Satellite-ground laser ranging and communication integrated method based on difference

Abstract

The invention discloses a difference-based satellite-ground laser ranging and communication integrated method, which belongs to the technical field of optical measurement, and is characterized in that laser communication and differential laser ranging are carried out by using an integrated light source according to a satellite differential laser ranging principle of continuous laser, so that the satellite laser ranging and the laser communication share one laser light source; the functions of laser ranging and laser communication are completed, and integration of a light source is achieved. In order to realize a high-precision satellite-ground laser ranging technology, the precision of a communication satellite orbit algorithm is improved, a laser communication system can realize a data transmission rate higher than that of traditional radio communication, and the requirements of real-time transmission of high-resolution images or scientific data can be met.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical measurement, and in particular relates to a satellite-to-ground laser ranging communication integration method based on differential. Background Art

[0002] Satellite laser ranging is an important means of precise orbit determination for satellites, and has the advantages of high laser ranging power, good stability, and high accuracy. On the other hand, satellite laser communication technology is a technology that uses laser as a carrier to transmit information such as voice, images, and data between satellites or between satellites and the ground. Compared with radio frequency communication, the frequency of laser communication is 4 to 5 orders of magnitude higher, which makes laser communication have the advantages of large communication capacity, small system size, wide bandwidth, highly concentrated energy, and relatively low transmission power. Satellite laser communication technology is combined with satellite laser ranging technology, using the same laser beam and hardware platform to achieve the dual functions of high-speed communication and high-precision ranging, which not only improves efficiency but also reduces costs, bringing new opportunities for future communication and ranging technologies.

[0003] Currently, satellite laser ranging stations use pulsed lasers for laser ranging. Pulsed lasers emit light pulses that repeat at a fixed frequency. Each pulse has a peak power and a pulse width, but it is difficult to send high-speed communication information through pulsed lasers. Summary of the invention

[0004] In view of this, the purpose of the present invention is to propose a differential-based satellite-to-ground laser ranging communication integration method, which enables satellite laser ranging and laser communication to share a 1064nm continuous laser light source, complete the functions of laser ranging and laser communication, and improve the accuracy of satellite laser ranging.

[0005] The technical solution adopted by the present invention to achieve the above-mentioned purpose is: a satellite-to-ground laser ranging communication integration method based on differential, comprising the following steps:

[0006] Step 1: The satellite carries a satellite laser communication terminal into the satellite orbit, and the satellite laser communication terminal is equipped with a laser ranging corner reflector. The satellite aims at the ground terminal with very high accuracy (bit error difference is less than 1°). The two terminals capture each other in space and perform uplink and downlink laser communication and flight time measurement (laser ranging).

[0007] Step 2: Collect laser ranging and communication data in real time and process them using digital signal processing technology. Use timestamp or synchronization signal mechanism to synchronize data to ensure the consistency of laser ranging and communication data in time.

[0008] Step 3: Use continuous laser differential ranging technology and eliminate system errors and atmospheric effects. Obtain a more accurate distance between the ground terminal and the laser ranging corner reflector. Analyze the obtained ranging data and communication information and apply them to specific scenarios, such as navigation, orbit determination, and information transmission. Provide a user interface to facilitate users to obtain information. At this point, the integration of satellite-ground laser ranging communication based on differential is realized.

[0009] The entire satellite-to-ground laser ranging communication integrated system consists of a satellite laser communication terminal and a ground terminal. The satellite laser communication terminal consists of three parts: an optical telescope, a modem, and controller electronic components. The ground terminal consists of a 1.2m laser telescope system, a 0.6m laser telescope system, and an integrated light source.

[0010] The integrated light source of the ground terminal is realized by a high-power KW-level 1064nm continuous laser.

[0011] Principle of satellite differential laser ranging with continuous laser: The principle of differential laser ranging is a two-way link. For the uplink, the ground terminal of a laser ranging station on the earth sends laser to a laser ranging corner reflector on the satellite. For the downlink, the laser ranging corner reflector reflects the signal back to the laser ranging station, and the ground terminal receives the signal and determines the round-trip flight time.

[0012] A differential ranging measurement includes two ranging measurements from a ground terminal to two different laser ranging corner reflectors at two different transmission times t1 and t2. Suppose the uplink and downlink ranges of the first ranging measurement are ρ up1 and ρ dn1 , then the final range ρ1 is: The second ranging measurement, from the uplink ρ up2 and downlink ρ dn2 Calculate the final range ρ2:

[0013] Therefore, the differential ranging distance difference is:

[0014]

[0015] Where ε is the white noise added according to the differential ranging accuracy;

[0016] For the uplink, the range model ρ up for:

[0017]

[0018] For the downlink, the range model ρ dn for:

[0019]

[0020] Among them, B (tse) and sta B (tsr) are the positions of the ground terminal at the signal transmission time tse and reception time tsr respectively; in addition, ref B (tr) is the position of the laser ranging corner reflector when the signal is reflected;

[0021] sta B (tse), sta B (tsr) and ref B (tr) is considered in the barycentric celestial reference system BCRS; tse, tsr and tr are barycentric dynamic times; Indicates the error caused by the change of equipment, environment or target status in the uplink; Indicates the error caused by the change of equipment, environment or target status in the downlink; Indicates the ranging error or change caused by atmospheric refraction, turbulence, temperature and humidity in the uplink; They respectively represent the ranging error or change caused by atmospheric refraction, turbulence, temperature and humidity in the downlink.

[0022] Through the above design scheme, the present invention can bring the following beneficial effects: the present invention proposes a differential-based satellite-to-ground laser ranging communication integration method, using a high-power 1064nm continuous laser light source as an integrated light source to perform laser communication and differential laser ranging, so that satellite laser ranging and laser communication share a laser light source, complete the functions of laser ranging and laser communication, and realize the integration of light sources. To achieve high-precision satellite-to-ground laser ranging technology and improve the accuracy of communication satellite orbit algorithms, the laser communication system can achieve a higher data transmission rate than traditional radio communications, and can meet the needs of real-time transmission of high-resolution images or scientific data. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present application. The exemplary embodiments of the present invention and their descriptions are used to understand the present invention and do not constitute improper limitations of the present invention. In the drawings:

[0024] Figure 1 It is a flow chart of the integrated method of satellite-to-ground laser ranging communication based on differential;

[0025] Figure 2 This is a schematic diagram of the structure of the satellite-to-ground laser ranging communication integrated system;

[0026] Figure 3 This is a schematic diagram of the optical path structure of the distance measurement and communication working process of the ground terminal;

[0027] Figure 4 This is a simplified diagram of differential satellite-to-earth laser ranging. DETAILED DESCRIPTION

[0028] In order to explain the present invention more clearly, the present invention is further described below in conjunction with the preferred embodiments and the accompanying drawings. Those skilled in the art should understand that the content specifically described below is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein should be the common meanings understood by people with ordinary skills in the field to which the present invention belongs. The present invention provides a differential-based satellite-to-ground laser ranging communication integration method, which realizes the concept of sharing a laser light source for satellite laser ranging and laser communication, and completes the establishment of a differential-based satellite laser ranging communication integration system.

[0029] like Figure 1 , Figure 2 , Figure 3 and Figure 4 As shown in the figure, the entire satellite-to-ground laser ranging communication integrated system consists of a satellite laser communication terminal and a ground terminal. The satellite laser communication terminal is installed on the satellite and is responsible for sending and receiving laser signals; the ground terminal is located at the laser ranging station on the surface of the earth and is used for communication with the satellite and differential laser ranging functions.

[0030] The satellite laser communication terminal consists of three parts: an optical telescope, a modem, and control electronics. The close cooperation of the three parts determines the performance and reliability of the satellite laser communication terminal. The optical telescope is responsible for signal capture and transmission; the modem ensures the effective transmission of data; and the control electronics manage and monitor the system, enabling the satellite laser communication terminal to efficiently perform data communication and ranging tasks.

[0031] The ground terminal uses a laser telescope to receive downlink optical signals and transmit uplink optical signals. The ground terminal includes a 1.2-meter laser telescope system, a 0.6-meter laser telescope system, and a 1064nm continuous laser light source. The 1.2-meter laser telescope system consists of a laser communication subsystem and a 1.2m laser telescope. The 0.6-meter laser telescope system consists of a laser ranging subsystem and a 0.6m laser telescope. The laser communication subsystem is mainly composed of a PPM (pulse phase modulation) transmitter and receiver, and its main function is to modulate and demodulate high-speed optical signals; the 0.6m laser telescope and the 1.2m laser telescope are mainly composed of a primary mirror, a secondary mirror, and a relay optical path, and their main function is to transmit signal light or receive beacons / signal light; the beacon or signal light received by the 1.2m laser telescope is split by a visible light spectrometer, and a part of the beacon or signal light is used for camera imaging, and the other part of the beacon or signal light is split by a 1064nm spectrometer for laser communication and communication receiving detectors respectively. The beacon or signal light received by the 0.6m laser telescope enters the ranging detector, converts the optical signal into an electrical signal, and amplifies it. The total time (round trip time) required for the laser pulse to be emitted and returned is calculated by the data processing system. The differential ranging technology of continuous lasers has a high power requirement for the laser. The integrated laser ranging and communication light source is realized by a high-power KW-level 1064nm continuous laser, which can complete the functions of laser ranging and laser communication, realizing the integration of the light source.

[0032] Principle of satellite differential laser ranging with continuous laser: The principle of differential laser ranging is a two-way link. For the uplink, a ground terminal on the earth sends a continuous laser to a laser ranging reflector on the satellite. For the downlink, the laser ranging corner reflector reflects the signal back to the ground terminal. The ground terminal receives the signal and determines the round-trip flight time. Using the speed of light, the distance between the ground terminal and the laser ranging corner reflector is obtained. The measurement process of differential laser ranging is more complicated than the laser ranging process. At time t1, the ground terminal of a laser ranging station on the earth sends the amplitude modulated signal generated by a 1064nm continuous wave laser to the laser ranging corner reflector of the first satellite or the laser ranging corner reflector of the relay satellite. Then, it receives the reflected signal. Just like laser ranging, for this part of differential laser ranging, it is still a two-way link. The distance between the ground terminal and the laser ranging corner reflector is obtained from the phase difference of the output and return signals. After a short time interval, at time t2, the same ground terminal will track another relay satellite and obtain another range. Differentiate these two continuous ranges, that is, Range2 minus Range1, and obtain the difference distance measurement observable value, that is, the distance difference. The switching time interval is the difference between t2 and t1.

[0033] The satellite-to-ground laser ranging communication integrated system is designed and the link is analyzed and studied based on the existing satellites. The satellite-to-ground laser ranging communication integrated system consists of a satellite laser communication terminal and a ground terminal. When the satellite carries the satellite laser communication terminal into orbit, after multiple orbital introduction maneuvers, it is operated when atmospheric conditions permit, so that the model of the satellite-to-ground laser ranging communication integrated system can be established under different conditions to analyze the feasibility of the system.

[0034] Simulation of continuous laser differential satellite laser ranging data: A differential ranging measurement includes two ranging measurements from a ground terminal to two different laser ranging corner reflectors at two different launch times (i.e., t1 and t2), such as Figure 4 Assume that the uplink and downlink ranges of the first ranging measurement are ρ up1 and ρ dn1 , then the final range ρ1 is:

[0035]

[0036] Similarly, for the second ranging measurement, from the uplink ρ up2 and downlink ρ dn2 Calculate the final range ρ2:

[0037]

[0038] Therefore, the differential ranging distance difference is:

[0039]

[0040] Where ε is the white noise added according to the differential ranging accuracy.

[0041] In the differential ranging simulation, the most important part is the simulation of the distance from a ground terminal to a satellite's laser ranging corner reflector, with an uplink and a downlink. For the uplink, the range model is:

[0042]

[0043] For the downlink, the range model is:

[0044]

[0045] Among them, B (tse) and sta B (tsr) are the positions of the ground terminal at the signal transmission time tse and reception time tsr respectively. B(tr) is the position of the laser ranging corner reflector at the time of signal reflection. These positions are considered in the barycentric celestial reference system (BCRS). Where tse, tsr and tr are barycentric dynamical time; tse is initially given in Coordinated Universal Time (UTC), which requires a conversion from Coordinated Universal Time to Barycentric Dynamical Time (TDB). Indicates the error caused by the change of equipment, environment or target status in the uplink; Indicates the error caused by the change of equipment, environment or target status in the downlink; Indicates the ranging error or change caused by atmospheric refraction, turbulence, temperature and humidity in the uplink; They respectively represent the ranging error or change caused by atmospheric refraction, turbulence, temperature, humidity, etc. in the downlink.

[0046] The initial coordinates of the ground terminal of the laser ranging station and the laser ranging corner reflector of the satellite are in the fixed coordinate system of the earth and the satellite, that is, the International Terrestrial Reference System. IR ), and is corrected according to solid tides, ocean tidal loads, atmospheric loads, polar motions, and plate tectonics. Then, the Earth orientation parameters EOPs (precession, nodal motion, Earth rotation, polar motion) and micro-arc rotation angles aligned by lunar laser ranging (LLR) and Very Long Baseline Interferometry (VLBI) are used as the main parameters for EOPs estimation, and the sta IR Convert to the coordinates sta in the Geocentric Celestial Reference System (GCRS) G Using three parameterized satellite orientation Euler angles (Φ S ,θ S ,ψ S ) Establish the coordinates of the satellite-centered celestial reference system (SCRS) ref s , where Φ S is the roll angle, θ s is the pitch angle, ψ s is the yaw angle.

[0047] The laser ranging station coordinates sta in the geocentric celestial reference system (GCRS) G and the coordinates of the laser ranging corner reflector in the Satellite Centered Celestial Reference System (SCRS) s Convert to BCRS B and ref B The equation is:

[0048]

[0049] The position vector r of the Earth in BCRS e and the satellite position vector r s .U e and U s is the gravitational potential of the sun at the center of the earth and the center of the satellite. C =1.48082686741×10 -8 ,L B =1.550519768×10 -8 , C is the speed of light. In BCRS, the Earth's velocity vector v e 、The satellite's velocity vector v S 、The Earth's position vector r e and the satellite position vector r S , by numerically integrating their equations of motion based on some initial positions and velocities. The most important part of the equations of motion is the interaction of the objects as mass points, described by the Einstein-Infeld-Hoffmann (EIH) equations.

[0050] There are two types of range corrections included in equations (4) and (5). The first type - the uplink and (5) where the downlink ——is caused by Shapiro time delay. The second type——In (4), the uplink and (5) where the downlink ——It is caused by the earth's atmosphere, referred to as AR. AR is related to the meteorological data of the weather station, namely pressure (ps); temperature (ts); relative humidity (hum), etc.

[0051] Pressure (ps), temperature (ts) and relative humidity (hum) can change in a short or long time. This makes it necessary to study the impact of changes in pressure (ps), temperature (ts) and relative humidity (hum) on differential ranging. The difference in AR between two moments (i.e., t1 and t2) of differential ranging measurement is a part of the distance difference caused by atmospheric delay (called atmospheric range difference (ARD)). According to equations (1) and (2), for differential ranging, the AR at t1 or t2 is calculated as half of the sum of the uplink and downlink ARs. For simulating different changes in pressure (ps), temperature (ts) and relative humidity (hum), the impact on the accuracy of differential ranging under different time lengths can be calculated.

[0052] Satellite laser communication is based on existing technology and high-power KW-level 1064nm continuous laser.

[0053] Downlink communication design: In order to achieve high-speed transmission, the proposed satellite laser communication terminal can generate a 64-PPM downlink laser signal through a modem. The downlink channel is divided into 64 sub-channels, and different data sources can be multiplexed in the downlink, including high-speed telemetry data, high-speed spacecraft data and uplink signal loops, while pseudo-random binary sequences (PN codes) are added to other channels with unclear practical uses, which can generate signals with data rates up to 1.2Gb / s when working at full efficiency. In terms of communication coding, a 1 / 2 code rate serial cascade Turbo code can be used to frame and encode the data source; the encoded data is interleaved through a deep memory buffer, which can provide time diversity and reduce the impact of atmospheric turbulence on the downlink. The downlink communication design belongs to the prior art and will not be described in detail here.

[0054] For the ground terminal, the downlink laser signal will be received and focused by a 1.2-meter telescope. The large-aperture telescope is designed to achieve higher coupling efficiency under atmospheric turbulence while maintaining the polarization of the downlink signal. The multi-mode polarization-maintaining fiber couples each received signal to the focusing lens and transmits it to the single-photon detector. The output of each detector is digitized and summed using high-speed digital electronics. The synthesized high-speed digital signal is deserialized and input into an FPGA-based digital receiver for synchronization, demodulation, decoding, and analysis. The electronics can also compare the timing of the uplink and downlink, thereby inferring and calculating the high-precision round-trip time.

[0055] Uplink communication design: For satellite laser communication terminals, the uplink communication rate can reach about 1 to 2 Mb / s, including sending control instructions to the satellite laser communication terminal and user data for the loop. The data source is framed and multiplexed in the ground terminal electronic equipment. The data can be encoded and interleaved using the same serial cascade Turbo code and interleaver as the downlink. The laser signal is emitted by the optical telescope of the satellite laser communication terminal, and the data is modulated onto the optical carrier using PPM modulation, so that each photon represents two bits. The wavelength of each transmitter is detuned by about 1 GHz, so that each wavelength can be received and incoherently combined by the satellite laser communication terminal with minimal power loss. The uplink signal is received by the satellite laser communication terminal optical telescope and focused into the optical fiber for modem processing. The received optical signal is preamplified by a low-noise EDFA, filtered by a 10 GHz fiber Bragg grating filter, and then directly detected. The signal is demodulated by a near-optimal hard-decision PPM demodulator, and the signal is decoded, deinterleaved, and further processed by an FPGA. Control commands received by the satellite laser communication terminal are relayed to the controller electronics for execution, and these commands and received high-speed user data are also sent back to the optical downlink.

Claims

1. A satellite-to-ground laser ranging communication integration method based on differential, characterized in that: The steps include: Step 1: The satellite carries a satellite laser communication terminal into the satellite orbit, and the satellite laser communication terminal is equipped with a laser ranging corner reflector; the satellite aims at the ground terminal of the laser ranging station, and the satellite laser communication terminal and the ground terminal capture each other in space, and perform uplink and downlink laser communication and flight time measurement; Step 2: Collect laser ranging and communication data in real time, and synchronize the data to ensure the time consistency of laser ranging and communication data; Step 3: Use continuous laser differential ranging to eliminate system errors and atmospheric effects to obtain the precise distance between the ground terminal and the laser ranging corner reflector. Thus, the integration of satellite-to-ground laser ranging communication based on differential is realized. Among them: Continuous laser differential ranging is performed through a satellite-to-ground bidirectional link to obtain bidirectional ranging information. For the uplink, a ground terminal of a laser ranging station on the earth sends a laser to a laser ranging corner reflector on the satellite; for the downlink, the laser ranging corner reflector reflects the signal back to the laser ranging station, and the ground terminal receives the signal and determines the round-trip flight time; a differential ranging measurement includes two ranging measurements from a ground terminal to two different laser ranging corner reflectors at two different transmission times t1 and t2. Assume that the uplink and downlink ranges of the first ranging measurement are ρ up1 and ρ dn1 , then the final range ρ1 is: The second ranging measurement, from the uplink ρ up2 and downlink ρ dn2 Calculate the final range ρ2: Therefore, the differential ranging distance difference is: Where ε is the white noise added according to the differential ranging accuracy; For the uplink, the range model ρ up for: r up =|ref B (tr)-sta B (tse)|+Drrel up +Dr atm up For the downlink, the range model ρd n for: Among them, B (tse) and sta B (tsr) are the positions of the ground terminal at the signal transmission time tse and reception time tsr respectively; in addition, ref B (tr) is the position of the laser ranging corner reflector when the signal is reflected; sta B (tse), sta B (tsr) and ref B (tr) is considered in the barycentric celestial reference system BCRS; tse, tsr and tr are barycentric dynamic times; Indicates the error caused by the change of equipment, environment or target status in the uplink; Indicates the error caused by the change of equipment, environment or target status in the downlink; Indicates the ranging error or change caused by atmospheric refraction, turbulence, temperature and humidity in the uplink; They respectively represent the ranging error or change caused by atmospheric refraction, turbulence, temperature and humidity in the downlink.

2. The satellite-to-ground laser ranging communication integration method based on differential according to claim 1 is characterized by: In step 1, the satellite is aimed at the ground terminal with an accuracy of less than 1° bit error.

3. The satellite-to-ground laser ranging communication integration method based on differential according to claim 2 is characterized in that: In step 2, the time synchronization method based on timestamp synchronizes data.

4. The differential-based satellite-to-ground laser ranging communication integration method according to claim 3 is characterized in that: In step 3, the initial coordinates of the ground terminal of the laser ranging station and the laser ranging corner reflector of the satellite are in the fixed coordinate system of the earth and the satellite, that is, the international terrestrial reference system; the coordinates of the laser ranging station are calculated as sta IR , and corrected for solid tides, ocean tidal loading, atmospheric loading, polar motions, and plate tectonics; Then, the Earth orientation parameters EOPs and micro-radian rotation angles aligned by lunar laser ranging (LLR) and very long baseline interferometry (VLBI) were used as parameters for EOPs estimation. IR Convert to the coordinate sta in the geocentric celestial reference system GCRS G ; Using three parameterized satellite orientation Euler angles (Φ s ,θ s , ψ s ) establishes the coordinates of the satellite-centered celestial reference system SCRS) s , where Φ s is the roll angle, θ s is the pitch angle, ψ s is the yaw angle; The laser ranging station coordinates sta in the geocentric celestial reference system GCRS G and the laser ranging corner reflector coordinates in the satellite-centered celestial reference system SCRS ref s Convert to BCRS B and ref B The equation is: The position vector r of the Earth in BCRS e and the satellite position vector r s .U e and U s is the gravitational potential of the sun at the center of the earth and the center of the satellite. C =1.48082686741×10 -8 , L B =1.550519768×10 -8 , C is the speed of light.

5. The satellite-to-ground laser ranging communication integration method based on differential according to claim 1 is characterized in that: The satellite-to-ground laser ranging communication integrated system on which the method is based consists of a satellite laser communication terminal and a ground terminal, and the ground terminal consists of a 1.2m laser telescope system, a 0.6m laser telescope system and an integrated light source.

6. The differential-based satellite-to-ground laser ranging communication integrated method according to claim 5, characterized in that: The integrated light source of the ground terminal is realized by a high-power KW-level 1064nm continuous laser.

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