Underwater wireless optical communication system based on adaptive emission and lightweight reception

Abstract

The invention discloses an underwater wireless optical communication system based on adaptive emission and lightweight reception, and relates to the field of underwater wireless optical communication, comprising an adaptive emission module which adaptively selects a signal processing path according to an underwater channel condition and performs electro-optical conversion; the lightweight receiving module receives weak optical signals transmitted underwater and converts the weak optical signals into digital signals; the power supply control module outputs a stable current source; the FPGA module carries out modulation and demodulation and filtering pre-equalization on the signal; the system adopts a modular layered architecture, takes blue and green light bands as communication carriers, realizes full duplex underwater wireless optical communication, fundamentally meets the core requirements of an underwater combat environment on communication concealment and high data transmission rate, remarkably reduces the power consumption of the system, and realizes a short-distance and low-power-consumption communication link.

Description

Technical Field

[0001] This invention relates to the field of underwater wireless optical communication technology, and in particular to an underwater wireless optical communication system based on adaptive transmission and lightweight reception. Background Technology

[0002] Underwater communication is a key technological support for collaborative operations among submarines, unmanned underwater vehicles, surface ships, underwater vehicles, and underwater special operations personnel. Traditional submarines can only conduct radio communication by using buoys or surfacing to shallow water, which easily exposes them and results in poor stealth. Although underwater acoustic communication can achieve long-distance transmission underwater, it is susceptible to eavesdropping and has a slow communication rate.

[0003] In pursuit of longer communication distances and higher communication rates, existing underwater wireless optical communication equipment generally adopts high-power transmitting devices. However, this severely restricts the long-term stealth operation capabilities of underwater special forces personnel and small unmanned underwater vehicles in environments where energy resupply is difficult, and makes it difficult to meet the practical application requirements of underwater short-range low-power communication. Summary of the Invention

[0004] To address the aforementioned challenges, this invention provides an underwater wireless optical communication system based on adaptive transmission and lightweight reception. Employing a modular, layered architecture, the system fundamentally meets the core requirements of underwater combat environments for both communication concealment and high data transmission rates through a full-duplex underwater wireless optical communication system. By introducing an adaptive transmission module based on an LED array and a lightweight reception module based on a PIN, system power consumption is significantly reduced, achieving a short-range, low-power communication link.

[0005] To achieve the above objectives, the present invention provides an underwater wireless optical communication system based on adaptive transmission and lightweight reception, including an adaptive transmission module, a lightweight reception module, a power control module, and an FPGA module; An adaptive transmission module is used to adaptively select the signal processing path and perform electro-optical conversion according to the underwater channel conditions; A lightweight receiver module is used to receive weak optical signals transmitted underwater and convert them into digital signals; The power control module is used to output a stable current source; FPGA module, used for signal modulation, demodulation, filtering and pre-equalization; The system adopts a modular layered architecture and uses the blue-green light band as the communication carrier to realize full-duplex underwater wireless optical communication.

[0006] Preferably, the adaptive transmission module includes a signal modulation and path selection unit, a light source driving unit, and an electro-optic conversion unit; The signal modulation and path selection unit is used to receive the modulation signal generated by the FPGA module and control the analog switch to switch between the equalization-bias path and the through bias path according to the channel quality monitoring results; The light source driving unit is used to receive the signal processed by the signal modulation and path selection unit and provide a stable constant current output to prevent optical power jitter due to power fluctuations. The electro-optical conversion unit is an LED array, used to convert electrical signals into optical signals and emit them.

[0007] Preferably, the equalization-bias path includes an equalizer and an biaser, used to compensate for high-frequency components of the signal and broaden the system bandwidth when the channel quality is poor or frequency-selective fading is severe; the direct bias path is an biaser, used to reduce system power consumption and complexity when the channel quality is good.

[0008] Preferably, the light source driving unit includes a digitally adjustable constant current source circuit. The constant current source circuit uses an operational amplifier and a MOS transistor to provide a stable constant voltage output, and uses a digital potentiometer to control the voltage division of the reference voltage source. The output current is adjusted through two voltage pins, thereby achieving the highest efficiency transmission with flexible and variable power consumption and optical power in different water environments and transmission distances.

[0009] Preferably, the constant current source circuit further includes a gate driver, which adopts a dual-channel high-speed low-side gate driver chip to achieve fast switching of the MOSFET through fast turn-off technology.

[0010] Preferably, the power control module includes a low-ripple and high dynamic load regulation DC-DC converter chip and an RF LDO to ensure the lowest voltage noise floor in the power rail of the transmitter circuit.

[0011] Preferably, the equalizer employs a T-type equalization circuit to compensate for the frequency response of the LED.

[0012] Preferably, the electro-optical conversion unit utilizes the 450nm and 520nm blue-green light bands for bidirectional visible light communication; the LED array includes a 450nm blue LED and a 520nm green LED, wherein the 450nm blue LED has a center wavelength of 450nm, an operating voltage of 2.8-3.0V, and an operating current of 700mA; and the 520nm green LED has a center wavelength of 520nm, an operating voltage of 3.0-3.2V, and an operating current of 700mA.

[0013] Preferably, the lightweight receiver module includes a photodetector, a transimpedance amplifier, and a signal shaper; The photodetector uses a PIN photodiode to capture weak light signals transmitted underwater and convert them into photocurrent. The transimpedance amplifier is used to convert the photocurrent into a voltage signal and perform preliminary amplification; The signal shaper is a Schmitt trigger, used to perform binarization processing on the signal using hysteresis characteristics, filter out noise, and shape it into a digital pulse signal.

[0014] Preferably, the FPGA module uses the Xilinx ZYNQ7000 series XC7Z020-CLG400-2 chip.

[0015] Therefore, this invention employs an underwater wireless optical communication system based on adaptive transmission and lightweight reception. The adaptive transmission module selects the signal processing path in real time according to channel quality: when the channel quality is poor or frequency selective fading is severe, an equalization-bias path is used to compensate for high-frequency components, widening the system bandwidth; when the channel is good, it switches to a direct bias path, reducing system power consumption and complexity, thus solving the problem of long-term operation for energy-constrained platforms such as underwater special operations personnel. The lightweight reception module uses a PIN photodiode combined with a transimpedance amplifier and a Schmitt trigger architecture. Compared to traditional APD or PMT solutions, it eliminates the need for complex temperature control compensation circuits, simplifying the circuit structure and achieving low power consumption and miniaturization of the receiver. The system is based on blue-green light band communication, avoiding the exposure risks associated with submarine surfacing or releasing buoys, and has advantages over underwater acoustic communication in terms of speed and anti-eavesdropping capabilities.

[0016] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the underwater wireless optical communication system based on adaptive transmission and lightweight reception in this invention. Figure 2 This is a schematic diagram of the underwater wireless optical communication system based on adaptive transmission and lightweight reception in an embodiment of the present invention; Figure 3 The above are the simulation results of the frequency response of the T-type equalization circuit in the embodiment of the present invention. Detailed Implementation

[0018] The following detailed description of embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0019] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0020] The terms "comprising" or "including" as used in this invention mean that the element preceding the term encompasses the element listed after the term, and do not exclude the possibility of encompassing other elements. Terms such as "inner," "outer," "upper," and "lower" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. When the absolute position of the described object changes, the relative positional relationship may also change accordingly. In this invention, unless otherwise explicitly specified and limited, the term "attached" and similar terms should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral part; it can refer to a direct connection or an indirect connection through an intermediate medium; it can refer to the internal communication of two elements or the interaction relationship between two elements. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0021] Example An underwater wireless optical communication system based on adaptive transmission and lightweight reception, such as Figures 1-2 As shown, it includes an adaptive transmission module, a lightweight receiver module, a power control module, and an FPGA module; An adaptive transmission module is used to adaptively select the signal processing path and perform electro-optical conversion according to the underwater channel conditions; The design focus of the transmitter is to adapt to the complex and ever-changing underwater channel environment and ensure the transmission quality of optical signals.

[0022] The adaptive transmission module includes a signal modulation and path selection unit, a light source driving unit, and an electro-optic conversion unit; it achieves OOK modulation and stable constant voltage output.

[0023] The signal modulation and path selection unit is used to receive the modulation signal generated by the FPGA module and control the analog switch to switch between the equalization-bias path and the through bias path according to the channel quality monitoring results; The equalization-bias path includes an equalizer and an biaser, used to compensate for high-frequency components of the signal when the channel quality is poor or frequency-selective fading is severe, thereby widening the system bandwidth and optimizing signal integrity; the direct bias path is an biaser, used to reduce system power consumption and complexity when the channel quality is good.

[0024] The equalizer uses a T-type equalization circuit to compensate for the frequency response of the LEDs.

[0025] Specifically, in visible light communication systems, the severe channel unevenness poses a significant obstacle to achieving high-speed data transmission. Although higher-order modulation techniques such as OFDM can optimize system performance to some extent, further improvements in system capacity require various pre-equalization techniques at the transmitting end to compensate for the LED's frequency response, thereby increasing the system's modulation bandwidth. Pre-equalization techniques are mainly divided into two types: hardware equalization and software equalization. The former refers to using traditional analog circuits to compensate for signal attenuation; the latter mainly refers to designing a suitable FIR filter based on a Field Programmable Gate Array (FPGA) to achieve equalization. An improved equalization circuit based on a T-type equalizer was designed and simulated using Advanced Design System (ADS), yielding the expected results. This circuit can extend the LED's modulation bandwidth from 2kHz to 45MHz. The ADS simulation results are as follows: Figure 3 As shown.

[0026] The light source driving unit is used to receive the signal processed by the signal modulation and path selection unit and provide a stable constant current output to prevent optical power jitter due to power fluctuations. The light source driving unit includes a digitally adjustable constant current source circuit. The constant current source circuit uses an operational amplifier and a MOSFET to provide a stable constant voltage output, and uses a digital potentiometer to control the voltage division of the reference voltage source. The output current is adjusted through two voltage pins, thereby achieving the highest efficiency transmission with flexible and variable power consumption and optical power in different water environments and transmission distances.

[0027] The constant current source circuit also includes a gate driver, which uses a dual-channel high-speed low-side gate driver chip to achieve fast switching of the MOSFET through fast turn-off technology.

[0028] Based on design requirements, a high-impedance input driver is selected for the drive switch to ensure low waveform distortion during high-speed transmission of control signals. The UCC27624 is a dual-channel high-speed low-side gate driver suitable for high-frequency switching power supplies, perfectly meeting the design requirements of this drive circuit. Furthermore, the MOSFETs in this transmitter section employ fast turn-off technology, offering a faster turn-off rate compared to traditional resistor-based and reverse diode-based voltage dissipation.

[0029] To ensure maximum transmission efficiency with flexible and variable power consumption and optical power across different aquatic environments and transmission distances, a digitally controlled constant current section was incorporated, using operational amplifiers and MOSFETs to provide a stable constant voltage output. Two voltage pins were also provided to determine the output value, and a digital potentiometer was used to control the voltage divider for the reference voltage source design.

[0030] The electro-optical conversion unit is an LED array used to convert electrical signals into optical signals and transmit them. The array design aims to increase the transmitted optical power to overcome the high attenuation characteristics underwater and extend the communication distance.

[0031] This system utilizes the 450nm and 520nm blue-green light bands for bidirectional visible light communication, with significantly lower attenuation compared to other bands. This theory lays the foundation for the development of underwater wireless optical communication. The LED array comprises 450nm blue LEDs and 520nm green LEDs. The 450nm blue LEDs have a center wavelength of 450nm, an operating voltage of 2.8-3.0V, and an operating current of 700mA; the 520nm green LEDs have a center wavelength of 520nm, an operating voltage of 3.0-3.2V, and an operating current of 700mA. Both blue and green LEDs can be Cisco 3535 ceramic LEDs.

[0032] A lightweight receiver module is used to receive weak optical signals transmitted underwater and convert them into digital signals; The receiver follows a "lightweight" design principle, simplifying the filter circuit design compared to most underwater wireless optical communication receiver systems. This aims to maintain high sensitivity while simplifying the circuit structure and reducing system power consumption. Details are as follows: The lightweight receiver module includes a photodetector, a transimpedance amplifier, and a signal shaper; The front end uses a PIN photodiode as a photodetector to capture weak light signals transmitted underwater and convert them into photocurrent. Specifically, commercially available photodetectors mainly include PIN photodiodes, avalanche photodiodes (APDs), and photomultiplier tubes (PMTs). Due to the high cost and complex peripheral circuitry required for PMTs, they are unsuitable for this lightweight receiving system and will not be considered here. Compared to APDs, PIN photodiodes offer excellent signal-to-noise ratios at medium to high optical power levels because their noise primarily originates from shot noise and thermal noise, and they lack the avalanche multiplication noise of APDs. Furthermore, their manufacturing process is simpler than that of APDs, resulting in higher reliability, lower cost, and easier integration. They also exhibit better temperature stability, and their gain, breakdown voltage, and other performance parameters are less sensitive to temperature than APDs, typically eliminating the need for complex temperature control compensation circuits. Therefore, the Hamamatsu S16839 PIN photodiode is selected.

[0033] The photocurrent then enters the transimpedance amplifier (TIA). The TIA converts the weak current signal into a voltage signal and performs preliminary amplification, which is a key stage that determines the receiver's sensitivity and bandwidth.

[0034] The operational amplifier OPA847ID amplifies and processes signals with high precision. As a transimpedance amplifier, it converts the weak current signal output by the photodiode into a voltage signal. Its high bandwidth and low noise characteristics significantly improve the receiving sensitivity.

[0035] Amplified analog signals are often accompanied by noise. By using a Schmidt trigger and taking advantage of its hysteresis characteristics, polarization is performed to effectively filter out noise interference and shape the analog waveform into a digital pulse signal with steep edges and standard levels.

[0036] The SN74LVC1G17DBVR is a high-performance single-channel Schmitt trigger buffer chip that shapes and denoises received signals. It integrates filtering, waveform shaping, and anti-interference functions, and features high frequency bandwidth to solve signal distortion caused by underwater channel environments and improve the signal-to-noise ratio.

[0037] Signal feedback: The shaped digital signal is directly input into the FPGA for subsequent clock recovery, decoding and data processing.

[0038] The power control module is used to output a stable current source; The power supply section employs low-ripple and high dynamic load regulation DC-DC chips and an RF LDO to ensure the lowest possible voltage noise floor on the power rails of the transmitter circuit. The TPS54560DDA is a high-performance synchronous buck DC-DC converter chip that converts the input voltage to a lower, stable output voltage. The TPS61175PWPR is a high-performance boost switching regulator that converts the input voltage to a higher, stable output voltage. These two components regulate the voltage to achieve a stable output voltage.

[0039] FPGA module, used for signal modulation, demodulation, filtering and pre-equalization; Specifically, it uses the Xilinx ZYNQ7000 series chip, model XC7Z020-CLG400-2. It features 85K logic cells, 4.9 Mbits of embedded memory, 220 DSP units, 4 clock management units (CMTs), 16 global clock networks, 6 user I / O banks, and a maximum of 253 user I / Os, making it a very cost-effective chip. The device's programmable logic section is based on Xilinx's 7-series FPGA using a 28nm process, meeting requirements for complex logic programming, high-speed data transmission, high performance, low power consumption, and multi-core processing capabilities. It provides ample hardware resources for high-speed signal processing and complex algorithms (such as channel coding and error correction algorithms).

[0040] The system adopts a modular layered architecture and uses the blue-green light band as the communication carrier to realize full-duplex underwater wireless optical communication.

[0041] Therefore, the present invention adopts the above-mentioned underwater wireless optical communication system based on adaptive transmission and lightweight reception. Through the design of the adaptive transmission module and the lightweight reception module, it effectively solves the problems of traditional underwater communication methods in terms of concealment, security, communication rate and power consumption. It can dynamically optimize the transmission strategy and energy consumption according to the real-time channel conditions. While ensuring high bandwidth and low bit error rate communication, it significantly improves energy utilization efficiency and the concealment and survivability of equipment. It is particularly suitable for application scenarios with strict requirements for concealment and endurance, such as submarines, unmanned underwater vehicles and underwater special operations personnel.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. An underwater wireless optical communication system based on adaptive transmission and lightweight reception, characterized in that, It includes an adaptive transmit module, a lightweight receive module, a power control module, and an FPGA module; An adaptive transmission module is used to adaptively select the signal processing path and perform electro-optical conversion according to the underwater channel conditions; A lightweight receiver module is used to receive weak optical signals transmitted underwater and convert them into digital signals; The power control module is used to output a stable current source; FPGA module, used for signal modulation, demodulation, filtering and pre-equalization; The system adopts a modular layered architecture and uses the blue-green light band as the communication carrier to realize full-duplex underwater wireless optical communication.

2. The underwater wireless optical communication system based on adaptive transmission and lightweight reception as described in claim 1, characterized in that, The adaptive transmission module includes a signal modulation and path selection unit, a light source driving unit, and an electro-optic conversion unit. The signal modulation and path selection unit is used to receive the modulation signal generated by the FPGA module and control the analog switch to switch between the equalization-bias path and the through bias path according to the channel quality monitoring results; The light source driving unit is used to receive the signal processed by the signal modulation and path selection unit and provide a stable constant current output to prevent optical power jitter due to power fluctuations. The electro-optical conversion unit is an LED array, used to convert electrical signals into optical signals and emit them.

3. The underwater wireless optical communication system based on adaptive transmission and lightweight reception as described in claim 2, characterized in that, The equalization-bias path includes an equalizer and a biaser, which are used to compensate for the high-frequency components of the signal when the channel quality is poor or the frequency-selective fading is severe, thereby widening the system bandwidth. The direct bias path is an biaser used to reduce system power consumption and complexity when the channel quality is good.

4. The underwater wireless optical communication system based on adaptive transmission and lightweight reception as described in claim 3, characterized in that: The light source driving unit includes a digitally adjustable constant current source circuit. The constant current source circuit uses an operational amplifier and a MOSFET to provide a stable constant voltage output, and uses a digital potentiometer to control the voltage division of the reference voltage source. The output current is adjusted through two voltage pins, thereby achieving the highest efficiency transmission with flexible and variable power consumption and optical power in different water environments and transmission distances.

5. The underwater wireless optical communication system based on adaptive transmission and lightweight reception as described in claim 4, characterized in that, The constant current source circuit also includes a gate driver, which uses a dual-channel high-speed low-side gate driver chip to achieve fast switching of the MOSFET through fast turn-off technology.

6. The underwater wireless optical communication system based on adaptive transmission and lightweight reception as described in claim 5, characterized in that, The power control module includes a low-ripple and high dynamic load regulation DC-DC converter chip and an RF LDO, ensuring the lowest voltage noise floor in the power rail of the transmitter circuit.

7. An underwater wireless optical communication system based on adaptive transmission and lightweight reception as described in claim 6, characterized in that, The equalizer uses a T-type equalization circuit to compensate for the frequency response of the LEDs.

8. An underwater wireless optical communication system based on adaptive transmission and lightweight reception as described in claim 7, characterized in that, The electro-optical conversion unit utilizes the 450nm and 520nm blue-green light bands for bidirectional visible light communication; the LED array includes a 450nm blue LED and a 520nm green LED, wherein the 450nm blue LED has a center wavelength of 450nm, an operating voltage of 2.8-3.0V, and an operating current of 700mA; the 520nm green LED has a center wavelength of 520nm, an operating voltage of 3.0-3.2V, and an operating current of 700mA.

9. An underwater wireless optical communication system based on adaptive transmission and lightweight reception as described in claim 8, characterized in that, The lightweight receiver module includes a photodetector, a transimpedance amplifier, and a signal shaper; The photodetector uses a PIN photodiode to capture weak light signals transmitted underwater and convert them into photocurrent. The transimpedance amplifier is used to convert the photocurrent into a voltage signal and perform preliminary amplification; The signal shaper is a Schmitt trigger, used to perform binarization processing on the signal using hysteresis characteristics, filter out noise, and shape it into a digital pulse signal.

10. An underwater wireless optical communication system based on adaptive transmission and lightweight reception as described in claim 9, characterized in that: The FPGA module uses the Xilinx ZYNQ7000 series XC7Z020-CLG400-2 chip.

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