Time synchronization method for space laser communication

Abstract

The invention provides a time synchronization method for space laser communication, which relates to the technical field of laser communication, and comprises the following steps: encoding a time signal, modulating a frequency signal, compounding into an original communication signal, transmitting the original communication signal from a ground end to a space end, and receiving the signal by the space end after the signal is transmitted in the space; the space end demodulates the received communication signal, and performs synchronization processing on the obtained received time signal through a time synchronization algorithm; and the space end demodulates the received communication signal, performs phase error compensation on the obtained frequency signal, and composites the synchronized time signal and the frequency signal after phase error compensation through a multiplexing module to complete frequency time synchronization of the communication signal.

Description

Technical Field

[0001] The present invention relates to the technical field of laser communication, and in particular to a time synchronization method for space laser communication. Background Art

[0002] With the continuous advancement of space technology, space laser communication technology has become increasingly mature and is constantly integrated with other technologies such as quantum communication. Space laser communication, with its advantages of high bandwidth and strong confidentiality, is widely used in data transmission, quantum communication, time-frequency transfer and ranging. In particular, in space quantum communication, laser communication can provide services such as time synchronization for quantum communication. The combination of the two has great application prospects.

[0003] In many fields, such as basic research, aerospace, and national security, high-precision time measurement and time synchronization technologies are crucial. With the development of related technologies, the requirements for time synchronization accuracy are becoming higher and higher. For example, when the quantum communication rate increases, the time synchronization accuracy and the time accuracy of the detector are required to be better than 50ps to meet the needs of high-speed data transmission and precise control.

[0004] Traditional time synchronization methods based on electronics have certain limitations when facing high-speed space laser communications. Generally, the synchronization accuracy of low-frequency synchronization signals directly extracted from laser communications is around 100ps, which is difficult to meet the synchronization requirements of higher precision, prompting researchers to explore new time synchronization methods to improve synchronization accuracy. Summary of the invention

[0005] In order to solve the above technical problems, the present invention proposes a time synchronization method for space laser communication, comprising the following steps:

[0006] S1. Encode the time signal and modulate the frequency signal to form the original communication signal, and transmit the original communication signal from the ground end to the space end. The signal is transmitted in space and received by the space end.

[0007] S2, the space end demodulates the received communication signal and performs synchronization processing on the obtained received time signal through a time synchronization algorithm;

[0008] S3. The space end demodulates the received communication signal, performs phase error compensation on the obtained frequency signal, and combines the synchronized time signal and the frequency signal after phase error compensation through a multiplexing module to complete the frequency and time synchronization of the communication signal.

[0009] Furthermore, in step S2, the linear correction clock expression is:

[0010]

[0011] Among them, Li (t) is the logic time of the second time signal node i at time t, is the drift correction parameter of the second time signal node i, is the offset correction parameter of the second time signal node i, τ i (t) is the hardware time, and V is the set of time nodes.

[0012] 3. The time synchronization method for space laser communication according to claim 2, characterized in that the drift correction parameter and drift correction parameters The update iteration expression is:

[0013]

[0014] Among them, η is the learning rate and E is the time error function.

[0015] Furthermore, in step S3, the actual crystal oscillator frequency f i (t) is expressed as:

[0016] f i (t) = α i (t)f 0 , i∈V

[0017] Among them, α i (t) is the clock drift of communication signal node i at time t, f 0 is the nominal frequency of the crystal oscillator, V is the set of time nodes;

[0018] At time t, the phase expression of the oscillation source of the signal transmitted by the ground transmitter i is:

[0019]

[0020] f i =f 0 +Δf i

[0021] Among them, i is the transmitting end, j is the receiving end, and f i The ground transmitter is at t 0 The frequency at the moment, f 0 is the nominal frequency, Δf i is the frequency deviation relative to the nominal frequency, is the initial phase, n i (t) is the phase noise;

[0022] At t+t ij At time , the phase expression of the oscillation source of the synchronization signal received by the spatial receiving end j is:

[0023]

[0024] in, is the initial phase of the signal received by the spatial receiver, n j (t+t ij ) is the spatial receiving end phase noise.

[0025] Furthermore, after receiving the signal in the space and on the ground, the signal is modulated to obtain the phase synchronization error compensation expression:

[0026]

[0027] in, For space end The initial phase of the signal received by the space receiving end after modulation The phase difference, For ground side The initial phase of the signal received by the ground receiving end after modulation The phase difference.

[0028] Furthermore, in step S1, the time signal is divided into several time nodes, corresponding pulse positions are set for different time nodes, and the time signal is encoded using the pulse positions. The encoded signal obtained carries the original time signal information in the distribution of pulses at different time nodes.

[0029] Compared with the prior art, the present invention has the following beneficial technical effects:

[0030] Precise time synchronization effect: By encoding the time signal on the ground side and then processing it with a time synchronization algorithm on the space side, the time base of the space side and the ground side can be effectively calibrated. For example, in some satellite communication systems, this method can accurately synchronize the time of the equipment on the satellite with the time of the ground control center, providing a unified time standard for subsequent data transmission and command interaction. Precise time synchronization helps improve the overall efficiency of the communication system. For example, in scheduled data transmission tasks, it can ensure that data is sent and received at the exact time point, reducing data transmission errors caused by time deviations.

[0031] High-precision compensation effect of frequency signals: Phase error compensation of frequency signals can correct the frequency deviation caused by various interferences (such as atmospheric refraction, equipment noise, etc.) during the transmission of signals in space. This is like in a high-precision audio transmission system, compensating for phase errors to restore the true frequency of the sound and ensure the quality of the sound. In space laser communications, high-precision compensation of frequency signals can improve communication quality and reduce bit error rates. For example, in high-speed data transmission scenarios, accurate frequency signals can ensure the correct demodulation of digital signals and avoid bit errors in data transmission.

[0032] Efficient communication signal multiplexing effect: The time signal after time synchronization and the frequency signal after phase error compensation are compounded through the multiplexing module to realize the frequency and time synchronized communication signal. This multiplexing method can make more effective use of communication channel resources and improve the transmission capacity of the communication system. Just like in a multi-task communication system, signals with different functions (such as voice signals and data signals) are transmitted in the same channel through multiplexing technology, which increases the practicality and flexibility of the system. In space laser communication, this multiplexed signal can simultaneously transmit multiple types of data, such as scientific exploration data, control instructions, etc., while ensuring time and frequency accuracy, enhancing the comprehensive performance of the communication system.

[0033] Enhanced communication reliability effect: The entire process, from signal transmission and transmission to post-reception processing, improves the anti-interference ability of communication signals through precise control of time and frequency. In a complex space environment, signals are easily affected by various interference factors and become distorted or erroneous. This technical means of time synchronization and frequency compensation can correct these problems, allowing the communication system to work more stably in the face of interference. For example, during the peak of solar activity, electromagnetic interference in the space environment is enhanced. Communication systems using this technology can better maintain communication reliability and ensure accurate transmission of information. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0035] Figure 1 It is a schematic diagram of the flow of the time synchronization method of space laser communication of the present invention;

[0036] Figure 2 It is a schematic diagram of the space laser communication system of the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0038] In the drawings of the specific embodiments of the present invention, in order to better and more clearly describe the working principles of the various components in the system, the connection relationship of the various parts in the device is shown, which only clearly distinguishes the relative position relationship between the various components, and cannot constitute a limitation on the signal transmission direction, connection sequence and size, dimensions and shape of the components or structures.

[0039] like Figure 1 FIG. 1 is a flow chart of a method for time synchronization of space laser communication of the present invention, and the method for time synchronization of space laser communication comprises the following steps:

[0040] S1. Encode the time signal and modulate the frequency signal to form the original communication signal, which is then transmitted from the ground end to the space end. The signal is transmitted in space and then received by the space end.

[0041] like Figure 2 As shown in the figure, in space laser communication, the transmission and reception of the communication signal of each ground station needs to pass through the laser radar. The laser radar at the transmitting end and the laser radar at the receiving end are not on the same carrier platform, and the transmitting end and the receiving end use independent frequency local oscillator sources, which causes the signal to be affected by synchronization errors during the communication process. At this time, the laser radar at the receiving end and the laser radar at the transmitting end have inconsistent trigger pulse timing, and various factors in space cause time synchronization errors. On the other hand, the signals of the ground station and the space satellite come from different oscillation sources. The fixed frequency deviation and random frequency deviation between the receiving and transmitting frequency local oscillator sources will cause phase errors in the communication signal, further affecting the accuracy of the frequency signal.

[0042] This embodiment divides the time signal into several time nodes, and sets corresponding pulse positions for different time nodes, so that the time signal is encoded by the pulse position, which is more convenient for subsequent time synchronization operations.

[0043] Time node division: Determine the total duration of the time signal, and reasonably divide the entire time signal into several equally spaced or unequally spaced time nodes according to the subsequent synchronization operation accuracy requirements, signal characteristics and other factors. For example, if the total duration of the time signal is T, and it is planned to be divided into n time nodes, it can be divided according to the equal interval Δt = T / n to obtain the time node sequence where t 0 =0,t 1 =Δt,t 2 =2Δt, and so on.

[0044] Pulse position setting: For each divided time node, determine whether to set a pulse at the time node and the specific characteristics of the pulse (such as pulse amplitude, if there are relevant requirements) according to the pre-set coding rules. For example, a simple rule can be set: pulses are set at odd-numbered time nodes, and pulses are not set at even-numbered time nodes. Or according to more complex coding logic, such as according to the binary code corresponding to certain data, set or not set pulses at the corresponding time nodes to represent 0 and 1.

[0045] Coding implementation: According to the above pulse position setting rules, the entire time signal is processed one time node at a time, and finally the time signal is encoded by the pulse position. The obtained encoded signal carries the relevant information of the original time signal by the distribution of pulses at different time nodes, so as to facilitate subsequent operations such as time synchronization.

[0046] Phase modulation is performed on the frequency signal to reflect the change of frequency by changing the phase of the carrier.

[0047] Determine the carrier signal: First, you need to select a suitable carrier signal, which is generally in the form of, where is the carrier amplitude, is the carrier angular frequency, and is the carrier initial phase. The parameters of this carrier signal should be determined according to the actual application scenario, such as transmission channel characteristics, receiving end requirements and other factors.

[0048] Analyze the change of frequency signal: Get the frequency signal to be phase modulated, and set its expression as. It is necessary to clarify the change law of the frequency signal over time. For example, it may be a frequency signal that changes according to a certain function law (such as a sine function, a sawtooth function, etc.), or a complex signal containing multiple frequency components.

[0049] Determine the phase modulation rule: Establish the phase modulation rule based on the relationship between the frequency signal change and the change expected to be reflected through phase modulation. A common simple rule is linear phase modulation, that is, the phase of the carrier changes linearly with the change of the frequency signal, for example, where is a proportional constant whose value can be determined according to the specific modulation requirements, in order to accurately reflect the frequency change through the change of the carrier phase.

[0050] Implement phase modulation: Apply the determined phase modulation rules to the carrier signal to obtain the modulated signal. Taking linear phase modulation as an example, the expression of the modulated signal becomes. In this way, the change of the frequency signal is reflected by changing the phase of the carrier, so that the signal characteristics after modulation can be used in subsequent signal transmission, processing and other links.

[0051] The encoded time signal and the modulated frequency signal are combined onto the laser carrier through a wavelength division multiplexing module to obtain the original communication signal. After the original communication signal is transmitted through space communication, it will be interfered by various media and noise in space, so the original communication signal received at the space end is called the received communication signal.

[0052] S2, the space end demodulates the received communication signal and performs synchronization processing on the obtained received time signal through a time synchronization algorithm;

[0053] When processing and receiving communication signals at the space end, a time synchronization algorithm is used to calculate the time synchronization of the communication. The time synchronization algorithm has the characteristics of strong stability and high reliability. The consistency time synchronization algorithm combines the time data of all or most time nodes to obtain the time benchmark, and will not cause a significant impact on the time synchronization of the entire network due to the failure of individual time nodes or clock confusion. At the same time, the consistency time synchronization algorithm has no hierarchical distinction between each time node, which makes the energy consumption of each node balanced during the time synchronization process, effectively extending the network life of space communication.

[0054] Synchronize each time node to a consistent time, which is called global time. The choice of global time is the combination of all or most node times. The linear correction clock expression is:

[0055]

[0056] Among them, L i (t) is the logical time of node i at time t in receiving the communication signal, is the drift correction parameter of node i in the received communication signal, is the offset correction parameter of node i in the received communication signal, τ i (t) is the hardware time, and V is the set of time nodes.

[0057] The drift correction parameter and the update iterative expression of the drift correction parameter are:

[0058]

[0059] Among them, η is the learning rate and E is the time error function.

[0060] Iteratively update your drift correction parameters based on the algorithm's expression and offset correction parameters

[0061] After multiple iterations of the time synchronization algorithm, the drift correction parameters and cost correction parameters in the above model are updated. The logical time of all time nodes tends to the global time. Global time refers to a consistent time base that all time nodes follow during the time synchronization process. For the consistency time synchronization algorithm, the global time is based on the synthesis of all or most node times. After the time synchronization starts, the node periodically broadcasts the time data packet. The time data packet contains at least the hardware time when the time node sends the data packet. After receiving the time data packet, any time node i records the hardware time τ when the data packet is received i (t), based on the current parameter values ​​and the received time information, the logical time of the node can be calculated, and the logical time can be compared with the time of other nodes or the global time to calculate the time error. The time difference with a reference node or the deviation from the global time obtained by combining the times of multiple nodes can be calculated.

[0062] The space end demodulates the received communication signal to obtain the received time signal. Through the above steps, the logical time obtained by iterating the received time signal is used as the global time, that is, the time we need to obtain time synchronization. We will use this synchronized time signal as the reply time signal.

[0063] S3. The space end demodulates the received communication signal, performs phase error compensation on the obtained frequency signal, and combines the synchronized time signal and the frequency signal after phase error compensation through a multiplexing module to complete the frequency and time synchronization of the communication signal.

[0064] During the communication transmission process, the time of a time node is usually composed of a crystal oscillator and its peripheral circuits. The crystal oscillator is a key component for generating clock signals. The actual oscillation frequency of the crystal oscillator cannot be exactly the same as its nominal frequency. These problems make it impossible to provide absolutely accurate time.

[0065] So the actual crystal oscillator frequency expression is:

[0066] f i (t) = α i (t)f 0 , i∈V

[0067] Among them, α i (t) is the clock drift of communication signal node i at time t, f 0 is the nominal frequency of the crystal oscillator, and V is the set of time nodes.

[0068] After obtaining the actual crystal oscillator frequency, we can eliminate the frequency error caused by the difference in nominal frequency and other factors.

[0069] In order to improve the accuracy and security of space laser communication, the time synchronization of the communication signal should be corrected by compensating the phase synchronization error. Therefore, at time t, the phase expression of the oscillation source of the signal transmitted by the ground transmitter i is:

[0070]

[0071] Among them, i is the transmitting end, j is the receiving end, and f i The ground transmitter is at t 0 The frequency at the moment, f 0 is the nominal frequency, Δf i is the frequency deviation relative to the nominal frequency, is the initial phase of the signal received by the ground receiving end, n i (t) is the phase noise.

[0072] At t+t ij At time , the phase expression of the oscillation source of the synchronization signal received by the spatial receiving end j is:

[0073]

[0074] in, is the initial phase of the signal received by the spatial receiver, n j (t+t ij ) is the spatial receiving end phase noise.

[0075] After receiving the signal in space and on the ground, the signal is modulated and the phase synchronization error compensation expression is obtained:

[0076]

[0077] in, For space end The initial phase of the signal received by the space receiving end after modulation The phase difference, For ground side The initial phase of the signal received by the ground receiving end after modulation The phase difference.

[0078] Since the frequency signal was phase modulated before, we use the phase change of the signal demodulated in the communication signal to reflect the change of the signal frequency, and use phase synchronization error compensation The phase of the demodulated frequency signal of the transmitted communication signal is compensated to eliminate the phase error of the frequency signal during the communication signal transmission, and further reduce the influence of the frequency on the accuracy of the frequency signal.

[0079] The synchronized time signal and the phase error compensated frequency signal in S2 and S3 above are combined onto the laser carrier through the wavelength division multiplexing module. This multiplexing module plays a vital role. It can effectively integrate these two key signals that have been processed differently to complete the frequency and time synchronization of the communication signal.

[0080] The synchronized time signal is highly accurate and stable. In the communication system, time synchronization is the basis for ensuring accurate coordination and interaction between nodes. After synchronization, this time signal can provide an accurate time reference for the communication process, so that communication between different devices can be carried out at the correct time node, avoiding communication confusion and errors caused by time inconsistency.

[0081] The frequency signal after phase error compensation also has higher quality and reliability. The existence of phase error may have an adverse effect on the transmission and processing of the signal, but through effective compensation measures, this impact can be greatly reduced. The compensated frequency signal has been significantly improved in terms of frequency stability, etc., providing a strong guarantee for the high-quality transmission of communication signals.

[0082] By using the phase synchronization error compensation mentioned above, the unestablished phase caused by factors such as non-ideal antenna characteristics and changes in transmission path length can be reduced. The receiving and transmitting phase noise can be extracted more conveniently, and the phase noise can be better removed from the signal, reducing the impact on signal communication transmission.

[0083] By extracting and removing frequency and phase errors, the reliability and security of signals in space laser communications are greatly improved. During the time synchronization process, the impact is also greatly reduced, resulting in lower time delays for communication signals.

[0084] In a preferred embodiment, according to the above-mentioned time synchronization method of space laser communication, space laser communication is not easily affected by electromagnetic interference and radio frequency interference. Compared with traditional radio communication, laser communication has stronger anti-interference ability and can achieve reliable time synchronization in a complex electromagnetic environment.

[0085] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware or any combination thereof. When implemented using software, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the process or function described in the embodiment of the present application is generated in whole or in part. The computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions may be stored in a computer-readable storage medium or transmitted through the computer-readable storage medium. The computer-readable storage medium may be any available medium that a computer can access or a data storage device such as a server or a data center that includes one or more available media integrated. The available medium may be a magnetic medium, (e.g., a floppy disk, a hard disk, a tape), an optical medium (e.g., a DVD), or a semiconductor medium (e.g., a solid state disk (SSD)), etc.

[0086] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A time synchronization method for space laser communication, characterized in that: The steps include: S1. Encode the time signal and modulate the frequency signal to form the original communication signal, and transmit the original communication signal from the ground end to the space end. The signal is transmitted in space and received by the space end. S2, the space end demodulates the received communication signal and performs synchronization processing on the obtained received time signal through a time synchronization algorithm; S3. The space end demodulates the received communication signal, performs phase error compensation on the obtained frequency signal, and combines the synchronized time signal and the frequency signal after phase error compensation through a multiplexing module to complete the frequency and time synchronization of the communication signal.

2. The time synchronization method for space laser communication according to claim 1, characterized in that: In step S2, the linear correction clock expression is: Among them, L i (t) is the logic time of the second time signal node i at time t, is the drift correction parameter of the second time signal node i, is the offset correction parameter of the second time signal node i, τ i (t) is the hardware time, and V is the set of time nodes.

3. The time synchronization method for space laser communication according to claim 2, characterized in that: Drift correction parameters and drift correction parameters The update iteration expression is: Among them, η is the learning rate and E is the time error function.

4. The time synchronization method for space laser communication according to claim 1, characterized in that: In step S3, the actual crystal oscillator frequency f i (t) is expressed as: f i (t)=α i (t)f0, i∈V Among them, α i (t) is the clock drift of the communication signal node i at time t, f0 is the nominal frequency of the crystal oscillator, and V is the set of time nodes; At time t, the phase expression of the oscillation source of the signal transmitted by the ground transmitter i is: f i =f0+Δf i Among them, i is the transmitting end, j is the receiving end, and f i is the frequency of the ground transmitter at time t0, f0 is the nominal frequency, Δf i is the frequency deviation relative to the nominal frequency, is the initial phase, n i (t) is the phase noise; At t+t ij At time , the phase expression of the oscillation source of the synchronization signal received by the spatial receiving end j is: in, is the initial phase of the signal received by the spatial receiver, n j (t+t ij ) is the spatial receiving end phase noise.

5. The time synchronization method for space laser communication according to claim 4, characterized in that: After receiving the signal in space and on the ground, the signal is modulated and the phase synchronization error compensation expression is obtained: in, For space end The initial phase of the signal received by the space receiving end after modulation The phase difference, For ground side The initial phase of the signal received by the ground receiving end after modulation The phase difference.

6. The time synchronization method for space laser communication according to claim 1, characterized in that: In step S1, the time signal is divided into several time nodes, corresponding pulse positions are set for different time nodes, and the time signal is encoded using the pulse positions. The encoded signal obtained carries the original time signal information in the distribution of pulses at different time nodes.

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