A Modeling Method for Underwater Electromagnetic Wave Communication Channels near the Sea Surface

Abstract

The present invention discloses a method for modeling an underwater electromagnetic wave communication channel near the sea surface, and the present invention relates to the technical field of marine electromagnetic communication. This method for modeling an underwater electromagnetic wave communication channel near the sea surface can construct a simple and accurate underwater electromagnetic wave communication channel model near the sea surface. Using this model to evaluate the performance of underwater electromagnetic wave communication, and then guiding the design and implementation of underwater sensor networks, it overcomes the deficiencies and limitations of existing methods. This application can not only obtain the underwater electromagnetic wave communication channel response and link loss, but also obtain the attenuation change of the electromagnetic wave energy with distance in the transmission link. The entire derivation process has a clear physical meaning. Through the establishment and solution of this channel model, it helps to evaluate the performance of underwater electromagnetic wave communication, and then guides the design and implementation of underwater sensor networks.

Description

Technical Field

[0001] The present invention relates to the technical field of marine electromagnetic communication, and specifically relates to a method for modeling an underwater electromagnetic wave communication channel near the sea surface. Background Technique

[0002] Underwater sensor networks are widely used in marine environmental monitoring, military reconnaissance, coastline protection, marine resource development, tsunami prediction and warning systems due to their low deployment and operation costs and high military and commercial values (Felemban E, Shaikh F K, Qureshi U M, et al. Underwater sensor network applications: A comprehensive survey[J]. International Journal of Distributed Sensor Networks, 2015, 11(11): 896832.). To ensure the stable operation of underwater sensor networks, high-speed and robust data transmission between nodes must be guaranteed. Underwater electromagnetic wave communication is one of the important means to achieve data interaction between nodes of underwater sensor networks (Quintana-Díaz G, Mena-Rodríguez P, Pérez- I, et al. Underwater electromagnetic sensor networks—Part I: Link characterization[J]. Sensors, 2017, 17(1): 189.). However, different from land, the marine environment is complex and changeable, and seawater is a lossy medium, and there is a large absorption loss of underwater electromagnetic waves (Wang Honglei. Research on the propagation characteristics of electromagnetic waves across the sea-air interface[D]. Xi'an: Northwestern Polytechnical University, 2015.). Therefore, constructing a simple and accurate channel model helps to improve the communication rate and robustness of underwater electromagnetic waves near the sea surface, which will further affect the design and performance evaluation of underwater sensor networks;

[0003] According to a modeling method of electromagnetic fields during the propagation of electromagnetic waves in a multi-layer marine medium disclosed in the existing Chinese patent CN114491987A, it is a new modeling method that first models two layers of media separately and then synthesizes them by vector superposition. During the implementation of this method, for example, when the radiation source is located in the seawater medium, first model and calculate for the air-seawater two-layer medium, then model and calculate for the seawater-seabed two-layer medium, and finally vectorially synthesize the calculation results of each model to obtain the results for the three-layer medium. By doing so, while reducing the modeling complexity, the calculation efficiency, calculation accuracy, and physical interpretability of the results can be ensured. The results show that compared with the complex process of modeling the propagation of electromagnetic waves in traditional three-layer media, the model derivation process of the present invention is simple. On the premise of ensuring the calculation efficiency and result accuracy of the model, the modeling process is greatly simplified, and each term in the obtained electric and magnetic field components also has a clear physical meaning;

[0004] According to a system and method for electromagnetic wave transmission across the seawater-air interface disclosed in the existing Chinese patent CN104618032A, it includes one or more underwater acoustic-electromagnetic wave buoys and a monitoring platform. The underwater acoustic-electromagnetic wave buoys first convert the underwater acoustic signals of underwater devices received by underwater acoustic sensors into electromagnetic signals, and mainly transmit them to the monitoring platform for reception through the lateral wave propagation path of electromagnetic waves in a medium with a relatively small conductivity; conversely, the electromagnetic wave control signals transmitted by the monitoring platform are transmitted to the underwater acoustic-electromagnetic wave buoys through a similar link;

[0005] According to the above prior art, the channel models used in the existing research on underwater electromagnetic wave communication are overly simplistic, mostly only involving the link loss model (Hattab G, El-Tarhuni M, Al-Ali M, et al. An underwater wireless sensor network with realistic radio frequency path loss model[J]. International journal of distributed sensor networks, 2013, 9(3):508708.), and are unable to calculate the losses of each part in the propagation link, with certain limitations in application. At the same time, due to the significant differences in the electromagnetic propagation characteristics of air, seawater, and the seabed, some channel modeling methods applicable near the seawater-seabed interface are not generalizable (Nie ZQ, Wang S L, Chen D H, et al. Seabed-rock-layer electromagnetic communication channel model with low path loss based on evanescent wave[J]. Radioengineering, 2018, 27(2):431-439.). Therefore, it is extremely urgent to construct an accurate and widely applicable underwater electromagnetic wave communication channel model near the sea surface.

[0006] Therefore, it is necessary to provide a method for modeling an underwater electromagnetic wave communication channel near the sea surface to solve the above technical problems. Summary of the Invention

[0007] (1) Technical Problems to be Solved

[0008] To solve the above technical problems, the present invention provides a method for modeling an underwater electromagnetic wave communication channel near the sea surface.

[0009] (2) Technical Solutions

[0010] To achieve the above objectives, the present invention is realized through the following technical solutions: A method for modeling an underwater electromagnetic wave communication channel near the sea surface specifically includes the following steps:

[0011] S1. When the positions of the transmitting antenna and the receiving antenna in seawater are determined, the propagation distances of electromagnetic waves in seawater and air are obtained respectively;

[0012] S2. Construct an underwater electromagnetic wave propagation model near the sea surface to obtain the field strength attenuation and phase delay of each electromagnetic field component;

[0013] S3. Based on the solution process of the electromagnetic wave propagation model in step S2, construct an underwater electromagnetic wave communication channel model near the sea surface to obtain the channel amplitude-frequency response and link loss, as well as the attenuation change of the electromagnetic wave energy with distance in the transmission link, thereby laying a foundation for the design and node placement of the underwater sensor network.

[0014] Preferably, in step S1, the propagation distances of electromagnetic waves in seawater and air are obtained by using the Goos-Hänchen shift theory.

[0015] Preferably, step S1 is specifically that when the electromagnetic wave irradiates from seawater to the seawater-air interface at an incident angle greater than the critical angle, there is a certain lateral displacement of the reflection point compared with the incident point. Part of the electromagnetic wave energy enters the air at the incident point and reaches the receiving antenna in the form of an evanescent wave and finally enters the seawater from the reflection point. The incident angles of the electromagnetic waves and the magnitudes of the Goos-Hänchen shifts corresponding to different transceiver antenna positions are different.

[0016] Preferably, in step S2, an underwater electromagnetic wave propagation model near the sea surface is constructed according to the generation mechanism of the Goos-Hänchen shift.

[0017] Preferably, step S2 is specifically to obtain the field strength attenuation and phase delay of each part of the electromagnetic wave component according to the propagation characteristics and propagation distances of the electromagnetic wave between the transmitting antenna-incident point, incident point-reflection point, and reflection point-receiving antenna in step S1, and then combine the transmitting electromagnetic field components to obtain the receiving electromagnetic field components.

[0018] Preferably, both step S1 and step S2 use the stationary phase method to solve the Goos-Hänchen shift.

[0019] Preferably, the incident point is regarded as a virtual antenna placed at the seawater-air interface.

[0020] Preferably, in step S3, the Friis law is used to calculate the link loss.

[0021] (III) Beneficial effects

[0022] The present invention provides a method for modeling an underwater electromagnetic wave communication channel near the sea surface. Compared with the prior art, it has the following beneficial effects:

[0023] Since the existing near-surface underwater electromagnetic wave communication channel model is too simplistic and has limitations, it cannot guarantee the data interaction performance between nodes in an underwater sensor network. However, this model plays an extremely important role in the deployment and design of an underwater sensor network. This application can construct a simple and accurate near-surface underwater electromagnetic wave communication channel model, use this model to evaluate the performance of underwater electromagnetic wave communication, and then guide the design and implementation of an underwater sensor network, overcoming the deficiencies and limitations of existing methods. This application can not only obtain the underwater electromagnetic wave communication channel response and link loss, but also obtain the attenuation change of the electromagnetic wave energy in the transmission link with distance. The entire derivation process has a clear physical meaning. Through the establishment and solution of this channel model, it helps to evaluate the performance of underwater electromagnetic wave communication and then guide the design and implementation of an underwater sensor network. Brief Description of the Drawings

[0024] Figure 1 It is a schematic diagram of the Goos-Hänchen shift at the sea-water / air interface of the present invention;

[0025] Figure 2 It is a schematic diagram of a near-surface underwater electromagnetic wave communication link of the present invention;

[0026] Figure 3 It is an amplitude-frequency response diagram of the characteristics of a near-surface underwater electromagnetic wave communication channel of the present invention;

[0027] Figure 4 It is a phase-frequency response diagram of the characteristics of a near-surface underwater electromagnetic wave communication channel of the present invention;

[0028] Figure 5 It is a schematic diagram of the link loss of a near-surface underwater electromagnetic wave communication of the present invention;

[0029] Figure 6 It is a diagram showing the variation of the received power of a near-surface underwater electromagnetic wave with the communication horizontal distance of the present invention;

[0030] Figure 7 It is a comparison diagram of the intensities of the electromagnetic field components obtained by the present invention and the electric field components of the traditional model;

[0031] Figure 8 It is a comparison diagram of the phases of the electromagnetic field components obtained by the present invention and the electric field components of the traditional model;

[0032] Figure 9 It is a flowchart of the method of the present invention. Detailed Description of the Invention

[0033] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0034] Please refer to Figures 1 to 9 , the embodiments of the present invention provide a technical solution: a method for constructing a near-sea surface underwater electromagnetic wave communication channel model. The technical solution adopted can be divided into the following three steps:

[0035] Based on the Goos–Hänchen shift, the propagation distances of electromagnetic waves in each part of the transmission link are solved. As Figure 1 shown, when an electromagnetic wave is incident from seawater to the seawater–air interface at an incident angle greater than the critical angle, the reflected wave produces a lateral displacement in the incident plane, which is called the Goos–Hänchen shift. This also causes the emission point to deviate from the incident point. At this time, part of the electromagnetic wave energy propagates in the air in the form of an evanescent wave, so that the near-sea surface underwater electromagnetic wave communication distance is much greater than the skin depth of the electromagnetic wave.

[0036] There are mainly two methods for solving the Goos–Hänchen shift: the stationary-phase method and the energy-flux method (Yasumoto K, ōishi Y. A new evaluation of the Goos– shift and associated time delay[J]. Journal of Applied Physics, 1983, 54(5): 2170-2176.). In this application, the former is used to solve the Goos–Hänchen shift. The stationary-phase method believes that an electromagnetic wave with a finite beam width can be regarded as a superposition of a series of single-frequency plane waves with different wave vector directions. After total reflection occurs, each single-frequency plane wave will generate a different phase shift, but this phase shift does not change with the wave vector direction (incident direction). The specific representation is as follows:

[0037]

[0038] where θ is Figure 1 the incident angle of the electromagnetic wave at the sea–air interface in

[0039]

[0040] δ is the phase shift generated by reflection and can be obtained by solving the reflectivity. Since seawater is a lossy medium and the refractive index n1 of electromagnetic waves is a complex number, the reflectivities of TE wave and TM wave are as follows:

[0041]

[0042]

[0043] where θ t satisfies Re(n1)sinθ = Re(n2)sinθ t According to (Zhen W, Deng D. Goos– and Imbert–Fedorov shifts in temporally dispersive attenuative materials[J]. Journal of Physics D: Applied Physics, 2020, 53(25): 255104.), the propagation distance of electromagnetic waves in air can be obtained as:

[0044]

[0045] where rs,p represents the reflectivity amplitude, and its expression is rs / rp, δs,p represents the reflectivity phase, and λs represents the wavelength of electromagnetic waves in seawater.

[0046] As Figure 2 shown, the propagation distance of electromagnetic waves underwater is divided into two parts: one is from the transmitting antenna O to the incident point A, and the other is from the reflection point B to the receiving antenna P. Assuming the distance between the underwater transmitting antenna and the seawater–air interface is d, the depth of the receiving antenna is z, and the propagation distance of electromagnetic waves underwater is:

[0047]

[0048] Combining (4), (5) and the known transceiver positions, the propagation distances of electromagnetic waves in air and underwater can finally be calculated.

[0049] On the basis of 1), the field strength attenuation and phase delay of each electromagnetic field component in each part are solved respectively, and then each electromagnetic field component at the receiving point is obtained. Among them, the propagation attenuation of electromagnetic waves in seawater mainly comes from absorption loss, as follows:

[0050]

[0051] The phase delay of electromagnetic waves underwater is:

[0052]

[0053] In this application, the incident point is regarded as a virtual antenna placed at the seawater-air interface, and its type is the same as that of the transmitting antenna at point O. In this way, the propagation attenuation and phase delay in the air can be obtained from the differences in the electromagnetic field components at points A and B. Taking the electric field component as an example:

[0054] FA a =20lg(|E B / E A |)(dB)

[0055]

[0056] In the above formula, the electric field component E A at point A is the radiation field component of the virtual antenna in the θ direction, and E B is the electric field component generated by the virtual antenna at point B, which can be specifically obtained from (Bannister P R. New formulas that extend Norton’s farfieldelementary dipole equations to the quasi-nearfield range[J]. Nav. Underw. Syst. Cent. NEW LONDON CT, 1984.).

[0057] Combining (5)-(8) and the radiation field E o of the antenna at point O, the electric field component at the receiving point P can be obtained as follows:

[0058]

[0059] Based on the derivation process in 2), a near-sea-surface underwater electromagnetic wave communication channel model is constructed to obtain the channel response and link loss. The channel response is divided into the amplitude-frequency response and the phase-frequency response, which is related to the type of received electromagnetic field components. Taking the electric field component as an example, the near-sea-surface underwater electromagnetic wave communication channel response is as follows:

[0060]

[0061]

[0062] The calculation method of the link loss is similar to that of calculating the field strength in 2). Among them, the link loss underwater is the same as the field strength attenuation, while the link loss in the air needs to first calculate the radiation power of the virtual antenna at point A and the received power at point B using the electromagnetic field components in 2), and then calculate the link loss in the air according to the Friis law. The specific calculation process is as follows:

[0063]

[0064] Among them, Ar is the effective area of the receiving antenna, G t is the directivity of the transmitting antenna, G r is the directivity of the receiving antenna.

[0065] The losses of the entire communication link are as follows:

[0066] PL = PL a + PL s = PL a + FA s (12);

[0067] Since the existing near-sea surface underwater electromagnetic wave communication channel model is too simplistic and has limitations, it cannot guarantee the data interaction performance between underwater sensor network nodes. However, this model plays an extremely important role in the deployment and design of underwater sensor networks. This application can construct a simple and accurate near-sea surface underwater electromagnetic wave communication channel model, use this model to evaluate the underwater electromagnetic wave communication performance, and then guide the design and implementation of underwater sensor networks, overcoming the deficiencies and limitations of existing methods. This application can not only obtain the underwater electromagnetic wave communication channel response and link losses, but also obtain the attenuation change of the electromagnetic wave energy with distance in the transmission link. The entire derivation process has clear physical significance. Through the establishment and solution of this channel model, it helps to evaluate the underwater electromagnetic wave communication performance and then guide the design and implementation of underwater sensor networks.

[0068] To verify the correctness and effectiveness of the present invention, the inventor conducted a verification theoretical simulation:

[0069] The simulation conditions are as follows: the relative permittivity of seawater is 81, the permeability, and the conductivity; the relative permittivity of air is 1, the permeability; the magnetic dipole moment of the transmitting antenna is 10 A·m2, the depth is 10 m, and the signal frequency band is 1 - 100 kHz; the depth of the receiving antenna is 20 m, the effective area is 1 m2, and the receiving directivity is 1. The antenna positions and signal frequency bands under these simulation conditions are applicable to the constraint conditions of the present invention.

[0070] 1) The modeling method is simple and clear

[0071] The modeling method proposed in this application book corresponds to the propagation process of near-sea surface underwater electromagnetic waves and has clear physical significance; compared with the complex Sommerfeld integral equation solution in the traditional model, this method is simpler and easier to calculate.

[0072] 2) The richness of the channel model

[0073] As Figure 3 , Figure 4 and Figure 5 shown, this modeling method can calculate the channel response and link losses of the near-sea surface underwater electromagnetic wave communication channel model, and can obtainFigure 6 The curve of received power varying with communication distance, which has important guiding significance for the selection of communication frequency bands and the deployment of underwater communication nodes.

[0074] 3) Accuracy of the modeling method

[0075] As Figure 6 、 Figure 7 and Figure 8 shown, by comparing with the intensity and phase of the electric field component at the receiving point calculated by the electromagnetic wave propagation model under the traditional two-layer model, the results show that the method in this application is in good agreement with the traditional model, which proves the accuracy of the modeling method in this application from the side.

[0076] 4) According to the implementation examples, it can be considered that:

[0077] The modeling method for the near-sea surface underwater electromagnetic wave communication channel model proposed by the present invention is feasible. While reducing the complexity of the traditional modeling process and enhancing the richness of the channel model, it ensures the calculation efficiency and accuracy of the model, and the whole method corresponds to the propagation process of near-sea surface underwater electromagnetic waves, having a clear physical meaning.

[0078] Meanwhile, the content not described in detail in this specification belongs to the prior art well-known to those skilled in the art.

[0079] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device.

[0080] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for modeling an underwater electromagnetic wave communication channel near the sea surface, characterized in that Specifically, it includes the following steps: S1. When the positions of the transmitting antenna and the receiving antenna in seawater are determined, the propagation distances of electromagnetic waves in seawater and air are obtained by solving using the Goos-Hänchen shift theory. S2. Based on the generation mechanism of the Goos-Hänchen shift, a propagation model of underwater electromagnetic waves near the sea surface is constructed to obtain the field strength attenuation and phase delay of each electromagnetic field component. Specifically, according to the propagation characteristics and propagation distances of the electromagnetic waves between the transmitting antenna - incident point, incident point - reflection point, and reflection point - receiving antenna in step S1, the field strength attenuation and phase delay of each part of the electromagnetic wave component are obtained, and then the received electromagnetic field component is obtained by combining the transmitted electromagnetic field components. S3. According to the solution process of the electromagnetic wave propagation model in step S2, a communication channel model of underwater electromagnetic waves near the sea surface is constructed to obtain the channel amplitude-frequency response and link loss, as well as the attenuation change of the electromagnetic wave energy with distance in the transmission link, thereby laying a foundation for the design and node placement of the underwater sensor network.

2. A method for modeling a near-sea-surface underwater electromagnetic wave communication channel according to claim 1, characterized in that: Specifically, in step S1, when the electromagnetic wave is incident from seawater to the seawater-air interface at an incident angle greater than the critical angle, there is a certain lateral displacement of the reflection point compared to the incident point. Part of the energy of the electromagnetic wave enters the air at the incident point and finally enters the seawater from the reflection point in the form of an evanescent wave and reaches the receiving antenna. The incident angles of the electromagnetic waves and the magnitudes of the Goos-Hänchen shifts corresponding to different positions of the transmitting and receiving antennas are different.

3. A method for modeling a near-sea-surface underwater electromagnetic wave communication channel according to claim 1, characterized in that: In both step S1 and step S2, the steady-state phase method is used to solve the Goos-Hänchen shift.

4. A method for modeling a near-sea surface underwater electromagnetic wave communication channel according to claim 3, characterized in that: The incident point is regarded as a virtual antenna placed at the seawater-air interface.

5. A method for modeling a near-surface underwater electromagnetic wave communication channel according to claim 1, characterized in that: In step S3, the Friis law is used to calculate the link loss.

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