Three-way antenna underwater magnetic induction positioning system and method based on received signal strength

Abstract

The present invention discloses a three-way antenna underwater magnetic induction positioning system and method based on received signal strength. The positioning system includes a positioning signal generating module in an underwater magnetic induction transmitter, a magnetic induction transmitting module, and a magnetic induction receiving module, a positioning signal processing module, and a position estimation module in an underwater magnetic induction receiver. First, the underwater magnetic induction transmitter sequentially loads the processed positioning signal on the three coils of the three-way transmitting antenna. The underwater magnetic induction receiver obtains the signal from the three-way receiving antenna and processes it, estimates the received signal strength and the relative phase information between the multi-channel received signals, and calculates the estimated position of the transmitter in the receiving coordinate system. The positioning system of the present invention has low implementation complexity and is compatible with the underwater magnetic induction communication system; the positioning method used has low computational complexity and can directly estimate the position of the transmitter at the receiving end while communicating, avoiding the communication overhead caused by the additional feedback of the position information.

Description

Technical Field

[0001] The present invention belongs to the field of underwater magnetic induction communication technology, and in particular to the field of positioning technology in underwater magnetic induction communication. The present invention relates to a three-directional antenna underwater magnetic induction positioning system and method based on received signal strength, which realizes position estimation of a transmitting end at a receiving end. Background Art

[0002] With the growing demand for marine resource exploration and environmental monitoring, underwater wireless communication technology has become a hot topic. Wireless magnetic induction communication, as a near-field communication, has the advantages of low propagation delay, stable channel response, and negligible multipath effect, and can achieve high-speed short-distance transmission in underwater environments. In underwater magnetic induction communication, if a magnetic induction communication node can obtain the position of another node communicating with it, it can bring many gains, such as moving toward the position of the node, or by adjusting the feeding strategy during transmission, so that the energy of the transmitted signal reaches the receiving end more concentratedly, thereby improving communication reliability. Therefore, how to achieve position estimation while communicating is of great practical significance.

[0003] Normally, a single point-to-point antenna cannot achieve positioning in three-dimensional space, but the use of a three-way antenna can better solve this problem. There are three mutually orthogonal coils in a three-way antenna, which has a certain spatial position resolution capability. The traditional magnetic induction positioning method processes the signal received from the ground transmitting antenna array at the receiving end to estimate its own position in the transmitting coordinate system. For example, the Chinese invention patent application No. 201711455499.5 applies for a three-dimensional magnetic induction positioning system for underground space, and the Chinese invention patent application No. 202011303948.6 applies for a magnetic beacon positioning method and system based on magnetic induction intensity and characteristic vector, but their limitations are that they only estimate their own position at the receiving end. In underwater magnetic induction communication, it is assumed that there are two magnetic induction nodes, namely node A and node B. Node A sends a data request message to node B. When node B returns data, it needs to know the location information of node A to adjust the feeding strategy. The above positioning method needs to execute the steps of sending a data request message from node A to node B, sending a positioning signal from node B to node A, and feedback of position information from node A to node B before communication starts, which brings additional communication overhead. If node B can directly estimate the position of node A based on the received signal after node A sends a request message to node B, the above cumbersome information exchange can be avoided.

[0004] There are also some existing methods for locating the transmitter. For example, Chinese invention patent application No. 201911086599.4 applies for a magnetic induction through-the-ground positioning method based on signal direction, and Chinese invention patent application No. 201911086621.5 applies for a magnetic induction through-the-ground positioning method based on path loss. However, their limitations are that the receiver contains two three-way antennas and only achieves vertical positioning, that is, it can only determine the vertical depth of the transmitter underground.

[0005] In summary, the existing underwater magnetic induction communication position estimation method still has the following problems:

[0006] (1) Most magnetic induction positioning methods focus on estimating their own position at the receiving end. However, for application scenarios where the sending end obtains the receiving end's position or the receiving end obtains the sending end's position, feedback of position information is required, which introduces additional communication overhead.

[0007] (2) The method for estimating the position of the transmitter does not achieve three-dimensional spatial positioning, but remains at the vertical positioning of a single dimension.

[0008] (3) Most magnetic induction positioning methods require the use of multiple antennas at the transmitting or receiving end, and have requirements for the location of the antenna. However, it is difficult to deploy an antenna array with a large area on a single underwater magnetic induction node. Therefore, these methods have a certain degree of implementation complexity and are not suitable for underwater environments.

[0009] Therefore, in underwater magnetic induction communication, where the antenna structure is simple and the energy is limited, it is very necessary to achieve transmitter position estimation without feedback. Summary of the invention

[0010] An object of the present invention is to provide a three-directional antenna underwater magnetic induction communication transmitter positioning system in response to the demand that communication and positioning can be carried out simultaneously with low design complexity.

[0011] The positioning system of the present invention is a subsystem integrated into the magnetic induction communication system, and the positioning system includes an underwater magnetic induction transmitting node and an underwater magnetic induction receiving node in any position and posture. The underwater magnetic induction transmitting node and the underwater magnetic induction receiving node have the same working angular frequency and can communicate with each other.

[0012] The underwater magnetic induction transmitting node has a built-in positioning signal generating module and a magnetic induction transmitting module. The positioning signal generating module is used to generate a positioning signal sequence; the magnetic induction transmitting module includes a transmitting end processing module and a three-way transmitting antenna; the transmitting end processing module is used to process the positioning signal sequence, including spectrum shifting, digital-to-analog conversion and power amplification, perform transmitting coil selection, use the analog positioning signal as an excitation source, and load it on the three transmitting coils of the three-way transmitting antenna in time-sharing order; the three-way transmitting antenna includes three transmitting coils with mutually perpendicular coil planes, the same number of turns, and the same coil radius. The three-way transmitting antenna generates a magnetic field in space and transmits analog positioning signals.

[0013] The underwater magnetic induction receiving node has a built-in magnetic induction receiving module, a positioning signal processing module and a positioning module. The magnetic induction receiving module includes a three-way receiving antenna and a receiving end processing module; the three-way receiving antenna includes three receiving coils with mutually perpendicular coil planes, the same number of turns and the same coil radius, which are used to receive the analog positioning signal sent by the underwater magnetic induction sending node; the receiving end processing module performs analog-to-digital conversion on the three receiving signals received by the three receiving coils to obtain three digital positioning signals. The positioning signal processing module processes the three digital positioning signals to obtain the receiving signal strength information and relative phase information required by the positioning module. The positioning module is used to execute the positioning algorithm to locate the underwater magnetic induction sending node.

[0014] Another object of the present invention is to provide a method for underwater magnetic induction positioning using the above system.

[0015] The method of the present invention comprises the following steps:

[0016] Step (1) The underwater magnetic induction transmitting node generates a positioning signal and sends it to the underwater magnetic induction receiving node through a three-way transmitting antenna, specifically:

[0017] (1-1) The positioning signal generation module in the underwater magnetic induction sending node generates a positioning signal sequence: if the positioning signal also serves as a data request message, the signal sequence of the data request message is directly used as the positioning signal sequence; if the positioning signal is only used for positioning, a random sequence of a fixed length is generated as the positioning signal sequence. In order to maintain consistency, the length of the random sequence is the same as the length of the data request message;

[0018] (1-2) The magnetic induction sending module in the underwater magnetic induction sending node converts the positioning signal sequence into an analog positioning signal through spectrum shifting, digital-to-analog conversion and power amplification by the sending end processing module;

[0019] (1-3) The magnetic induction sending module loads the analog positioning signal on the three transmitting coils of the three-way transmitting antenna in a time-sharing manner; the three-way transmitting antenna generates a magnetic field in space, and the three transmitting coils send the analog positioning signal in a time-sharing manner.

[0020] Step (2) the underwater magnetic induction receiving node listens to the analog positioning signal: the three-way receiving antenna of the magnetic induction receiving module receives the analog positioning signal sent by the underwater magnetic induction sending node, and the receiving end processing module performs analog-to-digital conversion on the three receiving signals received by the three receiving coils to obtain three digital positioning signals;

[0021] Step (3) The positioning signal processing module processes the three-way digital positioning signal to obtain the received signal strength information and relative phase information required by the positioning module, specifically:

[0022] (3-1) The positioning signal processing module estimates the noise energy of the time slots where the digital positioning signal is not received: the average of the square sum of the sampling points of each receiving link is calculated as the noise energy E on each receiving link. n1 、E n2 、E n3 ;

[0023] (3-2) When the i-th transmitting coil of the underwater magnetic induction transmitting node sends an analog positioning signal, the signals received by the three receiving coils of the underwater magnetic induction receiving node are converted into three digital positioning signals y wi1 ,y wi2 and wi3 , and obtain the pure signal energy E(y received by each channel) ij )=E(y wij )-E nj , i∈{1,2,3} represents the transmitting coil number of the three-way transmitting antenna, j∈{1,2,3} represents the receiving coil number of the three-way receiving antenna, and E(·) represents the operation of calculating the energy of the signal (calculating the average of the sum of squares). The pure signal amplitude is obtained based on the pure signal energy estimation U ij That is, when the transmitting coil numbered i sends, the induced voltage intensity obtained by the receiving coil numbered j, i, j = 1, 2, 3.

[0024] Will U ij Constructing the induced voltage intensity matrix Among them, the induced voltage intensity vector U m1 , U m2 , U m3 They are the 3×1 dimensional induced voltage intensity vectors obtained by the underwater magnetic induction receiving node when the transmitting coils numbered 1, 2, and 3 send analog positioning signals. Represents the transpose of the matrix; U m This is the received signal strength information required by the positioning module.

[0025] (3-3) When the i-th transmitting coil of the underwater magnetic induction transmitting node sends the analog positioning signal, the relative phase mark of the j-th receiving coil of the underwater magnetic induction receiving node ⊙ represents dot product, Judge(·) represents the number of values ​​greater than 0 in the sequence, and Count(·) represents the number of points in the sequence;

[0026] S ij Phase marker matrix Among them, vectors S1, S2, and S3 respectively represent the three relative phase mark vectors of the three receiving coils when the transmitting coils numbered 1, 2, and 3 send analog positioning signals. i1 is always 1; the signals received by the receiving coils numbered 1 and 2 are in phase, so S i2 is 1, and is inverted if S i2 is -1, the signals received by the receiving coils numbered 1 and 3 are in phase, then S i3 is 1, and is inverted if S i3 is -1; S is the relative phase information required by the positioning module.

[0027] Step (4) The positioning module is based on U m and S, to locate the underwater magnetic induction sending node; specifically:

[0028] (4-1) Calculate the communication distance between two nodes Where ω is the operating angular frequency, μ is the magnetic permeability of the medium (for example, under water, it is the magnetic permeability of water), N t 、N r Respectively represent the number of turns of the transmitting coil and the receiving coil, a t 、a r are the coil radii of the transmitting coil and the receiving coil, respectively; G is the induced voltage attenuation coefficient caused by eddy current loss in the conductive medium; I t1 ,I t2 and I t3 are the current intensities loaded on the three transmitting coils in sequence. If the signal strengths loaded three times are the same, then I t1 =I t2 =I t3 The above parameters are antenna parameters, circuit parameters and medium parameters, which are known input parameters.

[0029] (4-2) The three axis coordinate values ​​of node B in the coordinate system of node A are Node A is the underwater magnetic induction sending node, and node B is the underwater magnetic induction receiving node:

[0030] Intermediate Estimator A possible coordinate of node B in the coordinate system of node A The possible coordinate cases are numbered k∈{1,2,3,4,5,6,7,8}, and the remaining coordinates are located in other quadrants of the coordinate system, which are axially symmetric or centrally symmetric to it.

[0031] (4-3) For each Calculate the possible position of node A in the coordinate system of node B:

[0032] according to The magnetic field direction matrix in the coordinate system of node A is obtained as follows:

[0033]

[0034] According to U m The magnetic field direction matrix in the coordinate system of node B is obtained by S:

[0035]

[0036] Get the rotation matrix

[0037] The origin of the A coordinate system Substituting into ΩX+D=Y, the estimated coordinates of node A in the coordinate system of node B are Translation Matrix

[0038] (4-4) After traversing the eight situations, choose The value corresponding to the minimum As a result of positioning.

[0039] This transmission uses the relative phase information between the received signal strength and the received signal to locate the underwater magnetic induction sending node. The structure of the positioning system is relatively simple, and only a positioning signal processing module and a positioning module need to be added to the original underwater magnetic induction communication system. After the underwater magnetic induction receiving node receives the positioning signal from the sending node, it can estimate the position of the underwater magnetic induction sending node based on the received signal after simple processing, so that in the process of feedback data, it can use the estimated position information to adjust its own behavior such as sending feeding strategy. Compared with the traditional receiving end position estimation method, the present invention can obtain the position information of the other end without feedback from the other end, and does not need to construct an additional positioning signal. It can directly use data request messages, thereby reducing the additional communication overhead caused by positioning and reducing energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 is a schematic diagram of a positioning system in the method of the present invention;

[0041] Figure 2It is a schematic diagram of the relative positions of the underwater magnetic induction sending and receiving node coordinate systems in the method of the present invention;

[0042] Figure 3 It is a schematic flow chart of the method of the present invention. DETAILED DESCRIPTION

[0043] In order to explain the invention in more detail, an illustrative description is provided in conjunction with the accompanying drawings, but the invention is not limited to the accompanying drawings. The structures in the accompanying drawings are omitted or the proportions do not conform to the actual sizes, and the drawings are only used for reference.

[0044] like Figure 1 As shown, the three-way antenna underwater magnetic induction positioning system based on received signal strength includes an underwater magnetic induction sending node and an underwater magnetic induction receiving node in any position and posture. The underwater magnetic induction sending node and the underwater magnetic induction receiving node have the same working angular frequency and can communicate with each other.

[0045] The underwater magnetic induction transmitting node has a built-in positioning signal generating module and a magnetic induction transmitting module. The positioning signal generating module is used to generate a positioning signal sequence; the magnetic induction transmitting module includes a transmitting end processing module and a three-way transmitting antenna; the transmitting end processing module is used to process the positioning signal sequence, including spectrum shifting, digital-to-analog conversion and power amplification, perform transmitting coil selection, use the analog positioning signal as an excitation source, and load it on the three transmitting coils of the three-way transmitting antenna in time-sharing order; the three-way transmitting antenna includes three transmitting coils with mutually perpendicular coil planes, the same number of turns, and the same coil radius. The three-way transmitting antenna generates a magnetic field in space and transmits analog positioning signals.

[0046] The underwater magnetic induction receiving node has a built-in magnetic induction receiving module, a positioning signal processing module and a positioning module. The magnetic induction receiving module includes a three-way receiving antenna and a receiving end processing module; the three-way receiving antenna includes three receiving coils with mutually perpendicular coil planes, the same number of turns and the same coil radius, which are used to receive the analog positioning signal sent by the underwater magnetic induction sending node; the receiving end processing module performs analog-to-digital conversion on the three receiving signals received by the three receiving coils to obtain three digital positioning signals. The positioning signal processing module processes the three digital positioning signals to obtain the receiving signal strength information and relative phase information required by the positioning module. The positioning module is used to execute the positioning algorithm to locate the underwater magnetic induction sending node.

[0047] In the above underwater magnetic induction positioning system, the underwater magnetic induction sending node loads the positioning signal in the three transmitting coils of the three-way transmitting antenna in time-sharing order, and the underwater magnetic induction receiving node estimates the position of the underwater magnetic induction sending node in its own coordinate system based on the received signal. The positioning coordinate system model is as follows: Figure 2 As shown in the figure, point O A and O Bare the origins of the coordinate systems of node A and node B, respectively. T1, T2, and T3 are three transmitting coils, and R1, R2, and R3 are three receiving coils. Assuming A is the transmitting end and B is the receiving end, then B needs to estimate O based on the received signal. A Coordinates in the B coordinate system. First, consider a more general case. If the coordinates of a point P in space are represented by X in the B coordinate system and Y in the A coordinate system, then according to the coordinate transformation formula, we get ΩX+D=Y, where Ω is the rotation matrix and D is the translation matrix. As long as Ω and D are estimated, we can get any transformation of the coordinates in both coordinate systems. Therefore, let the origin O of the A coordinate system be A Substitute the coordinates of node A into Y, and the solved X is the position of node A in the coordinate system of node B. The specific method is:

[0048] Step (1) The underwater magnetic induction transmitting node generates a positioning signal and sends it to the underwater magnetic induction receiving node through a three-way transmitting antenna, specifically:

[0049] (1-1) The positioning signal generation module in the underwater magnetic induction sending node generates a positioning signal sequence: if the positioning signal also serves as a data request message, the signal sequence of the data request message is directly used as the positioning signal sequence; if the positioning signal is only used for positioning, a random sequence of a fixed length is generated as the positioning signal sequence. In order to maintain consistency, the length of the random sequence is the same as the length of the data request message;

[0050] (1-2) The magnetic induction sending module in the underwater magnetic induction sending node converts the positioning signal sequence into an analog positioning signal through spectrum shifting, digital-to-analog conversion and power amplification by the sending end processing module;

[0051] (1-3) The magnetic induction sending module loads the analog positioning signal on the three transmitting coils of the three-way transmitting antenna in a time-sharing manner; the three-way transmitting antenna generates a magnetic field in space, and the three transmitting coils send the analog positioning signal in a time-sharing manner.

[0052] Step (2) the underwater magnetic induction receiving node listens to the analog positioning signal: the three-way receiving antenna of the magnetic induction receiving module receives the analog positioning signal sent by the underwater magnetic induction sending node, and the receiving end processing module performs analog-to-digital conversion on the three receiving signals received by the three receiving coils to obtain three digital positioning signals;

[0053] Step (3) The positioning signal processing module processes the three-way digital positioning signal to obtain the received signal strength information and relative phase information required by the positioning module, specifically:

[0054] (3-1) The positioning signal processing module estimates the noise energy of the time slots where the digital positioning signal is not received: the average of the square sum of the sampling points of each receiving link is calculated as the noise energy E on each receiving link. n1 、E n2 、E n3 ;

[0055] (3-2) When the i-th transmitting coil of the underwater magnetic induction transmitting node sends an analog positioning signal, the signals received by the three receiving coils of the underwater magnetic induction receiving node are converted into three digital positioning signals y wi1 ,y wi2 and wi3 , and obtain the pure signal energy E(y received by each channel) ij )=E(y wij )-E nj , i∈{1,2,3} represents the transmitting coil number of the three-way transmitting antenna, j∈{1,2,3} represents the receiving coil number of the three-way receiving antenna, and E(·) represents the operation of calculating the energy of the signal (calculating the average of the sum of squares). The pure signal amplitude is obtained based on the pure signal energy estimation U ij That is, when the transmitting coil numbered i sends, the induced voltage intensity obtained by the receiving coil numbered j, i, j = 1, 2, 3.

[0056] Will U ij Constructing the induced voltage intensity matrix Among them, the induced voltage intensity vector U m1 , U m2 , U m3 They are the 3×1 dimensional induced voltage intensity vectors obtained by the underwater magnetic induction receiving node when the transmitting coils numbered 1, 2, and 3 send analog positioning signals. Represents the transpose of the matrix; U m This is the received signal strength information required by the positioning module.

[0057] (3-3) According to the mechanism of magnetic induction, the changing magnetic field in space generates an induced voltage, but the direction of the induced voltage will reverse as the coil flips. Similarly, under the excitation of AC power at the transmitting end, the induced current at the receiving end will also experience a phase inversion phenomenon due to the flipping of the coil. Therefore, in addition to the signal amplitude, it is also necessary to obtain the phase conditions in the three receiving coils. The phase conditions here do not require the accurate phase of the three signals, but only need to use the phase of the first signal as a reference to determine whether the other two signals are in phase or out of phase with the reference. Since the three signals received at the same time are sent by the same coil and the communication distance is the same, it can be assumed that there is no relative phase offset, and the two signals are directly multiplied with the first signal. If the result is positive, it is in phase, and if the result is negative, it is out of phase. This process can be performed simultaneously when calculating the signal energy. However, due to the presence of noise, it is impossible to guarantee that each sampling point will obtain the correct result. Therefore, if more than half of the multiplication results are positive, it is in phase, otherwise it is out of phase. Specifically:

[0058] When the i-th transmitting coil of the underwater magnetic induction transmitting node sends the analog positioning signal, the relative phase mark of the j-th receiving coil of the underwater magnetic induction receiving node ⊙ represents dot product, Judge(·) represents the number of values ​​greater than 0 in the sequence, and Count(·) represents the number of points in the sequence;

[0059] S ij Phase marker matrix Among them, vectors S1, S2, and S3 respectively represent the three relative phase mark vectors of the three receiving coils when the transmitting coils numbered 1, 2, and 3 send analog positioning signals. i1 is always 1; the signals received by the receiving coils numbered 1 and 2 are in phase, so S i2 is 1, and is inverted if S i2 is -1, the signals received by the receiving coils numbered 1 and 3 are in phase, then S i3 is 1, and is inverted if S i3 is -1; S is the relative phase information required by the positioning module.

[0060] Step (4) The positioning module is based on U m and S, to locate the underwater magnetic induction sending node; Figure 3 , specifically:

[0061] (4-1) Calculate the communication distance between two nodes Where ω is the operating angular frequency, μ is the magnetic permeability of the medium (for example, under water, it is the magnetic permeability of water), N t 、N r Respectively represent the number of turns of the transmitting coil and the receiving coil, a t 、a rare the coil radii of the transmitting coil and the receiving coil, respectively; G is the induced voltage attenuation coefficient caused by eddy current loss in the conductive medium; I t1 ,I t2 and I t3 are the current intensities loaded on the three transmitting coils in sequence. If the signal strengths loaded three times are the same, then I t1 =I t2 =I t3 The above parameters are antenna parameters, circuit parameters and medium parameters, which are known input parameters.

[0062] (4-2) The three axis coordinate values ​​of node B in the coordinate system of node A are Node A is the underwater magnetic induction sending node, and node B is the underwater magnetic induction receiving node:

[0063] Intermediate Estimator A possible coordinate of node B in the coordinate system of node A The possible coordinate cases are numbered k∈{1,2,3,4,5,6,7,8}, and the remaining coordinates are located in other quadrants of the coordinate system, which are axially symmetric or centrally symmetric to it.

[0064] (4-3) For each Calculate the possible position of node A in the coordinate system of node B:

[0065] according to The magnetic field direction matrix in the coordinate system of node A is obtained as follows:

[0066]

[0067] According to U m The magnetic field direction matrix in the coordinate system of node B is obtained by S:

[0068]

[0069] Get the rotation matrix

[0070] The origin of the A coordinate system Substituting into ΩX+D=Y, the estimated coordinates of node A in the coordinate system of node B are Translation Matrix

[0071] (4-4) After traversing the eight cases in (4-3), choose The value corresponding to the minimum As a result of positioning.

[0072] In the method of the present invention, most of the symmetrical false positions are removed according to the relative phase information between the three received signals, but two estimated positions that are centrally symmetrical about the origin are still obtained in space. It is possible to choose whether to eliminate the false positions according to the purpose of the positioning result. For example, when the positioning result is used to adjust the feeding strategy, due to the central symmetry of the magnetic field, the centrally symmetrical false positions will not affect the feeding strategy.

Claims

1. A three-way antenna underwater magnetic induction positioning method based on received signal strength, characterized in that: The three-directional antenna underwater magnetic induction positioning system adopted includes an underwater magnetic induction sending node and an underwater magnetic induction receiving node in any position and posture, and the working angular frequency of the underwater magnetic induction sending node and the underwater magnetic induction receiving node is the same; The underwater magnetic induction sending node has a built-in positioning signal generating module and a magnetic induction sending module; the positioning signal generating module is used to generate a positioning signal sequence; the magnetic induction sending module includes a sending end processing module and a three-way sending antenna; the sending end processing module is used to process the positioning signal sequence, including spectrum shifting, digital-to-analog conversion and power amplification, perform sending coil selection, use the analog positioning signal as an excitation source, and load it on the three sending coils of the three-way sending antenna in time-sharing order; the three-way sending antenna includes three sending coils with mutually perpendicular coil planes, the same number of turns and the same coil radius, and the three-way sending antenna generates a magnetic field in space and sends an analog positioning signal; The underwater magnetic induction receiving node has a built-in magnetic induction receiving module, a positioning signal processing module and a positioning module; the magnetic induction receiving module includes a three-way receiving antenna and a receiving end processing module; the three-way receiving antenna includes three receiving coils with mutually perpendicular coil planes, the same number of turns and the same coil radius, which are used to receive the analog positioning signal sent by the underwater magnetic induction sending node; the receiving end processing module performs analog-to-digital conversion on the three receiving signals received by the three receiving coils to obtain three digital positioning signals; the positioning signal processing module processes the three digital positioning signals to obtain the receiving signal strength information and relative phase information required by the positioning module; the positioning module is used to execute the positioning algorithm to locate the underwater magnetic induction sending node; The specific positioning method is as follows: Step (1) The underwater magnetic induction transmitting node generates a positioning signal and sends it to the underwater magnetic induction receiving node through a three-way transmitting antenna, specifically: (1-1) A positioning signal generation module in the underwater magnetic induction sending node generates a positioning signal sequence; (1-2) The magnetic induction sending module in the underwater magnetic induction sending node converts the positioning signal sequence into an analog positioning signal through spectrum shifting, digital-to-analog conversion and power amplification by the sending end processing module; (1-3) The magnetic induction transmission module sequentially loads the analog positioning signal on the three transmitting coils of the three-way transmitting antenna in a time-sharing manner; the three-way transmitting antenna generates a magnetic field in space, and the three transmitting coils sequentially transmit the analog positioning signal in a time-sharing manner; Step (2) the underwater magnetic induction receiving node listens to the analog positioning signal: the three-way receiving antenna of the magnetic induction receiving module receives the analog positioning signal sent by the underwater magnetic induction sending node, and the receiving end processing module performs analog-to-digital conversion on the three receiving signals received by the three receiving coils to obtain three digital positioning signals; Step (3) The positioning signal processing module processes the three-way digital positioning signal to obtain the received signal strength information and relative phase information required by the positioning module, specifically: (3-1) The positioning signal processing module estimates the noise energy of the time slots where the digital positioning signal is not received: the average of the square sum of the sampling points of each receiving link is calculated as the noise energy E on each receiving link. n1 、E n2 、E n3 ; (3-2) When the i-th transmitting coil of the underwater magnetic induction transmitting node sends an analog positioning signal, the signals received by the three receiving coils of the underwater magnetic induction receiving node are converted into three digital positioning signals y wi1 ,y wi2 and wi3 , and obtain the pure signal energy E(y received by each channel) ij )=E(y wij )-E nj , i∈{1,2,3} represents the transmitting coil number of the three-way transmitting antenna, j∈{1,2,3} represents the receiving coil number of the three-way receiving antenna, and E(·) represents the operation of calculating the energy of the signal (calculating the average of the sum of squares); the pure signal amplitude is estimated based on the pure signal energy U ij That is, when the transmitting coil number i sends, the receiving coil number j gets the induced voltage intensity, i, j = 1, 2, 3; Will U ij Constructing the induced voltage intensity matrix Among them, the induced voltage intensity vector U m1 , U m2 , U m3 They are the 3×1 dimensional induced voltage intensity vectors obtained by the underwater magnetic induction receiving node when the transmitting coils numbered 1, 2, and 3 send analog positioning signals. Represents the transpose of the matrix; U m That is the received signal strength information required by the positioning module; (3-3) When the i-th transmitting coil of the underwater magnetic induction transmitting node sends the analog positioning signal, the relative phase mark of the j-th receiving coil of the underwater magnetic induction receiving node ⊙ represents dot product, Judge(·) represents the number of values ​​greater than 0 in the sequence, and Count(·) represents the number of points in the sequence; S ij Phase marker matrix Among them, vectors S1, S2, and S3 respectively represent the three relative phase mark vectors of the three receiving coils when the transmitting coils numbered 1, 2, and 3 send analog positioning signals. i1 is always 1; the signals received by the receiving coils numbered 1 and 2 are in phase, so S i2 is 1, and is inverted if S i2 is -1, the signals received by the receiving coils numbered 1 and 3 are in phase, then S i3 is 1, and is inverted if S i3 is -1; S is the relative phase information required by the positioning module; Step (4) The positioning module is based on U m and S, to locate the underwater magnetic induction sending node; specifically: (4-1) Calculate the communication distance between two nodes Where ω is the operating angular frequency, μ is the magnetic permeability of the medium, N t 、N r Respectively represent the number of turns of the transmitting coil and the receiving coil, a t 、a r are the coil radii of the transmitting coil and the receiving coil, respectively; G is the induced voltage attenuation coefficient caused by eddy current loss in the conductive medium; I t1 ,I t2 and I t3 are the current intensities loaded on the three transmitting coils in sequence in time division; (4-2) The three axis coordinate values ​​of node B in the coordinate system of node A are Node A is the underwater magnetic induction sending node, and node B is the underwater magnetic induction receiving node: Intermediate Estimator A possible coordinate of node B in the coordinate system of node A k is the number of the possible coordinate situation, k∈{1,2,3,4,5,6,7,8}, and the remaining coordinates are located in other quadrants of the coordinate system, which are axially symmetric or centrally symmetric with it; (4-3) For each Calculate the possible position of node A in the coordinate system of node B: according to The magnetic field direction matrix in the coordinate system of node A is obtained as follows: According to U m The magnetic field direction matrix in the coordinate system of node B is obtained by S: Get the rotation matrix Set the origin of the A coordinate system Y = [0,0,0] T Substituting into ΩX+D=Y, the estimated coordinates of node A in the coordinate system of node B are Translation Matrix (4-4) After traversing the eight situations, choose The value corresponding to the minimum As a result of positioning.

2. The method for underwater magnetic induction positioning based on three-way antenna received signal strength according to claim 1, characterized in that: In (1-1), if the positioning signal also serves as a data request message, the signal sequence of the data request message is directly used as the positioning signal sequence; if the positioning signal is only used for positioning, a random sequence of fixed length is generated as the positioning signal sequence, and the length of the random sequence is the same as the length of the data request message.

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