CN111650613A - Distributed ephemeris calculation method - Google Patents
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- CN111650613A CN111650613A CN202010480167.8A CN202010480167A CN111650613A CN 111650613 A CN111650613 A CN 111650613A CN 202010480167 A CN202010480167 A CN 202010480167A CN 111650613 A CN111650613 A CN 111650613A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S19/00—Satellite radio beacon positioning systems; Determining position, velocity or attitude using signals transmitted by such systems
- G01S19/01—Satellite radio beacon positioning systems transmitting time-stamped messages, e.g. GPS [Global Positioning System], GLONASS [Global Orbiting Navigation Satellite System] or GALILEO
- G01S19/13—Receivers
- G01S19/24—Acquisition or tracking or demodulation of signals transmitted by the system
- G01S19/27—Acquisition or tracking or demodulation of signals transmitted by the system creating, predicting or correcting ephemeris or almanac data within the receiver
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Abstract
The invention discloses a distributed ephemeris calculation method, wherein a satellite gateway station calculates satellite perturbation acceleration according to six orbital parameters, calculates an ephemeris precomputation intermediate result according to a perturbation motion equation and a numerical integration method, and then repeatedly sends the ephemeris precomputation intermediate result in frame information broadcast at an air interface to avoid errors, a satellite user station receives the ephemeris precomputation intermediate result, obtains a high-precision satellite ephemeris through interpolation operation, and calculates communication results such as Doppler frequency deviation, transmission delay and the like. The distributed ephemeris calculation method disclosed by the invention reduces the calculation complexity of the satellite user station and provides a communication result based on ephemeris calculation for a low-orbit satellite communication system.
Description
Technical Field
The invention relates to the technical field of satellite communication, in particular to a distributed ephemeris calculation method.
Background
Satellite mobile communication systems are classified into three types, i.e., a geostationary Orbit (GEO), a Medium Earth Orbit (MEO), and a Low Earth Orbit (LEO), according to the orbital altitude of a satellite. The LEO system has the advantages of low orbit height, light weight, short research and development period, low research and development cost, short transmission delay, low link loss, avoidance of congestion of GEO orbits and the like, and has become a research hotspot in the global satellite communication field in recent years.
The low earth orbit satellite in high-speed motion state always has a radial velocity component relative to the ground receiver, which causes Doppler frequency shift and transmission delay variation of the satellite-ground signal. The position and the velocity vector of the satellite are deduced from the ephemeris information, a Doppler frequency shift and time delay calculation model is established according to the longitude and latitude high parameters of the ground receiver, and the prior information can be improved for the rapid acquisition and synchronization of satellite-ground signals.
The instantaneous orbit parameters of the satellite are defined in the J2000 epoch equatorial celestial coordinate system, while the position and velocity of the terrestrial receiver are usually defined in the protocol terrestrial coordinate system, and WGS-84 is an ECEF coordinate system which is commonly used at present and is also a protocol (flat) terrestrial coordinate system. In general, it is difficult for a terrestrial receiver to directly calculate the position and velocity vectors of a satellite in the ECEF coordinate system, so that it is necessary to convert the parameters of the satellite from the J2000 coordinate system to the WGS-84 coordinate system.
If the satellite subscriber station independently completes high-precision ephemeris calculation according to the instantaneous orbit parameters of the satellite, and then calculates Doppler frequency offset, transmission delay and the like by combining the position of the satellite, strong calculation capability is required, while the general satellite subscriber station is limited by the requirements of mobility, miniaturization and even miniaturization, and after signal processing, radio frequency antenna combination and the like are completed by a chip, precious calculation resources are used for the calculation, which is obviously uneconomical.
Therefore, how to implement high-precision ephemeris calculation under the condition that the computation resources and computation time of the satellite subscriber station are limited is an urgent problem to be solved by those skilled in the art.
Disclosure of Invention
In view of this, the invention provides a distributed ephemeris calculation method, which not only overcomes the problem of insufficient ephemeris accuracy caused by the fact that the traditional satellite ephemeris calculation is concentrated in the satellite user station, but also reduces the calculation complexity of the satellite user station and obtains an ephemeris in a larger time range.
In order to achieve the purpose, the invention adopts the following technical scheme:
a distributed ephemeris calculation method comprising:
step 1: the satellite gateway station calculates the position and the speed of the satellite at the current moment in a J2000 coordinate system according to the six orbital parameters, and calculates the perturbation acceleration of the satellite according to a perturbation model;
step 2: the satellite gateway station obtains ephemeris precalculated intermediate results of the satellite at other moments in a coarse-grained time system and a J2000 coordinate system according to the satellite perturbation acceleration, the motion equation and the RKF numerical integration method;
and step 3: the satellite gateway station converts the intermediate result of ephemeris precalculation from the J2000 coordinate system to the WGS-84 coordinate system, and repeatedly sends the converted intermediate result of ephemeris precalculation in the air interface broadcast frame information in the coarse granularity time interval;
and 4, step 4: the satellite user station receives the converted ephemeris precalculated intermediate result, and performs interpolation by using an interpolation algorithm to obtain a satellite ephemeris calculation result under a fine-grained time system;
and 5: and the satellite subscriber station calculates the WGS-84 coordinate position corresponding to the satellite according to the satellite ephemeris calculation result under the fine-grained time system and the latitude and longitude of the current satellite subscriber station, and calculates the Doppler frequency offset and the transmission delay.
Preferably, in step 2, the satellite gateway station obtains ephemeris precalculated intermediate results of the satellite at other moments in the coarse-grained time system and the J2000 coordinate system according to the shot motion equation and the RKF numerical integration method.
Preferably, in step 3, the satellite gateway station performs broadcast over the air transmission by using a representation of a satellite vector.
Preferably, in step 4, a third-order spline difference algorithm is used for interpolation.
According to the technical scheme, compared with the prior art, the distributed ephemeris calculation method is disclosed and provided, a satellite gateway station calculates satellite perturbation acceleration according to six orbital parameters, calculates an ephemeris pre-calculation intermediate result according to a shot motion equation and a numerical integration method, repeatedly sends the ephemeris pre-calculation intermediate result in frame information broadcast by an air interface to avoid errors, a satellite user station receives the ephemeris pre-calculation intermediate result, obtains a high-precision satellite ephemeris through interpolation operation, and calculates communication results such as Doppler frequency offset, transmission delay and the like.
Under the condition that the calculation resources and the calculation time of the satellite user station are limited, the estimation precision and the estimation range are obviously improved compared with the traditional method, and the method is simple to implement and good in effect. The method not only solves the problem that the ephemeris accuracy is insufficient due to the fact that the traditional satellite ephemeris calculation is concentrated on the satellite user station, but also reduces the calculation complexity of the satellite user station, and the ephemeris in a larger time range is obtained.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
FIG. 1 is a schematic diagram of six parameters of a satellite orbit provided by the present invention;
FIG. 2 is a diagram of a communication topology between a satellite gateway station and a satellite subscriber station provided by the present invention;
FIG. 3 is a basic process flow of a satellite gateway station provided by the present invention;
FIG. 4 is a flow chart of coordinate transformation provided by the present invention;
FIG. 5 is a basic process flow of a satellite subscriber station provided by the present invention;
FIG. 6 is a diagram showing the error between the position and the actual position of a satellite WGS84 coordinate system obtained by the satellite subscriber station using third-order spline interpolation according to the present invention;
fig. 7 is a diagram illustrating the results of calculating the doppler frequency offset and the transmission delay in a period of time and performing error analysis with the STK result by the satellite subscriber station according to the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In order to overcome the technical defect that the calculation amount of the traditional satellite ephemeris is concentrated in a satellite user station and precious calculation resources of the satellite user station are consumed, the invention provides a distributed ephemeris calculation method, namely, the satellite gateway station sends an ephemeris result format which is convenient for calculation, and the satellite user station performs interpolation calculation through the received ephemeris format, so that the calculation complexity of the satellite user station is reduced, and a communication result based on ephemeris calculation is provided for a low-orbit satellite communication system. The method has the advantages of simple principle, high accuracy, high operation speed and easy engineering realization.
The technical solution of the present invention is further discussed below with reference to the accompanying drawings.
Fig. 1 is a schematic diagram of six parameters of a satellite orbit provided by the present invention, which includes a set of parameters describing the motion of the satellite, or kepler orbit parameters, defined in an Earth Centered Inertial (ECI) coordinate system, as shown in fig. 1.
The specific parameters are defined as follows:
1.asmajor radius of orbital ellipse
2.esEccentricity of the orbital ellipse
The shape and the size of the Kepler ellipse are determined by the two parameters.
I-inclination of the orbital plane, i.e. the angle between the orbital plane of the satellite and the equatorial plane of the earth.
4. Omega-right ascension, i.e. the center-to-center angle between the ascension point and the spring equinox on the equatorial plane of the earth. The elevation point is an intersection of the orbit of the satellite with the earth's equator when the satellite travels from north to south.
The two parameters uniquely determine the included angle between the plane of the satellite orbit and the earth sphere.
5.ωsThe perigee angular separation, i.e. the geocentric angle between the point of intersection and the perigee in the orbital plane. On an elliptical orbit, the point of the satellite farthest from the earth's centroid (short for the centroid) is called the apogee, and the point closest to the centroid is called the perigee, and their positions in the inertial space are fixed.
This parameter expresses the orientation of the keplerian ellipse in the orbital plane.
6.fsThe true anomaly of the satellite, i.e. the geocentric angular separation between the satellite and the perigee in the orbital plane. This parameter is a function of time and determines the instantaneous position of the satellite in orbit.
The six parameters described above constitute an orbital coordinate system, which is widely used to describe the motion of the satellites. In this system, once the 6 orbital parameters have been determined, the satellite's spatial position and its velocity relative to the earth's sphere at any instant can be uniquely determined.
Fig. 2 shows a communication topology diagram between a satellite gateway station and a satellite subscriber station, in which a low earth orbit satellite keeps communication with the satellite gateway station and the satellite subscriber station, the satellite gateway station performs high-precision orbit prediction and coordinate system transformation in advance, and then broadcasts data in a coarse-grained time system to the satellite subscriber station through an air interface. And the satellite user station interpolates to obtain the satellite position and speed in fine-grained time by using an interpolation algorithm. And finally, estimating communication results such as Doppler frequency offset, transmission delay and the like by combining the longitude and latitude positions of the satellite subscriber stations.
The satellite gateway station adopts a high-precision orbit prediction model, the prediction interval is a coarse-grained time system, the coarse-grained time is adjustable, and then the coordinate system conversion is carried out, so that the calculation amount of the satellite subscriber station is reduced. The basic flow of the satellite gateway station is shown in figure 3.
(1) Satellite gateway station six parameters (a) according to orbits,e,Ω,i,ωs,fs) Calculating the position vector of the satellite at the current moment in the J2000 coordinate system
Sum velocity vector
Wherein r is the distance from the satellite to the geocentric, unit vector
G is the constant of universal gravitation, and M is the earth mass.
(2) And integrating the satellite motion equation by a set of initial values to obtain the position vector and the velocity vector of the satellite at other moments.
The component form of the motion equation of the satellite in the J2000 coordinate system is expressed as follows:
wherein f is (f)x,fy,fz) The three-axis perturbation acceleration is respectively, and r is the distance from the satellite to the geocentric; mu is the product of gravity and earth mass, x, y, z, vx,vy,vzThe J2000 position and velocity of the satellite at the current time are used as the initial values of the numerical integration.
By performing numerical integration on the motion equation set of the satellite, the position vector and the velocity vector of the satellite at other moments in a coarse-grained time system and a J2000 coordinate system can be predicted.
It should be noted that the solution of the satellite motion equation involved in this step belongs to the prior art, and the specific method is not described in detail here.
(3) The J2000 coordinate system belongs to the epoch equatorial celestial coordinate system, and the satellite subscriber station is usually defined in the protocol terrestrial coordinate system, and the WGS-84 is an ECEF coordinate system commonly used at present and is also a protocol (flat) terrestrial coordinate system, so that the J2000 coordinate system needs to be converted to the WGS-84 coordinate system, and the general conversion process is shown in fig. 4.
(4) The pre-calculation intermediate result format of the air interface broadcast ephemeris of the satellite gateway station does not adopt the representation mode of the original six numbers, but adopts the satellite vector (the satellite position X/Y/Z and the satellite velocity vector v)x/vy/vz) The expression of (1); the data transmitted in each adjacent coarse granularity time interval may be different, but the data transmitted in the same coarse granularity time interval is the same and is transmitted repeatedly; the broadcast air interface frame structure is aligned to the second pulse of GPS standard time.
The time of the air interface broadcasting unit and the ephemeris calculation unit of the satellite gateway station is obtained by the unified time service of an external GPS, and the synchronization among the units is ensured.
(5) The satellite user station receives a high-precision orbit prediction result from the satellite gateway station, obtains a more precise satellite position and speed through interpolation, and estimates communication results such as Doppler frequency offset, transmission delay and the like by combining the position of the user station. The basic flow of the subscriber station is shown in figure 5.
Specifically, a cubic spline interpolation function formula is utilized to convert the satellite gateway station orbit prediction result stepped to coarse-grained time into an orbit result required by the satellite subscriber station stepped to fine-grained time.
And finally calculating Doppler frequency shift and transmission delay: the doppler shift of the signal received by the satellite subscriber station at this time can be expressed as:
wherein f is0Is the signal carrier frequency, c is the speed of light, v represents the relative speed of motion of the satellite and the subscriber station, vx,vy,vzThe projected components of the relative velocity in three directions β is the angle v makes with the line between the satellite and the subscriber station βx,βy,βzIs the angle between the projected components of the relative velocity in three directions and the radial vector.
R is the connection between the satellite and the subscriber station, i.e. the position vector of the satellite with respect to the subscriber station, and can be expressed as:
The transmission delay can be expressed as:
fig. 6 shows the position error of the WGS84 coordinate system of the satellite obtained by the satellite subscriber station through third-order spline interpolation from the actual position, and the error is mainly the error introduced during orbit prediction according to the analysis of the orbit prediction error, and the error can meet the design requirement. Fig. 7 is a diagram of doppler frequency offset and propagation delay over time calculated by a satellite subscriber station and error analyzed with the STK results. As can be seen from fig. 6 and 7, the satellite positions obtained by the present invention and the communication calculation errors based on the satellite positions are both small and fall within the range that the satellite communication system can receive, but the calculation resources of the satellite subscriber station are greatly optimized.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (4)
1. A distributed ephemeris calculation method, comprising:
step 1: the satellite gateway station calculates the position and the speed of the satellite at the current moment in a J2000 coordinate system according to the six orbital parameters, and calculates the perturbation acceleration of the satellite according to a perturbation model;
step 2: the satellite gateway station obtains ephemeris precalculated intermediate results of the satellite at other moments in a coarse-grained time system and a J2000 coordinate system according to the perturbation acceleration, the motion equation and the RKF numerical integration method of the satellite;
and step 3: the satellite gateway station converts the intermediate result of ephemeris precalculation from the J2000 coordinate system to the WGS-84 coordinate system, and repeatedly sends the converted intermediate result of ephemeris precalculation in the air interface broadcast frame information in the coarse granularity time interval;
and 4, step 4: the satellite user station receives the converted ephemeris precalculated intermediate result, and performs interpolation by using an interpolation algorithm to obtain a satellite ephemeris calculation result under a fine-grained time system;
and 5: and the satellite subscriber station calculates the WGS-84 coordinate position corresponding to the satellite according to the satellite ephemeris calculation result under the fine-grained time system and the latitude and longitude of the current satellite subscriber station, and calculates the Doppler frequency offset and the transmission delay.
2. A distributed ephemeris calculation method according to claim 1 wherein in step 2, the satellite gateway station obtains the intermediate ephemeris precalculated results of the satellite at other time points in the coarse time frame and the J2000 coordinate frame according to the equation of motion and the RKF numerical integration method.
3. A distributed ephemeris calculation method according to claim 1 wherein, in step 3, the satellite gateway station performs air interface broadcast transmission by using a representation of a satellite vector.
4. A distributed ephemeris calculation method according to claim 1 wherein in step 4 interpolation is performed using a third order spline difference algorithm.
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| CN112910541A (en) * | 2021-01-20 | 2021-06-04 | 华力智芯(成都)集成电路有限公司 | Satellite user side wave beam design method applied to satellite mobile communication system |
| CN113517907A (en) * | 2021-04-13 | 2021-10-19 | 北京国电高科科技有限公司 | Method for rapidly capturing burst signals of satellite Internet of things |
| CN117478207A (en) * | 2023-12-25 | 2024-01-30 | 广东世炬网络科技有限公司 | Satellite-to-ground link communication method, device, equipment and storage medium |
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