WO2024253253A1 - Procédé et dispositif de positionnement basé sur une optimisation de graphe de factorisation à l'aide de multiples satellites en orbite terrestre basse - Google Patents

Procédé et dispositif de positionnement basé sur une optimisation de graphe de factorisation à l'aide de multiples satellites en orbite terrestre basse Download PDF

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Publication number
WO2024253253A1
WO2024253253A1 PCT/KR2023/012106 KR2023012106W WO2024253253A1 WO 2024253253 A1 WO2024253253 A1 WO 2024253253A1 KR 2023012106 W KR2023012106 W KR 2023012106W WO 2024253253 A1 WO2024253253 A1 WO 2024253253A1
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Prior art keywords
factor
terminal
satellite
orbit
low
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Korean (ko)
Inventor
신원재
카비르 엠디.후마윤
하산 엠디.알리
박주하
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Ajou University Industry Academic Cooperation Foundation
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Ajou University Industry Academic Cooperation Foundation
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
    • G01S19/38—Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system
    • G01S19/39—Determining a navigation solution using signals transmitted by a satellite radio beacon positioning system the satellite radio beacon positioning system transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
    • G01S19/42—Determining position
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
    • G01S5/02—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using radio waves

Definitions

  • the present disclosure relates to positioning using multiple low-orbit satellites, and to a positioning method and device based on factor graph optimization (FGO).
  • FGO factor graph optimization
  • GNSS Global Navigation Satellite System
  • LEO low earth orbit
  • the present disclosure provides a method and device for performing precise positioning based on factor graph optimization (FGO) using multiple low-Earth orbit satellites.
  • FGO factor graph optimization
  • the present disclosure provides a method and device for determining factors of a factor graph in a positioning method.
  • the present disclosure provides a method and device for determining a delta range factor and a Doppler velocity factor in a positioning method.
  • the present disclosure provides a method and device in which state variables are linked by a Doppler velocity factor in a positioning method.
  • the present disclosure provides a method and device for performing positioning based on covariance and factor graph optimization in a positioning method.
  • a method for positioning a terminal using multiple low-orbit satellites may include the steps of receiving signals from at least one low-orbit satellite, obtaining ephemeris data of each of the low-orbit satellites, determining a Doppler shift based on the ephemeris data and the signal, determining a state variable and at least one factor to be used in factor graph optimization, and obtaining a positioning result using the factor graph optimization based on the Doppler shift.
  • the at least one factor may include a delta range factor and a Doppler velocity factor.
  • the state variables can be connected by a Doppler velocity factor.
  • the error function value of the delta range factor may be determined based on the difference between the delta range measurement vector and the observation function for measuring the Doppler shift, and the error function value of the Doppler velocity factor may be determined based on the difference between the velocity measurement vector and the observation function for measuring the velocity.
  • the covariance matrix of the delta range factor and the Doppler velocity factor can be determined based on the elevation angle and carrier-to-noise ratio of the low-orbit satellite.
  • the positioning result can be determined based on an error function value of the delta range factor, an error function value of the Doppler velocity factor, and a covariance matrix.
  • the state variable may include at least one of a position of the terminal, a velocity of the terminal, or a receiver clock bias.
  • the celestial data may include at least one of a status of each of the low-orbit satellites, an age of the data, a clock correction factor, or a parameter value regarding the orbit.
  • a terminal utilizing satellite communication may include a transceiver and at least one processor connected to the transceiver, wherein the at least one processor receives signals from at least one low-orbit satellite, respectively, acquires ephemeris data of each of the low-orbit satellites, determines a Doppler shift based on the ephemeris data and the signal, and determines state variables and at least one factor to be used in factor graph optimization; and obtains a positioning result using the factor graph optimization based on the Doppler shift.
  • a terminal can perform precise positioning using multiple low-orbit satellites.
  • a terminal can perform precise positioning based on the Doppler velocity factor.
  • FIG. 1 is a diagram illustrating an example of a network supporting satellite communication according to one embodiment of the present disclosure.
  • FIG. 2 is a diagram illustrating another example of a network system supporting satellite communication according to one embodiment of the present disclosure.
  • FIG. 3 is a diagram illustrating an example of a wireless device in a system supporting satellite communication according to one embodiment of the present disclosure.
  • FIG. 4 is a diagram showing a path along which a satellite and a terminal perform communication in an urban canyon according to one embodiment of the present disclosure.
  • FIG. 5 is a diagram showing an error distribution in a line of sight (LOS) environment according to one embodiment of the present disclosure.
  • FIG. 6 is a diagram showing an error distribution in a non-LOS environment according to one embodiment of the present disclosure.
  • FIG. 7 is a diagram showing an environment of a positioning method using a low-orbit satellite according to one embodiment of the present disclosure.
  • FIG. 8 is a diagram illustrating the structure of a factor graph according to one embodiment of the present disclosure.
  • FIG. 9 is a diagram illustrating an example in which a Doppler shift occurs according to one embodiment of the present disclosure.
  • FIG. 10 is a diagram illustrating a procedure for performing positioning using low-orbit satellites according to one embodiment of the present disclosure.
  • FIG. 1 is a diagram illustrating an example of a network supporting satellite communication according to an embodiment of the present disclosure.
  • the satellite network includes a terminal (110), satellites (120-1, 120-2), and a gateway (130).
  • the terminal (110) is a user device and may be a mobile or fixed device.
  • the terminal (110) may support variable service bands and operation information according to the capability and application operation of the terminal (110).
  • the terminal (110) may be operated in a fixed form, a form specialized for mobility, or various forms according to the characteristics of the terminal (110).
  • the terminal (110) may be referred to as a 'UE (user equipment)'.
  • the satellites (120-1, 120-2) fly/operate in a fixed orbit and form a beam toward the ground to provide a cell with a certain size of coverage.
  • the gateway (130) provides the satellites (120-1, 120-2) with a link to access the network.
  • a link between a terminal (110) and a satellite (120-1) is referred to as a service link
  • a link between satellites (120-1, 120-2) and a gateway (130) is referred to as a feeder link.
  • the link may be a link based on the NR standard.
  • a link newly defined in an evolved next-generation wireless communication system may be adaptively applied, or a link based on various interfaces of a communication system introduced by industry needs rather than the NR standard may be applied.
  • an inter-satellite link ISL
  • ISL inter-satellite link
  • the satellite radio interface of the feeder link and the service link may be NR-Uu.
  • the satellite performs radio frequency filtering and frequency conversion and amplification functions.
  • onboard functions are built into the satellite, whereby the satellite may perform some or all of the base station functions, such as switching and routing, coding and modulation, and decoding and demodulation, in addition to radio frequency filtering, frequency conversion and amplification.
  • FIG. 2 is a diagram illustrating another example of a network system supporting satellite communication according to one embodiment of the present disclosure.
  • FIG. 2 illustrates an example of an NTN that provides non-terrestrial connectivity to a terminal (210) by using an NTN payload (220) and an NTN gateway (230).
  • the link between the NTN payload (220) and the terminal (210) is a service link and may be based on a Uu interface.
  • the link between the NTN payload (220) and the NTN gateway (230) is a feeder link.
  • the link between the NTN gateway (230) and the AMF/UPF (240) may be based on an NG interface.
  • the NTN payload (220) may transparently forward a wireless protocol received from the terminal (210) to the NTN gateway (230) via the service link. Similarly, the NTN payload (220) can transparently forward a wireless protocol received from the NTN gateway (230) to the terminal (210) via a feeder link.
  • a base station may service multiple NTN payloads.
  • An NTN payload may be serviced by multiple base stations.
  • the NTN payload (220) can change the carrier frequency before retransmitting data on the service link. That is, the NTN payload (220) can use different carrier frequencies on the service link and the feed link.
  • a network identifier at least one of an AMF name, an NR cell global identifier (NCGI), a CgNB identifier (CgNB ID), a global gNB ID, a tracking area identity (TAI), a Single Network Slice Selection Assistance information (S-NSSAI), a Network Slice AS Group (NSAG), a Network Identifier (NID), a Closed Access Group (CAG) ID, and a Local NG-RAN node ID (Identifier) may be used, and additionally, a Mapped Cell ID may be further used.
  • the tracking area may correspond to a fixed geographical area.
  • Non-geosynchronous orbits include low earth orbits with altitudes of about 300 km to 1500 km and medium earth orbits with altitudes of about 7000 km to 25000 km.
  • Service links can be classified into three types: earth-fixed, quasi-earth-fixed, and earth-moving.
  • the earth-fixed type provides beam(s) that continuously cover the same geographic area at all times.
  • a satellite having a geosynchronous orbit (GSO) can provide an earth-fixed type service link.
  • the quasi-earth-fixed type provides beam(s) that continuously cover the same geographic area for a limited period of time, and provides beams that cover different geographic areas for different periods of time.
  • a satellite having a non-earth-synchronous orbit can provide a quasi-earth-fixed type service link using steerable beams.
  • the earth-moving type provides beams whose coverage area slides over the surface of the Earth.
  • a satellite with a non-Earth-synchronous orbit could provide an Earth-mobile type service link using fixed or steerable beams.
  • the base station can provide quasi-Earth-fixed cell coverage or Earth-mobile cell coverage.
  • the base station can provide Earth-fixed cell coverage.
  • a change in the service link can be referred to a change in the serving satellite.
  • Pre-compensation by the terminal can be performed as follows.
  • the network can broadcast common TA (timing advance) parameters and ephemeris information.
  • the common TA means an offset corresponding to the RTT between the NTN payload and the RP (reference point).
  • the terminal before connecting to the NTN cell, the terminal has information about the satellite orbit and the common TA, and further, will have a valid GNSS (global navigation satellite system) position.
  • the terminal can calculate the RTT (round trip time) of the serving link based on the GNSS position and the satellite orbit, and pre-compensate the frame time difference between the downlink and uplink (e.g., T TA ).
  • the terminal can compute the frequency Doppler shift considering the terminal's position and the satellite orbit. If the terminal does not have a valid GNSS position and/or a valid satellite orbit, the terminal will not be able to communicate with the network until it acquires a valid GNSS position and a valid satellite orbit.
  • the terminal can continuously update the TA and frequency pre-compensation.
  • the terminal can be configured to report the TA during the random access procedure or in the connected mode. In the connected mode, event-triggered based TA reporting can be supported.
  • the O&M (operations and maintenance) requirements are as follows.
  • the following NTN related parameters can be provided to the base station providing non-terrestrial connectivity by the O&M.
  • orbital information describing coordinates or orbital trajectory information of an NTN satellite can be provided.
  • the orbital information can be provided upon request of the base station or on a regular basis.
  • the format of the orbital information two different sets can be supported.
  • the first set includes satellite position and velocity state vectors, i.e., position and velocity.
  • the second set can include at least one of semi-major axis, eccentricity, argument of periapsis, longitude of ascending node, inclination, and mean anomaly at epoch time to.
  • additional information may be provided to enable location information of NTN gateways and base station operation for feeder/service link switches.
  • Information related to the satellite's orbit and the position of the NTN gateway may be used for at least one of uplink timing and frequency synchronization. Additionally, information related to the satellite's orbit and the position of the NTN gateway may also be used for mobility management purposes and random access.
  • the NTN related parameters provided to the base station by the O&M may depend on the type of service link supported (e.g., Earth-fixed beam, quasi-Earth-fixed beam, moving beam, etc.).
  • FIG. 3 is a diagram showing an example of a wireless device (300) in a system supporting satellite communication according to an embodiment of the present disclosure.
  • the wireless device (300) included in the positioning system according to an embodiment of the present disclosure may be a mobile terminal such as a smart phone, a tablet PC, or a wearable device, but may not be limited thereto.
  • the wireless device (300) may include at least one control unit (310), at least one memory (320), at least one power supply unit (330), at least one transceiver unit (340), at least one input unit (350), at least one output unit (360), and/or at least one antenna (370).
  • the control unit (310) can control the memory (320) and/or the transceiver (340), and can be configured to implement the descriptions, functions, procedures, suggestions, methods, and/or operation flowcharts disclosed in this document.
  • the memory (320) can be connected to the control unit (310) and can store various information related to the operation of the control unit (310). For example, the memory (320) can perform some or all of the controls controlled by the control unit (310), or store software codes including commands for performing the descriptions, functions, procedures, suggestions, methods, and/or operation flowcharts disclosed in this document.
  • the transceiver (340) can be connected to the control unit (310) and can transmit and/or receive wireless signals via at least one antenna (370).
  • the transceiver (340) can include a transmitter and/or a receiver.
  • the transceiver (340) may include a receiver that receives signals from a low-orbit satellite.
  • At least one control unit (310) may be referred to as a controller, a microcontroller, a microprocessor, or a microcomputer.
  • the at least one control unit (310) may be implemented by hardware, firmware, software, or a combination thereof.
  • ASIC application specific integrated circuit
  • DSP digital signal processor
  • DSPD digital signal processing device
  • PLD programmable logic device
  • FPGA field programmable gate array
  • the descriptions, functions, procedures, suggestions, methods, and/or operational flowcharts disclosed in this document may be implemented by firmware or software that is configured to perform the at least one control unit (310), or may be stored in at least one memory (320) and driven by the at least one control unit (310).
  • the descriptions, functions, procedures, suggestions, methods and/or flow charts disclosed in this document may be implemented using firmware or software in the form of code, instructions and/or sets of instructions.
  • At least one transceiver (340) can transmit user data, control information, wireless signals/channels, etc. mentioned in the methods and/or the flowcharts of this document to at least one other device. At least one transceiver (340) can receive user data, control information, wireless signals/channels, etc. mentioned in the descriptions, functions, procedures, proposals, methods and/or the flowcharts of this document from at least one other device.
  • at least one transceiver (340) can be connected to at least one control unit (310) and can transmit and receive wireless signals.
  • at least one control unit (310) can control at least one transceiver (340) to transmit user data, control information, or wireless signals to at least one other device.
  • At least one antenna (370) can be multiple physical antennas or multiple logical antennas (e.g., antenna ports).
  • At least one transceiver (340) can convert received user data, control information, wireless signals/channels, etc. from RF band signals to baseband signals in order to process the received user data, control information, wireless signals/channels, etc. using at least one control unit (310).
  • At least one transceiver (340) can convert processed user data, control information, wireless signals/channels, etc. from baseband signals to RF band signals using at least one control unit (310).
  • the input unit (350) is a configuration for obtaining information such as user input, images, and audio, and may include various input means such as various mechanical/electronic input means, cameras, and microphones.
  • the output unit (360) is for providing information to users, etc. by generating output related to sight, hearing, or touch, and may include a display, a speaker, a vibration module, and the like.
  • the wireless device (300) supplies power through the power supply unit (330), and the power supply unit (330) may include a wired/wireless charging circuit, a battery, and the like.
  • the wireless device (300) may be a mobile device such as a mobile robot, a vehicle, a train, an aerial vehicle (AV), a ship, etc.
  • the device may further include a driving unit including at least one of an engine, a motor, a power train, wheels, brakes, and a steering device of the device, a sensor unit that supplies power and senses status information, environmental information, and user information around the device, an autonomous driving unit that performs functions such as path maintenance, speed control, and destination setting, and at least one of a position measuring unit that obtains mobile location information through a global positioning system (GPS) and various sensors.
  • GPS global positioning system
  • GNSS-based positioning methods may have low accuracy in urban canyon environments.
  • satellite signals may not be directly transmitted to terminals, and terminals may be forced to receive satellite signals through multiple paths. Therefore, there may be a large amount of error in current GNSS-based terminal position estimation.
  • FIG. 4 is a diagram showing a path along which a satellite and a terminal (410) perform communication in an urban canyon according to one embodiment of the present disclosure.
  • GNSS can perform globally referenced positioning in an outdoor environment.
  • the terminal (410) can perform positioning based on a pseudorange.
  • the pseudorange can be affected by non-line-of-sight (NLOS) and multipath.
  • NLOS non-line-of-sight
  • the strength of a GNSS signal can be reduced in an indoor environment and an urban canyon.
  • an inertial navigation system INS
  • INS inertial navigation system
  • INS can be less sensitive than GNSS under conditions in which the environment changes.
  • INS can be implemented by measuring linear acceleration and angular velocity in a high frequency domain.
  • INS has a disadvantage in that errors accumulate over time.
  • the GNSS-INS integration method can be an alternative method in an environment where GNSS is blocked.
  • a Kalman filter (KF), an extended Kalman filter (Extended KF), and an unscented KF which are types of Bayesian filters, can be used.
  • a first-order Markov chain can be applied to these methods, and noise can be modeled as a Gaussian distribution.
  • a signal transmitted by the first satellite (420#1) can experience only a line-of-sight (LOS) environment.
  • LOS line-of-sight
  • the error distribution of the measurement data can appear similar to a Gaussian distribution, as shown in FIG. 5. Therefore, the terminal (410) can perform relatively accurate positioning.
  • the positioning quality may deteriorate.
  • a signal transmitted by the second satellite (420#2) can experience both an LOS environment and a non-LOS environment. Therefore, the error distribution of the measurement data may vary depending on the position of the satellite.
  • the error distribution of GNSS measurement data can be shown as a non-Gaussian distribution, as shown in Fig. 6, and since the environment changes over time in the case of non-geostationary satellites, the error distribution in the urban canyon can have a high time-correlation.
  • LEO-based communications can have several advantages over traditional medium earth orbit (MEO) and geostationary (GEO) satellite-based communications.
  • MEO medium earth orbit
  • GEO geostationary
  • LEO-PNTRC LEO-based positioning, navigation, timing, remote sensing and communications
  • LEO satellite constellations can be a reliable source for measuring Doppler frequency shifts.
  • GNSS global navigation satellite systems
  • FGO Factor graph optimization
  • the present disclosure proposes a factor graph optimization based on a positioning method utilizing robust Doppler shift measurements using a low-orbit satellite constellation.
  • the delta range factor and the Doppler velocity factor which can act as error functions, can be considered.
  • the delta range factor can indicate the error between the Doppler shift measurement and the observation.
  • the Doppler velocity factor can indicate the error between the Doppler velocity measurement and the observation between two consecutive epochs.
  • the estimation state can be connected using the Doppler velocity factor. In this case, communication with the satellite may be required in order to measure the Doppler shift.
  • FIG. 7 is a diagram showing an environment of a positioning method using a low-orbit satellite according to an embodiment of the present disclosure.
  • a low-orbit satellite can approach the Earth relatively closer than a geostationary or medium-orbit satellite of a GNSS. Since a low-orbit satellite can have an orbit of 780 km in altitude, it can transmit a signal that is 20 dB stronger than a GNSS signal to a terminal.
  • a low-orbit satellite constellation can provide sufficiently diverse LOS vectors.
  • a terminal can select a satellite most suitable for network communication and registration procedures among a plurality of satellites beyond the horizon.
  • a signal from a low-orbit satellite can penetrate indoors, and a low-orbit satellite communication system can provide good coverage even in a deep urban canyon environment.
  • a communication delay time can be shortened from 700 ms to 100 ms, and a low-orbit satellite close to the Earth's orbit can provide strong signal power and a high Doppler frequency shift range ( ⁇ 40 kHz). Therefore, the Doppler shift-based positioning technology of LEO satellite signals can be an alternative to the current pseudorange-based GNSS.
  • a factor graph optimization system based on Doppler shift measurement using LEO satellite constellation can be proposed without using data of other types of sensors (INS, IMU), etc.
  • the Doppler shift measurement of LEO satellite signals can be utilized.
  • each factor can act as an error function, and the delta range factor and the Doppler velocity factor can be considered.
  • the delta range factor can indicate the error between the Doppler measurement and the observation.
  • the Doppler velocity factor can indicate the error between the Doppler velocity measurement and the observation between two consecutive epochs.
  • the estimation state can be connected using the Doppler velocity factor.
  • a factor graph is a bipartite undirected graph, and can be used for modeling large functions with many variables by factoring them into small local subsets. Since the joint probability distribution can be expressed as a product of several single factors as in [Mathematical Formula 1] below, the large function can be analyzed more easily.
  • [Mathematical Formula 1] stands for a joint probability distribution, is a variable means a local subset of , represents a factor of a joint probability distribution. Also, a factor graph can be used to express the relationship between an unknown state and a factor.
  • FIG. 8 is a diagram illustrating a structure of a factor graph according to an embodiment of the present disclosure.
  • a factor graph is a visual representation of unknown state variables (e.g., variable nodes) and factors that are functions of the state variables (e.g., factor nodes).
  • a delta range factor and a Doppler velocity factor may be considered as factors.
  • the Doppler velocity factor may be used to connect state variables.
  • the delta range factor may be connected to each state variable as many as the number of satellites.
  • the Doppler velocity factor may mean a factor related to the position of the terminal, and the delta range factor may mean a factor related to a Doppler shift, which is a frequency difference between a signal transmitted from 7 satellites and a signal received by the terminal.
  • four delta range elements are connected to each state node, which assumes a situation where the number of satellite signals considered is four.
  • the number of satellite signals may vary depending on the performance of the terminal and the target positioning accuracy.
  • the state variable may include at least one of the position of the terminal, the velocity of the terminal, and the clock bias of the terminal. Therefore, the state variable may be configured as in the following [Mathematical Formula 2].
  • [Mathematical Formula 2] represents the state of the terminal (receiver) at the kth epoch, means the location of the terminal, refers to the speed of the terminal, refers to the clock drift of the terminal.
  • the Doppler velocity factor can be determined based on two continuous state variables, and thus can be a factor related to velocity.
  • the states of all terminals and the positions of the satellites can be considered based on the earth-entered earth-fixed (ECEF) frame. Since the state variables include the velocity and clock drift together with the position of the terminal, the velocity of the terminal can be considered when performing positioning, and more precise positioning can be enabled. Referring to Fig.
  • the terminal receives a signal from a satellite, the terminal measures a Doppler shift, and determines a delta range factor and a Doppler velocity factor based on the measured Doppler shift, and performs optimization based on a factor graph, thereby determining a set of state variables, x, and a specific method can be used as described below.
  • FIG. 9 is a diagram illustrating an example in which a Doppler shift occurs according to one embodiment of the present disclosure.
  • the Doppler shift refers to a change in the frequency of an electromagnetic signal due to the relative movement between a terminal (910) and a low-orbit satellite (920).
  • the terminal (910) and the low-orbit satellite (920) are moving. and At this point, the positions of the low-orbit satellites (920) are and .
  • P and Q are respectively and At this point, it refers to the sub-satellite point of the low-orbit satellite (920).
  • the LOS vector r between the terminal (910) and the low-orbit satellite (920) is indicated by a dotted line.
  • the Doppler shift can be expressed as in [Mathematical Formula 3] below.
  • the frequency of the signal transmitted by the low-orbit satellite (920) About can be expressed as in [Mathematical Formula 4] below.
  • the LOS vector r between the terminal (910) and the low-orbit satellite (920) can be expressed as in [Mathematical Formula 5] below.
  • Equation 6 refers to the speed of a low-orbit satellite (920), refers to the speed of the terminal (910).
  • the clock used in the terminal (910) may not be as accurate as a GNSS satellite having an atomic clock. Therefore, the clock of the terminal (910) may have an error (bias).
  • the clock error of the terminal (910) may be called a receiver clock drift.
  • the clock drift of the terminal (910) If so, the error that occurs in the estimation of the frequency of the received signal can be expressed as in [Mathematical Formula 8] below.
  • the terminal (910) can extract multiple signals from multiple different low-orbit satellites. Accordingly, the Doppler shift for each signal of the multiple low-orbit satellites can be calculated. Accordingly, the delta range for n low-orbit satellites can be expressed as in the following [Mathematical Formula 12].
  • Equation 12 means the delta range of the kth low-orbit satellite, denotes the position of the kth satellite, represents the velocity of the kth satellite.
  • the number of low-orbit satellites can be used, such as GNSS.
  • the number of low-orbit satellites is not limited to a specific number, and the number of low-orbit satellites received can be implemented differently depending on the performance and purpose of the terminal.
  • [Mathematical expression 12] Based on the actually measured delta range Theoretically, it can be identical to the calculation of the right-hand side of [Equation 12]. Since the terminal can know the velocity and position of the satellite through celestial data, the right-hand side of [Equation 12] can be viewed as a function of the position, velocity, and clock drift of the terminal. That is, the right-hand side of [Equation 12] can be viewed as a value that can change depending on the result estimated by the terminal of the position, velocity, and clock drift of the terminal, and an observation function can be defined based on this.
  • the Jacobian matrix can be expressed as [Mathematical Formula 14] below.
  • the terminal measures the delta range vector based on the frequency shift measured from the satellite. can be determined, and the error function for the delta range factor is can be expressed as [Mathematical Formula 15] below.
  • Equation 15 stands for the covariance matrix, is the covariance matrix It refers to the Mahalanobis distance based on .
  • the satellite's elevation angle and carrier-to-noise ratio ( ) can be calculated based on.
  • the terminal can estimate the initial position of the terminal by using the least square method based on [Mathematical Formula 12] and [Mathematical Formula 14]. Since the position of the satellite can be obtained based on celestial data, the terminal can calculate the elevation angle based on the estimated initial position and the position of the satellite.
  • the observation model for the speed of the terminal (910) can be expressed as [Mathematical Formula 16] below.
  • Equation 16 means a speed measurement vector determined based on the least square method using [Mathematical Formula 12] and [Mathematical Formula 14], stands for the observation function for speed measurement, refers to the noise associated with speed measurement.
  • Equation 17 represents the time interval between two consecutive epochs.
  • Delta range measurement vector Error function for Doppler velocity factor can be expressed as [Mathematical Formula 18] below.
  • Equation 18 stands for the covariance matrix, is the covariance matrix It refers to the Mahalanobis distance based on .
  • the satellite's elevation angle and carrier-to-noise ratio ( ) can be calculated based on the Doppler velocity factor.
  • the Doppler velocity factor is determined based on two consecutive state variables. Therefore, as shown in Fig. 9, class The Doppler velocity factor in between can be connected to the edge.
  • the objective function for positioning based on factor graph optimization can be expressed as a sum of error functions, and the terminal can perform positioning by estimating the state variable x that minimizes the value of the objective function as in [Mathematical Formula 19] below.
  • FIG. 10 is a diagram illustrating a procedure for performing positioning using low-orbit satellites according to one embodiment of the present disclosure.
  • a terminal can estimate the current position of the terminal by receiving a signal from at least one satellite.
  • the terminal receives signals from low-orbit satellites.
  • the received signals may be signals for mobile communication, etc., but are not limited to specific signals. At least one of a signal for communication between the satellite and the terminal or a separate reference signal for positioning may be used.
  • the terminal in the urban canyon can select a satellite that is not obscured from the view among the numerous satellites deployed in the low-orbit satellite constellation.
  • the terminal acquires ephemeris data of low-orbit satellites.
  • the ephemeris data can be acquired in various ways.
  • the low-orbit satellites can transmit their ephemeris data to the terminal in a broadcast manner.
  • the ephemeris data can be transmitted in a unicast manner through an RRC connection between the terminal and the low-orbit satellites.
  • the ephemeris data can include at least one of a week number, satellite accuracy and status, data age, satellite clock correction coefficient, and orbital parameter values.
  • the satellites periodically transmit ephemeris data, so that the terminals can estimate the positions and velocities of the satellites.
  • the ephemeris data can be provided in the form of a TLE (two-line element) file.
  • Assisted GPS (A-GPS) technology can be used to acquire the ephemeris data.
  • the ephemeris data can be transmitted to the terminal through a terrestrial communication network.
  • the terminal measures the Doppler shift.
  • the terminal can measure the Doppler shift by measuring the frequency of the received signal, and the difference between the frequency actually transmitted by the satellite and the frequency measured by the terminal.
  • the measured Doppler shift can be used to calculate an error function.
  • the frequency of the signal transmitted by the satellite can be preset to a specific frequency. Therefore, the terminal can measure the Doppler shift by comparing the frequency of the received signal with the preset frequency when it already knows it.
  • the satellite can transmit celestial data including information about the frequency transmitted by the satellite to the terminal.
  • the terminal determines the delta range factor and the Doppler velocity factor.
  • the terminal may first set the state variables to be used in the factor graph optimization method.
  • the state variables may include at least one of the position of the terminal, the velocity of the terminal, or the receiver clock bias.
  • the delta range factor may be determined based on the state variables of the terminal, and the Doppler velocity factor may be determined based on two consecutive state variables. Therefore, two consecutive state variables may be connected by the Doppler velocity factor.
  • the error function for the delta range factor may be determined based on the difference between the delta range measurement vector and the observation function for measuring the Doppler shift, as in [Mathematical Formula 15].
  • the error function for the Doppler velocity factor may be determined based on the difference between the velocity measurement vector and the observation function for measuring the velocity, as in [Mathematical Formula 18].
  • the terminal may determine the elevation angle and carrier-to-noise ratio ( ) can be used to determine the covariance matrix, and the error function can be calculated using the Mahalanobis distance based on the covariance matrix.
  • the elevation angle of the satellite can be determined based on the position of the terminal and the position of the satellite.
  • the terminal can determine the position of the satellite based on celestial data.
  • the position of the terminal can use a position estimated primarily using the least square method based on the calculated Doppler shift.
  • the position of the terminal estimated primarily can be estimated using the least square method based on the delta range factor as in [Mathematical Formula 12] and [Mathematical Formula 14].
  • step S1009 the terminal determines the position of the terminal based on factor graph optimization.
  • the value calculated in the error function may change. Therefore, the position estimation of the terminal using the factor graph can be determined by finding a state x where the sum of the values of the error function for the delta range factor and the error function for the Doppler velocity factor is minimized based on covariance, as in [Mathematical Formula 19].
  • receiving celestial data is for obtaining basic data for determining the position and velocity of the satellite and can be performed before the step of receiving satellite signals.

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  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Position Fixing By Use Of Radio Waves (AREA)

Abstract

La présente divulgation concerne un procédé de positionnement d'un terminal, à l'aide de multiples satellites en orbite terrestre basse (LEO). Le procédé de positionnement peut comprendre les étapes consistant à : recevoir un signal provenant de chacun d'un ou de plusieurs satellites en LEO ; acquérir des données d'éphémérides de chacun des satellites en LEO ; déterminer le décalage Doppler sur la base des données d'éphémérides et du signal ; déterminer des variables d'état et au moins un facteur devant être utilisé lors d'une optimisation de graphe de factorisation ; et acquérir un résultat de positionnement à l'aide de l'optimisation de graphe de factorisation sur la base du décalage Doppler.
PCT/KR2023/012106 2023-06-08 2023-08-16 Procédé et dispositif de positionnement basé sur une optimisation de graphe de factorisation à l'aide de multiples satellites en orbite terrestre basse Pending WO2024253253A1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
KR10-2023-0073497 2023-06-08
KR20230073497 2023-06-08
KR1020230093104A KR20240174441A (ko) 2023-06-08 2023-07-18 다중 저궤도 위성을 이용한 요인 그래프 최적화 기반의 측위 방법 및 장치
KR10-2023-0093104 2023-07-18

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