A terminal time delay compensation method for low-orbit internet satellite communication

Abstract

The application provides a terminal time delay compensation method for low-orbit Internet satellite communication and belongs to the technical field of satellite communication. Through a double-processor asynchronous cooperation architecture, a first processor with rich computing power resources is used to perform high-dimensional satellite orbit extrapolation, terminal trajectory prediction and initial compensation amount calculation; a second processor is used to obtain fine-grained time delay parameters through light-weight interpolation and accurately control the transmission time of uplink data. The scheme realizes high-precision real-time compensation of transmission time delay under the condition of high-speed movement of the terminal, and effectively solves the contradiction between limited terminal resources and high-frequency time delay compensation amount calculation.

Description

Technical Field

[0001] This invention belongs to the field of satellite communication technology, and specifically relates to a terminal delay compensation method for low-Earth orbit internet satellite communication. Background Technology

[0002] In low-Earth orbit (LEO) satellite communication systems, Timing Advance (TA) compensation refers to the time offset that a terminal makes when transmitting uplink signals relative to the downlink frame reference time, based on its spatial distance and relative motion with the satellite. Its core purpose is to offset the round-trip time (RTT) caused by electromagnetic waves transmitting over thousands of kilometers of space, ensuring that signals from terminals in different geographical locations arrive precisely within the predetermined time slots on the satellite side, thus avoiding inter-symbol interference (ISI) and multi-user collisions within the cell caused by time mismatch.

[0003] When the terminal is moving at high speed, the TA value depends not only on the satellite's motion but also is significantly affected by the terminal's motion. This results in a highly time-varying TA value. Without real-time compensation, the uplink signal will quickly slip out of the preset cyclic prefix (CP) guard interval, leading to demodulation failure. Furthermore, the terminal's processor computing resources are often limited. For high-speed moving terminals, how to utilize limited computing resources to perform real-time TA value compensation, achieving a balance between computing resources and compensation accuracy, is a problem worthy of in-depth research. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes a terminal delay compensation method for low-Earth orbit internet satellite communication. This method achieves high-precision real-time compensation for transmission delay under high-speed terminal movement conditions, effectively resolving the contradiction between limited terminal resources and the calculation of high-frequency delay compensation.

[0005] To achieve the above effects, the technical solution adopted by the present invention is as follows:

[0006] A terminal delay compensation method for low-Earth orbit internet satellite communication includes the following steps:

[0007] Step 1: The terminal's first processor reads the first information broadcast by the serving satellite from the received information and uses the first information to perform extrapolation calculations to obtain the first data;

[0008] The first information includes the satellite's position and velocity information at the time of broadcast; the first data is the satellite's position and velocity data obtained by extrapolating the orbit according to a preset time step within the time period from the time of broadcast to the time of satellite orbit extrapolation.

[0009] Step 2: The terminal's first processor acquires the second information and performs extrapolation calculations based on the second information to obtain the second data;

[0010] The second information is the terminal's own position and speed information at the current moment; the second data is the terminal position data obtained by extrapolating the position according to a specific time step within the time period from the current moment to the terminal's position.

[0011] Step 3: The terminal's first processor interpolates the first data to each time point of the second data to obtain the satellite position data at the corresponding time point, and calculates the third data by combining it with the second data;

[0012] The third data is the transmission delay data between the terminal and the satellite during the time period extrapolated from the current time to the terminal's location;

[0013] Step 4, the terminal's second processor processes the third data with a time step of... The interpolation operation yields the fourth data, and the transmission time of the uplink data sent to the satellite is adjusted based on the fourth data to complete the terminal's transmission delay compensation; the fourth data is a time interval of Fine-grained latency data.

[0014] Furthermore, during the period from the satellite broadcast time to the satellite orbit extrapolation, the terminal periodically updates the second information through the first processor at intervals shorter than the terminal position extrapolation time, and repeats steps 2 to 4 using the updated information.

[0015] Furthermore, the terminal updates the first information periodically via the first processor at intervals shorter than the satellite orbit extrapolation time, and repeats steps 1 to 4 using the updated information.

[0016] Furthermore, the interval is less than the time interval extrapolated from the terminal position. satisfy:

[0017] ;

[0018] Where c is the speed of light. This is the maximum allowable time delay offset when the satellite receives signals from the terminal. Represents the maximum speed of the terminal. This is the minimum elevation angle of the satellite when the terminal communicates with the satellite.

[0019] Furthermore, the duration of satellite orbit extrapolation in step 1 The value of is not less than the update time interval of the first information transmitted by the satellite. ,Right now .

[0020] Furthermore, the preset time step in step 1 The value of satisfies the following conditions:

[0021] ;

[0022] Where c is the speed of light. The orbital radius of a circular orbiting satellite. The gravitational constant is the constant of gravity. This is the threshold for the equivalent time delay offset error caused by the position interpolation error during the interpolation calculation process in step 3.

[0023] Furthermore, in step 2, the terminal extrapolation time is less than the satellite orbit extrapolation time, and the terminal's current time is within one step after the satellite broadcast time, which is the time step preset in step 1.

[0024] Furthermore, the time step in step 4 This is equal to the time interval between uplink information frames sent by the terminal, so that the terminal receives the delay adjustment amount at the current moment each time it sends uplink information, thereby completing the terminal's transmission delay compensation.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] This invention employs a dual-processor asynchronous collaborative architecture: a first processor (high-performance side) with abundant computing resources performs high-dimensional satellite orbit extrapolation, terminal trajectory prediction, and initial compensation calculation; a second processor (real-time control side) obtains fine-grained latency parameters through lightweight interpolation and precisely controls the timing of uplink data transmission. This solution achieves high-precision real-time compensation for transmission latency under high-speed terminal movement, effectively resolving the contradiction between limited terminal resources and high-frequency latency compensation calculation. Attached Figure Description

[0027] Figure 1 This is a flowchart of a terminal delay compensation method for low-Earth orbit internet satellite communication according to the present invention.

[0028] Figure 2 This is a timing relationship diagram for calculating the delay compensation information in this invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0030] The typical TA compensation process mainly relies on "two-stage prediction": First, the terminal obtains its own position through GNSS and extracts the ephemeris from satellite broadcasts (such as SIB19) to calculate the instantaneous distance between itself and the satellite to complete open-loop pre-compensation; then, in the random access phase (RACH), the satellite issues fine-tuning instructions through RAR messages based on the residual deviation of the received signal to complete closed-loop calibration.

[0031] However, when the terminal moves at high speed, the additional TA compensation value generated by the terminal's own movement must also be considered and compensated in real time to ensure the normal operation of the uplink communication process. Furthermore, considering the limited computing resources of the terminal, the adopted real-time TA compensation scheme should also balance the trade-off between computational resource consumption and accuracy, achieving minimal algorithmic overhead while ensuring that the TA compensation error threshold required by the system is met.

[0032] In addition, communication terminals typically adopt a layered processing architecture, with the core consisting of an application processor (AP) and a communication processor (CP). The AP, as the main control core of the terminal, is mainly responsible for running the operating system, user interface logic, multimedia processing, and various high-level applications, focusing on the scheduling of general computing power and the asynchronous processing of complex logic; while the CP (also known as the baseband processor) is the execution carrier of the communication protocol stack, focusing on physical layer signal modulation and demodulation, physical channel mapping, synchronization acquisition, and real-time processing of access layer protocol specifications.

[0033] This invention provides a terminal delay compensation method for low-Earth orbit internet satellite communication, such as... Figure 1 As shown, it includes the following steps:

[0034] Step 1: The terminal's first processor reads the first information broadcast by the serving satellite from the received information, and uses the first information to perform extrapolation calculations to obtain the first data. The first information includes the time of the first information broadcast. The position of the satellite and speed information The first data is to Within a time period, according to the time step Satellite position data obtained by orbit extrapolation and speed data ,in, For the satellite orbit extrapolation duration, For each data point in the first dataset, .

[0035] In low-Earth orbit satellite communication systems, satellites broadcast their orbital information so that terminals can calculate and obtain real-time information such as relative position, velocity, elevation angle, and azimuth angle with the satellite during communication, enabling continuous beam tracking of the terminal. In this embodiment, the first information broadcast by the serving satellite is generally its PVT information, which includes the current position of the satellite. Self-position vector at time and velocity vector In some practices, this PVT information is broadcast once per second and updated periodically to ensure that the terminal can accurately deduce the satellite's orbital information based on it. In some practices, the update interval for the first information... It lasts for 10 seconds.

[0036] After receiving the first information, the terminal uses the first processor to obtain the satellite information based on the orbit extrapolation algorithm. to Position and velocity data within a time period and The time step of the obtained data is .

[0037] The first message sent by the satellite was Location at any moment and speed information In the Earth-centered Earth-fixed (ECEF) frame, after receiving the information, the terminal first performs coordinate transformation calculations to obtain the satellite's position and velocity in the inertial (ECI) frame. Then, based on the information in the ECI frame, and according to the Earth's perturbation dynamics model, it calculates... The step size is obtained by extrapolation using numerical integration. The satellite's position and velocity information in the ECI frame is obtained, and then converted to the ECEF frame through coordinate system transformation to complete the satellite orbit extrapolation described in step 1. The final extrapolated data corresponds to the following time points: ,like Figure 2 As shown, coordinate axis a represents and The representation of the time corresponding to each data point on the time axis.

[0038] The above process requires a large amount of computing resources, thus requiring the processor to have strong computing power. In this embodiment, the first processor is a high-performance AP processor.

[0039] Step 2: The terminal's first processor updates the second information and performs extrapolation calculations based on the second information to obtain the second data. The second information is... Location information of the terminal itself and speed information This information is provided by the GNSS positioning module or the high-precision inertial navigation unit, and the second data is... to Within a time period, according to the time step Terminal location data obtained by location extrapolation ,in, Extrapolate duration based on terminal location. For each data point in the second set of data, the corresponding time point is... , , .

[0040] Terminals designed for high-speed motion are typically equipped with GNSS positioning modules or high-precision inertial navigation units to periodically update their position and velocity information, i.e., the second piece of information. This second piece of information is usually represented in the ECEF frame, and therefore can be obtained using the formula... You can get the terminal at The representation of the location information at the i-th time point in the ECEF system. For example... Figure 2 As shown, the coordinate axis aa represents The time corresponding to each data point is represented on the time axis. Since the satellite's orbital motion pattern is known, while the terminal velocity is dynamically changing, the time is typically calculated over a satellite extrapolation arc segment. Within this timeframe, multiple updates to the terminal's second information and calculations are required. To conserve computing resources, the timeframe for extrapolating the terminal's own location should meet certain conditions. Furthermore, since the terminal's first processor completes the satellite orbit extrapolation calculation described in step 1 before performing its own position extrapolation calculation, therefore... Furthermore, in most practices, it should be ensured that... That is, to ensure the first extrapolation of the orbit The terminal completes the second information update and the second data calculation so that the terminal can use all the satellite orbit extrapolation data obtained in step 1 without wasting the calculation results.

[0041] Step 3, the terminal's first processor processes the first data in... Interpolation calculations are performed at each time step to obtain... Satellite position data at any time and combined The second data at a given time receives the third data, and the third data is transmitted to the second processor of the terminal. The third data is... to The time delay TA between the terminal and the satellite during the time period ).

[0042] As mentioned earlier, the time points corresponding to the data points in the first and second sets of discrete data are usually not aligned. Therefore, the first processor needs to perform time interpolation on the first data to obtain the corresponding position of the first data at the time point of the second data. Then the communication between the terminal and the satellite... The time delay at a given moment (i.e., the third data point) can be calculated as TA ( )= , where c represents the speed of light.

[0043] In this embodiment, the interpolation calculation of the first data is implemented using the first-order Lagrange interpolation algorithm.

[0044] In practice, other interpolation algorithms, such as Hermite interpolation, can also be used to complete the interpolation operation described in step 3.

[0045] After the first processor completes the calculation of the third data, it sends it to the second processor in the terminal. The required transmission time is [duration missing]. .like Figure 2 As shown, the coordinate axis aaa represents the position of the data packet on the time axis after the third data is transmitted to the second processor. At this time, the first usable data TA is obtained on the second processor. (in the third data) The data corresponding to the first moment.

[0046] In this embodiment, the second processor is a high real-time CP processor, and the terminal's final uplink signal transmission and TA compensation are both completed on the second processor.

[0047] Step 4: The terminal's second processor receives the third data sent by the first processor and processes the third data with a time step of... The interpolation operation yields the fourth data, and the transmission time of the uplink data sent to the satellite is adjusted based on the fourth data to complete the terminal's transmission delay compensation. The fourth data is a time interval of... Fine-grained latency data.

[0048] In this embodiment, the interpolation operation on the third data is performed using a first-order Lagrange interpolation algorithm. In practice, other interpolation algorithms, such as Hermitian interpolation, can also be used to perform the interpolation operation. Through interpolation calculation, fine-grained TA data can be obtained, which can then be used for time delay pre-compensation of satellite uplink transmission signals.

[0049] Specifically:

[0050] exist to During the time period, every During the specified time, the terminal updates the second information once through the first processor, and uses the updated information to repeat steps 2 to 4 above, wherein... .

[0051] In the indivual When repeating steps 2 through 4 at intervals, the time update relationships in step 2 are as follows: the corresponding time of the second information. Updated to The second data is updated to to Data within a time period, The range of values ​​is updated to The third data in step 3 is updated to to Data within a time period, ,in, , This represents rounding down to the nearest integer.

[0052] Because the terminal is in a high-speed motion state, and the extrapolation time of the second data Therefore, in Within the time period, it is necessary to use The second information is updated for the sliding time interval, and the second data is extrapolated to obtain... All location information of the terminal within the time period. For example... Figure 2 As shown, the coordinate axis ab is the first one. The position of the second data updated by the terminal after the interval on the timeline is typically required to avoid situations where no terminal position is available for a certain period. At this time, different There will be overlap between the second data obtained from the interval, such as Figure 2 The coordinate axes aa and ab are shown in the diagram. In this case, the terminal's first processor will use the latest calculated second data to complete the calculation of the third data. That is, in When using the second data corresponding to coordinate axis aa, and in When that happens, the second data corresponding to coordinate axis ab is used, and so on. Accordingly, Figure 2 In the coordinate system, aba represents the position of the data packet on the time axis after the data corresponding to the third data transmission to the second processor. Similarly, due to transmission delay... The reason is that, at this time, the first updated TA is obtained on the second processor. The available data is in the third data. The data corresponding to the first moment. Similarly, the second processor will process the data corresponding to the coordinate axis aba at time intervals of... The interpolation operation is performed to obtain the corresponding fourth data.

[0053] In this embodiment, when the second processor performs transmission time compensation, the principle of "new data priority" is adopted, giving priority to the use of the fourth data newly generated after the second information update. Figure 2 For example, Figure 2 The middle coordinate axis b represents the data source of the available data for time delay compensation, where TA0, TA1, and TA2 are based on the 0th... The second data extrapolated from the initial second information of the interval, TA3, TA4, TA5, are based on the first. The second data extrapolated from the second information.

[0054] Every During the specified time, the terminal updates the first information once through the first processor, and uses the updated information to repeat steps 1 to 4 above, wherein... .

[0055] The initial information broadcast by the satellite is updated periodically, therefore, on the terminal side, it is necessary to... The first information is updated at time intervals, and extrapolation of the first data is performed using a sliding calculation method. To avoid situations where no satellite position is available for a certain period of time, it is usually required that... At this time, different There will be overlap between the first data obtained. Similarly, adopting the principle of "new data first", in the process of calculating the subsequent TA compensation value based on the first data, the first data generated after the first information is updated will be used first.

[0056] Time interval It should satisfy:

[0057]

[0058] Where c is the speed of light. This is the maximum allowable time delay offset when the satellite receives signals from the terminal. Represents the maximum speed of the terminal. This is the minimum elevation angle of the satellite when the terminal communicates with the satellite.

[0059] In satellite communication scenarios using OFDM as the communication system, a cyclic prefix (CP) interval is preset as a "buffer" for received signal delay. This eliminates inter-symbol interference (ISI) and maintains the orthogonality between subcarriers, ensuring correct signal demodulation. During uplink communication, the terminal should adjust the transmission time of the transmitted data by calculating the delay compensation amount to ensure that the residual delay of the received signal falls within the CP protection interval. When calculating the uplink transmission delay compensation amount in scenarios where the terminal is moving at high speed, the time interval needs to be determined based on the terminal's speed. The TA compensation value is updated in real time based on this time interval to compensate for the additional time delay deviation introduced by the terminal movement and ensure that uplink communication can proceed normally.

[0060] set up This represents the maximum allowable time delay offset when the satellite receives signals from the terminal. The minimum communication angle between the terminal and the satellite is... The maximum speed of the terminal is Then in the time interval Within, the change in radial distance between the terminal and the satellite caused by the terminal's movement is: The time required for an electromagnetic wave to travel this distance is Then it should satisfy ,that is,

[0061]

[0062] By updating the second information based on the above time interval and repeating steps 2 to 4, the jitter in the time delay compensation caused by the high-speed movement of the terminal can be compensated.

[0063] With a terminal velocity of 306 m / s and a minimum elevation angle Maximum time delay offset Taking ns as an example, at this time there is ms, settings The compensation requirement can be met in milliseconds.

[0064] The orbit extrapolation time mentioned in step 1 The value of is not less than the update time interval of the first information transmitted by the satellite. ,Right now This ensures that the terminal has access to satellite ephemeris data in every time period to complete the calculation process described in this embodiment.

[0065] Time step in step 1 The value of should satisfy the following conditions:

[0066]

[0067] Where c is the speed of light. The orbital radius of a circular orbiting satellite. The gravitational constant is the constant of gravity. This is the threshold for the equivalent time delay offset error caused by the position interpolation error during the interpolation calculation of the first data in step 3.

[0068] In step 1, the time step was calculated using orbit extrapolation. The satellite orbit data is used as a basis, and in step 3, the data is interpolated to obtain... The required satellite position information at any given time. Because interpolation introduces truncation errors, the sampling step size... The selection of [the appropriate parameter] should be based on this premise, ensuring that the truncation error introduced by interpolation is within the system's allowable range. In this embodiment, the threshold for the equivalent time delay offset error introduced by satellite orbit interpolation that the system allows is [a certain value]. Based on this, it is determined in the following manner. The range.

[0069] Consider using Lagrange interpolation to calculate the satellite position vector. Perform n interpolation calculations to obtain the interpolation polynomial. At any moment truncation error for:

[0070]

[0071] in, For n+1 known position vector time points; For any point within the interpolated time arc; For the position vector in The (n+1)th derivative at point n. Then the truncation error. The upper limit is:

[0072]

[0073] in, It is the maximum modulus of the (n+1)th derivative within the interpolation interval.

[0074] In this embodiment, considering the trade-off between computational complexity and interpolation accuracy, first-order Lagrange interpolation is used to interpolate the satellite orbital position vector. Therefore, the truncation error is:

[0075]

[0076] This value is measured at equal intervals. Down, The maximum value is reached at the midpoint of the interval. Therefore, the formula for the upper limit of error for first-order interpolation is:

[0077]

[0078] In this embodiment, a circular satellite orbit is considered, and two-body motion is taken as a condition for the operation. Solving for the satellite's position vector in Earth's inertial frame, we can express it as:

[0079]

[0080] in, The radius of the satellite's orbit; The average angular velocity of the orbit can be expressed as: ; This is the initial phase; Let be the orbital inclination angle. Then we have,

[0081]

[0082] Therefore, the upper limit of the truncation error is:

[0083]

[0084] Given a threshold of equivalent time delay offset error Then it should satisfy ,that is:

[0085]

[0086] Based on satellite orbital radius threshold For example, the set time step Should meet 0.543s, at this point, set The accuracy requirement can be met with s.

[0087] The interpolation time step mentioned in step 4 It equals the time interval for the terminal to send uplink information frames, so that the terminal can obtain the delay adjustment amount at the current moment each time it sends uplink information.

[0088] In the embodiment, satellite orbital radius is taken into consideration. ,Every The first broadcast information is updated by s, the terminal's movement speed is 306 m / s, and the minimum elevation angle is... Maximum time delay offset ns, the threshold of equivalent time delay offset error Then the following typical values ​​satisfy the implementation requirements of the method described in this invention: s, ms, s, s, =50ms 500ms ms, ms. Here Determined by hardware performance and the size of the data transmitted. The frame format determines that the terminal sends one frame of uplink data every 10ms.

[0089] It should be noted that the above description is merely a preferred embodiment of this application and is not intended to limit 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 terminal delay compensation method for low-Earth orbit internet satellite communication, characterized in that, Includes the following steps: Step 1: The terminal's first processor reads the first information broadcast by the serving satellite from the received information and uses the first information to perform extrapolation calculations to obtain the first data; The first information includes the satellite's position and velocity information at the time of broadcast; the first data is the satellite's position and velocity data obtained by extrapolating the orbit according to a preset time step within the time period from the time of broadcast to the time of satellite orbit extrapolation. Step 2: The terminal's first processor acquires the second information and performs extrapolation calculations based on the second information to obtain the second data; The second information is the terminal's own position and speed information at the current moment; the second data is the terminal position data obtained by extrapolating the position according to a specific time step within the time period from the current moment to the terminal's position. Step 3: The terminal's first processor interpolates the first data to each time point of the second data to obtain the satellite position data at the corresponding time point, and calculates the third data by combining it with the second data; The third data is the transmission delay data between the terminal and the satellite during the time period extrapolated from the current time to the terminal's location; Step 4, the terminal's second processor processes the third data with a time step of... The interpolation operation yields the fourth data, and the transmission time of the uplink data sent to the satellite is adjusted based on the fourth data to complete the terminal's transmission delay compensation; the fourth data is a time interval of Fine-grained latency data.

2. The terminal delay compensation method for low-Earth orbit internet satellite communication according to claim 1, characterized in that, During the period from the satellite broadcast time to the satellite orbit extrapolation, the terminal updates the second information periodically through the first processor at intervals shorter than the terminal position extrapolation time, and repeats steps 2 to 4 using the updated information.

3. The terminal delay compensation method for low-Earth orbit internet satellite communication according to claim 1, characterized in that, The terminal updates the first information periodically via the first processor at intervals shorter than the satellite orbit extrapolation time, and repeats steps 1 to 4 using the updated information.

4. A terminal delay compensation method for low-Earth orbit internet satellite communication according to claim 2, characterized in that, Intervals shorter than the terminal position extrapolation time satisfy: ； Where c is the speed of light. This is the maximum allowable time delay offset when the satellite receives signals from the terminal. Represents the maximum speed of the terminal. This is the minimum elevation angle of the satellite when the terminal communicates with the satellite.

5. A terminal delay compensation method for low-Earth orbit internet satellite communication according to claim 1, characterized in that, The duration of satellite orbit extrapolation in step 1 The value of is not less than the update time interval of the first information transmitted by the satellite. ,Right now .

6. The terminal delay compensation method for low-Earth orbit internet satellite communication according to claim 1, characterized in that, The preset time step in step 1 The value of satisfies the following conditions: ； Where c is the speed of light. The orbital radius of a circular orbit satellite. The gravitational constant is the constant of gravity. This is the threshold for the equivalent time delay offset error caused by the position interpolation error during the interpolation calculation process in step 3.

7. A terminal delay compensation method for low-Earth orbit internet satellite communication according to claim 1, characterized in that, In step 2, the terminal extrapolation time is less than the satellite orbit extrapolation time, and the terminal's current time is within one step after the satellite broadcast time. This step is the time step preset in step 1.

8. A terminal delay compensation method for low-Earth orbit internet satellite communication according to claim 1, characterized in that, Time step in step 4 This is equal to the time interval between uplink information frames sent by the terminal, so that the terminal receives the delay adjustment amount at the current moment each time it sends uplink information, thereby completing the terminal's transmission delay compensation.

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