Time-frequency synchronization system for space optical communication link

Abstract

The invention provides a time-frequency synchronization system for a space optical communication link, relates to the technical field of photoelectric information, and is used for solving the technical problem that an optical fiber time-frequency synchronization technology in the prior art is not suitable for free space transmission due to being limited by an optical fiber network. The system comprises a first terminal device which is deployed at a station A and is configured to generate a clock signal through pseudo code modulation; the second terminal equipment is deployed at the station B and is configured to recover the clock signal synchronous with the station A by utilizing a pseudo code regeneration technology according to the clock signal; a first terminal device generates a clock signal through a station A and sends the clock signal to a station B, and a second terminal device receives the clock signal through the station B, analyzes code phase information, locally recovers the clock signal synchronized with the station A according to the code phase information, and sends the recovered clock signal back to the station A again. And the self clock signal is adjusted by comparing pseudo code phase information, so that bidirectional time-frequency synchronization and data transmission between the station A and the station B are completed.

Description

Technical Field

[0001] The present disclosure relates to the field of optoelectronic information technology, and more specifically, to a time-frequency synchronization system for a space optical communication link. Background Art

[0002] The integrated transmission and synchronization of time and frequency is an emerging technology science developed by the needs of long-distance or ultra-long-distance measurement and control. The synchronous transmission of high-precision and high-stability time and frequency signals is of great significance to the fields of space non-homologous distributed collaborative positioning systems, satellite navigation and positioning systems, space exploration, etc.

[0003] In recent years, researchers have been continuously conducting research on time-frequency-phase transmission based on optical fiber links, and have achieved unprecedented accuracy using optical fiber time-frequency-phase synchronous transmission. However, signals based on optical fiber time-frequency-phase transmission are limited to optical fiber networks. For special occasions where optical fiber cannot be laid, synchronization and transmission between moving platforms (such as automotive interconnection, three-dimensional coherent detection, and drone swarms) are not suitable, and free space time-frequency transmission methods are needed. Summary of the invention

[0004] In view of this, the present disclosure provides a time-frequency synchronization system for a space optical communication link, so as to solve the technical problem that the optical fiber time-frequency synchronization technology in the prior art is not suitable for free space transmission due to the limitation of the optical fiber network.

[0005] One aspect of the present disclosure provides a time-frequency synchronization system for a space optical communication link, including: a first terminal device, deployed at station A, configured to generate a clock signal through pseudo-code modulation; a second terminal device, deployed at station B, configured to recover a clock signal synchronized with station A based on the clock signal using pseudo-code regeneration technology; wherein the first terminal device generates a clock signal through station A and sends it to station B, the second terminal device receives the clock signal through station B, parses out code phase information, and locally recovers a clock signal synchronized with station A based on the code phase information, and resends the recovered clock signal back to station A, the first terminal device adjusts its own clock signal by comparing the pseudo-code phase information, and completes two-way time-frequency synchronization and data transmission between station A and station B.

[0006] According to an embodiment of the present disclosure, the first terminal device and the second terminal device respectively include: a field programmable gate array chip and a flash memory device, which are configured to perform pseudo-code modulation and demodulation processing on the clock signal based on on-off keying and store the processing results.

[0007] According to an embodiment of the present disclosure, the first terminal device and the second terminal device also include: an optical module wireless optical front-end device, which is used to build a wireless laser link interconnected from station A to station B, including: an optoelectronic signal conversion interface, which is used to convert electrical signals into optical signals for transmission, or convert received optical signals into electrical signals for processing; an erbium-doped fiber amplifier, which is used to amplify the converted optical signals; and a lens swinging mirror group, which is used to dynamically adjust the direction of the transmitted or received light beam to ensure that the optical signal can be transmitted along the specified path in the air.

[0008] According to an embodiment of the present disclosure, the optical module wireless optical front-end device is provided with a crosspoint switch, wherein the crosspoint switch is configured to be able to be controlled by a field programmable gate array chip to switch modes, the modes including a closed-loop self-test mode and a radio frequency transceiver mode.

[0009] According to an embodiment of the present disclosure, the first terminal device and the second terminal device also include: an optical fiber communication and network cable connection device, which is used to establish a wired optical link between station A and station B to process the transmission of user data and time-frequency synchronization information; wherein the optical fiber communication and network cable connection device is configured as a four-way parallel optical transceiver module with a special pin chip package, and the wired optical link adopts the GTX transmission protocol.

[0010] According to an embodiment of the present disclosure, the first terminal device and the second terminal device also include: a high-speed analog-to-digital converter, which is used to digitize the received optical signal and send the processing result to the field programmable gate array chip and the flash memory device; wherein the high-speed analog-to-digital converter adopts an 8-bit AD083000 high-speed analog-to-digital converter, performs non-integer multiple sampling on the optical signal, the transmission rate of the on-off keying is 1 Gbps, the transmission rate of the GTX transmission protocol is 2.5 Gbps, and the sampling rate of the high-speed analog-to-digital converter is 2.5 Gbps.

[0011] According to an embodiment of the present disclosure, the first terminal device also includes: a clock manager and a clock source input and output device, which is used to adjust the ranging value and the phase frequency control word by analyzing the return data using the clock manager and the field programmable gate array chip.

[0012] According to an embodiment of the present disclosure, the second terminal device further includes: a frequency synthesizer and a clock recovery device, which is used to recover the clock signal using the phase frequency control word in the clock manager.

[0013] According to an embodiment of the present disclosure, the second terminal device further includes: a low-pass filter circuit and a band-pass filter circuit, which are respectively used to filter the data before entering the frequency synthesizer and the clock recovery device.

[0014] According to an embodiment of the present disclosure, the first terminal device and the second terminal device respectively further include: a pulse per second device configured to be able to perform serial communication based on the RS-422 communication protocol and provide an accurate time synchronization signal.

[0015] The time-frequency synchronization system for a space optical communication link provided by the embodiments of the present disclosure has at least the following beneficial effects:

[0016] (1) The time-frequency synchronization system for a space optical communication link provided by the embodiment of the present disclosure includes two terminal devices, which are respectively deployed at station A and station B, wherein station A is responsible for actively sending signals, and station B is responsible for receiving and passively forwarding signals. After receiving the signal from station A, station B uses high-precision pseudo-code phase information to recover the clock synchronized with station A and sends it back to station A, thereby realizing two-way time-frequency transmission. Since the system adopts pseudo-code regeneration ranging technology and clock recovery algorithm, pulse generation and clock recovery are performed at station B, and ranging is completed at station A, it is possible to realize high-precision time-frequency synchronization between two stations in free space.

[0017] (2) The time-frequency synchronization system for space optical communication links provided in the embodiments of the present disclosure is based on FPGA (field programmable gate array) and high-speed ADC (analog-to-digital converter), and is designed to solve the problem of free space communication that cannot be covered by traditional optical fiber networks. It realizes time-frequency synchronization through pseudo-code regeneration ranging technology, and combines OOK (on-off keying) modulation and demodulation of clock and data signals. It can support a data transmission rate of more than 1 Gbps, meeting the needs of high-speed transmission of large amounts of data.

[0018] (3) The time-frequency synchronization system for the space optical communication link provided by the embodiment of the present disclosure can maintain the stability of the link in a dynamic environment through the swing mirror and pod design of the wireless optical front end, has strong anti-interference ability, and is adaptable to moving platforms.

[0019] (4) The time-frequency synchronization system for space optical communication links provided by the embodiments of the present disclosure designs a crosspoint switch in the wireless optical front end part, and the switching mode is controlled by FPGA. It can not only obtain the initial value and correction through closed-loop self-check, but also switch to the RF transceiver mode when the optical path is blocked. Therefore, it can be widely used in the fields of marine communication, space exploration and intelligent interconnection. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0021] Figure 1 The structure block diagram of the time-frequency synchronization system for a space optical communication link according to an embodiment of the present disclosure is schematically shown;

[0022] Figure 2 The functional principle block diagram of the time-frequency synchronization system for a space optical communication link according to an embodiment of the present disclosure is schematically shown;

[0023] Figure 3 The high-precision synchronization algorithm and control principle block diagram according to an embodiment of the present disclosure are schematically shown;

[0024] Figure 4 A model diagram of the front end of a full-view optoelectronic pod in a time-frequency synchronization system for a space optical communication link according to an embodiment of the present disclosure is schematically shown;

[0025] Figure 5 A simulation diagram schematically shows a low-pass filter circuit in a time-frequency synchronization system for a spatial optical communication link according to an embodiment of the present disclosure;

[0026] Figure 6 A simulation diagram schematically shows a bandpass filter circuit in a time-frequency synchronization system for a spatial optical communication link according to an embodiment of the present disclosure;

[0027] Figure 7 A prototype diagram of a time-frequency synchronization system for a spatial optical communication link according to an embodiment of the present disclosure is schematically shown. DETAILED DESCRIPTION

[0028] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present disclosure. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present disclosure.

[0029] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0030] All terms (including technical and scientific terms) used herein have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0031] When using expressions such as "at least one of A, B, and C, etc.", they should generally be interpreted according to the meaning of the expression commonly understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0032] The integrated transmission and synchronization of time and frequency is an emerging technology science developed by the needs of long-distance or ultra-long-distance measurement and control. The synchronous transmission of high-precision and high-stability time and frequency signals is of great significance to the fields of space non-homologous distributed collaborative positioning systems, satellite navigation and positioning systems, space exploration, etc.

[0033] In recent years, researchers have been continuously conducting research on time-frequency-phase transmission based on optical fiber links, and have achieved unprecedented accuracy using optical fiber time-frequency-phase synchronous transmission. However, signals based on optical fiber time-frequency-phase transmission are limited to optical fiber networks. For special occasions where optical fiber cannot be laid, synchronization and transmission between moving platforms (such as automotive interconnection, three-dimensional coherent detection, and drone swarms) are not suitable, and free space time-frequency transmission methods are needed.

[0034] Based on this, the embodiments of the present disclosure provide a time-frequency synchronization system for a space optical communication link, so as to solve the technical problem that the optical fiber time-frequency synchronization technology in the prior art is not suitable for free space transmission due to the limitation of the optical fiber network.

[0035] Figure 1 The structural block diagram of a time-frequency synchronization system for a spatial optical communication link according to an embodiment of the present disclosure is schematically shown.

[0036] like Figure 1 As shown, the time-frequency synchronization system for a space optical communication link according to an embodiment of the present disclosure includes two sets of terminal devices, namely: a first terminal device and a second terminal device.

[0037] Among them, the first terminal device is deployed at station A, and is configured to generate a clock signal through pseudo code modulation.

[0038] The second terminal device is deployed at station B, and is configured to recover a clock signal synchronized with station A based on the clock signal using pseudo code regeneration technology.

[0039] The interactive process of the system is:

[0040] The first terminal device generates a clock signal through station A and sends it to station B. The second terminal device receives the clock signal through station B, parses the code phase information, and locally recovers the clock signal synchronized with station A based on the code phase information, and resends the recovered clock signal back to station A. The first terminal device adjusts its own clock signal by comparing the pseudo-code phase information, thereby completing two-way time and frequency synchronization and data transmission between station A and station B.

[0041] In this embodiment, each terminal device can be implemented by, for example, an FPGA board with functional components such as a high-speed ADC (analog-to-digital converter) with a rate of more than 2G, an SFP optical port (Small Form Pluggable gigabit optical-to-electrical signal conversion interface), a clock management chip, a constant temperature crystal oscillator, etc., in order to achieve functions such as communication above 1Gbps and clock management.

[0042] In this embodiment, the system adopts pseudo-code regeneration ranging technology and clock recovery algorithm to realize two-way time and frequency transmission. Specifically: station A sends a signal to station B. Station B performs capture, frame synchronization and tracking operations on the received signal, and then uses the extracted code phase information to locally recover the clock homologous to station A, and coherently forwards the signal back to station A; station A receives the forwarded signal and performs capture, frame synchronization and tracking operations to obtain a high-precision code chip phase difference between stations A and B, thereby realizing high-precision measurement.

[0043] The time-frequency synchronization system for a space optical communication link provided by the embodiment of the present disclosure includes two terminal devices, which are respectively deployed at station A and station B, wherein station A is responsible for actively sending signals, and station B is responsible for receiving and passively forwarding signals. After receiving the signal from station A, station B uses high-precision pseudo-code phase information to recover the clock synchronized with station A and sends it back to station A, thereby realizing two-way time-frequency transmission. Since the system adopts pseudo-code regeneration ranging technology and clock recovery algorithm, pulse generation and clock recovery are performed at station B, and ranging is completed at station A, it is possible to realize high-precision time-frequency synchronization between two stations in free space.

[0044] Figure 2 The functional principle block diagram of a time-frequency synchronization system for a spatial optical communication link according to an embodiment of the present disclosure is schematically shown.

[0045] like Figure 2 As shown, the time-frequency synchronization system for a space optical communication link of an embodiment of the present disclosure, each set of terminal equipment includes: an FPGA chip and a flash memory device, an optical module wireless optical front-end device, an optical fiber communication and network cable connection device, a high-speed ADC and a second pulse device.

[0046] The difference is that the first terminal device (station A) also includes: a clock manager and a clock source input and output device, and the second terminal device (station B) also includes: a frequency synthesizer and a clock recovery device.

[0047] The functions and working principles of each device will be introduced in detail below.

[0048] (1) Regarding FPGA chips and flash memory devices:

[0049] According to an embodiment of the present disclosure, an FPGA chip and a flash memory device are configured to be able to perform pseudo code modulation and demodulation processing on a clock signal based on on-off keying, and store the processing results.

[0050] In this embodiment, each terminal device adopts a free space time-frequency data integrated high-speed transmission technology based on pseudo-code regeneration ranging, and uses FPGA to perform OOK pseudo-code modulation and demodulation on clock and data signals. The specific working principle of the FPGA chip and the flash memory device is as follows:

[0051] After the system power is turned on, the FPGA chip will control the crosspoint switch to switch to build a self-transmitting and self-receiving closed loop for self-detection. The closed-loop self-detection mode is the calibration state before the system works normally. In the self-detection mode, the data transmitted by the transmitter is directly sampled and received by the ADC through the crosspoint switch, and is not transmitted externally. In this mode, the link delay is fixed, and phase ambiguity can be resolved and system processing delay can be corrected.

[0052] In the normal mode of the system, the OOK regenerated pseudo code measurement technology based on coherent forwarding is used to complete the high-precision time-frequency phase transmission using the high-precision pseudo code phase information obtained by measurement. The receiver uses the randomness of the data in the frame itself and uses the data decoded after frame synchronization as the regenerated pseudo code to re-correlate with the delayed received data.

[0053] In this embodiment, the FPGA chip includes a set of high-precision synchronization program design, which is internally configured with multiple functional modules. The specific synchronization algorithm and control principle are shown in Figure 3 .

[0054] Figure 3 The high-precision synchronization algorithm and control principle block diagram according to an embodiment of the present disclosure are schematically shown.

[0055] like Figure 3 As shown, the high-precision synchronization algorithm and control principle of the embodiment of the present disclosure are as follows:

[0056] The module functions of the FPGA chip such as the interface, send buffer, and receive buffer are not introduced in detail here. The functions of other modules follow the workflow of the time-frequency synchronization algorithm. The interaction of the program module functions between the AB stations is as follows:

[0057] Station A - Timestamp Generation Module: The timestamp generation module of station A reads the second pulse from the outside, generates a timestamp accurate to 1ps, and sends it out through the frame header generation module. The frame header generation module also contains a large amount of other time and frequency synchronization control information.

[0058] Station A - Frame header generation module: packages various control data including timestamp, packet sequence number, etc.

[0059] Station A - frame header and data transmission control: data is sent through the GTX interface according to the station A clock.

[0060] Station B-mirror high-power transmission module: Use ADC data for simple binarization, determine the seat sequence for high-power data transmission, and transmit back the Station B information.

[0061] Station B-Gardener CDR (Clock and Data Recovery) algorithm: is a general conventional signal clock recovery algorithm that can recover data with a clock error of 100ps.

[0062] Station B - Correlation detection algorithm: Use the native data of ADC and the data of CDR to calculate the precise phase with an error of ps level.

[0063] Station A-Gardener CDR algorithm: same as Station B.

[0064] Station A - Correlation detection algorithm: same as Station B.

[0065] Station A - Transmission delay calculation module: The return delay can be accurately calculated with ps level accuracy by using the triple data of the sending timestamp of station A, the timestamp of the return data of station B, and the output delay of the correlation delay calculation module of station A, and then sent to station B through the frame header generation module.

[0066] Station B - DDC clock regeneration module: The DDC clock adjustment is calculated using the return delay of Station A, the output of the relevant phase detection module of Station B, and the current clock phase.

[0067] Station B - Timestamp Recovery Module: Generates ps-level timestamps based on the timestamp of the data packet received by Station B and the absolute delay of link transmission, and generates pps signals periodically.

[0068] (2) Regarding optical module wireless optical front-end device:

[0069] According to an embodiment of the present disclosure, an optical module wireless optical front-end device is used to build a wireless laser link interconnecting station A and station B, including: an optoelectronic signal conversion interface (SFP optical module), an erbium-doped fiber amplifier and a lens swing mirror group.

[0070] Among them, the optoelectronic signal conversion interface is used to convert electrical signals into optical signals for transmission, or to convert received optical signals into electrical signals for processing.

[0071] The erbium-doped fiber amplifier is used to amplify the converted optical signal.

[0072] The lens swing mirror group is used to dynamically adjust the direction of the transmitted or received light beam to ensure that the optical signal can be transmitted along the specified path in the air.

[0073] According to an embodiment of the present disclosure, the optical module wireless optical front-end device is provided with a crosspoint switch, wherein the crosspoint switch is configured to be able to be controlled by a field programmable gate array chip to switch modes, the modes including a closed-loop self-test mode and a radio frequency transceiver mode.

[0074] In this embodiment, stations AB rely on SFP optical modules, erbium-doped fiber amplifiers and lens swing mirrors for optical communication to build an interconnected wireless laser link. The circuit system modulates the electrical signal onto the laser and transmits it to the other party. The optical module can support a maximum rate of more than 2.5GbpsOOk signal input and output.

[0075] In order to adapt to the conditions of motion and vibration, the wireless optical front end is equipped with a multi-dimensional swing mirror and a full-view optoelectronic pod to adjust the direction of the laser emission and the detector detection surface. The specific structure is shown in Figure 4 .

[0076] Figure 4 A model diagram of the front end of a full-view optoelectronic pod in a time-frequency synchronization system for a space optical communication link according to an embodiment of the present disclosure is schematically shown.

[0077] like Figure 4 As shown, the front end of the full-view optoelectronic pod in the time-frequency synchronization system for the space optical communication link in the embodiment of the present disclosure includes: a camera, a turntable, a PCB (Printed Circuit Board) and a waterproof pad.

[0078] The role of the camera in the wireless optical communication system is to collect real-time images. Through image recognition, it can dynamically lock the remote laser receiver or transmitter and perform adaptive alignment to ensure that the link remains symmetrical and stable under motion or vibration conditions.

[0079] The main function of the turntable is to provide multi-dimensional adjustment capabilities, so that the laser emitter or detector can be adjusted accurately at an angle. Combined with the feedback provided by the camera, the turntable can automatically adjust the direction to ensure that the laser beam is always aimed at the target, and maintain stable communication even when the system is subject to vibration or other external interference. The turntable supports full-view adjustment of the wireless optical front end, improving the reliability of the link.

[0080] The PCB is the core circuit board of the entire wireless optical front end, responsible for controlling and managing all electronic functions. In this embodiment, the PCB controls the operation of components such as the camera and turntable to ensure the closed-loop control and automatic adjustment functions of the system.

[0081] The waterproof pad is used to seal and protect the delicate optical and electrical components inside from the external environment, especially moisture, dust and other factors that may damage the system performance. Since the wireless optical front end may need to work outdoors or in complex environments, the waterproof pad ensures that the device can operate reliably for a long time and maintain stable communication performance.

[0082] In this embodiment, a crosspoint switch is also designed in the wireless optical front end, and the switching mode is controlled by FPGA. It can not only obtain the initial value and correction through closed-loop self-check, but also switch to the RF transceiver mode when the optical path is blocked.

[0083] The time-frequency synchronization system for space optical communication links provided by the embodiments of the present disclosure designs a crosspoint switch in the wireless optical front-end part, and the switching mode is controlled by FPGA. It can not only obtain the initial value and correction through closed-loop self-check, but also switch to the RF transceiver mode when the optical path is blocked. Therefore, it can be widely used in the fields of marine communication, space exploration, and intelligent interconnection.

[0084] (3) Regarding optical fiber communication and network cable connection devices:

[0085] According to an embodiment of the present disclosure, the optical fiber communication and network cable connection device is used to establish a wired optical link between station A and station B to process the transmission of user data and time-frequency synchronization information; wherein, the optical fiber communication and network cable connection device is configured as a four-way parallel optical transceiver module with a special pin chip package, and the wired optical link adopts the GTX transmission protocol.

[0086] In this embodiment, the connection between the platform users on each side of the AB station and the time-frequency synchronization system terminal is achieved by wired optical fiber communication. This part adopts a PLCC (special pin chip package) four-way parallel optical transceiver integrated module. In order to support communication rates above G bits, the wired optical link adopts the GTX transmission protocol. The function of the optical fiber communication and network cable connection device sending end can be summarized as the user packages and encodes the data that needs to be communicated according to the specified coding protocol requirements with the system phase information, timestamp, autocorrelation sequence, etc. In this way, it is possible to update the synchronization data while transmitting user data to achieve real-time high-precision time-frequency synchronization and data transmission, so that the AB stations can establish communication in real time. The function of the receiving end can be summarized as performing the inverse operation of balanced coding and the inverse operation of RS coding on the data after being received by the detector and ADC to complete the de-equalization and de-error correction. The received data is split into a frame header and data, etc. The receiving end implements sending data to the user and updating the time, frequency, and phase control parameters in real time to achieve synchronization. Both the AB station terminals have self-transmitting and self-receiving optical modules, so it is actually a two-way simultaneous transmission process. The system has two independent network ports and supports Gigabit Ethernet at the same time. The KSZ9031RNX Gigabit Ethernet transceiver is used for communication between the GTX interface and the network port on the FPGA.

[0087] (4) About high-speed ADC:

[0088] According to an embodiment of the present disclosure, a high-speed ADC is used to digitally process a received optical signal and send the processing result to an FPGA chip and a flash memory device.

[0089] In this embodiment, the high-speed ADC uses an 8-bit AD083000 high-speed ADC produced by Texas Instruments. The AD083000 can support a single-channel rate of up to 3.4 Gsps and provide LVDS standard digital output to the FPGA.

[0090] In this embodiment, communication is in the form of continuous frames. In order to meet the requirements of accurate ranging and clock synchronization and avoid the influence of threshold effect on tracking, it is necessary to perform non-integer multiple sampling of the optical signal, wherein the transmission rate of on-off keying is 1 Gbps, the transmission rate of the GTX transmission protocol is 2.5 Gbps, and the sampling rate of the high-speed ADC is 2.5 Gbps.

[0091] (5) Regarding the clock manager and clock source input and output devices:

[0092] According to an embodiment of the present disclosure, a clock manager and a clock source input and output device are used to adjust the ranging value and the phase frequency control word by analyzing the return data using the clock manager and the FPGA chip.

[0093] In this embodiment, the clock manager and the clock source input and output device are independent functions of the first terminal device (station A), and the purpose is to use the clock manager and the FPGA chip to adjust the ranging value and the phase frequency control word by analyzing the return data. At the same time, in order to cope with the ever-increasing accuracy and requirements of time-frequency synchronization in the future, a clock source input that can choose one of three is added. Through internal amplification, attenuation and other components and clock buffers, the signal source voltage is controlled within a reasonable range and then an analog switch chip is introduced. The two analog switches realize the three-choice function, specifically: the clock output can choose the constant temperature crystal oscillator (SOXO17A) provided on its own board or the external atomic clock and tamed crystal oscillator (such as SCMX012) or the user-defined reference clock as input according to the frequency stability to be achieved and the clock second stability requirements.

[0094] (6) Regarding frequency synthesizers and clock recovery devices:

[0095] According to an embodiment of the present disclosure, a frequency synthesizer and a clock recovery device are used to recover a clock signal by using a phase frequency control word in a clock manager.

[0096] In this embodiment, the frequency synthesizer and clock recovery device are independent functions of the second terminal device (station B). Station B uses the DAC (digital-to-analog converter) function of the DCM (clock manager) for clock recovery, specifically using the frequency control word in the clock manager to drive the DDS (direct digital synthesizer) of the clock recovery module, which can generate a dirty clock with the same source as the main station. The dirty clock is similar to an atomic clock signal with a very stable center value but poor phase noise, which drives the VC-OCXO module with a loop bandwidth of sub-Hz, and finally achieves an output that is coherent with the main station clock and has high stability and high phase noise. After that, the frequency control word of the received signal extracted locally is used as the time-frequency reference to synthesize the response data. The above clock recovery principle can be used to achieve high-stability and high-precision time-frequency transmission and synchronization at station B.

[0097] According to an embodiment of the present disclosure, the second terminal device further includes: a low-pass filter circuit and a band-pass filter circuit, which are respectively used to filter the data before entering the frequency synthesizer and the clock recovery device. Figure 5 and Figure 6 .

[0098] Figure 5 A simulation diagram of a low-pass filter circuit in a time-frequency synchronization system for a spatial optical communication link according to an embodiment of the present disclosure is schematically shown.

[0099] like Figure 5 As shown, the low-pass filter circuit in the time-frequency synchronization system for the space optical communication link in the embodiment of the present disclosure adopts an LC low-pass filter circuit.

[0100] The LC low-pass filter circuit is a component composed of an inductor (L) and a capacitor (C) that can block unwanted frequency signals or allow only the required frequency signals to pass.

[0101] Figure 6 A simulation diagram of a bandpass filter circuit in a time-frequency synchronization system for a spatial optical communication link according to an embodiment of the present disclosure is schematically shown.

[0102] like Figure 6 As shown, the bandpass filter circuit in the time-frequency synchronization system for the space optical communication link according to the embodiment of the present disclosure adopts an LC bandpass 10M circuit.

[0103] The LC bandpass 10M circuit allows signals with a frequency of about 10 MHz to pass through while suppressing signals of other frequencies.

[0104] In this embodiment, the data entering the frequency synthesizer and the clock recovery device from the FPGA chip must first pass through the LC low-pass filter circuit and the LC bandpass 10M circuit respectively.

[0105] (7) Regarding the pulse-per-second device:

[0106] According to an embodiment of the present disclosure, the pulse-per-second device is configured to be able to perform serial communication based on the RS-422 communication protocol and provide an accurate time synchronization signal.

[0107] In this embodiment, the pulse-per-second device is a serial interface, using 485 differential transmission, 485 impedance matching design on the board, and each 485 transmission and reception enable can be independently controlled to ensure that the 2-wire 485 can be converted into 422 communication. This part is to realize auxiliary functions, including the input and output of pulse-per-second, equipment status data, power supply and remote control telemetry, JTAG test and DEBUG interface, acceptance comparison test, reserved interface, etc.

[0108] Figure 7 A prototype diagram of a time-frequency synchronization system for a spatial optical communication link according to an embodiment of the present disclosure is schematically shown.

[0109] like Figure 7 As shown, there are two prototypes of the time-frequency synchronization system for the space optical communication link according to the embodiment of the present disclosure, which are deployed at stations AB respectively to realize data communication and time-frequency synchronization functions between the two stations AB.

[0110] The flowcharts and block diagrams in the accompanying drawings illustrate the possible implementation architecture, functions and operations of the systems, methods and computer program products according to various embodiments of the present disclosure. In this regard, each box in the flowchart or block diagram may represent a module, a program segment, or a part of a code, and the above-mentioned module, program segment, or a part of the code contains one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the box may also occur in an order different from that marked in the accompanying drawings. For example, two boxes represented in succession can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram or flowchart, and the combination of boxes in the block diagram or flowchart, can be implemented with a dedicated hardware-based system that performs a specified function or operation, or can be implemented with a combination of dedicated hardware and computer instructions. It can be understood by those skilled in the art that the features recorded in the various embodiments of the present disclosure can be combined and / or combined in a variety of ways, even if such a combination or combination is not explicitly recorded in the present disclosure. In particular, without departing from the spirit and teaching of the present disclosure, the features described in the various embodiments of the present disclosure may be combined and / or combined in a variety of ways. All of these combinations and / or combinations fall within the scope of the present disclosure.

[0111] The embodiments of the present disclosure are described above. However, these embodiments are only for illustrative purposes and are not intended to limit the scope of the present disclosure. Although the embodiments are described above, this does not mean that the measures in the various embodiments cannot be used in combination to advantage. Without departing from the scope of the present disclosure, those skilled in the art may make a variety of substitutions and modifications, which should all fall within the scope of the present disclosure.

Claims

1. A time-frequency synchronization system for a space optical communication link, characterized in that: The system comprises: A first terminal device, deployed at station A, is configured to generate a clock signal by pseudo code modulation; A second terminal device, deployed at station B, is configured to recover a clock signal synchronized with station A using a pseudo code regeneration technique based on the clock signal; Among them, the first terminal device generates a clock signal through the A station and sends it to the B station, the second terminal device receives the clock signal through the B station, and parses the code phase information, and locally restores the clock signal synchronized with the A station according to the code phase information, and resends the recovered clock signal back to the A station, the first terminal device adjusts its own clock signal by comparing the pseudo code phase information, and completes the two-way time and frequency synchronization and data transmission between the A station and the B station.

2. The time-frequency synchronization system for a space optical communication link according to claim 1, characterized in that: The first terminal device and the second terminal device respectively include: The field programmable gate array chip and the flash memory device are configured to perform pseudo code modulation and demodulation processing on the clock signal based on on-off keying and store the processing results.

3. The time-frequency synchronization system for a space optical communication link according to claim 2, characterized in that: The first terminal device and the second terminal device respectively further include: An optical module wireless optical front-end device, used to construct a wireless laser link interconnected from the A station to the B station, includes: Optoelectronic signal conversion interface, used to convert electrical signals into optical signals for transmission, or convert received optical signals into electrical signals for processing; An erbium-doped fiber amplifier is used to amplify the converted optical signal; The lens swinging mirror group is used to dynamically adjust the direction of the transmitted or received light beam to ensure that the optical signal can be transmitted along the specified path in the air.

4. The time-frequency synchronization system for a space optical communication link according to claim 3, characterized in that: The optical module wireless optical front-end device is provided with a crosspoint switch, wherein the crosspoint switch is configured to be able to be controlled by a field programmable gate array chip to switch modes, wherein the modes include a closed-loop self-test mode and a radio frequency transceiver mode.

5. The time-frequency synchronization system for a space optical communication link according to claim 2, characterized in that: The first terminal device and the second terminal device respectively further include: Optical fiber communication and network cable connection device, used to establish a wired optical link between the A station and the B station to process the transmission of user data and time-frequency synchronization information; Among them, the optical fiber communication and network cable connection device is configured as a four-way parallel optical transceiver integrated module using a special pin chip package, and the wired optical link adopts the GTX transmission protocol.

6. The time-frequency synchronization system for a space optical communication link according to claim 5, characterized in that: The first terminal device and the second terminal device respectively further include: A high-speed analog-to-digital converter, used for digitally processing the received optical signal and sending the processing result to the field programmable gate array chip and the flash memory device; Among them, the high-speed analog-to-digital converter adopts an 8-bit AD083000 high-speed analog-to-digital converter to perform non-integer multiple sampling on the optical signal, the transmission rate of the on-off keying is 1 Gbps, the transmission rate of the GTX transmission protocol is 2.5 Gbps, and the sampling rate of the high-speed analog-to-digital converter is 2.5 Gbps.

7. The time-frequency synchronization system for a space optical communication link according to claim 2, characterized in that: The first terminal device also includes: The clock manager and the clock source input and output device are used to adjust the ranging value and the phase frequency control word by analyzing the returned data using the clock manager and the field programmable gate array chip.

8. The time-frequency synchronization system for a space optical communication link according to claim 7, characterized in that: The second terminal device also includes: The frequency synthesizer and clock recovery device are used to recover the clock signal by using the phase frequency control word in the clock manager.

9. The time-frequency synchronization system for a space optical communication link according to claim 8, characterized in that: The second terminal device also includes: The low-pass filter circuit and the band-pass filter circuit are used to filter the data before entering the frequency synthesizer and the clock recovery device respectively.

10. The time-frequency synchronization system for a space optical communication link according to any one of claims 1 to 9, characterized in that: The first terminal device and the second terminal device respectively further include: The second pulse device is configured to be able to perform serial communication based on the RS-422 communication protocol and provide a precise time synchronization signal.

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