Photomultiplier signal adaptive threshold setting method and system for ultraviolet communication

Abstract

The invention discloses a photomultiplier signal adaptive threshold setting method and system for ultraviolet communication. The method comprises the following steps: setting an initial threshold, a threshold change step length and a parallel threshold number of a photomultiplier; taking the set initial threshold value as a center, and generating a set comprising n different threshold values by using a threshold value change step length; for each signal received by the photomultiplier, generating a plurality of groups of judgment results according to different threshold values in the set; calculating and comparing performance indexes of each group of judgment results according to the judgment results, and evaluating advantages and disadvantages of different threshold values in the obtained set; updating the selected optimal threshold value as the current working threshold value; and continuously monitoring and processing signal data received by the photomultiplier, repeating the operation, and dynamically adjusting the current threshold value. According to the method, the problems of inflexible threshold setting, large resource occupation and low response speed in a changeable communication scene can be solved, so that accurate detection and real-time processing of the PMT signal are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of signal processing in wireless optical communication, and in particular to a method and system for setting an adaptive threshold value of a photomultiplier tube (PMT) signal for ultraviolet communication. Background Art

[0002] After the photomultiplier tube PMT collects the signal, the signal is input into the analog-to-digital converter (ADC). During the photon counting process, the PMT will not only detect the photons from the target signal, but also the background noise photons. In order to extract the effective signal, a threshold needs to be set. Signals below this threshold are considered as noise, while signals above this threshold are considered as effective signals. Common threshold setting methods include empirical methods based on experimental data, and statistical methods that analyze the statistical distribution of noise and signals and select thresholds that can effectively distinguish between noise and signals.

[0003] In actual communication scenarios, there are some difficulties in setting the optimal threshold for PMT. First, in different environments, the signal strength and noise level may change dynamically, and a fixed threshold may not work well after drastic changes in environmental conditions. Second, the setting of the threshold also needs to consider the thermal noise level and sensitivity characteristics of the different PMTs themselves.

[0004] Existing adaptive algorithms, including mean-variance adaptive algorithms based on statistical characteristics, Kalman filters and other adaptive filter algorithms, as well as machine learning algorithms, have achieved remarkable results in a wide range of applications. However, these algorithms also face their own challenges in threshold adaptation of PMT signals. The mean-variance adaptive threshold method relies on statistical characteristic calculations and is not adjusted quickly enough when the environment changes drastically; the adaptive filter algorithm may require more complex matrix operations and filtering operations, which require a lot of storage resources on the FPGA, limiting its application in resource-constrained environments; machine learning algorithms are usually complex in calculation and require a lot of memory and computing power, which is not suitable for rapidly changing environments and will significantly increase resource consumption. Therefore, in changing communication scenarios, it is necessary to develop an algorithm that can adapt quickly and occupy less resources. Summary of the invention

[0005] The purpose of the present invention is to provide a method and system for adaptive threshold setting of photomultiplier tube signals for ultraviolet communication, which can solve the problems of inflexible threshold setting, large resource occupation and slow response speed in variable communication scenarios, thereby realizing accurate detection and real-time processing of PMT signals.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] A method for setting an adaptive threshold value of a photomultiplier tube signal for ultraviolet communication, the method comprising:

[0008] Step 1, setting the initial threshold value, threshold change step size and parallel threshold number of the photomultiplier tube;

[0009] Step 2: With the set initial threshold as the center, a set of n different thresholds is generated by using the threshold change step, and the set is used for different decision conditions in subsequent signal processing;

[0010] Step 3: for each signal received by the photomultiplier tube, generate multiple groups of decision results according to different thresholds in the set obtained in step 2, wherein the decision results are signal detection results or conditions required for calculating other performance evaluations;

[0011] Step 4: Calculate and compare the performance indicators of each group of judgment results according to the generated multiple groups of judgment results, including bit error rate, signal strength and signal-to-noise ratio, and evaluate the advantages and disadvantages of different thresholds in the obtained set through the performance indicators;

[0012] Step 5: Select a threshold that optimizes system performance based on the evaluation result of step 4, and update the selected threshold as the current working threshold;

[0013] Step 6: Continuously monitor and process the signal data received by the photomultiplier tube, repeat the operations of steps 2-5, and dynamically adjust the current threshold to ensure that the system can maintain optimal detection performance under various environmental conditions.

[0014] A photomultiplier tube signal adaptive threshold setting system for ultraviolet communication, the system comprising:

[0015] The parameter initialization module is used to set the initial threshold of the photomultiplier tube, the threshold change step size and the number of parallel thresholds;

[0016] A threshold set generation module is used to generate a set of n different thresholds with the set initial threshold as the center and using the threshold change step, and the set is used for different decision conditions in subsequent signal processing;

[0017] A signal receiving and processing module, used for generating multiple groups of decision results according to different thresholds in the obtained set for each signal received by the photomultiplier tube, wherein the decision results are signal detection results or conditions required for calculating other performance evaluations;

[0018] A performance evaluation module is used to calculate and compare the performance indicators of each group of judgment results according to the generated multiple groups of judgment results, including bit error rate, signal strength and signal-to-noise ratio, and evaluate the advantages and disadvantages of different thresholds in the obtained set through the performance indicators;

[0019] An optimal threshold selection module is used to select a threshold that optimizes system performance according to the evaluation result, and update the selected threshold as the current working threshold;

[0020] The dynamic adjustment and feedback module is used to continuously monitor and process the signal data received by the photomultiplier tube, dynamically adjust the current threshold, and ensure that the system can maintain the best detection performance under various environmental conditions.

[0021] It can be seen from the technical solution provided by the present invention that the above method and system can solve the problems of inflexible threshold setting, large resource occupation and slow response speed in variable communication scenarios, thereby realizing accurate detection and real-time processing of PMT signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0023] Figure 1 A schematic flow chart of a method for setting an adaptive threshold value of a photomultiplier tube signal for ultraviolet communication provided by an embodiment of the present invention;

[0024] Figure 2 λ under different thresholds in the outdoor experiment of the present invention s and λ b Schematic diagram of the changing trend of

[0025] Figure 3 The figure is a schematic diagram of the structure of the system according to the embodiment of the present invention. DETAILED DESCRIPTION

[0026] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments, which does not constitute a limitation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] like Figure 1 FIG. 1 is a flow chart of a method for setting a photomultiplier tube signal adaptive threshold for ultraviolet communication provided by an embodiment of the present invention, wherein the method comprises:

[0028] Step 1, setting the initial threshold value, threshold change step size and parallel threshold number of the photomultiplier tube;

[0029] In this step, the initial threshold V is specifically set th , threshold change step ΔV th and the threshold number of parallelism n;

[0030] Among them, the initial threshold V th and threshold change step ΔV th They are all quantized values ​​of digital signals collected by analog-to-digital converter ADC, and n is an odd number not less than 3;

[0031] Threshold change step ΔV th The values ​​of and n are set according to the response speed requirements of the adaptive algorithm and the limitations of system resources to ensure the efficiency and accuracy of the adaptive process.

[0032] Step 2: With the set initial threshold as the center, a set of n different thresholds is generated by using the threshold change step, and the set is used for different decision conditions in subsequent signal processing;

[0033] In this step, the initial threshold V is calculated. th As the center, using the threshold change step ΔV th Generate a set of n different thresholds It is expressed as:

[0034]

[0035] Where k is the index, indicating arrive The integer value of .

[0036] Step 3: for each signal received by the photomultiplier tube, generate multiple groups of decision results according to different thresholds in the set obtained in step 2, wherein the decision results are signal detection results or conditions required for calculating other performance evaluations;

[0037] In this step, during the communication process, the optical signal received by the photomultiplier tube PMT is input into the analog-to-digital converter ADC, and the analog signal is converted into a digital signal by the analog-to-digital converter ADC;

[0038] For the digital signal collected by the ADC, n different thresholds in the set T obtained in step 2 are used to make judgments respectively, and n judgment results are generated;

[0039] The synchronization header is used to perform frame synchronization processing on the above n judgment result sequences, and the photon counting rate λ of the received optical signal is calculated based on the judgment result sequence of each threshold. s and the background noise photon count rate λ b .

[0040] In actual application scenarios, the calculated λs With λ b Rounding may be performed based on actual platform limitations.

[0041] Step 4: Calculate and compare the performance indicators of each group of judgment results according to the generated multiple groups of judgment results, including bit error rate, signal strength and signal-to-noise ratio, and evaluate the advantages and disadvantages of different thresholds in the obtained set through the performance indicators;

[0042] In this step, we obtain n different sets of λ s With λ b Afterwards, the bit error rate BER is calculated as a reference for comparing the pros and cons of the n groups of thresholds in the set. Specifically:

[0043] Based on the log-likelihood ratio L(N) used in the decision, it is expressed as:

[0044]

[0045] Where N represents the number of photon pulses in one symbol; assuming the N value of noise and signal, that is, N b and N s Each independently satisfies λ b With λ s Poisson distribution, N b and N s denote the number of photon pulses from the optical signal and the number of photon pulses from the background noise in a symbol respectively, and the probability of misjudging 0 as 1 is expressed as:

[0046]

[0047] P() means N b The probability of satisfying the conditions in brackets is the same as below;

[0048] The probability of misjudging 1 as 0 is expressed as:

[0049]

[0050] The calculated bit error rate BER is expressed as:

[0051]

[0052] In a specific implementation, the number of 0s and 1s in the frame synchronization header is designed to be close to 1:1.

[0053] Step 5: Select a threshold that optimizes system performance based on the evaluation result of step 4, and update the selected threshold as the current working threshold;

[0054] In this step, according to the evaluation result of step 4, the threshold corresponding to the group with the lowest bit error rate BER is set as the current optimal threshold. The index corresponding to the group with the lowest bit error rate BER is expressed as:

[0055] i opt = arg min i BER i

[0056] The subscript i represents the bit error rate BER corresponding to the i-th threshold; argmin represents finding the index i that minimizes the bit error rate BER. opt ;

[0057] The optimal threshold is V th +i opt ΔV th , assign the optimal threshold to the initial threshold V th , updated to the current working threshold.

[0058] Step 6: Continuously monitor and process the signal data received by the photomultiplier tube, repeat the operations of steps 2-5, and dynamically adjust the current threshold to ensure that the system can maintain optimal detection performance under various environmental conditions.

[0059] In the specific implementation, when calculating the bit error rate BER, in order to further save platform resources, this embodiment adopts a method of importing a bit error rate BER relative size sorting table into the ROM, and the sorting table pre-calculates and stores different λ b With λ s The relative size of the bit error rate BER under the combination. In actual operation, the system quickly compares the results under each threshold by looking up the table, thereby reducing the burden of real-time calculation. The partial structure of the sorting table is shown in Appendix 1:

[0060] Appendix 1: Some examples of BER relative size ranking table

[0061]

[0062] The actual table may contain more combinations and the corresponding relative sizes of the bit error rate BER.

[0063] Based on the above method embodiment, the present invention also provides a photomultiplier tube signal adaptive threshold setting system for ultraviolet communication, such as Figure 3 FIG. 1 is a schematic diagram of the structure of a system according to an embodiment of the present invention, wherein the system comprises:

[0064] The parameter initialization module is used to set the initial threshold of the photomultiplier tube, the threshold change step size and the number of parallel thresholds;

[0065] A threshold set generation module is used to generate a set of n different thresholds with the set initial threshold as the center and using the threshold change step, and the set is used for different decision conditions in subsequent signal processing;

[0066] A signal receiving and processing module, used for generating multiple groups of decision results according to different thresholds in the obtained set for each signal received by the photomultiplier tube, wherein the decision results are signal detection results or conditions required for calculating other performance evaluations;

[0067] A performance evaluation module is used to calculate and compare the performance indicators of each group of judgment results according to the generated multiple groups of judgment results, including bit error rate, signal strength and signal-to-noise ratio, and evaluate the advantages and disadvantages of different thresholds in the obtained set through the performance indicators;

[0068] An optimal threshold selection module is used to select a threshold that optimizes system performance according to the evaluation result, and update the selected threshold as the current working threshold;

[0069] The dynamic adjustment and feedback module is used to continuously monitor and process the signal data received by the photomultiplier tube, dynamically adjust the current threshold, and ensure that the system can maintain the best detection performance under various environmental conditions.

[0070] The specific implementation of each module in the above system is described in the above method embodiment.

[0071] In specific implementation, the general framework of the adaptive threshold setting system can be extended to various adaptive systems in other fields, such as adaptive control and adaptive data processing systems. Each module can be customized according to the needs of specific applications to adapt to different working conditions and performance requirements.

[0072] It is worth noting that the contents not described in detail in the embodiments of the present invention belong to the prior art known to professional and technical personnel in the field.

[0073] The method described in the embodiment of the present invention is illustrated below with a specific example. In this example, the experimental system uses an ultraviolet LED as a transmitting end and a PMT as a receiving end. The experiment is conducted outdoors on a sunny day. The distance between the transmitting end and the receiving end is about 50 meters. Each chip of the system contains 80 sampling points, and each symbol consists of 10 chips. The specific steps include:

[0074] Step 1: Set the initial threshold V th =30, threshold change step ΔV th =3, the number of parallel thresholds n=3, that is, 3 groups of thresholds are in parallel. ΔV th The values ​​of and n are set according to the response speed requirements of the adaptive algorithm and the limitations of system resources.

[0075] Step 2: Calculate V th The threshold value is centered and the step length is ΔV. th , a total of 3 threshold values ​​are included, expressed as: That is, collection

[0076] Step 3: During the communication process, the optical signal received by the photomultiplier tube PMT is input into the analog-to-digital converter ADC to convert the analog signal into a digital signal; for the digital signal collected by the ADC, the collection There are three different thresholds for making decisions respectively.

[0077] The synchronization header is used to perform frame synchronization processing on the above three decision result sequences, and the photon counting rate λ of the received optical signal is calculated based on each threshold decision result sequence. s and the background noise photon count rate λ b , the calculated λ s With λ b Rounding is performed due to platform limitations.

[0078] Step 4: Get 3 different sets of λ s and λ b Afterwards, the theoretical bit error rate BER is estimated as a reference for comparing the advantages and disadvantages of the three groups of thresholds. Specifically:

[0079] Based on the log-likelihood ratio L(N) used in the decision, assume the N values ​​of noise and signal, that is, N b and N s Each independently satisfies λ b With λ s If the Poisson distribution is , the probability of misjudging 0 as 1 is:

[0080]

[0081] The probability of misjudging 1 as 0 is:

[0082]

[0083] The estimated bit error rate is

[0084] Step 5: For each set of decision results, according to the calculated channel parameter λ s With λ b , estimate the bit error rate BER of each group respectively, and set the threshold corresponding to the group with the lowest bit error rate as the current optimal threshold.

[0085] The index corresponding to the group with the lowest bit error rate is i opt = arg min i BERi ;

[0086] The optimal threshold is V th +i opt ΔV th , assign the optimal threshold to the initial threshold V th , updated to the current working threshold.

[0087] Step 6: Continuously monitor and process the signal data received in real time, repeat steps 2 to 5, and dynamically adjust the threshold to ensure that the system can maintain optimal detection performance under various environmental conditions.

[0088] During the experiment, the values ​​of λ under different thresholds were recorded. s and λ b The trend of change is shown in Figure 2, and a trend graph is drawn, such as Figure 2 The figure shows the different threshold values ​​of λ in the outdoor experiment of the present invention. s and λ b Schematic diagram of the changing trend of Figure 2 It can be seen that the initial threshold V set when the system starts th = 30 has a poor effect, making λ s Ratio b After about 10 frames of transmission, the threshold is adaptively adjusted to λ s Ratio b Great location.

[0089] At about the 80th frame, the experimenter used an umbrella to block the sunlight on the receiving end PMT, but did not block the light path from the UV LED to the PMT. It can be seen that λ b A sudden drop occurs, and λ s It rises sharply. After threshold adaptation, λ s Raised to a higher value.

[0090] At about the 270th frame, the experimenter retracted the umbrella that blocked the sun, causing λ s drops sharply, while λ b After a period of time, the threshold is adaptively adjusted again so that λ s Restore to λ b Great location.

[0091] The above experimental results show that the method described in the embodiment of the present invention can effectively cope with changes in ambient light intensity, ensure that the optimal threshold setting can be maintained under different environmental conditions, and improve the reliability and performance of the ultraviolet communication system.

[0092] In summary, the method described in the embodiment of the present invention has the following advantages:

[0093] 1. The method proposed in the present invention can significantly improve the accuracy of signal detection by dynamically adjusting the threshold value compared with the fixed threshold value, thereby improving the overall performance and reliability of the communication system;

[0094] 2. The method proposed in the present invention can respond to changes in environmental conditions in real time, such as light intensity, meteorological factors, etc., to ensure that the optimal threshold setting can be maintained in different environments and improve communication quality;

[0095] 3. Compared with the existing adaptive algorithms, the method proposed in the present invention can reduce the system's demand for storage and computing resources, optimize the use of hardware resources, and improve the overall performance of the system.

[0096] In addition, a person skilled in the art can understand that all or part of the steps in the above-mentioned embodiment method can be implemented by instructing related hardware through a program, and the corresponding program can be stored in a computer-readable storage medium. The above-mentioned storage medium can be a read-only memory, a disk or an optical disk, etc.

[0097] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed in the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims. The information disclosed in the background technology section of this article is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as an admission or in any form that the information constitutes prior art known to those skilled in the art.

Claims

1. A method for setting an adaptive threshold value of a photomultiplier tube signal for ultraviolet communication, characterized in that: The method comprises: Step 1, setting the initial threshold value, threshold change step size and parallel threshold number of the photomultiplier tube; Step 2: With the set initial threshold as the center, a set of n different thresholds is generated by using the threshold change step, and the set is used for different decision conditions in subsequent signal processing; Step 3: for each signal received by the photomultiplier tube, generate multiple groups of decision results according to different thresholds in the set obtained in step 2, wherein the decision results are signal detection results or conditions required for calculating other performance evaluations; Step 4: Calculate and compare the performance indicators of each group of judgment results according to the generated multiple groups of judgment results, including bit error rate, signal strength and signal-to-noise ratio, and evaluate the advantages and disadvantages of different thresholds in the obtained set through the performance indicators; Step 5: Select a threshold that optimizes system performance based on the evaluation result of step 4, and update the selected threshold as the current working threshold; Step 6: Continuously monitor and process the signal data received by the photomultiplier tube, repeat the operations of steps 2-5, and dynamically adjust the current threshold to ensure that the system can maintain optimal detection performance under various environmental conditions.

2. The method for setting an adaptive threshold value of a photomultiplier tube signal for ultraviolet communication according to claim 1, characterized in that: In step 1, set the initial threshold V th , threshold change step ΔV th and the threshold number of parallelism n; Among them, the initial threshold V th and threshold change step ΔV th They are all quantized values ​​of digital signals collected by analog-to-digital converter ADC, and n is an odd number not less than 3; Threshold change step ΔV th The values ​​of and n are set according to the response speed requirements of the adaptive algorithm and the limitations of system resources.

3. The method for setting an adaptive threshold value of a photomultiplier tube signal for ultraviolet communication according to claim 1, characterized in that: The process of step 2 is specifically as follows: Calculate the initial threshold V th As the center, using the threshold change step ΔV th Generate a set of n different thresholds It is expressed as: Where k is the index, indicating arrive The integer value of .

4. The method for setting an adaptive threshold value of a photomultiplier tube signal for ultraviolet communication according to claim 3, characterized in that: In step 3, during the communication process, the optical signal received by the photomultiplier tube PMT is input into the analog-to-digital converter ADC, and the analog signal is converted into a digital signal by the analog-to-digital converter ADC; For the digital signal collected by ADC, the set obtained in step 2 n different thresholds are used to make judgments respectively, and n judgment results are generated; The synchronization header is used to perform frame synchronization processing on the above n judgment result sequences, and the photon counting rate λ of the received optical signal is calculated based on the judgment result sequence of each threshold. s and background noise photon count rate λ b .

5. The method for setting an adaptive threshold value of a photomultiplier tube signal for ultraviolet communication according to claim 4, characterized in that: The process of step 4 is specifically as follows: After getting n different sets of λ s With λ b Afterwards, the bit error rate BER is calculated as a reference for comparing the pros and cons of the n groups of thresholds in the set. Specifically: Based on the log-likelihood ratio L(N) used in the decision, it is expressed as: Where N represents the number of photon pulses in one symbol; assuming the N value of noise and signal, that is, N b and N s Each independently satisfies λ b With λ s Poisson distribution, N b and N s denote the number of photon pulses from the optical signal and the number of photon pulses from the background noise in a symbol respectively, and the probability of misjudging 0 as 1 is expressed as: P() means N b The probability of satisfying the conditions in brackets; The probability of misjudging 1 as 0 is expressed as: The calculated bit error rate BER is expressed as:

6. The method for setting an adaptive threshold value of a photomultiplier tube signal for ultraviolet communication according to claim 5, characterized in that: In step 5, according to the evaluation result of step 4, the threshold corresponding to the group with the lowest bit error rate BER is set as the current optimal threshold. The index corresponding to the group with the lowest bit error rate BER is expressed as: i opt =argmin i BER i The subscript i represents the bit error rate BER corresponding to the i-th threshold; argmin represents finding the index i that minimizes the bit error rate BER. opt ; The optimal threshold is V th +i opt ΔV th , assign the optimal threshold to the initial threshold V th , updated to the current working threshold.

7. A photomultiplier tube signal adaptive threshold setting system for ultraviolet communication, characterized in that: The system comprises: The parameter initialization module is used to set the initial threshold of the photomultiplier tube, the threshold change step size and the number of parallel thresholds; A threshold set generation module is used to generate a set of n different thresholds with the set initial threshold as the center and using the threshold change step, and the set is used for different decision conditions in subsequent signal processing; A signal receiving and processing module, used for generating multiple groups of decision results according to different thresholds in the obtained set for each signal received by the photomultiplier tube, wherein the decision results are signal detection results or conditions required for calculating other performance evaluations; A performance evaluation module is used to calculate and compare the performance indicators of each group of judgment results according to the generated multiple groups of judgment results, including bit error rate, signal strength and signal-to-noise ratio, and evaluate the advantages and disadvantages of different thresholds in the obtained set through the performance indicators; An optimal threshold selection module is used to select a threshold that optimizes system performance according to the evaluation result, and update the selected threshold as the current working threshold; The dynamic adjustment and feedback module is used to continuously monitor and process the signal data received by the photomultiplier tube, dynamically adjust the current threshold, and ensure that the system can maintain the best detection performance under various environmental conditions.

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