Underwater AUV blue laser-SiPM detection equalization communication system and method

Abstract

The invention relates to the technical field of underwater communication, in particular to an underwater AUV (Autonomous Underwater Vehicle) blue laser-SiPM detection equalization communication system and method, and particularly relates to a signal processing method applying a linear and nonlinear equalization technology. The underwater AUV blue light laser communication system integrates four modules of optical communication transmitting and receiving, signal processing and balancing, and underwater positioning and tracking. The transmitting module generates a blue laser signal, the receiving module converts the blue laser signal into an electric signal, the signal processing module suppresses distortion, and the positioning and tracking module adjusts the transmitting direction in real time to ensure signal alignment. According to the system, the underwater optical communication transmission distance is remarkably increased, and the underwater optical communication transmission distance can reach 250 meters under the standard seawater condition and is far beyond that of a traditional system. And meanwhile, the data transmission rate is greatly improved, and the high-bandwidth application requirement is met. The underwater communication performance is optimized through the overall design, and an efficient and stable communication solution is provided for deep sea detection, underwater robots and other high-requirement applications.

Description

Technical Field

[0001] The present invention relates to the field of underwater communication technologies, and particularly to an underwater AUV blue light laser - SiPM detection and equalization communication system and method, especially an underwater optical communication system based on blue light laser emission and silicon photomultiplier (SiPM) reception, as well as a signal processing method applying linear and non - linear equalization technologies. Background Art

[0002] With the continuous growth of underwater application requirements, especially in the fields of ocean exploration, resource development, environmental monitoring, and autonomous underwater vehicles (AUVs), a breakthrough in underwater communication technology has become particularly urgent. Traditional underwater communication mainly relies on acoustic communication and radio frequency (RF) communication technologies. Although these technologies can work effectively over short distances, they have significant limitations in terms of data transmission rate, communication latency, and the ability to adapt to complex environments.

[0003] Acoustic communication technology is the current mainstream method for underwater communication, but its transmission rate is usually limited to a few kbps to dozens of kbps, and there is a relatively large transmission delay. In addition, the multipath effect and Doppler effect of sound waves in water can also lead to a decline in signal quality. The transmission distance of RF communication in water is even more limited, usually only working effectively within a range of several meters to dozens of meters, and is significantly affected by the characteristics of the water body.

[0004] In contrast, underwater wireless optical communication (UWOC), with its high bandwidth, low latency, and strong anti - interference ability, is gradually becoming a key technology for future underwater communication systems. However, the practical application of underwater optical communication still faces many challenges, mainly including:

[0005] 1. Underwater channel attenuation problem: The absorption and scattering of light by water will cause a sharp attenuation of the optical signal intensity, especially in turbid waters, where the attenuation effect is more significant.

[0006] 2. Non - linear distortion problem: Due to the complexity of the water body composition and the non - linear effects caused by the high - intensity propagation of optical signals, the received signal is often accompanied by severe distortion.

[0007] 3. Light source power limitation: Traditional light sources have limited power and it is difficult to achieve long - distance transmission.

[0008] 4. Insufficient receiving sensitivity: Conventional photodetectors have limited response capabilities to weak optical signals.

[0009] 5. Alignment difficulty: In the underwater environment, especially during the movement of AUVs, it is very difficult to maintain the precise alignment of the light beam and the receiver.

[0010] The prior art mainly focuses on improving the light source power, detector sensitivity, and optimizing signal processing algorithms to overcome the above challenges. However, there is currently no comprehensive solution that can address all of the above problems simultaneously. In particular, the technology for achieving long-distance and high-speed underwater optical communication is still insufficient.

[0011] Therefore, developing an underwater optical communication system that can effectively overcome underwater channel attenuation, nonlinear distortion, and has high stability and reliability is of great significance for improving the communication capabilities of underwater unmanned vehicles. Summary of the Invention

[0012] The present invention aims to solve the technical bottlenecks of existing underwater optical communication systems in long-distance transmission and high data rate, and provides an underwater AUV blue laser - SiPM detection and equalization communication system and method that can effectively overcome underwater channel attenuation and nonlinear distortion.

[0013] The present invention proposes an underwater AUV blue laser - SiPM detection and equalization communication system, including:

[0014] An optical communication transmitting module, configured to generate and transmit a blue laser signal;

[0015] An optical communication receiving module, configured to receive the blue laser signal and convert it into an electrical signal;

[0016] A signal processing and equalization module, electrically connected to the optical communication receiving module, configured to process the electrical signal to suppress signal distortion; and an underwater positioning and tracking module, connected to the optical communication transmitting module and the optical communication receiving module, configured to adjust the emission direction of the optical communication transmitting module in real time to maintain the alignment of the blue laser signal with the optical communication receiving module.

[0017] Preferably, the optical communication transmitting module includes:

[0018] A multi-channel cascaded laser diode array, including a plurality of blue laser diodes;

[0019] A beam combining unit, connected to the multi-channel cascaded laser diode array, configured to combine the output beams of the plurality of blue laser diodes into a single beam; and a modulation unit, connected to the multi-channel cascaded laser diode array, configured to perform on-off keying modulation on the blue laser diodes.

[0020] Preferably, the multi-channel cascaded laser diode array includes 8 blue laser diodes with a wavelength of 450 nm, and the power of the single beam reaches 26.2 W.

[0021] Preferably, the optical communication receiving module includes:

[0022] A high-precision optical lens for focusing the blue laser signal;

[0023] A silicon photomultiplier tube detector optically coupled to the high-precision optical lens for converting the focused blue laser signal into an electrical signal; and a pre-amplification unit electrically connected to the silicon photomultiplier tube detector for amplifying the electrical signal.

[0024] Preferably, the signal processing and equalization module includes:

[0025] A linear equalizer for performing inter-symbol interference suppression processing on the electrical signal and generating a pre-processed signal;

[0026] A downsampling unit connected to the linear equalizer for performing downsampling processing on the pre-processed signal; and an artificial neural network equalizer connected to the downsampling unit for performing non-linear distortion suppression processing on the downsampled signal.

[0027] Preferably, the linear equalizer uses the least mean square error algorithm for coefficient optimization.

[0028] Preferably, the artificial neural network equalizer includes two hidden layers, the first hidden layer contains 10 neurons, and the second hidden layer contains 1 neuron.

[0029] Preferably, the underwater positioning and tracking module includes:

[0030] A camera unit for capturing an image of the beam position;

[0031] A laser spot detector for detecting the beam position;

[0032] A position calculation unit connected to the camera unit and the laser spot detector for calculating a position deviation based on the beam position image and the beam position; and an automatic adjustment unit connected to the position calculation unit for adjusting the emission direction of the optical communication transmitting module according to the position deviation.

[0033] Preferably, it further includes:

[0034] A data format conversion module connected to the optical communication transmitting module and the signal processing and equalization module for converting the input data into a signal format suitable for on-off keying modulation at the transmitting end, and restoring the equalized signal to the original data format at the receiving end.

[0035] An underwater AUV blue laser - SiPM detection and equalization communication method, including the following steps:

[0036] Generating a blue laser signal through a multi-channel cascaded laser diode array;

[0037] Use the beam combination technique to combine the blue laser signals into a single beam and emit it; are the proportional, integral, and differential coefficients.

[0038] Focus the received blue laser signals through a high-precision optical lens;

[0039] Use a silicon photomultiplier tube detector to convert the focused blue laser signals into electrical signals;

[0040] Perform inter-symbol interference suppression processing on the electrical signals through a linear equalizer to obtain preprocessed signals;

[0041] Perform downsampling processing on the preprocessed signals;

[0042] Use an artificial neural network equalizer to perform non-linear distortion suppression processing on the downsampled signals; and monitor the beam position in real time and automatically adjust the emission direction to maintain the precise alignment of the blue laser signals with the receiving end.

[0043] Through the combination of a multi-channel cascaded laser diode array and a silicon photomultiplier tube detector, the double-layer equalization architecture of a linear equalizer and an artificial neural network equalizer, and an accurate underwater positioning and tracking system, the present invention achieves the following remarkable effects:

[0044] 1. Significantly improves the transmission distance of underwater optical communication, reaching 250 meters under standard seawater conditions, far exceeding the performance of traditional underwater optical communication systems;

[0045] 2. Greatly increases the data transmission rate to meet the requirements of high-bandwidth applications;

[0046] 3. Effectively overcomes the influence of underwater channel attenuation and non-linear distortion, improving the communication stability and reliability;

[0047] 4. Achieves precise beam alignment during the movement of the AUV, ensuring the continuity and stability of the communication link;

[0048] 5. Through low-complexity signal processing algorithms, while ensuring performance, reduces the system power consumption and computational resource occupancy. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 Is a schematic diagram of the overall architecture of the system of the present invention;

[0050] Figure 2 Is a schematic diagram of the structure of the optical communication transmitting module of the present invention;

[0051] Figure 3 Is a schematic diagram of the structure of the optical communication receiving module of the present invention;

[0052] Figure 4Schematic diagram of the signal processing and equalization module of the present invention;

[0053] Figure 5 Schematic diagram of the underwater positioning and tracking module of the present invention;

[0054] Figure 6 Flowchart of the communication method of the present invention. Detailed implementation manners

[0055] Please refer to the appendix Figure 1-6 and the present invention will be further described in detail below in conjunction with specific embodiments and the drawings.

[0056] Embodiment 1: Overall system architecture

[0057] Please refer to Figure 1 The underwater AUV blue light laser - SiPM detection and equalization communication system provided by the present invention includes: an optical communication transmitting module 1, an optical communication receiving module 2, a signal processing and equalization module 3, and an underwater positioning and tracking module 4.

[0058] The optical communication transmitting module 1 is used to generate and transmit a blue light laser signal. Preferably, this module adopts a multi - channel cascading technology to realize the generation and transmission of high - power optical signals to overcome the strong attenuation effect of the underwater channel.

[0059] The optical communication receiving module 2 is used to receive the blue light laser signal and convert it into an electrical signal. The present invention selects a super - sensitive silicon photomultiplier (SiPM) detector as the core receiving element, combined with a high - precision optical system, significantly improving the receiving ability of weak optical signals.

[0060] The signal processing and equalization module 3 is electrically connected to the optical communication receiving module 2 and is used to process the electrical signal to suppress signal distortion. This module innovatively combines a linear equalizer and an artificial neural network equalizer to form a two - layer equalization architecture, effectively dealing with the inter - symbol interference (ISI) and non - linear distortion problems.

[0061] The underwater positioning and tracking module 4 is connected to the optical communication transmitting module 1 and the optical communication receiving module 2 and is used to adjust the emission direction of the optical communication transmitting module 1 in real time to keep the blue light laser signal aligned with the optical communication receiving module 2. This module solves the problem of beam alignment in the AUV motion environment and ensures the stability of the communication link.

[0062] In addition, the present invention may further include a data format conversion module 5, which is connected to the optical communication transmitting module 1 and the signal processing and equalization module 3 and is used to convert the input data into a signal format suitable for on - off keying modulation at the sending end and restore the equalized signal to the original data format at the receiving end.

[0063] In a specific example, the system is installed between two underwater unmanned vehicles. One AUV carries the transmitting module, and the other carries the receiving module to achieve high-speed point-to-point data transmission. Under standard seawater conditions (the attenuation coefficient at a wavelength of 450 nm is approximately ), stable communication over 200 meters can be achieved, the data transmission rate can reach 100 Mbps, and the bit error rate is lower than 10 -6 .

[0064] Example 2: Optical communication transmitting module

[0065] Please refer to Figure 2 , the optical communication transmitting module 1 of the present invention includes: a multi-channel cascaded laser diode array 11, a beam combining unit 12, and a modulation unit 13.

[0066] The multi-channel cascaded laser diode array 11 includes a plurality of blue laser diodes for generating high-power blue laser signals. The present invention selects blue laser based on its low attenuation characteristics in seawater. Especially in clear seawater, blue light with a wavelength of 450 nm has the best transmission characteristics.

[0067] The beam combining unit 12 is connected to the multi-channel cascaded laser diode array 11 for combining the output beams of the plurality of blue laser diodes into a single beam. This unit uses precision optical elements to ensure that the combined beam has good spatial coherence and directivity, minimizing the loss of light energy.

[0068] The modulation unit 13 is connected to the multi-channel cascaded laser diode array 11 for performing on-off keying (OOK) modulation on the blue laser diodes. OOK modulation is a simple and effective modulation method, characterized by simple implementation and strong anti-interference ability, and is particularly suitable for the underwater communication environment.

[0069] In a preferred embodiment of the present invention, the multi-channel cascaded laser diode array 11 includes 8 blue laser diodes with a wavelength of 450 nm. Through carefully designed beam combining technology, the power of the finally synthesized single beam can reach 26.2 W. This high-power output is the key to achieving long-distance underwater optical communication.

[0070] Specifically, the output power of each laser diode is approximately 3.5 W. After beam combination, considering the combination loss of about 10%, the final output power is calculated as follows:

[0071] ,

[0072] Among them, is the final output power, is the output power of a single laser diode, is the number of laser diodes, is the beam combination loss. Substituting the values gives:

[0073] ,

[0074] In actual tests, the output power of the system can reach 26.2 W, slightly higher than the theoretical calculated value, mainly because the performance of the actually used laser diodes is slightly better than the nominal value.

[0075] The modulation unit 13 uses a high-speed switching circuit to achieve OOK modulation, and the modulation rate can reach 200 Mbps. The modulation depth is optimally set to 85%, and this parameter is determined based on a large number of pool experiments, avoiding signal distortion caused by overmodulation while ensuring modulation efficiency.

[0076] Embodiment 3: Optical communication receiving module

[0077] Please refer to Figure 3 , the optical communication receiving module 2 of the present invention includes: a high-precision optical lens 21, a silicon photomultiplier detector 22, and a preamplification unit 23.

[0078] The high-precision optical lens 21 is used to focus the received blue laser signal. The lens adopts a multi-layer coating process and has a light transmittance as high as 98% near the wavelength of 450 nm, effectively capturing the weak optical signal attenuated during transmission. The aperture of the lens is designed to be 100 mm and the focal length is 150 mm, providing a large light collection area and appropriate focusing effect.

[0079] The silicon photomultiplier detector 22 is optically coupled with the high-precision optical lens 21 and is used to convert the focused blue laser signal into an electrical signal. The SiPM detector is one of the core innovations of the present invention. It has extremely high photoelectric conversion efficiency and sensitivity, and the photoelectric conversion efficiency at the wavelength of 450 nm is as high as 40%, far higher than that of traditional photodiodes.

[0080] In the present invention, the selected SiPM detector has the following key parameters:

[0081] Effective detection area: ;

[0082] Peak response wavelength: 420 ;

[0083] Quantum efficiency (@450 nm): 40%;

[0084] Gain: 1 ;

[0085] Dark count rate: < 1 ;

[0086] Rise time: < 1 ;

[0087] The preamplifier unit 23 is electrically connected to the silicon photomultiplier detector 22 and is used to amplify the weak electrical signal output by the SiPM. This unit adopts a low-noise transimpedance amplifier design with a conversion gain of 10 5 V / A and a bandwidth of 200 MHz, ensuring high-fidelity amplification of the signal.

[0088] The receiving module of the present invention can effectively receive the optical signal transmitted at a distance of 250 meters under standard seawater conditions. According to the underwater optical transmission attenuation model, the attenuation of the optical signal in water can be expressed as:

[0089] ,

[0090] where is the optical intensity at a distance from the light source ; is the initial optical intensity; is the attenuation coefficient at a specific wavelength ; is the propagation distance.

[0091] For blue light with a wavelength of 450 nm in standard seawater, the attenuation coefficient is approximately . Assuming the transmission power is 26.2 W, after propagating 250 meters, the received optical power is approximately:

[0092] ,

[0093] Considering the aperture (100 mm) and optical efficiency (98%) of the receiving lens, the actual optical power entering the SiPM detector is approximately:

[0094] ,

[0095] Although this power is extremely low, due to the high sensitivity and high gain characteristics of the SiPM detector, the system can still effectively detect and recover the communication signal. The minimum detectable power of the SiPM detector is approximately 10^-21 W, providing sufficient sensitivity margin for the system.

[0096] Example 4: Signal Processing and Equalization Module

[0097] Please refer to Figure 4 , the signal processing and equalization module 3 of the present invention includes: a linear equalizer 31, a downsampling unit 32, and an artificial neural network equalizer 33.

[0098] The linear equalizer 31 is used to perform inter-symbol interference (ISI) suppression processing on the electrical signal and generate a preprocessed signal. In underwater optical communication, due to water body scattering and multipath effects, the received signal is often accompanied by severe ISI, which affects the communication quality. The present invention adopts an adaptive linear equalizer to optimize the equalization coefficient based on the least mean square (LMS) algorithm, effectively suppressing ISI.

[0099] The core of the LMS algorithm is to continuously adjust the equalizer coefficient through an iterative method to minimize the output error. Its update formula is:

[0100] ,

[0101] where, is the equalizer coefficient vector at the th iteration, is the step size parameter, is the error signal, is the input signal vector.

[0102] In the implementation of the present invention, the linear equalizer adopts a 21-order FIR filter structure, and the step size parameter is set to 0.005. This value is determined based on system simulation and experiments, which ensures the convergence speed while avoiding system oscillation.

[0103] The downsampling unit 32 is connected to the linear equalizer 31 and is used to perform downsampling processing on the preprocessed signal. The main function of this unit is to reduce the computational complexity of the subsequent ANN equalizer. In the implementation of the present invention, the downsampling ratio is 2:1, that is, one sample point is retained for every two sample points.

[0104] The artificial neural network equalizer 33 is connected to the downsampling unit 32 and is used to perform non-linear distortion suppression processing on the downsampled signal. In underwater optical communication, due to factors such as the non-linear characteristics of the light source and the response change of the detector, the received signal is often accompanied by non-linear distortion, and this kind of distortion is difficult to be effectively suppressed by the linear equalizer. The present invention innovatively introduces a low-complexity ANN equalizer, which is specifically used to process non-linear distortion.

[0105] In the preferred embodiment of the present invention, the ANN equalizer adopts a two-layer hidden layer structure. The first hidden layer contains 10 neurons, and the second hidden layer contains 1 neuron. This structure provides sufficient non-linear fitting ability while maintaining a relatively low computational complexity.

[0106] The forward propagation process of the ANN equalizer can be described as:

[0107] ,

[0108] ,

[0109] ,

[0110] Among them, is the input vector, and are the outputs of the first and second hidden layers respectively, is the network output, , and are weight matrices, , and are bias vectors, and are activation functions.

[0111] In the present invention, the ReLU activation function is adopted for the first hidden layer, the Sigmoid activation function is adopted for the second hidden layer, and no activation function is used for the output layer. This design enables the network to effectively capture the non-linear features in the signal while maintaining the stability of the output.

[0112] The network is trained using the backpropagation algorithm, and the loss function is the mean squared error (MSE):

[0113] ,

[0114] Among them, is the expected output, is the actual output of the network, is the number of training samples.

[0115] The optimization algorithm adopts the Adam algorithm, the initial learning rate is set to 0.001, and the training batch size is 64. Before actual deployment, the network is trained by collecting data under actual channel conditions to adapt to a specific underwater environment.

[0116] The double-layer equalization architecture (linear equalizer + ANN equalizer) of the present invention significantly improves the system's ability to suppress ISI and non-linear distortion while maintaining a low computational complexity. Under standard test conditions, compared with simply using a linear equalizer, this architecture can reduce the bit error rate by about one order of magnitude.

[0117] Example 5: Underwater positioning and tracking module

[0118] Please refer to Figure 5 , the underwater positioning and tracking module 4 of the present invention includes: a camera unit 41, a laser point detector 42, a position calculation unit 43, and an automatic adjustment unit 44.

[0119] The camera unit 41 is used to capture the beam position image. This unit adopts a high-sensitivity CMOS image sensor with a resolution of 1280×1024 pixels and a frame rate of 30fps. Combined with a band-pass filter (center wavelength 450nm, bandwidth 10nm), it can effectively capture the position information of the laser spot in an underwater environment.

[0120] The laser spot detector 42 is used to detect the beam position. Different from the camera unit, the laser spot detector is specifically designed for high-precision beam position detection. It adopts a four-quadrant photodetector (QPD) design with a position resolution of up to 10μm and a response time <1ms, providing fast and accurate position feedback for the system.

[0121] The position calculation unit 43 is connected to the camera unit 41 and the laser spot detector 42, and is used to calculate the position deviation based on the beam position image and the beam position. This unit is implemented by an embedded processor and integrates image processing and position calculation algorithms.

[0122] The beam position deviation calculation uses a weighted fusion algorithm, taking into account both the camera image and the QPD output to improve the accuracy and robustness of position estimation:

[0123] ,

[0124] where, is the estimated position deviation vector, and are the position deviations measured by the camera and the QPD respectively, and are the weight coefficients, satisfying .

[0125] Under standard working conditions, is set to 0.3, is set to 0.7, giving priority to the high-precision output of the QPD while using the global vision of the camera to improve the system robustness. In the case of weak light intensity, the system will automatically increase the value of , relying more on the image information of the camera.

[0126] The automatic adjustment unit 44 is connected to the position calculation unit 43 and is used to adjust the emission direction of the optical communication transmitting module 1 according to the position deviation. This unit is implemented by a two-axis servo mechanism with an adjustment accuracy of 0.01° in both the horizontal and vertical directions and a maximum adjustment range of ±30°, meeting the beam tracking requirements in the AUV motion environment.

[0127] The adjustment control uses a PID algorithm, and the control output is calculated as follows:

[0128] ,

[0129] Among them, is for controlling the output, is the position deviation, , and are the proportional, integral, and differential coefficients respectively.

[0130] In the implementation of the present invention, through parameter optimization, , and are set to 0.8, 0.2, and 0.1 respectively. This set of parameters ensures the fast response of the system while avoiding overshoot and oscillation.

[0131] Under the condition that the relative speed of the AUV does not exceed 2 m / s, this system can keep the beam pointing deviation less than 0.5°, ensuring the stability of the communication link. For scenarios with higher speeds, the system will automatically adjust the control parameters to improve the tracking ability.

[0132] Embodiment 6: Data Format Conversion Module

[0133] The present invention further includes a data format conversion module 5, which is connected to the optical communication transmission module 1 and the signal processing and equalization module 3, and is used to convert the input data into a signal format suitable for on-off keying modulation at the sending end, and restore the equalized signal to the original data format at the receiving end.

[0134] At the sending end, the data format conversion includes the following processes:

[0135] 1. Data frame encapsulation: Add a frame header, frame tail, and check code to the original data to form a standard communication frame structure;

[0136] 2. Manchester coding: Convert the binary data into Manchester code to ensure the clock information in the data;

[0137] 3. Pulse shaping: Shape the encoded digital signal through a raised cosine filter to reduce the signal bandwidth.

[0138] At the receiving end, the data format conversion includes:

[0139] 1. Signal decision: Make a decision on the equalized analog signal to restore it to a digital signal;

[0140] 2. Manchester decoding: Decode the Manchester code into the original binary data;

[0141] 3. Frame parsing and verification: Extract the valid data and perform verification to ensure the correctness of the data.

[0142] The addition of the data format conversion module 5 endows the system with complete data processing capabilities, realizing the conversion from raw data to optical signals and the entire process from receiving optical signals to restoring raw data.

[0143] Embodiment 7: Underwater AUV Blue Laser - SiPM Detection Equalization Communication Method

[0144] Please refer to Figure 6 , the present invention also provides an underwater AUV blue laser - SiPM detection equalization communication method, including the following steps:

[0145] Step S1: Generate a blue laser signal through a multi - channel cascaded laser diode array.

[0146] In this step, an array is composed of 8 blue laser diodes with a wavelength of 450 nm. The output power of each laser diode is about 3.5 W, and a high - power light source is provided through a cascaded manner.

[0147] Step S2: Use beam combination technology to combine the blue laser signals into a single beam and emit it.

[0148] In this step, precision optical elements are used to combine multiple laser beams into a single high - power beam. The final output power can reach 26.2 W, and the beam is emitted through an emission optical system.

[0149] Step S3: Focus the received blue laser signal through a high - precision optical lens.

[0150] In this step, a high - precision optical lens with an aperture of 100 mm and a focal length of 150 mm is used to capture and focus the weak optical signal after transmission, improving the receiving sensitivity.

[0151] Step S4: Use a silicon photomultiplier tube detector to convert the focused blue laser signal into an electrical signal.

[0152] In this step, the SiPM detector, relying on its high sensitivity and high gain characteristics, converts the weak optical signal into a processable electrical signal. The photoelectric conversion efficiency of SiPM at a wavelength of 450 nm is 40%, and the gain is as high as 10^6, which can effectively detect the weak optical signal after long - distance transmission.

[0153] Step S5: Perform inter - symbol interference suppression processing on the electrical signal through a linear equalizer to obtain a pre - processed signal.

[0154] In this step, a linear equalizer with a 21 - order FIR filter structure is used to adaptively update the equalization coefficients based on the LMS algorithm, effectively suppressing the inter - symbol interference caused by the underwater channel.

[0155] Step S6: Downsample the preprocessed signal.

[0156] In this step, a downsampling ratio of 2:1 is adopted to reduce the amount of data and computational complexity for subsequent processing, improving the system efficiency while maintaining the signal quality.

[0157] Step S7: Use an artificial neural network equalizer to perform non - linear distortion suppression on the downsampled signal.

[0158] In this step, an ANN equalizer with two hidden layers (10 - 1 neuron configuration) is adopted to compensate for and correct the common non - linear distortions in underwater optical communication, further improving the signal quality.

[0159] Step S8: Monitor the beam position in real - time and automatically adjust the emission direction to maintain the precise alignment of the blue laser signal with the receiving end.

[0160] In this step, the beam position information is obtained through a camera and a laser spot detector, the position deviation is calculated, and the emission direction is adjusted in real - time through a two - axis servo mechanism to ensure the stability of the communication link.

[0161] Through the above steps, the communication method provided by the present invention can effectively achieve high - speed and stable optical communication in an underwater environment, and is particularly suitable for the communication requirements of underwater mobile platforms such as AUVs.

[0162] In an actual application scenario, this method can achieve stable communication in a 250 - meter - deep underwater channel, with a data transmission rate of up to 100 Mbps and a bit error rate lower than 10 -6 . In addition, this method has good adaptability to the movement of AUVs. When the relative speed of the AUV does not exceed 2 m / s, a stable communication link can still be maintained.

[0163] Example 8: Adaptability of the system under different water conditions

[0164] The underwater AUV blue - laser - SiPM detection and equalization communication system of the present invention has good environmental adaptability and can work in different types of water body environments. The following are the performance parameters of the system under three typical water conditions:

[0165] 1. Clear sea water (attenuation coefficient c = 0.15m -1 )

[0166] Effective communication distance: 250 meters;

[0167] Data transmission rate: 100 Mbps;

[0168] Bit error rate: <10 -6；

[0169] 2. Turbid Seawater (attenuation coefficient c = 0.4m -1 )

[0170] Effective communication distance: 90 meters;

[0171] Data transmission rate: 50 Mbps;

[0172] Bit error rate: <10 -5 ;

[0173] 3. Harbor Water Area (attenuation coefficient c = 0.8m -1 )

[0174] Effective communication distance: 40 meters;

[0175] Data transmission rate: 20 Mbps;

[0176] Bit error rate: <10 -4 ;

[0177] The system will automatically adjust the working parameters according to the water body conditions, including laser power, modulation depth, equalizer parameters, etc., to obtain the best performance. This adaptability enables the system to perform tasks in a variety of marine environments, greatly expanding the application range of underwater AUVs.

[0178] Example 9: System Energy Consumption and Thermal Management

[0179] In the design process of the present invention, the energy limitations of the underwater AUV platform are fully considered, and a number of measures are taken to optimize the system energy consumption:

[0180] 1. Power Consumption Control of the Laser Emission Module

[0181] During the actual communication process, the emission module will dynamically adjust the laser output power according to the communication distance and water body conditions. When the communication distance is short or the water body is relatively clear, the system will automatically reduce the emission power to reduce energy consumption. Specifically, the system sets three power levels:

[0182] High power mode: 26.2W output, total power consumption about 85W;

[0183] Medium power mode: 13.1W output, total power consumption about 45W;

[0184] Low power mode: 6.5W output, total power consumption about 25W;

[0185] 2. Energy Efficiency Optimization of the Signal Processing Module

[0186] The low-complexity equalization algorithm adopted by the present invention significantly reduces the computational resource requirements and energy consumption. The power consumption of the signal processing and equalization module is about 3.5W, which is much lower than the power consumption required by traditional high-complexity equalization algorithms (usually 10 - 15W).

[0187] 3. Thermal management system

[0188] To solve the heat dissipation problem of high-power lasers, the system integrates a micro liquid cooling system, including a microchannel cold plate, a circulation pump, and a radiator. This cooling system can control the laser temperature within the range of 25 ± 2°C, ensuring the stable operation of the laser and extending its service life.

[0189] In the standard working mode, the total power consumption of the entire system is approximately 95W, which can be continuously powered by the battery system of a modern AUV platform for 4 - 6 hours, meeting the requirements of most underwater missions.

[0190] Example 10: Communication protocol in actual application of the system

[0191] To ensure stable communication of the system in a complex underwater environment, the present invention designs a dedicated communication protocol, which mainly includes the following aspects:

[0192] 1. Link establishment protocol:

[0193] When two AUVs need to establish a communication link, first the sending AUV emits a low-power detection signal (intermittent laser pulses). After the receiving party detects the detection signal, it activates the underwater positioning and tracking module for preliminary alignment. After the alignment is completed, the receiving party sends an acknowledgment signal (if equipped with two-way communication capabilities), and both parties start formal communication.

[0194] The time threshold for link establishment is set to 5 seconds. If the link fails to be successfully established after this time, the system will automatically adjust the parameters and retry, with a maximum of 3 attempts. After multiple failures, the system will report the failure of link establishment to the AUV main controller.

[0195] 2. Data frame structure

[0196] The communication frame structure is as follows:

[0197] Frame header (8 bytes): Contains a synchronization code (4 bytes), a destination address (2 bytes), and a source address (2 bytes);

[0198] Frame length (2 bytes): Represents the length of the payload;

[0199] Timestamp (4 bytes): Used for data synchronization and delay calculation;

[0200] Payload (variable length, maximum 4096 bytes): The actual data to be transmitted;

[0201] CRC checksum (4 bytes): Used for error detection;

[0202] Frame tail (2 bytes): Used for frame boundary detection;

[0203] 3. Error control mechanism

[0204] The system adopts an error control mechanism that combines forward error correction (FEC) and automatic repeat request (ARQ). The FEC uses Reed-Solomon(255,223) coding, which can correct errors of up to 16 bytes, enabling the system to still work properly under conditions of relatively high bit error rates. For errors that cannot be corrected by FEC, the system will trigger the ARQ mechanism to request retransmission of the erroneous data frames.

[0205] 4. Flow control

[0206] Considering the instability of the underwater communication link, the system implements a flow control mechanism based on a sliding window. The window size can be dynamically adjusted according to the link quality, with a range of 8 - 64 frames. When the link quality is good, the window size is increased to improve the transmission efficiency; when the link quality deteriorates, the window size is decreased to improve the transmission reliability.

[0207] Through the above protocol design, the system can provide reliable communication services in complex and changing underwater environments, supporting various task requirements of AUVs.

[0208] The present invention provides an underwater AUV blue light laser - SiPM detection and equalization communication system and method. By combining a multi - channel cascaded laser diode array with a super - sensitive silicon photomultiplier detector, and cooperating with a low - complexity double - layer equalization architecture and an accurate underwater positioning and tracking system, it effectively solves the key challenges such as attenuation, distortion, and alignment faced by underwater optical communication, and realizes long - distance and high - rate underwater optical communication.

[0209] The present invention has the following outstanding advantages:

[0210] 1. Long transmission distance: It can reach 250 meters under standard seawater conditions, far exceeding the existing technology level;

[0211] 2. High data rate: Up to 100 Mbps, meeting the requirements of high - bandwidth applications;

[0212] 3. Strong system reliability: The stability and reliability of the communication link are ensured through a number of innovative technologies;

[0213] 4. Good environmental adaptability: It can adapt to various water body conditions and work properly in different marine environments;

[0214] 5. High energy efficiency ratio: Low - complexity algorithms and intelligent power management are adopted to optimize the system energy consumption;

[0215] 6. High integration level: Each module of the system is closely combined to form a complete communication solution, which is easy to integrate into existing AUV platforms.

[0216] The successful implementation of the present invention provides an efficient and reliable communication means for underwater unmanned vehicles, significantly enhancing the application capabilities of AUVs in deep-sea exploration, resource monitoring, environmental investigation, underwater robot control and other fields, promoting the development of underwater communication technology, and having broad application prospects and important practical values.

[0217] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. Underwater AUV blue laser-SiPM detection balanced communication system, characterized in that: include: An optical communication transmitting module, used to generate and transmit a blue laser signal; An optical communication receiving module, used for receiving the blue laser signal and converting it into an electrical signal; A signal processing and equalization module, electrically connected to the optical communication receiving module, and used for processing the electrical signal to suppress signal distortion; as well as The underwater positioning and tracking module is connected to the optical communication transmitting module and the optical communication receiving module, and is used to adjust the transmitting direction of the optical communication transmitting module in real time to keep the blue laser signal aligned with the optical communication receiving module.

2. The system according to claim 1, characterized in that The optical communication transmitting module comprises: A multi-channel cascaded laser diode array, including a plurality of blue laser diodes; a beam combining unit connected to the multi-channel cascade laser diode array and configured to combine the output beams of the plurality of blue laser diodes into a single beam; and A modulation unit is connected to the multi-channel cascade laser diode array and is used to perform on-off keying modulation on the blue laser diode.

3. The system according to claim 2, characterized in that The multi-channel cascade laser diode array includes 8 blue laser diodes with a wavelength of 450nm, and the power of the single light beam reaches 26.2W.

4. The system according to claim 1, characterized in that The optical communication receiving module comprises: A high-precision optical lens, used for focusing the blue laser signal; a silicon photomultiplier tube detector, optically coupled to the high-precision optical lens, for converting the focused blue laser signal into an electrical signal; and The preamplifier unit is electrically connected to the silicon photomultiplier tube detector and is used to amplify the electrical signal.

5. The system according to claim 1, characterized in that The signal processing and equalization module comprises: A linear equalizer, used for performing inter-symbol interference suppression processing on the electrical signal and generating a pre-processed signal; a down-sampling unit connected to the linear equalizer and configured to perform down-sampling processing on the pre-processed signal; and The artificial neural network equalizer is connected to the down-sampling unit and is used for performing nonlinear distortion suppression processing on the down-sampled signal.

6. The system according to claim 5, characterized in that The linear equalizer uses a minimum mean square error algorithm to optimize coefficients.

7. The system according to claim 5, characterized in that The artificial neural network equalizer includes two hidden layers, the first hidden layer includes 10 neurons, and the second hidden layer includes 1 neuron.

8. The system according to claim 1, characterized in that The underwater positioning and tracking module includes: a camera unit for capturing an image of the beam position; A laser point detector for detecting the beam position; a position calculation unit connected to the camera unit and the laser point detector, and configured to calculate a position deviation based on the beam position image and the beam position; and An automatic adjustment unit is connected to the position calculation unit and is used to adjust the emission direction of the optical communication emission module according to the position deviation.

9. The system according to claim 1, characterized in that Also includes: The data format conversion module is connected to the optical communication transmission module and the signal processing and equalization module, and is used to convert the input data into a signal format suitable for on-off keying modulation at the transmitting end, and to restore the equalized signal to the original data format at the receiving end.

10. An underwater AUV blue laser-SiPM detection balanced communication method, using the system according to any one of claims 1 to 9, comprising the following steps: Generate a blue laser signal by a multi-channel cascaded laser diode array; Using beam combining technology to combine the blue laser signal into a single beam and emit it; Focus the received blue laser signal through high-precision optical lens; Converting the focused blue laser signal into an electrical signal using a silicon photomultiplier tube detector; Performing inter-symbol interference suppression processing on the electrical signal through a linear equalizer to obtain a preprocessed signal; Performing down-sampling processing on the pre-processed signal; The artificial neural network equalizer is used to suppress the nonlinear distortion of the downsampled signal; as well as The beam position is monitored in real time and the emission direction is automatically adjusted to keep the blue laser signal precisely aligned with the receiving end.

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