Atmospheric channel parameter extraction method based on double JohnsonSB distribution

Abstract

The invention belongs to the technical field of atmospheric laser communication, and particularly relates to an atmospheric channel parameter extraction method based on double Johnson SB distribution. Comprising the following steps: S1, a receiving and measuring device comprising a telescope optical system, an APD detector and an acquisition card; s2, data processing and analysis: normalizing light intensity data obtained by measurement, then analyzing probability distribution of light intensity, and fitting by using a probability density distribution model; and S3, atmospheric channel parameter calculation: obtaining a probability density function through fitting, establishing a light intensity distribution model of the optical fiber coupling receiving system, and calculating atmospheric channel parameters. According to the atmospheric channel parameter extraction method based on the double Johnson SB distribution, in the process of applying experimental measurement data to calculation, due to the fact that the light intensity fluctuation probability density distribution is described based on the double Johnson SB distribution, and the fitting effect is better, compared with an existing method, the obtained result is more accurate, and the applicable atmospheric conditions are wider.

Description

Technical Field

[0001] The invention relates to the technical field of atmospheric laser communication, and in particular to an atmospheric channel parameter extraction method based on double Johnson SB distribution. Background Art

[0002] The traditional space optical communication receiving technology mainly transmits the optical signal through the space optical path and focuses the receiving optical system, and then directly illuminates the photoelectric detector for reception and subsequent photoelectric signal processing. However, most of the main ground communication networks are now optical fiber communication networks, and the optical signal processing devices in optical fiber communication are very mature, which is convenient for amplifying and processing optical domain signals. Therefore, the traditional space photoelectric detection and receiving method is increasingly unable to meet and adapt to the future development needs of space optical communication.

[0003] For atmospheric laser communications, the random characteristics of the atmospheric channel cause the channel state to change over time. Atmospheric turbulence can cause fluctuations in the intensity of the light received at the receiving end, phase fluctuations, beam drift and beam expansion, etc., which seriously affect the stability and reliability of laser transmission. In wireless communication systems, when the fluctuating signal amplitude is statistically analyzed, it is found that its probability density distribution (PDF) conforms to a certain distribution law. Traditionally, the light intensity probability density function model is used to describe the light intensity probability density distribution, such as log-normal distribution, Gamma-Gamma distribution, K distribution, etc. The light intensity fluctuations in the actual turbulent atmosphere have more complex characteristics, and these models are often difficult to accurately fit the actual measured data. The accuracy of existing atmospheric channel parameter extraction methods is limited.

[0004] The double Johnson SB distribution is a four-parameter distribution model that can describe the entire process from Gaussian distribution to negative exponential distribution. However, the existing light intensity fluctuation probability density models rarely use the double Johnson SB distribution for modeling, which limits its application in complex communication environments. Therefore, we propose an atmospheric channel parameter extraction method based on the double Johnson SB distribution to solve the above problem. Summary of the invention

[0005] 1. Technical issues to be resolved

[0006] In view of the deficiencies of the prior art, the present invention provides an atmospheric channel parameter extraction method based on double Johnson SB distribution, which solves the problems raised in the above background technology.

[0007] (II) Technical solution

[0008] In order to achieve the above-mentioned purpose, the present invention specifically adopts the following technical solutions:

[0009] A method for extracting atmospheric channel parameters based on double Johnson SB distribution includes the following steps:

[0010] S1, receiving and measuring device: including telescope optical system, APD detector, and acquisition card;

[0011] S2, data processing and analysis: by denoising the measured light intensity data, then analyzing the probability density distribution of light intensity fluctuations, and fitting using a probability density distribution model;

[0012] S3, atmospheric channel parameter calculation: through the probability density function obtained after fitting, the optical intensity distribution model of the fiber-coupled receiving system is established, and the atmospheric channel parameters are calculated.

[0013] Furthermore, the tail end of the optical fiber in S1 is connected to a laser power detector for signal detection, and a data acquisition card obtains time domain data at a sampling frequency of 1 kHz.

[0014] Furthermore, the data normalization process in S2 includes subtracting background noise from each data point of the collected original light intensity data, and normalizing the light intensity signal to the maximum value to ensure that the real experimental irradiance is obtained.

[0015] Furthermore, the double Johnson SB distribution function in S2 is specifically expressed as:

[0016]

[0017] in

[0018]

[0019] In the formula, the double Johnson SB distribution model has four free parameters γ 1 , γ 2 , δ 1 , δ 2 And satisfy the condition δ 1 >0,δ 2 > 0, without loss of generality: γ 1 ≤γ 2 ;p z (·) represents the PDF of Johnson SB distribution. It can be seen that equation (1) is obtained by combining the probability density functions of two standard Johnson SB distributions.

[0020] Furthermore, the double Johnson SB distribution in S3 has four free parameters, which control the shape and position of the probability distribution. The optimization of the parameters is performed by fitting the light intensity data using the least squares method. The goodness of fit R 2 Rating. 2The closer it is to 1, the better the fitting result.

[0021]

[0022] The frequency value of each I in the fitting process is y, which corresponds to the value Y of the fitting curve.

[0023] Furthermore, the channel parameter in S3, i.e., the flicker index The calculation uses the following formula:

[0024]

[0025] Where I represents the normalized light intensity data value after denoising, and <·> is the symbol for mean calculation.

[0026] (III) Beneficial effects

[0027] Compared with the prior art, the present invention provides an atmospheric channel parameter extraction method based on double Johnson SB distribution, which has the following beneficial effects:

[0028] The present invention studies the probability density function and its characteristics under different turbulence intensities during propagation in a horizontal atmospheric path through experiments. The model based on the double Johnson SB distribution can more accurately fit the light intensity fluctuation data under a complex turbulent atmospheric environment, reduce the error between the model and the actual data, and can more accurately fit the light intensity fluctuation under actual atmospheric turbulence. Its free parameters are associated with the turbulence intensity, providing a new model for atmospheric channel performance estimation. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic diagram of the structure of a receiving and measuring device system of an atmospheric channel parameter extraction method based on double Johnson SB distribution according to the present invention;

[0030] Figure 2 A schematic diagram of light intensity distribution provided by an embodiment of the present invention;

[0031] Figure 3 The embodiment of the present invention provides Figure 2 The light intensity distribution diagram is fitted using log-normal distribution and Gamma-Gamma distribution;

[0032] Figure 4 The embodiment of the present invention provides Figure 2 Schematic diagram of light intensity distribution, and the double Johnson SB distribution is used for fitting;

[0033] Figure 5 A flow chart of an atmospheric channel parameter extraction method based on double Johnson SB distribution provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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. 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.

[0035] Example

[0036] like Figure 1-5 As shown, an atmospheric channel parameter extraction method based on double Johnson SB distribution proposed in one embodiment of the present invention comprises the following steps:

[0037] S1, receiving and measuring device: including telescope optical system, APD detector, and acquisition card;

[0038] like Figure 1 As shown, the system structure diagram of the receiving and measuring device is shown. In the figure, the transmitting end emits a laser in the 1550nm band through a laser, and the optical signal is transmitted to the transmitting optical system (transmission telescope). The laser outputs the optical signal and is connected to the optical antenna through an optical fiber. The optical signal passes through the atmospheric channel, and the receiving end uses an optical system with the same structure and convergence function to receive it. At the tail end of the antenna, it is directly transmitted to the APD detector module through an optical fiber, and then the detector module performs corresponding processing and transmits it to the acquisition card. The acquisition card measures and obtains time domain data at a sampling frequency of 1kHz, and then the data is stored by the computer.

[0039] S2, data processing and analysis: by denoising the measured light intensity data, then analyzing the probability density distribution of light intensity fluctuations, and fitting using a probability density distribution model;

[0040] Data normalization processing includes subtracting background noise from each data point from the collected raw light intensity data, and normalizing the light intensity signal to the maximum value to ensure that the real experimental irradiance is obtained.

[0041] In order to obtain the probability distribution of normalized light intensity, the following steps should be followed: 1) first find the maximum value max[I] and the minimum value min[I] of each group of normalized light intensity, 2) then divide the interval {min[I], max[I]} into n equal intervals. 3) then select the median of the n intervals to form the light intensity sequence I = {I 1 ,I 2 ,...,I n}, and at the same time, the frequency of each light intensity value is counted to form another sequence y = {y 1 ,y2 ,...,y n}. 4) Finally, according to the values ​​of the two sequences, the frequency distribution histogram of the normalized light intensity is obtained, and the third sequence Y={Y 1 ,Y 2 ,...,Y n}. The frequency value of each I in the fitting process is y, which corresponds to the value Y of the fitting curve.

[0042] like Figure 2 As shown, a schematic diagram of light intensity distribution is shown. The horizontal axis in the figure is the acquisition time, and the vertical axis is the light intensity received by the detector converted into voltage (the light signal is converted into an electrical signal, and the light intensity is calculated based on this voltage value and the detector responsivity). The light intensity distribution curve can be used to observe the jitter of the light intensity.

[0043] like Figure 3 As shown, it is shown based on Figure 2 The normalized probability distribution curve diagram of the light intensity distribution diagram is shown in Figure 1. The horizontal axis is the light intensity received by the detector converted into current, and the vertical axis is the number of corresponding current intensities. Figure 3 As shown, the light intensity distribution can be seen, where the highest peak indicates that the light power is concentrated near this value. It can also be shown that the signal under weak turbulence is log-normally distributed, and is fitted using the log-normal distribution function and the Gamma-Gamma distribution function.

[0044] like Figure 4 As shown, it is shown based on Figure 2 The normalized probability distribution curve diagram of the light intensity distribution diagram is shown in Figure 1. The horizontal axis is the light intensity received by the detector converted into current, and the vertical axis is the number of corresponding current intensities. Figure 4 The light intensity distribution is shown in FIG. 1 , where the highest peak indicates that the light power is concentrated near this value, and a double Johnson SB distribution is used for fitting.

[0045] The double Johnson SB distribution function is specifically expressed as:

[0046]

[0047] in

[0048]

[0049] In the formula, the double Johnson SB distribution model has four free parameters γ 1 , γ 2 , δ 1 , δ 2 And satisfy the condition δ 1 >0,δ2 > 0, without loss of generality: γ 1 ≤γ 2 ;p z (·) represents the PDF of the Johnson SB distribution. It can be seen that equation (9) is obtained by combining the probability density functions of two standard Johnson SB distributions.

[0050] The lognormal distribution model was used for fitting and the goodness of fit R was calculated. 2 Equal to 0.97005.

[0051] Gamma-Gamma distribution model was used for fitting and the goodness of fit R was calculated. 2 Equal to 0.97644.

[0052] The fitting parameter γ is obtained by using the double Johnson SB distribution model. 1 =0.67,γ 2 =0.18,δ 1 =3.10,δ 2 =2.06, goodness of fit R 2 Equal to 0.97804.

[0053] After comparing the goodness of fit R 2 , the double Johnson SB distribution model fitting has a better fitting effect.

[0054] S3, atmospheric channel parameter calculation: through the probability density function obtained after fitting, the light intensity distribution model of the fiber-coupled receiving system is established, and the atmospheric channel parameters are calculated. The expression of the obtained probability density function is as follows:

[0055]

[0056] Channel parameter is flicker index The calculation uses the following formula:

[0057]

[0058] Where I represents the normalized light intensity data value, and <·> is the symbol for mean calculation.

[0059] like Figure 5 As shown, this embodiment provides a flow chart of an atmospheric channel parameter extraction method based on double Johnson SB distribution.

[0060] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for extracting atmospheric channel parameters based on double Johnson SB distribution, characterized in that: The following steps are involved: S1, receiving and measuring device: including telescope optical system, APD detector, and acquisition card; S2, data processing and analysis: normalize the measured light intensity data, analyze the probability distribution of the light intensity, and use the probability density distribution model to fit; S3, atmospheric channel parameter calculation: obtain the probability density function through fitting, establish the light intensity distribution model of the fiber-coupled receiving system, and calculate the atmospheric channel parameters.

2. The atmospheric channel parameter extraction method based on double Johnson SB distribution according to claim 1, characterized in that: The telescope optical system in S1 is arranged at a predetermined receiving position, so that the emitted laser enters the optical system just after the light wave passes through the atmospheric channel, ensuring that the incident light is fully coupled into the optical fiber.

3. The atmospheric channel parameter extraction method based on double Johnson SB distribution according to claim 1, characterized in that: The tail end of the optical fiber in S1 is connected to a laser power detector to detect the signal, and the data acquisition card obtains time domain data at a sampling frequency of 1 kHz.

4. The atmospheric channel parameter extraction method based on double Johnson SB distribution according to claim 1, characterized in that: The data normalization process in S2 includes subtracting the background noise from each data point of the collected original light intensity data and normalizing the light intensity signal to the maximum value to ensure that the real experimental irradiance is obtained.

5. The atmospheric channel parameter extraction method based on double Johnson SB distribution according to claim 1, characterized in that: The double Johnson SB distribution function in S2 is specifically expressed as: in: Wherein, the double Johnson SB distribution model has four free parameters γ1, γ2, δ1, δ2 and satisfies the conditions δ1>0, δ2>0, without loss of generality: γ1≤γ2; p z (·) represents the PDF of the Johnson SB distribution; it can be seen that equation (1) is obtained by combining the probability density functions of two standard Johnson SB distributions.

6. The atmospheric channel parameter extraction method based on double Johnson SB distribution according to claim 1, characterized in that: The Johnson SB distribution in S3 has four free parameters, which control the shape and position of the probability distribution. The parameters are optimized by fitting the light intensity data using the least squares method, and the fitting effect is evaluated by the goodness of fit. 2 The closer it is to 1, the better the fitting result; The frequency value of each I in the fitting process is y, which corresponds to the value Y of the fitting curve.

7. The atmospheric channel parameter extraction method based on double Johnson SB distribution according to claim 1, characterized in that: The flicker index in S3 The calculation uses the following formula: Where I represents the normalized light intensity data value after denoising, < · > Compute the sign for the mean.

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