Satellite Terminal and Crystal Oscillator Error Estimation Method, Device and Application

Abstract

The present invention discloses a satellite terminal, a crystal oscillator error estimation method, device and application, which relate to the field of wireless communication and are used to quickly estimate the crystal oscillator error between a satellite and a terminal, ensuring that the uplink signal can be smoothly accessed to the satellite network after frequency offset pre-compensation. The present invention estimates the carrier frequency offset of the monitored downlink signal, calculates the frequency offset change rate, matches the Doppler frequency offset according to the frequency offset change rate, and then calculates the crystal oscillator error from the carrier frequency offset and the Doppler frequency offset. Repeating multiple rounds can also improve the estimation accuracy of the crystal oscillator error. The present invention does not need to rely on ephemeris information in real time to calculate the Doppler frequency offset, avoiding the problem of large estimation errors caused by low timeliness of ephemeris; by separately considering the compensation for the crystal oscillator error, it is ensured that the terminal can be smoothly synchronized to the satellite network.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication, and in particular to a crystal oscillator error estimation method and apparatus, an uplink synchronization method and apparatus, and a satellite terminal. Background Art

[0002] In a satellite communication system including a satellite terminal and a satellite, for the terminal-side uplink transmission link, during initial uplink frequency synchronization, each terminal usually needs to perform frequency offset pre-compensation on the signals it transmits (i.e., uplink signals). Otherwise, uplink signal frequency domain aliasing will occur on the base station side, causing performance degradation.

[0003] Most of the current frequency offset pre-compensation methods can only be applied to scenarios where the crystal oscillator error in the satellite communication system is small. When the performance of the crystal oscillator itself is poor, or due to long-term disuse or other environmental reasons such as temperature and humidity, the performance of the crystal oscillator deteriorates significantly, resulting in a large crystal oscillator error between the satellite and the terminal. The above frequency offset pre-compensation methods will cause a large frequency offset error in the uplink signal. When it is large enough to exceed the frequency offset adjustment range that the network side can tolerate, the terminal will have difficulty completing normal satellite communication. Therefore, it is necessary to estimate the crystal oscillator error between the satellite and the terminal and separately consider it in the frequency offset pre-compensation of the uplink signal. Summary of the Invention

[0004] The object of the present invention is to provide a crystal oscillator error estimation method to quickly estimate the crystal oscillator error between a satellite and a terminal, so as to facilitate separately considering the crystal oscillator error when performing frequency offset pre-compensation, etc., for all or part of the above problems.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A crystal oscillator error estimation method, comprising:

[0007] Monitoring a downlink signal;

[0008] Estimating the carrier frequency offset of the downlink signal and calculating the first frequency offset change rate of the downlink signal;

[0009] Obtaining a first Doppler frequency offset corresponding to the first frequency offset change rate;

[0010] Calculating a crystal oscillator error based on the estimated carrier frequency offset of the downlink signal and the first Doppler frequency offset.

[0011] On the other hand, the present invention also provides a crystal oscillator error estimation apparatus, comprising:

[0012] A first processing module configured to: monitor a downlink signal;

[0013] A second processing module, configured to: estimate the carrier frequency offset of the downlink signal and calculate a first frequency offset change rate of the downlink signal;

[0014] A third processing module, configured to: obtain a first Doppler frequency offset corresponding to the first frequency offset change rate;

[0015] A fourth processing module, configured to: calculate an oscillator error based on the carrier frequency offset estimated for the downlink signal and the first Doppler frequency offset.

[0016] On the other hand, the present invention further provides another oscillator error estimation device, including a first processor and a first storage medium, where the first storage medium stores a computer program, and the first processor executes the computer program to run the above-mentioned oscillator error estimation method.

[0017] On the other hand, the present invention further provides a satellite terminal, and the satellite terminal is configured with the above-mentioned oscillator error estimation device.

[0018] On the other hand, the present invention further provides an uplink synchronization method, which includes:

[0019] The terminal listens to the downlink signal;

[0020] The terminal estimates the oscillator error by using the above-mentioned oscillator error estimation method;

[0021] The terminal performs frequency offset pre-compensation on the uplink signal based on the estimated oscillator error.

[0022] On the other hand, the present invention further provides an uplink synchronization device, including a second processor and a second storage medium, where the second storage medium stores a computer program, and the second processor executes the computer program to run the above-mentioned uplink synchronization method.

[0023] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention are:

[0024] Based on the carrier frequency offset and the frequency offset change rate calculated for the listened-downlink signal, and from the mapping relationship between the Doppler frequency offset caused by the relative motion between the satellite and the terminal and the frequency offset change rate of the downlink signal, the present application estimates the Doppler frequency offset of the downlink signal without relying on real-time ephemeris information, and completes the estimation of the oscillator errors of the satellite and the terminal. When performing frequency offset pre-compensation, the compensation for the oscillator error is considered separately, ensuring that even in a scenario with a large oscillator error, the frequency deviation of the uplink signal can be compensated to a state not exceeding the tolerance range on the satellite side, guaranteeing that the terminal can be successfully synchronized to the satellite network. In addition, the present application can control the granularity of the pre-constructed mapping relationship according to the tolerance range of the frequency offset on the satellite side in a specific application scenario, so as to achieve the effect of balancing the computing power and storage resource costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be described by way of examples with reference to the accompanying drawings, where:

[0026] Figure 1 is a signal flow diagram of the satellite - terminal synchronization process in a satellite communication system.

[0027] Figure 2 is a flowchart of the crystal oscillator error estimation method provided by an embodiment of the present application.

[0028] Figure 3 is a three - dimensional spatial schematic diagram of a satellite communication system in an embodiment of the present application.

[0029] Figure 4 is Figure 3 a schematic diagram of the geometric relationship within the STO plane in

[0030] Figure 5 is Figure 3 a schematic diagram of the geometric relationship within the MNO plane in

[0031] Figure 6 is a flowchart of the uplink synchronization method provided by an embodiment of the present application.

[0032] Figure 7 is a signal flow diagram of the theory of the uplink synchronization method provided by an embodiment of the present application.

[0033] Figure 8 is a signal flow diagram of the actual uplink synchronization method provided by an embodiment of the present application.

[0034] Figure 9 is a structural diagram of the crystal oscillator error estimation device provided by an embodiment of the present application.

[0035] Figure 10 is a structural diagram of the satellite terminal provided by an embodiment of the present application.

[0036] Figure 11 is a structural diagram of the electronic device provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE INVENTION

[0037] All features disclosed in this specification, or all steps in the disclosed methods or processes, except for mutually exclusive features and / or steps, can be combined in any manner.

[0038] Any feature disclosed in this specification (including any additional claims, abstract) can, unless specifically recited, be replaced by other equivalent or similar - purpose alternative features. That is, unless specifically recited, each feature is only an example of a series of equivalent or similar features.

[0039] In this specification, ordinal terms such as "first" and "second" are only used to more clearly refer to the described objects, unless otherwise specified, and do not have a special restrictive effect on the corresponding objects. The azimuth prepositions such as "upper", "lower", "left", and "right" mentioned in this specification are for the perspective of specific embodiments of this application. After the perspective changes, unless otherwise specified, the corresponding azimuth should change synchronously.

[0040] Due to the relatively high-speed movement between the satellite and the terminal, there will be a large Doppler frequency offset in the downlink signal received by the terminal. In addition, there will be a certain deviation between the output frequency of the crystal oscillator and the nominal frequency. Therefore, the crystal oscillator error between the terminal side and the satellite side always exists. Assume that the Doppler frequency offset introduced by the relative movement between the satellite and the terminal in the downlink signal is ; the crystal oscillator error caused by the crystal oscillator on the terminal side relative to the satellite side is , where , is the actual carrier frequency generated by the crystal oscillator on the satellite side, is the actual carrier frequency generated by the crystal oscillator on the terminal side.

[0041] Currently, the frequency offset pre-compensation performed on the terminal side generally includes two methods:

[0042] Method 1: The terminal uses its own position, movement speed, ephemeris information, etc. to estimate the Doppler frequency offset value of the downlink signal, and performs frequency pre-compensation on the uplink signal according to .

[0043] Method 2: The terminal uses the downlink signal to complete the downlink frequency offset estimation, and records the frequency offset estimation value as . The terminal uses to perform frequency offset pre-compensation on the uplink signal according to . Among them, the estimated downlink frequency offset value is the superimposed value of the Doppler frequency offset and the frequency offset caused by the crystal oscillator error , that is, .

[0044] The above Method 1 requires accurate estimation of the Doppler frequency offset , which requires relatively accurate real-time satellite position, and thus requires relatively quasi-real-time satellite ephemeris information. However, in actual applications, the satellite ephemeris may only guarantee the information timeliness at the minute level, which will introduce a large deviation to the real-time relative position between the satellite and the terminal, and further bring a large error to the estimation of the Doppler frequency offset . Eventually, it may cause the terminal to be unable to successfully access the network due to the inability to complete the uplink frequency synchronization. On the other hand, the actually compensated frequency offset value It will cause the uplink frequency offset to have a crystal oscillator error remaining. Only when is small, the satellite communication system will assist the terminal to complete the uplink frequency synchronization adjustment through the closed-loop frequency synchronization mechanism.

[0045] The above-mentioned Method 2 directly uses to perform frequency offset pre-compensation on the uplink signal, which will introduce a new frequency offset . Therefore, this method is also only applicable to the application scenarios where the crystal oscillator errors of the satellite and the terminal basically remain constant or the error fluctuations are within a small range. For the introduced new frequency offset , when it is small, the satellite communication system can also assist the terminal to complete the uplink synchronization adjustment through the closed-loop frequency synchronization mechanism, so that the synchronization accuracy meets the service channel synchronization requirements.

[0046] As Figure 1 shown is the signal flow diagram of the satellite and terminal synchronization process. The satellite sends down the downlink signal (such as broadcasting). After the terminal monitors the downlink signal, it sends an uplink signal in order to access the satellite communication network. Before sending the uplink signal, it is necessary to perform frequency offset pre-compensation on its uplink signal. The two existing methods can only be used in the scenarios where the crystal oscillator error is small. Once the crystal oscillator error exceeds the tolerance limit of the frequency offset on the satellite side, the terminal cannot synchronize to the satellite network smoothly. Therefore, in the frequency offset pre-compensation of this application, the compensation for the crystal oscillator error is considered separately.

[0047] For the requirement of separately compensating the crystal oscillator error of the satellite communication system, it is necessary to first estimate the crystal oscillator error. The embodiment of this application provides a method for estimating the crystal oscillator error. As Figure 2 shown, this method includes:

[0048] S1: Monitor the downlink signal.

[0049] The so-called downlink signal is the signal sent by the satellite to the terminal, which has forms such as directional transmission or broadcast transmission. This application does not limit this.

[0050] The downlink signal of the satellite carries ephemeris information of the current service beam, which includes information characterizing the real-time position of the satellite and information characterizing the satellite orbit. When the first method mentioned above estimates the real-time Doppler frequency offset, it uses the real-time position information of the satellite. Therefore, when the timeliness of the ephemeris information is poor, it will cause a deviation in the estimation of the satellite position, resulting in a large deviation in the estimated Doppler frequency offset. The satellite orbit information usually includes the semi-major axis, eccentricity, orbital inclination, right ascension of the ascending node, argument of perigee, etc. The satellite orbit information basically does not change within the time limit of minutes. Through the satellite orbit information, using the existing orbit fitting methods of aerospace orbital kinematics, etc., the satellite orbit (or satellite trajectory) within the time limit of the orbit parameters can be simulated.

[0051] S2: Estimate the carrier frequency offset of the downlink signal and calculate the first frequency offset change rate of the downlink signal.

[0052] Calculating the carrier frequency offset of the downlink signal based on the monitored downlink signal can be achieved using existing frequency estimation algorithms, which is the same as the downlink frequency offset estimation performed in the second method mentioned above. Among the estimated carrier frequency offsets, it includes the Doppler frequency offset generated by the relative motion between the satellite and the terminal , and the crystal oscillator error between the satellite and the terminal . Since the aging of the crystal oscillator is a relatively slow process, therefore, in the short term, this crystal oscillator error usually remains stable. Therefore, the difference between the estimated carrier frequency offsets within a short period of time is actually the difference between the estimated Doppler frequency offsets between two moments .

[0053] In step S2, it is also necessary to calculate the first frequency offset change rate of the downlink signal. The so-called frequency offset change rate is a parameter characterizing the frequency offset change speed. Therefore, when calculating the frequency offset change rate, at least one reference frequency offset value and one reference frequency offset value, as well as the time interval for generating these two frequency offset values are required.

[0054] As an optional implementation method, the method for calculating the first frequency offset change rate of the downlink signal includes:

[0055] Calculate the first frequency offset change rate of the downlink signal based on the carrier frequency offsets estimated for at least two continuously monitored downlink signals.

[0056] Taking the continuous monitoring of two downlink signals as an example, assume that the carrier frequency offsets estimated for the two continuously monitored downlink signals are successively and . As mentioned above, the carrier frequency offset estimated for the downlink signal includes the Doppler frequency offset corresponding to the satellite communication system state and the crystal oscillator error , and here assume The included Doppler frequency offset is , The included Doppler frequency offset is . Since two consecutive downlink signals are continuously monitored, and The included crystal oscillator error can be regarded as equal. Then there is:

[0057] (1),

[0058] (2).

[0059] Assume that the time interval between monitoring the above two downlink signals is . Then, according to the following formula (3), the frequency offset change rate between the two downlink signals can be calculated :

[0060] (3).

[0061] For the scenario of continuously monitoring multiple downlink signals, it can be that after calculating the frequency offset change rate between every two consecutive downlink signals in the above manner, the average value is calculated as the first frequency offset change rate. Or, it can also be that the frequency offset change rate between any two of the multiple downlink signals is calculated as the first frequency offset change rate.

[0062] S3: Obtain the first Doppler frequency offset corresponding to the first frequency offset change rate.

[0063] As an optional implementation manner, in step S3, based on the pre-constructed mapping relationship between the Doppler frequency offset and the frequency offset change rate, the corresponding first Doppler frequency offset is matched by the first frequency offset change rate.

[0064] The so-called pre-construction means that the construction is completed before matching the first frequency offset change rate, and its time node can be before step S1, or after step S1 and before step S3.

[0065] In this application, by using the mapping relationship between the Doppler frequency offset and the frequency offset change rate, the required Doppler frequency offset can be quickly matched. Compared with the method of calculating the Doppler frequency offset in real time through ephemeris information mentioned in the previous method one, on the one hand, it does not require frequent information interaction with the satellite, and the Doppler frequency offset can be quickly matched from the mapping relationship according to the frequency offset change rate of the downlink signal, improving the Doppler frequency offset estimation speed; on the other hand, the matching method based on the mapping relationship also reduces the dependence on the timeliness of ephemeris information, so it is less affected by the timeliness of ephemeris information.

[0066] In some feasible embodiments, the mapping relationship between the Doppler frequency offset and the rate of change of the frequency offset can be constructed in the form of a mapping table, in which there is a one-to-one correspondence between the Doppler frequency offset and the rate of change of the frequency offset. In addition, for the convenience of explaining the technical solution, hereinafter, the mapping relationship between the Doppler frequency offset and the rate of change of the frequency offset will be referred to by taking the mapping table as an example.

[0067] As an alternative embodiment, the mapping table is constructed from the Doppler frequency offset estimated at multiple moments within the visible range of the satellite and the corresponding calculated rate of change of the frequency offset.

[0068] Doppler frequency offset is calculated by the following formula (4):

[0069] (4),

[0070] wherein, is the carrier frequency of the satellite downlink signal. c is the speed of light, usually taking the value of 3×10 8 m / s. v represents the relative motion speed between the satellite and the terminal, which is obtained by vector operation of the satellite motion speed vector and the terminal motion speed vector. represents the angle between the direction of v and the line connecting the satellite to the terminal. As Figure 3 shown, taking to represent the satellite motion speed vector, taking to represent the terminal motion speed vector, taking to represent the satellite motion speed vector and the angle between the line connecting the satellite to the terminal, taking to represent the terminal motion speed vector and the angle between the line connecting the satellite to the terminal, then represents the component of v in the direction of the line connecting the satellite to the terminal, which is equivalent to and performing vector addition.

[0071] Satellite motion speed can be calculated by the following formula (5):

[0072] (5),

[0073] wherein, g represents the acceleration due to gravity, usually taking the value of 9.8m / s 2 ; R represents the radius of the earth; h represents the height of the satellite from the earth's surface, that is, the satellite orbit height, which can be obtained by analyzing the satellite orbit information in the ephemeris information.

[0074] Since the movement of the terminal relative to the satellite can be considered as being stationary on the Earth's surface, the trajectory of the terminal can be considered as the parallel line of the latitude where it is located, and the direction of the terminal movement velocity vector is the tangent direction of the parallel line. The magnitude of the terminal movement velocity is the rotation speed at the location of the terminal, and the magnitude can be calculated by the following formula (6):

[0075] (6),

[0076] In the formula, represents the geographical latitude where the terminal is located, which can be obtained through the positioning information of the terminal; T represents the rotation period, with a value of 86400 s. The magnitude range of the terminal movement velocity vector is between 0 and 465 m / s (465 m / s is the velocity at the equator), and the direction is the tangent direction of the circular plane of the latitude parallel to the Earth's equatorial plane.

[0077] Particularly, when the satellite orbit is a near-polar orbit, that is, the satellite orbit inclination is 90°, when the terminal is at the sub-satellite point position, the terminal movement velocity vector is perpendicular to the satellite orbit plane, that is is always perpendicular to the satellite movement velocity vector There is At this time Then the method of calculating the Doppler frequency shift through formula (4) can be equivalent to:[[]]

[0078] (7).

[0079] The previous text introduced the method of calculating the Doppler frequency shift of the downlink signal. When the satellite is within the visible range, at a determined moment, the position of the satellite and the position of the terminal at this moment can be determined, so as to determine v and and then calculate the Doppler frequency shift at this moment through formula (4) (or equivalent method). The so-called visible range is the satellite trajectory segment visible to the terminal relative to the satellite. In this satellite trajectory segment, the range of the elevation angle ε of the satellite orbit plane is .

[0080] By determining multiple moments of the satellite within the visible range (assuming a total of n moments are set), the Doppler frequency shifts of the satellite at these multiple moments during the overpass period (that is, the flight period within the visible range) can be correspondingly calculated. Assuming that the Doppler frequency shifts at these multiple moments are sequentially recorded as , represents the Doppler frequency shift obtained at moment i .

[0081] Correspondingly, when multiple moments are determined, the time intervals between the moments can be known. By calculating the difference between the estimated Doppler frequency offsets at every two moments and then dividing it by the time interval between the two moments, the frequency offset change rate at the corresponding moment (usually the previous moment of the two moments) can be obtained. , and the calculation method is as follows:

[0082] (8),

[0083] In the formula, is the time interval between moment j and moment i . In some feasible implementation manners, in the constructed mapping table, . In some feasible implementation manners, in the constructed mapping table, j the moment is the next moment of moment i , that is, the frequency offset change rate between the Doppler frequency offsets estimated at every two adjacent moments is used as the frequency offset change rate of the previous moment i . Of course, this is only one of the feasible manners, and it is not limited to this in specific implementation. It can also be the frequency offset change rate between the Doppler frequency offsets estimated at non - adjacent moments, that is, in formula (8), j the moment and i the moment are not adjacent when calculating the frequency offset change rate.

[0084] As an alternative implementation manner, the states of the satellite at multiple moments within the visible range can be simulated to estimate the Doppler frequency offsets of the satellite at multiple moments and calculate the corresponding frequency offset change rates.

[0085] The so - called simulation of the states of the satellite at multiple moments within the visible range means simulating the positions, flight speeds, flight directions, etc. of the satellite at multiple moments within the visible range, so as to estimate the Doppler frequency offset at each moment according to the method introduced above, and then calculate the frequency offset change rate corresponding to each moment.

[0086] In some alternative implementation manners, the satellite trajectory can be simulated, such as the complete flight trajectory of the satellite or the flight trajectory within the visible range. Then, based on the set step size, multiple moments are determined. Since the satellite trajectory has been simulated, the states of the satellite at each determined moment can be obtained respectively. According to the state of the satellite at each moment, the Doppler frequency offset at that moment can be calculated; according to the Doppler frequency offsets calculated at multiple moments, the frequency offset change rate at each moment can be calculated respectively, and the Doppler frequency offset and the frequency offset change rate at each moment are associated one by one, thereby constructing a mapping table.

[0087] As a feasible implementation manner, the step size set for sampling the simulated satellite trajectory can be the step size set in the time dimension, such as the time step size, that is, determining a sampling moment at every interval of how much time; it can also be the step size set in the distance dimension, such as the satellite motion arc length step size, that is, determining a sampling moment when the satellite flies a certain distance; it can also be the step size set in the angle dimension, such as the step size of the elevation angle in the satellite orbital plane, that is, determining a sampling moment at every interval of how many degrees of the elevation angle in the satellite orbital plane. No matter what kind of step size is set, preferably, equal-step sampling is performed on the entire visible range of the satellite. As a simple and effective way, the step size of the elevation angle in the satellite orbital plane can be considered to determine each moment. For example, in interval, determine all moments at every interval of . In this way, the angle difference between adjacent moments is determined, which is more beneficial for calculating the Doppler frequency shift at each moment when constructing the mapping table.

[0088] Considering the matching accuracy of the later Doppler frequency shift, if the granularity of the constructed mapping table is finer (i.e., the step size is lower), the sampled satellite positions will be denser, and the frequency shift rate and the corresponding Doppler frequency shift in the mapping table will be more consistent with the actual situation. Therefore, in some alternative embodiments, the duration corresponding to the set step size does not exceed the duration between two consecutive downlink signals listened by the terminal. That is, in the constructed mapping table, the time difference between two adjacent moments should be shorter than the shortest time interval for the terminal to listen to the downlink signal. For example, assuming that the time interval between two consecutive downlink signals listened by the terminal is 200 ms, when constructing the mapping table, the set time interval between adjacent moments should be less than 200 ms, such as 50 ms - 100 ms. In this way, when the terminal listens to the downlink signal at any two moments, in the mapping table, there is more finely granular data available for matching, so as to ensure the matching degree between the Doppler frequency shift and the actual state.

[0089] The simulated satellite trajectory can be completed according to the ephemeris information. In some alternative implementation manners, the method for simulating the satellite trajectory includes:

[0090] Receiving a downlink signal;

[0091] Parsing the ephemeris information of the satellite from the received downlink signal;

[0092] Simulating the satellite trajectory based on the satellite orbit information in the ephemeris information.

[0093] Different from the aforementioned Method 1 and Method 2, in the embodiments of the present application, the satellite orbit information is obtained from the ephemeris information, rather than the satellite position information. Since the accuracy of the satellite orbit information in the ephemeris information is still relatively high within the minute-level timeliness, only the satellite orbit information needs to be parsed and obtained within the effective time to simulate the satellite trajectory, without the need to synchronize the ephemeris information for a long time or frequently. Therefore, the method of constructing the mapping table by simulating the satellite trajectory is hardly affected by the timeliness of the ephemeris information.

[0094] In addition, the inclination angle of the satellite orbit plane has a certain influence on the Doppler frequency offset of the downlink signal received by the terminal, and the terminal is not always accessing the satellite at the sub-satellite point. Therefore, using the same mapping table constructed under the same conditions in different situations may introduce a large deviation. Considering this, in some optional embodiments, the mapping table constructed in the present application includes the mapping relationship between the Doppler frequency offset and the frequency offset change rate at different over-the-top elevation angles of the satellite. The so-called over-the-top elevation angle is the elevation angle of the terminal position relative to the satellite at the over-the-top moment, denoted by as shown.

[0095] As Figure 3 shown, in a three-dimensional space, assuming that the terminal position is at point T on the earth's surface, the projection of the satellite on the earth's surface is called the sub-satellite point. Calculate the straight-line distance between the terminal position point T and all sub-satellite points, and find the sub-satellite point closest to the terminal and denote it as P point. This P point is the sub-satellite point position at the over-the-top moment of the satellite. Denote the satellite position corresponding to point P as S , and denote the shortest straight-line distance, i.e., the side length TP = l . Draw a perpendicular line from the terminal position point T to the satellite orbit plane, and the intersection point is the projection position of the terminal in the satellite orbit plane, denoted as C point. Then ∠ STC is the over-the-top elevation angle of point T . When the terminal is at the sub-satellite point, its over-the-top elevation angle is 90°, and at this time, T point, C point and P point coincide. Figure 3 In SC , draw a perpendicular line to C through M point or S point and intercept the earth. Then the angle between the connection line of the satellite ( C point) and εRepresentation. In some alternative embodiments of the present application, for different overhead elevation angles, the Doppler frequency offset of the satellite is estimated at multiple moments within the visible range, the corresponding frequency offset change rate is calculated, and the mapping relationship between the Doppler frequency offset and the frequency offset change rate of the satellite at different overhead elevation angles is constructed. Assuming that a mapping table is constructed for each different overhead elevation angle, then when matching the first Doppler frequency offset in step S3, it is to match the corresponding Doppler frequency offset from the calculated frequency offset change rate in the mapping table corresponding to the overhead elevation angle.

[0096] As Figure 4 shown is the cross-sectional view of the Earth passing through T point, P point and S point. Taking O point as the center position of the Earth's sphere, the side length TC is the distance from the terminal to the satellite orbital plane, and the side length OC is the distance between the center of the Earth and the projection position of the terminal within the satellite orbital plane. Here, in combination with Figure 3 , Figure 4 and Figure 5 , a feasible implementation manner for solving the angle β is described.

[0097] In ΔOTP , it is known that OT = OP = R ( R is the radius of the Earth), the side length TP = l is known. Assuming that the central angle of the Earth ∠ TOS = δ , according to the cosine theorem: . Therefore, the central angle of the Earth δ is:

[0098] (9).

[0099] In the right triangle Δ OCT, from the central angle of the Earth δ and the side length OT = R, it can be known that: the distance from the terminal to the satellite orbital plane, i.e., the side length , and the distance between the center position of the Earth O point and the projection position of the terminal within the satellite orbital plane, i.e., the side length .

[0100] As Figure 5 shown, extend the line connecting the center position of the Earth O point and the projection position of the terminal within the satellite orbital plane C point until it intersects with the moving speed direction of the satellite M point, and mark the intersection position as N point. Based on the satellite elevation angle εand the position of the center of the Earth O The distance between the point and the projection position of the terminal in the satellite orbit plane C The distance between points is used to calculate the satellite position M The distance between the point and the projection position of the terminal in the satellite orbit plane is the side length MC and the intersection position N The distance between the point and the projection position of the terminal in the satellite orbit plane C The distance between points is the side length NC and the satellite position M The distance between the point and the intersection position N The distance between points is the side length MN 。

[0101] Such as Figure 5 shown, in ΔMOC Given the side length OC , OM = R + h , ∠OCM = ε + 90°, according to the cosine theorem: Let , Solve the quadratic equation to obtain the side length MC as:

[0102] (10)。

[0103] Assume ∠MOC = η ,according to the cosine theorem can be obtained η 。Then use the formulas and to obtain the side lengths MN and ON ,finally obtain: side length NC = ON - OC 。

[0104] Based on the distance from the terminal to the satellite orbit plane which is the side length TC 、the distance between the satellite position and the projection position of the terminal in the satellite orbit plane C The distance between points is the side length MC 、the intersection position N The distance between the point and the projection position of the terminal in the satellite orbit plane C The distance between points is the side length NC 、and the distance between the satellite position and the intersection position N The distance between points is the side length MN ,calculate the satellite motion velocity vector corresponding to the satellite elevation angle and the angle MT between the satellite and the connection line of the terminal β :

[0105] Since the terminal position T point and the projection position of the terminal in the satellite orbit planeC The line connecting the points is perpendicular to the satellite orbit plane. Therefore, in the right triangles ΔMCT and ΔNCT , by using the Pythagorean theorem, the side lengths MT and NT are obtained:

[0106] (11),

[0107] (12).

[0108] In ΔMNT , ∠NMT is the satellite motion velocity vector and the angle MT between the satellite and the terminal connection line β . By using the cosine theorem , it is obtained:

[0109] (13).

[0110] When the remaining angles need to be calculated, they can be completed by using trigonometric functions, and the embodiments of the present application will not be described in detail one by one.

[0111] In addition, in the same mapping table, there may be more than two Doppler frequency offsets corresponding to the same frequency offset change rate. For example, in the mapping table constructed by symmetrically sampling the satellite elevation angle at an over-the-top elevation angle of 90°, the frequency offset change rates calculated at the two satellite elevation angles with a complementary relationship may be the same, and the corresponding Doppler frequency offsets may also be the same or similar. Then, when performing the first frequency offset change rate matching in step S3, more than two Doppler frequency offsets may be matched. In this regard, in some alternative embodiments, when more than one Doppler frequency offset is matched from the mapping table by the first frequency offset change rate, the one closest to the carrier frequency offset among all the matched Doppler frequency offsets is used as the first Doppler frequency offset.

[0112] Here, taking the one closest to the carrier frequency offset of the first downlink signal being listened to among all the matched Doppler frequency offsets as the first Doppler frequency offset as an example. As introduced above, the carrier frequency offsets of the two downlink signals being listened to are and in sequence, and the calculated frequency offset change rate is . The frequency offset change rate is matched in the pre-constructed mapping table. The matching principle is to first find the frequency offset change rate closest to in the corresponding mapping table, and the closest frequency offset change rate is represented by . Assuming that in the mapping table, there are two Doppler frequency offsets associated with , which are respectively denoted as and , then the one closest to The closest one is taken as the first Doppler frequency offset, denoted as , then there is:

[0113] (14).

[0114] Among them, abs represents taking the absolute value. Taking the closest one to the carrier frequency offset of the second downlink signal for distance monitoring among all the Doppler frequency offsets matched by distance as the first Doppler frequency offset as an example, then in formula (14) needs to be modified to .

[0115] Through the above steps, the current Doppler frequency offset can be quickly estimated without relying on real-time ephemeris information.

[0116] For example, assume that the satellite orbit altitude is h = 1800 km, the satellite orbit inclination is 0°, that is, a near-polar orbit, the synchronization channel operating frequency point = 17 GHz, the terminal is in a stationary state, and after the terminal side completes the parsing of the broadcast message to obtain the ephemeris information and estimates through satellite trajectory simulation, the over-the-top elevation angle of the terminal relative to the satellite orbit plane is 90°, that is, the terminal is located at the sub-satellite point position of the satellite trajectory.

[0117] Construct a mapping table for the satellite elevation angle ε in the interval [0:180]° with a step of 0.05°, and obtain the Doppler frequency offset caused by the relative motion between the satellite and the terminal during the entire over-the-top period when the over-the-top elevation angle and the frequency offset change rate are shown in Table 1.

[0118] Similarly, under the same conditions, when , the constructed mapping table is shown in Table 2.

[0119] When estimating the crystal oscillator error, it is necessary to first look up the mapping table corresponding to the over-the-top elevation angle based on the over-the-top elevation angle of the terminal's location, and then match the Doppler frequency offset from the frequency offset change rate in this mapping table.

[0120] Table 1 Mapping table between Doppler frequency offset and frequency offset change rate ( )

[0121]

[0122] Table 2 Mapping table between Doppler frequency offset and frequency offset change rate ( )

[0123]

[0124] In addition, the embodiments of the present application also consider the influence of the estimation error of the crystal oscillator error on the feasibility of the solution, and denote this estimation error.

[0125] In the initial uplink frequency synchronization scenario, the satellite payload can assist the terminal to complete uplink synchronization adjustment through a closed-loop frequency synchronization mechanism, that is, it has a certain tolerance range for the frequency offset of the uplink signal. Therefore, when the frequency offset of the uplink signal transmitted by the terminal side estimated by the satellite side is within the frequency adjustment range that the satellite side can tolerate, the terminal can continue the subsequent synchronization adjustment or the initial access process. Therefore, as long as the estimation error introduced by the present application is within the frequency adjustment range that the satellite side can tolerate, the solution provided by the embodiments of the present application is feasible.

[0126] For example, for a low-earth orbit (LEO) satellite communication system, during its initial uplink synchronization phase, the tolerance threshold of the satellite side for the frequency deviation of the uplink signal is generally on the order of ten KHz. For example, taking the middle value of 5 KHz, therefore, as long as the introduced estimation error is lower than this tolerance threshold, the terminal can successfully complete uplink synchronization, that is, the solution of the present application has a certain tolerance interval and is feasible. Of course, all the designs of the present application can also be applied to other satellite communication systems, such as medium-earth orbit (MEO) satellite communication systems and high-earth orbit (HEO) satellite communication systems, and the tolerance principle is the same. In addition, the design concept of the present application can also be applied to non-terrestrial network (NTN) communication systems.

[0127] The estimation error has three influencing factors:

[0128] Influencing factor 1: The error between the satellite orbit parameters carried in the broadcast message and the real satellite orbit parameters.

[0129] Influencing factor 2: The influence brought by the change of orbit parameters within the minute-level aging.

[0130] Influencing factor 3: The positioning error of the terminal's own position.

[0131] In influencing factor 1, the satellite orbit parameters in the ephemeris information are configured by the satellite side and carried by the broadcast channel. The parameter errors in the configuration are determined by the satellite side. The satellite orbit parameters obtained by the terminal side within the timeliness will not introduce errors. Therefore, influencing factor 1 can be ignored. Moreover, the changes in each satellite orbit parameter within the minute-level timeliness are very small. Therefore, influencing factor 2 can also be ignored. The positioning error of influencing factor 3 is determined by the positioning mechanism and positioning algorithm adopted by the terminal side and cannot be ignored. Therefore, in the embodiments of the present application, for the verification of the feasibility of the solution, it is mainly concentrated on considering the influence of the estimation error introduced by the terminal positioning error on the feasibility of the solution.

[0132] The problem directly caused by the terminal positioning error is the impact on the estimated elevation angle In the embodiments of the present application, what is directly affected is that when matching the Doppler frequency offset based on the frequency offset change rate calculated from the downlink signal, it may lead to finding the wrong mapping table.

[0133] Assume that the satellite orbit height is h = 1800 km, the satellite orbit inclination is 0°, and the working frequency point of the synchronization channel = 17 GHz, and the terminal is in a stationary state. Now assume two scenarios:

[0134] Scenario 1: The elevation angle of the terminal relative to the satellite orbit plane . The downlink carrier frequency offsets of two adjacent intervals of 200 ms measured by the terminal through downlink signal synchronization are respectively: = 193954.392 Hz and = 193812.597 Hz. The calculated frequency offset change rate is:

[0135] .

[0136] Through The closest frequency offset change rate -708.981 Hz / s is matched in the mapping table of Table 1. There are two corresponding Doppler frequency offsets, which are F1 = 186.394 kHz and F2 = -186.394 kHz respectively. Select the one closest to The Doppler frequency offset F1 = 186.394 kHz is the final first Doppler frequency offset. Based on this, the crystal oscillator error of the satellite communication system is calculated as:

[0137] .

[0138] Scenario 2: The elevation angle of the terminal relative to the satellite orbit plane . The frequency offset change rate between the downlink carrier frequency offsets of two adjacent intervals of 200 ms measured by the terminal through downlink signal synchronization is still -708.969 Hz / s.

[0139] Through In the mapping table of Table 2, the closest frequency offset change rate is -709.2382 Hz / s, and the corresponding Doppler frequency offsets are F1 = 185.458 kHz and F2 = -185.458 kHz respectively. Select the Doppler frequency offset F1 = 185.458 kHz that is closest to the frequency offset estimated value = 193954.392 Hz of the downlink signal as the final first Doppler frequency offset. Based on this, the crystal oscillator error of the satellite communication system is calculated as:

[0140] . Assume that Scenario 1 (i.e., ) is the real scenario, and Scenario 2 (i.e., ) is the scenario actually measured due to the terminal positioning error. Therefore, the estimation error of the crystal oscillator error introduced by the terminal positioning error is:

[0141] .

[0142] According to the above experiments, when the change in the overhead elevation angle of the terminal position due to the terminal positioning error is within 5°, the difference between the estimated crystal oscillator errors (i.e., the estimation error ) is within 1 KHz. Even considering the time delay (usually on the order of dozens of Hz) in the carrier frequency offset estimation of the downlink signal, it is far lower than the tolerance threshold of the satellite side for the frequency deviation of the uplink signal. Therefore, the solution of this application is at least effective within the range of 5° estimation deviation of the overhead elevation angle.

[0143] On the other hand, based on the above phenomenon, in some preferred embodiments, for each overhead elevation angle corresponding in the pre-constructed mapping table, the maximum angular difference between adjacent overhead elevation angles should be adapted to the frequency offset range tolerable by the satellite side and should not exceed this tolerance range. For example, for a low-orbit satellite communication system with a frequency offset tolerance range on the order of ten KHz, the angular difference between adjacent overhead elevation angles in the pre-constructed mapping table is set at about 5°.

[0144] S4: Calculate the crystal oscillator error based on the carrier frequency offset estimated from the downlink signal and the first Doppler frequency offset.

[0145] Since in the previous embodiments, the one closest to the carrier frequency offset of the first downlink signal listened to among all the matched Doppler frequency offsets is taken as the first Doppler frequency offset as an example, in this step, subtract the first Doppler frequency offset estimated in step S3 from the carrier frequency offset of the first downlink signal listened to to obtain the crystal oscillator error of the satellite communication system:

[0146] (15).

[0147] As an alternative embodiment, the crystal oscillator error estimation method provided in this application further includes:

[0148] S5: Monitor the downlink signal in multiple rounds and calculate the crystal oscillator error for each round, that is, repeat the above steps S1 - S4 multiple times, and a crystal oscillator error will be calculated for each repetition. The average value of the crystal oscillator errors calculated in multiple rounds is used as the finally estimated crystal oscillator error. This can further improve the accuracy of estimating the crystal oscillator error of the satellite communication system.

[0149] Assume that the crystal oscillator errors calculated in each round of the loop are respectively , m represents the total number of loops, represents the crystal oscillator error calculated in the k-th round of the loop. Then the finally evaluated crystal oscillator error is:

[0150] (16).

[0151] The above embodiments introduce the crystal oscillator error estimation method provided in this application. On this basis, this application also provides an uplink synchronization method.

[0152] As Figure 6 shown, the uplink synchronization method provided in this application includes the following steps:

[0153] Step1: Monitor the downlink signal. This step is the same as step S1 in the previous embodiment, and this is for describing the integrity of the above synchronization method.

[0154] Step2: Estimate the crystal oscillator error using the crystal oscillator error estimation method of the above embodiment .

[0155] Step3: Perform frequency offset pre-compensation on the uplink signal based on the estimated crystal oscillator error .

[0156] As known from the prior art introduced above, method one only considers the compensation for Doppler frequency offset, while method two, although considering the crystal oscillator error during frequency offset pre-compensation, directly pre-compensates the uplink signal according to the frequency offset estimated value in the manner of , and this method will introduce a new frequency offset .

[0157] In some alternative embodiments of this application, a pre-compensation method that takes into account both the crystal oscillator error and does not introduce a new frequency offset during frequency offset pre-compensation is provided, that is, the above step Step3 includes:

[0158] Step 31: Based on the estimated crystal oscillator error and the carrier frequency offset estimated for the downlink signal, calculate the estimated value of the Doppler frequency offset of the downlink signal.

[0159] As mentioned before, the carrier frequency offset estimated for the downlink signal includes two parts: the Doppler frequency offset and the crystal oscillator error. Therefore, by subtracting the estimated crystal oscillator error from the carrier frequency offset, the estimated value of the Doppler frequency offset can be obtained. In the previous embodiment, by taking the calculation of the crystal oscillator error as an example (the calculation is the same for ), this process is expressed as:

[0160] (17).

[0161] For the implementation method that only estimates the crystal oscillator error once (such as in Equation (15)), the estimated value of the Doppler frequency offset is the first Doppler frequency offset matched from the mapping table. For the implementation method that estimates the crystal oscillator error multiple times and then takes the average as the final estimated crystal oscillator error (such as in Equation (16)), the estimated value of the Doppler frequency offset needs to be calculated by subtracting the estimated crystal oscillator error from the carrier frequency offset.

[0162] Step 32: Perform frequency offset pre-compensation on the uplink signal by subtracting the estimated value of the Doppler frequency offset and adding the estimated crystal oscillator error.

[0163] The compensation value for the frequency offset pre-compensation of the uplink signal in this step is , as Figure 7 shown. In this way, after the frequency offset pre-compensation, theoretically no other frequency offsets will be introduced, and the estimated value of the frequency offset of the uplink signal received by the satellite side after the frequency offset pre-compensation is expected to be 0. In fact, the compensated uplink signal only carries the frequency offset caused by the errors introduced during terminal positioning, carrier frequency offset estimation, and mapping table construction. The errors introduced by terminal positioning and carrier frequency offset estimation have been proven to be much lower than the deviation range that the satellite side closed-loop frequency synchronization mechanism can tolerate. The error introduced during mapping table construction can be minimized by increasing the granularity of the mapping table (such as reducing the step size) to reduce the error caused by matching as much as possible. This factor is highly controllable and can be effectively reduced or even avoided under a certain mapping table granularity, and this factor does not affect the effectiveness of the solution of this application. As Figure 8 shown, taking the estimation error caused by the terminal positioning error, which is the most serious among the above three factors, as an example, the compensation value of the frequency offset pre-compensation of the uplink signal by the terminal side is at this time, and the estimated value of the frequency offset of the uplink signal estimated by the satellite side after the frequency offset pre-compensation There is only this estimation error .

[0164] Based on the concept of this application, an oscillator error estimation device is also provided in the embodiments of this application. As Figure 9 shown, the device includes:

[0165] A first processing module, configured to: monitor the downlink signal.

[0166] A second processing module, configured to: estimate the carrier frequency offset of the downlink signal and calculate the first frequency offset change rate of the downlink signal.

[0167] A third processing module, configured to: obtain a first Doppler frequency offset corresponding to the first frequency offset change rate.

[0168] A fourth processing module, configured to: calculate the oscillator error based on the estimated carrier frequency offset of the downlink signal and the first Doppler frequency offset.

[0169] In addition, a fifth processing module can also be configured in the oscillator error estimation device proposed in this application to improve the accuracy of oscillator error estimation.

[0170] The fifth processing module is configured to: control the first to fourth processing modules to work in multiple rounds. Each time a cycle is completed, the fourth processing module will obtain an oscillator error. In addition, the mean value of the oscillator errors output by the fourth processing module in multiple rounds is also calculated as the finally estimated oscillator error.

[0171] In a specific embodiment, the specific configured data of the above first to fifth processing modules can respectively refer to steps S1 to S5 in the embodiment of the oscillator error estimation method described above. For example, the third processing module is configured or connected to a storage medium storing a mapping table (i.e., a pre-built mapping relationship between the Doppler frequency offset and the frequency offset change rate).

[0172] As another feasible method, in this application, another oscillator error estimation device is provided. The device includes a first processor and a first storage medium. The first storage medium stores a computer program, and the first processor executes the computer program to run the oscillator error estimation method of the above embodiment.

[0173] This application also configures the oscillator error estimation device of the above embodiment into a satellite terminal, obtaining a satellite terminal that can evaluate the oscillator error of a satellite communication system. As Figure 10 shown.

[0174] In addition, the satellite terminal designed in this application also performs frequency offset pre-compensation on the uplink signal based on the estimated oscillator error. In some optional implementation manners, the satellite terminal further includes:

[0175] The sixth processing module is configured to perform frequency offset pre - compensation on the uplink signal based on the estimated crystal oscillator error.

[0176] The frequency offset pre - compensation performed by the sixth processing module is the same as the principle of the frequency offset pre - compensation in the foregoing embodiment of the uplink synchronization method. Specifically, in some feasible embodiments, the sixth processing module performs frequency offset pre - compensation on the uplink signal through the following configuration:

[0177] Calculate the Doppler frequency offset estimated value of the downlink signal based on the estimated crystal oscillator error and the carrier frequency offset estimated for the downlink signal; and perform frequency offset pre - compensation on the uplink signal by subtracting the Doppler frequency offset estimated value and adding the estimated crystal oscillator error.

[0178] In some other feasible embodiments, the present application further provides another uplink synchronization device, which includes a second processor and a second storage medium. The second storage medium stores a computer program, and the second processor executes the computer program to run the uplink synchronization method of the foregoing embodiment.

[0179] As an optional embodiment, in the present application, the structural relationship between the processor and the storage medium is as Figure 11 shown. The processor is communicatively connected to a communication port. By executing the computer program in the storage medium, the corresponding device can execute the corresponding method through the communication interface. Figure 11 The structure is described in a way that the processor, the storage medium, and the communication interface are connected by a bus. The bus is represented by a thick line in Figure 11 The connection manners between other components are only for illustrative purposes and are not limited thereto. The bus can be divided into an address bus, a data bus, a control bus, etc. For the sake of convenience of representation, Figure 11 only a thick line is used to represent it in

[0180] However, it does not mean that there is only one bus or one type of bus. It should be understood that the processor mentioned in the embodiments of the present application can be implemented by hardware or by software. When implemented by hardware, the processor can be a logic circuit, an integrated circuit, etc. When implemented by software, the processor can be a general - purpose processor that realizes it by reading the software code stored in the storage medium.

[0181] Exemplarily, the processor can be a Central Processing Unit (CPU), or can also be other general-purpose processors, Digital Signal Processors (DSPs), Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor can be a microprocessor or the processor can also be any conventional processor, etc.

[0182] It should be understood that the storage medium mentioned in the embodiments of this application can be a volatile storage medium or a non-volatile storage medium, or can include both volatile and non-volatile storage media. Among them, the non-volatile storage medium can be a Read-Only Memory (ROM), Programmable ROM (PROM), Erasable PROM (EPROM), Electrically EPROM (EEPROM), or flash memory. The volatile storage medium can be a Random Access Memory (RAM), which is used as an external cache. By way of example but not limitation, many forms of RAM are available, such as Static RAM (SRAM), Dynamic RAM (DRAM), Synchronous DRAM (SDRAM), Double Data Rate SDRAM (DDR SDRAM), Enhanced SDRAM (ESDRAM), Synchlink DRAM (SLDRAM), and Direct Rambus RAM (DR RAM).

[0183] It should be noted that when the processor is a general-purpose processor, DSP, ASIC, FPGA, or other programmable logic device, discrete gate or transistor logic device, discrete hardware component, the storage medium (storage module) can be integrated in the processor.

[0184] It should be noted that the storage media described herein are intended to include, but are not limited to, these and any other suitable types of storage media.

[0185] As another possible product form, an embodiment of the present application further provides a computer-readable storage medium storing computer program instructions, which, when executed by a processor or the like, cause a computer to execute any of the method steps in the above method examples.

[0186] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-readable storage media (including but not limited to disk memories, CD-ROMs, optical memories, etc.) containing computer-usable program code.

[0187] The present invention is not limited to the foregoing specific embodiments. The present invention extends to any new feature or any new combination disclosed in this specification, as well as any new combination of the steps of any new method or process disclosed.

Claims

1. A crystal oscillator error estimation method, characterized in that Including: Listening to the downlink signal; Estimating the carrier frequency offset of the downlink signal and calculating the first frequency offset change rate of the downlink signal; Obtaining a first Doppler frequency offset corresponding to the first frequency offset change rate, including: based on a pre-constructed mapping relationship between the Doppler frequency offset and the frequency offset change rate, matching the corresponding first Doppler frequency offset from the first frequency offset change rate; Calculating the crystal oscillator error based on the carrier frequency offset estimated for the downlink signal and the first Doppler frequency offset.

2. The crystal oscillator error estimation method according to claim 1, characterized in that Calculating the first frequency offset change rate of the downlink signal includes: Calculating the first frequency offset change rate of the downlink signal according to the carrier frequency offsets estimated for at least two continuously listened downlink signals.

3. The crystal oscillator error estimation method according to claim 1, wherein The mapping relationship includes the mapping relationship between the Doppler frequency offset and the frequency offset change rate when the satellite is at different over-the-top elevation angles, and the over-the-top elevation angle is the elevation angle relative to the satellite at the over-the-top moment.

4. The crystal oscillator error estimation method according to claim 1, characterized in that The mapping relationship is constructed from the Doppler frequency offsets estimated at multiple moments within the visible range of the satellite and the corresponding calculated frequency offset change rates.

5. The crystal oscillator error estimation method according to claim 4, characterized in that, By simulating the states of the satellite at multiple moments within the visible range, estimating the Doppler frequency offsets of the satellite at the multiple moments and calculating the corresponding frequency offset change rates.

6. The crystal oscillator error estimation method according to claim 5, wherein, By simulating the satellite trajectory and based on a set step size, simulating the states of the satellite at multiple moments within the visible range.

7. The crystal oscillator error estimation method according to claim 6, wherein The duration corresponding to the set step size does not exceed the duration between two continuously listened downlink signals.

8. The crystal oscillator error estimation method according to claim 6, characterized in that, The set step size is the step size of the elevation angle within the satellite orbital plane, or the time step size, or the step size of the satellite motion arc length.

9. The crystal oscillator error estimation method according to any one of claims 1, 3-8, characterized in that, The matching of the corresponding first Doppler frequency offset from the first frequency offset change rate based on the pre-constructed mapping relationship between the Doppler frequency offset and the frequency offset change rate includes: When more than one Doppler frequency offset is matched from the mapping relationship by the first frequency offset change rate, using the one closest to the carrier frequency offset among all the matched Doppler frequency offsets as the first Doppler frequency offset.

10. The crystal oscillator error estimation method according to claim 1, characterized in that The method listens to the downlink signal in multiple rounds and calculates the crystal oscillator error for each round, and uses the mean value of the crystal oscillator errors calculated in multiple rounds as the finally estimated crystal oscillator error.

11. A crystal oscillator error estimation device, characterized in that, Including: A first processing module configured to: listen to the downlink signal; A second processing module configured to: estimate the carrier frequency offset of the downlink signal and calculate the first frequency offset change rate of the downlink signal; A third processing module configured to: obtain a first Doppler frequency offset corresponding to the first frequency offset change rate, including: based on a pre-constructed mapping relationship between the Doppler frequency offset and the frequency offset change rate, matching the corresponding first Doppler frequency offset from the first frequency offset change rate; A fourth processing module configured to: calculate the crystal oscillator error based on the carrier frequency offset estimated for the downlink signal and the first Doppler frequency offset.

12. A crystal oscillator error estimation device, comprising a first processor and a first storage medium, the first storage medium storing a computer program, characterized in that, The first processor executes the computer program to run the crystal oscillator error estimation method according to any one of claims 1-10.

13. A satellite terminal, characterized in that, The satellite terminal is configured with the crystal oscillator error estimation device according to claim 11 or 12.

14. The satellite terminal according to claim 13, wherein, Further including: A sixth processing module configured to: perform frequency offset pre-compensation on the uplink signal based on the estimated crystal oscillator error.

15. The satellite terminal according to claim 14, wherein The sixth processing module performs frequency offset pre-compensation on the uplink signal through the following configuration: Calculate the estimated value of the Doppler frequency offset of the downlink signal based on the estimated crystal oscillator error and the estimated carrier frequency offset of the downlink signal; And Perform frequency offset pre-compensation on the uplink signal by subtracting the estimated value of the Doppler frequency offset and adding the estimated crystal oscillator error.

16. An uplink synchronization method, characterized in that, Comprising: Monitor the downlink signal; Estimate the crystal oscillator error by using the crystal oscillator error estimation method according to any one of claims 1-10; Perform frequency offset pre-compensation on the uplink signal based on the estimated crystal oscillator error.

17. The uplink synchronization method according to claim 16, characterized in that, The performing frequency offset pre-compensation on the uplink signal based on the estimated crystal oscillator error includes: Calculate the estimated value of the Doppler frequency offset of the downlink signal based on the estimated crystal oscillator error and the estimated carrier frequency offset of the downlink signal; Perform frequency offset pre-compensation on the uplink signal by subtracting the estimated value of the Doppler frequency offset and adding the estimated crystal oscillator error.

18. An uplink synchronization device, comprising a second processor and a second storage medium, the second storage medium storing a computer program, characterized in that, The second processor executes the computer program to run the uplink synchronization method according to claim 16 or 17.

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