An integrated satellite-to-ground laser ranging and communication method based on differential

Abstract

This invention discloses a differential-based integrated satellite-to-ground laser ranging and communication method, belonging to the field of optical measurement technology. This method utilizes the principle of satellite differential laser ranging using a continuous laser to perform laser communication and differential laser ranging using an integrated light source. This allows satellite laser ranging and laser communication to share a single laser light source, completing the functions of laser ranging and laser communication, and achieving light source integration. This method is beneficial for implementing high-precision satellite-to-ground laser ranging technology and improving the accuracy of communication satellite orbit algorithms. The laser communication system can achieve higher data transmission rates than traditional radio communications, meeting the needs of real-time transmission of high-resolution imagery or scientific data.

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 satellite orbit determination, offering the advantages of high power, good stability, and high accuracy. Satellite laser communication technology, on the other hand, uses lasers as a carrier to transmit information such as voice, images, and data between satellites or between satellites and the Earth. Compared to radio frequency communications, laser communication has a frequency that is four to five orders of magnitude higher. This gives laser communication the advantages of high communication capacity, compact system size, wide bandwidth, highly concentrated energy, and relatively low transmission power. Satellite laser communication technology, combined with satellite laser ranging technology, utilizes the same laser beam and hardware platform to achieve the dual functions of high-speed communication and high-precision ranging, improving efficiency and reducing 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 and 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 differential-based satellite-to-ground laser ranging communication integrated method, comprising the following steps:

[0006] Step 1: The satellite, carrying a satellite laser communication terminal equipped with a laser ranging corner reflector, enters orbit. The satellite aims the ground terminal with very high accuracy (bit error less than 1°). The two terminals acquire spatial recognition and conduct uplink and downlink laser communication, as well as time-of-flight measurements (laser ranging).

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

[0008] Step 3: Utilize continuous laser differential ranging technology and eliminate systematic errors and atmospheric effects to obtain a more accurate distance between the ground terminal and the laser ranging corner reflector. Analyze the acquired ranging data and communication information for specific applications, such as navigation, orbit determination, and information transmission. Provide a user interface to facilitate user access to information. This completes the integration of satellite-ground laser ranging communication based on differential ranging.

[0009] The entire satellite-to-ground laser ranging and communication integrated system consists of a satellite laser communication terminal and a ground terminal. The satellite laser communication terminal consists of an optical telescope, a modem, and controller electronics. The ground terminal comprises 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 using continuous laser technology: Differential laser ranging is based on a two-way link. For the uplink, a ground terminal at a laser ranging station on Earth transmits laser light 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, where the ground terminal receives the signal and determines the round-trip flight time.

[0012] A differential ranging measurement consists of 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:

[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 the 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 in the uplink caused by changes in equipment, environment or target status; Indicates the downlink error caused by changes in equipment, environment or target status; Indicates the ranging error or change caused by atmospheric refraction, turbulence, temperature and humidity in the uplink; They represent the ranging errors or changes in the downlink caused by atmospheric refraction, turbulence, temperature, and humidity respectively.

[0022] The above-mentioned design scheme can bring the following beneficial effects: The present invention proposes a differential-based integrated satellite-to-ground laser ranging communication method, utilizing a high-power 1064nm continuous laser light source as an integrated light source for laser communication and differential laser ranging. This allows satellite laser ranging and laser communication to share a single laser light source, completing the functions of laser ranging and laser communication, and achieving light source integration. This method is beneficial for achieving high-precision satellite-to-ground laser ranging technology and improving the accuracy of communication satellite orbit algorithms. The laser communication system can achieve higher data transmission rates than traditional radio communications, meeting the needs of real-time transmission of high-resolution imagery 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 this 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 This is a flow chart of the integrated satellite-to-ground laser ranging communication method 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 ranging and communication working process of the ground terminal;

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

[0028] In order to more clearly illustrate the present invention, the present invention is further described below in conjunction with preferred embodiments and accompanying drawings. Those skilled in the art should understand that the content 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 have the common meanings understood by persons with ordinary skills in the field to which the present invention belongs. The present invention provides a differential-based integrated satellite-to-ground laser ranging and communication 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 integrated satellite laser ranging and communication 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 Earth's surface and is responsible for communicating with the satellite and performing differential laser ranging functions.

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

[0031] The ground terminal uses a laser telescope to receive downlink optical signals and transmit uplink optical signals. It includes a 1.2-meter laser telescope system, a 0.6-meter laser telescope system, and a 1064nm continuous laser source. The 1.2-meter laser telescope system consists of a laser communication subsystem and a 1.2-meter laser telescope. The 0.6-meter laser telescope system consists of a laser ranging subsystem and a 0.6-meter laser telescope. The laser communication subsystem primarily consists of a PPM (pulse phase modulation) transmitter and receiver, responsible for modulating and demodulating high-speed optical signals. The 0.6-meter and 1.2-meter laser telescopes primarily consist of a primary mirror, a secondary mirror, and a relay optical path, responsible for transmitting and receiving beacon / signal light. The beacon or signal light received by the 1.2-meter laser telescope is split by a visible light spectrometer. Part of the beacon or signal light is used for camera imaging, while the remaining part 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, which converts the optical signal into an electrical signal and amplifies it. A data processing system calculates the total time required for the laser pulse to be emitted and returned (round-trip time). Continuous laser differential ranging technology requires high laser power. The integrated laser ranging and communication light source is implemented using a high-power kW-class 1064nm continuous laser. This continuous laser can perform both laser ranging and laser communication functions, achieving an integrated light source.

[0032] Principle of satellite differential laser ranging using continuous laser technology: Differential laser ranging is based on a bidirectional link. For the uplink, a ground terminal on Earth transmits a continuous laser beam to a laser ranging reflector on a 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 calculated. The measurement process for differential laser ranging is more complex than that for laser ranging. At time t1, a ground terminal at a laser ranging station on Earth transmits an amplitude-modulated signal generated by a 1064nm continuous-wave laser to the laser ranging corner reflector on the first satellite or the relay satellite. It then receives the reflected signal. Like laser ranging, this portion of differential laser ranging is still a bidirectional link. The phase difference between the outgoing and return signals is used to determine the distance between the ground terminal and the laser ranging corner reflector. After a short interval, at time t2, the same ground terminal tracks another relay satellite and obtains another range. Differentiating these two consecutive ranges, that is, subtracting Range1 from Range2, yields the distance difference that can be observed through differential ranging. The switching time interval is the difference between t2 and t1.

[0033] The satellite-to-ground laser ranging communication integrated system was designed and its links analyzed based on existing satellites. The system consists of a satellite laser communication terminal and a ground terminal. After the satellite carrying the satellite laser communication terminal enters orbit and undergoes multiple orbital maneuvers, it is operated under atmospheric conditions. This allows for the development of models of the satellite-to-ground laser ranging communication integrated system under various conditions and analysis of the system's feasibility.

[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 the 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 in the uplink caused by changes in equipment, environment or target status; Indicates the downlink error caused by changes in equipment, environment or target status; Indicates the ranging error or change caused by atmospheric refraction, turbulence, temperature and humidity in the uplink; They respectively represent the ranging errors or changes in the downlink caused by atmospheric refraction, turbulence, temperature, humidity, etc.

[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 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-radian rotation angles aligned by lunar laser ranging (LLR) and very long baseline interferometry (VLBI) were used as the main parameters for EOPs estimation, and the sta 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 ) 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 Earth's position vector r in BCRS e and the satellite's 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's 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 point masses, 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 is the uplink and (5) the downlink ——is caused by Shapiro time delay. The second type——in (4), the uplink and (5) the downlink ——It is caused by the Earth's atmosphere and is referred to as AR. AR is related to the meteorological data from the weather station, namely pressure (ps), temperature (ts), relative humidity (hum), etc.

[0051] Pressure (ps), temperature (ts), and relative humidity (hum) can change over short or long periods of 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 in differential ranging measurement (i.e., t1 and t2) is the portion of the distance difference caused by atmospheric delay (called the atmospheric range difference (ARD)). According to equations (1) and (2), for differential ranging, the AR at t1 or t2 is calculated as half the sum of the uplink and downlink ARs. By simulating different changes in pressure (ps), temperature (ts), and relative humidity (hum), the impact of different time periods on differential ranging accuracy can be calculated.

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

[0053] Downlink communication design: In order to achieve high-speed transmission, the proposed satellite laser communication terminal is capable of generating 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. Pseudo-random binary sequences (PN codes) are added to other channels with unclear practical uses, and a data rate of up to 1.2Gb / s can be generated when working at full efficiency. In terms of communication coding, a 1 / 2 code rate serial concatenated Turbo code can be used to frame and encode the data source; the encoded data is interleaved through a deep memory buffer to provide time diversity and reduce the impact of atmospheric turbulence on the downlink. The downlink communication design belongs to the existing technology and will not be described in detail here.

[0054] For the ground terminal, the downlink laser signal is received and focused by a 1.2-meter telescope. The large aperture of the telescope is designed to achieve higher coupling efficiency in atmospheric turbulence while maintaining the polarization of the downlink signal. Multimode polarization-maintaining fiber couples each received signal to a focusing lens for transmission to a single-photon detector. High-speed digital electronics digitize and sum each detector's output. The resulting high-speed digital signal is deserialized and input to an FPGA-based digital receiver for synchronization, demodulation, decoding, and analysis. The electronics also compare the timing of the uplink and downlink signals, thereby inferring the highly accurate round-trip time.

[0055] Uplink Communication Design: For satellite laser communication terminals, the uplink communication rate can reach approximately 1-2 Mbps, including control commands for the satellite laser communication terminal and user data for the loopback. Data sources are framed and multiplexed in the ground terminal electronics. Data encoding and interleaving can be performed using the same serial cascade turbo code and interleaver as for the downlink. Laser signals are transmitted from the satellite laser communication terminal's optical telescope and modulated onto an optical carrier using PPM modulation, with each photon representing two bits. The wavelengths of each transmitter are detuned by approximately 1 GHz, enabling incoherent beam combining with minimal power loss when received by the satellite laser communication terminal. The uplink signal is received by the satellite laser communication terminal's optical telescope and focused into an 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 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 temporal consistency of the laser ranging and communication data; Step 3: Utilize 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. This achieves integrated satellite-ground laser ranging communication based on differential measurement. Among them: continuous laser differential ranging is performed through a two-way link between the satellite and the ground to obtain two-way ranging information. For the uplink, the 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 the 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 in the uplink caused by changes in equipment, environment or target status; Indicates the downlink error caused by changes in equipment, environment or target status; Indicates the ranging error or change caused by atmospheric refraction, turbulence, temperature and humidity in the uplink; They represent the ranging errors or changes in the downlink caused by atmospheric refraction, turbulence, temperature, and humidity respectively.

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

3. The differential-based satellite-to-ground laser ranging communication integrated method according to claim 2, 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 integrated method according to claim 3, 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) are 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 Earth's position vector r in BCRS e and the satellite's 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, where: L C =1.48082686741×10 -8 , L B =1.550519768×10 -8 , C is the speed of light.

5. The differential-based satellite-to-ground laser ranging communication integrated method according to claim 1, characterized in that: The satellite-to-ground laser ranging communication integrated system on which this 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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