Rate estimation method for multi-rate baseband OOK signal

Abstract

The invention discloses a rate estimation method of a multi-rate baseband OOK signal, which comprises the following steps: sending a sent communication data frame to a free space through a light source after baseband OOK modulation, transmitting the communication data frame to a receiving end through a free space optical channel, at the receiving end, firstly converting an optical signal into a digital signal through an optical detector and an analog-to-digital conversion module, after digital oversampling is carried out through a fixed-frequency clock, the signals are input into a rate estimation module, and the rate estimation module estimates the currently transmitted code element rate in real time by calculating an autocorrelation function of the input signals and counting the number of sampling points between adjacent peak values of the autocorrelation function. According to the rate estimation method for the multi-rate baseband OOK signal, rate estimation can be autonomously carried out on the received data frame under the condition that the communication rate of the sending end is unknown, and therefore the flexibility of a bit synchronization module is improved.

Description

Technical Field

[0001] The present invention relates to the field of wireless optical communication, and particularly to a method for estimating the rate of a multi-rate baseband OOK signal. Background Art

[0002] The technology of unmanned aerial vehicles (UAVs) is playing an increasingly important role in modern military and commercial fields. Whether in reconnaissance and surveillance or logistics distribution, the usage scenarios of UAVs are increasing rapidly, and the resulting demand for air data exchange has become more urgent. In these diverse applications, the stability and reliability of the communication link between UAVs and ground command posts or between UAVs are key factors to ensure the successful completion of tasks. Since optical communication technology can provide high-bandwidth communication capabilities that are not restricted by the radio spectrum, and it has strong anti-interference and good confidentiality characteristics, it is very suitable for the high-bandwidth and high-security communication requirements of UAVs.

[0003] However, many studies on wireless optical communication do not fully consider the application requirements in dynamic environments. Patent No. CN202210694849.8 discloses a laser arbitrary multi-user full-duplex wireless optical communication system, and the communication rate of this system is fixed. A system with a fixed rate is difficult to support real-time communication under poor channel conditions, and a system with a fixed rate cannot utilize all channel capacities for transmission under good channel conditions either. Patent No. CN202110801844.6 discloses a method and system for receiving and transmitting multi-rate subcarrier modulation signals. In this system, a multi-rate communication system is achieved by changing the modulation order of the transmitted data. However, its receiving end needs to know the modulation parameters of the transmitting end in advance to perform synchronous reception, the system rate switching time is long, and the real-time performance is poor, making it difficult to cope with rapidly changing channel conditions. Wang Jianping et al. from the University of Science and Technology Beijing proposed a CDMA-based multi-rate visible light communication method and simulation in "Research on CDMA Technology and Its Applications for Visible Light Communication" in 2020. Multi-rate communication is achieved by spreading and despreading using communication code groups with different rates. The selection of the communication rate in this system is limited by the spreading code group. Since the orthogonality of the spreading code group must be maintained, the system can only transmit at a fixed number of rates, resulting in poor flexibility of the system. In a dynamic environment, such as when a UAV is performing a flight mission, the channel conditions are affected by various dynamic factors such as distance, weather, and flight angle. To ensure the reliability of the communication link at all times, the system needs to adapt to the channel in real time with high flexibility for data transmission.

[0004] In summary, current multi-rate communication systems often focus on higher static communication performance, are difficult to support high-real-time multi-rate communication, and have low flexibility, which is not conducive to their deployment in dynamic scenarios. Summary of the Invention

[0005] In view of the above defects of the prior art, the technical problem to be solved by the present invention is that existing multi-rate communication systems usually focus on higher static communication performance, are difficult to support high-real-time multi-rate communication, and have low flexibility, which is not conducive to their deployment in dynamic scenarios. Therefore, the present invention provides a method for estimating the rate of a multi-rate baseband OOK signal, which can autonomously evaluate the rate of received data frames without knowing the communication rate of the sending end, thereby improving the flexibility of the bit synchronization module.

[0006] To achieve the above object, the present invention provides a method for estimating the rate of a multi-rate baseband OOK signal. The transmitted communication data frame is modulated by baseband OOK and then sent to free space through a light source. It is transmitted to the receiving end through the free space optical channel. At the receiving end, the optical signal is first converted into a digital signal by an optical detector and an analog-to-digital conversion module, and then digitally oversampled by a clock with a fixed frequency and input into the rate estimation module. The rate estimation module estimates the current transmitted symbol rate in real time by calculating the autocorrelation function of the input signal and counting the number of sampling points between adjacent peaks of the autocorrelation function.

[0007] Further, the transmitted communication data frame includes a preamble, a data frame header, communication data, RS coding, and a CRC check field. Among them, the preamble uses 8 groups of consecutive Barker code sequences.

[0008] Further, the symbol rate within the same communication data frame remains unchanged, while different communication data frames can adopt different symbol rates. After being modulated by baseband OOK, the data frame is converted into an optical signal by a light source and sent to the free space channel.

[0009] Further, the receiving end receives the optical signal through an optical detector and directly outputs the digital signal after OOK demodulation through the analog-to-digital conversion module. The digital signal is oversampled by the oversampling module at a fixed frequency f s and output to the rate estimation module in parallel after oversampling.

[0010] Further, the rate estimation module caches and slices the input data, and selects the slice length where l is the length of the Barker code, and R bmin is the lowest symbol rate transmitted in the system.

[0011] Further, the rate estimation module performs an autocorrelation operation on each slice. The autocorrelation function of each slice is expressed as

[0012]

[0013] The autocorrelation function at A peak will appear here. Excluding the peak when k = 0, which is the maximum peak generated when the signal is correlated with itself, the remaining peaks are obtained by performing a correlation operation between the Barker code and another set of Barker codes in the preamble. By counting the number of sampling points at which two adjacent peaks appear and performing calculations, the symbol rate R currently being transmitted is obtained. b 。

[0014] Further, the rate estimation module will evaluate the symbol rate of the current data frame by counting the mean value of the number of sampling points between n adjacent peaks, and the rate estimation output can be obtained by the following formula

[0015]

[0016] In the formula, R b is the symbol rate, l is the length of the Barker code, f s is the oversampling frequency, n is the number of detected peaks, and m i is the peak point at which the peak is detected.

[0017] Further, the autocorrelation peak detection is based on a detection mechanism with multiple criteria. First, the position of the peak is detected in real time through a sliding window. When the autocorrelation value of a sampling point is greater than the autocorrelation value of the adjacent sampling point and this value is greater than the height threshold, then this point is determined to be a peak.

[0018] Further, it includes the following modules:

[0019] An optoelectronic conversion module, an oversampling module, and a rate estimation module; among them,

[0020] The optoelectronic conversion module is responsible for converting the received optical signal into a digital electrical signal and outputting it to the oversampling module;

[0021] The oversampling module is responsible for oversampling the input signal at a fixed frequency and outputting the sampled data to the rate estimation module;

[0022] The rate estimation module estimates the current transmission data rate in real time by calculating the autocorrelation function of the input signal and counting the mean value of the number of sampling points between adjacent peaks of the autocorrelation function.

[0023] Technical effects

[0024] The present invention proposes a dynamic rate estimation method for multi-rate baseband OOK signals. By adopting autocorrelation operation and peak detection technology at the receiving end, real-time rate evaluation is achieved, enabling the receiving end to adaptively receive data frames at different rates based on this method. This method combines the preamble design based on continuous Barker code sequences and the frame structure suitable for burst transmission. Among them, the Barker code sequence significantly improves the accuracy of rate detection with its excellent autocorrelation characteristics, while the optimized burst frame structure effectively reduces the overhead of rate switching. In a dynamically changing communication scenario, when the channel condition is good, the system can switch to a higher transmission rate to improve throughput; when the channel condition deteriorates, it can quickly reduce the speed to ensure communication reliability. The rate adaptation mechanism of this method is particularly suitable for dynamic transmission scenarios. By adjusting the frame rate in real time, the utilization rate of channel capacity is maximized, thereby achieving highly flexible and efficient data transmission in a rapidly changing communication environment.

[0025] The following will further illustrate the concept, specific structure and technical effects of the present invention in conjunction with the accompanying drawings to fully understand the purpose, features and effects of the present invention. Brief Description of the Drawings

[0026] Figure 1 is a schematic diagram of the system structure of a rate estimation method for multi-rate baseband OOK signals according to a preferred embodiment of the present invention;

[0027] Figure 2 is a schematic diagram of the data structure of a rate estimation method for multi-rate baseband OOK signals according to a preferred embodiment of the present invention;

[0028] Figure 3 is a simulation diagram of the peak detection structure of the preamble field of a rate estimation method for multi-rate baseband OOK signals according to a preferred embodiment of the present invention;

[0029] Figure 4 is a simulation diagram of the peak detection result of the data field of a rate estimation method for multi-rate baseband OOK signals according to a preferred embodiment of the present invention;

[0030] Figure 5 is a simulation diagram of the performance result of a rate estimation method for multi-rate baseband OOK signals according to a preferred embodiment of the present invention. Detailed Embodiment

[0031] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0032] In the following description, specific details such as specific internal programs and technologies are presented for the purpose of illustration rather than limitation, so as to thoroughly understand the embodiments of the present invention. However, those skilled in the art should clearly understand that the present invention can also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to avoid unnecessary details from hindering the description of the present invention.

[0033] The present invention provides a method for estimating the rate of a multi-rate baseband OOK signal, including the following steps:

[0034] Step 100, the transmitted communication data frame is modulated by baseband OOK and then sent to free space through a light source, and is transmitted to the receiving end through a free space optical channel. At the receiving end, the transmitted communication data frame includes a preamble, a data frame header, communication data, RS coding, and a CRC check field. Among them, the preamble uses 8 groups of consecutive Barker code sequences, which have good autocorrelation characteristics. The symbol rate of the communication data frame remains unchanged within the same frame, while different communication data frames can use different symbol rates; after being modulated by baseband OOK, the data frame is converted into an optical signal by the light source and sent to the free space channel.

[0035] The receiving end uses the rate information extracted from the preamble through characteristics as the clock reference for bit synchronization, and the rate estimation module continuously extracts the rate information from the preamble, and the rate information is updated with the transmission of each frame.

[0036] Step 200, the optical signal is first converted into a digital signal through a photodetector and an analog-to-digital conversion module. The incident optical signal is converted into a photocurrent I by a photodiode through the photoelectric effect p , where I p = R * P opt + I d , where R is the detector responsivity, P opt is the incident optical power of the detector, and I d is the dark current of the detector. This current is further converted into a voltage signal V by a transimpedance amplifier, where V = R f * I p , where R f is the feedback resistance of the transimpedance amplifier. The analog-to-digital conversion module makes a hard decision on this voltage signal according to the following formula to further convert the voltage signal into a digital signal, where V threhold is the voltage threshold for hard decision.

[0037]

[0038] Step 300, the digital signal then passes through a preset fixed frequency f sAfter digital oversampling the clock, the input rate estimation module. The selection of the sampling frequency depends on the fastest symbol rate R transmitted in the system bmax , the sampling frequency f s = 4 * R bma , that is, 4-fold oversampling is performed. The output of the oversampling module satisfies the following formula, where y(n) is the output of the oversampling module and x(n) is the output signal of the analog-to-digital conversion module.

[0039]

[0040] Step 400, the rate estimation module estimates the current transmitted symbol rate in real time by calculating the autocorrelation function of the input signal and counting the number of sampling points between adjacent peaks of the autocorrelation function.

[0041] The rate estimation module caches and slices the input data, and selects the slice length where l is the length of the Barker code and R bmin is the lowest symbol rate transmitted in the system.

[0042] Since the data segment in the communication data frame does not have strong periodicity, when participating in the autocorrelation operation, the autocorrelation output of the data segment will have no obvious peak. When the data segment participates in the autocorrelation operation together with the preamble, the more the proportion of the data segment, the lower the autocorrelation peak. When selecting the slice length, as many preambles at different rates as possible should be included while including as few data segments as possible. Therefore, select the slice length N. At this slice length, when transmitting at the lowest rate, half of the preamble will be retained in the window, and multiple peaks will appear in the autocorrelation operation; when transmitting at the highest rate, this window includes all the preambles and relatively few data segments, and multiple peaks will also appear in the autocorrelation operation.

[0043] The rate estimation module will perform autocorrelation operations on each slice. The autocorrelation function of each slice is expressed as

[0044]

[0045] The autocorrelation function will have a peak at . Excluding the peak at k = 0, which is the maximum peak generated when the signal is correlated with itself, the remaining peaks are obtained by correlating the Barker code with another set of Barker codes in the preamble. By counting the number of sampling points at which two adjacent peaks appear and performing calculations, the currently transmitted symbol rate R b is obtained. The peak at k = 0 is the highest. As k increases, the number of Barker codes participating in the autocorrelation operation decreases, and the amount of input non-periodic data increases. Therefore, its peak will continue to decrease. When k > 7, since the preamble no longer participates in the autocorrelation operation, no obvious peak will appear in the autocorrelation output. To improve the anti-interference ability of the signal estimation module.

[0046] The rate estimation module evaluates the symbol rate of the current data frame by statistically averaging the number of sampling points between adjacent n peaks, and the rate evaluation output can be obtained by the following formula

[0047]

[0048] In the formula, R b is the symbol rate, l is the length of the Barker code, f s is the oversampling frequency, n is the number of detected peaks, m i is the peak point where the peak is detected.

[0049] When, due to the too small size of the autocorrelation window, except for the main peak, there is only one peak in the autocorrelation function; When, due to the too large size of the autocorrelation window, the autocorrelation values of the data segments in the sliced data submerge the autocorrelation peak of the preamble, making it difficult to find the peak. Therefore, R b is selected

[0050] In addition, the embodiment of the present invention further includes detecting peaks. The autocorrelation peak detection is based on a detection mechanism with multiple criteria. First, the position of the peak is extracted in real time through a sliding window detection. When the autocorrelation value of a sampling point is greater than the autocorrelation values of adjacent sampling points, and this value is greater than the height threshold R th at this time, it is determined that this point is a peak. That is, the peak detection output P[m] is determined by the following formula. In the formula, R[m] is the calculated autocorrelation function, R th is the threshold for peak detection, and R′[m] is the difference of the autocorrelation function, that is, R′[m] = R[m + 1] - R[m].

[0051]

[0052] To exclude the influence of data segments and noise on the autocorrelation peak, the peak detection module designs a minimum peak spacing constraint to ensure that the peak spacing P Interval meets the preset symbol rate range, that is, P Interval ≥ 4 * l. When the detected adjacent peaks are less than the minimum spacing, it indicates that sub-peaks near the main peak are detected, and the module selects the peak with a larger amplitude as the peak output.

[0053] To ensure the reliability of rate estimation, the present invention adopts the following protection measures. Since within the working rate range set by the system, the preamble field theoretically contains at least 3 peaks (including the peak at m = 0), when the number of peaks output by the peak detection module is less than 3, the rate estimation module will consider that the current peak is caused by bursty bit errors or noise interference, and thus will not output a valid rate estimation result. When the number of peaks is greater than or equal to 3, by statistically operating on the average peak interval, the estimation deviation is reduced and the system's adaptability to noise is improved.

[0054] The present invention provides a method for estimating the rate of a multi-rate baseband OOK signal, including the following modules:

[0055] An optoelectronic conversion module, an oversampling module, and a rate estimation module; wherein,

[0056] The optoelectronic conversion module is responsible for converting the received optical signal into a digital electrical signal and outputting it to the oversampling module;

[0057] The oversampling module is responsible for oversampling the input signal at a fixed frequency and outputting the sampled data to the rate estimation module;

[0058] The rate estimation module estimates the current data transmission rate in real time by calculating the autocorrelation function of the input signal and statistically calculating the mean of the number of sampling points between adjacent peaks of the autocorrelation function.

[0059] Next, a specific embodiment will be used to illustrate in detail a method for estimating the rate of a multi-rate baseband OOK signal implemented by the present invention in conjunction with the accompanying drawings.

[0060] An embodiment of the present invention proposes a method for estimating the rate of a multi-rate baseband OOK signal. The overall system structure schematic diagram is as Figure 1 shown. The transmitted communication data frame is modulated by baseband OOK and then sent to free space through a light source, and is transmitted to the receiving end through a free space optical channel. At the receiving end, the optical signal is first converted into a digital signal through a photodetector and an analog-to-digital conversion module. After the digital oversampling module oversamples the signal using a clock with a fixed frequency, it is input to the rate estimation module. The rate estimation module first calculates the autocorrelation function of the input signal, obtains the peak positions that meet the conditions through the peak detection module, and finally estimates the current data frame rate by calculating the average number of sampling points between the peaks.

[0061] As Figure 2As shown in the figure, the transmitted communication data frame consists of a 7-byte preamble, a 4-byte data frame header, 864 bytes of communication data, 128 bytes of RS coding, and 4 bytes of CRC check. The preamble is a sequence of 8 consecutive groups of 7-bit Barker codes, with each group of Barker codes being 1100101, which has good autocorrelation characteristics; RS coding provides forward error correction capabilities and enhances communication reliability; the CRC check field provides guarantee for data integrity verification. The system adopts a baseband OOK modulation scheme, and the modulated optical signal is transmitted to the receiving end through a free-space optical channel. At the receiving end, the optical signal is first converted into an analog electrical signal by a photodetector, and then digitized through an analog-to-digital conversion module. After digital oversampling with a fixed-frequency clock, the signal is input to the rate estimation module respectively. The rate estimation module calculates the autocorrelation function of the input signal, counts the number of sampling points corresponding to the adjacent peak intervals, and estimates the current transmission rate in real time. This method effectively solves the problem of insufficient bit synchronization flexibility in multi-rate transmission scenarios through an adaptive rate estimation method.

[0062] The embodiment of the present invention is implemented based on an FPGA and a 3mm APD photodetector, where the oversampling module and the rate estimation module are implemented by the FPGA. The sampling frequency of the oversampling module is 400 MHz, so the symbol rate range supported by the synchronization module of this method is 20 MHz to 100 MHz.

[0063] The oversampling module performs oversampling on the signal received by the photodetector based on the SelectIO IP core provided by Xilinx official. Inside the FPGA, a 400 MHz clock is generated through the MMCM as the sampling clock. The data is input from the HR bank pin of the FPGA, passed through the IOB register for buffering, and then output to the IDELAY module for delay output. Further, after serial-to-parallel conversion through the ISERDES, it is output to the inside of the FPGA. The output of the oversampling module is a 4-bit parallel output.

[0064] The rate estimation module slices with a length of and stores the input bits through the design of a double buffer. The first-level buffer stores all the data output by the oversampling module. When the number of bits stored in the first-level buffer is greater than or equal to 560, the first 560 bits are taken out and entered into the second-level buffer. The rate estimation module performs the following autocorrelation operation on the data in the second-level buffer. After the current autocorrelation operation is completed, the second-level buffer takes out 560 bits (if any) from the first-level buffer to replace the original data and continues the autocorrelation operation.

[0065]

[0066] Since the input signal is already a digital signal, the multiplication operation can be simplified to an exclusive OR (XOR) logical operation. By adding the results of the XOR operations, the corresponding autocorrelation value can be obtained. Since the autocorrelation value at m = 0 (obtained by correlating the signal with itself) must be the maximum peak value, it is defaulted to have a peak at this point when implemented on an FPGA. When calculating the autocorrelation peak, all the XOR operations can be completed within one clock cycle through the pipelining feature of the FPGA, and then the accumulation operation can be completed in the next clock cycle.

[0067] The FPGA detects and extracts the position of the peak in real time through a 10-point sliding window. When the autocorrelation value of the sampling points within the window is greater than the autocorrelation values of the two adjacent sampling points, and this value is greater than the height threshold R th then this point is determined as a peak. Since the selected window size is 560, the threshold is selected as 160 when implementing the system, and the minimum peak spacing constraint of the peak detection module is P Interval ≥28. This is because the distance between adjacent Barker codes is 28 points at the highest system rate of 100 Mbps. When the detected adjacent peaks are less than the minimum spacing, it indicates that the signal-to-noise ratio of the received signal is relatively low at this time, and thus sub-peaks near the main peak are detected. The module will select the peak with a larger amplitude as the peak output.

[0068] By counting the average number of sampling points between the peaks (including the peak at m = 0), the symbol rate information of the input signal can be obtained. As Figures 3-4 shown, they are respectively the autocorrelation function results and peak detection results obtained by operating according to the method of the present invention when the communication symbol rates in MATLAB simulation are 100 Mbps, 50 Mbps, and 20 Mbps. When the data slice is located in the preamble field, the lower the rate, the more Barker code sequences enter the window, so the autocorrelation peak is sharper. The higher the rate, the more aperiodic data enter the window, and thus the autocorrelation peak is reduced. When the data slice is located in the data field, since the autocorrelation of the transmitted data (taking PRBS-7 code as an example) is not as good as that of the Barker code in the preamble field, the autocorrelation peak is lower than the decision threshold, and the peak detection module has no output. Taking the 20 M rate as an example, except for the zero point, the second and third peaks appear at 140 and 280 respectively, and the average number of sampling points between them is 140. The symbol rate of the signal is calculated as And in the data field, the autocorrelation value of the received signal is always less than 100, so there will be no situation where the data field affects the rate estimation. Similarly, it can be obtained that at 100 Mbps and 50 Mbps, the method proposed by the present invention can search for the autocorrelation peak and calculate the correct symbol rate based on this and output it, so that subsequent modules can use this symbol rate for bit synchronization.

[0069] In addition, to ensure the reliability of rate estimation, the system adopts the protection measures described below. Since within the working rate range set by the system, the preamble field theoretically contains at least 3 peaks (including the peak at m = 0), when the number of peaks output by the peak detection module is less than 3, the rate estimation module will consider that the current peaks are caused by bursty bit errors or noise interference, and thus will not output a valid rate estimation result. When the number of peaks is greater than or equal to 3, by statistically operating on their average peak intervals, the estimation deviation is reduced, and the system's adaptability to noise is improved.

[0070] Figure 5 For the performance simulation results of the above method using MATLAB, it can be seen from the figure that when the signal-to-noise ratio is greater than or equal to 4 dB, the proposed method can correctly estimate the data frame with a symbol rate of 100 Mbps; when the signal-to-noise ratio is greater than or equal to 0.5 dB, it can correctly estimate the data frame with a symbol rate of 50 Mbps; when the signal-to-noise ratio is greater than or equal to 1 dB, it can correctly estimate the data frame with a symbol rate of 20 Mbps. When the signal-to-noise ratio is less than or equal to 0 dB, the amplitude of the noise is greater than or equal to the amplitude of the OOK baseband signal, and there are large bit errors in the output of the analog-to-digital conversion module, so the output of the rate estimation module is no longer accurate. In addition, since the window size used matches the symbol rate of 50 Mbps best, the rate of 50 Mbps is recognized with the best effect during the simulation. Compared with the existing multi-rate transmission technologies, such as the multi-rate method based on high-order modulation mentioned in the background, this method realizes the adaptation of multi-rate transmission with a fixed modulation format, reduces the complexity of system implementation, and avoids the problem that the transceiver needs to perform manual switching to achieve multi-rates; the multi-rate communication method based on CDMA is restricted by the selection of spreading code groups, so it can only be applied to a fixed number of rates, while this method is adaptable to any rate within the proposed rate range. The method of the present invention has higher flexibility, and thus is more suitable for wireless optical communication in dynamic scenarios. The present invention is applicable to dynamic scenarios and improves the problem that the existing multi-rate technologies are only applicable to static scenarios. In addition, the existing technologies need manual mode switching at the transceiver to achieve multi-rates, while the present invention does not require manual mode switching.

[0071] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative efforts. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field of the present invention based on the concept of the present invention through logical analysis, reasoning, or limited experiments on the basis of the existing technology should fall within the protection scope determined by the claims.

Claims

1. A method for estimating the rate of a multi-rate baseband OOK signal, characterized in that, The transmitted communication data frame is modulated by baseband OOK and then sent to free space through a light source. It is transmitted through the free space optical channel to the receiving end. At the receiving end, the optical signal is first converted into a digital signal by an optical detector and an analog-to-digital conversion module, and then digitally oversampled by a clock with a fixed frequency and input to the rate estimation module. The rate estimation module estimates the symbol rate of the current transmission in real time by calculating the autocorrelation function of the input signal and counting the number of sampling points between adjacent peaks of the autocorrelation function.

2. The rate estimation method for a multi-rate baseband OOK signal according to claim 1, wherein The transmitted communication data frame includes a preamble, a data frame header, communication data, RS coding, and a CRC check field. Among them, the preamble uses 8 groups of consecutive Barker code sequences.

3. The rate estimation method for a multi-rate baseband OOK signal according to claim 2, characterized in that, The symbol rate of the communication data frame remains unchanged within the same frame, while different communication data frames can use different symbol rates; the data frame is modulated by baseband OOK and then converted into an optical signal by a light source and sent to the free space channel.

4. The rate estimation method of a multi-rate baseband OOK signal according to claim 2, characterized in that, The receiving end extracts the rate information contained in the preamble of the communication data frame through autocorrelation characteristics as the clock reference for bit synchronization. The rate estimation module continuously extracts the rate information in the preamble, and the rate information is updated with each frame transmission.

5. The rate estimation method for a multi-rate baseband OOK signal according to claim 4, wherein The receiving end receives the optical signal through a photodetector and directly outputs the digital signal after OOK demodulation through an analog-to-digital conversion module. The digital signal is oversampled by an oversampling module at a fixed frequency f s and then output to a rate estimation module in parallel after oversampling.

6. The rate estimation method for a multi-rate baseband OOK signal according to claim 5, characterized in that, The rate estimation module caches and slices the input data and selects the slice length where l is the length of the Barker code, and R bmin is the lowest symbol rate transmitted in the system.

7. The rate estimation method of a multi-rate baseband OOK signal according to claim 6, characterized in that The rate estimation module will perform an autocorrelation operation on each slice, and the autocorrelation function of each slice is expressed as The autocorrelation function will have a peak at except for the peak at k = 0 which is the maximum peak generated when the signal is correlated with itself. The remaining peaks are obtained by performing a correlation operation between the Barker code and another Barker code in the preamble. By counting the number of sampling points at which two adjacent peaks appear and performing calculations, the symbol rate R of the currently transmitted signal is obtained b .

8. The rate estimation method for a multi-rate baseband OOK signal according to claim 7, characterized in that, The rate estimation module will count the mean value of the number of sampling points between adjacent n peaks to evaluate the symbol rate of the current data frame, and the rate evaluation output can be obtained by the following formula where R b is the symbol rate, l is the length of the Barker code, f s is the oversampling frequency, n is the number of detected peaks, m i is the peak point where the peak is detected.

9. The rate estimation method for a multi-rate baseband OOK signal according to claim 8, characterized in that, The autocorrelation peak detection is based on a detection mechanism with multiple criteria. First, the position of the peak is detected in real time through a sliding window. When the autocorrelation value of a sampling point is greater than the autocorrelation value of adjacent sampling points and this value is greater than the height threshold, this point is judged as a peak.

10. The rate estimation method of a multi-rate baseband OOK signal according to claim 1, characterized in that, It includes the following modules: An optoelectronic conversion module, an oversampling module, and a rate estimation module; among them, The optoelectronic conversion module is responsible for converting the received optical signal into a digital electrical signal and outputting it to the oversampling module; The oversampling module is responsible for oversampling the input signal at a fixed frequency and outputting the sampled data to the rate estimation module; The rate estimation module estimates the current transmission data rate in real time by calculating the autocorrelation function of the input signal and counting the mean value of the number of sampling points between adjacent peaks of the autocorrelation function.

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