Underground equipment communication system and method based on visible light

Abstract

The invention relates to the technical field of communication, and discloses a visible light-based underground equipment communication system and method, underground equipment and a control method thereof. The system comprises a control end used for generating a control signal, a sending end used for sending an optical signal to an air channel, and a receiving end used for receiving the optical signal and recovering the optical signal into the control signal, the control end is connected with the sending end and used for transmitting control signals. The transmitting end comprises a light source of which the luminescence characteristic accords with the Lambert point light source characteristic, and a multi-stage voltage amplification control module for controlling the light source to flicker according to the control signal; the receiving end comprises a photodiode used for converting the captured optical signal into an electric signal, a transimpedance amplification module used for amplifying the converted signal, and a signal processing module used for recovering the control signal. According to the invention, reliable data transmission can be realized while uniform illumination is provided, the communication rate and the anti-interference capability are improved, and the adaptivity and the stability in a severe environment are ensured.

Description

Technical Field

[0001] The present invention relates to the field of communication technologies, and particularly to an underground equipment communication system and method based on visible light, as well as an underground equipment and its control method. Background Art

[0002] With the continuous advancement of the industrialization process, the demand for mineral resources in China is increasing continuously. The huge market demand puts forward higher requirements for the mining industry. The modern energy system plan points out that the transformation of the energy production and consumption mode towards green and low-carbon is the main direction of future development. Vigorously promoting the construction of green mines and digital mines, and listing the safe and efficient production of mines as a key development area. Mine communication, as an important foundation in the digital development of the mining industry, is an important field in the future intelligent production of mines.

[0003] Today, as mine production is becoming increasingly intelligent, how to ensure the stability and high efficiency of the communication system during the production process is an important issue that urgently needs to be solved at present. Due to factors such as the harsh underground environment, special production methods, and complex production links, the stability, reliability, and security of the communication system face huge challenges. Currently, the widely used underground radio frequency communication system, when facing the harsh environment of high dust and high humidity underground, the radio frequency signal is affected by dust particles and water molecules in the air, resulting in signal attenuation and multipath interference, leading to a relatively high transmission error rate of the system and poor signal quality. Secondly, the electromagnetic effect brought during the communication process becomes a major threat to the safety of mine production; some other underground communication systems that directly use cables for data transmission, such as the underground leaky communication system, which conducts information transmission and reception through special cables, resulting in the reliability of the system transmission depending on the leaky cable. The cable is relatively sensitive to the external storage environment, and the harsh environment accelerates the aging and wear of the cable, leading to increased signal loss and decreased quality. Moreover, due to a large number of underground devices being connected to the cable, a large amount of interference signals are generated during operation, easily resulting in unstable transmission of the system. Summary of the Invention

[0004] Aiming at the problems existing in the above-mentioned prior art, the present invention introduces visible light communication technology into mine communication. Visible light communication transmits data through optical signals, and this process is not affected by electromagnetic interference generated by devices such as motors and cables in the mine environment and does not generate electromagnetic radiation during the communication process, ensuring the stability and security of the communication process; this communication system is combined with the existing lighting system, reducing the probability of independent failure of the device and improving the overall reliability of the system.

[0005] The present invention discloses an underground equipment communication system based on visible light, including: a control end for generating a control signal, a sending end for sending an optical signal into the air channel, and a receiving end for receiving the optical signal and restoring it to a control signal;

[0006] Among them, the receiving end is used for communicating and connecting with downhole equipment, and the control end is connected to the sending end for transmitting control signals;

[0007] The sending end includes: a light source whose luminous characteristics conform to the Lambert point light source characteristics, and a multi-stage voltage amplification control module connected to the light source, which is used to control the flashing of the light source according to the control signal;

[0008] The receiving end includes: a photodiode for converting the captured optical signal into an electrical signal, a transimpedance amplification module for amplifying the converted signal, and a signal processing module for restoring the control signal.

[0009] Furthermore, the control end is used for:

[0010] Based on LabVIEW as the system control core to realize the functions of instruction generation, communication status display, and signal sending;

[0011] Based on the USB-TTL module for physical connection with the sending end, sending control instructions through keyboard input, and displaying the communication status in real time.

[0012] Furthermore, in the sending end:

[0013] The light source includes 42 LEDs, with a total power of 35W, a light color of white light, a color temperature of 6500K, a luminous efficacy of 120lm / W, and a modulation bandwidth of 375kHz; the LED array is installed on an 80mm×120mm perforated board in a rectangular architecture;

[0014] The multi-stage voltage amplification control module is used to realize the driving ability from low voltage to high voltage through multi-stage amplification of the control signal, so as to complete high-frequency flashing control and meet the high-power driving requirements of the LEDs;

[0015] The sending end also includes:

[0016] A signal shaping module, connected to the control end, is used to compare the control signal with the reference voltage, eliminate signal distortion during hardware transmission, and ensure stable signal output;

[0017] A power supply module is used to convert 220V alternating current into a stable direct current power supply to provide power support for the entire sending end.

[0018] Furthermore, in the receiving end:

[0019] The response wavelength of the photodiode covers 400~1100nm, the response time is 15ns, and the dark current is as low as 0.5pA, so as to be suitable for the mine environment;

[0020] The transimpedance amplifier has a gain of 10^6V / A and a bandwidth of 5MHz to ensure signal integrity;

[0021] A signal processing module, configured to receive the amplified signal, and complete signal shaping and filtering through an analog-to-digital converter to restore the original control signal.

[0022] The present invention also discloses a method for communicating between underground devices based on visible light, which is implemented based on the above-mentioned communication system for underground devices based on visible light. The method includes:

[0023] The control end generates a control signal and transmits it to the sending end. The sending end controls the flashing state of the light source based on the control signal to emit an optical signal into the air channel;

[0024] The optical signal is transmitted to the receiving end through line-of-sight. The receiving end converts the optical signal into an electrical signal, which is amplified and then subjected to signal processing and demodulation to obtain a demodulated signal;

[0025] The demodulated signal is sent to the device end.

[0026] Further, the signal processing after amplifying the electrical signal includes: performing a shaping method with a dynamic decision voltage that is adjusted in real time according to the magnitude of the waveform peak voltage. Specifically, as follows:

[0027] Step 1: Measure the voltage value of the original input signal in real time through an analog-to-digital converter, and capture the peak voltage V max , that is, the highest voltage of the signal;

[0028] Step 2: Generate a PWM signal. The duty cycle of the PWM signal determines the average voltage value of the output signal; the duty cycle is defined as:

[0029] DC = (T n / T) × 100%

[0030] where DC is the duty cycle, T n is the duration of the high level, and T is the total cycle time;

[0031] By adjusting the duty cycle, make the average voltage of the output PWM signal be V max / 2;

[0032] Step 3: Smooth the PWM signal through an RC low-pass filter. The RC low-pass filter is used to block high-frequency components higher than the cut-off frequency and only allow low-frequency components lower than the cut-off frequency to pass through; the cut-off frequency is expressed as:

[0033] f c = 1 / (2πRC)

[0034] Step 4: Set the decision voltage to V max / 2. For the signal after RC filtering, output a DC voltage, and this DC voltage is V max / 2, and this DC voltage is the decision voltage for comparing the voltage value of the preprocessed signal;

[0035] If the voltage of the signal is higher than the decision voltage, the signal is determined to be at a high level; if the voltage of the signal is lower than the decision voltage, the signal is determined to be at a low level.

[0036] Step 5: Implement signal shaping. By comparing the preprocessed signal and the decision voltage, the original input signal is reconstructed into a standard digital signal, so that the shaped signal resumes a square wave shape.

[0037] The present invention also discloses an underground device, including a device body, and the device body is communicatively connected to the receiving end in the above-mentioned visible light-based underground device communication system to execute instructions.

[0038] The present invention also discloses a control method for an underground device, including:

[0039] Obtain a demodulated signal through the above-mentioned visible light-based underground device communication method;

[0040] Execute corresponding instructions based on the demodulated signal.

[0041] By adopting the above technical solutions, the dual functions of mine lighting and data communication can be realized. Through the combination of OOK modulation and high-power LEDs, reliable data transmission is achieved while providing uniform illumination. The system has a low-power and low-complexity hardware design, uses multi-stage voltage amplification and high-performance PIN photodiodes to improve the communication rate and anti-interference ability, and ensures self-adaptability and stability in harsh environments. In addition, the system supports rapid deployment and maintenance, conforms to the existing mine power supply architecture, and uses visible light communication technology without electromagnetic interference to provide a safe and efficient solution for the intelligent and green development of mines.

[0042] Other beneficial effects of the present invention will be described in detail in the specific implementation part. Description of the Drawings

[0043] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0044] Figure 1 It is a system block diagram of a visible light-based underground device communication system disclosed in an embodiment of the present invention.

[0045] Figure 2It is a schematic diagram of the radiation range of the lighting system disclosed in the embodiments of the present invention.

[0046] Figure 3 It is a schematic diagram of the channel transmission of visible light communication underground in the embodiments of the present invention.

[0047] Figure 4 It is a schematic diagram of the signal transmission process disclosed in the embodiments of the present invention.

[0048] Figure 5 It is a schematic diagram of the simulation of the lighting effect of the square structure disclosed in the embodiments of the present invention.

[0049] Figure 6 It is a schematic diagram of the simulation of the lighting effect of the circular structure disclosed in the embodiments of the present invention.

[0050] Figure 7 It is a color temperature diagram disclosed in the embodiments of the present invention.

[0051] Figure 8 It is a relative spectral power distribution diagram under different color temperatures disclosed in the embodiments of the present invention.

[0052] Figure 9 It is an LED modulation bandwidth diagram disclosed in the embodiments of the present invention.

[0053] Figure 10 It is an architecture diagram of the lighting module disclosed in the embodiments of the present invention.

[0054] Figure 11 It is an illuminance simulation diagram disclosed in the embodiments of the present invention.

[0055] Figure 12 It is a waveform diagram of the received end response voltage signal disclosed in the embodiments of the present invention.

[0056] Figure 13 It is a signal shaping logic diagram disclosed in the embodiments of the present invention.

[0057] Figure 14 It is a reference voltage waveform diagram disclosed in the embodiments of the present invention.

[0058] Figure 15 It is a demodulated signal waveform diagram disclosed in the embodiments of the present invention.

[0059] Figure 16 It is a waveform diagram of the control signal disclosed in the embodiments of the present invention.

[0060] Figure 17 It is a response waveform diagram under a harsh channel environment disclosed in the embodiments of the present invention.

[0061] Figure 18 It is a schematic circuit diagram of the principle of the low-pass filter disclosed in the embodiments of the present invention.

[0062] Figure 19 It is the demodulation waveform diagram in a harsh channel environment disclosed by an embodiment of the present invention.

[0063] Figure 20 It is the physical diagram of the controlled vehicle disclosed by an embodiment of the present invention.

[0064] Figure 21 It is the experimental scenario diagram disclosed by an embodiment of the present invention.

[0065] Figure 22 It is the harsh channel state diagram disclosed by an embodiment of the present invention.

[0066] Figure 23 It is the system architecture diagram disclosed by an embodiment of the present invention. Detailed implementation manners

[0067] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other implementation manners obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope protected by the present invention.

[0068] The professional terms involved in the embodiments of the present invention are as follows:

[0069] OOK, On-Off Keying, refers to a modulation method;

[0070] LabVIEW refers to a program development environment;

[0071] USB-TTL refers to a commonly used electronic conversion module;

[0072] ADC, Analog-to-Digital Converter, analog-to-digital converter;

[0073] LOS, Line-of-Sight Transmission, line-of-sight transmission;

[0074] NLOS, Non-Line-of-Sight Transmission, non-line-of-sight transmission.

[0075] Embodiment 1

[0076] As Figure 1 shown, the present invention discloses an underground equipment communication system based on visible light, including: a control end for generating a control signal, a sending end for sending an optical signal into an air channel, and a receiving end for receiving the optical signal and restoring it to the control signal.

[0077] Among them, the receiving end is used for communication connection with downhole equipment, and the control end is connected to the sending end for transmitting control signals.

[0078] The sending end includes: a light source whose luminous characteristics conform to the Lambert point light source characteristics, and a multi-stage voltage amplification control module connected to the light source for controlling the flashing of the light source according to the control signal.

[0079] The receiving end includes: a photodiode for converting the captured optical signal into an electrical signal, a transimpedance amplification module for amplifying the converted signal, and a signal processing module for restoring the control signal.

[0080] Specifically, this embodiment mainly includes the following steps:

[0081] Step 1: Implementation of the control end. The control end uses LabVIEW software as the system control core, with functions of instruction generation, communication status display, and signal sending. Physically connected to the sending end through a USB-TTL module, the control end can input and send various control instructions through the keyboard and display the communication status in real time. When the connection is interrupted, the control end can stop signal sending in time to avoid misoperation; after the connection is restored, the system can automatically restart. The control end interface is intuitive and easy to operate, suitable for the complex working environment of the mine.

[0082] Step 2: Implementation of the sending end. The sending end mainly includes the following sub-modules:

[0083] Light source module. The light source uses a 2W white LED with a color temperature of 6500K, a luminous efficacy of 120lm / W, and a modulation bandwidth of 375kHz. The LED array is installed on an 80mm×120mm perforated board in a rectangular structure, with high light uniformity, meeting the downhole lighting requirements.

[0084] Signal shaping module. The STM32F103C8T6 microcontroller is used to compare the control signal with the reference voltage to eliminate signal distortion during hardware transmission and ensure stable signal output.

[0085] Multi-stage voltage amplification module. The signal is amplified through multiple stages to achieve the driving ability from low voltage (3.3V) to high voltage (19.5V). The IRF520 MOSFET is used to complete high-frequency flashing control, meeting the high-power driving requirements of the LED.

[0086] Power supply module. The SM-GPA40B-24 industrial control power supply module is used to convert 220V alternating current into a stable direct current power supply, providing efficient and reliable power support for the entire sending end.

[0087] Step 3: Implementation of the control end. The receiving end is designed with a PIN photodiode and a transimpedance amplifier as the core to complete signal capture, amplification, and demodulation functions.

[0088] Photodiode module, using LSSPD-1.2PIN photodiode, with response wavelength covering 400 - 1100nm, response time of 15ns, and dark current as low as 0.5pA, suitable for high-dust and high-humidity environments in mines.

[0089] Transimpedance amplification module, using a transimpedance amplifier based on AD825, converting weak photocurrent signals into processable voltage signals, with a gain as high as 10^6V / A and a bandwidth of 5MHz, ensuring signal integrity.

[0090] Signal processing module, the microcontroller STM32F103C8T6 receives the amplified signal, and completes signal shaping and filtering through a high-resolution ADC module to restore the original control instruction.

[0091] Step 4: Communication process, when the control end sends an instruction, the signal is transmitted to the sending end through the USB-TTL module, and after shaping, it controls the high-frequency flashing of the LED; the optical signal is transmitted to the receiving end through the line-of-sight channel (LOS), the photodiode captures the optical signal and converts it into an electrical signal, which is amplified by the transimpedance amplifier and then the signal processing and demodulation are completed by the microcontroller, and finally the demodulated signal is fed back to the control system to achieve point-to-point communication.

[0092] Step 5: Environmental adaptability, the system automatically adjusts the signal shaping and demodulation strategies by analyzing the characteristics of the optical signal in the channel. In a good channel environment, a simple OOK demodulation method is used; in a harsh channel environment (high dust, high humidity), the system optimizes signal shaping and filtering through a dynamic algorithm to ensure the accuracy of demodulation.

[0093] Step 6: Experimental verification, the system is installed in a simulated mine environment for testing. When the communication distance is 3.5 meters, the illumination uniformity reaches above 50lx, the data transmission rate reaches 19.2Kbps, and the signal error rate is lower than 10 ^-6 . In a high-humidity and high-dust environment, by adjusting the demodulation strategy, the system can still maintain stable communication performance, verifying its reliability and practicality.

[0094] As Figure 2 shown, this embodiment shows the radiation range diagram of the lighting system. The emitting LED has light-emitting characteristics that conform to the Lambertian point light source characteristics, that is, its illumination intensity gradually decreases as the emission angle increases. In the vertical direction, the illumination intensity is the largest, and its brightness distribution conforms to the isotropic brightness characteristics, that is, the brightness distribution is the same no matter from which direction it is viewed, and the light is evenly distributed; although the illumination intensity changes with the angle, its total radiation power is constant.

[0095] As Figure 3As shown, this embodiment shows a schematic diagram of the transmission channel. It describes the transmission process of signals from the transmitter to the receiver in a visible light communication system, including line-of-sight transmission (LOS) and non-line-of-sight transmission (NLOS). The transmitter generates an optical signal by controlling the high-frequency blinking of the LED. The optical signal propagates in the air and reaches the receiver through a direct path (LOS) or after reflection (NLOS). The photodiode at the receiver captures the optical signal and converts it into an electrical signal, which is amplified by a transimpedance amplifier and then transmitted to the microcontroller for demodulation and recovery.

[0096] As Figure 4 shown, this embodiment shows a signal transmission process diagram. It shows the entire communication process from generating a control signal at the control end to completing signal recovery at the receiver end. The control end generates a digital signal through the microcontroller and transmits it to the transmitter. The transmitter modulates the on / off state of the LED according to the control signal and emits the optical signal into the air channel. The receiver receives the optical signal through the photodiode and converts it into an electrical signal. After being amplified by a transimpedance amplifier, it is transmitted to the microcontroller for filtering, shaping, and demodulation, and finally restored to the original control signal. The whole process clearly demonstrates the full-link operation of the signal from generation, modulation, transmission to demodulation.

[0097] As Figure 5 and Figure 6 shown, this embodiment shows simulation diagrams of the lighting effects of square and circular structures. In terms of the lighting module architecture, the differences in lighting effects between the square and circular cases are fully considered, and under the condition of the same type and number of LED configurations, TracePro software is used to simulate the lighting effects of the two shapes respectively.

[0098] As Figure 7 shown, this embodiment shows a color temperature diagram. The 6500K color temperature LED selected in this embodiment has a cooler white light color closer to sunlight compared to the 5500K color temperature LED applied in the market. In the color composition, the blue light component increases significantly, its photon density increases, and the spectral power is stronger. Since blue light has higher energy than red light, it has stronger penetration in the face of a harsh channel environment, thus ensuring the stability of the communication system transmission.

[0099] As Figure 8 shown, this embodiment shows the relative spectral power distribution diagrams at different color temperatures.

[0100] As Figure 9As shown, this embodiment shows the LED modulation bandwidth diagram. The lighting module needs to achieve fast strobing for information transmission while taking into account lighting, so the modulation bandwidth of the LED used in it largely determines the modulation bandwidth of the visible light communication system. By applying a square wave signal with the same amplitude and duty cycle to both ends of a single LED, changing the frequency of the square wave signal, observing the change process of its light intensity, and conducting a large number of experiments, a data result diagram is obtained.

[0101] like Figure 10 As shown, this embodiment shows the lighting module architecture diagram. This design proposes a 6*7 rectangular architecture as the lighting system architecture, forming a lighting LED with a total voltage of 19.5V, a total current of 1.8A, and a total power of 35W, which is installed in an 80mm*120mm perforated board to ensure heat dissipation during the lighting process.

[0102] like Figure 11 As shown in the figure, this embodiment shows an illumination simulation diagram. This time, the illumination of the designed lighting module was simulated in an environment of 2m to 4m. According to the illumination simulation results, when the communication distance is 3.5m, the illumination is greater than 50lx, which meets the national standard; when the communication distance is 3m, the illumination is greater than 70lx, which is better than the existing lighting devices on the market.

[0103] like Figure 12 As shown, this embodiment shows the waveform of the receiving end response voltage signal. It can be seen from the figure that the receiving waveform does have an obvious tailing phenomenon, which is consistent with the above theoretical analysis. The level of the low level response is not uniform, and the high level response is about 2.2V. Such a signal input to the receiving end controller cannot be recognized.

[0104] like Figure 13 As shown in the figure, this embodiment shows the signal shaping logic diagram. This embodiment uses STM32F103C8T6 as a controller, and uses the ADC function in the controller to convert the demodulated analog signal into a digital signal V1 that can be mathematically compared. By introducing the judgment voltage V2, the demodulated signal voltage V1 read each time is compared with the judgment voltage V2. When V1<V2时,引脚输出低电平;当V1> When V2, the pin outputs a high level.

[0105] like Figure 14 As shown, this embodiment shows a reference voltage waveform diagram. The DC signal in the figure is the reference voltage magnitude, and it can be seen that when the peak voltage is 50%, the reference voltage passes through all the mutation points in the demodulated signal.

[0106] like Figure 15As shown, this embodiment presents a demodulated signal waveform diagram. The demodulated signal is a square wave signal, with the peak voltage of the demodulated signal being 3.3V and the low voltage signal being 0V, meeting the TTL signal demodulation standard.

[0107] As Figure 16 shown, this embodiment presents a waveform diagram of the control signal. The change trend of the demodulated signal well replicates the signal at the control end, and the duration of its signal is approximately the same as that of the control end signal, meeting the time error of system demodulation.

[0108] As Figure 17 shown, this embodiment presents a response waveform diagram under a harsh channel environment. Compared with a good channel environment, the shape of the received waveform does not change under a harsh channel environment, but the peak voltage will decrease.

[0109] As Figure 18 shown, this embodiment presents a schematic circuit diagram of the low-pass filter. Low-pass filters are generally divided into analog low-pass filters and digital low-pass filters. Analog filters are usually composed of resistors, capacitors or inductors. A common low-pass filter is the RC low-pass filter, which consists of a resistor and a capacitor.

[0110] As Figure 19 shown, this embodiment presents a demodulation waveform diagram under a harsh channel environment. The waveform of the demodulated signal is the same as that of the transmitted signal, and the peak voltage of the demodulated signal is 3.3V and the lowest voltage is 0V, meeting the characteristics of the TTL waveform and can be effectively read in the input system.

[0111] As Figure 20 shown, this embodiment presents a physical diagram of the controlled vehicle. To simulate the formal working environment in the mine, the controlled object verified in this embodiment is a remotely controlled intelligent vehicle, simulating an underground mine vehicle. And a transmission scenario with a communication distance of 3.5m is set up under dark conditions.

[0112] As Figure 21 shown, this embodiment presents an experimental scenario diagram. During the experiment, when the control end sends command content at a rate of 19.2Kbps, the vehicle can quickly identify the control information and make corresponding actions, and within the extreme illumination range of the lighting module, the vehicle still maintains an effective communication state. After measurement, the delay of the entire system is about 10 microseconds, and this communication delay is within the acceptable range.

[0113] As Figure 22 shown, this embodiment presents a harsh channel state diagram. To simulate the communication state in the mine, this embodiment experimentally builds a closed communication environment of 3.5m * 1m * 1m, and water mist and smoke are added to the scenario to simulate the high dust and high water vapor states during underground mine operations.

[0114] Embodiment 2

[0115] Based on the content disclosed in Embodiment 1, this embodiment further illustrates the present invention.

[0116] The construction method of the underground equipment communication system based on visible light disclosed in this embodiment is as follows:

[0117] (1) Overall design of the underground visible light communication system

[0118] First, analyze the environmental characteristics of the mine, propose corresponding design indicators, then model the underground visible light communication system, analyze the visible light communication system from a theoretical level, and select an LED lighting model, modulation method, and system model suitable for the underground environment. Finally, propose corresponding design schemes for each part of the underground visible light communication system. This part provides theoretical support for subsequent designs.

[0119] (1.1) Analyze requirements and environmental characteristics. In the mine environment, roadways are usually long and narrow and enclosed, and high humidity and high dust pose severe challenges to signal propagation. The system needs to meet the dual requirements of mine lighting and communication, where the communication distance is at least 3.5 meters, and the lighting coverage is without dead angles and uniform. In addition, the system must be portable to adapt to dynamic deployment and be able to achieve stable and highly reliable communication under harsh channel conditions.

[0120] (1.2) Theoretical model and technology selection. According to optical characteristics, construct a light source and channel model based on the Lambert model, and distinguish the line-of-sight (LOS) and non-line-of-sight (NLOS) transmission characteristics. In terms of modulation technology, by comparing methods such as OOK, FSK, and PSK, select OOK modulation, whose simple and efficient characteristics are suitable for the complex mine environment. At the same time, propose a system model based on theoretical analysis, emphasizing improving transmission reliability by enhancing the incident light power and optimizing the receiver design.

[0121] (1.3) System architecture and module design. Design a system architecture including a control end, a sending end, and a receiving end, and clarify the functions of each module. The control end realizes signal generation and interface communication through LabVIEW; the sending end uses a high-power LED to achieve modulation and lighting functions, and at the same time uses a multi-stage voltage amplification circuit to improve the driving ability; the receiving end completes signal reception, shaping, and demodulation through a PIN photodiode, a transimpedance amplifier, and a microcontroller. Finally, clear requirements are provided for the functions and performance indicators of the system, including communication rate, signal reliability, and hardware adaptability.

[0122] The model construction of the LED is specifically as follows. The light-emitting LED has light-emitting characteristics that conform to the Lambertian point light source characteristics, that is, its light intensity gradually decreases as the emission angle increases. In the vertical direction, the light intensity is the largest, as shown in formula (1). Its brightness distribution conforms to the isotropic brightness characteristics, that is, the brightness distribution is the same regardless of the viewing direction, and the light is evenly distributed. Although the light intensity changes with the angle, its total radiation power is constant.

[0123] I θ = I0 * cos(θ) #(1)

[0124] Where: I0 - the maximum radiation intensity in the normal direction, lux;

[0125] θ - the angle between the radiation direction and the normal, degree.

[0126] In practical applications, the LEDs of the lighting module are regularly distributed, and the position of each LED can be represented by the r l position vector, and n l is the normal vector of the light-emitting surface, and its mathematical model can be expressed as:

[0127] S = {r l , n l , m, FOV} #(2)

[0128] Where: FOV - the field of view of the light-emitting LED (Field of View, FOV);

[0129] m - the mode parameter of the light-emitting directivity.

[0130]

[0131] That is, the light intensity distribution of the LED light source can be expressed as:

[0132]

[0133] Then the incident light power of the LED is:

[0134]

[0135] Where: γ - the small solid angle, degree;

[0136] S r - the effective receiving area of the receiver, m 2 ;

[0137] d - the distance from the LED to the receiver, m.

[0138] In the transmission channel with d = 3.5 m, the overall radiation range of the LED is as Figure 2As shown, its radiation range can be expressed as:

[0139] X = tanα * 3.5 * 2#(6)

[0140] Where: α — half of the field of view (FOV) of the LED lighting system, in degrees;

[0141] X — horizontal radiation distance, in m.

[0142] As Figure 3 shown in the schematic diagram of the channel transmission of visible light communication in the mine, when the transmitted signal is transmitted to the receiving end, due to different relative positions, the transmission path is divided into line-of-sight transmission (LOS) and non-line-of-sight transmission (NLOS). The signal transmission process is as Figure 4 shown. The control signal passes through the microcontroller and is transmitted to the transmission control circuit to control the LED to emit light and flash. The receiving end PD receives the light intensity signal sent by the LED and transmits it to the microcontroller through the receiving circuit to complete the entire signal transmission. This process can be expressed as:

[0143]

[0144] Where: R — responsivity of the photodiode;

[0145] X(t) — emitted light intensity of the LED, in lux;

[0146] h(t) — unit impulse response of the channel;

[0147] N(t) — Gaussian noise in the channel.

[0148] This unit impulse response is composed of the unit impulse responses of n light-emitting LEDs and m PDs. Fundamentally, it is the sum of the unit impulse responses of n*m single LEDs and single PDs. That is, the unit impulse response h(t) can be expressed as:

[0149]

[0150] Where: h (0) (t) — unit impulse response generated in the LOS channel;

[0151] represents the unit impulse response generated after k reflections in the NLOS channel.

[0152] In the mine communication system, the communication distance is much larger than the size of the PD receiving surface. Moreover, due to the uneven inner wall of the mine, the absorption and reflection of light are serious. The impulse response of the system is mainly contributed by the LOS channel. In this embodiment, only the LOS channel is considered, that is:

[0153]

[0154] In the formula: A R —— Effective acceptance area of PD, m 2 ;

[0155] —— Angle between PD receiving line and normal line, degree.

[0156] The PD response is given by the following formula:

[0157] I r = R I * P in #(10)

[0158] In the formula: I r —— Response current, A;

[0159] R I —— Responsivity of PD. When the wavelength of incident light is fixed, the responsivity is a constant value.

[0160] According to the above formula for PD response, to enhance the response current of the system, it is necessary to increase the incident optical power under the LOS channel, that is, to increase the unit impulse response h(t) of the system, and ensure the Furthermore, to ensure the reliability of system transmission, in point-to-point communication, the incident optical power should be increased as much as possible to increase the system response current and ensure the stable transmission of the system.

[0161] (2) Design of OOK modulation LED lighting communication module applicable to underground environment.

[0162] In this embodiment, the underground LED lighting communication module is designed mainly considering the lighting aspect and the communication aspect. Selection and design are carried out from aspects such as the lighting characteristics and modulation bandwidth of the lighting module; for the problem of control signal interference in the communication process, the design of a signal shaping module is proposed; for the coupling problem between the lighting control circuit and the communication circuit, the design of a multi-stage voltage amplification control circuit is proposed; in the face of the power supply problems in the lighting aspect and the communication aspect, the circuit design to meet the power supply requirements is proposed.

[0163] In terms of the lighting module architecture, the lighting effect differences between the square and circular cases are fully considered, and under the condition of the same type and number of LED configurations, the lighting effects of the two shapes are respectively simulated using TracePro software, as Figure 5 and Figure 6 shown.

[0164] From the results, we can see that the maximum value of the illumination of the square structure is 1.0444e-005lx, and the minimum value is 3.6018e-018lx; the maximum value of the illumination of the circular structure is 1.1259e-004lx, and the minimum value is 1.2418e-017lx. The absolute difference in illumination of the square structure is significantly smaller than that of the circular structure, indicating that in practical applications, the lighting effect of the square structure is more uniform, less likely to form a spot effect, and the light source utilization rate is higher.

[0165] See also Figure 7 As shown in the color temperature diagram, the color of LED light with higher color temperature is more inclined to cool white light, similar to daylight. In the color composition, the blue light component increases significantly, thereby increasing the photon density and spectral power. The simulation results of its spectral power are shown in Figure 7 As shown in the figure, since the energy of blue light is higher than that of red light, blue light has stronger penetration in harsh channel environments, which helps to ensure the stability of communication system transmission.

[0166] The lighting module needs to achieve fast strobing for information transmission while taking into account lighting. Therefore, the modulation bandwidth of the LED used largely determines the modulation bandwidth of the visible light communication system. By applying a square wave signal with the same amplitude and duty cycle to both ends of a single LED and changing the frequency of the square wave signal, its light intensity change process can be observed. Through a large number of experiments, the collected data results are as follows Figure 9 shown.

[0167] The LED modulation bandwidth is usually defined by the 3dB frequency of the LED, that is, the half-power point. From the results, it can be seen that the frequency corresponding to the 3dB frequency point of the LED used is 750KHz. Since this embodiment adopts OOK modulation, the period of sending a single 0 or 1 signal is 750KHz, so in theory the modulation bandwidth of the LED is 375KHz (should be the frequency of half a period, that is, half of 750KHz), which meets the rate requirements for controlling signal transmission under normal circumstances.

[0168] To ensure the reliability of the communication system, this embodiment uses Fangpu 2W bright white LED as the lighting source. This LED has good characteristics in terms of color temperature, light efficiency, maximum allowable junction temperature, etc. The main parameters are shown in Table 1. In order to integrate the advantages of the above architecture, this design proposes a 6*7 rectangular architecture as the lighting system architecture, forming a lighting LED with a total voltage of 19.5V, a total current of 1.8A, and a total power of 35W, which is installed in an 80mm*120mm perforated board to ensure heat dissipation during the lighting process. Figure 10 shown.

[0169] Table 1 Main parameters of lighting LED

[0170]

[0171] In mine lighting, to ensure the safety of underground operations, the requirements for lighting illuminance vary for different working environments. Based on these requirements and the specific parameters and architecture of LEDs, the LED illuminance is simulated, as Figure 11 shown.

[0172] In this embodiment, the illuminance of the designed lighting module is simulated in the working environment of 2m to 4m. According to the lighting simulation results, when the communication distance is 3.5m, the illuminance is greater than 50lx, meeting the national standard; when the communication distance is 3m, the illuminance is greater than 70lx, superior to the existing lighting devices in the market.

[0173] (3) Design of an environment adaptive demodulation module based on OOK modulation.

[0174] First, the core devices of the demodulation module are introduced and selected, and the corresponding device models are given according to the design indicators; secondly, by analyzing the OOK demodulation waveform characteristics in a good channel environment, the corresponding demodulation scheme is proposed; finally, the demodulation waveform in a harsh environment is analyzed, and an adaptive demodulation scheme is proposed.

[0175] When the sending end outputs a control instruction, the lighting module adjusts the supply voltage of the LED according to the control instruction to achieve high-frequency flashing of the LED. According to the volt-ampere characteristics of the LED, the law of the current change at both ends of the LED with the voltage change can be obtained:

[0176]

[0177] In the formula: I LED ——The current at both ends of the LED, A;

[0178] I s ——The reverse saturation current of the LED, A;

[0179] V——The voltage at both ends of the LED, V;

[0180] n——The ideal factor of the LED;

[0181] V T ——The thermal voltage, V.

[0182] According to formula (11), it can be obtained that the current change of the LED is proportional to the voltage change at both ends of the LED. The current increases with the increase of the voltage. When it increases to the maximum thermal voltage, the current at both ends of the LED tends to be stable at I s . At this time, the emission optical power of a single LED can be expressed as:

[0183]

[0184] The transmission power P s of this lighting module is:

[0185]

[0186] Where: n -- the total number of LEDs constituting the lighting module.

[0187] It can be obtained from formula (12) that the emission power of the LED is related to the electro-optical conversion efficiency η of the LED, and this value is usually in the range of 10% to 50%, and the specific value is related to the LED material and structure.

[0188] At this time, the number of photons N generated by the lighting module s :

[0189]

[0190] Where: E -- the energy of a single photon, KJ;

[0191] h -- Planck's constant;

[0192] λ -- the central wavelength of the LED, nm.

[0193] The channel environment is filled with photon signals emitted by the lighting module at the sending end. In an excellent channel environment, the concentrations of dust and water mist in the air are both at a low level, and the impact on the communication system can be ignored.

[0194] At the receiving end, it is known that the light intensity distribution characteristic of the LED at the sending end follows the Lambert model, and the light rays diverge uniformly in free space. At a distance h, the distribution of its photons can be approximated as spherical diffusion, resulting in an area of 4πh 2 , and the received optical power density at this distance is I r :

[0195] I r = (εN s × E) / (4πh 2 ) #(15)

[0196] Where: εN s -- the number of photons received at this distance, and ε is a constant from 0 to 1.

[0197] It is known that the effective receiving area at the receiving end is S r , then at this distance, the receiving power of the photodiode is P r :

[0198] P r = I r × S r = S r × (εN s × E) / (4πh 2 ) #(16)

[0199] The response current of the photodiode can be obtained from Equation (16). After passing through the transimpedance amplifier, the final response signal can be obtained.

[0200] During the entire communication process, since the frequency of the control signal sent is relatively high, the LED is in a high-frequency switching state. The electron transition state inside its PN junction is unstable, resulting in a small number of electrons still being in the transition state within a very short time after the LED is turned off, that is, the LED still emits weak light. This phenomenon is called the "afterglow effect" of the LED. Due to the existence of this effect, when the 0 control signal is sent, there are still a part of photons N in the channel s , resulting in the photodiode being unable to instantaneously reach the 0-level state and having a large tail.

[0201] According to the bandwidth parameter of the photodiode, it can be known that due to the charge storage effect inside the photodiode, when the light source stops irradiating, the charges in the depletion layer and the minority carrier region need a long time to reset. Therefore, the fall time T d is often greater than the rise time T u .

[0202] According to the above theory and selection, a visible light communication system was built to conduct a physical experiment with a communication distance of 3.5 m. The waveform at the receiving end is as Figure 12 shown. It can be seen that there is indeed an obvious tailing phenomenon in its received waveform, which is consistent with the above theoretical analysis. The magnitude of the low-level response is not uniform, and the peak voltage of the response signal is approximately 2.2 V. Such signals cannot be recognized when input to the receiving end controller.

[0203] Based on the above analysis, it is proposed to add a decision voltage for signal shaping. The overall idea is as Figure 13 shown. In this embodiment, STM32F103C8T6 is used as the controller for shaping. Using the ADC function inside the controller, the demodulated analog signal is converted into a digital signal V1 that can be mathematically compared. By introducing the decision voltage V2, the demodulated signal voltage V1 read each time is compared with the decision voltage V2. When V1 < V2, the pin outputs a low level; when V1 > V2, the pin outputs a high level.

[0204] The setting of the decision voltage V2 will be an important factor affecting the demodulation effect. The value of the decision voltage should be reasonably selected so that it can effectively distinguish the high level and the low level of the signal, thereby ensuring the integrity of the signal. In addition, the signal period after demodulation according to the decision voltage should be consistent with the signal period sent by the control end.

[0205] Figure 12The peak voltage of the shown response signal is approximately about 2.2V. When the decision voltage V2 is half of the peak voltage, it passes through all the mutation points of the response waveform, including all the information in the signal; and the corresponding duration is approximately equal to half of the signal period, meeting the error condition of the demodulated signal.

[0206] According to the above scheme, the reference voltage of the demodulated signal is taken as Figure 14 shown.

[0207] The demodulated signal under this decision voltage is as Figure 15 shown. The signal sent by the control end of the system is as Figure 16 shown.

[0208] Refer to Figure 15 , the demodulated signal is a square wave signal. The peak voltage of the demodulated signal is 3.3V, and the low voltage signal is 0V, meeting the TTL signal demodulation standard. Compared with Figure 16 , the change trend of the demodulated signal well replicates the signal of the control end, and its signal duration is approximately the same as that of the control end signal, meeting the time error of the system demodulation.

[0209] The analysis of the demodulated signal and the proposed adaptive demodulation scheme in the described harsh channel environment are specifically as follows. In general environments, when optical signals propagate in the channel, due to the low concentration and small volume of dust and water vapor in the air, the influence of these particulate matters on the propagation of optical signals can be ignored. During the mining process in the mine, operations such as drilling, cutting, and grinding result in the crushing of ores, and a large amount of tiny water vapor and dust particles fill the air, maintaining a relatively high concentration.

[0210] In visible light communication, optical signals will collide with opaque fine particulate matters and refract in transparent water vapor molecules as the channel environment changes, resulting in fewer optical signals reaching the PD and an increase in the propagation distance. From the attenuation characteristics of optical signals, the energy of optical signals decays exponentially as the propagation distance increases, leading to an exponential decay of the received optical intensity at the receiving end:

[0211] P r =P s ×e -αl #(17)

[0212] In the formula:

[0213] α —— attenuation coefficient, indicating the degree of attenuation of the signal during channel propagation;

[0214] l —— distance that the optical signal passes through to reach the PD end, m.

[0215] The influence of dust particles in the air on optical signals is mainly manifested in the scattering effect and absorption effect on optical signals:

[0216] 1. Scattering effect

[0217] Scattering refers to the change in the propagation direction of an optical signal after it interacts with dust particles during propagation. For larger particles in the channel, the main types of scattering that occur are Rayleigh Scattering and Mie Scattering.

[0218] 2. Absorption effect

[0219] Dust particles not only scatter light but also absorb a portion of the light energy. Especially for certain dust particles with absorption characteristics, such as coal dust and organic dust, these particles convert the absorbed photon energy into heat energy, resulting in a loss of photon energy. The strength of the absorption effect is usually affected by the chemical composition, morphology, and surface characteristics of the particles.

[0220] According to the above analysis, the attenuation effect of particulate dust on photons is affected by its concentration and particle size. In the same spatial range, the higher the dust concentration ρ dust the greater the attenuation coefficient α dust will be.

[0221] α dust = K × ρ dust #(18)

[0222] Where: K - a constant related to the characteristics of the dust particles.

[0223] Water vapor in the air usually exists in the form of water vapor. Although its concentration is lower than that of dust, in a high-humidity channel environment, it still has a significant impact on the propagation of visible light communication. In long-distance communication and short-wavelength light communication, there is no phenomenon where photons cannot penetrate water vapor, and the attenuation of the channel is mainly manifested as an absorption effect.

[0224] The absorption effect is mainly manifested in the interaction between water molecules and photons. Absorbing the energy of the passing photons and converting it into heat energy results in signal attenuation. In this process, the magnitude of the absorption effect is related to the relative humidity. The greater the relative humidity, the stronger the absorption effect.

[0225] α water = N × ρ water #(19)

[0226] Where: α water - the attenuation coefficient generated by the absorption of water molecules;

[0227] N - a coefficient related to the absorption characteristics of water molecules;

[0228] ρ water——Relative humidity of water molecules.

[0229] In a harsh channel environment with high humidity and high dust, the received power at the receiving end can be expressed as:

[0230]

[0231] Summarizing the above analysis, when photons propagate in a harsh channel environment, they are attenuated by dust and water molecules in the channel, resulting in lower photon energy, which is manifested as lower received optical power at the receiving end. From formula (16), it can be obtained that in the same communication distance, the harsh channel environment affects the number of photons reaching the photodiode during each strobing, manifested as a smaller response voltage compared to the excellent channel environment.

[0232] In this embodiment, the communication distance is 3.5 m. Even if the photons are absorbed by the photodiode after multiple reflections and refractions, the distance l they travel is approximately 3.5 m. The time taken for the photons to travel is at the nanosecond level and can be ignored, which makes the strobing phenomenon of the optical signal the same as that in the excellent channel, ensuring that the shape of the signal does not change.

[0233] Summarizing the above conclusion, compared to the excellent channel environment, the shape of the received waveform in the harsh channel environment does not change, but the peak voltage will decrease.

[0234] According to the above theory and selection, a physical 3.5 m communication system is built, and dust and a small amount of water mist are incorporated into the channel. The received waveform is as Figure 17 shown.

[0235] Analyzing the received waveform, it can be seen that the peak voltage of its response waveform is 1.5 V. When the same control instruction is sent, the shape of its waveform does not change significantly, which is consistent with the theoretical analysis.

[0236] The experimental results prove that this scheme has a good effect when shaping such waveforms. However, when applied to the demodulation waveform in a harsh channel environment, the fixed decision voltage value is no longer suitable for the peak voltage of this waveform. Therefore, the research focus should be on designing a decision voltage that can change in real time according to the peak voltage of the decision voltage to ensure the shaping effect of the signal.

[0237] In this embodiment, the controller STM32F103C8T6 is used to read the peak voltage V max magnitude, and according to V max change the duty cycle of the output pulse modulation signal. Combining with an RC low-pass filter, a decision voltage signal with a magnitude of 50% of the peak voltage is output for signal shaping.

[0238] Pulse Width Modulation (PWM) signal is a technology that regulates the average power or voltage of a signal by adjusting the pulse width of the signal (i.e., the high-level time). PWM signals are usually square wave signals. Their basic characteristic is that the frequency remains constant, and the average voltage of the output signal is changed by varying the duration of the high level of the signal. Its main characteristics are frequency and duty cycle.

[0239] 1. Frequency

[0240] The frequency f refers to the number of cycles of the PWM signal, that is, the number of complete cycles of the PWM signal per second, with the unit of Hz; the period T refers to the time required for the PWM signal to go from the start of one cycle to the end of the next cycle, with the unit of s. The relationship between the two is:

[0241] f = 1 / T #(21)

[0242] 2. Duty Cycle

[0243] The duty cycle (Duty Cycle, DC) refers to the proportion of the duration T of the high level of the PWM signal in a complete cycle, usually expressed as a percentage, ranging from 0% to 100%. n DC = (T

[0244] / T) × 100% #(22) n / T) × 100% #(22)

[0245] PWM signals play an important role in many fields, especially when controlling and regulating output power. By adjusting the duty cycle of the PWM signal, control similar to that of analog signals can be achieved. The principle formula is:

[0246] V out = D × V o #(23)

[0247] In the formula: V out —— The magnitude of the output voltage, V;

[0248] D —— The duty cycle of the PWM signal;

[0249] V o —— The peak voltage of the microcontroller, V.

[0250] In the STM32 microcontroller, the reading of the magnitude V of the input voltage is completed through the built-in 12-bit ADC digital-to-analog converter. The principle formula of its output voltage becomes: in The principle formula of its output voltage becomes:

[0251] V out = V in / 4096 × V o #(24)

[0252] Since the PWM wave signal can be regarded as a signal containing a DC component and multiple high-frequency components, where the DC component is determined by the duty cycle and is the signal that needs to be output finally, and the high-frequency components are composed of the frequency and harmonics of the PWM and need to be filtered out. By using the attenuation characteristic of RC for high-frequency signals, the high-frequency part in the PWM wave signal is filtered out, and the DC component is retained.

[0253] A low-pass filter is an electronic circuit that allows low-frequency signals to pass through and suppresses high-frequency signals. Its basic function is to transmit signals with frequencies lower than a certain specific cut-off frequency f c . That is, when the frequency of the original input signal is lower than the cut-off frequency, its intensity and form can be retained and passed through; when the frequency of the original input signal is higher than the cut-off frequency, the energy of the high-frequency part of the signal is absorbed by the capacitor and attenuated under the impedance of the capacitor, and the degree of attenuation is proportional to the magnitude of the frequency. In this embodiment, the original input signal and the preprocessed signal actually refer to the representation forms of the same physical signal at different processing stages. Essentially, they are the same signal. Specifically, this signal is an electrical signal received from a visible light communication system and amplified.

[0254] Low-pass filters are usually divided into analog low-pass filters and digital low-pass filters. Analog filters are usually composed of resistors, capacitors or inductors. A common low-pass filter is an RC low-pass filter, which consists of a resistor and a capacitor. Its principle circuit is as Figure 18 shown:

[0255] The cut-off frequency f c is the key to determining the performance of the filter. The cut-off frequency is determined by determining the specific values of the resistor and capacitor in the circuit. Its principle formula is;

[0256] f c = 1 / (2πRC) #(25)

[0257] To sum up, in this embodiment, the STM32 pin is used to read the input analog signal, the peak voltage V max of the original input signal is determined by formula (24), the duty cycle of the output PWM wave signal is determined by formula (22), and the original input signal and the output signal are connected according to the schematic diagram of the low-pass filter, and then the judgment DC signal that changes with the peak voltage of the original input signal can be obtained.

[0258] According to the above theory and selection, a physical experiment is built, and the final demodulated signal is as Figure 19 shown.

[0259] It can be seen from the experimental results that the waveform of the demodulated signal is the same as that of the transmitted signal, and the peak voltage of the demodulated signal is 3.3V and the lowest voltage is 0V, which conforms to the characteristics of the TTL waveform and can be effectively read in the input system.

[0260] (4) System verification. Through physical verification of the above-designed content and in combination with the design indicators, verify whether the designed system meets the requirements;

[0261] For the system verification under the excellent channel environment, to simulate the formal working environment in the simulated mine, the controlled object verified in this embodiment is a remotely controlled intelligent vehicle, such as Figure 20 shown, simulating an underground mine vehicle. And a transmission scenario with a communication distance of 3.5 m is built under dark conditions, as Figure 21 shown. The remotely controlled intelligent vehicle can achieve actions of "forward", "backward", "left turn", and "right turn" through different instruction contents. When the control end sends the corresponding instruction content, the vehicle can complete the specified action.

[0262] During the experiment, when the control end sends the instruction content at a rate of 19.2 Kbps, the vehicle can quickly recognize the control information and make corresponding actions, and within the limit illumination range of the lighting module, the vehicle still maintains an effective communication state. After measurement, the delay of the entire system is about 10 microseconds, and this communication delay is within the acceptable range.

[0263] For the system verification under the poor channel environment, to simulate the communication state in the simulated mine, in this embodiment, an enclosed communication environment of 3.5 m * 1 m * 1 m is built for the experiment, and water mist and smoke are added to the scenario to simulate the high-dust and high-water-vapor states during underground mine operation, as Figure 22 shown. Conduct the above verification process again.

[0264] During the experiment, the system still sends the control signal at the same communication distance and communication rate, and the controlled vehicle still completes the corresponding instructions well. After measurement, the communication delay this time is about 17.5 microseconds, which is within the acceptable range.

[0265] Embodiment 3

[0266] This embodiment discloses a visible-light-based underground equipment communication method, which is implemented based on the visible-light-based underground equipment communication system disclosed in the above embodiment. The method includes:

[0267] The control end generates a control signal and transmits it to the sending end, and the sending end controls the light source flashing state based on the control signal to emit the optical signal into the air channel;

[0268] The optical signal is transmitted to the receiving end through line-of-sight, and the receiving end converts the optical signal into an electrical signal, which is amplified and then subjected to signal processing and demodulation to obtain a demodulated signal;

[0269] Send the demodulated signal to the equipment end.

[0270] There are two possible scenarios for the channel environment during underground mine production: In the initial stage of operation, the channel between the transceiver ends is in a relatively stable state, that is, there is no high water vapor or high dust in the channel; in the middle and late stages of operation, due to the characteristics of the operation process, there is a large amount of dust and water vapor in the channel, which makes the channel environment relatively harsh. Under the condition of simulating a harsh channel environment, the present invention constructs a 3.5-meter communication system, and adds dust and a small amount of water mist to the channel for experimental verification, as Figure 22 shown.

[0271] When using the voltage decision method to shape the demodulated signal waveform in a good channel environment, the effect is good. However, when applied to waveform demodulation in a harsh channel environment, due to its fixed decision voltage value, the single-threshold voltage decision method is no longer suitable for the peak voltage of the waveform in a harsh channel environment. Therefore, in this embodiment, a dynamic decision voltage that can be adjusted in real time according to the magnitude of the waveform peak voltage is provided to ensure the shaping effect of the signal. Combining Figure 23 with the system architecture diagram, the dynamic decision disclosed in this embodiment is as follows:

[0272] Step 1: Read the peak voltage V max . After the receiving end signal captures the optical signal through the photodiode and is converted into an electrical signal, it will be affected by environmental noise and transmission characteristics, resulting in inconsistent fluctuations in the high and low levels of the signal.

[0273] The analog-to-digital converter (ADC) built into the STM32F103C8T6 microcontroller can measure the voltage value of the original input signal in real time. By detecting the voltage change of the received signal, the system captures its peak voltage V max , that is, the highest voltage of the signal.

[0274] Step 2: Dynamically adjust the duty cycle of the pulse modulation signal. The STM32F103C8T6 generates a pulse width modulation (PWM) signal, and the duty cycle of the PWM signal determines the average voltage value of the output signal. The duty cycle is defined as:

[0275] DC=(T n / T)×100% #(26)

[0276] where, T n is the high-level duration, and T is the total cycle time.

[0277] To generate a dynamic decision voltage, the duty cycle of the PWM signal needs to be proportional to the measured peak voltage V max . By adjusting the duty cycle, the average voltage of the output PWM signal can be made V max / 2, that is, half of the peak voltage.

[0278] Step 3: The RC low-pass filter is used to implement the DC signal. The PWM signal is essentially a square wave signal with its high and low levels switching rapidly. To generate a stable DC voltage, an RC low-pass filter is required to smooth the PWM signal.

[0279] The function of the RC low-pass filter is to block the high-frequency components from passing through and only allow the low-frequency components to pass through. Its cut-off frequency f c is:

[0280] f c = 1 / (2πRC) #(27)

[0281] Step 4: The decision voltage is set to V max / 2. After the signal passes through the RC filter, a DC voltage is output, and this voltage is V max / 2. This is the dynamic decision voltage. The decision voltage is used to compare the voltage value of the preprocessed signal:

[0282]

[0283] Step 5: Implement signal shaping. Utilize the logic judgment function of STM32. By comparing the preprocessed signal and the decision voltage, the original input signal is reconstructed into a standard digital signal (high level or low level). The shaped signal restores the ideal square wave shape and eliminates the trailing and low-level drift problems caused by signal distortion.

[0284] Embodiment 4

[0285] This embodiment discloses an underground device and a control method. The underground device includes a device body, and the device body is communicatively connected to the receiving end in the underground device communication system based on visible light disclosed in the above embodiment to execute instructions.

[0286] Correspondingly, the control method of the underground device disclosed in this embodiment includes: obtaining a demodulated signal through the underground device communication method based on visible light disclosed in the above embodiment; executing corresponding instructions based on the demodulated signal.

[0287] The above description is only for the preferred embodiments of the present disclosure and the explanation of the applied technical principles. Those skilled in the art should understand that the scope of the invention involved in the embodiments of the present disclosure is not limited to the technical solutions formed by the specific combination of the above technical features, and should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the above inventive concept. For example, the technical solutions formed by mutually replacing the above features with the technical features (but not limited to) having similar functions disclosed in the embodiments of the present disclosure.

[0288] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered within the protection scope of the present invention.

Claims

1. A downhole equipment communication system based on visible light, characterized in that: include: A control end for generating a control signal, a transmitting end for transmitting an optical signal into an air channel, and a receiving end for receiving the optical signal and restoring it into a control signal; Among them, the receiving end is used to communicate with the downhole equipment, and the control end is connected to the sending end to transmit the control signal; The transmitting end includes: a light source whose luminous characteristics conform to the characteristics of a Lambertian point light source, and a multi-stage voltage amplification control module connected to the light source, for controlling the flickering of the light source according to a control signal; The receiving end includes: a photodiode for converting the captured light signal into an electrical signal, a transimpedance amplifier module for amplifying the converted signal, and a signal processing module for restoring the control signal.

2. The downhole equipment communication system based on visible light according to claim 1, characterized in that: The control terminal is used for: Based on LabVIEW as the system control core, it realizes the functions of command generation, communication status display and signal sending; Based on the physical connection between the USB-TTL module and the sending end, control instructions are sent through keyboard input and the communication status is displayed in real time.

3. The downhole equipment communication system based on visible light according to claim 1, characterized in that: In the sending end: The light source includes 42 LEDs with a total power of 35W, white light, a color temperature of 6500K, a luminous efficiency of 120lm / W, and a modulation bandwidth of 375kHz. The LED array is mounted on a 80mm×120mm perforated board in a rectangular structure. The multi-stage voltage amplification control module is used to amplify the control signal in multiple stages to achieve the driving capability from low voltage to high voltage, so as to complete high-frequency flicker control and meet the high-power driving requirements of LEDs; The transmitting end further includes: The signal shaping module is connected to the control terminal and is used to compare the control signal with the reference voltage to eliminate signal distortion during hardware transmission and ensure stable signal output; The power module is used to convert 220V AC power into stable DC power to provide power support for the entire sending end.

4. The downhole equipment communication system based on visible light according to claim 1, characterized in that: In the receiving end: The response wavelength of the photodiode covers 400-1100nm, the response time is 15ns, and the dark current is as low as 0.5pA, which is suitable for the mine environment; Transimpedance amplifier with gain up to 10^6V / A and bandwidth up to 5MHz to ensure signal integrity; The signal processing module is used to receive the amplified signal, and complete signal shaping and filtering through an analog-to-digital converter to restore the original control signal.

5. A downhole equipment communication method based on visible light, characterized in that: The method is implemented based on the downhole equipment communication system based on visible light as described in claims 1 to 4, and the method comprises: The control end generates a control signal and transmits it to the transmitting end, and the transmitting end controls the flashing state of the light source based on the control signal to transmit the light signal into the air channel; The optical signal is transmitted to the receiving end through line of sight, where the optical signal is converted into an electrical signal, amplified, and then processed and demodulated to obtain a demodulated signal; Send the demodulated signal to the device end.

6. The downhole equipment communication method based on visible light according to claim 5, characterized in that: The signal processing after the electrical signal is amplified includes: a shaping method using a dynamic decision voltage that is adjusted in real time according to the peak voltage of the waveform, as follows: Step 1: Measure the voltage value of the original input signal in real time through the analog-to-digital converter and capture the peak voltage V max , which is the highest voltage of the signal; Step 2: Generate a PWM signal. The duty cycle of the PWM signal determines the average voltage value of the output signal. The duty cycle is defined as: DC=(T n / T)×100% Where DC is the duty cycle, T n is the high level duration, T is the total cycle time; By adjusting the duty cycle, the average voltage of the output PWM signal is V max / 2; Step 3: Smooth the PWM signal through an RC low-pass filter. The RC low-pass filter is used to block high-frequency components above the cutoff frequency and only allow low-frequency components below the cutoff frequency to pass. The cutoff frequency is expressed as: in c =1 / (2πRC) Step 4: Set the decision voltage to V max / 2, the signal after RC filtering outputs a DC voltage, which is V max / 2, the DC voltage is the decision voltage used to compare the voltage value of the preprocessing signal; If the voltage of the preprocessing signal is higher than the decision voltage, the signal is judged to be a high level, and if the voltage of the preprocessing signal is lower than the decision voltage, the signal is judged to be a low level; Step 5: Implement signal shaping. By comparing the preprocessed signal and the decision voltage, the original input signal is reconstructed into a standard digital signal so that the shaped signal can be restored to a square wave shape.

7. A downhole device, characterized in that: It comprises a device body, which is communicatively connected to a receiving end in a downhole equipment communication system based on visible light as described in any one of claims 1 to 4 to execute instructions.

8. A method for controlling downhole equipment, characterized in that: include: Acquire a demodulated signal by the downhole equipment communication method based on visible light as claimed in claim 5 or 6; The corresponding instructions are executed based on the demodulated signal.

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