Method for determining optimal relay position of UWOC system based on AUV relay in complex marine environment

Abstract

The invention discloses a UWOC system optimal relay position determination method based on an AUV relay in a complex marine environment, and belongs to the technical field of underwater wireless optical communication. According to received signals of a UWOC system at a relay node and a destination node in a complex ocean fading environment with underwater obstacles, an average outage probability mathematical expression Pout (psi s, psi d) of a two-hop UWOC system working in an R-space for AUV relay is solved, namely, the system outage probability is a binary function of a source elevation angle psi s and a destination elevation angle psi d. And calculating a change curve of Pout (psi s, psi D) along with the target elevation angle psi d in a mode of fixing the source elevation angle psi s, and searching the psi d corresponding to the minimum value of the outage probability of the system, so as to obtain the optimal relay position of the AUV corresponding to different source elevation angles psi s. According to the method for determining the optimal relay position of the UWOC system based on the AUV relay provided by the invention, a strategy of optimal position layout can be carried out on the AUV mobile relay node on a communication link with direct path obstacles and complex ocean fading, so that reference is provided for upper network planning of the system.

Description

Technical Field

[0001] The present invention belongs to the field of underwater wireless optical communications (UWOC), and relates to a method for determining an optimal relay position of a UWOC system operating in a complex and obstructed ocean fading environment with an autonomous underwater vehicle (AUV) as a relay node. Background Art

[0002] Underwater wireless optical communication (UWOC) has become one of the core technologies that may lead the underwater wireless multimedia communication revolution in the future with its many advantages such as high transmission rate, low latency and strong directivity. However, compared with traditional underwater acoustic communication, UWOC has obvious disadvantages, that is, the complex ocean transmission channel fading, such as the absorption and scattering effects of seawater, ocean turbulence, and pointing errors caused by transceiver jitter, which seriously affect the quality of visible light communication and result in a relatively short transmission distance (≤120 meters); another point is that due to the strong directivity of the laser beam, when there is a relatively large obstacle between the source and the target receiver, it cannot produce a large range of diffraction like sound waves, resulting in communication interruption. In these two cases, relay transmission becomes a powerful means to resist ocean fading, increase transmission distance, and especially overcome obstacle shielding.

[0003] Although the relay communication technology based on satellites or drones in the air / sky, and fixed nodes such as high-rise base stations in the terrestrial cellular environment has been widely studied, the channel transmission model in the complex marine environment is quite different from that on land. It is necessary to conduct channel modeling for the UWOC system and analyze its system performance and subsequent system optimization design based on this. Studies have shown that under the existing UWOC background, there are no reports on the optimization design of the system using unmanned autonomous underwater vehicles (AUVs) as relay auxiliary communication means in complex marine environments, especially when there are underwater obstacles. In the real marine environment, there are a large number of moving fish schools, patches of marine plants, and even underwater mountains and hills. In addition, the complex marine transmission channel fades. Therefore, it is necessary to propose and design a UWOC communication system with autonomous underwater vehicles (AUVs) as convenient relay nodes to obtain the optimal deployment strategy of AUV nodes under the premise of ensuring communication quality constraints. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to find a strategy for optimally deploying AUV mobile relay nodes on a communication link with direct path obstacles and complex ocean fading while ensuring the transmission quality of the UWOC system, so as to provide a reference for the upper-level network planning of the system.

[0005] Technical solution: A method for determining the optimal relay position of a UWOC system based on AUV relay, comprising the following steps:

[0006] Step 1: According to the received signals of the UWOC system at the relay node and the destination node in a complex marine fading environment with underwater obstacles, the mathematical expression of the average interruption probability of the two-hop UWOC system working in R-space for AUV relay is obtained: out (ψ s ,ψ d ), that is, the system outage probability is the source elevation angle ψ s and the target elevation angle ψ d A binary function of ;

[0007] Step 2: By fixing the source elevation angle ψ s P is calculated by out (ψ s ,ψ D ) with the target elevation angle ψ d The change curve of , find the ψ corresponding to the minimum value of system outage probability d , we can get different source elevation angles ψ s The optimal relay position of AUV corresponding to the value.

[0008] As a preferred solution, the mathematical expression of the received signal at each node of the UWOC system, that is, each link, is:

[0009] r i =ηh i s+n,i∈{S,D}

[0010] In the above formula, n is the mean of 0 and the variance of σ 2 The photocurrent noise, s is the average optical power P i The transmission symbol, η is the photo-electric detector responsivity, h i =h a h li h pi is the mixed channel fading coefficient, where h a represents the generalized gamma distribution (GDD) ocean turbulence attenuation factor, h li represents the underwater path loss of link i, h pi represents the zero boresight pointing error of link i, i∈{S,D} is the link label, that is, S represents the SR (source node S to relay node R) link, and D represents the RD (relay node R to destination node D) link.

[0011] As a preferred solution, the complex ocean fading environment includes the comprehensive impact of GDD ocean turbulence fading, zero line of sight pointing error and Elamassie underwater path loss on the transmission channel;

[0012] As a preferred solution, the R-space of the AUV operation refers to the minimum elevation angle ψ formed by the light emitted by the emission source S and the top of the seabed mountain. s,m The minimum receivable signal elevation angle ψ formed by the target node D and the top of the seabed mountain d,m The triangle area formed by the ray where the ray is located and the sea level;

[0013] As a preferred solution, the mathematical expression of the average interruption probability of the two-hop relay UWOC system is:

[0014]

[0015] In the above formula, where a and c are the shape parameters of the GGD distribution, b is the scale parameter of the GGD distribution, Γ(·) represents the Gamma function; σ 2 is the variance of the photocurrent noise; A 0_i and i∈{S,D} is a parameter related to the link pointing error; η is the photoelectric detector responsivity; P i , i∈{S,D} is the power of link transmission symbol; h li , i∈{S,D} represents the Elamassie loss of the underwater path of the link; Γ th is the signal-to-noise ratio threshold; represents the higher transcendental Meijer-G function, Represents an m-dimensional vector, where m and n are both integers greater than 0.

[0016] As a preferred solution, the link pointing error A 0_i and The expression of i∈{S,D} is

[0017] A 0_S =[erf(v S )] 2 and They are parameters related to the SR link pointing error, where represents the aperture radius r of the receiver at node R R With beam width w z_S The ratio of represents the equivalent beam width of the SR link;

[0018] A 0_D =[erf(v D )] 2 and is a parameter related to the RD link pointing error, where represents the receiver aperture radius r at node D DWith beam width w z_D The ratio of It represents the equivalent beam width of the RD link; is the error function.

[0019] In the above formula, w z_S =θ S L SR , w z_D =θ D L RD , where θ S and θ D are the beam divergence angles of the source transmitter and the relay transmitter, L SR and L RD are the lengths of the SR link and the RD link respectively; and are the beam jitter variances at the source node, destination node and AUV relay node, respectively. is the variance of the AUV transmitter angle deviation.

[0020] As a preferred solution, the underwater path Elamassie loss of the SR and RD links is h li , the calculation formula of i∈{S,D} is

[0021] Where c0 is the extinction coefficient and T is the correction coefficient; and are the lengths of the SR link and the RD link, respectively, and Z SD is the straight-line distance between the source node S and the destination node D, (ψ s ,ψ d ) is the angular coordinate of the AUV in R-space.

[0022] As a preferred solution, the source elevation angle ψ s and the target elevation angle ψ d The value ranges are ψ s ∈[ψ s,m ,π / 2] and ψ d ∈[ψ d,m ,π / 2], where ψ s,m and ψ d,m are the minimum receivable signal elevation angles of the source node S and the destination node D respectively.

[0023] Beneficial effects:

[0024] Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects: The present invention proposes an optimal relay position acquisition strategy for the UWOC system based on AUV relay in a complex marine fading environment. According to the strategy, when there is an obstacle blocking the direct communication link, the optimal relay position of the AUV as a relay node can be flexibly obtained with the system minimizing the interruption probability as the optimization goal. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the working principle of the UWOC system based on AUV relay in a complex ocean fading environment with underwater obstacles proposed by the present invention;

[0026] Figure 2 It is a flowchart for realizing the optimal relay position acquisition of the UWOC system based on AUV relay in a complex marine environment proposed by the present invention;

[0027] Figure 3 The proposed UWOC system based on AUV relay has a system outage probability in a complex ocean fading environment with the offset angle ψ representing the AUV relay position. d Schematic diagram of changes. DETAILED DESCRIPTION

[0028] The present invention is further described below in conjunction with specific embodiments. 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 forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0029] When the underwater wireless optical communication (UWOC) system based on the visible light band works in a complex marine environment, its communication quality is not only affected by mixed channel fading such as ocean turbulence effects, underwater path loss, and pointing errors, but the presence of some large underwater obstacles will also hinder the line-of-sight transmission of highly directional light source signals. At this time, it is necessary to introduce additional relay transmission technology. The present invention is a deployment strategy for how to obtain the optimal AUV relay position that achieves the minimum system interruption probability when the line-of-sight link between the source node and the destination node is blocked by underwater obstacles in a UWOC system that encounters complex mixed channel fading. Its specific implementation method and application examples are described as follows:

[0030] Step 1: Modeling the hybrid fading signal reception model of the UWOC system based on AUV relay;

[0031] Assumptions Figure 1 The current receiving signal expression of the UWOC system relay or destination node receiver is shown as:

[0032] r i =ηh is+n,i∈{S,D}

[0033] In the above formula, n is the mean of 0 and the variance of σ 2 The photocurrent noise, s is the average optical power P i The transmission symbol, η is the photo-electric detector responsivity, h i =h a h li h pi is the mixed channel fading coefficient, where h a represents the attenuation factor caused by ocean turbulence, h li represents the underwater path loss of link i, h pi represents the zero boresight pointing error of link i, i∈{S,D} is the link label, that is, S represents the SR (source node S to relay node R) link and D represents the RD (relay node R to destination node D) link.

[0034] Depend on Figure 1 It can be seen that the minimum receivable signal elevation angles of the source node S and the destination node D are ψ s,m and ψ d,m The triangular AUV activity space formed by the rays of these angles and the sea level constitutes the so-called "R-space". As shown in the figure, each point in the R-space is represented by (ψ s ,ψ d ) is uniquely determined, where ψ s ∈[ψ s,m ,π / 2],ψ d ∈[ψ d,m ,π / 2] are the source elevation angle and the destination elevation angle respectively. It can be seen that the lengths of the SR link and the RD link are and

[0035] Step 2: Derive the fading coefficient h of the link complex mixed fading channel that comprehensively considers the generalized Gamma distribution (GGD) ocean turbulence, zero boresight pointing error, and Elamassie path loss i =h a h li h pi , PDF of i∈{S,D};

[0036] 1) The GGD model is often used to describe the ocean turbulence effects caused by changes in temperature and salinity. a , its probability density function (PDF) has the following expression:

[0037]

[0038] In the above formula, a and c are shape parameters, b is the scale parameter, and Γ(·) represents the Gamma function.

[0039] 2) With zero boresight jitter error, the pointing error h pi The PDF of can be expressed as:

[0040]

[0041] In the above formula, A 0_i and It is a parameter related to link pointing error.

[0042] 3)h li represents the underwater path loss of the UWOC link, which can be expressed using the Elamassie continuous path loss closed-form formula as follows:

[0043]

[0044] Where D R is the receiver aperture diameter, θ i is the link light source beam divergence angle, d i is the transmission distance between the link transceiver nodes, c0 is the extinction coefficient, and T is the correction coefficient. Obviously, when these system variables are determined, h li Is a constant.

[0045] Through (1) to (3), we can get the mixed fading channel h including GGD turbulent fading, zero boresight pointing error, and underwater path loss: i The joint PDF is:

[0046]

[0047] In the above formula, represents the higher transcendental Meijer-G function; Represents an m-dimensional vector, where m and n are both integers greater than 0.

[0048] Step 3: Calculate the end-to-end outage probability P of the relay UWOC system using the “decode-forward” mechanism out ;

[0049] Since the channel fading coefficients of the SR link and the RD link are independent of each other, the mixed fading channel h obtained in step 2 is i , the joint PDF of i∈{S,D}, and the average signal-to-noise ratio at the SR link (i.e., S link) and the RD link (i.e., D link) obtained from the received current signal expression in step 1, i.e., Γ S =(ηP S h S ) 2 / σ 2 and Γ D =(ηP D h D) 2 / σ 2 , the end-to-end interruption probability P of the relay UWOC system under the “decode-forward” mechanism can be obtained out for

[0050]

[0051] In the above formula, P S is the SR link transmit power, h S is the SR link channel fading coefficient, P D is the transmission power of the RD link, h D is the channel fading coefficient of the RD link, σ 2 is the photocurrent noise variance; Γ th is the signal-to-noise ratio threshold.

[0052] Based on the mixed fading PDF expression of formula (4), the cumulative distribution function (CDF) F of the SR link and the RD link in formula (5) can be further expressed as S (Γ th ) and F D (Γ th ) are written in the following integral form:

[0053]

[0054] In the above formula, A 0_S =[erf(v S )] 2 and is a parameter related to the SR link pointing error, where represents the aperture radius r of the receiver at node R R With beam width w z_S The ratio of A represents the equivalent beam width of the SR link; 0_D =[erf(v D )] 2 and is a parameter related to the RD link pointing error, where represents the receiver aperture radius r at node D D With beam width w z_D The ratio of It represents the equivalent beam width of the RD link; is the error function. In addition, w z_S =θ S L SR and w z_D =θ D L RD , where θ S and θ Dare the divergence angles of the source transmitter and the relay transmitter, L SR and L RD Then they are the lengths of the SR link and the RD link respectively; and are the beam jitter variances at the source node, destination node and AUV relay node, respectively. is the variance of the AUV transmitter angle deviation.

[0055] Since the AUV is mobile, the path lengths of the SR and RD links at each position in the R space are different, so the path losses are also different. Therefore, the underwater path losses of the SR and RD links expressed by formula (3) can be written as

[0056] By solving the integral of formula (6), the system outage probability shown in formula (5) can be finally expressed as

[0057]

[0058] In the above formula

[0059] Step 4: The system outage probability expression (7) given in step 3 above is obviously the source elevation angle ψ s and the target elevation angle ψ d The binary function of Figure 2 The algorithm flow shown can be used to obtain the s The target elevation angle ψ that can make the system outage probability take the lowest value d Obviously, the intersection of these two elevation angles is the best relay position for the AUV.

[0060] Application example of the optimal relay position determination method for UWOC system based on AUV relay in marine environment

[0061] Next, we take a specific ocean fading channel with an obstacle environment as an example to verify the effectiveness of the optimal relay position determination method for the UWOC system based on AUV relay proposed in the present invention through computer simulation.

[0062] Figure 3 For the water quality in the coastal area (corresponding to the extinction coefficient c0 = 0.305m -1 ), correction factor T = 0.13, the aperture radius r of the receiver of the relay AUV node R R =5cm, the aperture radius r of the receiver at the destination node D D =10cm, source transmitter laser source divergence angle θ S =10mrad, relay transmitter laser source emission divergence angle θ D=50mrad, GGD ocean turbulence fading coefficient a=1.2027, b=1.0333, c=3, turbulence scintillation index σ I 2 =0.1074, SR link and RD link transmission power P S =P D =30dBm, signal-to-noise ratio threshold Γ th =5dB, photocurrent noise variance σ 2 =10 -7 A / Hz, photoelectric detector responsivity η = 0.4547, straight-line distance Z from source node S to destination node D SD =120m, standard deviation of beam jitter at source and destination nodes σ S =σ D = 10 cm, standard deviation of beam jitter at the AUV relay node σ R = 30cm, standard deviation of AUV transmitter angle deviation σ θ =5mrad, the optimal relay position determination method of the UWOC system based on AUV relay proposed in the present invention is used to obtain the fixed source elevation angle ψ s The system outage probability varies with the target elevation angle ψ d Change curve chart. Figure 3 The data show that when the source elevation angle ψ is fixed s When the corresponding “interruption probability - ψ d "The change curve obviously has a minimum value. This shows that Figure 1 Within the specified R-space range, there is indeed an optimal relay position for the AUV to minimize the system interruption probability; and the ψ corresponding to the minimum system interruption probability obtained from the numerical simulation curve is s and ψ d The optimal deployment position of the AUV can be obtained by calculating the value.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for determining the optimal relay position of a UWOC system based on AUV relay, comprising the following steps: Step 1: According to the received signals of the UWOC system at the relay node and the destination node in a complex marine fading environment with underwater obstacles, the mathematical expression of the average interruption probability of the two-hop UWOC system working in R-space for AUV relay is obtained: out (ψ s ,ψ d ), that is, the system outage probability is the source elevation angle ψ s and the target elevation angle ψ d A binary function of . Step 2: By fixing the source elevation angle ψ s P is calculated by out (ψ s ,ψ D ) with the target elevation angle ψ d The change curve of , find the ψ corresponding to the minimum value of system outage probability d , we can get different source elevation angles ψ s The optimal relay position of AUV corresponding to the value.

2. The method for determining the optimal relay position of the UWOC system based on AUV relay according to claim 1 is characterized in that: The mathematical expression of the received signal at each node of the UWOC system, that is, each link, is: r i =ηh i s+n,i∈{S,D} In the above formula, n is the mean of 0 and the variance of σ 2 The photocurrent noise, s is the average optical power P i The transmission symbol, η is the photo-electric detector responsivity, h i =h a h li h pi is the mixed channel fading coefficient, where h a represents the generalized gamma distribution (GDD) ocean turbulence attenuation factor, h li represents the underwater path loss of link i, h pi represents the zero boresight pointing error of link i, i∈{S,D} is the link label, that is, S represents the SR (source node S to relay node R) link, and D represents the RD (relay node R to destination node D) link.

3. The method for determining the optimal relay position of the UWOC system based on AUV relay according to claim 1 is characterized in that: The complex ocean fading environment includes the combined effects of GDD ocean turbulence fading, zero boresight pointing error and Elamassie underwater path loss on the transmission channel.

4. The method for determining the optimal relay position of the UWOC system based on AUV relay according to claim 1 is characterized in that: The R-space of the AUV operation refers to the minimum elevation angle ψ formed by the light emitted by the emission source S and the top of the seabed mountain. s,m The minimum receivable signal elevation angle ψ formed by the target node D and the top of the seabed mountain d,m The triangular area formed by the ray where the sky is located and the sea level.

5. The method for determining the optimal relay position of the UWOC system based on AUV relay according to claim 1 is characterized in that: The mathematical expression of the average outage probability of the two-hop relay UWOC system is: In the above formula, where a and c are the shape parameters of the GGD distribution, b is the scale parameter of the GGD distribution, Γ(·) represents the Gamma function; σ 2 is the variance of the photocurrent noise; A 0_i and i∈{S,D} is a parameter related to the link pointing error; η is the photo-electric detector responsivity; P i , i∈{S,D} is the power of link transmission symbol; h li , i∈{S,D} represents the Elamassie loss of the underwater path of the link; Γ th is the signal-to-noise ratio threshold; represents the higher transcendental Meijer-G function, Represents an m-dimensional vector, where m and n are both integers greater than 0.

6. The method for determining the optimal relay position of the UWOC system based on AUV relay according to claim 5 is characterized in that: The link pointing error A 0_i and The expression of i∈{S,D} is: A 0_S =[erf(v S )] 2 and They are parameters related to the SR link pointing error, where represents the aperture radius r of the receiver at node R R With beam width w z_S The ratio of Represents the equivalent beam width of the SR link. A 0_D =[erf(v D )] 2 and is a parameter related to the RD link pointing error, where represents the receiver aperture radius r at node D D With beam width w z_D The ratio of It represents the equivalent beam width of the RD link; is the error function. In the above formula, w z_S =θ S L SR , w z_D =θ D L RD , where θ S and θ D are the beam divergence angles of the source transmitter and the relay transmitter, L SR and L RD are the lengths of the SR link and the RD link respectively; and are the beam jitter variances at the source node, destination node and AUV relay node, respectively. is the variance of the AUV transmitter angle deviation.

7. The method for determining the optimal relay position of the UWOC system based on AUV relay according to claim 5 is characterized in that: The underwater path Elamassie loss of the SR and RD links is h li , the calculation formula of i∈{S,D} is: Where c0 is the extinction coefficient and T is the correction coefficient; and are the lengths of the SR link and the RD link, respectively, and Z SD is the straight-line distance between the source node S and the destination node D, (ψ s ,ψ d ) is the angular coordinate of the AUV in R-space.

8. The method for determining the optimal relay position of the UWOC system based on AUV relay according to claim 1 is characterized in that: The source elevation angle ψ s and the target elevation angle ψ d The value ranges are ψ s ∈[ψ s,m ,π / 2] and ψ d ∈[ψ d,m ,π / 2], where ψ s,m and ψ d,m are the minimum receivable signal elevation angles of the source node S and the destination node D respectively.

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