Satellite-ground communication time offset and doppler frequency offset pre-compensation device

Abstract

The application discloses a satellite-ground communication time offset and Doppler frequency offset pre-compensation device, which has high estimation accuracy and can complete wide-range time offset and frequency offset estimation and pre-compensation without acquiring satellite ephemeris information of a terminal. The application is realized by the following technical scheme: a DoA estimation unit estimates the arrival angle DoA of a satellite signal by using an array signal processing algorithm; the estimation unit estimates the arrival angle DoA of a satellite signal; the acquired satellite azimuth angle and elevation angle information is divided into two paths, one path is sent to a distance calculation unit, a time offset calculation unit and a time offset pre-compensation unit, the propagation time delay between the satellite and the terminal is calculated and time offset pre-compensation is performed; the other path is output to a velocity vector calculation unit, a Doppler frequency offset calculation unit, a Doppler ambiguity resolution unit and a frequency offset pre-compensation unit, the Doppler frequency offset caused by satellite movement is calculated and frequency offset pre-compensation is performed, the residual time offset and frequency offset are estimated, and the residual time offset and frequency offset are accurately adjusted.

Description

Technical Field

[0001] This invention belongs to the field of air-to-ground wireless communication, and specifically relates to a method and device for time-frequency offset pre-compensation. Technical Background

[0002] In communication systems, due to the Doppler effect and clock accuracy, there is a certain frequency offset between the receiver and transmitter. Furthermore, due to the propagation distance, there is a certain time offset between them. These frequency and time offsets affect the receiver's demodulation.

[0003] According to satellite communication protocols, low-Earth orbit satellite communication uses a combination of Orthogonal Frequency Division Multiplexing (OFDM) and Time Division Multiplexing (TDM). OFDM signals consist of several orthogonal subcarriers, each occupying a portion of the signal bandwidth and transmitted simultaneously on each transmission channel. Time division multiplexing divides the time available for transmitting information across the entire channel into several time slots and allocates these slots to different users. However, OFDM systems are highly sensitive to time and frequency offsets. Time offset introduces inter-symbol interference (ISI), while frequency offset disrupts the orthogonality between subcarriers, causing inter-carrier interference (ICI), leading to signal distortion and degraded system performance. Therefore, time and frequency offsets need to be compensated for and tracked. For terrestrial cellular systems, terminals typically use pilot signals to calculate time and frequency offset values, and then adjust and track these offsets. However, satellite communication systems suffer from inherent problems such as high Doppler frequency offset and large time delay: due to the high speed of satellite movement and the large range of Doppler variation, the Doppler frequency offset exceeds the frequency offset estimation capability of pilot signals; similarly, due to the wide coverage area and large range of time delay variation, the time delay exceeds the time offset estimation capability of pilot signals. Therefore, for satellite communication systems, it is impossible to directly estimate high Doppler frequency offset and large time delay from pilot signals. Summary of the Invention

[0004] To address the problem of limited estimation range in traditional time and frequency offset estimation methods, this invention proposes a pre-compensation device for time and Doppler frequency offset in satellite-to-ground communication that features a large estimation range, high estimation accuracy, and low system resource consumption.

[0005] The present invention is achieved through the following technical solution: a time-frequency offset and Doppler frequency offset pre-compensation device for satellite-to-ground communication, comprising: a time-frequency offset pre-compensation module based on DoA estimation that communicates with an array antenna subsystem 1 and a GPS or Beidou navigation system 2, wherein the time-frequency offset pre-compensation module based on DoA estimation comprises a distance calculation unit 4, a time offset calculation unit 5 and a time offset pre-compensation unit 6 connected in series at the output of a DoA estimation unit 3, a velocity vector calculation unit 7, a Doppler frequency offset calculation unit 8, a Doppler deambiguation unit 9 and a frequency offset pre-compensation unit 10. The specific processing flow is as follows: The array antenna subsystem 1 outputs the received multi-antenna satellite signals to the DoA estimation unit 3. The DoA estimation unit 3 uses the array signal processing algorithm to perform DoA estimation on the received multi-antenna satellite signals, estimating the angle of arrival (DoA) of the satellite signals. Based on the DoA estimation, the acquired azimuth and elevation angle information of the satellite in the station-centered coordinate system is divided into two paths. One path is sent to the distance calculation unit 4, which calculates the distance between the satellite and the terminal using the geometric relationship between the satellite and the terminal, and outputs it to the time offset calculation unit 5 to calculate the propagation delay between the satellite and the terminal. The time offset pre-compensation unit 6 uses the calculated propagation delay to compensate for the timing of the terminal's transmission and reception, realizing time offset pre-compensation. The other path is output to the velocity vector calculation unit 5. Unit 7, the velocity vector calculation unit 7, calculates the satellite's velocity vector relative to the ground based on the terminal's own position information obtained from GPS or Beidou navigation system 2 and the satellite's azimuth, elevation, orbital altitude, and orbital inclination in the station-centered coordinate system. This vector is then output to the Doppler frequency offset calculation unit 8. The Doppler frequency offset calculation unit 8 calculates two Doppler frequency offset values ​​based on the satellite's velocity vector. The Doppler deambiguity unit 9 verifies the two Doppler frequency offset values, selects the true Doppler frequency offset value, and outputs it to the frequency offset pre-compensation unit 10. The calculated Doppler frequency offset is used to pre-compensate the frequency offset of the terminal's transmitted and received signals. Finally, the pilot or synchronization signal is used to estimate the accurate residual time offset and frequency offset, and the residual time offset and frequency offset are precisely adjusted.

[0006] Compared with the prior art, the present invention has the following advantages:

[0007] This invention utilizes the terminal's array antenna to perform DoA (Direction of Arrival) estimation on the signals transmitted by the satellite, obtaining the satellite's azimuth and elevation information. Then, the terminal uses its own GPS position information, along with the satellite's azimuth, elevation, orbital altitude, and orbital inclination, to calculate the propagation delay between the satellite and the terminal, as well as the Doppler frequency offset caused by the satellite's motion. Furthermore, the terminal performs time and frequency offset pre-compensation on the transmitted and received signals to reduce the difficulty of synchronizing the terminal's time and frequency.

[0008] The advantage of this invention is that it can complete large-scale time offset and frequency offset estimation and pre-compensation without requiring the terminal to acquire satellite ephemeris information. When the terminal lacks the ability to acquire satellite ephemeris, the DoA estimation unit 3 uses an array signal processing algorithm to perform DoA estimation on the received multi-antenna satellite signals, estimating the angle of arrival (DoA) of the satellite signals. Based on the DoA estimation, the acquired azimuth and elevation angle information of the satellite in the station-centric coordinate system is divided into two paths. One path is sent to the distance calculation unit 4, which calculates the distance between the satellite and the terminal using the geometric relationship between them, and outputs it to the time offset calculation unit 5 to calculate the propagation delay between the satellite and the terminal. The time offset pre-compensation unit 6 uses the calculated propagation delay to compensate for the terminal's transmission and reception timing, achieving time offset pre-compensation. The other path is output to the speed... The degree vector calculation unit 7 and velocity vector calculation unit 7 calculate the satellite's velocity vector relative to the ground based on the terminal's own position information obtained from GPS or BeiDou navigation system 2 and the satellite's azimuth, elevation, orbital altitude, and orbital inclination in the station-centered coordinate system. The calculated velocity vector is then output to the Doppler frequency offset calculation unit 8. The Doppler frequency offset calculation unit 8 calculates two Doppler frequency offset values ​​based on the satellite's velocity vector. The Doppler deambiguity unit 9 verifies both Doppler frequency offset values, selects the true Doppler frequency offset value, and outputs it to the frequency offset pre-compensation unit 10. The frequency offset pre-compensation unit 10 uses the calculated Doppler frequency offset to pre-compensate the frequency offset of the terminal's transmitted and received signals. This reduces the difficulty of synchronizing the terminal's time and frequency. Attached Figure Description

[0009] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0010] Figure 1 This is a schematic diagram of the principle of the satellite-to-ground communication time offset and Doppler frequency offset pre-compensation device of the present invention;

[0011] In the diagram: 1. Array antenna subsystem, 2. GPS or BeiDou navigation system, 3. DoA estimation unit, 4. Distance calculation unit, 5. Time offset calculation unit, 6. Time offset pre-compensation unit, 7. Velocity vector calculation unit, 8. Doppler frequency offset calculation unit, 9. Doppler deambiguation unit, 10. Frequency offset pre-compensation unit.

[0012] Figure 2 This is a schematic diagram of the signal coverage of a satellite communication system;

[0013] Figure 3 This is a schematic diagram of the geocentric coordinate system;

[0014] Figure 4 This is a schematic diagram of the station center coordinate system;

[0015] Figure 5 This is a schematic diagram of the geometric relationship between the satellite and the terminal;

[0016] Figure 6 This is a schematic diagram of two motion directions when the satellite's position and orbital inclination are known.

[0017] In the diagram: 1. Array antenna subsystem; 2. GPS or BeiDou navigation system; 3. DoA estimation unit; 4. Distance calculation unit; 5. Time offset calculation unit; 6. Time offset pre-compensation unit; 7. Velocity vector calculation unit; 8. Doppler frequency offset calculation unit; 9. Doppler deambiguation unit; 10. Frequency offset pre-compensation unit.

[0018] The invention will be further described below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0019] See Figure 1In the preferred embodiment described below, a satellite-to-ground communication time offset and Doppler frequency offset pre-compensation device includes: a DoA-based time and frequency offset pre-compensation module that communicates with an array antenna subsystem 1 and a GPS or BeiDou navigation system 2. The DoA-based time and frequency offset pre-compensation module includes a distance calculation unit 4, a time offset calculation unit 5, and a time offset pre-compensation unit 6 connected in series at the output of a DoA estimation unit 3; a velocity vector calculation unit 7; a Doppler frequency offset calculation unit 8; a Doppler deambiguation unit 9; and a frequency offset pre-compensation unit 10. The specific processing flow is as follows: The array antenna subsystem 1 outputs the received multi-antenna satellite signals to the DoA estimation unit 3. The DoA estimation unit 3 uses the array signal processing algorithm to perform DoA estimation on the received multi-antenna satellite signals, estimating the angle of arrival (DoA) of the satellite signals. Based on the DoA estimation, the acquired azimuth and elevation angle information of the satellite in the station-centered coordinate system is divided into two paths. One path is sent to the distance calculation unit 4, which calculates the distance between the satellite and the terminal using the geometric relationship between the satellite and the terminal, and outputs it to the time offset calculation unit 5 to calculate the propagation delay between the satellite and the terminal. The time offset pre-compensation unit 6 uses the calculated propagation delay to compensate for the timing of the terminal's transmission and reception, realizing time offset pre-compensation. The other path is output to the velocity vector calculation unit 5. Unit 7, the velocity vector calculation unit 7, calculates the satellite's velocity vector relative to the ground based on the terminal's own position information obtained from GPS or Beidou navigation system 2 and the satellite's azimuth, elevation, orbital altitude, and orbital inclination in the station-centered coordinate system. This vector is then output to the Doppler frequency offset calculation unit 8. The Doppler frequency offset calculation unit 8 calculates two Doppler frequency offset values ​​based on the satellite's velocity vector. The Doppler deambiguity unit 9 verifies the two Doppler frequency offset values, selects the true Doppler frequency offset value, and outputs it to the frequency offset pre-compensation unit 10. The calculated Doppler frequency offset is used to pre-compensate the frequency offset of the terminal's transmitted and received signals. Finally, the pilot or synchronization signal is used to estimate the accurate residual time offset and frequency offset, and the residual time offset and frequency offset are precisely adjusted.

[0020] See Figure 2 The absolute value of the satellite's velocity is v, and the range of the angle between the satellite's direction of motion and the ground coverage ray is α. min ~α max The corresponding Doppler frequency offset range is The closest and farthest distances between the satellite and the ground coverage area are d and d, respectively. min and d max The corresponding propagation delay range is Where C is the speed of light, f c This refers to the communication carrier frequency.

[0021] See Figure 3 , Figure 4 First, we define two coordinate systems:

[0022] 1) Definition as follows Figure 3 The geocentric coordinate system ECEF shown has the Earth's center as the origin, the 0-degree longitude direction as the x-axis, the 90-degree longitude direction as the y-axis, and the North Pole direction as the z-axis.

[0023] 2) Definition as follows Figure 4 The station-centered coordinate system shown is as follows: with the terminal as the origin, the east direction as the x-axis, the north direction as the y-axis, and the zenith direction as the z-axis.

[0024] See Figure 5 To illustrate the time-frequency offset pre-compensation method based on DoA estimation, we consider that the terminal has known the satellite's orbital altitude h and orbital inclination i, and assume that the terminal's position in the geocentric coordinate system is l. t =[x t ,y t ,z t ] T The satellite's position in the geocentric coordinate system is l s =[x s ,y s ,z s ] T In this diagram, the subscript t represents the terminal, the subscript s represents the satellite, and the superscript T represents the transpose of a vector or matrix. The array antenna subsystem 1 outputs the received multi-antenna satellite signals to the DoA estimation unit 3. The DoA estimation unit 3 uses an array signal processing algorithm to perform DoA estimation on the received multi-antenna satellite signals, thereby obtaining the azimuth angle θ and elevation angle of the satellite in the station-centered coordinate system. Here, azimuth is the angle between the x-axis and the x-axis in the counterclockwise direction on the xy-plane, and pitch is the angle between the xy-axis and the xy-plane. DoA estimation unit 3 will use the azimuth angle θ and pitch angle... The information is output to the distance calculation unit 4 and the velocity vector calculation unit 7; the distance calculation unit 4 uses the satellite's elevation angle The distance d between the satellite and the terminal is calculated using the orbital altitude h, and then output to the time offset calculation unit 5. The specific method is as follows:

[0025] The geometric relationship between the satellite and the terminal is as follows: Figure 5 As shown, O, T, and S represent the Earth's center, the terminal position, and the satellite position, respectively. d is the satellite's elevation angle relative to the terminal, h is the satellite's orbital altitude, and r = 6371 km is the Earth's radius.

[0026] Given the satellite's elevation angle relative to the terminal Under the conditions of satellite orbital altitude h, by Figure 5 The geometric relationships between the elements in the equation can be obtained using the law of cosines: Furthermore, the distance d between the satellite and the terminal is related to r. The expression for h: The time offset calculation unit 5 calculates the propagation delay v between the satellite and the terminal and outputs it to the time offset pre-compensation unit 6. The satellite-terminal propagation delay is: The time offset pre-compensation unit 6 compensates for the timing of the terminal's transmission and reception using the propagation delay v. The time offset pre-compensation adjustment value is -v. Here, r = 6371 km is the Earth's radius, and h is the satellite's orbital altitude. The satellite's elevation angle, C = 3.10 8 m / s is the speed of light.

[0027] The GPS or BeiDou navigation system 2 obtains the terminal's own location information, that is, the terminal's position coordinates in the geocentric coordinate system. t =[x t ,y t ,z t ] T The result is then output to the velocity vector calculation unit 7.

[0028] The velocity vector calculation unit 7 uses the terminal's own position information, along with the satellite's azimuth, elevation, orbital altitude, and orbital inclination, to calculate the satellite's velocity vector in the geocentric coordinate system. Since the satellite's motion direction can be either northward or southward, there is ambiguity in the satellite's motion direction. Therefore, two solutions for the satellite's velocity vector, v1 and v2, can be calculated and output to the Doppler frequency offset calculation unit 8. The specific method is as follows:

[0029] 1) Calculate the direction vector l from the terminal to the satellite in the station-centered coordinate system. st0

[0030] The azimuth angle θ and elevation angle of the satellite in the station-centered coordinate system The direction vector l from the terminal to the satellite in the station-centered coordinate system can be obtained. st0 :

[0031] 2) Calculate the direction vector l from the terminal to the satellite in the geocentric coordinate system. st , for l st0 By performing appropriate rotation, l can be obtained. st The rotation process can be described as follows: the station-centered coordinate system rotates clockwise by 90-φ around the x-axis, and then rotates clockwise by 90+λ around the z-axis, where λ and φ are the azimuth and elevation angles of the terminal in the geocentric coordinate system, and we have:

[0032] λ=∠(x t +jy t )

[0033]

[0034] By l st0 Calculate the direction vector l of the terminal pointing to the satellite st :l st =Γ z (90+λ)Γ x (90-φ)l st0 , where Γ x (α) is the rotation matrix for rotating the coordinate system clockwise by α degrees around the x-axis: Γ z (α) is the rotation matrix for rotating the coordinate system clockwise by α degrees around the z-axis:

[0035] 3) Calculate the satellite's position l in the geocentric coordinate system s

[0036] For the satellite's position l in the geocentric coordinate system s =[x s ,y s ,z s ] T The distance between the terminal and the satellite can be calculated using the following formula: l s =l t +dl st Among them, l t The terminal coordinates in the geocentric coordinate system are represented by l. st This represents the direction vector from the terminal to the satellite in the geocentric coordinate system, and d represents the distance between the terminal and the satellite.

[0037] 4) Calculate the absolute value of the satellite's velocity using Kepler's theorem:

[0038] Wherein, the Kepler constant μ = 3.986004418 × 10 14 m 3 / s 2 .

[0039] 5) Calculate the satellite's velocity vector v

[0040] The satellite's position l in the geocentric coordinate system was obtained. s Afterwards, although the orbital inclination angle i is known, but due to Figure 6 It can be observed that the satellite's motion direction can be either northward or southward, thus creating ambiguity regarding the satellite's motion direction.

[0041] Assume the satellite's velocity vector is v = [v x ,v y ,v z ] T If at this point, the unit vector h = [x] perpendicular to the orbital plane is known... h,y h ,z h ] t Then the satellite's velocity vector is v = v(h × d). s ), where d s =l s / |l s | represents the unit direction vector of the satellite in the geocentric coordinate system, × represents the cross product operator, and || represents the modulo operator; h is the angular momentum, and the orbital inclination i is defined as the angle between h and the z-axis. Since h and l s Perpendicular to the z-axis, and the angle between it and the z-axis is the orbital inclination angle i, i.e., z h =cosi, from which we can obtain: h T l s =x s x h +y s y h +z s cosi = 0, which can be obtained from the constraint that h is a unit vector:

[0042] To solve for h using the two equations above, note the following: (The last part, "and l," appears to be a fragment and doesn't translate directly.) s A perpendicular plane and a cone with a fixed angle i to the z-axis are highly likely to have two lines of intersection. Therefore, solving the above equation introduces a fuzzy problem, which in physics means it's impossible to determine whether the satellite is moving north or south. When i = 0° or i = 180°, h has a unique solution; otherwise, h has two solutions: h1 and h2. Therefore, in the general case, the satellite's velocity vector has two solutions: v1 and v2, as shown below. Figure 6 As shown.

[0043] In summary, the velocity vector calculation unit 7 obtains the terminal's position coordinates l in the geocentric coordinate system based on the GPS or BeiDou navigation system 2. t =[x t ,y t ,z t ] T And using the satellite's azimuth angle θ and elevation angle in the station-centered coordinate system The distance d between the terminal and the satellite is calculated to obtain the direction vector l from the terminal pointing to the satellite in the station-centered coordinate system. st0 And the direction vector l of the terminal pointing to the satellite in the geocentric coordinate system. st and satellite position coordinates l s : Then for l st0 Perform rotation using a rotation matrix. Rotate the station-centered coordinate system clockwise by 90° - φ around the x-axis, and then use the rotation matrix. Rotate the station-centered coordinate system clockwise by 90°+λ around the z-axis to obtain the direction vector l from the terminal pointing to the satellite in the geocentric coordinate system. st =Γ z (90+λ)Γ x (90-φ)l st0 Then, the satellite's position coordinates l in the geocentric coordinate system are calculated. s :l s =l t +dl st Where λ and φ are the azimuth and elevation angles of the terminal in the geocentric coordinate system, and we have: λ=∠(x t +jy t ),

[0044] Velocity vector calculation unit 7 calculates the satellite's velocity vector v in the geocentric coordinate system based on the satellite's orbital altitude h and orbital inclination i: Define h = [x...] h ,y h ,z h ] T Let h be a unit vector perpendicular to the orbital plane, i.e., the angular momentum. Then the orbital inclination angle i is the angle between h and the z-axis. h =cosi, by solving the system of equations:

[0045] h T l s =x s x h +y s y h +z s cosi = 0

[0046]

[0047] We obtain two solutions for h: h1 and h2. Using Kepler's theorem, we calculate the absolute value of the satellite's velocity v. Calculate the unit direction vector d of the satellite in the geocentric coordinate system. s =l s / |l s Finally, we obtain the satellite's velocity vector v: v = v(h × d s The data is then output to the Doppler frequency offset calculation unit 8. Since h has two solutions, the corresponding satellite motion velocity vector also has two solutions: v1 and v2, where the Kepler constant μ = 3.986004418 × 10⁻⁶. 14 m 3 / s 2 , × represents the cross product operator, and || represents the modulo operator.

[0048] The Doppler frequency offset calculation unit 8 calculates the Doppler frequency offset based on the satellite motion velocity vector. Since the satellite's motion direction has two cases: moving northward and moving southward, there is ambiguity in the satellite's motion direction, and two Doppler frequency offset values can be estimated. First, calculate the angle β between the satellite's motion direction and the connection line of the satellite terminal: Then calculate the Doppler frequency offset according to the absolute value of the satellite motion velocity and β: Take values v1 and v2 to obtain two Doppler frequency offset values: f doppler1 and f doppler2 , and output them to the Doppler ambiguity resolution unit 9. Here, C represents the speed of light, f c represents the carrier frequency, v represents the absolute value of the satellite motion velocity, and v is the satellite motion velocity vector.

[0049] The Doppler ambiguity resolution unit 9 respectively verifies and compensates the two Doppler frequency offset values, and then selects the one with higher SINR or lower EVM after comparing the SINR or EVM of the two compensated signals as the true Doppler frequency offset value f doppler , and outputs it to the frequency offset pre-compensation unit 10. Here, SINR (Signal to Interference plus Noise Ratio) is the signal-to-interference-plus-noise ratio, which refers to the ratio of the intensity of the received useful signal to the intensity of the received interference signal noise and interference; EVM (Error Vector Magnitude) is the error vector magnitude. The error vector is the vector difference between the ideal error-free reference signal and the actual signal, which can comprehensively measure the amplitude error and phase error of the modulated signal. EVM is defined as the square root of the ratio of the average power of the error vector to the average power of the ideal reference signal, expressed as a percentage. The specific method is as follows: Select the frequency offset pre-compensation value as -f doppler1 , perform frequency offset pre-compensation on the received signal, and calculate the SINR1 or EVM1 of the signal; then select the frequency offset pre-compensation value as -f doppler2 , perform frequency offset pre-compensation on the received signal, and calculate the SINR2 or EVM2 of the signal; if SINR1 > SINR2 or EVM1 < EVM2, then judge f doppler1 as the true Doppler frequency offset value, and let f doppler = f doppler1 ; otherwise, judge f doppler2 as the true Doppler frequency offset value, and let f doppler = f doppler2 .

[0050] The frequency offset pre-compensation unit 10 performs frequency offset pre-compensation adjustment on the terminal's transmitted and received signals, and the frequency offset pre-compensation adjustment value is -f dopplerFinally, the terminal uses the pilot or synchronization signal to estimate the precise residual time offset and frequency offset according to the time-frequency offset synchronization tracking method, and then precisely adjusts the residual time offset and frequency offset.

[0051] The embodiments of the present invention have been described in detail above. Specific implementation methods have been used to illustrate the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and device of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A pre-compensation device for time offset and Doppler frequency offset in satellite-to-ground communication, comprising: A time-frequency offset pre-compensation module based on DoA estimation for communication with an array antenna subsystem (1) and a GPS or Beidou navigation system (2), wherein the time-frequency offset pre-compensation module based on DoA estimation includes: a distance calculation unit (4), a time offset calculation unit (5), and a time offset pre-compensation unit (6) connected in series at the output end of a DoA estimation unit (3), a velocity vector calculation unit (7), a Doppler frequency offset calculation unit (8), a Doppler deambiguation unit (9), and a frequency offset pre-compensation unit (10), characterized in that: the array antenna subsystem (1) outputs the received multi-antenna satellite signals to the DoA estimation unit (3), the DoA estimation unit (3) uses an array signal processing algorithm to perform DoA estimation on the received multi-antenna satellite signals, estimates the angle of arrival (DoA) of the satellite signals, and based on the DoA estimation, divides the obtained azimuth and elevation angle information of the satellite in the station-centered coordinate system into two paths, one path is sent to the distance calculation unit (4), the distance between the satellite and the terminal is calculated using the geometric relationship between the satellite and the terminal, and outputs the distance. The time offset calculation unit (5) calculates the propagation delay between the satellite and the terminal. The time offset pre-compensation unit (6) uses the calculated propagation delay to compensate for the timing of the terminal's transmission and reception, thus achieving time offset pre-compensation. Another output is sent to the velocity vector calculation unit (7). The velocity vector calculation unit (7) calculates the satellite's velocity vector relative to the ground based on the terminal's own position information obtained from the GPS or Beidou navigation system (2) and the satellite's azimuth, elevation, orbital altitude, and orbital inclination in the station center coordinate system. The output is sent to the Doppler frequency offset calculation unit (8). The Doppler frequency offset calculation unit (8) calculates two Doppler frequency offset values ​​based on the satellite's motion velocity vector. The Doppler deambiguity unit (9) verifies the two Doppler frequency offset values ​​respectively, selects the true Doppler frequency offset value, and outputs it to the frequency offset pre-compensation unit (10). The calculated Doppler frequency offset is used to pre-compensate the frequency offset of the terminal's transmission and reception signals. Finally, the pilot or synchronization signal is used to estimate the accurate residual time offset and frequency offset, and the residual time offset and frequency offset are precisely adjusted.

2. The satellite-to-ground communication time offset and Doppler frequency offset pre-compensation device as described in claim 1, characterized in that: Based on the acquired DoA information and the terminal's GPS location information, the terminal uses the geometric relationship between the satellite and the terminal to calculate the propagation delay and Doppler frequency offset. Then, the time offset pre-compensation unit (6) uses the calculated propagation delay to compensate for the timing of the terminal's transmission and reception, thus realizing time offset pre-compensation. The frequency offset pre-compensation unit (10) uses the calculated Doppler frequency offset to perform frequency offset pre-compensation for the transmitted and received signals.

3. The satellite-to-ground communication time offset and Doppler frequency offset pre-compensation device as described in claim 1, characterized in that: A geocentric coordinate system (ECEF) is defined with the Earth's center as the origin, 0 degrees longitude as the x-axis, 90 degrees longitude as the y-axis, and the North Pole direction as the z-axis. A station-centric coordinate system is defined with the terminal as the origin, due east as the x-axis, due north as the y-axis, and the zenith direction as the z-axis. The position of the terminal in the geocentric coordinate system is then obtained. The satellite's position in the geocentric coordinate system is , where subscript t Indicates terminal, subscript s Indicates satellite, superscript T Represents the transpose of a vector or matrix.

4. The satellite-to-ground communication time offset and Doppler frequency offset pre-compensation device as described in claim 3, characterized in that: The array antenna subsystem (1) outputs the received multi-antenna satellite signals to the DoA estimation unit (3). The DoA estimation unit (3) uses the array signal processing algorithm to perform DoA estimation on the received multi-antenna satellite signals and obtains the azimuth angle of the satellite in the station-centered coordinate system. Pitch angle DoA estimation unit (3) will estimate the azimuth angle Pitch angle The information is output to the distance calculation unit (4) and the velocity vector calculation unit (7); the distance calculation unit (4) calculates the velocity vector based on the known satellite elevation angle relative to the terminal. and satellite orbital altitude h Under the given conditions, based on the geometric relationship between the satellite and the terminal, and using the law of cosines, we obtain: This allows us to obtain the distance between the terminal and the satellite. d Regarding Earth's radius r , and h The expression: The time-off calculation unit (5) calculates the propagation delay between the satellite and the terminal based on the distance d and the speed of light c. , The time offset is then output to the time offset pre-compensation unit (6), which compensates for the timing of the terminal's transmission and reception using the propagation delay. The time offset pre-compensation adjustment value is... The azimuth angle is the angle between the x-axis and the counterclockwise direction on the xy-plane, and the pitch angle is the angle between the xy-plane and the xy-plane.

5. The satellite-to-ground communication time offset and Doppler frequency offset pre-compensation device as described in claim 4, characterized in that: The velocity vector calculation unit (7) obtains the terminal's position coordinates in the geocentric coordinate system based on the GPS or Beidou navigation system (2). And using the satellite's azimuth angle in the station center coordinate system Pitch angle Distance between terminal and satellite d Calculate the direction vector from the terminal to the satellite in the station-centered coordinate system. And the direction vector of the terminal pointing to the satellite in the geocentric coordinate system. and satellite position coordinates : Then to Perform rotation using a rotation matrix. Rotate the station center coordinate system x Rotate the axis clockwise Then use the rotation matrix Rotate the station center coordinate system Rotate the axis clockwise This yields the direction vector pointing from the terminal to the satellite in the geocentric coordinate system. Then, the satellite's position coordinates in the geocentric coordinate system are calculated. : ,in, and These are the azimuth and elevation angles of the terminal in the geocentric coordinate system.

6. The satellite-to-ground communication time offset and Doppler frequency offset pre-compensation device as described in claim 3, characterized in that: The velocity vector calculation unit (7) calculates the velocity vector based on the satellite's orbital altitude. h Track inclination Calculate the satellite's velocity vector in the geocentric coordinate system. :definition Let angular momentum be a unit vector perpendicular to the orbital plane, then the orbital inclination angle is... for The angle with the z-axis, then By solving the system of equations: get Two solutions: and The absolute value of the satellite's velocity was calculated using Kepler's theorem. : , where r is the Earth's radius, calculate the unit direction vector of the satellite in the geocentric coordinate system. Finally, the satellite's velocity vector was obtained. : And output to the Doppler frequency offset calculation unit (8), because There are two solutions, and correspondingly, there are also two solutions for the satellite's velocity vector: and Among them, Kepler constant , × represents the cross product operator, and || represents the modulo operator.

7. The satellite-to-ground communication time offset and Doppler frequency offset pre-compensation device as described in claim 3, characterized in that: The Doppler frequency offset calculation unit (8) calculates the angle between the satellite's motion direction and the line connecting the satellite terminal. : Then, based on the absolute value of the satellite's motion velocity and Calculate Doppler frequency shift: Values and Two Doppler frequency offset values ​​were obtained: and And output to the Doppler deblurring unit (9), where, Represents the speed of light. Indicates the carrier frequency. Represents the absolute value of the satellite's velocity. This is the satellite's velocity vector.

8. The satellite-to-ground communication time offset and Doppler frequency offset pre-compensation device as described in claim 1, characterized in that: The Doppler deambiguity unit (9) verifies and compensates for the two Doppler frequency offset values ​​respectively. Then, by comparing the SINR or EVM of the two compensated signals with interference plus noise, it selects the one with higher SINR or lower EVM as the true Doppler frequency offset value. And output to the frequency offset pre-compensation unit (10), where SINR is the signal-to-interference-plus-noise ratio and EVM is the error vector amplitude.

9. The satellite-to-ground communication time offset and Doppler frequency offset pre-compensation device as described in claim 8, characterized in that: The Doppler defuzzification unit (9) selects the frequency offset pre-compensation value as... The received signal is pre-compensated for frequency offset, and the SINR1 or EVM1 of the signal is calculated. Then select the frequency offset pre-compensation value as , perform frequency offset pre-compensation on the received signal, and calculate the SINR2 or EVM2 of the signal; if SINR1 > SINR2 or EVM1 < EVM2, then judge as the true Doppler frequency offset value, and let ; otherwise, judge as the true Doppler frequency offset value, and let .

10. The satellite-to-ground communication time offset and Doppler frequency offset pre-compensation device as described in claim 9, characterized in that: The frequency offset pre-compensation unit (10) performs frequency offset pre-compensation adjustment on the terminal's transmitted and received signals. The frequency offset pre-compensation adjustment value is... Finally, the terminal uses the pilot or synchronization signal to estimate the precise residual time offset and frequency offset according to the time-frequency offset synchronization tracking method, and then precisely adjusts the residual time offset and frequency offset.

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