Receiving end automatic awakening method for free space optical communication

Abstract

The invention provides an automatic receiving end awakening method for free space optical communication, which comprises the following steps that: a receiving end starts a signal guarding mode in an idle state and works in a weak sampling mode; a communication request of a transmitting end is automatically judged by analyzing specified characteristics in the weak sampling signal; when the transmitting end has a communication request, the system is automatically awakened, a communication mode is started, and high-precision signal acquisition is started. Wherein the signal guarding unit comprises a pre-filtering unit, an automatic gain control unit, a weak sampling unit, a calculation control unit, a length detection unit, a high-precision acquisition unit and an interactive debugging unit. The method is characterized in that the real-time performance of system signal acquisition is improved through automatic wake-up of the receiving end; shallow data extraction is carried out based on signal features, the idle state mode of a receiving end is increased, the signal acquisition data volume of a sampling unit is reduced, and the on-chip data storage pressure is reduced; the variable-length receiving of data is realized, and the accuracy of signal acquisition is improved.

Description

Technical Field

[0001] This invention patent relates to free space optical communication, and specifically to an automatic wake-up method for the receiving end in free space optical communication. Background Art

[0002] Free space optical communication (FSO) is an optical two-way transmission technology that uses the atmosphere as a channel, modulated near-infrared or visible light as a carrier, and completes point-to-point, point-to-multipoint, or multipoint-to-multipoint transmission of information such as voice, data, and video. It is a relatively new type of broadband wireless access technology that covers multiple fields such as optics, mechanics, and electronics. Compared with traditional communication methods such as fiber optic communication, free space optical communication technology has advantages such as a wide communication bandwidth, rich optical wave resources, small device size, and good confidentiality, and has become a research hotspot in various countries in recent years. However, free space optical communication technology also has some deficiencies, such as limited communication transmission distance, difficult alignment between nodes, and great influence of the atmospheric channel environment on the transmission quality, which hinder the development of free space optical communication technology. In a free space optical communication system, the signal acquisition and reception method at the receiving end is an important factor affecting the signal-to-noise ratio and bit error rate of the system.

[0003] For example, the paper "Design and Implementation of a Large-Area APD Receiving Circuit" with article number "1002-5561(2021)09-0024-04" / DOI number "10.13921 / j.cnki.issn1002-5561.2021.09.006" discloses a design of an APD receiving circuit for visible light communication. This receiving circuit realizes high-speed information acquisition of visible light and subsequent following and shaping recovery by increasing the area of the photodetector APD. The system needs to perform high-speed sampling on the received signal in real time, and the signal processing unit operates at full load all the time, increasing the load of the system signal processing unit.

[0004] For example, the patent publication document with application number "202011472653.1" discloses a working method for a visible light communication system based on carrier index modulation. It also processes the input information. First, it groups the input information bit stream and subcarriers, and restores the original information through OFDM modulation at the transmitting end and demodulation at the receiving end. The system does not screen the received data signals, and all the signals collected at the receiving end need to undergo fast Fourier transform to achieve demodulation and recovery, increasing the signal processing pressure at the receiving end of the system.

[0005] The optical signal receiving unit disclosed in the patent publication document with the application number "202010188295.5" obtains communication data by receiving polarized light with a specified target polarization angle through polarization reception; the optical receiving section disclosed in the patent publication document with the application number "202080009543.3" directly converts the optical signal into an electrical signal through a photodiode; neither of the receiving ends of the optical communication systems described in the above patents screens the received signal, but instead improves the accuracy and speed of data acquisition by adjusting the angle or area size of the receiving device.

[0006] The patent publication document with the application number "WO2017009808A3" discloses a set of orthogonal aberration mode encoding methods for free-space optical communication. This patent encodes the transmission signal in the orthogonal aberration mode at the transmitting end to transmit user-defined information. At the receiving end, a high-speed wavefront sensor measures the amplitudes of various orthogonal aberration modes in the incident light beam at different times, and then extracts the user information through the amplitudes of the orthogonal modes at a specific time interval. This scheme extracts information from the received signal based on the encoding characteristics in the transmission signal, improving the system acquisition accuracy. However, similarly, it does not screen the transmitted light beam in the signal acquisition unit.

[0007] The patent publication document with the application number "202110763182.8" discloses a visible light communication system based on FPGA and a CMOS camera. The CMOS camera of this system performs real-time acquisition of the optical signal. After converting it into an electrical signal, a phase-locked loop is used to detect the phase difference of the output signal of the real-time detection signal receiving module and perform frequency adjustment. The data optimization module is used to extract and optimize the received signal. First, advanced timing matching is performed, and then grayscale processing is carried out. At this time, validity selection and threshold judgment are performed on the received data, and the result data is generated through grayscale value correction processing of the received data. This scheme effectively improves the system bit error rate, but still requires a large amount of data signals to be acquired for analysis, and the receiving end performs real-time acquisition with a large amount of data.

[0008] Such as Figure 1As shown in the figure, it is a basic method for signal acquisition at the receiving end of a free space optical communication system based on threshold comparison, including a signal input unit 1, a preamplification unit 2, a signal acquisition unit 3, a decoding unit 4, and a user terminal 5. The signal acquisition unit includes: a prefilter unit 301, a manual gain control unit 302, a threshold comparison and decision unit 303, and a signal acquisition unit 304. The character or voice signal sent from the transmitting end received by the photodetector is input by the signal input unit 2, and the preamplification unit 3 and the prefilter unit 301 perform amplification and filtering processing on the signal; the manual gain control unit 302 performs manual threshold gain control according to the signal amplitude range received under different communication distances and atmospheric environments, increasing or decreasing the threshold size of signal acquisition; the threshold comparison and decision unit 303 compares the received signal amplitude with the threshold size to determine whether the system receives an effective signal at this time and whether to start data signal acquisition; the signal acquisition unit 304 decides whether to start signal acquisition at the receiving end of the system according to the signal given by the threshold comparison and decision unit 303; the decoding unit 4 decodes the acquired data signal and outputs it to the user terminal 5; the user terminal 5 outputs the decoded signal to the upper computer screen for observation and display.

[0009] It can be seen from this that the following problems exist in the prior art:

[0010] (1) It is difficult to determine the threshold of signal acquisition at the receiving end of the optical communication system. As the communication distance changes, the strength of the signal received at the receiving end varies, and it is impossible to determine the optimal threshold point applicable to any communication distance. Therefore, it is relatively difficult to judge and separate the signal noise at the receiving end. When the channel noise is large, the signal characteristics received at the receiving end are not obvious, which may lead to signal distortion.

[0011] (2) Since no interrupt command is set for the acquisition module of the system, the acquisition unit at the receiving end of the system needs to maintain a continuous high-precision acquisition working state, start the ADC for uninterrupted acquisition, and the system acquisition unit runs for a relatively long time, increasing the load of the acquisition unit at the receiving end of the system and reducing the stability of the free space optical communication system. Summary of the Invention

[0012] The technical problem actually solved by this application is how to improve the real-time performance of signal acquisition at the receiving end of the free space optical communication system and obtain a better acquisition effect, and improve the stability of the receiving end of the free space optical communication system.

[0013] To solve the above problems, an embodiment of the present application provides an automatic wake-up method for the receiving end of free space optical communication. The method is characterized in that the receiving end enables a signal monitoring mode in the idle state and operates in a weak sampling manner; by analyzing specified characteristics in the weakly sampled signal, it automatically judges the communication request of the transmitting end; when there is a communication request from the transmitting end, it automatically wakes up the system and starts the communication mode to perform high-precision and high-speed signal acquisition. The automatic wake-up method includes the following steps:

[0014] The pre-amplified signal is input into the signal monitoring unit, and the signal monitoring unit realizes the automatic judgment of the start signal representing the start of communication and the automatic wake-up of the receiving end.

[0015] Among them, after the pre-filtering unit filters out high-frequency noise in the received signal, the automatic gain control unit adaptively compensates the signal according to the signal amplitude size, adjusts the signal amplitude to a specified amplitude range, and outputs it to the weak sampling unit for low-precision sampling; in the idle state of the receiving end, the calculation control unit performs digital signal processing on the channel noise when there is no signal transmission based on the specified characteristics of the signal and a specific signal transformation analysis method to obtain the signal reception threshold in the current communication environment. At this time, the system is in the idle state during the signal monitoring process.

[0016] The calculation control unit continuously performs transformation analysis calculations on the received signal, and compares the obtained received signal amplitude with the above-mentioned reception threshold; when the received signal amplitude is greater than the preset threshold, it is automatically determined that there is a communication request from the transmitting end of the current system, the receiving end automatically wakes up the signal acquisition function, and after the length detection unit extracts the length information of the signal, the high-precision acquisition unit starts sampling signals with a higher frequency.

[0017] The flow structure of the automatic wake-up method includes: a signal input unit, a pre-amplification unit, a signal monitoring unit, a decoding unit, and a user terminal; the signal monitoring unit includes: a pre-filtering unit, an automatic gain control unit, a weak sampling unit, a calculation control unit, a length detection unit, a high-precision acquisition unit, and an interactive debugging unit.

[0018] The signal input unit inputs the data signal received by the photodetector of the receiving end into the subsequent functional units for processing.

[0019] The pre-amplification unit amplifies the input signal.

[0020] The pre-filtering unit performs low-pass / band-pass filtering on the amplified digital signal to filter out high-frequency noise.

[0021] The automatic gain control unit controls the received signal amplitude within a specific range, including the following steps:

[0022] When the received signal amplitude is too large, the signal is compressed proportionally to reduce the system gain and prevent signal saturation distortion; when the signal amplitude is too small, the signal is amplified proportionally to increase the system gain and stabilize the amplitude average value of the signal within the specified amplitude range of 2.5V ± 2V (i.e., 0.5 - 4.5V), which is beneficial for subsequent calculation and processing of the received signal.

[0023] The weak sampling unit performs low-sampling-rate signal acquisition in the idle state of the receiving end, including the following steps:

[0024] In the idle state of the receiving end, that is, before officially starting signal acquisition, continuous low-precision signal acquisition is performed at a lower sampling frequency f1, and the collected data signal is output to the next unit.

[0025] The calculation and control unit performs signal processing on the received signal, including the following steps:

[0026] In the first aspect, the calculation and control unit first performs calculation and processing on the low-sampling-rate received signal collected by the weak sampling unit based on its specified characteristics in the idle state of the receiving end, obtains the amplitude of the received signal after transformation, calculates its average value multiple times and uses it as the threshold point to wake up the signal acquisition of the receiving end; after the calculation and control unit obtains the signal reception threshold, it continues signal monitoring; when the amplitude of the signal after transformation and analysis collected by the weak sampling unit is greater than the reception threshold, it is automatically determined that there is a communication request for the transmitting end to send a signal. At this time, there is signal transmission in the optical communication system channel, the weak sampling unit stops working, the signal acquisition function of the receiving end is automatically awakened, and the calculation and control unit sends the data signal received at this time to the length detection unit for processing;

[0027] In the second aspect, the calculation and control unit obtains the amplitude size of the received signal in the time domain, compares it with the set rated amplitude range (0.5 - 4.5V), calculates the gain control ratio of the received signal, and feeds it back to the automatic gain control unit.

[0028] The specified characteristics of the signal include: spectral characteristics, carrier characteristics, optical characteristics, coding characteristics, intensity characteristics, etc. of the signal generated by modulation of the system transmitting end. The signal processing methods include: transform analysis methods such as fast Fourier transform (FFT) or continuous wavelet transform (CWT) of the received signal.

[0029] The length detection unit includes the following steps:

[0030] Based on various transform analysis methods of the signal, the data information in the encrypted signal containing the signal length received is extracted, the length L of the data signal is obtained, and the length information of the signal is output to the next unit.

[0031] After the high-precision acquisition unit is automatically awakened at the receiving end, it starts high-precision signal acquisition of the received signal, including the following steps:

[0032] After the high-precision acquisition unit receives the signal length information output by the length detection unit, it performs continuous high-precision signal acquisition at a high sampling frequency of N*f1.

[0033] The signal length collected by the high-precision acquisition unit is consistent with the data size extracted by the above length detection unit; the high-precision acquisition unit will only be turned on after being automatically awakened at the receiving end, that is, after detecting that there is signal transmission in the optical communication system channel.

[0034] The decoding unit decodes the high-speed acquired data signal and outputs it to the user terminal;

[0035] The user terminal outputs the decoded signal to the upper computer screen for observation and display;

[0036] The interactive debugging unit debugs each step and unit of the automatic wake-up method.

[0037] The beneficial effects of this application are:

[0038] According to an automatic wake-up method for the receiving end of free space optical communication in the above embodiment, the automatic wake-up method includes: a signal input unit, a preamplification unit, a prefilter unit, an automatic gain control unit, a weak sampling unit, a calculation control unit, a length detection unit, a high-precision acquisition unit, an interactive debugging unit, a decoding unit, and a user terminal. The characteristics of this invention patent are as follows. Firstly, it automatically judges the communication signal and detects whether the transmitting end has a request to send a signal, realizing the automatic wake-up of the receiving end of the free space optical communication system and improving the real-time performance of signal acquisition in the communication system. Secondly, based on a specific signal transformation analysis method, the signal is transformed in the time domain. The signal amplitude changes with time and is very unstable in the time domain. After being transformed into the frequency domain, the signal characteristics change from amplitude to frequency, and each signal has its specific spectral characteristics and will not change with time, which is beneficial for signal acquisition analysis and system reliability. Thirdly, based on threshold comparison, signal estimation is performed on the characteristics of the received signal, adding an idle state mode for signal acquisition, realizing the adaptive signal acquisition of the system, reducing the huge data volume generated by continuous acquisition of the sampling unit, and reducing the on-chip data storage pressure. Fourthly, shallow data feature extraction is performed based on signal characteristics, reducing the weight of noise in the received signal and enhancing the anti-interference ability of the system. Fifthly, the length detection unit extracts the length information of each segment of the signal, realizing variable-length reception of data, not generating data redundancy of the received signal, improving the accuracy of signal acquisition of the system, and enhancing the stability of the free space optical communication system. Brief Description of the Drawings

[0039] Figure 1 is a flowchart of a signal acquisition method for a receiving end of a free space optical communication based on threshold comparison;

[0040] Figure 2 is a flowchart of an automatic wake-up method for a receiving end of a free space optical communication;

[0041] Figure 3 is a schematic diagram of a communication request signal transmitted by a transmitting end of a free space optical communication system;

[0042] Figure 4 is a specific schematic diagram of a communication request signal transmitted by a transmitting end of a free space optical communication system;

[0043] Figure 5 is a signal processing flowchart of a calculation and control unit in the automatic wake-up method for the receiving end of the present application;

[0044] Figure 6 is a signal processing flowchart of a length detection unit in the automatic wake-up method for the receiving end of the present application. Detailed Description of the Invention

[0045] The present application will be further described in detail below with reference to the accompanying drawings in conjunction with specific embodiments.

[0046] Please refer to Figure 2 , an automatic wake-up method for a receiving end of a free space optical communication, which includes a signal input unit 6, a preamplifier unit 7, a signal monitoring unit 8, a decoding unit 9, and a user terminal 10. The signal monitoring unit includes: a prefilter unit 801, an automatic gain control unit 802 for adjusting the signal size, a weak sampling unit 803 for performing low-precision signal acquisition, a calculation and control unit 804, a length detection unit 805 for extracting data information, a high-precision sampling unit 806, and an interactive debugging unit 807. Among them:

[0047] The signal input unit 6 inputs the character or voice signal collected by the photodetector into the subsequent unit.

[0048] The preamplifier unit 7 amplifies the input signal by a certain ratio and filters out a part of the noise at the same time.

[0049] The prefilter unit 801 filters out the high-frequency noise in the signal and initially improves the signal-to-noise ratio of the receiving end signal.

[0050] The automatic gain control unit 802 stabilizes the amplitude of the signal between 2.5V ± 2V (i.e., 0.5 to 4.5V), facilitating subsequent calculation and processing of the received signal. After obtaining the input signal, the calculation and control unit 804 calculates the gain control ratio G for the signal to be amplified or reduced proportionally based on the median voltage A0, the minimum amplitude A1, and the peak-to-peak value A2 of the signal, and feeds it back to the automatic gain control unit 802. The automatic gain control unit performs adaptive gain compensation on the input signal, amplifying small signals and reducing large signals, stabilizing the median voltage of the input signal at 2.5V, with the peak-to-peak value of the signal not exceeding 4.5V and the minimum value not less than 0.5V; when the average value of the signal amplitude is between 0.5V and 4.5V, the automatic gain control unit does not change the signal amplitude.

[0051] The weak sampling unit 803 performs low-sampling-rate signal acquisition. Before officially starting signal acquisition, it continuously acquires signals at a low sampling frequency f1 and outputs the acquired data signals to the next unit simultaneously; when the system subsequently starts high-precision signal acquisition, the weak sampling unit 803 stops the low-precision acquisition of the received signal;

[0052] Please refer to Figure 3 , for the communication request signal sent by the transmitter, in order to implement the automatic wake-up method for the receiver in free-space optical communication proposed in this application, the system transmitter will send a communication request signal before transmitting data, which is sequentially composed of three identical data modules 1101, 1102, and 1103. The system can enter the next step after receiving any one of the modules. After receiving the request signal, the receiver automatically determines whether there is data being transmitted in the current channel and then decides whether to start signal acquisition at the receiver.

[0053] In a specific embodiment, the composition of each data module in the communication request signal please refer to Figure 4 , which is composed of two identical coding sequences 1201, 1202 and an auxiliary sequence 13. The frame start signal 1201 and the frame end signal 1202 are independent square wave signals with a coding frequency of 100KHz, having relatively large amplitudes at its fundamental frequency 100KHz and higher harmonic frequencies such as 300KHz, and are very easy to distinguish from the noise when there is no data transmission; at the same time, an auxiliary sequence is added to the request signal to describe the signal length. The auxiliary sequence 13 in the middle of the coding sequences 1201, 1202 is composed of an 8-bit unsigned binary square wave signal, whose frequency can be set to 100KHz ± f3. The size of the auxiliary sequence 13 represents the length of the data signal to be transmitted, with a range of 0 to 255.

[0054] The calculation and control unit 804 can mainly implement two functions:

[0055] In the first aspect, as in Figure 4In the specific embodiments described above, the calculation and control unit 804 performs signal monitoring and signal processing at the receiving end of the system, mainly including steps S101, S102, S103, S104, S105, S106, S107. Please refer to Figure 5 , which are described separately as follows:

[0056] S101, System initialization. At this time, there is no signal transmission in the system, and it is in the idle state during signal monitoring. The data signal collected by the weak sampling unit 803 is the channel noise at the current moment. Since the square wave signals with a frequency of 100KHz in the coding series 1201 and 1202 have relatively large amplitudes at its fundamental frequency of 100KHz and high-order harmonic frequencies such as 300KHz, it is very easy to distinguish from the noise when there is no data transmission. Therefore, it is possible to determine whether there is signal transmission by obtaining the frequency-domain amplitudes of the signal at 100KHz and high-order harmonics.

[0057] S102, Collect these noise signals with low sampling rates, and calculate the amplitudes of the noise signals at 100KHz and 300KHz in the frequency domain based on the fast Fourier transform or wavelet transform and the frequency characteristics of the signal.

[0058] S103, Repeat step S102 multiple times. In the present invention, it is set to 3 times. Collect and calculate the amplitudes of the noise signals at 100KHz and 300KHz three times, and take their average value to reduce errors. Then, take k times the average value (the value of k needs to be adjusted according to the system and actual situation) as the signal reception threshold for waking up the receiving end to turn on the subsequent high-precision acquisition unit.

[0059] S104, Continue signal monitoring in the idle state, continuously perform weak sampling on the received signal at the receiving end of the system, and repeat step S102.

[0060] S105, Compare and judge the amplitudes of the signal obtained at this time after time-frequency transform analysis at 100KHz and 300KHz with the reception threshold calculated in step S103. If the signal amplitude is greater than the threshold, go to step S106; otherwise, if the signal amplitude is less than the threshold, repeat step S104 to continue signal monitoring without turning on the high-precision signal acquisition at the receiving end.

[0061] S106, Automatically determine that there is a communication request from the transmitting end of the current system. At this time, there is signal transmission in the channel of the optical communication system.

[0062] S107, The calculation and control unit 804 sends the received signal at this time to the next unit for processing, and outputs a signal representing the opening of the signal acquisition at the receiving end. Here, it is set to output a high-level signal with a pulse width of 50us at a specified IO port to wake up the signal acquisition function at the receiving end and trigger the subsequent high-precision acquisition unit to work.

[0063] In a second aspect, the calculation and control unit 804 is configured to obtain the median voltage A0, the minimum amplitude A1, and the peak-to-peak value A2 of the received signal in the time domain, calculate the gain control magnification G for signal equal-proportion amplification or reduction, and feed it back to the automatic gain control unit 802.

[0064] The length detection unit 805 extracts the length information of the data signal from the received communication request signal based on various signal transformation analysis methods. In a specific embodiment, for example Figure 4 the binary number represented by the auxiliary sequence 13 in this request signal is 00100101, indicating that the length of the transmitted signal is 37;

[0065] Please refer to Figure 6 The length detection unit 805 includes steps S201, S202, S203, and S204, which are described as follows:

[0066] S201, first, perform unit initialization and enablement, and receive the weak sampling signal processed by the calculation and control unit;

[0067] S202, during the receiving process, detect the frame start signal and the frame end signal in real time. Detecting the frame start signal 1201 and the frame end signal 1202 indicates that the 8-byte auxiliary sequence 13 containing the length information has been received;

[0068] S203, based on various signal transformation analysis methods, such as fast Fourier transform (FFT), continuous wavelet transform (CWT) and its inverse transform, perform information extraction on the input serial data stream, convert the auxiliary sequence 13 in the communication request signal into data representing the signal length, obtain the length of the transmitted signal as L, and output the length information L of the transmitted signal to the next unit;

[0069] S204, output the length information of the transmitted data signal, and the received byte count of the subsequent receiving unit starts from 0 and increases to the target byte count.

[0070] After the high-precision acquisition unit 806 is automatically awakened at the receiving end, it starts high-precision signal acquisition of the system received signal. At this time, the system stops weak sampling, including the following steps:

[0071] The high-precision acquisition unit 806 will be activated after the system receiver is automatically awakened. That is, after the high-precision acquisition unit 806 receives both the signal length information output by the length detection unit 805 and the high-level signal with a pulse width of 50 us output by the calculation and control unit 804, it will perform continuous high-precision signal acquisition on the received signal after adaptive gain compensation by the automatic gain control unit 802 at a high sampling frequency f2 = N * f1 (N = 2, 3, 4, 5... 10...). The acquisition length of the signal is L. After the acquisition is completed, the data signal with a length of L will be output to the next unit.

[0072] The interactive debugging unit 807 is connected to the host computer software through a specified serial port to debug the steps of each unit at the system receiver end, including the following steps:

[0073] When debugging is enabled, that is, when a debugging signal is input, the interactive debugging unit enables the debugging function, automatically matches the Uart_Debug serial port, and correspondingly outputs the received signal of the system at this time; set the corresponding serial port number in the host computer software and set the baud rate to 20000; open the serial port for debugging. After the user inputs any character or voice signal in the corresponding serial port terminal at the transmitter end and sends it, the information sent by the transmitter end can be observed at the corresponding Uart_Debug serial port terminal at the receiver end; when no debugging signal is input, that is, when the system is in the normal working mode, the interactive debugging unit will automatically output the input signal. At this time, this unit plays the role of connecting the front and back units;

[0074] The decoding unit 9 decodes the data signal output by the high-precision acquisition unit 806 and outputs it to the user terminal;

[0075] The user terminal 10 is used to output the decoded data signal to the host computer screen for observation and display.

[0076] In summary, the technical solution provided by this application is based on the stable characteristics of signal transmission in the free space optical communication system, realizes the automatic judgment of the communication request at the transmitter end and the automatic awakening of the receiver end, improves the reliability and real-time performance of system signal acquisition, performs shallow feature extraction based on signal characteristics, adaptively obtains the signal acquisition threshold point, adds an idle state mode to the system signal acquisition unit, reduces the data volume of signal acquisition at the receiver end, reduces the on-chip data storage pressure, thereby improving the accuracy of signal acquisition and the anti-interference ability of the system. At the same time, by extracting the signal length information, the variable-length reception of communication data is realized, the accuracy of system signal acquisition is improved, and the stability of the free space optical communication system is enhanced.

[0077] The above content is a further detailed description of the present application in combination with specific implementation manners, and it cannot be determined that the specific implementation of the present application is only limited to these descriptions. For those of ordinary skill in the technical field to which the present application pertains, without departing from the inventive concept of the present application, several simple deductions or substitutions can also be made.

Claims

1. An automatic wake-up method for the receiving end of free space optical communication, characterized in that, The receiving end enables the signal monitoring mode in the idle state and operates in a weak sampling manner; by analyzing the specified characteristics in the weakly sampled signals, it automatically determines the communication request of the transmitting end; when there is a communication request from the transmitting end, it automatically wakes up the system and starts the communication mode to begin high-precision and high-speed signal acquisition. The automatic wake-up method includes the following steps: The pre-amplified signal is input into the signal monitoring unit, and the signal monitoring unit realizes the automatic judgment of the start signal representing the start of communication and the automatic wake-up of the receiving end; Among them, after the pre-filtering unit filters out the high-frequency noise in the received signal, the automatic gain control unit performs adaptive gain compensation on the signal according to the signal amplitude, adjusts the signal amplitude to the specified amplitude range, and outputs it to the weak sampling unit for low-precision sampling; In the idle state of the receiving end, the calculation control unit performs digital signal processing on the channel noise when there is no signal transmission based on the specified characteristics of the signal and a specific signal transformation analysis method to obtain the signal reception threshold in the current communication environment. At this time, the system is in the idle state during the signal monitoring process; the calculation control unit continuously performs transformation analysis and calculation on the received signal, and compares the obtained received signal amplitude with the above-mentioned reception threshold; when the received signal amplitude is greater than the preset threshold, it is automatically determined that there is a communication request from the transmitting end of the current system, the receiving end automatically wakes up the signal acquisition function, and after the length detection unit extracts the length information of the signal, the high-precision acquisition unit starts signal sampling with a higher frequency.

2. The automatic wake-up method for the receiving end in free space optical communication according to claim 1, characterized in that, The automatic gain control unit controls the received signal amplitude within a specific range, including the following steps: When the received signal amplitude is too large, the signal is compressed proportionally to reduce the system gain and prevent signal saturation distortion; when the signal amplitude is too small, the signal is amplified proportionally to increase the system gain and stabilize the average signal amplitude within the specified amplitude range of 2.5V ± 2V (i.e., 0.5 to 4.5V), which is conducive to subsequent calculation and processing of the received signal.

3. The automatic wake-up method for a receiving end used in free space optical communication according to claim 1, wherein The weak sampling unit performs low-sampling-rate signal acquisition in the idle state of the receiving end, including the following steps: Before the formal signal acquisition is started in the idle state of the receiving end, continuous low-precision signal acquisition is performed at a lower sampling frequency f1, and the collected data signal is output to the next unit at the same time.

4. The automatic wake-up method for a receiving end used in free space optical communication according to claim 1, wherein The calculation control unit performs signal processing on the received signal, including the following steps: First, in the idle state of the receiving end, the calculation control unit performs calculation processing on the low-sampling-rate received signal collected by the weak sampling unit based on its specified characteristics to obtain the amplitude of the received signal after transformation, and obtains its average value through multiple calculations as the threshold point for waking up the signal acquisition of the receiving end; after the calculation control unit obtains the signal reception threshold, it continues signal monitoring; when the amplitude of the signal after transformation analysis collected by the weak sampling unit is greater than the reception threshold, it is automatically determined that there is a communication request for sending a signal from the transmitting end. At this time, there is a signal transmission in the optical communication system channel, the weak sampling unit stops working, the receiving end automatically wakes up the signal acquisition function, and the calculation control unit sends the data signal received at this time to the length detection unit for processing; In a second aspect, the calculation and control unit obtains the amplitude of the received signal in the time domain, compares it with the set rated amplitude range (0.5 - 4.5 V), calculates the gain control magnification of the received signal, and feeds it back to the automatic gain control unit.

5. The automatic wake-up method for the receiving end used in free space optical communication according to claim 1, characterized in that, The specified characteristics of the signal include: the spectral characteristics, carrier characteristics, optical characteristics, coding characteristics, intensity characteristics, etc. of the signal generated by modulation at the system transmitter end.

6. The automatic wake-up method for the receiving end in free space optical communication according to claim 1, characterized in that The signal transformation analysis method includes: signal processing methods such as performing a fast Fourier transform (FFT) or a continuous wavelet transform (CWT) on the received signal.

7. The automatic wake-up method for a receiving end used in free space optical communication according to claim 1, wherein The length detection unit includes the following steps: Based on various signal transformation analysis methods, extract the data information in the encrypted signal containing the signal length received, obtain the length L of the data signal, and output the signal length information to the next unit.

8. The automatic wake-up method for the receiving end in free space optical communication according to claim 1, characterized in that, After being automatically awakened at the receiving end, the high-precision acquisition unit starts high-precision signal acquisition of the received signal, including the following steps: After receiving the signal length information output by the length detection unit, the high-precision acquisition unit performs continuous high-precision signal acquisition at a high sampling frequency N*f1.

9. The automatic wake-up method for a receiving end used in free space optical communication according to claim 8, wherein The signal length collected by the high-precision acquisition unit is the same as the data size extracted by the above length detection unit.

10. The automatic wake-up method for a receiving end used in free space optical communication according to claim 8, wherein The high-precision acquisition unit will only be turned on after being automatically awakened at the receiving end, that is, after detecting signal transmission in the optical communication system channel.

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