A method and system for handling non-terrestrial network communication of global navigation satellite system signal interruptions

Abstract

The application provides a non-terrestrial network communication method and system for processing global navigation satellite system signal interruption, belonging to the technical field of wireless communication; the application aims to solve the problem of communication reliability decline caused by the inability to compensate for time-frequency offset when the global navigation satellite system positioning signal of a terminal is interrupted in non-terrestrial network communication; the method comprises the following steps: when a non-terrestrial network terminal detects that the global navigation satellite system signal state thereof changes from valid to invalid, the terminal sends an invalid state indication to a non-terrestrial network base station; after the base station receives the indication, the base station starts a synchronization timer; the base station manages the invalid state of the terminal based on the synchronization timer; through the cooperation of the terminal and the base station, the application establishes a closed-loop synchronization management mechanism, can maintain communication when the global navigation satellite system signal is interrupted, improves the communication reliability, and optimizes the utilization of wireless resources.

Description

Technical Field

[0001] This application relates to the field of wireless communication technology, and in particular to a non-terrestrial network communication method and system for handling signal interruptions in global navigation satellite systems. Background Technology

[0002] Non-terrestrial networks, as a supplement to terrestrial cellular communications, can provide wide-area coverage via satellites or high-altitude platforms. In non-terrestrial networks represented by low-Earth orbit satellites, due to the high-speed motion of the satellites, the wireless link between the terminal and the satellite base station experiences rapidly changing propagation delays and Doppler frequency offsets. To ensure communication quality, the terminal needs to pre-compensate for these time and frequency offsets.

[0003] In existing technologies, terminals typically rely on their built-in Global Navigation Satellite System (GNSS) modules to obtain their precise position and velocity information, and combine this with satellite ephemeris data sent from the network to estimate and compensate for the aforementioned time and frequency offsets. Therefore, the ability of a terminal to continuously obtain reliable GNSS positioning information is a crucial prerequisite for maintaining normal communication on non-terrestrial networks.

[0004] However, in practical applications, the terminal's Global Navigation Satellite System (GNSS) signal may be interrupted or become unstable due to complex environments such as urban canyons with tall buildings or indoor spaces, or due to factors such as severe weather and electromagnetic interference. In such cases, even if the non-terrestrial network communication link itself remains operational, the terminal will be unable to accurately perform time and frequency pre-compensation due to the loss of its real-time location information. This will lead to the continuous accumulation of time and frequency offset errors, which may eventually exceed the system's tolerance range, severely affecting communication reliability and even causing communication outages.

[0005] Currently, some technical solutions primarily focus on static communication methods for terminals without any Global Navigation Satellite System (GNSS) module. However, the mechanisms of these solutions are not entirely applicable to dynamic, intermittent scenarios where GNSS signals are sometimes present and sometimes absent. Therefore, designing a dynamic and efficient closed-loop management mechanism to address the instability of GNSS positioning signals during non-terrestrial network communication is a pressing technical problem that needs to be solved. Summary of the Invention

[0006] The purpose of this application is to provide a non-terrestrial network communication method and system for handling the interruption of Global Navigation Satellite System (GNSS) signals, so as to solve the technical problem that when the GNSS positioning signal of the terminal is interrupted in non-terrestrial network communication, the communication reliability is reduced or even interrupted because the time offset and frequency offset of the satellite-to-ground link cannot be accurately estimated and compensated.

[0007] To achieve the above objectives, this application provides a non-terrestrial network communication method for handling Global Navigation Satellite System (GNSS) signal interruptions, comprising: when a non-terrestrial network terminal detects that its GNSS signal status changes from valid to invalid, the terminal sends a status indication indicating that the GNSS signal is invalid to a non-terrestrial network base station; after receiving the status indication, the base station starts a synchronization timer; the base station manages the GNSS failure status of the terminal based on the synchronization timer, the management including: after the synchronization timer expires, the base station triggers the terminal to transmit an uplink signal for the base station to perform synchronization calibration; and during the operation of the synchronization timer, if an uplink signal is received from the terminal, the base station uses the uplink signal to perform synchronization calibration on the terminal and resets the synchronization timer.

[0008] Optionally, the terminal sends the status indication to the base station through the control unit of the media access control layer, wherein the status indication is implemented by using a reserved bit in the uplink timing report control unit as a global navigation satellite system status indication bit.

[0009] Optionally, the terminal sends the status indication to the base station via radio resource control signaling.

[0010] Optionally, the duration of the synchronization timer is set according to a predetermined shortest link failure time.

[0011] Furthermore, the determination of the shortest link failure time includes: based on a maximum offset model assuming the terminal motion velocity vector is coplanar with the satellite orbital plane, and a critical condition for communication failure, wherein the critical condition is that the time offset drift reaches half the cyclic prefix length of the orthogonal frequency division multiplexing symbol, and the shortest time required to reach the critical condition is calculated.

[0012] Optionally, the shortest link failure time is determined by querying a pre-configured table that stores the shortest link failure times corresponding to different satellite orbital parameters and terminal mobility states.

[0013] Optionally, the base station triggers the terminal to transmit an uplink signal, including: the base station sending a physical downlink control channel command to the terminal to instruct the terminal to send a physical random access channel preamble.

[0014] Optionally, the base station triggers the terminal to transmit an uplink signal, including: scheduling a dedicated uplink probe reference signal transmission for the terminal.

[0015] Optionally, the method further includes: when the base station receives a status indication from the terminal indicating that the global navigation satellite system signal has been restored to validity, the base station stops the synchronization timer.

[0016] To achieve the above objectives, this application also provides a non-terrestrial network communication system, including a non-terrestrial network terminal and a non-terrestrial network base station; the non-terrestrial network terminal is configured to: monitor the status of its Global Navigation Satellite System (GNSS) signal; and when the GNSS signal status is detected to change from valid to invalid, send a status indication indicating that the GNSS signal is invalid to the non-terrestrial network base station; the non-terrestrial network base station is configured to: receive the status indication from the terminal; and upon receiving the status indication, start a synchronization timer; and manage the GNSS failure status of the terminal based on the synchronization timer, the management including: after the synchronization timer expires, triggering the terminal to transmit an uplink signal for synchronization calibration; and during the operation of the synchronization timer, if an uplink signal is received from the terminal, using the uplink signal to perform synchronization calibration on the terminal and resetting the synchronization timer.

[0017] Compared with the prior art, this application has the following beneficial effects:

[0018] 1. Improved communication reliability. This application establishes a dynamic closed-loop synchronization management mechanism through the collaboration between the terminal and the base station. This mechanism can effectively manage and compensate for the accumulation of link time and frequency offsets caused by the lack of positioning information when the terminal's Global Navigation Satellite System signal is interrupted, preventing them from exceeding the system's tolerance range, thereby maintaining normal wireless link communication and significantly improving the reliability of non-terrestrial network communication in scenarios with intermittent signals.

[0019] 2. Optimized utilization of wireless resources. The base station in this application can not only proactively initiate calibration when the timer expires, but also opportunistically utilize the terminal's existing uplink transmission for synchronous calibration and reset the timer. This opportunistic approach reduces unnecessary forced random access processes, effectively saving wireless resources and signaling overhead.

[0020] 3. Enhanced system robustness. This application provides a scientific theoretical basis for configuring the duration of synchronous timers, making timer settings more efficient, avoiding resource waste or premature link interruption due to improper configuration, and enhancing system robustness. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 A schematic diagram of the overall process of a non-terrestrial network communication method for handling signal interruptions of a Global Navigation Satellite System provided in this application embodiment;

[0023] Figure 2 This is a schematic diagram of the uplink timing report control unit used to report the status of the global navigation satellite system in an embodiment of this application;

[0024] Figure 3 This is a schematic diagram of the state transition on the non-terrestrial network base station side in the embodiments of this application;

[0025] Figure 4 This is a flowchart illustrating the calculation of the shortest link failure time in an embodiment of this application;

[0026] Figure 5 This is a schematic diagram of the maximum offset model of the relative movement between the satellite and the terminal used to calculate the shortest link failure time in an embodiment of this application;

[0027] Figure 6 This is a schematic diagram illustrating the slant range geometry between the satellite and the terminal in an embodiment of this application;

[0028] Figure 7 This is a schematic diagram illustrating the protective effect of the cyclic prefix on OFDM symbols in the embodiments of this application;

[0029] Figure 8 This is a schematic diagram of the management process on the base station side in the "GNSS signal failure" state in an embodiment of this application;

[0030] Figure 9 This application provides a schematic diagram of the structure of a non-terrestrial network communication system according to an embodiment of the present application.

[0031] Figure 10 This is a timing diagram illustrating the signaling interaction between the terminal and the base station in an embodiment of this application.

[0032] Figure Label Explanation: 10 - Non-terrestrial network terminal; 11 - GNSS module; 12 - Monitoring and reporting module; 20 - Non-terrestrial network base station; 21 - Synchronization timer; 22 - Closed-loop synchronization calibration module; 100 - Communication system; 201 - MAC subheader; 202 - Uplink timing report MAC CE; 203 - R / R / GS / TA value field; 301 - GNSS valid status; 302 - GNSS invalid management status; 501 - Satellite orbit; 502 - Terminal trajectory; 701 - Cyclic prefix (CP); 702 - OFDM symbol valid data section; 703 - Guard interval; S - Satellite; U - Terminal; E - Geocenter; - Earth's radius; - Satellite altitude; - Terminal altitude; d - Satellite-to-ground slant distance; S101 - Terminal monitoring GNSS status step; S102 - Determining if GNSS is faulty step; S103 - Terminal reporting GNSS failure status step; S104 - Base station starting synchronization timer step; S105 - Base station performing closed-loop synchronization calibration management step; S401 - Establishing maximum offset model step; S402 - Determining maximum time offset drift step; S403 - Deriving shortest link failure time T step; S801 - Receiving GNSS failure report step; S802 - Starting / resetting synchronization timer step; S803 - Waiting for event step; S804 - Determining if timer timeout step; S805 - Determining if uplink signal received step; S806 - Triggering terminal uplink transmission step; S807 - Measuring and calibrating time-frequency offset step; S808 - Determining if GNSS recovery report received step; S809 - Stopping timer step. Detailed Implementation

[0033] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. It should be noted that the specific embodiments described herein are only for explaining this application and are not intended to limit the scope of protection of this application.

[0034] Example 1

[0035] This application provides a non-terrestrial network communication method for handling Global Navigation Satellite System (GNSS) signal interruptions. This method can be applied to communication systems consisting of non-terrestrial network terminals and non-terrestrial network base stations, aiming to solve the problem of decreased communication reliability caused by the inability to accurately compensate for time and frequency offsets in the satellite-to-ground link due to intermittent GNSS signals from the terminal.

[0036] Figure 9This is a schematic diagram of a non-terrestrial network communication system 100 provided in an embodiment of this application. The communication system 100 includes a non-terrestrial network terminal 10 and a non-terrestrial network base station 20. In one embodiment of this application, the non-terrestrial network base station 20 may be a satellite base station operating in low Earth orbit (e.g., at an altitude of 600 km), while the non-terrestrial network terminal 10 may be a mobile user equipment, such as a vehicle-mounted terminal with a maximum speed of 120 km / h. The communication system 100 uses orthogonal frequency division multiplexing (OFDM) technology for data transmission, with a cyclic prefix duration configured to 4.7 microseconds to combat inter-symbol interference caused by multipath propagation and timing errors.

[0037] The non-terrestrial network terminal 10 is equipped with a GNSS module 11 and a monitoring and reporting module 12. The GNSS module 11 is responsible for receiving navigation satellite signals and calculating the terminal's precise position and velocity information. The monitoring and reporting module 12 continuously monitors the working status of the GNSS module 11, that is, whether the positioning information it outputs is valid.

[0038] Accordingly, the non-terrestrial network base station 20 includes a synchronization timer 21 and a closed-loop synchronization calibration module 22. The closed-loop synchronization calibration module 22 is responsible for receiving and processing status reports from the terminal, managing the synchronization status of the terminal, and triggering corresponding synchronization calibration procedures according to different events. The synchronization timer 21, under the management of the closed-loop synchronization calibration module 22, is a key component used to time the duration of the terminal's Global Navigation Satellite System signal failure.

[0039] Combination Figure 1 and Figure 10 The specific process of the communication method provided in this embodiment will be described. Figure 1 This is a schematic diagram of the overall flow of the method provided in the embodiments of this application. Figure 10 This is a timing diagram illustrating the signaling interaction between the terminal and the base station.

[0040] In the initial state, the non-terrestrial network terminal 10 is located in an area with good GNSS signal coverage, and its GNSS module 11 can work normally and continuously output valid positioning information. When the monitoring and reporting module 12 executes step S101 (terminal monitoring GNSS status), it determines that the GNSS signal status is valid. At this time, the non-terrestrial network terminal 10 can use this positioning information and the satellite ephemeris broadcast by the non-terrestrial network base station 20 to accurately calculate and pre-compensate the propagation delay and Doppler frequency offset between itself and the satellite base station, thereby maintaining normal non-terrestrial network communication.

[0041] When the non-terrestrial network terminal 10 enters a specific area, such as an "urban canyon" filled with tall buildings, the GNSS module 11 cannot receive a sufficient number of navigation satellite signals due to severe obstruction by the tall buildings, resulting in positioning failure and its signal status changing from "valid" to "invalid". However, the communication link between the non-terrestrial network terminal 10 and the non-terrestrial network base station 20 may not be affected to the same extent and can still remain uninterrupted.

[0042] The monitoring and reporting module 12 detects this status change in step S102 (determining whether GNSS is faulty). To notify the network side of this critical information, the non-terrestrial network terminal 10 executes step S103 (terminal reports GNSS failure status). In this embodiment, the reporting process employs a method that is highly compatible with existing standards and has low signaling overhead. Specifically, as follows... Figure 2 The diagram illustrates the structure of an uplink timing report media access control layer control unit for reporting the status of a Global Navigation Satellite System (GNSS). The monitoring and reporting module 12 of the non-terrestrial network terminal 10 constructs an uplink timing report media access control layer control unit 202. This control unit logically includes a MAC subheader 201 to indicate that it is an uplink timing report control unit. Its payload is an R / R / GS / TA value field 203. This application extends the standard uplink timing report control unit by using its second reserved bit as a GNSS status indication bit. When the GNSS signal fails, the monitoring and reporting module 12 sets this status indication bit to "1" and sends this control unit to the non-terrestrial network base station 20 via the uplink (e.g., along with uplink data or as independent signaling).

[0043] After receiving and parsing the uplink timing report from the media access control layer control unit 202, the closed-loop synchronization calibration module 22 of the non-terrestrial network base station 20, upon determining that the status indicator bit is "1", knows that the global navigation satellite system of the non-terrestrial network terminal 10 has failed. At this time, the non-terrestrial network base station 20 needs to activate a special management mechanism to address potential time-frequency offset accumulation issues. For example... Figure 3 As shown, this is a schematic diagram of the state transition on the base station side. After receiving a Global Navigation Satellite System (GNSS) failure report, the non-terrestrial network base station 20 will change the management state of the terminal from GNSS valid state 301 to GNSS invalid management state 302.

[0044] Upon entering GNSS invalid management state 302, the closed-loop synchronization calibration module 22 of the non-terrestrial network base station 20 immediately executes step S104 (base station starts synchronization timer), that is, it starts a synchronization timer 21 bound to the terminal. The duration of this timer is not arbitrarily set, but is set according to a scientifically calculated "shortest link failure time". The setting of this time is crucial. If the duration is too long, the link may be interrupted due to excessive time offset before the timer expires; if the duration is too short, it will cause too frequent active calibration, thus wasting radio resources.

[0045] This embodiment provides a detailed method for calculating the shortest link failure time, the process of which is as follows: Figure 4 As shown. First, in step S401, a maximum offset model is established. To estimate the shortest time required for link failure in the worst-case scenario, a physical model that causes the fastest change in the relative distance between the satellite and the ground needs to be constructed. For example... Figure 5 As shown in the figure, this is a schematic diagram of the maximum offset model for the relative movement between the satellite and the terminal. This model assumes that the trajectory 502 of the non-terrestrial network terminal 10 and the orbit 501 of the satellite S are located in the same plane, and that the relative velocity components between the motion direction of the non-terrestrial network terminal 10 and the motion direction of the satellite S are maximized within a certain time period. Furthermore, the model also assumes that at the initial moment of GNSS signal failure, the observation elevation angle of the non-terrestrial network terminal 10 towards the satellite S is at the lowest value allowed by the system (e.g., 10 degrees). Under this low elevation angle condition, the change in the satellite-to-ground geometric angle per unit time is the greatest, resulting in the fastest change in the satellite-to-ground slant range.

[0046] Secondly, in step S402, the maximum time offset drift is determined. The time offset drift that a communication link can tolerate is limited. Figure 7 The diagram illustrates the protective effect of the cyclic prefix on OFDM symbols. An OFDM symbol consists of a cyclic prefix CP 701 and the effective data portion 702. The cyclic prefix 701 provides a protection interval 703, ensuring correct demodulation of the signal as long as the arrival time fluctuations are within this interval. If the time offset exceeds this range, severe inter-symbol interference will occur. To ensure communication robustness, this embodiment sets the maximum tolerable time offset drift of the communication link to a conservative and safe threshold, namely half the length of the cyclic prefix of the Orthogonal Frequency Division Multiplexing (OFDM) symbol (0.5 * CP). In this embodiment, the cyclic prefix duration is 4.7 microseconds, and the speed of light is approximately... meters per second, therefore the corresponding maximum tolerable distance drift. .

[0047] Finally, in step S403, based on the above model and critical conditions, the shortest link failure time T is derived through geometric relationships and kinematic formulas. For example... Figure 6As shown, it is a schematic diagram of the slant range geometry between the satellite and the terminal, where E represents the Earth's center, S represents the satellite, and U represents the terminal. It is the Earth's radius (approximately 6371 kilometers). This is the satellite's altitude (600 kilometers in this example). The terminal altitude is negligible and can be considered as 0. At the initial moment, based on the known minimum elevation angle, satellite altitude, and Earth radius, the initial satellite-to-ground slant distance d and the initial "satellite-Ground-center-terminal" angle Ω can be calculated using the law of sines. Then, based on the maximum tolerable distance drift (705 meters), the satellite-to-ground slant distance at the communication failure critical point can be calculated. By applying geometric relationships (such as the law of cosines), the corresponding "satellite-geocenter-terminal" angle can be calculated. The change in angle Ultimately, this is combined with the satellite's linear velocity. and the maximum moving speed of the terminal The shortest time T required for the motion to progress from the initial state to the critical state can be calculated. The formula can be simplified to:

[0048]

[0049] Under the parameters of this embodiment, it is assumed that the calculated shortest link failure time T is 2.5 seconds. Accordingly, the closed-loop synchronization calibration module 22 sets the duration of the synchronization timer 21 to 2.5 seconds and starts it.

[0050] After the timer is started, the non-terrestrial network base station 20 executes step S105 (the base station performs closed-loop synchronization calibration management). Details of this management process are as follows... Figure 8 As shown. After receiving a GNSS failure report (S801), the non-terrestrial network base station 20 starts or resets the synchronization timer (S802) and then enters a waiting event state (S803). In this state, the base station will monitor three possible events: timer timeout, receiving an uplink signal from the terminal, or receiving a GNSS recovery report.

[0051] As an example scenario, consider a critical situation where the non-terrestrial network terminal 10 has no uplink transmission within a 2.5-second timer duration. When the clock reaches 2.5 seconds, the synchronization timer 21 times out. The non-terrestrial network base station 20 detects "yes" in step S804 (determining if the timer has timed out). This result means that the accumulated time offset between the non-terrestrial network terminal 10 and the non-terrestrial network base station 20 may have approached the critical value of 705 meters, and immediate calibration is necessary to prevent link interruption. At this time, the closed-loop synchronization calibration module 22 of the non-terrestrial network base station 20 will actively execute step S806 (triggering terminal uplink transmission). Specifically, the non-terrestrial network base station 20 will send a Physical Downlink Control Channel (PDCCHORDER) command to the non-terrestrial network terminal 10. This command is a standard signaling used to command the terminal to perform non-contention-based random access, which instructs the non-terrestrial network terminal 10 to send a Physical Random Access Channel preamble on the specified time-frequency resources.

[0052] The PDCCH ORDER command is a control command used in wireless communication systems to trigger random access procedures. It is primarily used in 4G LTE and 5G NR networks and is sent by the base station (such as eNodeB or gNB) to the user equipment (UE) via the PDCCH (Physical Downlink Control Channel) to resolve uplink synchronization issues or resource scheduling problems.

[0053] The core function of the PDCCH ORDER command is to trigger a random access procedure. When a UE loses uplink synchronization with the network, the base station can use this command to force the UE to initiate random access to re-establish synchronization. For example, in 5G NR, when a UE loses synchronization, the gNB will send a PDCCH command carrying a dedicated RACH preamble to trigger the random access procedure (RACH).

[0054] Upon receiving the instruction, the monitoring and reporting module 12 (or its physical layer processing unit) of the non-terrestrial network terminal 10 immediately sends a preamble signal on the designated resource. After receiving the preamble, the non-terrestrial network base station 20 executes step S807 (measuring and calibrating the time-frequency offset). The closed-loop synchronization calibration module 22 can accurately calculate the current timing deviation (i.e., uplink timing advance TA) by measuring the arrival time of the preamble, and can also measure its frequency offset. Subsequently, the non-terrestrial network base station 20 generates a corresponding calibration instruction (e.g., a timing advance command media access control layer control unit containing a new TA value) and sends it to the non-terrestrial network terminal 10 via the downlink.

[0055] After applying the calibration command, the uplink time-frequency synchronization of the non-terrestrial network terminal 10 is restored to an accurate state. Upon successful calibration, the closed-loop synchronization calibration module 22 of the non-terrestrial network base station 20 does not cease management but instead resets and restarts the 2.5-second synchronization timer 21 (returning to step S802) to continue monitoring the terminal's GNSS failure status for the next round. This process forms a complete closed loop, ensuring that the communication link can be maintained through periodic active calibration during periods of continuous GNSS signal interruption.

[0056] In addition to the aforementioned timeout handling mechanism, this application also provides an opportunistic handling mechanism to improve resource utilization efficiency. During the 2.5-second execution of the synchronization timer 21, if the non-terrestrial network terminal 10 happens to have uplink data (e.g., transmitted on the physical uplink shared channel) or uplink control information (e.g., transmitted on the physical uplink control channel) to send, the non-terrestrial network base station 20 will detect "yes" in step S805 (determining whether an uplink signal has been received). At this time, the closed-loop synchronization calibration module 22 will take advantage of this opportunity to directly perform the measurement and calibration work in step S807 based on the existing uplink signal, without waiting for the timer to expire and then forcing the terminal to initiate additional random access. After completing this opportunistic calibration, the non-terrestrial network base station 20 will also reset and restart the synchronization timer 21 (returning to step S802). This opportunistic handling method avoids unnecessary uplink transmissions initiated solely for synchronization purposes, greatly optimizing the utilization efficiency of radio resources and signaling.

[0057] Finally, when the non-terrestrial network terminal 10 leaves the urban canyon and its GNSS module 11 recovers its signal and can output valid positioning information again, the monitoring and reporting module 12 will again construct an uplink timed report to the media access control layer control unit 202, but this time it will set the status indicator bit to "0" to indicate that the GNSS signal recovery is valid and report it to the non-terrestrial network base station 20. The closed-loop synchronization calibration module 22 of the non-terrestrial network base station 20 detects "yes" in step S808 (determining whether a GNSS recovery report has been received), and will then execute step S809 (stopping the timer), that is, stopping and turning off the synchronization timer 21 associated with the terminal. Meanwhile, if... Figure 3 As shown, the base station's management status for the terminal will also revert from GNSS invalid management status 302 to GNSS valid status 301. At this point, the entire dynamic closed-loop management process ends, and the system returns to normal communication mode.

[0058] This embodiment establishes a complete closed-loop mechanism that includes status reporting, timer management, active timeout calibration, and opportunistic passive calibration through close collaboration between the terminal and the base station. This mechanism can effectively maintain the stability and reliability of non-terrestrial network communication links even when the terminal's global navigation satellite system signal is interrupted for a long time.

[0059] Example 2

[0060] As an optional implementation, this embodiment provides a variant of the non-terrestrial network communication method for handling Global Navigation Satellite System (GNSS) signal interruptions. The core technical idea of ​​this embodiment, including starting a synchronization timer on the base station side and performing timeout or opportunistic synchronization calibration based on the timer, is basically the same as in Embodiment 1. The main difference lies in the method by which the non-terrestrial network terminal 10 reports the GNSS signal status to the non-terrestrial network base station 20.

[0061] In this embodiment, the monitoring and reporting module 12 of the non-terrestrial network terminal 10 no longer modifies and uses the uplink timing report control unit of the media access control layer to transmit the status of the global navigation satellite system signal, but instead uses a higher-level radio resource control signaling to realize status reporting.

[0062] The specific process is as follows: When the monitoring and reporting module 12 of the non-terrestrial network terminal 10 detects that the signal status of its internal GNSS module 11 changes from "valid" to "invalid", it will trigger a signaling reporting process of the radio resource control layer, such as a measurement report process of the radio resource control layer.

[0063] The monitoring and reporting module 12 constructs a measurement report message for the radio resource control layer. To carry the status information of the Global Navigation Satellite System (GNSS) signal, this measurement report message includes a new or extended information unit, which can be designed as a field specifically indicating the GNSS signal status. For example, an enumerated type variable named "GNSS-Status" can be defined, with values ​​of "valid" or "invalid". When the signal fails, the non-terrestrial network terminal 10 sets the value of this information unit to "invalid," encapsulates it in the measurement report message, and sends it to the non-terrestrial network base station 20 via the uplink.

[0064] The radio resource control layer protocol stack module of the non-terrestrial network base station 20 is responsible for receiving and parsing the measurement report message. When it parses out the "GNSS-Status" information element contained therein and finds its value to be "invalid," the radio resource control layer module of the non-terrestrial network base station 20 knows that the terminal's global navigation satellite system positioning capability has been lost. Subsequently, the radio resource control layer module will notify its media access control layer management module, namely the closed-loop synchronization calibration module 22 described in Embodiment 1, of this important status information through an internal interface.

[0065] Once the closed-loop synchronization calibration module 22 receives the internal notification, all subsequent processing steps are completely consistent with those described in Example 1. Specifically, the closed-loop synchronization calibration module 22 will immediately switch the management status of the terminal to the GNSS invalid management state 302, and start a synchronization timer 21 associated with the terminal based on the pre-determined or real-time calculated shortest link failure time (e.g., 2.5 seconds).

[0066] During the operation of synchronization timer 21, closed-loop synchronization calibration module 22 will also perform the following: Figure 8 The closed-loop synchronization calibration management process is shown. It waits for and judges timer timeout events and opportunistic uplink signal arrival events. If the timer times out, the non-terrestrial network base station 20 will actively trigger an uplink transmission (e.g., by instructing the terminal to send a physical random access channel preamble via a physical downlink control channel command) to perform synchronization calibration. If any uplink signal from the terminal is received during the timer's operation, the signal will be used for opportunistic synchronization calibration. After each successful calibration, the synchronization timer 21 is reset.

[0067] Similarly, when the GNSS signal of the non-terrestrial network terminal 10 is restored, it will again report to the non-terrestrial network base station 20 via radio resource control signaling (e.g., another measurement report in which the value of "GNSS-Status" is "valid"). Upon receiving this restoration information, the closed-loop synchronization calibration module 22 of the non-terrestrial network base station 20 will stop the synchronization timer 21 and restore the terminal's management state to GNSS valid state 301.

[0068] Therefore, the core method of this application does not depend on a specific signaling implementation method. Whether it adopts the control unit of the media access control layer (as in Embodiment 1) or the signaling of the radio resource control layer (as in this embodiment), it can effectively trigger and drive the subsequent closed-loop synchronization management mechanism. This provides a flexible choice for the deployment of this technical solution in future communication standards.

[0069] Example 3

[0070] This embodiment provides a variation of the non-terrestrial network communication method for handling signal interruptions in the Global Navigation Satellite System. The core ideas of this embodiment, including terminal status reporting, base station startup and management of synchronization timers, and opportunistic synchronization calibration mechanisms, are consistent with Embodiment 1. The innovation of this embodiment lies in the fact that when the synchronization timer expires, the non-terrestrial network base station 20 actively triggers the terminal to perform uplink transmission in a manner different from Embodiment 1 for synchronization measurement.

[0071] In this embodiment, the entire process from the non-terrestrial network terminal 10 reporting the global navigation satellite system signal failure status to the non-terrestrial network base station 20 receiving the report, switching status, and starting the synchronization timer 21 is exactly the same as described in Embodiment 1. The closed-loop synchronization calibration module 22 of the non-terrestrial network base station 20 will also set and start the synchronization timer 21 based on the calculated shortest link failure time (e.g., 2.5 seconds).

[0072] The key difference occurs after synchronization timer 21 times out. In embodiment 1, the base station commands the terminal to initiate a random access procedure by sending a physical downlink control channel command. However, in this embodiment, the closed-loop synchronization calibration module 22 of the non-terrestrial network base station 20, after detecting a timer timeout (e.g., ... Figure 8 In step S804, a different step S806 (triggering terminal uplink transmission) will be executed.

[0073] Specifically, the closed-loop synchronization calibration module 22 does not send physical downlink control channel commands. Instead, it schedules a dedicated uplink sounding reference signal transmission opportunity for the non-terrestrial network terminal 10, where the GNSS signal is unavailable. The uplink sounding reference signal is a known reference signal transmitted by the terminal in a mobile communication system. The network side can estimate the uplink channel quality, timing deviation, and frequency offset by receiving and measuring this signal.

[0074] To achieve this, the non-terrestrial network base station 20 sends the transmission configuration and resource location information of the uplink sounding reference signal to the non-terrestrial network terminal 10 via downlink control information. This downlink control information explicitly instructs the non-terrestrial network terminal 10 on which time slot, which frequency domain resource blocks, and which antenna port to use to transmit this dedicated uplink sounding reference signal. This uplink sounding reference signal can be periodic or a non-periodic uplink sounding reference signal triggered by the base station on demand. In this scenario, a non-periodic triggering method is more suitable.

[0075] After receiving and decoding the downlink control information, the non-terrestrial network terminal 10 will generate and send an uplink probe reference signal on the specified time and frequency resources in accordance with the instructions therein.

[0076] After receiving the uplink probe reference signal sent by the non-terrestrial network terminal 10, the receiver of the non-terrestrial network base station 20 can perform precise measurements using the closed-loop synchronization calibration module 22 (step S807). By analyzing the difference between the arrival time of the signal and the expected arrival time, the current timing deviation can be accurately obtained. Similarly, by analyzing the difference between its carrier frequency and the expected frequency, the frequency offset can be obtained.

[0077] After obtaining accurate time-frequency offset information, the subsequent calibration process is the same as in Example 1. The non-terrestrial network base station 20 generates a corresponding calibration command (e.g., a timing advance command to the media access control layer control unit) and sends it to the non-terrestrial network terminal 10 via the downlink to correct its time-frequency synchronization.

[0078] After successful calibration, the closed-loop synchronous calibration module 22 will also reset and restart the synchronous timer 21 to continue the next round of monitoring and management.

[0079] It is understood that the core step of "triggering the terminal to perform uplink transmission" can be achieved through various specific technical means, such as a physical random access channel preamble (as in Example 1) or an uplink sounding reference signal (as in this example), or any other signal that the base station can use to measure the uplink frequency offset. This flexibility allows the solution in this application to better adapt to different network deployment scenarios and system design choices, demonstrating its wide applicability.

[0080] Example 4

[0081] This embodiment further proposes a variant implementation of a non-terrestrial network communication method for handling signal interruptions in the Global Navigation Satellite System (GNSS), aiming to simplify the implementation complexity of the non-terrestrial network base station 20, particularly in determining the duration of the synchronization timer 21. In Embodiment 1, the base station needs to perform real-time calculations based on complex physical models and geometric relationships to determine the shortest link failure time. Although this method is the most accurate, it may impose a certain processing burden on some base stations with limited computing power or in scenarios requiring extremely fast response. This embodiment replaces real-time calculations with a pre-configured table lookup method, thereby improving the feasibility and efficiency of engineering implementation while ensuring the effectiveness of the solution.

[0082] In this embodiment, the mechanism for the terminal to report the signal failure status of the Global Navigation Satellite System, and the closed-loop synchronization calibration management logic on the base station side (including timeout handling and opportunistic handling), are consistent with those in Embodiment 1. The core difference lies in the method by which the closed-loop synchronization calibration module 22 of the non-terrestrial network base station 20 determines the duration of the synchronization timer 21.

[0083] The specific process is as follows: During the network deployment and maintenance phase, network operators or equipment manufacturers can perform a series of calculations offline. The methods used in these calculations are those described in Example 1. Figure 4 , Figure 5 , Figure 6 The detailed description of the precise calculation method based on the maximum offset model and physical derivation allows operators to pre-calculate the corresponding shortest link failure time for different combinations of scenarios that may exist in their networks.

[0084] These scenario combinations typically consist of two key dimensions: 1. Satellite orbital parameters: Non-terrestrial networks can be composed of satellites at different orbital altitudes, such as low Earth orbit (LEO) constellations at 600 km, LEO constellations at 1200 km, and even medium-high orbit (MEO) satellites. Orbital altitude directly affects the satellite's linear velocity and satellite-to-ground geometry, and is a key input for calculating the shortest link failure time. 2. Typical terminal mobility status: The terminal's movement speed is also an important factor affecting the cumulative time offset speed. Based on typical user behavior, terminal mobility can be divided into several levels, such as "stationary or low-speed movement" (e.g., walking, speed approximately 3-5 km / h), "medium-speed movement" (e.g., driving in the city, speed approximately 30-60 km / h), and "high-speed movement" (e.g., highways or high-speed trains, speeds reaching 120 km / h or higher).

[0085] For various combinations of these parameters (e.g., "600 km track" + "high-speed movement", "1200 km track" + "stationary"), the operator calculates a series of corresponding shortest link failure time values. Then, the correspondence between these "scenario combinations - time values" is created into one or more configuration tables and pre-stored in the memory of the non-terrestrial network base station 20. This configuration table can be a simple two-dimensional lookup table.

[0086] Once the actual communication process begins, the closed-loop synchronization calibration module 22 of the non-terrestrial network base station 20, upon receiving a Global Navigation Satellite System (GNSS) failure report from a non-terrestrial network terminal 10, needs to start the synchronization timer 21. At this time, it no longer performs complex real-time calculations, but instead performs the following query steps: First, it obtains the orbital information of the currently serving satellite. The base station itself knows the orbital parameters of its satellite constellation, for example, it operates in a 600 km orbit. Second, it obtains the mobility status of the non-terrestrial network terminal 10. The base station can determine the terminal's mobility in various ways, such as by analyzing the terminal's handover history over a period of time, Doppler frequency offset information in measurement reports, or directly classifying it as "stationary," "medium speed," or "high speed" based on the mobility level declared by the terminal in its reported capability information (such as supporting high-speed scenarios). Assume the base station determines that the terminal is "high-speed moving" (vehicle-mounted 120 km / h). Finally, it queries the configuration table. The closed-loop synchronization calibration module 22 uses "600 km orbit" and "high-speed moving" as indexes to query the configuration table stored internally. Assume the preset duration value in the table is 2.5 seconds.

[0087] After obtaining the duration value, the closed-loop synchronization calibration module 22 uses this value (2.5 seconds) to set the duration of the synchronization timer 21 and immediately starts the timer.

[0088] The subsequent management process, including waiting for and judging timeout events or opportunistic uplink signal events during the timer's operation, and performing corresponding active or passive calibration and resetting the timer after the event occurs, is exactly the same as described in Example 1.

[0089] This embodiment significantly reduces the real-time processing overhead of the base station and improves response speed by making the complex calculation process offline and the online process queryable. It is understood that the technical feature of "setting a synchronization timer based on a predetermined shortest link failure time" in this application can be implemented either through the real-time calculation method described in Embodiment 1 or through the method of consulting a pre-configuration table as described in this embodiment. Both methods aim to set a scientific and reasonable duration for the synchronization timer, jointly demonstrating the flexibility and practical value of the solution in engineering implementation.

[0090] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A non-terrestrial network (NTN) communication method for handling GNSS signal interruptions, characterized in that, include: When a non-terrestrial network terminal detects that its GNSS signal status has changed from valid to invalid, the terminal sends a status indication indicating that the GNSS signal is invalid to the non-terrestrial network base station. After receiving the status indication, the base station starts a synchronization timer; The base station manages the GNSS failure status of the terminal based on the synchronization timer, and the management includes: After the synchronization timer expires, the base station triggers the terminal to transmit an uplink signal for the base station to perform synchronization calibration; and during the operation of the synchronization timer, if an uplink signal is received from the terminal, the base station uses the uplink signal to perform synchronization calibration on the terminal and resets the synchronization timer. The duration of the synchronization timer is set according to a predetermined shortest link failure time, and the determination of the shortest link failure time includes: Based on a maximum offset model assuming the terminal's velocity vector is coplanar with the satellite's orbital plane, and a critical condition for communication failure, wherein the time drift reaches half the length of the cyclic prefix (CP) of an OFDM symbol, the shortest time required to reach the critical condition is calculated.

2. The method according to claim 1, characterized in that, The terminal sends the status indication to the base station through the control unit CE of the Media Access Control (MAC) layer, wherein the status indication is implemented by using a reserved bit in the uplink timing report control unit as a GNSS status indication bit.

3. The method according to claim 1, characterized in that, The shortest link failure time is determined by querying a pre-configured table that stores the shortest link failure times corresponding to different satellite orbital parameters and terminal mobility states.

4. The method according to claim 1, characterized in that, The base station triggers the terminal to transmit an uplink signal, including: the base station sends a Physical Downlink Control Channel (PDCCHORDER) command to the terminal to instruct the terminal to send a Physical Random Access Channel (PRACH) preamble.

5. The method according to claim 1, characterized in that, The base station triggers the terminal to transmit an uplink signal, including: scheduling a dedicated uplink sounding reference signal (SRS) transmission for the terminal.

6. The method according to claim 1, characterized in that, Also includes: When the base station receives a status indication from the terminal indicating that the GNSS signal has been restored to validity, the base station stops the synchronization timer.

7. A non-terrestrial network (NTN) communication system, characterized in that, This includes non-terrestrial network terminals and non-terrestrial network base stations; The non-terrestrial network terminal is configured to: monitor the status of its Global Navigation Satellite System (GNSS) signal; and when it detects that the GNSS signal status has changed from valid to invalid, send a status indication indicating that the GNSS signal is invalid to the non-terrestrial network base station. The non-terrestrial network base station is configured to receive the status indication from the terminal; Upon receiving the status indication, a synchronization timer is started; The GNSS failure status of the terminal is managed based on the synchronization timer. The management includes: after the synchronization timer expires, triggering the terminal to transmit an uplink signal for synchronization calibration; and during the operation of the synchronization timer, if an uplink signal is received from the terminal, using the uplink signal to perform synchronization calibration on the terminal and resetting the synchronization timer. The duration of the synchronization timer is set according to a predetermined shortest link failure time. The determination of the shortest link failure time includes: based on a maximum offset model assuming that the terminal's motion velocity vector is coplanar with the satellite orbital plane, and a critical condition for communication failure, the critical condition being that the time drift reaches half the length of the cyclic prefix (CP) of an OFDM symbol, and calculating the shortest time required to reach the critical condition.

Images