Method for acquiring optimal transmitting power and transmitting gain of UWOC system with light beam jitter

Abstract

The invention discloses a method for obtaining the optimal transmitting power and transmitting gain of a UWOC system with light beam jitter, and belongs to the technical field of underwater wireless optical communication. A mathematical expression of an instantaneous received signal-to-noise ratio gamma uw is determined according to a complex marine environment receiver received signal model, and a probability density function fh (h) of a mixed fading channel coefficient h is obtained, so that a cumulative distribution function F gamma uw (gamma uw) of the instantaneous signal-to-noise ratio gamma uw is obtained. And further solving a system average bit error rate # imgabs0 # and a partial derivative function of the bit error rate to the transmitter gain GT under OOK modulation, namely a system average bit error rate # imgabs1 #, and setting a constant value alpha of the system average bit error rate # imgabs2 #, and setting a partial derivative # imgabs3 # to form a simultaneous equation set to calculate and obtain the optimal transmitting power and transmitting gain. According to the method for acquiring the optimal transmitting power and the transmitting gain of the UWOC system provided by the invention, the optimal transmitting power and the gain value of the transmitter for ensuring normal communication of the system can be acquired under the condition that the transceiver jitters due to factors such as underwater turbulence, weak earthquakes and water body temperature changes, so that a reference is provided for upper-layer network planning of the system.

Description

Technical Field

[0001] The present invention belongs to the technical field of underwater wireless optical communications (UWOC), and relates to a method for obtaining the optimal transmission power and transmission gain of a transmitter to ensure normal communication of a UWOC system in complex environments such as water flow fluctuations, weak earthquakes, and water temperature changes. Background Art

[0002] With the increasing demand for underwater exploration, resource development, and military applications, the importance of underwater wireless communication technology has become increasingly prominent. Compared with traditional underwater acoustic communication technology, underwater wireless optical communication (UWOC) has become a hot topic of scientific exploration and research in recent years due to its many advantages such as high bandwidth, low latency, and strong anti-interference ability. However, UWOC faces many challenges in complex underwater environments. For example, factors such as turbulent ocean water movement, weak seismic geological activities, and changes in water temperature and salinity can cause jitter in the UWOC system transceiver, which requires increasing the transmitter's beam divergence angle to ensure stable communication between the transmitter and the receiver. However, in this way, the increased beam divergence angle requires us to increase the transmitter's transmission power and transmission gain to ensure the receiver's operating signal-to-noise ratio, which will correspondingly increase the system's power consumption and operating cost. Therefore, it is necessary to explore the optimal transmission power and transmission gain of the transmitter of the UWOC system with an increased beam divergence angle in a complex marine environment in order to obtain a reasonable and effective solution. Summary of the Invention

[0003] Purpose of the invention: The purpose of the present invention is to find a design strategy for optimal transmission power and transmission gain while meeting the communication quality of the UWOC system when the underwater transceiver is jittered due to factors such as turbulence, and therefore the beam divergence angle needs to be increased to ensure communication connectivity, so as to provide a reference for the upper-level network planning of the system.

[0004] Technical solution: A method for obtaining the optimal transmission power and transmission gain of a UWOC system transmitter with beam jitter, comprising the following steps:

[0005] Step 1: Determine the instantaneous received signal-to-noise ratio γ based on the photocurrent receiving signal model of the receiver in a complex ocean fading environment uw The mathematical expression of the channel coefficient h is obtained by obtaining the probability density function (PDF) f of the mixed fading channel coefficient h containing generalized Gamma (GGD) turbulent fading and pointing error. h (h), and based on this we can get the instantaneous signal-to-noise ratio γ uw Cumulative distribution function (CDF) of

[0006] Step 2: Based on the CDF function in step 1 Determine the average bit error rate (BER) of the system under on-off keying (OOK) modulation and bit error rate versus transmitter gain G T The partial derivative function is Let the system average BER take a fixed value α, that is, At the same time, set the partial derivative Thus constructing the average bit error rate Solving this set of equations can yield the optimal system transmit power and transmit gain for a given system bit error rate α.

[0007] As a preferred solution, the expression of the photocurrent signal received by the receiver is:

[0008] y=RhP T G T x+n

[0009] Where R is the conversion coefficient of the photodetector, R = ηq / hf, η, q, h, f are the quantum efficiency of the photodetector, electron charge, Planck constant and light frequency in water respectively; h = h a h p represents the mixed channel fading coefficient, where h a is the underwater turbulence attenuation coefficient, h p is the pointing error; P T is the transmitter power, G T is the transmitter gain; x∈{0,1} is the OOK transmission symbol; n is additive white Gaussian noise with a mean of 0 and a variance of σ N 2 .

[0010] As a preferred solution, the calculation formula for determining the instantaneous receiving signal-to-noise ratio of the UWOC link based on the photocurrent receiving signal model is:

[0011]

[0012] As a preferred solution, the PDF expression of the mixed fading channel coefficient h containing GGD turbulence fading and pointing error is:

[0013]

[0014] In the above formula, a and c are the shape parameters of GGD distribution, b is the scale parameter of GGD distribution; A0 and γ 2 is a parameter related to the pointing error; Γ(·) is the Gamma function, It is a higher transcendental Meijer-G function.

[0015] As a preferred solution, the instantaneous signal-to-noise ratio γ obtained based on the PDF of the mixed fading channel coefficient h is uw The CDF expression is:

[0016]

[0017] In the above formula, It is an advanced transcendental Fox-H function.

[0018] As a preferred solution, the basis The system average bit error rate calculation formula under on-off keying OOK modulation is obtained as follows:

[0019]

[0020] In the above formula, p and q are modulation parameters. When OOK is selected as the modulation method, p = 1 / 2 and q = 1 / 4.

[0021] As a preferred solution, the system average bit error rate Transmitter gain G T The partial derivative expression of is:

[0022]

[0023] As a preferred solution, the set of equations for obtaining the optimal transmit power and transmit gain when the system bit error rate α is given is:

[0024] Where α represents the system bit error rate as a certain specified value.

[0025] Beneficial effects:

[0026] Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects: the present invention provides a design strategy for the optimal transmission power and transmission gain of the UWOC system transmitter. According to this strategy, when the transceiver jitters due to factors such as underwater turbulence, weak earthquakes, and water temperature changes, the optimal transmission power and gain values ​​of the transmitter can be obtained to ensure normal communication of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the operation of the UWOC system proposed in the present invention in a complex ocean fading environment with factors such as turbulence, weak earthquakes and water temperature changes.

[0028] Figure 2 This is a flowchart of the principle implementation of the method for obtaining the optimal transmission power and transmission gain of the transmitter when the UWOC system proposed in the present invention increases the light beam divergence angle to overcome the jitter of the transceiver.

[0029] Figure 3This is the optimization result of transmission power and transmission gain obtained by the method proposed in the present invention in a complex ocean fading environment, that is, the curve of the optimal transmitter transmission power and transmission gain value of the UWOC system obtained by the optimization equation group under different bit error rate conditions. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with the accompanying drawings. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent modifications of the present invention by those skilled in the art will fall within the scope defined by the claims attached to this application.

[0031] like Figure 2 As shown in FIG, the method for obtaining the optimal transmission power and transmission gain of the UWOC system in a complex ocean environment includes the following steps:

[0032] Step 1: Determine the signal receiving model of the receiver in the ocean fading environment and the mathematical expression of the instantaneous signal-to-noise ratio.

[0033] To ensure the connectivity and reliability of the communication link, the fixed receiver's receiving field of view is set to a large value. This way, the receiver's swaying caused by environmental factors such as turbulence, weak earthquakes, and changes in water temperature will not affect the transmitter's line of sight. Then, the expression of the photocurrent signal received by the receiver is:

[0034] y=RhP T G T x+n (1)

[0035] Where R is the conversion coefficient of the photodetector R = ηq / hf, η, q, h, f are the quantum efficiency of the photodetector, electron charge, Planck constant and light frequency in water respectively; h = h a h p represents the mixed channel fading coefficient, where h a is the underwater turbulence attenuation coefficient, h p is the pointing error; P T is the transmitter power, G T is the transmitter gain; x∈{0,1} is the on-off keying (OOK) transmission symbol; n is additive white Gaussian noise with a mean of 0 and a variance of σ N 2 .

[0036] Using the intensity modulation-direct detection (IM / DD) method, the instantaneous signal-to-noise ratio (SNR) of the UWOC link can be modeled as:

[0037]

[0038] Step 2: Obtain the probability density function (PDF) of the mixed fading channel coefficient h containing turbulent fading and pointing error, and based on it, obtain the cumulative distribution function (CDF) of the instantaneous signal-to-noise ratio.

[0039] The generalized Gamma distribution (GGD) is used to characterize the turbulence effect that is widely present in the marine environment. a The statistical distribution characteristics of the radial displacement error h p The statistical characteristics of can be modeled by Rayleigh distribution, and the mixed fading channel coefficient h = h after comprehensive consideration of the two a h p The PDF of can be expressed as:

[0040]

[0041] In the above formula, a and c are the shape parameters of GGD distribution, b is the scale parameter of GGD distribution; A0 and γ 2 is a parameter related to the pointing error; Γ(·) is the gamma function, It is a higher transcendental Meijer-G function.

[0042] The instantaneous signal-to-noise ratio γ can be obtained by mixing the PDF of the fading channel coefficient h uw The cumulative distribution function CDF is:

[0043]

[0044] In the above formula, It is an advanced transcendental Fox-H function.

[0045] Step 3: Obtain the average bit error rate (BER) of the system under OOK modulation and the relationship between the bit error rate and the transmitter gain G T The partial derivative function of .

[0046] When the system adopts on-off keying OOK modulation, the system average bit error rate calculation formula is:

[0047]

[0048] Obviously, the system average bit error rate is the transmission gain G T Where p and q are modulation parameters. When OOK is selected as the modulation method, p = 1 / 2 and q = 1 / 4.

[0049] In order to obtain the optimal transmitter power under the bit error rate value required by the system when the transceiver is oscillating, it is necessary to calculate the system bit error rate to transmitter gain G T The partial derivatives of , that is:

[0050]

[0051] Step 4: Based on the given system average bit error rate requirement, let the above average bit error rate be used to calculate G T The partial derivatives of are set to zero, and a set of simultaneous equations is formed to calculate the optimal transmit power and transmit gain when the system has jitter.

[0052] In order to obtain the optimal transmission power and transmission gain of the system, first set the system average bit error rate to a given constant value α, that is, Then set the average bit error rate To G T The partial derivative of is zero, that is The two equations establish a system of simultaneous equations as follows:

[0053]

[0054] Solving the above simultaneous equations (7) can obtain the optimal system transmitter power and transmission gain under a given system bit error rate requirement.

[0055] An example of how to obtain the optimal transmit power and transmit gain of a UWOC system:

[0056] Below, we take the complex ocean fading environment as an example, that is, considering the presence of complex ocean turbulence fading and the pointing error caused by transceiver jitter caused by factors such as weak earthquakes, and verify the effectiveness and feasibility of the method for obtaining the optimal transmission power and transmission gain of the UWOC system proposed in this invention through computer simulation.

[0057] Figure 3 The embodiment of the present invention provides a curve diagram showing the optimal transmission power and transmission gain of the UWOC system transmitter under different bit error rate conditions obtained by solving the optimization equation group (7) as the bit error rate value α changes. Among them, the bit error rate α range is [10 -9 ,10 -2 ], GGD shape parameters and scale parameters are a=1.2027, b=1.0333, c=3, turbulence scintillation index Jitter dispersion σ s =20cm, A0=0.0678 and γ 2 =1.0376; noise variance σ N 2 =2.4×10 -13 W, modulation parameters p = 1 / 2, q = 1 / 4. Among them, Figure 3 (a) is the relationship curve between the optimal transmitter gain and the average bit error rate. Figure 3 (b) is the relationship curve between the selection of the optimal transmission power of the transmitter and the average bit error rate. Figure 3It can be seen that under the given system bit error rate value α, the optimal transmission power P T and the transmission gain G T It does exist, and it is unique. This means that, based on a given system bit error rate requirement, we can obtain the optimal transmit power and transmit gain for the system when transceiver jitter exists.

[0058] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for obtaining the optimal transmission power and transmission gain of a UWOC system transmitter with beam jitter, comprising the following steps: Step 1: Determine the instantaneous received signal-to-noise ratio γ based on the photocurrent receiving signal model of the receiver in a complex ocean fading environment uw The mathematical expression of the channel coefficient h is obtained by obtaining the probability density function (PDF) f of the mixed fading channel coefficient h containing generalized Gamma (GGD) turbulent fading and pointing error. h (h), and based on this we can get the instantaneous signal-to-noise ratio γ uw Cumulative distribution function (CDF) of (γ uw ). Step 2: Based on the CDF function in step 1 (γ uw ) Calculate the average bit error rate (BER) of the system under on-off keying (OOK) modulation and bit error rate versus transmitter gain G T The partial derivative function is Let the system average BER take a fixed value α, that is, At the same time, set the partial derivative Thus constructing the average bit error rate Solving this set of equations can yield the optimal system transmit power and transmit gain for a given system bit error rate α.

2. The method for obtaining the optimal transmission power and transmission gain of a UWOC system transmitter with beam jitter according to claim 1 is characterized in that: The expression of the photocurrent signal received by the receiver is: y=RhP T G T x+n Where R is the conversion coefficient of the photodetector, R = ηq / hf, η, q, h, f are the photodetector quantum efficiency, electron charge, Planck constant and light frequency in water respectively; h = h a h p represents the mixed channel fading coefficient, where h a is the underwater turbulence attenuation coefficient, h p is the pointing error; P T is the transmitter power, G T is the transmitter gain; x∈{0,1} is the OOK transmission symbol; n is the additive white Gaussian noise with a mean of 0 and a variance of σ N 2 .

3. The method for obtaining the optimal transmission power and transmission gain of a UWOC system transmitter with beam jitter according to claim 2 is characterized in that: The calculation formula for determining the instantaneous received signal-to-noise ratio of the UWOC link based on the photocurrent received signal model is:

4. The method for obtaining the optimal transmission power and transmission gain of a UWOC system transmitter with beam jitter according to claim 1 is characterized in that: The PDF expression of the mixed fading channel coefficient h containing GGD turbulence fading and pointing error is: In the above formula, a and c are the shape parameters of GGD distribution, b is the scale parameter of GGD distribution; A0 and γ 2 is a parameter related to the pointing error; Γ(·) is the Gamma function, It is a higher transcendental Meijer-G function.

5. The method for obtaining the optimal transmission power and transmission gain of a UWOC system transmitter with beam jitter according to claim 4 is characterized in that: The instantaneous signal-to-noise ratio γ obtained based on the PDF of the mixed fading channel coefficient h uw The CDF expression is: In the above formula, It is an advanced transcendental Fox-H function.

6. The method for obtaining the optimal transmission power and transmission gain of a UWOC system transmitter with beam jitter according to claim 5 is characterized in that: The CDF function The system average bit error rate calculation formula under on-off keying OOK modulation is obtained as follows: In the above formula, p and q are modulation parameters. When OOK is selected as the modulation method, p = 1 / 2 and q = 1 / 4.

7. The method for obtaining the optimal transmission power and transmission gain of a UWOC system transmitter with beam jitter according to claim 6 is characterized in that: The average bit error rate of the system Transmitter gain G T The partial derivative expression of is:

8. The method for obtaining the optimal transmission power and transmission gain of a UWOC system transmitter with beam jitter according to claim 1 is characterized in that: The equations for obtaining the optimal transmit power and transmit gain when the system bit error rate α is given are: Where α represents the system bit error rate as a certain specified value.

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