Demodulation accuracy degradation detection method and underwater visible light communication system using the same

Abstract

The present application relates to the field of communication technology, and in particular to a demodulation accuracy degradation detection method and an underwater visible light communication system using the same, wherein the pulse number value of a symbol 1 period is obtained through an on-off keying demodulation module, and the pulse number value is added to the pulse number value sample of the symbol 1 period, the degradation detection module calculates a statistic that can characterize the demodulation accuracy degradation of the on-off keying demodulation module based on the pulse number value sample, and obtains a first statistic, the communication system control module adds the first statistic to the statistic sample, obtains the first statistic sample, and calculates the first mean of the first statistic sample, and when the communication system control module receives a new second statistic, the demodulation accuracy of the on-off keying demodulation module is determined based on the second statistic, the first mean, and the demodulation accuracy degradation threshold interval. The present application improves the accuracy of demodulation data on the receiving side of the system, thereby improving the reliability of underwater visible light communication.

Description

Technical Field

[0001] The present application relates to the field of communication technology, and in particular to a demodulation accuracy degradation detection method and an underwater visible light communication system using the same. Background Art

[0002] Visible Light Communications (VLC) technology based on the visible light band has the advantages of ultra-wide spectral band, strong anti-interference ability, high speed, green environmental protection, good security and confidentiality, etc. It is widely used in underwater long-distance wireless communication, Internet of Things, sixth-generation mobile communication network and other scenarios. However, it has channel loss problems such as dielectric attenuation, multipath scattering, background light noise, turbulent fading, etc., which will seriously affect the performance of the visible light communication system and reduce the communication rate and maximum transmission distance.

[0003] In underwater long-distance wireless optical communication systems, accurate and fast signal detection can assist the system receiving side to more accurately restore the original data sent by the system sending side. Therefore, On-Off Keying Modulation (OOK) is usually used in underwater communication environments, especially in seawater communication environments. The absorption and scattering of water causes the optical signal passing through the water to be significantly attenuated, especially in long-distance transmission. The optical signal intensity is very weak, resulting in a larger fluctuation in the number of pulses of the on-off keying modulation signal received by the system receiving side, which is manifested as a degradation of phase accuracy, affecting the accuracy of the demodulated data on the system receiving side; and animals in the water body will swim autonomously, and marine debris will continue to move with the flow of seawater. These obstacles may block the visible light communication link, resulting in the on-off keying modulation signal received by the system receiving side losing part of its information, which is manifested as a degradation of phase accuracy, affecting the accuracy of the demodulated data on the system receiving side; secondly, the continuous flow of seawater will cause the optical signal to pass through the area The water temperature and density are unevenly distributed, and the refractive index of light in water is uneven, which causes the phase used by the receiving side to shift from the phase of the on-off keying modulation signal actually received, manifested as a degradation of phase accuracy, affecting the accuracy of the demodulated data on the receiving side; in addition, underwater long-distance wireless optical communication systems usually require equipment to run offline for a long time. The mechanical vibration, pressure changes, and temperature changes caused by the changeable ocean current movement will cause the clock circuit output clock frequency to drift. The complex and changeable magnetic field environment will cause electronic components to be out of step, and other factors will have a subtle effect on the accuracy of the equipment's operating clock, resulting in the inability to align the communications on both sides of the high-speed and high-bandwidth underwater long-distance wireless optical communication in time, manifested as a degradation of phase accuracy, affecting the accuracy of the demodulated data on the receiving side of the system. Summary of the invention

[0004] In order to overcome the shortcomings of the prior art, the present invention provides a demodulation accuracy degradation detection method and an underwater visible light communication system using the same, so as to improve the accuracy of demodulation data on the receiving side of the system, thereby improving the reliability of underwater visible light communication.

[0005] A first aspect of the present application provides a demodulation accuracy degradation detection method, which is applied to an underwater visible light communication system, wherein the underwater visible light communication system includes an on-off keying demodulation module, a degradation detection module, and a communication system control module, and the method includes:

[0006] The on-off keying demodulation module obtains the pulse quantity value of the symbol 1 period, and adds the pulse quantity value to the pulse quantity value sample of the symbol 1 period;

[0007] The degradation detection module calculates a statistic that can characterize the degradation of the demodulation accuracy of the on-off keying demodulation module based on the pulse number value samples to obtain a first statistic;

[0008] The communication system control module adds the first statistic to a statistic sample to obtain a first statistic sample, and calculates a first mean of the first statistic sample;

[0009] When the communication system control module receives a new second statistic, the demodulation accuracy of the on-off keying demodulation module is determined based on the second statistic, the first mean value and a preset demodulation accuracy degradation threshold interval.

[0010] In an optional implementation, the determining the demodulation accuracy of the on-off keying demodulation module based on the second statistic, the first mean value and a preset demodulation accuracy degradation threshold interval includes:

[0011] The communication system control module calculates a first difference between the second statistic and the first mean;

[0012] The communication system control module compares the first difference with a demodulation accuracy degradation threshold interval;

[0013] When the communication system control module determines that the first difference is within the demodulation accuracy degradation threshold interval, it is determined that the demodulation accuracy has not been degraded, and then the second statistic is added to the first statistic sample to obtain a second statistic sample;

[0014] The communication system control module updates the demodulation accuracy degradation threshold interval based on the second statistic.

[0015] In an optional implementation, the communication system control module updates the demodulation accuracy degradation threshold interval based on the second statistic, including:

[0016] Calculate a second mean and a sample sum of the second statistic sample;

[0017] determining a sample peak-to-peak value in the second statistic sample;

[0018] generating a target threshold interval upper limit value and a target threshold interval lower limit value based on the sample peak-to-peak value and a linear function used to calculate the demodulation accuracy degradation threshold interval;

[0019] The demodulation accuracy degradation threshold interval is updated based on the target threshold interval upper limit value and the target threshold interval lower limit value.

[0020] In an optional embodiment, the method further comprises:

[0021] When the communication system control module receives a newly input third statistic, calculating a second difference between the third statistic and the second mean;

[0022] The communication system control module compares the second difference with the updated demodulation accuracy degradation threshold interval;

[0023] When the communication system control module determines that the second difference is within the updated demodulation accuracy degradation threshold interval, it is determined that the demodulation accuracy has not been degraded, and the third statistic is added to the second statistic sample;

[0024] The communication system control module continues to adjust the updated demodulation accuracy degradation threshold interval based on the third statistic.

[0025] In an optional embodiment, the method further comprises:

[0026] When the communication system control module determines that the first difference is not within the demodulation accuracy degradation threshold interval, determining that the demodulation accuracy is degraded;

[0027] An optimization strategy for the on-off keying demodulation module is determined based on the second statistic and the demodulation accuracy degradation threshold interval.

[0028] In an optional embodiment, the first statistic includes a coefficient of variation and a variance-to-mean ratio, and the degradation detection module calculates a statistic that can characterize the accuracy degradation of the on-off keying demodulation module based on the pulse number value samples, and the first statistic obtained includes:

[0029] Calculating a third mean and variance of the pulse quantity value samples;

[0030] The coefficient of variation and the variance-to-mean ratio are determined based on the third mean and the variance.

[0031] In an optional implementation, determining the coefficient of variation and the variance-to-mean ratio based on the third mean and the variance includes:

[0032] The coefficient of variation is determined by the following formula:

[0033] ;

[0034] in, is the coefficient of variation, is the third mean, is the square of the third mean, is the fourth mean of the square of the pulse number samples, is the variance, ;

[0035] The variance-to-mean ratio is determined by the following formula:

[0036] ;

[0037] in, VMR is the variance-to-mean ratio.

[0038] In an optional embodiment, the method further comprises:

[0039] Determine the range of variation of the first statistic sample;

[0040] Determine an initial threshold interval upper limit value and an initial threshold interval lower limit value based on the variation amplitude range;

[0041] The accuracy degradation threshold interval is generated based on the initial threshold interval upper limit value and the initial threshold interval lower limit value.

[0042] A second aspect of the present application provides an underwater visible light communication system, the system comprising:

[0043] An on-off keying demodulation module, a degradation detection module and a communication system control module, wherein the on-off keying demodulation module is communicatively connected to the degradation detection module, and the degradation detection module is communicatively connected to the communication system control module;

[0044] The on-off keying demodulation module is used to obtain the pulse quantity value of the symbol 1 period and add the pulse quantity value to the pulse quantity value sample of the symbol 1 period;

[0045] The degradation detection module is used to calculate a statistic that can characterize the degradation of the demodulation accuracy of the on-off keying demodulation module based on the pulse number value samples to obtain a first statistic;

[0046] The communication system control module is used to add the first statistic to a statistic sample to obtain a first statistic sample, and calculate a first mean of the first statistic sample;

[0047] The communication system control module is further used to determine the demodulation accuracy of the on-off keying demodulation module based on the second statistic, the first mean value and a preset demodulation accuracy degradation threshold interval when a new second statistic is received.

[0048] A third aspect of the present application provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program implements the steps of the above-mentioned demodulation accuracy degradation detection method when executed by a processor.

[0049] In summary, the present application provides a demodulation accuracy degradation detection method and an underwater visible light communication system using the same. In the underwater visible light communication system, the on-off keying demodulation module is responsible for converting the received optical signal into an electrical signal and identifying symbols representing different data. Within a symbol 1 cycle, the on-off keying demodulation module will count the number of pulses received, so that the degradation detection module uses the sample of the number of pulses in the symbol 1 cycle to calculate one or more statistics for characterizing whether the demodulation transfer curve of the on-off keying demodulation module is degraded. The communication system control module is responsible for maintaining a statistical sample. And calculate the mean of this statistic sample. When a new second statistic is received, the communication system control module can determine whether the demodulation accuracy of the on-off keying demodulation module is still within an acceptable range based on the currently calculated mean, the new second statistic and the preset demodulation accuracy degradation threshold interval. It can monitor the demodulation accuracy degradation of the on-off keying demodulation module in the underwater visible light communication system in real time for further processing, which helps to improve the on-off keying demodulation performance of underwater visible light communication and improve the accuracy of demodulation data on the system receiving side, thereby improving the reliability of underwater visible light communication. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 is a structural schematic diagram of an underwater visible light communication system shown in an embodiment of the present application;

[0051] Figure 2 It is a schematic diagram of the structure of each module and signal direction of an underwater visible light communication system shown in an embodiment of the present application;

[0052] Figure 3 is a flow chart of a method for detecting degradation of demodulation accuracy shown in an embodiment of the present application;

[0053] Figure 4 It is a schematic diagram of a flow chart of a degradation detection module calculating a coefficient of variation of a sample shown in an embodiment of the present application;

[0054] Figure 5 A schematic diagram of a flow chart of a degradation detection module calculating a variance-mean ratio of a sample shown in an embodiment of the present application;

[0055] Figure 6 It is a schematic diagram of a flow chart of a communication system control module calculating a demodulation accuracy degradation threshold interval shown in an embodiment of the present application;

[0056] Figure 7 It is a simulation schematic diagram of a statistical change caused by a phase offset shown in an embodiment of the present application. DETAILED DESCRIPTION

[0057] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0058] The following will clearly and completely describe the concept, specific structure and technical effects of the present invention in combination with the embodiments and drawings, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by technicians in this field without creative work are all within the scope of protection of the present invention. In addition, all the connection / connection relationships involved in the patent do not refer to the direct connection of components, but refer to the formation of a better connection structure by adding or reducing connection accessories according to the specific implementation situation. The various technical features in the invention can be combined interchangeably without conflicting with each other.

[0059] Reference Figure 1 , which is a schematic diagram of the structure of an underwater visible light communication system shown in an embodiment of the present application.

[0060] The present application proposes a demodulation accuracy degradation detection method, which is applied to an underwater visible light communication system 1. The underwater visible light communication system 1 includes an on-off keying demodulation module 10, a degradation detection module 20 and a communication system control module 30, wherein the on-off keying demodulation module 10 is communicatively connected to the degradation detection module 20, and the degradation detection module 20 is communicatively connected to the communication system control module 30.

[0061] The underwater visible light communication system 1 may be an underwater long-distance wireless visible light communication system. In some embodiments, a field programmable gate array (FPGA), such as Xilinx's Zynq-7000 series FPGA, may be used as a computing unit of the on-off keying demodulation module 10 and the communication system control module 30.

[0062] In some embodiments, the on-off keying demodulation module 10 may include a symbol decision module for making a decision on the on-off keying modulation signal of the on-off keying demodulation module 10 during the communication process to obtain the number of pulses in the period of symbol 1. Specifically, the symbol period of the signal after on-off keying modulation will only have two states. If there is a carrier, it is called the symbol 1 period, otherwise it is the symbol 0 period. In some embodiments, a sine wave can be used as OOK modulation of the carrier, or a square wave can be used as modulation. In an embodiment of the present application, after the modulated signal enters the digital system, the signal is converted into a digital signal (only the high and low information of the signal amplitude is retained), and the sin carrier or the square wave carrier can be regarded as high-frequency pulses. Each time the symbol decision module decides only one symbol period, if the decision is symbol 0, the subsequent operation is skipped; if the decision is symbol 1, the number of pulses in this period is output to the degradation detection module 20, which originally stores the number of pulses samples of N symbol 1 periods in the previous period. After receiving the new sample, the oldest sample in the sample population is removed and the new sample is added to the sample population, so that the number of samples in the sample population can be kept at N all the time, and then the subsequent calculation is performed.

[0063] It should be noted that the sample population will only sample the number of pulses in a symbol 1 cycle. If the underwater visible light communication system 1 receives a large number of symbols 1 within a period of time, the sample population will be updated frequently, otherwise the sample population will be updated slowly.

[0064] Refer to Figure 2 As shown, at the current moment, after the symbol decision module in the on-off keying demodulation module 10 obtains the number of pulses in the symbol 1 cycle, it transmits the corresponding number of pulses in the symbol 1 cycle to the degradation detection module 20. After receiving the number of pulses in the symbol 1 cycle, the degradation detection module 20 adds the number of pulses in the symbol 1 cycle to the number of pulses sample in the symbol 1 cycle, that is, saves the number of pulses as a new sample to the N+1th element of the number of pulses sample in the symbol 1 cycle, wherein the number of pulses sample in the symbol 1 cycle includes N number of pulses before receiving a new number of pulses, where N is an integer greater than 1 and equal to 1. Then, the degradation detection module 20 can use the coefficient of variation and / or the variance-mean ratio as a statistic that characterizes the degradation of the demodulation accuracy of the on-off keying demodulation module 10, and thus can calculate the coefficient of variation and / or the variance-mean ratio of the number of pulses sample based on the newly received number of pulses in the symbol 1 cycle.

[0065] Refer to Figure 4 As shown, the degradation detection module 20 calculates the coefficient of variation of the pulse number samples, including:

[0066] 1) Calculate the square of the new sample mean of the number of pulses.

[0067] In some embodiments, the communication system control module 30 first calculates the new pulse number sample sum corresponding to the current moment using the sum of the pulse number samples stored at the previous moment, and calculates the new sample mean using the new pulse number sample sum. In this step, the degradation detection module 20 can comprehensively adjust the sample number N to multiple powers of 2 to simplify the division into a logical right shift operation to reduce the calculation delay.

[0068] Next, the degradation detection module 20 uses the new sample mean value and IP Multiplier to perform a multiplication operation to calculate the square of the new sample mean value.

[0069] 2) Calculate the mean of the new pulse number sample squares.

[0070] In some embodiments, the degradation detection module 20 uses the new pulse number value input at the current moment to perform multiplication using IPMultiplier to calculate a new sample square, then uses the sample square sum stored at the previous moment and the sample square to perform multiplication using IPMultiplier to calculate the new sample square sum, and finally calculates the new sample square mean based on the calculated new sample square sum. In this step, the degradation detection module 20 can comprehensively adjust the sample number N to multiple powers of 2 to simplify the division into a logical right shift operation to reduce calculation delay.

[0071] 3) Calculate the coefficient of variation of the new pulse number sample.

[0072] In some embodiments, the degradation detection module 20 uses the square of the new sample mean and the new mean of the sample squares to perform a division operation using IP DIVIDER to calculate the square of the sample variation coefficient, and then uses the square of the sample variation coefficient to perform a square root operation using IP CORDIC to calculate the variation coefficient of the new sample.

[0073] It should be noted that, in order to facilitate calculations within the FPGA, the dividend may be enlarged to ensure that the quotient of the division operation is an integer of a suitable size.

[0074] 4) Update the pulse quantity sample population and remove old data, that is, move the 2nd to N+1th elements in the sample population array of the pulse quantity sample to the 1st to Nth elements.

[0075] 5) Output the coefficient of variation as a statistic.

[0076] At the same time, refer to Figure 5 As shown, the degradation detection module 20 calculates the variance-mean ratio of the pulse number samples, including:

[0077] 1) Calculate the square of the new sample mean of the number of pulses.

[0078] 2) Calculate the mean of the new pulse number sample squares.

[0079] 3) Calculate the variance-mean ratio of the new pulse number samples.

[0080] In some embodiments, the degradation detection module 20 calculates the sample variance using the square of the new sample mean and the new mean of the sample squares, and calculates the sample variance-to-mean ratio by performing a division operation using IP DIVIDER using the sample variance and the sample mean.

[0081] Similarly, when the degradation detection module 20 calculates the variance-to-mean ratio, in order to facilitate the internal calculation of the FPGA, the dividend may be enlarged to ensure that the quotient of the division operation is an integer of a suitable size.

[0082] 4) Update the sample population and remove old data; move the 2nd to N+1st elements in the sample population array to the 1st to Nth elements.

[0083] 5) Output the variance-to-mean ratio as a statistic.

[0084] When the communication system control module 30 obtains the statistic output by the degradation detection module 20, it can determine whether the difference between the statistic and the statistic sample mean exceeds the demodulation accuracy degradation threshold interval. If not, the newly input statistic is added to the statistic sample, and a new demodulation accuracy degradation threshold interval is calculated using the newly input statistic. In other embodiments, the communication system control module 30 can also calculate the statistic.

[0085] Refer to Figure 6 As shown, the communication system control module 30 calculates a new demodulation accuracy degradation threshold interval, including:

[0086] 1) Calculate the mean of the new statistic sample.

[0087] In some embodiments, the sum of the statistic samples stored at the last moment and the new input statistic are used to calculate the sum of the new statistic samples, and the mean of the new statistic samples is calculated using the sum of the new statistic samples. In this step, the number of samples M can be adjusted to multiple powers of 2 to simplify the division into a logical right shift operation to reduce the calculation delay.

[0088] 2) Calculate a new demodulation accuracy degradation threshold interval.

[0089] In some embodiments, the maximum and minimum values ​​in the statistical sample stored at the previous moment are used to calculate the maximum and minimum values ​​in the new statistical sample, and the peak-to-peak value in the new statistical sample is calculated using the maximum and minimum values ​​in the new statistical sample. The peak-to-peak value in the new statistical sample is then used in combination with a preset function to calculate the upper and lower limits of the accuracy degradation threshold interval based on the peak-to-peak value of the change in the statistic.

[0090] In this embodiment, a linear function is used to generate the upper limit value of the degradation threshold interval:

[0091] ;

[0092] In this embodiment, the following function is used to generate the lower limit value of the degradation threshold interval:

[0093] ;

[0094] in, is the coefficient, which is pre-adjusted according to the variation range of the statistical sample measured by the underwater visible light communication system. J For the sample statistic T The range of variation, and They are functions for calculating the upper and lower limits of the accuracy degradation threshold interval according to the range of variation of the statistical samples, and are preset according to the characteristics of the problems that the underwater visible light communication system may face.

[0095] 3) Update the statistical sample population and remove old data; move the 2nd to M+1st elements in the statistical sample population array to the 1st to Mth element positions.

[0096] 4) Wait for the next threshold judgment.

[0097] If the difference exceeds the demodulation accuracy degradation threshold interval, the communication system control module 30 may decide on an optimization strategy for the key control demodulation module 10 according to the statistic and the demodulation accuracy degradation threshold interval.

[0098] In some embodiments, the underwater visible light communication system 1 also includes a phase detection module and a threshold calculation module. The phase detection module is used to determine the phase at the beginning of the symbol period in the on-off keying modulation signal received by the underwater visible light communication system 1; the threshold calculation module uses the symbol period starting phase output by the phase detection module as a reference to determine the pulse number threshold value that can accurately distinguish the symbol 1 period and the symbol 0 period in the on-off keying modulation signal received by the underwater visible light communication system 1, specifically calculating the arithmetic mean or logarithmic rate of change of the maximum and minimum values ​​of the pulse number within the symbol period.

[0099] Reference Figure 3, which is a flow chart of a demodulation accuracy degradation detection method shown in an embodiment of the present application, the demodulation accuracy degradation detection method includes the following steps.

[0100] S31, the on-off keying demodulation module obtains the pulse quantity value of the symbol 1 period, and adds the pulse quantity value to the pulse quantity value sample of the symbol 1 period.

[0101] During the communication process of underwater visible light communication system, due to the absorption and scattering effects of water, the optical signal attenuation and signal incompleteness caused by it will lead to the loss or phase shift of some modulation pulses of the on-off keying modulation signal of the on-off keying demodulation module of the underwater visible light communication system, thereby degrading the demodulation accuracy. Among them, the absorption effect of water refers to the absorption ability of water molecules to visible light of a specific wavelength, which can absorb part of the wavelength in the visible light and convert the light energy into heat energy, resulting in the attenuation of the signal intensity received by the sensor on the receiving side of the system; the scattering effect of water refers to the suspended particles or impurities in the water that will cause the scattering of light, causing part of the optical signal to deviate from the original propagation path and disperse in all directions, resulting in incomplete signals received by the sensor on the receiving side of the system.

[0102] Because the light signal generated by the obstruction in the water body is blocked, the pulse part of the on-off keying modulation signal will be lost, thereby degrading the demodulation accuracy. The obstruction in the water body includes but is not limited to objects such as animals, plankton, marine garbage, etc. in the water body that move autonomously or follow the ocean current; the obstruction has a probability of invading the area where the communication link of the underwater long-distance wireless visible light communication system is located. Large obstacles will completely block the light signal, and small or edge obstructions may cause partial attenuation of the light signal, resulting in random pulse loss. Secondly, the uneven density of the water body caused by the temperature stratification of the water body will also cause the pulse part of the on-off keying modulation signal to be lost, thereby degrading the demodulation accuracy. For visible light communication systems, especially underwater long-distance wireless communication systems working in complex sea areas, random pulse loss will cause the on-off keying modulation signal received by the sensor on the receiving side of the system to be lost, causing the demodulation accuracy to degrade. In addition, in long-term communication, the cumulative effect of clock drift is significant, which will cause the receiving side of the system to gradually lose synchronization with the sending side, so that the symbol 1 and symbol 0 states of the on-off keying modulation signal cannot be correctly identified. Therefore, in the embodiment of the present application, the pulse signal can be obtained first. During the communication process, the underwater visible light communication system first obtains the pulse quantity value of the period in which the symbol decision module in the on-off keying demodulation module judges to be symbol 1, that is, the symbol judged as "1" in the OOK demodulation process, that is, the pulse signal in the state of the carrier existence, and samples the pulse signal to determine the corresponding pulse quantity value, which is used to evaluate the stability and strength of the communication signal. Once the symbol decision module determines that the signal in a certain symbol period time period is interpreted as "1", and calculates the pulse quantity value in this time period, the pulse quantity value is added to a sample set for statistics or analysis, that is, the pulse quantity value sample of the symbol 1 period, so that the demodulation accuracy of the receiving side of the system can be judged based on the pulse quantity value sample in the future.

[0103] S32: The degradation detection module calculates a statistic that can characterize the degradation of the demodulation accuracy of the on-off keying demodulation module based on the pulse quantity value samples to obtain a first statistic.

[0104] Further, the underwater visible light communication system can calculate the statistic that can characterize the degradation of the demodulation accuracy of the on-off keying demodulation module by using the pulse number value samples of the symbol 1 period through the degradation detection module. In an embodiment of the present application, the electronic device uses the coefficient of variation (CV) or variance-to-mean ratio (VMR) of the pulse number value samples of the symbol 1 period as a statistic that characterizes the degradation of the demodulation accuracy of the on-off keying demodulation module. Therefore, after receiving the pulse number value samples of the symbol 1 period sent by the on-off keying demodulation module, the pulse number value samples of the symbol 1 period can calculate the coefficient of variation and / or variance-to-mean ratio of the pulse number value samples of the symbol 1 period at the current moment as the statistic of the degradation of the demodulation accuracy at the current moment, which is called the first statistic.

[0105] In an optional embodiment, the degradation detection module can first calculate the mean of the pulse number value samples, called the third mean, and calculate the mean of the squares of the pulse number value samples, called the fourth mean, and then calculate the variance of the pulse number value samples based on the third mean and the fourth mean, and finally calculate the coefficient of variation of the pulse number value samples based on the third mean and the variance.

[0106] For details, please refer to Figure 4 , the mean of the number of pulses in the symbol 1 cycle is determined by the following formula, which is also the third mean :

[0107] ;

[0108] in, X is the sample population of the number of pulses in one symbol cycle, The number of pulses in the symbol 1 cycle in the sample population i Sample elements, i is a positive integer and satisfies 0≤ i ≤ N , N is the number of pulse value samples in one symbol cycle, N Is a positive integer.

[0109] The mean of the square of the pulse number sample value, also known as the fourth mean, is determined by the following formula: :

[0110] ;

[0111] The variance of the number of pulses in a symbol cycle is determined by the following formula: :

[0112] ;

[0113] The coefficient of variation of the number of pulses in a symbol cycle is determined by the following formula: :

[0114] .

[0115] At the same time, the degradation detection module can calculate the variance-mean ratio of the pulse number value samples in the symbol 1 cycle. Figure 5 First, the mean value of the pulse number samples of symbol 1 cycle is calculated according to the same embodiment as above. , and calculate the mean of the square of the number of pulses in a symbol cycle , based on the mean and mean Calculate the variance of the number of pulses per symbol period. , and finally based on the mean and variance The variance-mean ratio of the pulse number samples of the symbol 1 cycle can be calculated VMR .

[0116] The variance-mean ratio of the pulse number value samples is determined by the following formula: VMR :

[0117] .

[0118] After obtaining the coefficient of variation and the variance-to-mean ratio of the pulse quantity value samples in the symbol 1 period, the degradation detection module may use the coefficient of variation and / or the variance-to-mean ratio as a statistic representing the discrete characteristic.

[0119] S33, the communication system control module adds the first statistic to the statistic sample to obtain the first statistic sample, and calculates a first mean of the first statistic sample.

[0120] In some embodiments, after the degradation detection module calculates and obtains the statistic representing the discrete characteristic, that is, the first statistic, it can send the first statistic to the communication system control module. After receiving the first statistic, the communication system control module can add the first statistic to the statistic sample to obtain the first statistic sample. , where the first statistic sample It is the sample population of the statistics output by the degradation detection module to the communication system control module.

[0121] Next, the communication system control module can also determine the first statistical sample by the following formula: The mean of , also known as the first mean:

[0122] ;

[0123] in, is the first statistic in the sample n Sample elements, n is a positive integer and satisfies 0< n ≤ M , M is the number of samples of the first statistic, M Is a positive integer.

[0124] S34, when the communication system control module receives a new second statistic, the demodulation accuracy of the on-off keying demodulation module is determined based on the second statistic, the first mean value and a preset demodulation accuracy degradation threshold interval.

[0125] In some embodiments, when the next moment comes, the on-off keying demodulation module obtains a new pulse number value of a symbol 1 period, and sends the new pulse number value of a symbol 1 period to the degradation detection module, so that the degradation detection module calculates a statistic representing the degradation of the demodulation accuracy of the on-off keying demodulation module based on the pulse number value sample, that is, a second statistic. After calculating the second statistic, the degradation detection module sends the second statistic to the communication system control module.

[0126] In an optional embodiment, the method further comprises:

[0127] Determine the range of variation of the first statistic sample;

[0128] Determine an initial threshold interval upper limit value and an initial threshold interval lower limit value based on the variation amplitude range;

[0129] The accuracy degradation threshold interval is generated based on the initial threshold interval upper limit value and the initial threshold interval lower limit value.

[0130] In some embodiments, the communication system control module may determine a first statistical sample The maximum value (called the first maximum sample value) and the minimum value (called the first minimum sample value) in are obtained, and the range of variation of the statistic sample is calculated based on the first maximum sample value and the first minimum sample value.

[0131] Determine the first statistic sample by the following formula: The range of variation:

[0132] ;

[0133] in, is the first maximum sample value, is the first minimum sample value.

[0134] In some embodiments, the communication system control module may preset a threshold interval upper limit value (In order to distinguish the updated upper limit value, it is called the initial threshold interval upper limit value) and a threshold interval lower limit value (Similarly, in order to distinguish the updated lower limit value, it is called the lower limit value of the initial threshold interval) as the demodulation accuracy degradation threshold, and constitute the demodulation accuracy degradation threshold interval .in, , ,and and They are all functions of calculating the accuracy degradation threshold interval according to the range of variation of the statistical sample, and are preset according to the characteristics of the problems that the underwater visible light communication system may face, which may include attenuation, scattering, noise level, etc. of the optical signal. Functions and Functions The specific form of depends on how to define and measure the demodulation accuracy degradation of underwater visible light communication systems, and which factors are considered to be the key factors affecting the demodulation accuracy.

[0135] Among them, the upper limit of the threshold interval The phenomenon of large statistical fluctuations caused by unstable pulse reception caused by water environment or clock drift can be detected. In some embodiments, the communication system control module can use the following linear function to generate the threshold interval upper limit value of the demodulation accuracy degradation threshold interval :

[0136] ;

[0137] in, is a coefficient, which is pre-adjusted according to the variation range of the statistical sample measured by the underwater visible light communication system.

[0138] The lower limit of the threshold interval is The phenomenon that the statistic is sharply reduced to 0 due to the complete loss of pulses caused by obstructions in the water can be detected. In some embodiments, the communication system control module can use the following function to generate the threshold interval lower limit value of the demodulation accuracy degradation threshold interval :

[0139] .

[0140] In an optional implementation, the determining the demodulation accuracy of the on-off keying demodulation module based on the second statistic, the first mean value and a preset demodulation accuracy degradation threshold interval includes:

[0141] The communication system control module calculates a first difference between the second statistic and the first mean;

[0142] The communication system control module compares the first difference with a demodulation accuracy degradation threshold interval;

[0143] When the communication system control module determines that the first difference is within the demodulation accuracy degradation threshold interval, it is determined that the demodulation accuracy has not been degraded, and then the second statistic is added to the first statistic sample to obtain a second statistic sample;

[0144] The communication system control module updates the demodulation accuracy degradation threshold interval based on the second statistic.

[0145] After receiving the newly input second statistic, the communication system control module can calculate the difference between the second statistic and the first mean (referred to as the first difference for distinction), and compare the first difference with the preset demodulation accuracy degradation threshold interval. A comparison is performed to determine whether the first difference is within the demodulation accuracy degradation threshold interval. When it is determined that the first difference is within the demodulation accuracy degradation threshold interval, it indicates that the demodulation accuracy of the on-off keying demodulation module is relatively stable and no obvious degradation occurs; otherwise, it indicates that the demodulation accuracy shows obvious degradation, and the demodulation part of the underwater visible light communication system needs to be optimized.

[0146] When it is determined that the first difference is within the demodulation accuracy degradation threshold interval, the communication system control module can further add the second statistic to the first statistic sample to obtain a new statistic sample, called the second statistic sample, and update the demodulation accuracy degradation threshold interval based on the second statistic.

[0147] Specifically, for the second statistic newly input to the communication system control module t , the communication system control module can calculate the difference between it and the first mean of the first statistical sample by the following formula D :

[0148] .

[0149] When the difference D When the demodulation accuracy degradation threshold interval is not exceeded, that is, when it is within the demodulation accuracy degradation threshold interval, that is, , then the newly input second statistic is added to the first statistic sample T , and using the newly input second statistic to calculate a new demodulation accuracy degradation threshold interval, including:

[0150] 1) Calculate a new statistic sample, that is, the mean of the second statistic sample, and obtain the second mean.

[0151] In some embodiments, the communication system control module can use the statistical samples stored at the last moment, that is, the sum of the first statistics, and the newly input second statistics to calculate the sum of the new second statistical samples, and then use the sum of the new second statistical samples to calculate the mean of the new second statistical samples, that is, the second mean. In this step, the communication system control module can comprehensively adjust the number of statistical samples M to multiple powers of 2 to simplify the division into a logical right shift operation to reduce the calculation delay.

[0152] 2) Calculate a new demodulation accuracy degradation threshold interval.

[0153] In some embodiments, the communication system control module can use the first maximum sample value and the first minimum sample value in the first statistical sample stored at the previous moment to calculate the maximum value (referred to as the second maximum sample value) and the minimum value (referred to as the second minimum sample value) of the newly obtained second statistical sample, and then use the second maximum sample value and the second minimum sample value of the new second statistical sample to calculate the sample peak-to-peak value in the new second statistical sample, and use the sample peak-to-peak value of the new second statistical sample to update the demodulation accuracy degradation threshold interval in conjunction with a preset linear function that calculates the threshold interval upper limit value and the threshold interval lower limit value of the demodulation accuracy degradation threshold interval based on the peak-to-peak value of the change in the statistic.

[0154] In the embodiment of the present application, a new threshold interval upper limit value is generated using a linear function with a coefficient of 3. (In order to distinguish the upper limit value before the update, it is called the upper limit value of the target threshold interval):

[0155] ;

[0156] ;

[0157] in, is the second statistic sample The range of variation, , is the second largest sample value, is the second largest small sample value.

[0158] Similarly, use the following function to generate a new threshold interval lower limit value (Similarly, in order to distinguish the lower limit value before the update, it is called the lower limit value of the target threshold interval):

[0159] ;

[0160] .

[0161] Therefore, the communication system control module can be based on the new threshold interval upper limit value and the new lower threshold value Generate a threshold interval for demodulation accuracy degradation Update to obtain a new demodulation accuracy degradation threshold interval .

[0162] Through the above optional implementation, the accuracy degradation of the on-off keying demodulation of underwater long-distance wireless visible light communication can be detected without increasing additional hardware costs, thereby improving the long-term operation stability of the communication system. At the same time, the accuracy of the on-off keying demodulation of underwater long-distance wireless visible light communication can be detected in real time, and real-time threshold interval generation can be realized to improve the accuracy of the on-off keying demodulation module and expand the communication system's adaptability in various complex scenarios. Secondly, the present application uses a threshold interval constructed with dual thresholds to deal with different types of problems in underwater long-distance wireless visible light communication systems, further expanding the communication system's adaptability in various complex scenarios.

[0163] Refer to Figure 6 , in some embodiments, after the demodulation accuracy degradation threshold interval is updated, the communication system control module may also update the second statistical sample to remove old data, for example, the 2nd to M+1st elements in the statistical sample population array are moved to the 1st to Mth element positions;

[0164] In an optional embodiment, the method further comprises:

[0165] When the communication system control module determines that the first difference is not within the demodulation accuracy degradation threshold interval, determining that the demodulation accuracy is degraded;

[0166] An optimization strategy for the on-off keying demodulation module is determined based on the second statistic and the demodulation accuracy degradation threshold interval.

[0167] In some embodiments, when it is determined that the difference is not within the demodulation accuracy degradation threshold interval, the communication system control module can optimize the interval deviation degree and retention time based on the first difference. Specifically, when the deviation degree of the difference is small and the retention time is short, the communication system control module sends a forced update instruction to the phase detection module and the threshold calculation module to recalibrate the symbol period start phase value and the decision threshold value; after recalibration, if the deviation degree of the difference is large or the retention time is long, the communication system control module sends a visible light communication channel realignment instruction to the front-end visible light signal receiving device in the underwater visible light communication system, and cooperates with the phase detection module and the threshold calculation module to further calibrate the reception of the visible light signal; after further recalibration, if the deviation degree of the difference is still large or the retention time is long, the communication system control module sends a communication interruption signal to the equipment master control end, and the master control end performs manual operation or on-site maintenance.

[0168] In an optional embodiment, the method further comprises:

[0169] When the communication system control module receives a newly input third statistic, calculating a second difference between the third statistic and the second mean;

[0170] The communication system control module compares the second difference with the updated demodulation accuracy degradation threshold interval;

[0171] When the communication system control module determines that the second difference is within the updated demodulation accuracy degradation threshold interval, it is determined that the demodulation accuracy has not been degraded, and the third statistic is added to the second statistic sample;

[0172] The communication system control module continues to adjust the updated demodulation accuracy degradation threshold interval based on the third statistic.

[0173] In some embodiments, when a new third statistic is received at the current moment, the communication system control module can calculate the difference between the third statistic and the mean of the statistic sample at the previous moment (called the second difference) according to the same embodiment as above, and compare the second difference with the demodulation accuracy degradation threshold interval. When it is determined that the second difference does not exceed the demodulation accuracy degradation threshold interval, the demodulation accuracy degradation threshold interval is updated. When the second difference exceeds the demodulation accuracy degradation threshold interval, the on-off keying demodulation module needs to be optimized. Similarly, when new statistics continue to be received at the current moment, it is determined whether to adjust the demodulation accuracy degradation threshold interval based on the newly received statistics or to optimize the on-off keying demodulation module according to the same implementation method as above. Underwater long-distance wireless visible light communication technology has the advantages of ultra-wide spectrum band, strong anti-interference ability, high speed, green environmental protection, good security and confidentiality, etc., and is used as an underwater communication system to realize communication within the sea area. The underwater long-distance wireless visible light communication system based on on-off keying modulation and demodulation is sensitive to the number of pulse signals and phase offset of the signal reception, so it is necessary to detect the communication process in real time, especially to detect the degradation of the on-off keying demodulation module. The present application utilizes the characteristic that the discreteness of the number of pulses in a symbol 1 period is low when the on-off keying signal is working stably, samples the number of pulses judged as being in a symbol 1 period by the statistical symbol decision module, calculates the sample discrete statistics, and calculates the threshold interval of the degradation of the accuracy of the sampled discrete statistics. Finally, the accuracy of the system demodulation module at the current moment is determined based on the statistics and the threshold interval, thereby reducing the risk of communication synchronization loss caused by the accumulation of phase offsets and partial pulse loss in the communication system. The present application is applicable to underwater long-distance visible light communication systems. The detection scheme has simple logic and low complexity. It can improve the on-off keying demodulation performance of underwater long-distance wireless visible light communication, improve the accuracy of the demodulation data on the receiving side of the system, and thus improve the accuracy of the underwater visible light communication system.

[0174] In order to facilitate understanding of the present application, an example is given below to describe the practical application of the embodiment of the present application. Figure 7 , simulated the coefficient of variation and variance-mean ratio of the pulse number samples of the period judged as symbol 1 in the stable condition and the phase shift condition (both statistics have been linearly amplified by the same factor), as well as the rate of change of the two statistics in the phase shift condition relative to the stable condition. Figure 7In the simulation example shown, the signal phase shifts of 10%, 15%, 20% and 30% are simulated respectively. The difference between the coefficient of variation of the phase shift sample and the mean of the coefficient of variation of the stable sample has obvious mutations of 332%, 679%, 992% and 1653% respectively relative to the variation of the coefficient of variation of the stable sample, and the change of the difference to mean ratio has obvious mutations of 432%, 1138%, 1961% and 4225% respectively, and the amplified variance to mean ratio has a larger absolute value. Figure 7 The simulation example shown demonstrates that the statistics selected in the embodiment of the present application have a significant ability to reflect the system demodulation accuracy, and confirms the effectiveness and real-time performance of the present application in the accuracy degradation of the on-off keying demodulation module in the underwater long-distance wireless visible light communication system.

[0175] Each functional module in each embodiment of the present invention may be integrated into one processing module, or each component may exist physically separately, or two or more modules may be integrated into one module. The above integrated modules may be implemented in the form of hardware or software functional modules.

[0176] If the integrated module is implemented in the form of a software function module and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium, including several instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc. Various media that can store program codes.

[0177] It should be noted that, for the convenience of description, the aforementioned method embodiments are all described as a series of action combinations, but those skilled in the art should be aware that the present invention is not limited by the described action sequence, because according to the present invention, certain steps can be performed in other sequences or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily required by the present invention.

[0178] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0179] The above is a specific description of the preferred implementation of the present invention, but the invention is not limited to the embodiments. Those skilled in the art can make various equivalent modifications or substitutions without violating the spirit of the present invention. These equivalent modifications or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A method for detecting demodulation accuracy degradation, characterized in that: Applied to an underwater visible light communication system, the underwater visible light communication system includes an on-off keying demodulation module, a degradation detection module and a communication system control module, and the method includes: The on-off keying demodulation module obtains the pulse quantity value of the symbol 1 period, and adds the pulse quantity value to the pulse quantity value sample of the symbol 1 period; The degradation detection module calculates a statistic that can characterize the degradation of the demodulation accuracy of the on-off keying demodulation module based on the pulse number value samples to obtain a first statistic, wherein the first statistic includes a coefficient of variation and a variance-to-mean ratio, including: calculating a third mean and variance of the pulse number value samples; and determining the coefficient of variation by the following formula: ;in, is the coefficient of variation, is the third mean, is the square of the third mean, is the fourth mean of the square of the pulse number samples, is the variance, ; Determine the variance-mean ratio by the following formula: ;in, VMR is the variance-mean ratio; The communication system control module adds the first statistic to a statistic sample to obtain a first statistic sample, and calculates a first mean of the first statistic sample; When the communication system control module receives a new second statistic, the demodulation accuracy of the on-off keying demodulation module is determined based on the second statistic, the first mean value and a preset demodulation accuracy degradation threshold interval.

2. The demodulation accuracy degradation detection method according to claim 1, characterized in that: The step of determining the demodulation accuracy of the on-off keying demodulation module based on the second statistic, the first mean value, and a preset demodulation accuracy degradation threshold interval includes: The communication system control module calculates a first difference between the second statistic and the first mean; The communication system control module compares the first difference with a demodulation accuracy degradation threshold interval; When the communication system control module determines that the first difference is within the demodulation accuracy degradation threshold interval, it is determined that the demodulation accuracy has not been degraded, and then the second statistic is added to the first statistic sample to obtain a second statistic sample; The communication system control module updates the demodulation accuracy degradation threshold interval based on the second statistic.

3. The demodulation accuracy degradation detection method according to claim 2, characterized in that: The communication system control module updates the demodulation accuracy degradation threshold interval based on the second statistic, including: Calculate a second mean and a sample sum of the second statistic sample; determining a sample peak-to-peak value in the second statistic sample; generating a target threshold interval upper limit value and a target threshold interval lower limit value based on the sample peak-to-peak value and a linear function used to calculate the demodulation accuracy degradation threshold interval; The demodulation accuracy degradation threshold interval is updated based on the target threshold interval upper limit value and the target threshold interval lower limit value.

4. The demodulation accuracy degradation detection method according to claim 3, characterized in that: The method further comprises: When the communication system control module receives a newly input third statistic, calculating a second difference between the third statistic and the second mean; The communication system control module compares the second difference with the updated demodulation accuracy degradation threshold interval; When the communication system control module determines that the second difference is within the updated demodulation accuracy degradation threshold interval, it is determined that the demodulation accuracy has not been degraded, and the third statistic is added to the second statistic sample; The communication system control module continues to adjust the updated demodulation accuracy degradation threshold interval based on the third statistic.

5. The demodulation accuracy degradation detection method according to claim 2, characterized in that: The method further comprises: When the communication system control module determines that the first difference is not within the demodulation accuracy degradation threshold interval, determining that the demodulation accuracy is degraded; An optimization strategy for the on-off keying demodulation module is determined based on the second statistic and the demodulation accuracy degradation threshold interval.

6. The demodulation accuracy degradation detection method according to claim 1, characterized in that: The method further comprises: Determine the range of variation of the first statistic sample; Determine an initial threshold interval upper limit value and an initial threshold interval lower limit value based on the variation amplitude range; The accuracy degradation threshold interval is generated based on the initial threshold interval upper limit value and the initial threshold interval lower limit value.

7. An underwater visible light communication system, characterized in that: The underwater visible light communication system comprises: An on-off keying demodulation module, a degradation detection module and a communication system control module, wherein the on-off keying demodulation module is communicatively connected to the degradation detection module, and the degradation detection module is communicatively connected to the communication system control module; The on-off keying demodulation module is used to obtain the pulse quantity value of the symbol 1 period and add the pulse quantity value to the pulse quantity value sample of the symbol 1 period; The degradation detection module is used to calculate a statistic that can characterize the degradation of the demodulation accuracy of the on-off keying demodulation module based on the pulse number value samples to obtain a first statistic, wherein the first statistic includes a coefficient of variation and a variance-to-mean ratio, including: calculating a third mean and variance of the pulse number value samples; and determining the coefficient of variation by the following formula: ;in, is the coefficient of variation, is the third mean, is the square of the third mean, is the fourth mean of the square of the pulse number samples, is the variance, ; Determine the variance-mean ratio by the following formula: ;in, VMR is the variance-mean ratio; The communication system control module is used to add the first statistic to a statistic sample to obtain a first statistic sample, and calculate a first mean of the first statistic sample; The communication system control module is further used to determine the demodulation accuracy of the on-off keying demodulation module based on the second statistic, the first mean value and a preset demodulation accuracy degradation threshold interval when a new second statistic is received.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the demodulation accuracy degradation detection method according to any one of claims 1 to 6 are implemented.

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