communication within the station is divided into critical data communication and non-critical data communication, and gateways can be set for each.

[0015] The location of the communication terminal of the station gateway and trackside equipment is fixed. The coordinate information of the fixed location can be uploaded or the coordinate information of the terminal is already contained in the satellite constellation management terminal.

[0016] The speed of medium- and low-speed trains relative to near-Earth satellites can be considered slow, while the speed of high-speed trains, including high-speed flying cars, relative to satellites in medium- and low-Earth orbits can be considered low. Trains can periodically upload location information (the faster the train speed, the shorter the period), which can be used for satellite constellation management of train beam and satellite communication switching.

[0017] To meet the data and voice service needs of numerous terminal devices on passenger trains, mobile communication gateways are installed in passenger train carriages. These gateways can interact with satellite communication, reducing the number of satellite communication connections. Wireless fiber optic communication can be used. To meet the real-time status monitoring needs of freight trains, near-Earth satellite constellation mobile communication technology can be used. For gateway terminals and mobile terminals on trains that do not have their own positioning capabilities, uplink data containing corresponding train identification information such as train number can be provided. The satellite constellation can then obtain the terminal's location and manage beam and satellite switching.

[0018] The satellite communication network switching of ground mobile terminals (trains, passengers) and ground trackside equipment and station communication stations involves storing or receiving the location information of fixed terminals at satellite terminals or gateway stations, or identifying the terminal location at the satellite terminal. The satellite constellation can predict the next adjacent beam or satellite based on the relationship between the terminal location and the beam or satellite communication coverage. The subsequent switchable beams or satellites of ground communication terminals and communication stations are comprehensively considered and prioritized. The terminal obtains the prioritization and switching plan, and can switch based on the monitored signal strength (such as signal threshold), or by measuring the changes in the strength of the broadcast or pilot signals of the current beam and adjacent beams (which can determine whether the terminal is crossing the boundary between adjacent beams or is in the overlapping area of ​​adjacent beams). When the terminal enters the overlapping area of ​​adjacent beams and meets the switching trigger condition, it selects the subsequent beam and satellite for switching. The terminal stops using the current beam for communication and uses the new beam for communication by allocating a new channel. That is, after the switching process begins, a channel needs to be allocated to the user in the newly arrived beam according to a certain channel allocation algorithm, and the channel used in the original beam is released.

[0019] During the handover, due to the change of serving satellites, satellite communication systems that require inter-satellite exchange and routing need to re-establish routes. The route establishment can follow the shortest path strategy.

[0020] The satellite comprehensively evaluates factors such as the duration of subsequent beam or satellite coverage over the terminal, signal strength, number of available channels, and minimum number of handovers.

[0021] Satellite signal strength is used as the initial method for selecting satellite, beam, and channel; if satellite communication is interrupted, calls are continued on the channel originally assigned to the beam. If a connection still cannot be established, the satellite terminal will proceed as if re-establishing a connection.

[0022] Initial authentication: The vehicle initiates communication verification. After the satellite verifies the terminal's identity, communication is established. Intra-satellite beam switching does not require verification. Inter-satellite switching can be re-authenticated or avoids re-authentication by transmitting authentication information between satellites. After disconnection, reconnection and authentication are performed.

[0023] Switching methods: Intra-satellite beam switching: A / B network mode, A network is the current connection, B network is pre-connected, and if the B network connection is successful, the switch will be made as long as the A network signal amplitude is lower than a certain value or is worse than the B network; or A / B network mode, A network is the current connection, B network is pre-connected, and the satellite end notifies the switch based on the terminal location; A / B network mode can be redundant and can be used to alternately establish communication during switching.

[0024] In single-network mode, the satellite terminal notifies the terminal to switch based on the terminal's location, or the terminal switches automatically based on signal strength.

[0025] Inter-satellite switching: Same as above.

[0026] Near-Earth satellite constellations used in rail transit can transmit and receive both critical and non-security data. They can support functions such as Virtual Local Area Networks (VLANs) and Access Control Lists (ACLs) to ensure secure isolation between devices and secure data transmission. By identifying terminal communication attributes, they can establish data communication link tables or routing tables and adopt corresponding communication mechanisms such as packet forwarding, directed routing, least route or fastest path, and setting communication priorities.

[0027] Wireless fiber optic communication based on near-Earth satellites can be applied to railways to enable communication between stations in remote areas and between stations and the central station, thus replacing the need for ground-based fiber optic networks.

[0028] By integrating near-Earth satellite constellations with medium- and high-orbit satellites to construct "wireless fiber optic" technology, ultra-fast broadband can be achieved. This technology can be used for big data interaction between railway stations and can serve as a backup for fiber optic communication.

[0029] The beneficial effects of this invention are as follows: by utilizing the communication, navigation, and timing functions or transmission channels of near-Earth satellite constellations to transmit navigation enhancement information, the accuracy of positioning is improved and the initial positioning time is shortened; and / or by utilizing the positioning satellite functions of near-Earth satellites, the strength of navigation signals is enhanced; by providing a method for switching between near-Earth satellite constellations or beams, reliable train-to-ground, train-to-train, train-to-train, trackside equipment and station, and station-to-station communication is achieved in the satellite communication section; by dividing the satellite communication section and marking it in the line data, the satellite communication section can be obtained through train positioning or prompted by the ground transponder, and the switching between the satellite communication section and other communication sections can be achieved, thereby improving transportation efficiency. Attached Figure Description

[0030] none. Implementation

[0031] The present invention will be further described below through specific embodiments: This invention proposes that train and vehicle positioning can utilize near-Earth orbit satellites to transmit navigation enhancement information and / or enhance navigation signals. It can integrate existing satellite positioning technologies such as differential positioning, PPP technology, multi-frequency modes, and space-ground-based augmentation to improve the satellite positioning accuracy and availability of trains. It can be used to achieve precise positioning, speed measurement, and direction of travel identification of trains; it can be used for positioning at the beginning and end of a train, and can be used for shunting, railcars, locomotives, and rolling stock.

[0032] Near-Earth satellites can include low-Earth orbit satellites and very low-Earth orbit satellites. Communication channels formed by near-Earth satellites can provide vehicle-to-ground communication (communication between the head and tail of the train and ground equipment), vehicle-to-vehicle communication, communication between the head and tail of the train, and communication between trackside equipment and the control center. Wireless communication provided by near-Earth satellites can enable data interaction between trackside equipment and the ground control center and onboard equipment, data interaction between the tail of the train and ground equipment, and data interaction between adjacent trains.

[0033] When a terrestrial network exists, the onboard equipment and trackside equipment of trains and vehicles can prioritize the terrestrial communication network as the data transmission channel, with near-Earth satellite communication serving as a backup. The train terminal will switch between the terrestrial communication network and the near-Earth satellite communication network based on beacons or line data location coordinates. The division of the train's satellite communication area and the area for communication via terrestrial wireless communication, as well as other vehicle-to-ground communication methods such as track circuits, will be determined by setting up ground transponders or beacons, or by setting switching points in the line data and reading them based on the train's positioning, prompting the switch to proceed.

[0034] The station uses a near-Earth satellite constellation for external communication and adopts a gateway approach to unify with low-Earth orbit satellite communication. Internal communication within the station is divided into critical data communication and non-critical data communication, and gateways can be set for each.

[0035] The communication terminals of station gateways and trackside equipment are located in fixed positions. They can upload fixed coordinate information via satellite communication, while the satellite constellation's on-board processing terminal stores the location information, or the satellite constellation management terminal has pre-stored the terminal's location coordinate information and distributed it in real time to near-Earth satellites covering that location. The movement speed of medium- and low-speed trains relative to near-Earth satellites can be considered slow movement. Trains periodically upload location information, and the near-Earth satellite constellation can consider medium- and low-speed trains as stationary equipment. The movement speed of high-speed trains, including high-speed overtaking trains, relative to satellites in medium- and low-orbit orbits can be considered low-speed movement. Trains can periodically upload location information, including their direction of travel and speed. The low-orbit satellite constellation can pre-store railway line data to achieve high-speed train location tracking, and the satellite constellation's on-board processing terminal updates the location information in real time. The location information of terminals (station gateways, trackside equipment, trains, and equipment on trains) can be used for beam switching between satellite constellation management terminals and satellites.

[0036] To meet the data and voice service needs of numerous terminal devices on passenger trains, mobile communication gateways are installed in passenger train carriages. These gateways can interact with satellite communication, reducing the number of satellite communication connections. Wireless fiber optic communication can be used. To meet the real-time status monitoring needs of freight trains, near-Earth satellite constellation mobile communication technology can be used. For gateway terminals and mobile terminals on trains that do not have autonomous positioning capabilities, uplink data containing corresponding train identification information such as train number can be provided. The satellite constellation management terminal can then obtain the terminal's location and manage beam and satellite switching.

[0037] Communication terminals with autonomous positioning capabilities can also perform elevation positioning. Terminal devices without autonomous positioning capabilities can be equipped with satellite positioning devices to achieve autonomous positioning, which may include elevation. Location management can be performed using latitude and longitude coordinates, or latitude and longitude coordinates plus elevation.

[0038] The ground terminal initially establishes a satellite communication connection by using satellite signal strength as the method for selecting the satellite, beam, and channel. If satellite communication is interrupted, it continues to call on the channel assigned by the original beam. If a connection still cannot be established, the satellite terminal will proceed with re-establishing the connection.

[0039] Initial authentication: Vehicle terminals, etc. initiate communication verification. After the satellite verifies the identity of the terminal, communication is established. Intra-satellite beam switching does not require verification. Inter-satellite switching can be re-authenticated or avoid re-authentication by transmitting authentication information between satellites. After disconnection, reconnection and authentication are performed.

[0040] The switching of satellite communication networks for ground mobile terminals (trains, onboard equipment, passenger handheld mobile communication devices, etc.) and communication gateways for ground trackside equipment and stations is achieved by storing the location information of fixed terminals at satellite terminals or gateway stations, receiving terminal location information in real time, or identifying terminal locations at satellite terminals. The satellite constellation can predict the next adjacent beam or satellite based on the relationship between the terminal location and the coverage area of ​​the beam or satellite communication (the management end or onboard processing end of near-Earth satellite constellations has terrain maps, which can reduce weak-field areas through cross-coverage). It then comprehensively considers the subsequent switchable beams or satellites of ground communication terminals and communication stations, prioritizing and sending them to the ground. The terminal acquires the sorting and switching plan, and can switch based on the monitored signal strength (such as signal threshold), or the terminal measures the changes in the strength of the broadcast or pilot signals transmitted by the current beam and neighboring beams (which can determine whether the terminal is crossing the boundary between adjacent beams or is in the overlapping area of ​​adjacent beams), enters the overlapping area of ​​adjacent beams and meets the conditions for switching triggering, and selects the beam and satellite for subsequent switching; the terminal stops using the current beam for communication and uses the new beam for communication by allocating a new channel. That is, after the switching process begins, a channel needs to be allocated for the user in the newly arrived beam according to a certain channel allocation algorithm, and the channel used in the original beam is released.

[0041] During the handover, due to the change of serving satellites, satellite communication systems that require inter-satellite exchange and routing need to re-establish routes. For real-time requirements such as vehicle-to-ground communication, the shortest path strategy can be followed.

[0042] The satellite comprehensively evaluates factors such as the duration of subsequent beam or satellite coverage over the terminal, signal strength, number of available channels, and minimum number of handovers.

[0043] Switching methods: Intra-satellite beam switching: A / B network mode, A network is the current connection, B network is pre-connected, and if the B network connection is successful, the switch will be made as long as the A network signal amplitude is lower than a certain value or is worse than the B network; or A / B network mode, A network is the current connection, B network is pre-connected, and the satellite end notifies the switch based on the terminal location; A / B network mode can be redundant and can be used to alternately establish communication during switching.

[0044] In single-network mode, the satellite terminal notifies the user to switch based on the terminal's location, and the terminal switches automatically based on signal strength.

[0045] Inter-satellite switching: Same as above.

[0046] Near-Earth satellite constellations used in rail transit can transmit and receive both critical and non-security data. They can support functions such as Virtual Local Area Networks (VLANs) and Access Control Lists (ACLs) to ensure secure isolation between devices and secure data transmission. By identifying terminal communication attributes, they can establish data communication link tables or routing tables and adopt corresponding communication mechanisms such as packet forwarding, directed routing, least route or fastest path, and setting communication priorities.

[0047] Wireless fiber optic communication based on near-Earth satellites can be applied to railways to enable communication between stations in remote areas and between stations and central stations, replacing ground-based fiber optic networks. By integrating near-Earth satellite constellations with medium- and high-orbit satellites to construct "wireless fiber optic" technology, ultra-fast broadband can be achieved, which can be used for big data interaction between railway stations and can serve as a backup for fiber optic communication. Communication links can be constructed using radio waves or lasers.

[0048] In summary, the beneficial effects of this invention are as follows: It utilizes the communication, navigation, and timing functions or transmission channels of near-Earth satellite constellations to transmit navigation enhancement information, thereby improving positioning accuracy and shortening initial positioning time; and / or utilizes the positioning satellite functions of near-Earth satellites to enhance navigation signal strength. By providing a switching method between near-Earth satellite constellations or beams, reliable train-to-ground, train-to-train, train-to-train, trackside equipment and station, and station-to-station communication can be achieved within the satellite communication section. By dividing the satellite communication section and marking it in the line data through train positioning or ground transponder prompts, switching between satellite communication sections and other communication sections can be realized, improving transportation efficiency.

[0049] The above embodiments are for illustrative purposes only and are not intended to limit the invention. Those skilled in the art can make various changes or modifications without departing from the spirit and scope of the invention. Therefore, all equivalent technical solutions should also fall within the protection scope of the invention, which should be defined by the claims.

Claims

1. A method for applying near-Earth satellites to achieve spatiotemporal positioning and three-dimensional communication in rail transit, characterized by: Data interaction between trackside equipment and ground control center and on-board equipment can be achieved through wireless communication provided by near-Earth satellites, as well as data interaction between train tail equipment and trackside equipment; The station uses a near-Earth satellite constellation for external communication and a gateway to enable low-Earth orbit satellite communication. Internal communication within the station is divided into critical data communication and non-critical data communication, and gateways can be set for each.

2. A method for applying near-Earth satellites to achieve spatiotemporal positioning and three-dimensional communication in rail transit, characterized by: When onboard and trackside equipment of trains and vehicles have a ground network, the ground communication network can be selected as the data transmission channel first, and near-Earth satellite communication can be used as a backup. The terminals of trains and vehicles can switch between the ground communication network and the near-Earth satellite communication network through beacon or line data location coordinate prompts. The division of the near-Earth satellite communication area of ​​trains and vehicles, the area of ​​ground wireless communication, and the area of ​​other vehicle-to-ground communication methods are determined by setting ground transponders or beacons, or by setting switching points in the line data and reading them according to the train positioning, and prompting for switching.

3. The method for achieving spatiotemporal positioning and three-dimensional communication using near-Earth satellites according to claims 1 and 2, characterized in that: The location of the communication terminal of the station gateway and trackside equipment is fixed. The location information can be identified by uploading the fixed location coordinate information and temporarily storing the location information on the satellite constellation's on-board processing terminal, or by the satellite constellation management terminal pre-storing the terminal's location coordinate information and distributing it in real time to the near-Earth satellites covering the location, or by the satellite constellation identifying the terminal's location. The speed of medium- and low-speed trains relative to near-Earth satellites can be considered slow. Trains or onboard equipment periodically upload position information, and the near-Earth satellite constellation can consider medium- and low-speed trains as stationary equipment in each processing cycle. The speed of high-speed trains, including high-speed flying cars, relative to satellites in medium- and low-Earth orbits can be considered low. Trains can periodically upload position information, including direction of travel and speed. The low-Earth orbit satellite constellation can pre-store railway line data to achieve position tracking of high-speed trains, and the onboard processing terminal of the satellite constellation updates position information in real time. Near-Earth satellite constellations can manage the beam and satellite switching of communication terminals through location information.

4. The method for achieving spatiotemporal positioning and three-dimensional communication using near-Earth satellites according to claims 1, 2, and 3, characterized in that: Passenger trains have numerous terminal devices for data and voice services. Satellite communication gateways are installed in passenger train carriages, which can interact with satellite communication through the gateways, reducing the number of satellite communication connections. Wireless fiber optic communication can be used. Data outside the rail transit system can be accessed through near-Earth satellite constellations and nearby ground gateway stations to access the ground network, or transmitted to the target ground gateway station via inter-satellite routing. Real-time monitoring of freight train vehicle status can be achieved using near-Earth satellite constellation wireless communication technology to meet data transmission requirements; For gateway terminals and mobile terminals on trains that do not have their own positioning function, uplink data containing the corresponding train identification information can be provided, and the terminal location can be obtained through near-Earth satellite constellations, thereby enabling management of beam and satellite switching. Communication terminals with autonomous positioning capabilities can also perform elevation positioning. Terminal devices without autonomous positioning capabilities can be equipped with satellite positioning devices to achieve autonomous positioning, which may include elevation. Location management can be performed using latitude and longitude coordinates, or latitude and longitude coordinates plus elevation.

5. The method for achieving spatiotemporal positioning and three-dimensional communication using near-Earth satellites according to claims 1, 2, and 3, characterized in that: The ground terminal initially establishes a satellite communication connection by using satellite signal strength as the initial method for selecting the satellite, beam, and channel. If satellite communication is interrupted, the terminal continues to call on the channel originally assigned by the beam for a period of time. If a connection still cannot be established, the satellite terminal will proceed with re-establishing the connection. Initial authentication: Train and vehicle onboard equipment, trackside equipment, and station equipment initiate communication verification. The satellite verifies the terminal's identity before establishing communication. Intra-satellite beam switching does not require further verification, while inter-satellite switching can be re-authenticated or avoid re-authentication by transmitting authentication information between satellites. Reconnect and authenticate after disconnection.

6. The method for achieving spatiotemporal positioning and three-dimensional communication using near-Earth satellites according to claims 1, 2, and 3, characterized in that: The switching of satellite communication networks between train and vehicle onboard equipment and onboard personnel's handheld communication terminals, and between ground trackside equipment and station communication gateways, is achieved by storing fixed terminal location information at the satellite end or gateway station, receiving terminal location information in real time, or identifying terminal location at the satellite end. The satellite constellation can prioritize and sort the available beams or satellites based on the relationship between terminal location and beam or satellite communication coverage. The management end or onboard processing end of the near-Earth satellite constellation has terrain maps and can predict the next adjacent beam or satellite. The system comprehensively considers the subsequent switchable beams or satellites of ground communication terminals and communication stations, prioritizing them accordingly. Terminal acquisition, sorting, and switching are then implemented. The system can change its course and switch based on the strength of the monitored signal. Alternatively, the terminal can determine whether it is crossing the boundary between adjacent beams or within the overlapping area of ​​adjacent beams by measuring the changes in the strength of the broadcast or pilot signals transmitted by the current beam and adjacent beams. Once it enters the overlapping area of ​​adjacent beams and meets the conditions for triggering a switchover, it selects the beam and satellite for subsequent switching. The ground terminal stops using the current beam for communication and uses the new beam for communication by allocating a new channel. That is, after the switchover process begins, a channel needs to be allocated for the user in the newly arrived beam according to a certain channel allocation algorithm, and the channel used in the original beam needs to be released. During the handover, due to the change of serving satellites, satellite communication systems that require inter-satellite exchange and routing need to re-establish routes. The route establishment can follow the shortest path strategy. The satellite comprehensively evaluates the duration of subsequent beam or satellite coverage over the terminal, signal strength, number of available channels, and minimum switching factor.

7. The method for achieving spatiotemporal positioning and three-dimensional communication using near-Earth satellites in rail transit according to claims 1, 2, and 3, characterized in that: Switching method:

1. Intra-satellite beam switching: A / B network mode, A network is the current connection, B network is the pre-connection, and the B network connection is successful. If the A network signal amplitude is lower than a certain value or is worse than the B network, the switch will be made; or A / B network mode, A network is the current connection, B network is the pre-connection, and the satellite end notifies the switch based on the terminal location; A / B network mode can be redundant and can be used to alternately establish communication during switching. In single-network mode, the satellite terminal notifies the terminal to switch based on the terminal's location, or the terminal switches automatically based on signal strength. II. Inter-satellite switching: Same as above.

8. The method for achieving spatiotemporal positioning and three-dimensional communication using near-Earth satellites according to claims 1 and 2, characterized in that: The near-Earth satellite constellation providing communication for rail transit systems carries a mixed transmission of secure and non-secure data. It supports Virtual Local Area Network (VLAN) and Access Control List (ACL) functions to ensure secure isolation between devices and secure data transmission. By identifying terminal communication attributes, it establishes data communication link tables or routing tables and adopts corresponding communication mechanisms, including but not limited to packet forwarding, directed routing, least route or fastest path, and setting communication priorities.

9. The method for achieving spatiotemporal positioning and three-dimensional communication using near-Earth satellites according to claims 1 and 2, characterized in that: Wireless fiber optic communication based on near-Earth satellites can be applied to railways to enable communication between stations in remote areas and between stations and the central station, thus replacing or as a backup for ground-based fiber optic networks. By integrating near-Earth satellite constellations with medium- and high-orbit satellites to construct wireless fiber optic technology, ultra-fast broadband can be achieved, which can be used for big data interaction between railway stations and can serve as a backup for fiber optic communication. Communication links can be constructed using electromagnetic waves or lasers.

10. A method for applying near-Earth satellites to achieve spatiotemporal positioning and three-dimensional communication in rail transit, characterized by: Train and vehicle positioning can utilize near-Earth orbit satellites to transmit navigation enhancement information and / or enhance navigation signals. This can integrate existing satellite positioning technologies, positioning satellites, and ground facilities to improve the accuracy and availability of train satellite positioning, enabling precise positioning, speed measurement, and direction of travel identification of trains. It can be used for positioning at the beginning and end of a train, and for positioning shunting vehicles, railcars, locomotives, and rolling stock.