High-precision optical communication ranging and positioning method and system suitable for underwater

Abstract

The invention relates to the technical field of ranging and positioning, in particular to a high-precision optical communication ranging and positioning method and system suitable for underwater. The method comprises the following steps: S1, generating and sending a laser signal through a laser; s2, encoding data to be transmitted and modulating the data to a laser signal through a quadrature amplitude modulation scheme for data transmission; s3, emitting the modulated laser signal, aligning the modulated laser signal with a target, and receiving an optical signal returned from target equipment; s4, demodulating the received laser signal based on a coherent demodulation method, and recovering information loaded by the laser signal; and S5, after receiving the demodulated signal, calculating the relative distance by using the distance measurement frame information contained in the signal through a distance measurement positioning unit. According to the invention, the laser communication technology is applied to underwater, and the flight time distance measurement positioning technology is combined, so that the advantages of high precision, high anti-interference performance and low energy consumption are satisfied under the condition of low power consumption.

Description

Technical Field

[0001] The present invention relates to the technical field of distance measurement and positioning, and in particular to a high-precision optical communication distance measurement and positioning method and system suitable for underwater use. Background Art

[0002] In recent years, as the guidance of the concept of building a community with a shared future for the ocean continues to deepen, underwater ranging and positioning has gradually become the focus of attention. Traditional underwater ranging and positioning are usually achieved using inertial navigation systems or acoustic systems. However, the main problems are insufficient accuracy, weak longitudinal resolution, weak anti-interference, and large time cumulative errors. They usually need to frequently surface to access space-based networks or underwater acoustic fixed nodes to correct their own information, which is not applicable in long-term high-precision and high-safety underwater operations. Therefore, a high-precision optical communication ranging and positioning method and system suitable for underwater are provided. Summary of the invention

[0003] The purpose of the present invention is to provide a high-precision optical communication ranging and positioning method and system suitable for underwater, so as to solve the problems of insufficient accuracy, weak longitudinal resolution, weak anti-interference ability and large time accumulation error of traditional underwater ranging and positioning proposed in the above background technology.

[0004] To achieve the above object, the present invention aims to provide a high-precision optical communication ranging and positioning method suitable for underwater, comprising:

[0005] S1, generating and sending a laser signal through a laser;

[0006] S2, encoding the data to be transmitted and modulating it onto the laser signal through an orthogonal amplitude modulation scheme for data transmission;

[0007] S3, transmitting the modulated laser signal and aiming it at the target, while receiving the optical signal returned from the target device;

[0008] S4, demodulating the received laser signal based on a coherent demodulation method to restore the information carried by the laser signal;

[0009] S5. After receiving the demodulated signal, the ranging frame information contained in the signal is used to calculate the relative distance through the ranging positioning unit, and the position coordinates of each node are determined by the single beacon positioning method;

[0010] S6. Synchronize the calculated relative distance and position coordinate information to all nodes in the entire network.

[0011] As a further improvement of the technical solution, in S2, encoding the data to be transmitted and modulating it onto the laser signal to prepare for data transmission includes the following steps:

[0012] S2.1, collect the data to be transmitted and convert the data into binary format;

[0013] S2.2, encoding the binary data using Manchester encoding;

[0014] S2.3, select a quadrature amplitude modulation scheme;

[0015] S2.4. Apply the modulated data signal to the laser signal sent from the laser through the signal modulation unit, so that the output laser signal carries the data information to be transmitted.

[0016] As a further improvement of the technical solution, in S2.3, the orthogonal amplitude modulation scheme is specifically:

[0017] s(t)=I[n]cos(2πf c t+φ)-Q[n]sin(2πf c t+φ)];

[0018] Where s(t) represents the modulated data signal; I[n] represents the in-phase component; n represents the discrete time index; Q[n] represents the orthogonal component; 2πf c t represents the phase of the carrier signal changing with time t; f c represents the carrier frequency; φ represents the initial phase offset; t represents the continuous time variable.

[0019] As a further improvement of the technical solution, in S3, the modulated laser signal is emitted and aimed at the target, and the optical signal returned from the target device is received, including the following steps:

[0020] S3.1. Determine that the laser has been loaded with the modulated data signal and check whether the laser is in normal working condition;

[0021] S3.2, using the optical communication unit to adjust the direction of the laser so that it points to the location of the target device and align the laser beam to the target area;

[0022] S3.3. After receiving the laser signal, the target device reflects a portion of the optical signal, and the optical communication unit is used to receive the optical signal reflected by the target device.

[0023] As a further improvement of the technical solution, in S4, the received laser signal is demodulated based on a coherent demodulation method to restore the information loaded by the laser signal, including the following steps:

[0024] S4.1, converting the received optical signal into an electrical signal through a photodetector;

[0025] S4.2, using a preamplifier to amplify the weak electrical signal output by the photodetector, using a bandpass filter to remove unwanted frequency components, and using an equalizer to restore the signal shape;

[0026] S4.3, using a local oscillator to generate a carrier signal identical to the received signal, multiplying the received signal by the local oscillator signal through a mixer to separate the in-phase (I) component and the quadrature (Q) component of the signal;

[0027] S4.4, sampling the demodulated in-phase component and quadrature component, and determining the constellation point corresponding to each symbol;

[0028] S4.5. Use grayscale coding to reduce the impact of bit errors and convert the points on the constellation diagram back to the original bit stream to achieve recovery of the information carried by the laser signal.

[0029] As a further improvement of the technical solution, in S5, the ranging and positioning unit uses the ranging frame information contained in the signal to calculate the relative distance and determine the position coordinates of each node, including the following steps:

[0030] S5.1. parse the signal frame structure from the received demodulated signal, identify the start and end flags of the signal frame, and find the part containing the ranging information in the signal frame;

[0031] S5.2, obtain a high-precision clock signal through a crystal oscillator;

[0032] S5.3, dividing the high-precision clock signal by a frequency division module to generate a clock signal used by a time interval measurement module;

[0033] S5.4, the time interval measurement module uses the divided clock signal to measure the round trip time of the signal, and records the sending time and receiving time to calculate the time interval;

[0034] S5.5. Use the ranging positioning FPGA module to receive the time interval data, calculate the distance information based on the speed of light according to the time interval, and use the single beacon positioning method to form the position coordinates, use the Bayesian filtering algorithm to update the position estimate, and gradually correct the preliminary position coordinates.

[0035] As a further improvement of the technical solution, in S5.5, the position coordinates are formed using a single beacon positioning method, including the following steps:

[0036] S5.51, given reference point A(x 1 ,y 1 , z 1 ) and the distance d from the target point to the reference point, construct the spherical equation (xx 1 ) 2 +(yy 1 )2 +(zz 1 ) 2 =d 2 ;

[0037] S5.52. The set of all possible positions is a sphere, i.e., all points that are at a distance d from the reference point A. S5.53. If there is other information, the range of possible positions can be further narrowed.

[0038] As a further improvement of the technical solution, in S5.5, the Bayesian filtering algorithm is:

[0039] Covariance prediction:

[0040]

[0041] Covariance update:

[0042]

[0043] in, represents the predicted covariance matrix; F u represents the Jacobian matrix; represents the state covariance matrix at the u-1th moment; Q u The covariance matrix represents the process noise and describes the uncertainty in the state transition process; represents the updated covariance matrix, I represents the identity matrix; K u represents the Kalman gain matrix; u represents the time vector index.

[0044] As a further improvement of the technical solution, in S6, synchronizing the calculated relative distance and position coordinate information to all nodes in the entire network includes the following steps:

[0045] S6.1. Packing the calculated relative distance and position coordinate information into a data packet, and ensuring that the data packet is encoded in a unified format;

[0046] S6.2. Select acoustic communication as the communication protocol and set the transmission parameters;

[0047] S6.3, the signal synchronization unit sends a data packet through the selected communication protocol and broadcasts the data packet to all nodes. After sending the data packet, it waits for confirmation information from the receiving end. If no confirmation information is received, the data packet is resent;

[0048] S6.4. The time of all nodes is synchronized through the time synchronization protocol, and the distributed consensus algorithm Raft is used to ensure data consistency.

[0049] On the other hand, the present invention provides a high-precision optical communication ranging and positioning system suitable for underwater use, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement any one of the high-precision optical communication ranging and positioning methods suitable for underwater use described above.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] 1. This high-precision optical communication ranging positioning method and system suitable for underwater uses laser communication technology underwater, and combines it with time-of-flight ranging positioning technology to simultaneously meet the advantages of high precision, high anti-interference, and low energy consumption under low power consumption conditions; by using laser signals and coherent demodulation technology, high-speed data transmission in underwater environments is achieved. In addition, by using the ranging frame information contained in the signal, combined with the time interval measurement module and the single beacon positioning method, the relative distance between targets can be accurately calculated, and the position coordinates of each node can be determined. This method not only improves the accuracy of positioning, but also enhances the robustness and reliability of the system, so that stable and accurate positioning can be achieved in complex and changeable underwater environments.

[0052] 2. This high-precision optical communication ranging and positioning method and system suitable for underwater use a two-way ranging and positioning method to avoid the time error caused by signal processing from the node, thereby improving the accuracy of the system's ranging and positioning; by packaging the calculated position coordinates and relative distance information into data packets and broadcasting them using an acoustic communication protocol, it is ensured that all nodes in the entire network can obtain the latest position information in a timely manner. At the same time, the use of time synchronization protocols and distributed consensus algorithms (such as the Raft algorithm) can effectively avoid data processing errors caused by time asynchrony, ensure the consistency and integrity of data within the network, and thus improve the coordination and operational efficiency of the overall system. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 is a flow chart of the overall method of the present invention;

[0054] Figure 2 This is a high-precision ranging and positioning method and system flow chart applicable to underwater in the present invention;

[0055] Figure 3 It is a structural block diagram of the ranging and positioning unit system of the present invention. DETAILED DESCRIPTION

[0056] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0057] Example 1: Please refer to Figure 1-3 As shown, this embodiment provides a high-precision optical communication ranging and positioning method suitable for underwater, comprising the following steps:

[0058] S1, generate and send laser signals through laser, which can provide a high-speed data transmission channel in underwater environment;

[0059] In this embodiment, the role of the laser is to generate a carrier of a communication signal so that the signal can be loaded onto the carrier for transmission. The laser can be used to send laser signals and can provide a communication channel for underwater high-speed transmission.

[0060] S2, encoding the data to be transmitted and modulating it onto the laser signal through an orthogonal amplitude modulation scheme for data transmission;

[0061] In this embodiment, encoding and modulating the data to be transmitted onto the laser signal in preparation for data transmission includes the following steps:

[0062] S2.1. Collect the data to be transmitted, including text, images, sounds, etc., and convert the data into binary format;

[0063] S2.2, binary data is encoded by Manchester encoding, the purpose of encoding is to improve the transmission efficiency and reliability of the signal;

[0064] Among them, Manchester encoding method realizes the embedding of synchronous clock signal by mapping each bit in the data stream to two different voltage levels;

[0065] S2.3, select a quadrature amplitude modulation scheme to map the encoded data onto a carrier signal, the modulation process involves changing a parameter of the carrier signal (such as amplitude, frequency or phase) to represent different data symbols;

[0066] Among them, the orthogonal amplitude modulation scheme can transmit multiple bits of information simultaneously on the same carrier frequency. By modulating the amplitude and phase of the carrier signal, more information can be transmitted within a given bandwidth. This not only improves the data transmission rate, but also effectively utilizes limited bandwidth resources, which is particularly important for underwater communications. Because in the underwater environment, due to the absorption and scattering effects, the propagation distance of the optical signal is limited, and the bandwidth resources are relatively tight; the orthogonal amplitude modulation scheme can increase the data rate by selecting an appropriate modulation order (such as QPSK, 16-QAM, 64-QAM, etc.) when the signal quality allows, while maintaining sufficient signal quality to resist noise and interference. In the underwater environment, due to signal attenuation and multipath effects caused by various factors, this feature of the orthogonal amplitude modulation scheme can ensure the reliability and accuracy of data transmission; the orthogonal amplitude modulation scheme is specifically:

[0067] s(t)=I[n]cos(2πf c t+φ)-Q[n]sin(2πf c t+φ)];

[0068] Where s(t) represents the modulated data signal, i.e., the signal strength at time t; I[n] represents the in-phase component, i.e., a part of the data signal at time n, expressed as a real number; n represents the discrete time index; Q[n] represents the orthogonal component, representing the other part of the data signal at time n; 2πf c t represents the phase of the carrier signal changing with time t; f c represents the carrier frequency; φ represents the initial phase offset; t represents the continuous time variable;

[0069] S2.4, applying the modulated data signal to the laser signal sent by the laser through the signal modulation unit, so that the output laser signal carries the data information to be transmitted;

[0070] Furthermore, the signal modulation unit can demodulate the signal detected by the detector and restore the information loaded by the laser, and it can load the external signal onto the laser carrier.

[0071] S3, transmitting the modulated laser signal and aiming it at the target, while receiving the optical signal returned from the target device;

[0072] In this embodiment, the modulated laser signal is emitted and aimed at the target, and the optical signal returned from the target device is received, including the following steps:

[0073] S3.1. Determine that the laser has been loaded with the modulated data signal and check whether the laser is in normal working condition;

[0074] S3.2, using the optical communication unit to adjust the direction of the laser so that it points to the location of the target device and align the laser beam to the target area;

[0075] Among them, the optical communication unit can align and capture the transmitted laser, and at the same time receive the optical signal emitted by the other end to ensure the stability of the communication link. It can send the laser carrying the signal to the other end and receive the communication signal transmitted back by the other end to establish a stable communication link;

[0076] S3.3. After receiving the laser signal, the target device reflects a portion of the optical signal, and the optical communication unit is used to receive the optical signal reflected by the target device.

[0077] S4, demodulating the received laser signal based on a coherent demodulation method to restore the information carried by the laser signal;

[0078] In this embodiment, the received laser signal is demodulated based on a coherent demodulation method to restore the information carried by the laser signal, including the following steps:

[0079] S4.1, converting the received optical signal into an electrical signal through a photodetector;

[0080] S4.2, use a preamplifier to amplify the weak electrical signal output by the photodetector, use a bandpass filter to remove unwanted frequency components, and use an equalizer to restore the signal shape and compensate for the distortion in transmission;

[0081] S4.3, using a local oscillator to generate a carrier signal identical to the received signal, multiplying the received signal by the local oscillator signal through a mixer to separate the in-phase (I) component and the quadrature (Q) component of the signal;

[0082] S4.4, sampling the demodulated in-phase component and quadrature component, and determining the constellation point corresponding to each symbol;

[0083] S4.5. Use grayscale coding to reduce the impact of bit errors and convert the points on the constellation diagram back to the original bit stream to achieve recovery of the information carried by the laser signal.

[0084] S5. After receiving the demodulated signal, the ranging frame information contained in the signal is used to calculate the relative distance through the ranging positioning unit, and the position coordinates of each node are determined by the single beacon positioning method;

[0085] In this embodiment, the ranging and positioning unit can communicate signal marking ranging frames and perform ranging and positioning through the ranging and positioning module. The ranging and positioning unit includes a ranging and positioning FPGA module, a crystal oscillator, a time interval measurement module, and a frequency division module. The system structure of the ranging and positioning unit is as follows: Figure 3 As shown;

[0086] The relative distance is calculated by the ranging positioning unit using the ranging frame information contained in the signal, and the position coordinates of each node are determined, including the following steps:

[0087] S5.1. parse the signal frame structure from the received demodulated signal, identify the start and end flags of the signal frame, and find the part containing the ranging information in the signal frame. The ranging frame contains information such as a timestamp, a sequence number, and an identifier;

[0088] S5.2. A high-precision clock signal is obtained through a crystal oscillator. The clock signal has a stable frequency and low phase noise, providing a reference for subsequent time measurements;

[0089] S5.3, dividing the high-precision clock signal through the frequency division module to generate a clock signal used by the time interval measurement module. The frequency division module can divide the clock signal provided by the crystal oscillator into a higher-frequency clock signal to improve the accuracy of the time interval measurement module;

[0090] S5.4, the time interval measurement module uses the divided clock signal to measure the round trip time of the signal, and records the sending time and receiving time to calculate the time interval;

[0091] S5.5, using the ranging positioning FPGA module to receive the time interval data, calculating the distance information based on the speed of light according to the time interval, and using the single beacon positioning method to form the position coordinates, using the Bayesian filtering algorithm to update the position estimate, and gradually correcting the preliminary position coordinates;

[0092] Among them, the single beacon positioning method only requires one fixed reference point (beacon). Compared with the positioning system of multiple beacons or multiple base stations, it reduces the demand for hardware equipment and simplifies the installation and maintenance of the system. In underwater environments, reducing the number of equipment means reducing the deployment cost and complexity, and also reducing potential failure points; the single beacon positioning method can be used in combination with other sensor data (such as angle information, accelerometer, magnetometer, etc.). By integrating multiple information sources, even if there is only one fixed reference point, the accuracy and reliability of positioning can be improved. This method can still provide effective positioning services when some information is missing; since only one reference point is needed to complete the positioning task, the energy consumption of the entire system is low, which is especially important for underwater monitoring equipment that runs for a long time. In addition, reducing the deployment of additional beacons also directly reduces the overall cost of the system; using the single beacon positioning method to form position coordinates includes the following steps:

[0093] S5.51, given reference point A(x 1 ,y 1 , z 1 ) and the distance d from the target point to the reference point, construct the spherical equation (xx 1 )2 +(yy 1 ) 2 +(zz 1 ) 2 =d 2 ;

[0094] S5.52. The set of all possible positions is a sphere, i.e., all points that are at a distance d from the reference point A. S5.53. If there is other information (such as angle information, rough position estimates of other reference points, etc.), the possible position range can be further narrowed. For example, if the approximate orientation of the target point is known (such as in a certain direction), the search range can be further narrowed in combination with the direction information;

[0095] Furthermore, the Bayesian filtering algorithm gradually corrects the initial position estimate by predicting the next state and correcting it according to the new observation data, making it closer to the true value; the Bayesian filtering algorithm can adaptively adjust its estimate of the system state according to the new observation data, which means that even if the environmental conditions change, the algorithm can adapt to these changes and continue to provide reliable estimates; the Bayesian filtering algorithm can integrate data from multiple sensors and use their complementarity to improve positioning accuracy. For example, in an underwater environment, optical communication signals may be affected by absorption and scattering, and by fusing data from inertial sensors such as accelerometers and gyroscopes, the accuracy of position estimation can be further improved; the Bayesian filtering algorithm can dynamically update the state estimate, and even in a rapidly changing environment, it can provide the latest position information in real time; the Bayesian filtering algorithm is:

[0096] Covariance prediction:

[0097]

[0098] Covariance update:

[0099]

[0100] in, represents the predicted covariance matrix; F u represents the Jacobian matrix; represents the state covariance matrix at the u-1th moment; Q u The covariance matrix represents the process noise and describes the uncertainty in the state transition process; represents the updated covariance matrix, I represents the identity matrix; K u represents the Kalman gain matrix; u represents the time vector index.

[0101] S6. Synchronize the calculated relative distance and position coordinate information to all nodes in the entire network (i.e., master nodes and slave nodes);

[0102] In this embodiment, the calculated relative distance and position coordinate information is synchronized to all nodes in the entire network, including the following steps:

[0103] S6.1. Pack the calculated relative distance and position coordinate information into a data packet, which includes information such as node ID, timestamp, position coordinate, relative distance, etc., and ensure that the data packet is encoded in a unified format to facilitate parsing by the receiving end;

[0104] S6.2. Select acoustic communication as the communication protocol and set transmission parameters such as transmission rate, retransmission strategy, error detection and correction, etc.

[0105] Among them, in the underwater environment, the propagation ability of electromagnetic waves (such as radio waves, microwaves, etc.) is greatly limited. In particular, as the frequency increases, the signal will be quickly absorbed by the water body. In contrast, the propagation loss of sound waves in water is small and the penetration ability is stronger. It can effectively penetrate deeper water layers and realize long-distance communication. Although optical communication can provide high-speed data transmission within a short distance, its effective communication distance is limited because light is easily affected by absorption and scattering when propagating in water. Therefore, when it is necessary to cover a larger area or deeper waters, acoustic communication can be used as a supplementary means in combination with optical communication to form a complete underwater communication network.

[0106] S6.3, the signal synchronization unit sends a data packet through the selected communication protocol to ensure that the data packet can reach all nodes in the network, and broadcasts the data packet to all nodes. After sending the data packet, it waits for confirmation information from the receiving end. If no confirmation information is received, the data packet is resent;

[0107] Among them, the signal synchronization unit can synchronize the distance and position information received by the slave node with the master node;

[0108] S6.4. The time of all nodes is synchronized through the time synchronization protocol. Time synchronization helps to correctly sort and process data packets, and the distributed consensus algorithm Raft is used to ensure data consistency.

[0109] In this embodiment, the specific workflow (workflow as shown in FIG. Figure 2The master node loads the laser beam on the laser with a modulated signal, where the modulation mode is not limited, and transmits it to the ranging and positioning unit after modulation; the ranging and positioning unit loads the ranging frame to the frame header of the communication signal frame, marks the frame header, and transmits the communication signal with the ranging frame after modulation to the optical communication unit; the signal is received by the optical communication unit of the slave node through the alignment and capture of the galvanometer, and the master and slave nodes establish two-way communication; after the slave node receives the signal, the information passes through the ranging and positioning unit of the slave node, and immediately returns the ranging frame signal after receiving the marked ranging frame signal; after the master node ranging and positioning unit receives the marked return ranging frame, it obtains the high-precision distance information of the master and slave nodes through the measurement of its own precise clock and time interval measurement module, and obtains the position information according to the positioning method through the ranging and positioning FPGA module; the master node again transmits the distance and position information to the slave node through the optical communication link, which is demodulated by the slave node; the demodulated signal is sent to the information synchronization unit, and at this point, the slave node also receives the distance and position information between itself and the master node.

[0110] This embodiment provides a high-precision optical communication ranging and positioning system suitable for underwater use, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement any one of the above-mentioned high-precision optical communication ranging and positioning methods suitable for underwater use.

[0111] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and the above embodiments and descriptions are only preferred examples of the present invention, and are not intended to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A high-precision optical communication ranging and positioning method suitable for underwater, characterized in that: The following steps are involved: S1, generating and sending a laser signal through a laser; S2, encoding the data to be transmitted and modulating it onto the laser signal through an orthogonal amplitude modulation scheme for data transmission; S3, transmitting the modulated laser signal and aiming it at the target, while receiving the optical signal returned from the target device; S4, demodulating the received laser signal based on a coherent demodulation method to restore the information carried by the laser signal; S5. After receiving the demodulated signal, the ranging frame information contained in the signal is used to calculate the relative distance through the ranging positioning unit, and the position coordinates of each node are determined by the single beacon positioning method; S6. Synchronize the calculated relative distance and position coordinate information to all nodes in the entire network.

2. The high-precision optical communication ranging and positioning method suitable for underwater use according to claim 1, characterized in that: In S2, the data to be transmitted is encoded and modulated onto the laser signal, and preparation for data transmission includes the following steps: S2.1, collect the data to be transmitted and convert the data into binary format; S2.2, encoding the binary data using Manchester encoding; S2.3, select a quadrature amplitude modulation scheme; S2.

4. Apply the modulated data signal to the laser signal sent from the laser through the signal modulation unit, so that the output laser signal carries the data information to be transmitted.

3. The high-precision optical communication ranging and positioning method suitable for underwater use according to claim 2, characterized in that: In S2.3, the orthogonal amplitude modulation scheme is specifically: s(t)=I[n]cos(2πf c t+φ)-Q[n]sin(2πf c t+φ)]; Where s(t) represents the modulated data signal; I[n] represents the in-phase component; n represents the discrete time index; Q[n] represents the orthogonal component; 2πf c t represents the phase of the carrier signal changing with time t; f c represents the carrier frequency; φ represents the initial phase offset; t represents the continuous time variable.

4. The high-precision optical communication ranging and positioning method suitable for underwater use according to claim 3, characterized in that: In S3, the modulated laser signal is emitted and aimed at the target, and the optical signal returned from the target device is received, including the following steps: S3.

1. Determine that the laser has been loaded with the modulated data signal and check whether the laser is in normal working condition; S3.2, using the optical communication unit to adjust the direction of the laser so that it points to the location of the target device and align the laser beam to the target area; S3.

3. After receiving the laser signal, the target device reflects a portion of the optical signal, and the optical communication unit is used to receive the optical signal reflected by the target device.

5. The high-precision optical communication ranging and positioning method applicable to underwater according to claim 4, characterized in that: In S4, the received laser signal is demodulated based on a coherent demodulation method to restore the information carried by the laser signal, including the following steps: S4.1, converting the received optical signal into an electrical signal through a photodetector; S4.2, using a preamplifier to amplify the weak electrical signal output by the photodetector, using a bandpass filter to remove unwanted frequency components, and using an equalizer to restore the signal shape; S4.3, using a local oscillator to generate a carrier signal identical to the received signal, multiplying the received signal by the local oscillator signal through a mixer to separate the in-phase (I) component and the quadrature (Q) component of the signal; S4.4, sampling the demodulated in-phase component and quadrature component, and determining the constellation point corresponding to each symbol; S4.

5. Use grayscale coding to reduce the impact of bit errors and convert the points on the constellation diagram back to the original bit stream to achieve recovery of the information carried by the laser signal.

6. The high-precision optical communication ranging and positioning method applicable to underwater according to claim 5, characterized in that: In S5, the ranging frame information contained in the signal is used by the ranging positioning unit to calculate the relative distance and determine the position coordinates of each node, including the following steps: S5.

1. parse the signal frame structure from the received demodulated signal, identify the start and end flags of the signal frame, and find the part containing the ranging information in the signal frame; S5.2, obtain a high-precision clock signal through a crystal oscillator; S5.3, dividing the high-precision clock signal by a frequency division module to generate a clock signal used by a time interval measurement module; S5.4, the time interval measurement module uses the divided clock signal to measure the round trip time of the signal, and records the sending time and receiving time to calculate the time interval; S5.

5. Use the ranging positioning FPGA module to receive the time interval data, calculate the distance information based on the speed of light according to the time interval, and use the single beacon positioning method to form the position coordinates, use the Bayesian filtering algorithm to update the position estimate, and gradually correct the preliminary position coordinates.

7. The high-precision optical communication ranging and positioning method applicable to underwater according to claim 6, characterized in that: In S5.5, the position coordinates are formed using a single beacon positioning method, comprising the following steps: S5.

51. Given the reference point A (x1, y1, z1) and the distance d from the target point to the reference point, construct the spherical equation (x-x1) 2 +(y-y1) 2 +(z-z1) 2 =d 2 ; S5.

52. The set of all possible positions is a sphere, i.e., all points that are at a distance d from the reference point A. S5.

53. If there is other information, the range of possible positions can be further narrowed.

8. The high-precision optical communication ranging and positioning method applicable to underwater according to claim 7, characterized in that: In S5.5, the Bayesian filtering algorithm is: Covariance prediction: Covariance update: in, represents the predicted covariance matrix; F u represents the Jacobian matrix; represents the state covariance matrix at the u-1th moment; Q u The covariance matrix represents the process noise and describes the uncertainty in the state transition process; represents the updated covariance matrix, I represents the identity matrix; K u represents the Kalman gain matrix; u represents the time vector index.

9. The high-precision optical communication ranging and positioning method applicable to underwater according to claim 8, characterized in that: In S6, the calculated relative distance and position coordinate information is synchronized to all nodes in the entire network, including the following steps: S6.

1. Packing the calculated relative distance and position coordinate information into a data packet, and ensuring that the data packet is encoded in a unified format; S6.

2. Select acoustic communication as the communication protocol and set the transmission parameters; S6.3, the signal synchronization unit sends a data packet through the selected communication protocol and broadcasts the data packet to all nodes. After sending the data packet, it waits for confirmation information from the receiving end. If no confirmation information is received, the data packet is resent; S6.

4. The time of all nodes is synchronized through the time synchronization protocol, and the distributed consensus algorithm Raft is used to ensure data consistency.

10. A high-precision optical communication ranging and positioning system suitable for underwater use, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: The processor executes a computer program to implement the high-precision optical communication ranging and positioning method suitable for underwater use as described in any one of claims 1 to 9.

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