A data link terminal space-ground fusion method

Abstract

The application discloses a data link terminal space-ground fusion method and belongs to the technical field of satellite communication. The method comprises the following steps: selecting an equivalent position of a data link satellite-borne terminal as a data link service area Doppler center position; acquiring orbit parameters according to resolved ephemeris and calculating a satellite earth-fixed coordinate system position coordinate, and then calculating a position coordinate of a geometric center of the data link service area; calculating the data link service area Doppler center position according to the satellite earth-fixed coordinate system position coordinate and the position coordinate of the geometric center of the data link service area; calculating a time delay value and a Doppler value at the Doppler center position according to the data link service area Doppler center position and the satellite earth-fixed coordinate system position coordinate; and pre-compensating the Doppler value on a data link terminal signal frequency based on the time delay value to correct the time delay. The application solves the problem that data link terminals are incompatible due to long time delay and high Doppler frequency shift in a high dynamic environment of satellite-ground communication in the prior art.

Description

TECHNICAL FIELD

[0001] The application relates to a data link terminal space-ground integration method and belongs to the technical field of satellite communication. BACKGROUND

[0002] With the rapid development of science and technology, a low-orbit satellite communication system occupies an increasingly important position in the modern communication field. The low-orbit satellite communication has the advantages of wide coverage, low transmission delay and small path loss, and can break through the geographical condition limitation to realize seamless communication coverage in the global range. In the military and defense field, the low-orbit satellite communication system is the key infrastructure for guaranteeing the long-range operation command, information transmission and stable operation of the military communication network, and plays an irreplaceable role in improving the operation efficiency, strategic deployment capability and emergency response speed of the army; in the civil field, the low-orbit satellite communication is widely applied to the communication in remote areas, aviation and navigation communication, emergency rescue communication and Internet of Things data transmission, greatly promotes the interconnection of global information, drives the development and progress of social economy and improves the quality of human life and production efficiency, so the importance of the low-orbit satellite communication scene is self-evident.

[0003] Carrying the data link terminal to the low-orbit satellite for network relay can expand the communication distance of the data link, expand the guarantee range of the tactical information and increase the situation awareness distance of the data link. The satellite data link has the characteristics of wide coverage, rapid deployment, large communication capacity and stable transmission channel, and has the advantage that other data links cannot match in the broadcast distribution of information and battlefield situation due to the unique broadcast characteristics of the satellite. The satellite data link can connect the geographically dispersed troops, various detectors and weapon systems together, realize real-time grasp of the battlefield situation, shorten the decision-making time, improve the command speed and cooperative combat capability, so as to implement rapid, accurate and continuous attack on the enemy, and is an important guarantee for effectively implementing the cross-sea and large-range joint operation. The low-orbit satellite has the characteristics of long communication distance and fast moving speed relative to the ground platform, how to adaptively transplant the data link technology system into the space-ground communication and solve the long time delay and high Doppler frequency shift caused by the high dynamic environment in the space-ground transmission becomes a problem to be solved. SUMMARY

[0004] The application aims to provide a data link terminal space-ground integration method, which pre-compensates the data link terminal sending signal frequency by calculating the Doppler value at the Doppler center, so as to solve the problem of incompatibility of the data link terminal caused by the long time delay and high Doppler frequency shift in the high dynamic environment of the space-ground communication in the prior art.

[0005] To solve the above technical problems, the application is implemented by using the following technical scheme:

[0006] The application provides a data link terminal space-ground integration method, which comprises the following steps:

[0007] selecting an equivalent position of a data link space terminal as a Doppler center position of a data link service area;

[0008] acquiring ephemeris data, solving orbit parameters, and calculating a satellite position coordinate in an earth-fixed coordinate system according to the orbit parameters;

[0009] calculating a position coordinate of a geometric center of the data link service area according to the satellite position coordinate in the earth-fixed coordinate system;

[0010] calculating the Doppler center position of the data link service area according to the satellite position coordinate in the earth-fixed coordinate system and the position coordinate of the geometric center of the data link service area;

[0011] calculating a time delay value and a Doppler value at the Doppler center position according to the Doppler center position of the data link service area and the satellite position coordinate in the earth-fixed coordinate system;

[0012] correcting the time delay based on the time delay value, sending a message in advance using the time delay value at the Doppler center position, so that the message is at a typical time of a time slot when reaching a ground node, and receiving the message in delay using the time delay value at the Doppler center position, so that the message is at the typical time of the time slot when reaching a satellite node;

[0013] pre-compensating the Doppler value on a signal frequency of the data link terminal.

[0014] Further, the equivalent position of the data link space terminal is selected as the Doppler center position of the data link service area, and under the coverage of a low-orbit satellite, the Doppler center of the data link service area is a position where an average value of a minimum Doppler value and a maximum Doppler value of the data link service area terminal is located.

[0015] Further, the orbit parameters include an orbit inclination, an ascending node right ascension, an argument of perigee, a mean anomaly, an eccentricity, and an average motion.

[0016] Further, the satellite position coordinate in the earth-fixed coordinate system is calculated according to the orbit parameters, including:

[0017] calculating the mean anomaly according to the average motion;

[0018] solving a perigee according to a calculation formula of the mean anomaly;

[0019] calculating a true anomaly according to the perigee and the eccentricity;

[0020] calculating an orbit radius according to an orbit semi-major axis, the true anomaly, and the eccentricity;

[0021] calculating a position of the satellite in an orbit plane according to the orbit radius and the true anomaly;

[0022] According to the position coordinates of the satellite in the orbit plane and the orbit parameters, the coordinates of the satellite in the orbit plane are converted to the Earth-Centered Inertial coordinate system (ECI) to obtain the position coordinates of the satellite in the Earth-Centered Inertial coordinate system (ECI);

[0023] According to the angular velocity of the Earth rotation and the definition of the Earth-fixed coordinate system, the Earth-Centered Inertial coordinate system (ECI) and the Earth-fixed coordinate system are coordinate-transformed to obtain the satellite Earth-fixed coordinate system position coordinates.

[0024] Further, the position coordinates of the geometric center of the data link service area are the projection points of the ground center points covered by the beam below the satellite orbit, i.e. the ground meridian points of the satellite, wherein the position coordinates of the geometric center of the data link service area are calculated according to the satellite Earth-fixed coordinate system position coordinates, including:

[0025] According to the position coordinates of the satellite in the satellite Earth-fixed coordinate system and the distance between the satellite and the Earth center, the longitude and latitude of the meridian point are calculated;

[0026] According to the longitude and latitude of the meridian point and the Earth radius, the Earth-fixed coordinate of the meridian point is calculated, i.e. the position coordinates of the geometric center of the data link service area.

[0027] Further, the position of the Doppler center of the data link service area is calculated according to the satellite Earth-fixed coordinate system position coordinates and the position coordinates of the geometric center of the data link service area, wherein,

[0028] The center position of the satellite in the satellite Earth-fixed coordinate system position coordinates and the position coordinates of the geometric center of the data link service area is usually located between the beam center point and the beam edge point, i.e. the Doppler center position of the data link service area.

[0029] Further, the abscissa, ordinate and ordinate of the Doppler center position of the data link service area are respectively represented as:

[0030] ;

[0031] In the formula, 、 and represent the abscissa, ordinate and ordinate of the Doppler center position coordinates of the data link service area, represent the Doppler center of the data link service area.

[0032] Further, the time delay value and the Doppler value at the Doppler center are calculated according to the Doppler center position of the data link service area and the satellite Earth-fixed coordinate system position coordinates, including:

[0033] According to the Doppler center position of the data link service area and the position coordinates of the satellite in the satellite earth fixed coordinate system, the vector of the satellite and the Doppler center position of the data link service area and the geometric distance of the satellite and the Doppler center position of the data link service area are calculated;

[0034] According to the vector of the satellite and the Doppler center position of the data link service area and the radial velocity of the satellite, the radial velocity, i.e. the velocity component in the projection direction, is calculated;

[0035] According to the geometric distance of the satellite and the Doppler center position of the data link service area and the speed of light, the time delay value at the Doppler center is calculated;

[0036] According to the radial velocity, the speed of light and the signal frequency, the Doppler value at the Doppler center is calculated.

[0037] Further, the time delay is corrected based on the time delay value, the message is sent in advance at the Doppler center by using the time delay value, so that the message reaches the ground node at the typical time of the time slot, and the message is received in delay by using the time delay value at the Doppler center, so that the message reaches the satellite node at the typical time of the time slot, comprising:

[0038] For the uplink, the satellite receives the time slot start time of the ground data link terminal transmission time slot, and the ground transmission time slot is adaptively delayed ; for the downlink, the satellite data link terminal transmission time slot start time is adaptively advanced , wherein, The time delay value at the Doppler center is represented.

[0039] Further, the Doppler value is pre-compensated on the data link terminal transmission signal frequency, which is represented as:

[0040] ;

[0041] In the formula, The compensated data link terminal transmission signal frequency is represented, The data link terminal transmission signal frequency before compensation is represented, The Doppler value at the Doppler center is represented.

[0042] Compared with the prior art, the beneficial effects achieved by the present application are:

[0043] 1、 The present application can accurately determine the geometric center position of the satellite and the data link service area by selecting the equivalent position of the data link satellite terminal as the Doppler center position of the data link service area, and based on ephemeris calculation and orbit parameter calculation, and then accurately calculate the Doppler center position and the corresponding time delay value and Doppler value, so as to ensure the time synchronization and frequency accuracy of data transmission between the earth and the sky.

[0044] 2、 Meanwhile, the application also uses the time delay value at the Doppler center to make the correction strategy of early sending and late receiving messages, effectively ensures that the messages are at the typical time of time slot when reaching the ground node and satellite node, thereby significantly reducing the data transmission error caused by time delay and Doppler effect, and improving the real-time performance and reliability of data transmission.

[0045] 3、 In addition, the application pre-compensates the Doppler value on the signal frequency of the data link terminal, further compensates the frequency offset caused by relative motion, and ensures the stability and quality of signal transmission. The application significantly improves the overall performance and communication efficiency of the space-ground data link system, and solves the problem of incompatibility of the data link terminal caused by long time delay and high Doppler frequency shift in the high dynamic environment of satellite-ground communication in the prior art. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 is a flowchart of a data link terminal space-ground fusion method provided by an embodiment of the application;

[0047] Figure 2 is a flowchart of time delay correction provided by an embodiment of the application;

[0048] Figure 3 is a time delay diagram before compensation of a satellite data link in the case of an elevation angle of 20° provided by an embodiment of the application;

[0049] Figure 4 is a time delay diagram before compensation of a satellite data link in the case of an elevation angle of 40° provided by an embodiment of the application;

[0050] Figure 5 is a time delay diagram before compensation of a satellite data link in the case of an elevation angle of 60° provided by an embodiment of the application;

[0051] Figure 6 is a time delay diagram after compensation of a satellite data link in the case of an elevation angle of 20° provided by an embodiment of the application;

[0052] Figure 7 is a time delay diagram after compensation of a satellite data link in the case of an elevation angle of 40° provided by an embodiment of the application;

[0053] Figure 8 is a time delay diagram after compensation of a satellite data link in the case of an elevation angle of 60° provided by an embodiment of the application;

[0054] Figure 9 is a Doppler frequency shift diagram before compensation of a satellite data link in the case of an elevation angle of 20° provided by an embodiment of the application;

[0055] Figure 10is a Doppler frequency shift schematic diagram before compensation of a satellite data link in the case of an elevation angle of 40° provided by an embodiment of the present application;

[0056] Figure 11 is a Doppler frequency shift schematic diagram before compensation of a satellite data link in the case of an elevation angle of 60° provided by an embodiment of the present application;

[0057] Figure 12 is a Doppler frequency shift schematic diagram after compensation of a satellite data link in the case of an elevation angle of 20° provided by an embodiment of the present application;

[0058] Figure 13 is a Doppler frequency shift schematic diagram after compensation of a satellite data link in the case of an elevation angle of 40° provided by an embodiment of the present application;

[0059] Figure 14 is a Doppler frequency shift schematic diagram after compensation of a satellite data link in the case of an elevation angle of 60° provided by an embodiment of the present application. DETAILED DESCRIPTION

[0060] The technical solutions of the present application will be described in detail below with the drawings and specific embodiments. It should be understood that the specific features in the embodiments and the specific embodiments of the present application are detailed descriptions of the technical solutions of the present application, and are not limitations of the technical solutions of the present application. In the case of no conflict, the technical features in the embodiments and the specific embodiments can be combined with each other.

[0061] The term "and / or", only describes the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which means that there are three cases of A alone, A and B together, and B alone. In addition, the character " / ", generally represents that the associated objects before and after are in an "or" relationship.

[0062] Embodiment 1

[0063] As shown in the figure, the present embodiment introduces a data link terminal space-ground fusion method, which comprises: Figure 1

[0064] Step 1: Select the equivalent position of the data link space terminal as the Doppler center position of the data link service area.

[0065] Doppler effect is a common phenomenon in wireless communication. Due to the relative movement between the sending end and the receiving end, the frequency of the received signal will change. The present application selects the equivalent position of the space terminal as the Doppler center, in order to simplify the subsequent Doppler effect calculation and compensation. A reference point is provided for the subsequent steps, which is convenient for unified processing of Doppler effect.

[0066] ​Step two: obtain ephemeris data, solve the orbit parameters, and calculate the satellite position coordinates in the earth-fixed coordinate system according to the orbit parameters.

[0067] The ephemeris is data describing the satellite motion trajectory, and the orbit parameters of the satellite can be obtained by solving the ephemeris. The present application can calculate the position coordinates of the satellite in the earth-fixed coordinate system by using the orbit parameters.

[0068] Step three: calculate the position coordinates of the geometric center of the data link service area according to the satellite position coordinates in the earth-fixed coordinate system.

[0069] The data link service area refers to the area covered by the satellite and the ground node communication. The present application can further simplify the calculation of the Doppler effect by calculating the geometric center position of the service area, and determine the center point of the service area, which provides a basis for the subsequent calculation of the Doppler center position.

[0070] Step four: calculate the Doppler center position of the data link service area according to the satellite position coordinates in the earth-fixed coordinate system and the position coordinates of the geometric center of the data link service area.

[0071] The present application can more accurately determine the Doppler center position by combining the satellite position and the geometric center position of the service area, which provides a basis for the subsequent compensation of the Doppler effect.

[0072] Step five: calculate the time delay value and the Doppler value at the Doppler center according to the Doppler center position of the data link service area and the satellite position coordinates in the earth-fixed coordinate system.

[0073] The time delay and the Doppler value are key parameters in wireless communication, which directly affect the communication quality. The present application compensates the signal frequency sent by the data link terminal by calculating the time delay and the Doppler value at the Doppler center.

[0074] Step six: correct the time delay based on the time delay value, send the message in advance using the time delay value at the Doppler center, so that the message arrives at the ground node at the typical time of the time slot, and receive the message in lag using the time delay value at the Doppler center, so that the message arrives at the satellite node at the typical time of the time slot.

[0075] The time delay correction is to compensate for the time delay difference caused by the change of the propagation distance and the speed. The present application can ensure that the message arrives in a specific time slot by sending / receiving the message in advance or lag, thereby improving the synchronization and reliability of the communication, realizing the accurate correction of the time delay, and ensuring the synchronous arrival of the message.

[0076] Step seven: pre-compensate the Doppler value on the signal frequency sent by the data link terminal.

[0077] The Doppler compensation is to eliminate the frequency offset caused by the Doppler effect. The present application can ensure that the signal frequency received by the receiving end is consistent with the sending end by pre-compensating the frequency of the sending signal, eliminating the influence of the Doppler effect on the signal frequency, and ensuring the accuracy and stability of the communication.

[0078] In summary, the embodiment realizes efficient and accurate data communication between the earth and the sky through accurate calculation and compensation, and provides an effective sky-ground integration method for the wireless communication field.

[0079] Embodiment 2

[0080] Based on the same inventive concept as embodiment 1, the present embodiment introduces a specific implementation step of a data link terminal sky-ground integration method, which includes:

[0081] Step 1: Selecting the equivalent position of the data link satellite terminal as the Doppler center position of the data link service area.

[0082] In some embodiments, under the coverage of the low-orbit satellite, the Doppler center of the data link service area is the position where the average of the minimum Doppler value and the maximum Doppler value of the data link service area terminal is located.

[0083] Step 2: Calculating the satellite geodetic coordinate according to the orbit parameters.

[0084] In some embodiments, the orbit parameters include orbit inclination, ascending node right ascension, perigee amplitude, mean anomaly, eccentricity and mean motion.

[0085] In the present embodiment, calculating the satellite geodetic coordinate according to the orbit parameters includes:

[0086] According to the mean motion, the mean anomaly is calculated, and the calculation formula of the mean anomaly is:

[0087] ;

[0088] In the formula, n represents the mean motion, which is the average angular velocity of the satellite, t represents the current time, represents the reference time when the satellite passes the perigee;

[0089] According to the calculation formula of the mean anomaly, the eccentric anomaly is solved, and the calculation formula of the mean anomaly is:

[0090] ;

[0091] In the formula, represents the mean anomaly, E represents the eccentric anomaly, represents the eccentricity, represents the sine function;

[0092] The true anomaly angle is calculated based on the anomalous point and the eccentricity, wherein the formula for calculating the true anomaly angle is expressed as:

[0093] ;

[0094] In the formula, Indicates the true nearest point angle. Represents the tangent function. Represents the arctangent function;

[0095] Calculate the orbital radius based on the orbital semi-major axis, the true anomaly angle, and the eccentricity:

[0096] ;

[0097] In the formula, r represents the orbital radius, and a represents the semi-major axis of the orbit;

[0098] Based on the orbital radius and the true anomaly angle, the satellite's position in the orbital plane is calculated, where the abscissa, ordinate, and ordinate of the satellite's position in the orbital plane are expressed as follows:

[0099] ;

[0100] ;

[0101] ;

[0102] In the formula, The x-coordinate representing the satellite's position in the orbital plane. The ordinate representing the satellite's position in the orbital plane. The vertical coordinates representing the satellite's position in the orbital plane. Represents the cosine function. Represents the sine function;

[0103] Based on the satellite's position coordinates in the orbital plane and the orbital parameters, the satellite's coordinates in the orbital plane are transformed to the geocentric inertial coordinate system (ECI) to obtain the satellite's position coordinates in the ECI. The abscissa, ordinate, and ordinate of the satellite's position coordinates in the ECI are expressed as follows:

[0104] ;

[0105] In the formula, The x-coordinate represents the satellite's position coordinates in the geocentric inertial coordinate system (ECI). The ordinate represents the satellite's position coordinates in the geocentric inertial coordinate system (ECI). a vertical coordinate representing a position coordinate of the satellite in an earth-centered inertial coordinate system ECI represents a right ascension of the ascending node, represents an argument of perigee, represents an orbital inclination;

[0106] According to the angular velocity of the earth rotation and the definition of the earth-fixed coordinate system, the earth-centered inertial coordinate system ECI and the earth-fixed coordinate system are coordinate-transformed to obtain a satellite earth-fixed coordinate system position coordinate, wherein the horizontal coordinate, the longitudinal coordinate and the vertical coordinate of the position of the satellite in the earth-fixed coordinate system are respectively represented as:

[0107] ;

[0108] In the formula, represents a horizontal coordinate of the position of the satellite in the earth-fixed coordinate system, represents a longitudinal coordinate of the position of the satellite in the earth-fixed coordinate system, represents a vertical coordinate of the position of the satellite in the earth-fixed coordinate system, is a rotation angle of the earth G relative to a fixed celestial body, which is obtained by Greenwich Mean Time GMT or Universal Time UT.

[0109] Step 3: According to the satellite earth-fixed coordinate system position coordinate, the position coordinate of the geometric center of the data link service area is calculated.

[0110] In some embodiments, the position coordinate of the geometric center of the data link service area is a projection point of a beam coverage ground center point located below the satellite orbit, i.e. a ground meridian point of the satellite.

[0111] In this embodiment, according to the satellite earth-fixed coordinate system position coordinate, the position coordinate of the geometric center of the data link service area is calculated, including:

[0112] According to the position coordinate of the satellite in the satellite earth-fixed coordinate system and the distance between the satellite and the earth center, the longitude and latitude of the meridian point are calculated.

[0113] In this embodiment, the longitude and latitude of the meridian point are respectively represented as:

[0114] ;

[0115] ;

[0116] In the formula, represents the longitude of the meridian point , represents the position coordinate of the satellite in the earth-fixed coordinate system, represents the longitudinal coordinate of the position coordinate of the satellite the horizontal coordinate of the position coordinate in the satellite geo-fixed coordinate system, denotes the meridian point the latitude of the meridian point, denotes the inverse sine function, denotes the satellite the vertical coordinate of the position coordinate in the satellite geo-fixed coordinate system, denotes the satellite the distance from the center of the earth, wherein, , denotes the radius of the earth, the orbital height of the satellite ;

[0117] According to the longitude and latitude of the meridian point and the radius of the earth, the geo-fixed coordinates of the meridian point, i.e. the position coordinates of the geometric center of the data link service area, are calculated.

[0118] In the present embodiment, the horizontal coordinate, the longitudinal coordinate and the vertical coordinate of the geo-fixed coordinates of the meridian point are respectively denoted as:

[0119]

[0120]

[0121]

[0122] In the formula, , and respectively denote the horizontal coordinate, the longitudinal coordinate and the vertical coordinate of the geo-fixed coordinates of the meridian point .

[0123] Step 4: According to the position coordinates in the satellite geo-fixed coordinate system and the position coordinates of the geometric center of the data link service area, the position of the Doppler center of the data link service area is calculated.

[0124] In some embodiments, the position of the satellite at the center of the position coordinates in the satellite geo-fixed coordinate system and the position coordinates of the geometric center of the data link service area is usually located at the middle position between the beam center point and the beam edge point, i.e. the position of the Doppler center of the data link service area.

[0125] In the present embodiment, the horizontal coordinate, the longitudinal coordinate and the vertical coordinate of the position of the Doppler center of the data link service area are respectively denoted as:

[0126] ;

[0127] In the formula, , and respectively denote the horizontal coordinate, the longitudinal coordinate and the vertical coordinate of the position coordinates of the Doppler center of the data link service area, representing the Doppler center of the data link service area.

[0128] Step 5: calculating the time delay value and Doppler value at the Doppler center according to the Doppler center position of the data link service area and the position coordinate of the satellite in the satellite Earth-fixed coordinate system.

[0129] In the embodiment, the time delay value and Doppler value at the Doppler center are calculated according to the Doppler center position of the data link service area and the position coordinate of the satellite in the satellite Earth-fixed coordinate system, including:

[0130] calculating the vector of the satellite and the Doppler center position of the data link service area Doppler center and the geometric distance of the satellite and the Doppler center position of the data link service area Doppler center according to the Doppler center position of the data link service area Doppler center and the position coordinate of the satellite in the satellite Earth-fixed coordinate system.

[0131] The vector of the satellite and the Doppler center position of the data link service area Doppler center is represented as:

[0132] ;

[0133] In the formula, the vector of the satellite and the Doppler center position of the data link service area Doppler center is represented as;

[0134] The geometric distance of the satellite and the Doppler center position of the data link service area Doppler center is represented as:

[0135] ;

[0136] In the formula, the geometric distance of the satellite and the Doppler center position of the data link service area Doppler center is represented as;

[0137] calculating the radial velocity, i.e. the velocity component in the projection direction, according to the vector of the satellite and the Doppler center position of the data link service area Doppler center and the radial velocity of the satellite, the radial velocity is represented as:

[0138] ;

[0139] In the formula, the radial velocity is represented as, the vector of the satellite and the Doppler center position of the data link service area Doppler center is represented as, the radial velocity of the satellite is represented as;

[0140] calculating the time delay value at the Doppler center according to the geometric distance of the satellite and the Doppler center position of the data link service area Doppler center and the speed of light, the time delay value at the Doppler center is represented as:

[0141] ;

[0142] wherein, denotes the time delay value at the Doppler center, denotes the speed of light;

[0143] According to the radial velocity, the speed of light and the signal frequency, the Doppler value at the Doppler center is calculated, which is expressed as:

[0144]

[0145] wherein, denotes the Doppler value at the Doppler center, denotes the signal frequency, denotes the maximum Doppler shift, denotes the minimum Doppler shift, wherein, ,

[0146] Step 6: Correct the time delay based on the time delay value, send the message in advance using the time delay value at the Doppler center, so that the message is at the typical time of the time slot when it reaches the ground node, and receive the message in delay using the time delay value at the Doppler center, so that the message is at the typical time of the time slot when it reaches the satellite node.

[0147] In some embodiments, for the uplink, the satellite receives the time delay of the ground data link terminal sending time slot starting time reference ground transmission time slot adaptive delay ; for the downlink, the satellite data link terminal sends the time slot starting time reference ground transmission time slot adaptive advance , wherein, denotes the time delay value at the Doppler center, as shown in Figure 2 .

[0148] Step 7: Pre-compensate the Doppler value on the data link terminal sending signal frequency.

[0149] In this embodiment, the Doppler value is pre-compensated on the data link terminal sending signal frequency, which is expressed as:

[0150]

[0151] wherein, denotes the compensated data link terminal sending signal frequency, denotes the data link terminal sending signal frequency before compensation, denotes the Doppler value at the Doppler center.

[0152] In summary, under the condition that the on-orbit satellite orbital height is 550 km and the beam coverage service area range radius is 550 km, as Figures 3-5 ​​The figure shows the variation of propagation delay for different data link terminals with satellite elevation angle. At an elevation angle of 20°, the average propagation delay is 7.7. The minimum propagation delay is approximately 5.7 seconds. At an elevation angle of approximately 40°, the maximum propagation delay is around 8.8 ms; at an elevation angle of 40°, the average propagation delay is around 5 ms. The minimum propagation delay is approximately 2.9 seconds. The maximum propagation delay is approximately 6.1 seconds. At an elevation angle of 60°, the average propagation time delay is 3.9 seconds. The minimum propagation delay is approximately 2.3 seconds. The maximum propagation delay is around 5. Around 4.4 hours. The maximum protection period for data link time slot propagation is generally 4.4 hours. The propagation delay is approximately [value missing], therefore it cannot support normal communication with existing satellite data links. However, the propagation delay after the delay correction method described in this invention can meet the requirements, such as [value missing]. Figures 6-8 As shown, after time delay correction, the maximum propagation time delay at different elevation angles is 2.375. Up to 2.528 It fully meets the requirements of the existing data link time slot propagation protection period and can carry out normal satellite-to-ground communication.

[0153] The satellite is in orbit at an altitude of 550 km, with a beam coverage service area radius of 550 km, and a satellite speed of 7.5 km / h. Under the condition that the data link terminal signal transmission frequency is 1GHz, such as Figures 9-11 The image shows the variation of Doppler frequency shift at different data link terminals with satellite elevation angle. At an elevation angle of 20°, the mean Doppler value is 11.758. The maximum Doppler frequency shift is 23.309. The minimum Doppler frequency shift is 0.306. At a 40° elevation angle, the mean Doppler value is 9.587. The maximum Doppler frequency shift is 18.758. The minimum Doppler frequency shift is 0.08. At a 60° elevation angle, the mean Doppler value is 6.261. The maximum Doppler frequency shift is 12.102. The minimum Doppler frequency shift is 0.053. The maximum frequency offset tolerance range of existing general data link terminals is... The left and right angles can cause signal reception problems and affect signal demodulation. However, with the Doppler compensation method described in this invention, the Doppler frequency shift after compensation is less than 10° at different elevation angles. This can meet the signal reception requirements of the data link terminal. For example... Figures 12-14As shown, the compensated Doppler shift is maximum 5.144 and minimum -5.286 , which meets the existing data link terminal frequency offset tolerance and does not affect the normal reception and demodulation of signals.

[0154] In summary, in actual work, the satellite position coordinates, the position coordinates of the geometric center of the data link service area, the position coordinates of the Doppler center of the data link service area, the time delay value of the Doppler center, and the Doppler value are successfully calculated in the existing foreign low-orbit satellite scene. The present application also provides ideas and breakthroughs for the time delay compensation scheme and the Doppler shift compensation scheme. The present application successfully solves the influence of excessive time delay and high Doppler frequency offset in low-orbit satellite data link communication. The compensated time delay and Doppler can completely realize the integrated access of the existing data link terminal and the satellite terminal, which has practical significance in the data link terminal space integration technology.

[0155] Those skilled in the art will 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 usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer usable program code.

[0156] The present application is described with reference to flowcharts and / or block diagrams according to the method, device (system), and computer program product of the embodiments of the present application. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of flows and / or blocks in the flowcharts and / or block diagrams can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device produce a device that implements the functions specified in the flowcharts and / or block diagrams. Figure 1 one or more flows and / or blocks Figure 1 an apparatus that performs the functions specified in one or more flows and / or blocks.

[0157] These computer program instructions can also be stored in a computer readable storage medium that can direct the computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable storage medium produce a product including instruction apparatus, which implements the functions specified in the flowcharts and / or block diagrams. Figure 1 one or more flows and / or blocks Figure 1 an apparatus that performs the functions specified in one or more flows and / or blocks.

[0158] These computer program instructions can also be loaded into a computer or other programmable data processing devices, so that a series of operational steps are generated to realize the computer-implemented processes, and the instructions executed on the computer or other programmable devices provide a process for implementing the functions specified in the flowchart Figure 1 one flow or multiple flows and / or the functions specified in the block Figure 1 one flow or multiple flows and / or the functions specified in the block

[0159] The embodiments of the present application are described above with reference to the accompanying drawings, but the present application is not limited to the specific embodiments described above, and the specific embodiments described above are merely illustrative, but not restrictive, and those of ordinary skill in the art can make many forms under the inspiration of the present application without departing from the purpose of the present application and the scope protected by the claims, which are all within the protection of the present application.

Claims

1. A method for space-ground integration of a data link terminal, characterized in that, The method comprises the following steps: selecting an equivalent position of a data link satellite terminal as a Doppler center position of a data link service area; acquiring ephemeris data, calculating orbit parameters, and calculating a satellite position coordinate in an earth-fixed coordinate system according to the orbit parameters; calculating a position coordinate of a geometric center of the data link service area according to the satellite position coordinate in the earth-fixed coordinate system; calculating the Doppler center position of the data link service area according to the satellite position coordinate in the earth-fixed coordinate system and the position coordinate of the geometric center of the data link service area; calculating a time delay value and a Doppler value at the Doppler center position according to the Doppler center position of the data link service area and the satellite position coordinate in the earth-fixed coordinate system; correcting the time delay based on the time delay value, sending a message in advance by using the time delay value at the Doppler center position, so that the message is at a typical time of a time slot when reaching a ground node, and receiving a message in lag by using the time delay value at the Doppler center position, so that the message is at the typical time of the time slot when reaching a satellite node; pre-compensating the Doppler value on a signal frequency of the data link terminal.

2. The data link terminal sky-ground fusion method according to claim 1, characterized in that, The method selects an equivalent position of a data link satellite terminal as a Doppler center position of a data link service area, wherein, under the coverage of a low-orbit satellite, the Doppler center of the data link service area is a position where an average value of a minimum Doppler value and a maximum Doppler value of the data link service area terminal is located.

3. The data link terminal sky-ground fusion method according to claim 1, characterized in that, The orbit parameters include an orbit inclination, an ascending node right ascension, an argument of perigee, a mean anomaly, an eccentricity, and a mean motion.

4. The data link terminal sky-ground fusion method according to claim 3, characterized in that, The method comprises the following steps of calculating the satellite position coordinate in the earth-fixed coordinate system according to the orbit parameters: calculating the mean anomaly according to the mean motion; solving a true anomaly according to a calculation formula of the mean anomaly; calculating a true argument of perigee according to the true anomaly and the eccentricity; calculating an orbit radius according to a major axis of the orbit, the true argument of perigee, and the eccentricity; calculating a position of the satellite in an orbit plane according to the orbit radius and the true argument of perigee; converting the coordinate of the satellite in the orbit plane to an earth-centered inertial coordinate system (ECI) according to the position of the satellite in the orbit plane and the orbit parameters, to obtain a position coordinate of the satellite in the earth-centered inertial coordinate system (ECI); performing coordinate transformation between the earth-centered inertial coordinate system (ECI) and an earth-fixed coordinate system according to an angular velocity of the earth rotation and a definition of the earth-fixed coordinate system, to obtain the satellite position coordinate in the earth-fixed coordinate system.

5. The data link terminal sky-ground fusion method according to claim 4, characterized in that, The position coordinate of the geometric center of the data link service area is a projection point of a ground center point covered by a beam under the satellite orbit, that is, a ground meridian point of the satellite, wherein the method comprises the following steps of calculating the position coordinate of the geometric center of the data link service area according to the satellite position coordinate in the earth-fixed coordinate system: calculating a longitude and a latitude of the meridian point according to the position coordinate of the satellite in the earth-fixed coordinate system and a distance between the satellite and the center of the earth; calculating an earth-fixed coordinate of the meridian point, that is, the position coordinate of the geometric center of the data link service area, according to the longitude and the latitude of the meridian point and an earth radius.

6. The data link terminal sky-ground fusion method according to claim 5, characterized in that, The method calculates the Doppler center position of the data link service area according to the satellite position coordinate in the earth-fixed coordinate system and the position coordinate of the geometric center of the data link service area, wherein The center position of the satellite in the satellite earth fixed coordinate system position coordinate and the data link service area geometric center position coordinate is usually located in the middle position between the beam center point and the beam edge point, i.e. the data link service area Doppler center position.

7. The data link terminal sky-ground fusion method according to claim 6, characterized in that, The horizontal coordinate, the vertical coordinate and the vertical coordinate of the data link service area Doppler center position are respectively represented as: ； In the formula, , and respectively represent the horizontal coordinate, the vertical coordinate and the vertical coordinate of the Doppler center position coordinate of the data link service area, represent the Doppler center of the data link service area.

8. The data link terminal sky-ground fusion method according to claim 6, characterized in that, According to the data link service area Doppler center position and the satellite in the satellite earth fixed coordinate system position coordinate, the time delay value and the Doppler value at the Doppler center are calculated, including: According to the data link service area Doppler center position and the satellite in the satellite earth fixed coordinate system position coordinate, the vector of the satellite and the data link service area Doppler center position, the geometric distance of the satellite and the data link service area Doppler center position are calculated; According to the vector of the satellite and the data link service area Doppler center position and the satellite radial velocity, the radial velocity, i.e. the velocity component in the projection direction, is calculated; According to the geometric distance of the satellite and the data link service area Doppler center position and the speed of light, the time delay value at the Doppler center is calculated; According to the radial velocity, the speed of light and the signal frequency, the Doppler value at the Doppler center is calculated.

9. The data link terminal sky-to-ground fusion method of claim 1, wherein, The time delay is corrected based on the time delay value, the message is sent in advance using the time delay value at the Doppler center, so that the message reaches the ground node at the typical time of the time slot, and the message is received in delay using the time delay value at the Doppler center, so that the message reaches the satellite node at the typical time of the time slot, including: For the uplink, the satellite receives the ground data link terminal transmit time slot start time reference the ground transmission time slot adaptive delay ; for the downlink, the satellite data link terminal transmit time slot start time reference the ground transmission time slot adaptive advance wherein denotes the time delay value at the Doppler center.

10. The data link terminal sky-to-ground fusion method of claim 1, wherein, The Doppler value is pre-compensated on the data link terminal signal frequency, represented as: ； wherein represents the compensated data link terminal transmit signal frequency, represents the uncompensated data link terminal transmit signal frequency, represents the Doppler value at the Doppler center.

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