Wireless data transmission system and wireless data transmission method

Abstract

To allow large capacity data communication to be stably performed at high speed in a wide range such as in the sea.SOLUTION: A wireless data transmission system includes: N (N is an integer of two or more) transmission coils that have opening surfaces and are arranged in water so that the opening surfaces face vertically upward; and N communication devices that are connected one-on-one with connection transmission coils that are any of the N transmission coils, and perform data communication via the connection transmission coils. The communication devices perform multi-hop transmission of data acquired by a data acquisition device capable of moving in water based on topology indicating a form of connection between the N communication devices generated in advance and magnetic field coupling that occurs between the connection transmission coils and at least one other adjacent connection transmission coil.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a wireless data transmission system and a wireless data transmission method. [Background technology]

[0002] Patent Document 1 discloses an ocean network system in which a large number of floats floating on the sea surface and buoys equipped with communication units connected to the floats and floating in the sea are deployed in the ocean, and the large number of buoys communicate with each other within a certain range. The communication units perform underwater communication using laser light with multiple other communication units located within a certain distance around it. At least one of the buoys functions as a base station relay buoy that communicates with a base station, and the float of the base station relay buoy is equipped with a communication cable that communicates with the communication units connected to the float and a wireless communication unit that performs wireless communication with the base station.

[0003] Patent Document 2 discloses an information communication system in which transmission data generated by a data management server is distributed by ultrasonic waves to an underwater vehicle that conducts marine surveys via an artificial satellite and a first data transmission / reception terminal. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-184034 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-56831 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, when underwater vehicles are deployed in the ocean to conduct marine exploration and other such activities, the efficiency of data collection has been improved by transmitting the data acquired by the underwater vehicle to surface vessels via wireless communication. In particular, in marine exploration using underwater vehicles, the exploration area often extends over a wide area, and there is a demand for data communication over a wider area.

[0006] Laser light communication as in Patent Document 1 has a high communication speed, but communication can be difficult depending on the installation location or underwater conditions (e.g., turbidity), or when the topography of the exploration area is undulating or curved, making long-distance communication difficult. Ultrasonic communication as in Patent Document 2 allows long-distance communication, but has the problem of slow data transmission speed. In other words, with the above-mentioned Patent Documents 1 and 2, it is difficult to perform high-volume data communication quickly and stably over a wide area such as underwater, and there is thought to be room for improvement.

[0007] The present disclosure has been devised in view of the above-described conventional situation, and provides a wireless data transmission system and a wireless data transmission method that perform high-speed and stable large-capacity data communication over a wide area such as underwater. [Means for solving the problem]

[0008] The present disclosure provides a data transmission system comprising: N (N: an integer of 2 or greater) transmission coils each having an opening surface and arranged in water with the opening surface facing vertically upward; and N communication devices each connected one-to-one to a connection transmission coil that is any one of the N transmission coils and performing data communication via the connection transmission coil, wherein the communication devices perform multi-hop transmission of data acquired by a data acquisition device movable underwater based on a pre-generated topology indicating the connection form between the N communication devices and magnetic field coupling occurring between the connection transmission coil and at least one other adjacent connection transmission coil.

[0009] The present disclosure also provides a data transmission method using N (N: an integer of 2 or more) transmission coils each having an opening surface and arranged in water with the opening surface facing vertically upward, and N communication devices each connected one-to-one to a connection transmission coil that is any of the N transmission coils and performing data communication via the connection transmission coil, and performing multi-hop transmission of data acquired by a data acquisition device movable underwater based on a pre-generated topology indicating the connection form between the N communication devices and magnetic field coupling occurring between the connection transmission coil and at least one other adjacent connection transmission coil. [Effects of the Invention]

[0010] According to the present disclosure, large-capacity data communication can be performed quickly and stably over a wide area such as underwater. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing a schematic example of a usage environment in which a wireless data transmission system is installed. [Figure 2] FIG. 1 is a diagram illustrating a system configuration example of a wireless data transmission system. [Figure 3] Diagram showing an example of magnetic field coupling between transmission coils arranged in a horizontal direction [Figure 4] Block diagram showing an example of the hardware configuration of a PLC adapter [Figure 5] Block diagram showing an example of the functional configuration of the CPU of a PLC adapter [Figure 6] A sequence diagram showing an example of the authentication process performed between M-PLC and t-PLC [Figure 7] A diagram showing a first example of the placement of PLC adapters and the link costs between PLC adapters. [Figure 8] A diagram showing a first topology example [Figure 9] A sequence diagram showing an example of the authentication process performed between the various PLC adapters shown in Figure 7. [Figure 10]Figure 2 shows a second example of the layout of PLC adapters and the link costs between PLC adapters. [Figure 11] A diagram showing a second topology example [Figure 12] A sequence diagram showing an example of the authentication process performed between the various PLC adapters shown in Figure 10. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, with reference to the drawings as appropriate, detailed descriptions of embodiments specifically disclosing a wireless data transmission system and a wireless data transmission method according to the present disclosure will be provided. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters or redundant descriptions of substantially identical configurations may be omitted. This is to avoid unnecessary redundancy in the following description and to facilitate understanding by those skilled in the art. Note that the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter recited in the claims.

[0013] (System Configuration) FIG. 1 is a diagram schematically illustrating an example of a usage environment in which a wireless data transmission system 100 is installed. FIG. 2 is a diagram schematically illustrating an example of a system configuration of the wireless data transmission system 100. As shown in FIG. 1, the wireless data transmission system 100 is placed underwater (e.g., under the sea). The wireless data transmission system 100 includes N (N: an integer of 2 or more) transmission coils and N PLC adapters. The transmission coils are, for example, composed of transmission coils CL1, CL2, CL3, CL4, CL5, CL6, and CL7. The PLC adapter is an example of a communication device and is, for example, composed of PLC adapters P1, P2, P3, P4, P5, P6, and P7. Note that, although N=7 in the example of FIG. 1, N is not limited to 7 as long as it is 2 or more.

[0014] Each of the transmission coils CL1 to CL7 is formed, for example, in a ring shape and insulated by being covered with a resin cover. It transmits not only power but also data between other transmission coils that are magnetically coupled by a magnetic coupling method (in other words, an electromagnetic induction method). Each of the transmission coils CL1 to CL7 is formed, for example, by a cabtyre cable, a helical coil, or a spiral coil. A helical coil is a ring-shaped coil that is wound helically along the direction of power transmission by the magnetic coupling method, not within the same plane. The use of a helical coil ensures a large internal space for each of the wound transmission coils CL1 to CL7. A spiral coil is a ring-shaped coil formed in a spiral shape within the same plane. The use of a spiral coil enables each of the transmission coils CL1 to CL7 to be made thinner. Note that FIG. 1 illustrates an example of a spiral coil.

[0015] The transmission coils CL1, CL2, CL3, CL4, CL5, CL6, and CL7 have openings OP1, OP2, OP3, OP4, OP5, OP6, and OP7, respectively, and are disposed in the sea (e.g., on the seabed) so that the openings face vertically upward. Here, vertically upward refers to the direction toward the sea surface that is substantially perpendicular to the seabed surface, which can be considered to be substantially flat.

[0016] The transmission coils CL1 to CL7 are arranged at equal intervals, for example. The distance between adjacent transmission coils (in other words, the interval) is, for example, 5 m. The interval is, for example, about half the diameter of the transmission coil. Considering the attenuation of magnetic field strength underwater (for example, under the sea), the transmission frequency is, for example, 40 kHz or less, and preferably less than 10 kHz. When transmitting power at a transmission frequency of 10 kHz or more, a predetermined simulation must be performed in accordance with the provisions of the Radio Law, but this process can be omitted when the frequency is less than 10 kHz. Note that the lower the transmission frequency, the longer the power transmission distance, the larger the transmission coils, and the longer the intervals. Note that the transmission frequency may be higher than 40 kHz, for example, when a data communication signal is superimposed.

[0017] The transmission frequency is determined based on various coil characteristics such as the inductance, diameter, and number of turns of the transmission coil. The diameter of the transmission coil is, for example, several meters to several tens of meters. Furthermore, the thicker the transmission coil (i.e., the larger the wire diameter of the transmission coil), the lower the electrical resistance in the transmission coil and the smaller the power loss. Furthermore, the power transmitted via the transmission coil is, for example, 50 W or more, and may be on the order of kW.

[0018] As shown in Fig. 2, capacitors CA, CA, ..., CA, and CB are connected in series to each of the transmission coils CL1, CL2, ..., CL7, and CL8. A resonant circuit is formed by the transmission coil CL1 and capacitor CA, the transmission coil CL2 and capacitor CA, ..., the transmission coil CL7 and capacitor CA, and the transmission coil CL8 and capacitor CB. Each of the transmission coils CL1 to CL7 transmits data or power from the corresponding PLC adapter connected to it (for example, PLC adapter P1 for transmission coil CL1) to other adjacent transmission coils.

[0019] The PLC adapter P1 is placed, for example, on the seabed. The PLC adapter P1 is connected by wire to a communication facility (for example, the PLC adapter P0 shown in FIG. 2) installed on a ship SH1 anchored at sea (an example of a surface water) so as to be able to communicate with the communication facility, and is further connected by a power cable or the like so as to be able to receive power from a power supply facility 70 installed on land. The PLC adapter P1 is connected by wire to a transmission coil CL1 (an example of a connected transmission coil) and acquires data transmitted from other transmission coils (for example, various data acquired by the AUV 30 during marine exploration, etc.) via the transmission coil CL1. The PLC adapter P1 performs data communication with the PLC adapter P0, and transmits power to other transmission coils while receiving and supplying power transmitted from the power supply facility 70. A detailed configuration example of the PLC adapter P1 will be described later with reference to FIG. 4.

[0020] Each of the PLC adapters P2, P3, P4, P5, P6, and P7 is placed, for example, on the seabed and is wired to transmission coils CL2, CL3, CL4, CL5, CL6, and CL7 (examples of connection transmission coils). The PLC adapters P2, P3, P4, P5, P6, and P7 acquire, receive, and supply data (e.g., various data acquired by the AUV 30 during oceanographic exploration) or power transmitted from the other transmission coils via the transmission coils CL2, CL3, CL4, CL5, CL6, and CL7. Each of the PLC adapters P2, P3, P4, P5, P6, and P7 transmits data (e.g., various data acquired by the AUV 30 during oceanographic exploration) to the other transmission coils or transmits power to the other transmission coils via the transmission coils CL2, CL3, CL4, CL5, CL6, and CL7. A detailed configuration example of the PLC adapters P2 to P7 will be described later with reference to FIG. 4.

[0021] The wireless data transmission system 100 may further include an AUV 30 (Autonomous Underwater Vehicle), which is an underwater vehicle. The AUV 30 may be, for example, a remotely operated vehicle (ROV), an unmanned underwater vehicle (UUV), or an autonomous underwater vehicle (AUV). The AUV 30 may be equipped with a built-in battery (not shown).

[0022] The AUV30 is equipped with a transmission coil CL8 and a PLC adapter P8. The AUV30 may also be equipped with an acquisition mechanism (not shown) capable of acquiring various data related to ocean exploration (see above), and transmits the data acquired by the acquisition mechanism to another transmission coil via the transmission coil CL8. The data includes, for example, data on the results of underwater exploration or bottom exploration performed by the AUV30. The AUV30 can submerge underwater and move freely to predetermined data acquisition points based on instructions from the ship SH1 (specifically, PC1). Instructions from the ship SH1 may be transmitted by data communication via each of the transmission coils CL1 to CL8, or by other communication methods.

[0023] The PLC adapter P8 is disposed within the AUV 30 and is connected by wire to the transmission coil CL8. The PLC adapter P8 acquires data or power transmitted from other transmission coils, or receives and supplies power via the transmission coil CL8. The PLC adapter P8 also transmits data acquired by the AUV 30 (see above) to other transmission coils via the transmission coil CL8. A detailed configuration example of the PLC adapter P8 will be described later with reference to FIG. 4. The source and destination of the data (see above) from the transmission coils are determined by the topology that is generated, and will be described in detail later.

[0024] A part of the ship SH1 on which the communication equipment is arranged is above the water surface (e.g., sea surface), i.e., above the water, and another part of the ship SH1 is below the water surface, i.e., underwater (e.g., under the sea). The ship SH1 is movable on the water (e.g., at sea) and can freely move to a data acquisition location on the water (e.g., at sea) for the AUV 30, for example.

[0025] Next, multi-hop transmission between transmission coils will be briefly described with reference to Fig. 3. Fig. 3 is a diagram showing an example of magnetic field coupling between transmission coils arranged side by side in the horizontal direction. For simplicity of explanation, Fig. 3 illustrates three transmission coils (specifically, transmission coils CL1, CL2, and CL3) and PLC adapters (specifically, PLC adapters P1, P2, and P3) corresponding to the respective transmission coils.

[0026] In the resonant circuit of the transmission coil CL1, when a current iCL1 from the PLC adapter P1 (hereinafter also referred to as "t-PLC1") flows through the transmission coil CL1, a magnetic field φCL1 is generated around the transmission coil CL1. The oscillation of the generated magnetic field φCL1 is transmitted wirelessly to the resonant circuit of the transmission coil CL2, which resonates at the same frequency as the resonant frequency of the resonant circuit of the transmission coil CL1. In this way, the magnetic field generated around the transmission coil CL1 and transmitted wirelessly to the transmission coil CL2 is sometimes referred to as magnetic flux linkage.

[0027] Similarly, in the resonant circuit of the transmission coil CL2, the oscillation of the magnetic field φCL1, which is a flux linkage (in other words, magnetic field coupling), excites the magnetic field φCL1 in the transmission coil CL2, generating a current iCL2. Therefore, a similar magnetic field φCL2, which is a flux linkage, is also generated around the transmission coil CL2. Note that the current iCL2 generated in the transmission coil CL2 due to the oscillation of the magnetic field φCL1 is smaller than the current iCL1. For this reason, the PLC adapter 2 (hereinafter also referred to as "t-PLC2") controls the level (magnitude) of the current iCL2, such as by amplifying it to a predetermined level. This predetermined level may be common to each of the PLC adapters P1 to P8. This makes the level (magnitude) of the magnetic field φCL2 equivalent to the level (magnitude) of the magnetic field φCL1, thereby suppressing attenuation in data communication or power transmission between the transmission coils. Furthermore, the oscillation of the generated magnetic field φCL2 is wirelessly transmitted to the resonant circuit of the transmission coil CL3, which resonates at the same frequency as the resonant frequency of the resonant circuit of the transmission coils CL1 and CL2.

[0028] Similarly, in the resonant circuit of the transmission coil CL3, the oscillation of the magnetic field φCL2, which is a flux linkage (in other words, magnetic field coupling), excites the magnetic field φCL2 in the transmission coil CL3, generating a current iCL3. Therefore, a similar magnetic field (not shown), which is a flux linkage, is generated around the transmission coil CL3. Note that the current iCL3 generated in the transmission coil CL3 by the oscillation of the magnetic field φCL2 is smaller than the amplified current iCL2. Therefore, the PLC adapter 3 (hereinafter also referred to as "t-PLC3") controls the level (magnitude) of the current iCL3 to a predetermined level, such as by amplifying it. This makes the level (magnitude) of the magnetic field φCL3 equal to the level (magnitude) of the magnetic field φCL2, thereby suppressing attenuation in data communication or power transmission between the transmission coils. Furthermore, the oscillation of the generated magnetic field φCL3 is wirelessly transmitted to the resonant circuit of the transmission coil CL4, which resonates at the same frequency as the resonant frequency of the resonant circuits of the transmission coils CL1, CL2, and CL3. In this way, multi-hop transmission between transmission coils enables continuous data communication or power transmission over a wide area.

[0029] Note that the above explanation has been given of an example in which data communication or power transmission is performed in the order of transmission coils CL1, CL2, and CL3, but it is equally applicable to the case in which data communication or power transmission is performed in the opposite direction, i.e., in the order of transmission coils CL3, CL2, and CL1.

[0030] 4 is a block diagram showing an example of the hardware configuration of PLC adapters P0, P1, P2, P3, P4, P5, P6, P7, and P8. Since the hardware configuration of each PLC adapter is the same, the following description will be given using PLC adapter P1 as an example. In other words, the following description can also be applied to the description of the hardware configuration of each of PLC adapters P0, P2 to P8.

[0031] The PLC adapter P1 performs digital signal processing and communication using, for example, orthogonal frequency division multiplexing (ODFM). The PLC adapter P1 includes a controller 10, a memory 20, and an AFE 24. The controller 10 includes a CPU (Central Processing Unit) 11, a PLC (Power Line Communication)_PHY (Physics) block 12, and a PLC_MAC (Media Access Control) block 13.

[0032] The CPU 11 uses the programs and data stored in the memory 20 to control the processing of the PLC_MAC block 13 and the PLC_PHY block 12, and to control the processing of each part of the PLC adapter P1. An example of the functional configuration of the CPU 11 will be described later with reference to FIG.

[0033] The PLC_PHY block 12 manages the processing of transmission signals and reception signals at the PHY layer (Physical Layer) for data communication via a transmission coil (see FIG. 1).

[0034] The PLC_MAC block 13 manages the processing of transmission signals and reception signals in the MAC layer (Media Access Control Layer) for data communication via the transmission coil (see FIG. 1).

[0035] The AFE 24 has a DA (Digital-Analog) converter (not shown), an AD (Analog-Digital) converter (not shown), and a variable amplifier (not shown). The AFE 24 converts a digital signal, which is a transmission signal input to the DA converter, into an analog signal and outputs the analog signal to a transmission coil (an example of a connection transmission coil) connected to the PLC adapter. The AFE 214 adjusts the gain of an analog signal, which is a reception signal input to the variable amplifier from the transmission coil (an example of a connection transmission coil), amplifies the signal appropriately, and inputs it to the AD converter, where it converts the analog signal input to the AD converter into a digital signal.

[0036] The PLC adapter P1 may also include, for example, a wired LAN (Local Area Network)_MAC block 19 compatible with Ethernet (registered trademark), an SDRAM controller 18, a flash memory interface 17, a GPIO (General-Purpose Input / Output) 15, a UART (Universal Asynchronous Receiver / Transmitter) 16, and a clock IC 14. In Fig. 4, the interface is abbreviated as "IF" and the clock is abbreviated as "CLK" for convenience.

[0037] A wired LAN_PHY block 23 compatible with Ethernet (registered trademark) is connected to the wired LAN_MAC block 19. The wired LAN_MAC block 19 manages the processing of transmission signals and reception signals in the MAC layer for data communication via a wired LAN cable (not shown).

[0038] The wired LAN_PHY block 23 manages the processing of transmission signals and reception signals at the PHY layer for performing data communication via a wired LAN cable (not shown).

[0039] The SDRAM controller 18 controls read and write operations to the SDRAM 22 .

[0040] The flash memory interface 17 controls read and write operations to the flash memory 21 .

[0041] The SDRAM 22 and the flash memory 21 may be part of the memory 20 .

[0042] GPIO15 is a general-purpose input / output interface.

[0043] The UART 16 performs serial-to-parallel conversion or parallel-to-serial conversion on the input data and outputs it.

[0044] The clock IC 14 supplies each part with a clock synchronized with a signal oscillated by an oscillator (OSC) 25. In Fig. 4, the oscillator is abbreviated as "OSC" for convenience.

[0045] The controller 10 performs digital signal processing, including, for example, basic control or modulation / demodulation for data communication. The controller 10 modulates data acquired in the wired LAN_PHY block 23 to generate a transmission signal and outputs the signal to the AFE 24. The controller 10 also demodulates a reception signal input from the transmission coil acquired in the AFE 24 to generate reception data and outputs the reception data to the wired LAN_PHY block 23.

[0046] Data communication by the PLC adapter P1 is performed in the following procedure.

[0047] In the case of transmission, the controller 10 inputs data to be transmitted via the wired LAN_PHY block 23 and performs digital signal processing on the input data to generate a digital signal to be transmitted. This generated digital signal is input from the controller 10 to the AFE 24 and converted into an analog signal. This converted analog signal is transmitted to another transmission coil via a transmission coil (e.g., transmission coil CL1). In the digital signal processing, for example, modulation by ODFM is performed.

[0048] In the case of reception, an analog signal received from another transmission coil via a transmission coil (e.g., transmission coil CL1) is input to the AFE 24, where it is gain-adjusted and then converted into a digital signal. This converted digital signal is input to the controller 10. The controller 10 performs digital signal processing on the input digital signal to obtain digital data. When this digital data is transmitted (e.g., sent) for multi-hop transmission, the transmission procedure described above is performed in the same manner.

[0049] 5 is a block diagram showing an example of the functional configuration of the CPU 11 of PLC adapters P0, P1, P2, P3, P4, P5, P6, P7, and P8. Since the functional configuration of the CPU of each PLC adapter may be the same, the following description will be given using the CPU 11 of PLC adapter P1 as an example. In other words, the following description can be similarly applied to the description of the functional configuration of each of the CPUs of PLC adapters P0, P2 to P8.

[0050] The CPU 11 has, as its functional configuration, a packet analysis unit 101, an authentication processing unit 102, a link cost calculation unit 103, a topology management unit 104, and a packet generation unit 105. H packets, authentication packets, and normal packets (e.g., data acquired by the AUV 30) are input to the CPU 11. H packets are packets that are broadcast simultaneously from one PLC adapter to all PLC adapters that are currently connected (in other words, connected so that data communication via the transmission coil is possible) prior to the authentication process (see FIG. 6) performed between the PLC adapters. Authentication packets are packets that are sent and received during the authentication process (see FIG. 6) performed between the PLC adapters.

[0051] The packet analysis unit 101 analyzes the data structure of various input packets (specifically, H packet, authentication packet, normal packet) to determine the type of packet, and allocates the packet to a forwarding destination based on the determination result. For example, if the packet analysis unit 101 determines that the input packet is an H packet, it sends the H packet to the link cost calculation unit 103. For example, if the packet analysis unit 101 determines that the input packet is an authentication packet, it sends the authentication packet to the authentication processing unit 102. For example, if the packet analysis unit 101 determines that the input packet is a normal packet, it sends the normal packet to the topology management unit 104.

[0052] When the authentication processing unit 102 receives an authentication packet from the packet analysis unit 101, it uses the authentication packet to perform authentication processing with the PLC adapter that is the sender of the authentication packet. The authentication processing unit 102 sends an authentication packet, which is a packet generated during the authentication processing, or a response to an authentication packet sent from another PLC adapter, to the topology management unit 104. Details of the operation procedure of the authentication processing will be described later with reference to FIG. 6.

[0053] When the link cost calculation unit 103 receives an H packet from the packet analysis unit 101, it uses the H packet to calculate a link cost (an example of a first cost or a second cost) indicating the reception quality of the H packet received by the PLC adapter of the CPU 11 from the source PLC adapter. The link cost calculation unit 103 writes the link cost calculation result into the data structure of the H packet. The H packet also stores the value of each link cost when the H packet is sent from the PLC adapter P0 (hereinafter referred to as "M-PLC"). The link cost calculation unit 103 sends the H packet storing the link cost calculation result to the topology management unit 104.

[0054] The topology management unit 104 manages data indicating the topology (i.e., the connection configuration of each of the PLC adapters P1 to P7 that make up the wireless data transmission system 100) generated by the M-PLC (i.e., the PLC adapter P0), and based on this data, allocates and outputs various packets to an output destination (for example, the PLC_MAC block 13 or the packet generation unit 105). This topology data is saved in the topology management unit 104 of each of the CPUs 11 of the PLC adapters P0 to P8. The topology management unit 104 of the CPU 11 of the M-PLC (i.e., the PLC adapter P0) generates (forms) the topology based on each link cost calculated by the link cost calculation unit 103 in response to an H packet sent from each of one or more PLC adapters that are the subject of authentication processing. Details of an example of the processing procedure for generating a topology using link costs will be described later with reference to FIG. 9 or FIG. 12.

[0055] When the packet generation unit 105 receives an authentication packet or a normal packet from the topology management unit 104, it generates and outputs a packet for data communication to another transmission coil as a destination or an H packet for performing authentication processing.

[0056] An example of the processing procedure for authentication processing performed between PLC adapters will now be described with reference to Fig. 6. Fig. 6 is a sequence diagram showing an example of the processing procedure for authentication processing performed between M-PLC and t-PLC. In explaining Fig. 6, for simplicity, the processing procedure for authentication processing performed between M-PLC (i.e., PLC adapter P0 that generates the topology) and a PLC adapter to be authenticated by PLC adapter P0 (hereinafter referred to as "t-PLC") will be simply explained. The processing shown in Fig. 6 is mainly executed by the authentication processing unit 102 of each CPU 11. Prior to explaining Fig. 6, the M-PLC transmits an H packet to the t-PLC, and the t-PLC receives the H packet sent from the M-PLC.

[0057] 6, the t-PLC issues an authentication packet including a participation request frame to the M-PLC (i.e., PLC adapter P0) of the network it wishes to join (e.g., wireless data transmission system 100) and sends it to the M-PLC (St1). When the M-PLC receives the authentication packet sent from the t-PLC in step St1, it sets a predetermined text string to create an authentication packet and sends it to the requesting t-PLC (i.e., the t-PLC that issued the authentication packet sent in step St1) (St2).

[0058] The t-PLC encodes the predetermined text string included in the authentication packet sent in step St2 using a unique key that the t-PLC has stored in advance in memory 20 or the like (for example, a unique key stored in advance in each of PLC adapters P0 to P8), generates an authentication packet including the encoded output text string, and sends it to the M-PLC (St3). When the M-PLC receives the authentication packet sent from the t-PLC in step St3, it decodes the encoded output text string included in the authentication packet using a unique key (see above) that has been set in advance and stored in memory 20 or the like (St4). The M-PLC also determines whether the decoded output text string matches the predetermined text string set in step St2 (St4). If the M-PLC determines that the decoded output text string matches the predetermined text string set in step St2 (in other words, if it determines that participation in the wireless data transmission system 100 is permitted), it encodes a network key specific to the wireless data transmission system 100 with the unique key (see above) and sends it to the t-PLC (St4).

[0059] The t-PLC decodes the encoded network key sent from the M-PLC in step St4 using the unique key (see above) to obtain the network key (St5). By obtaining this network key, the t-PLC is officially authenticated as a data communication destination of the M-PLC. When communicating data within the network (i.e., the wireless data transmission system 100), the t-PLC performs data communication by encoding or decoding using the network key (St5).

[0060] 6 is based on the 4-way handshake defined in the HD-PLC (High Definition Power Line Communication) standard, but the authentication process may be based on a method other than the above-mentioned standard. For example, it may be based on the G.hn (Gigabit Home Networking) standard, which is a unified standard for high-speed wired network communication technology, or the HomePlug (HomePlug Powerline Alliance) standard, which is an industry organization for power line communication.

[0061] (First operation example) Next, a first processing example of topology generation and multi-hop transmission between M-PLC and each t-PLC (specifically, t-PLC1, t-PLC2, t-PLC3, t-PLC4, t-PLC5, t-PLC6, t-PLC7, and PLC adapter P8 provided in AUV30) in the wireless data transmission system 100 according to the first embodiment will be described with reference to Figures 7, 8, and 9.

[0062] Fig. 7 is a diagram showing a first example of the arrangement of PLC adapters and link costs between the PLC adapters. Fig. 8 is a diagram showing a first topology example. Fig. 9 is a sequence diagram showing an example of the processing procedure of authentication processing performed between the various PLC adapters shown in Fig. 7. The authentication processing shown in Fig. 9 is executed at least once before the start of actual operation of the wireless data transmission system 100 according to the first embodiment, for example.

[0063] The PLC adapters shown in Fig. 7 (i.e., M-PLC, t-PLC1, t-PLC2, t-PLC3, t-PLC4, t-PLC5, t-PLC6, and t-PLC7) are arranged in accordance with the example of the arrangement of various PLC adapters constituting the wireless data transmission system 100 shown in Fig. 1. The numbers written in the middle of the lines connecting the PLC adapters indicate the link cost, which corresponds to the reception quality at one PLC adapter of an H packet transmitted (sent) from the other PLC adapter to the other PLC adapter.

[0064] For example, in Figure 7, the link cost between M-PLC and t-PLC1 is 10, the link cost between t-PLC1 and t-PLC2 is 12, and the link cost between t-PLC2 and t-PLC3 is 4. The link cost between t-PLC1 and t-PLC4 is 9, and the link cost between t-PLC4 and t-PLC5 is 10. The link cost between t-PLC1 and t-PLC7 is 11, and the link cost between t-PLC7 and t-PLC6 is 4.

[0065] Note that the link cost between t-PLC2 and t-PLC4 is 8, the link cost between t-PLC4 and t-PLC3 is 9, the link cost between t-PLC4 and t-PLC7 is 8, the link cost between t-PLC4 and t-PLC6 is 9, the link cost between t-PLC3 and t-PLC5 is 10, and the link cost between t-PLC6 and t-PLC5 is 10.

[0066] The topology TOP1 shown in Fig. 8 is generated by M-PLC (i.e., PLC adapter P0) in accordance with the processing procedure of the authentication processing shown in Fig. 9. Note that the topology TOP1 may also be generated by a PLC adapter other than M-PLC (for example, any of t-PLC1 to t-PLC7). According to this topology TOP1, a first multi-hop transmission route is formed as "M-PLC, t-PLC1, t-PLC2, t-PLC3," a second multi-hop transmission route is formed as "M-PLC, t-PLC1, t-PLC4, t-PLC5," and a third multi-hop transmission route is formed as "M-PLC, t-PLC1, t-PLC7, t-PLC6."

[0067] Therefore, for example, if AUV30 performs authentication processing with t-PLC3, data acquired by AUV30 during marine exploration, etc., will be transmitted in the order of "t-PLC3 → t-PLC2 → t-PLC1 → M-PLC" according to the first multi-hop transmission route.

[0068] Furthermore, for example, if AUV30 performs authentication processing with t-PLC5, data acquired by AUV30 during marine exploration, etc., will be transmitted in the order of "t-PLC5 → t-PLC4 → t-PLC1 → M-PLC" according to the second multi-hop transmission route.

[0069] Furthermore, for example, if AUV30 performs authentication processing with t-PLC6, the data acquired by AUV30 during marine exploration, etc., will be transmitted in the order of "t-PLC6 → t-PLC7 → t-PLC1 → M-PLC" according to the third multi-hop transmission route.

[0070] In Fig. 9, M-PLC simultaneously broadcasts an H packet to all t-PLCs (for example, t-PLC1, t-PLC2, t-PLC3, t-PLC4, t-PLC5, t-PLC6, and t-PLC7) (St11). Assume that only t-PLC1 receives the H packet in response to this broadcast. Then, the authentication process described with reference to Fig. 6 is executed between M-PLC and t-PLC1 (St11). This enables data communication between M-PLC and t-PLC1.

[0071] Next, t-PLC1 simultaneously broadcasts an H packet to the other t-PLCs (e.g., M-PLC, t-PLC2, t-PLC3, t-PLC4, t-PLC5, t-PLC6, and t-PLC7) other than its own terminal (St12). Assume that only t-PLC2, t-PLC4, and t-PLC7 receive the H packet in response to this broadcast. Then, the authentication process described with reference to FIG. 6 is executed between t-PLC2 and M-PLC via t-PLC1 (St12). Similarly, the authentication process described with reference to FIG. 6 is executed between t-PLC4 and M-PLC via t-PLC1 (St12). The authentication process described with reference to FIG. 6 is executed between t-PLC7 and M-PLC via t-PLC1 (St12). As a result, data communication becomes possible between M-PLC and t-PLC2 via t-PLC1, between M-PLC and t-PLC4 via t-PLC1, and between M-PLC and t-PLC7 via t-PLC1.

[0072] Furthermore, t-PLC2 simultaneously broadcasts an H packet to other t-PLCs (e.g., M-PLC, t-PLC1, t-PLC3, t-PLC4, t-PLC5, t-PLC6, and t-PLC7) other than its own terminal (St13). Assume that only t-PLC3 receives the H packet in response to this broadcast. Then, the authentication process described with reference to FIG. 6 is executed between t-PLC3 and M-PLC via t-PLC1 and t-PLC2 (St13). This enables data communication between M-PLC and t-PLC3 via t-PLC1 and t-PLC2.

[0073] Furthermore, t-PLC4 simultaneously broadcasts an H packet to other t-PLCs (e.g., M-PLC, t-PLC1, t-PLC2, t-PLC3, t-PLC5, t-PLC6, and t-PLC7) other than its own terminal (St14). Assume that only t-PLC5 receives the H packet in response to this broadcast. Then, the authentication process described with reference to FIG. 6 is executed between t-PLC5 and M-PLC via t-PLC1 and t-PLC4 (St14). This enables data communication between M-PLC and t-PLC5 via t-PLC1 and t-PLC4.

[0074] Furthermore, t-PLC7 simultaneously broadcasts an H packet to other t-PLCs (e.g., M-PLC, t-PLC1, t-PLC2, t-PLC3, t-PLC4, t-PLC5, and t-PLC6) other than its own terminal (St15). Assume that only t-PLC6 receives the H packet in response to this broadcast. Then, the authentication process described with reference to FIG. 6 is executed between t-PLC6 and M-PLC via t-PLC1 and t-PLC7 (St15). This enables data communication between M-PLC and t-PLC6 via t-PLC1 and t-PLC7.

[0075] Now, suppose that the t-PLC 7 has completed authentication processing with the M-PLC and is now connectable with the M-PLC, when the AUV 30 approaches the t-PLC 7 (St16). At this time, the t-PLC 7 and the AUV 30 prepare to connect to each other for data communication via the transmission coils CL7 and CL8.

[0076] The t-PLC7 transmits an H packet to the AUV30 (in other words, the PLC adapter P8) (St16). Assume that the PLC adapter P8 receives the H packet in response to this transmission. Then, the authentication process described with reference to FIG. 6 is executed between the PLC adapter P8 and the M-PLC via the t-PLC7 and t-PLC1 (St16). This enables data communication between the PLC adapter P8 (in other words, the AUV30) and the M-PLC via the t-PLC7 and t-PLC1. That is, the data acquired by the AUV30 is transmitted in the order PLC adapter P8 → t-PLC7 → t-PLC1 → M-PLC and acquired by the M-PLC (St17).

[0077] (Second operation example) Next, a second processing example of topology generation and multi-hop transmission between M-PLC and each t-PLC (specifically, t-PLC1, t-PLC2, t-PLC3, t-PLC4, t-PLC5, t-PLC6, t-PLC7, and PLC adapter P8 provided in AUV30) in the wireless data transmission system 100 according to the first embodiment will be described with reference to Figures 10, 11, and 12.

[0078] FIG. 10 is a diagram illustrating a second example of the arrangement of PLC adapters and the link costs between the PLC adapters. FIG. 11 is a diagram illustrating a second example topology. FIG. 12 is a sequence diagram illustrating an example of the processing procedure of authentication processing performed between the various PLC adapters illustrated in FIG. 10. The authentication processing illustrated in FIG. 12 is executed at least once, for example, before the start of actual operation of the wireless data transmission system 100 according to the first embodiment. In the description of FIG. 12, the same step numbers are assigned to the same descriptions as those in FIG. 9, and the description is simplified or omitted, and only different contents are described. In addition, in FIG. 12, the same processing procedure as the processing procedure for transmitting data acquired by the AUV30 illustrated in FIG. 9 to the M-PLC is executed in the same manner after generation of the topology TOP2, and therefore is not illustrated.

[0079] The PLC adapters shown in Fig. 10 (i.e., M-PLC, t-PLC1, t-PLC2, t-PLC3, t-PLC4, t-PLC5, t-PLC6, and t-PLC7) are arranged in accordance with the example of the arrangement of various PLC adapters constituting the wireless data transmission system 100 shown in Fig. 1. The numbers written in the middle of the lines connecting the PLC adapters indicate the link cost, which corresponds to the reception quality at one PLC adapter of an H packet transmitted (sent) from the other PLC adapter to the other PLC adapter.

[0080] For example, in FIG. 10, the link cost between M-PLC and t-PLC1 is 10, and the link cost between t-PLC1 and t-PLC2 is 12. However, as a difference from FIG. 7, the link cost between t-PLC2 and t-PLC3 is 50. In other words, compared to the state shown in FIG. 7, the link cost between t-PLC2 and t-PLC3 is higher, making it difficult to connect t-PLC2 and t-PLC3. The link cost between t-PLC1 and t-PLC4 is 9, and the link cost between t-PLC4 and t-PLC5 is 10. The link cost between t-PLC1 and t-PLC7 is 11, but as a difference from FIG. 7, the link cost between t-PLC7 and t-PLC6 is 50. In other words, compared to the state shown in FIG. 7, the link cost between t-PLC7 and t-PLC6 is higher, making it difficult to connect t-PLC7 and t-PLC6.

[0081] Note that the link cost between t-PLC2 and t-PLC4 is 8, the link cost between t-PLC4 and t-PLC3 is 9, the link cost between t-PLC4 and t-PLC7 is 8, the link cost between t-PLC4 and t-PLC6 is 9, the link cost between t-PLC3 and t-PLC5 is 10, and the link cost between t-PLC6 and t-PLC5 is 10.

[0082] The topology TOP2 shown in Fig. 11 is generated by M-PLC (i.e., PLC adapter P0) in accordance with the processing procedure of the authentication processing shown in Fig. 12. Note that the topology TOP2 may also be generated by a PLC adapter other than M-PLC (for example, any of t-PLC1 to t-PLC7). According to this topology TOP2, the following are formed: a first multihop transmission route "M-PLC, t-PLC1, t-PLC2", a second multihop transmission route "M-PLC, t-PLC1, t-PLC4, t-PLC5", a third multihop transmission route "M-PLC, t-PLC1, t-PLC4, t-PLC3", a fourth multihop transmission route "M-PLC, t-PLC1, t-PLC4, t-PLC6", and a fifth multihop transmission route "M-PLC, t-PLC1, t-PLC7".

[0083] Therefore, for example, if AUV30 performs authentication processing with t-PLC3, the data acquired by AUV30 during marine exploration, etc., will be transmitted in the order of "t-PLC3 → t-PLC4 → t-PLC1 → M-PLC" according to the third multi-hop transmission route.

[0084] Furthermore, for example, if AUV30 performs authentication processing with t-PLC2, data acquired by AUV30 during marine exploration or other activities will be transmitted in the order of "t-PLC2 → t-PLC1 → M-PLC" according to the first multi-hop transmission route.

[0085] Furthermore, for example, if AUV30 performs authentication processing with t-PLC6, data acquired by AUV30 during marine exploration, etc., will be transmitted in the order of "t-PLC6 → t-PLC4 → t-PLC1 → M-PLC" according to the fourth multi-hop transmission route.

[0086] In FIG. 12, t-PLC2 simultaneously broadcasts an H packet to other t-PLCs (e.g., M-PLC, t-PLC1, t-PLC3, t-PLC4, t-PLC5, t-PLC6, and t-PLC7) other than its own terminal (St21). Assume that only t-PLC1, t-PLC3, and t-PLC4 are able to receive the H packet in response to this broadcast. Furthermore, t-PLC4 simultaneously broadcasts an H packet to other t-PLCs (e.g., M-PLC, t-PLC1, t-PLC2, t-PLC3, t-PLC5, t-PLC6, and t-PLC7) other than its own terminal (St22). Assume that only t-PLC3, t-PLC5, and t-PLC6 are able to receive the H packet in response to this broadcast.

[0087] t-PLC3 calculates the link cost of the H packet transmitted from t-PLC2 and the link cost of the H packet transmitted from t-PLC4, and compares the calculation results.

[0088] Then, t-PLC3 compares the sum of the link cost indicating the reception quality of the H packet sent in step St21 (e.g., "50" shown in Figure 10) and the link cost indicating the reception quality from t-PLC2 to M-PLC (e.g., "12" + "10" = "22" shown in Figure 10) with the sum of the link cost indicating the reception quality of the H packet sent in step St22 (e.g., "9" shown in Figure 10) and the link cost indicating the reception quality from t-PLC4 to M-PLC (e.g., "9" + "10" = "19" shown in Figure 10) (St22).

[0089] Based on the comparison in step St22, the t-PLC3 determines the t-PLC4 with the smallest total link cost (i.e., the best connection status) as the data communication partner for multi-hop transmission (St22). Then, the authentication process described with reference to Fig. 6 is executed between the t-PLC3 and the M-PLC via the t-PLC1 and t-PLC4 (St22). This enables data communication between the M-PLC and the t-PLC3 via the t-PLC1 and t-PLC4.

[0090] Furthermore, t-PLC7 simultaneously broadcasts an H packet to the other t-PLCs (e.g., M-PLC, t-PLC1, t-PLC2, t-PLC3, t-PLC4, t-PLC5, and t-PLC6) other than its own terminal (St23). Assume that only t-PLC6 receives the H packet in response to this broadcast. Furthermore, t-PLC4 simultaneously broadcasts an H packet to the other t-PLCs (e.g., M-PLC, t-PLC1, t-PLC2, t-PLC3, t-PLC5, t-PLC6, and t-PLC7) other than its own terminal (St24). Assume that only t-PLC5 and t-PLC6 receive the H packet in response to this broadcast. Then, the authentication process described with reference to FIG. 6 is executed between t-PLC5 and M-PLC via t-PLC1 and t-PLC4 (St24). In addition, t-PLC6 compares the sum of the link cost indicating the reception quality of the H packet sent in step St23 (e.g., "50" shown in Figure 10) and the sum of the link costs indicating the reception quality from t-PLC7 to M-PLC (e.g., "11" + "10" = "21" shown in Figure 10) with the sum of the link cost indicating the reception quality of the H packet sent in step St24 (e.g., "9" shown in Figure 10) and the sum of the link costs indicating the reception quality from t-PLC4 to M-PLC (e.g., "9" + "10" = "19" shown in Figure 10) (St24).

[0091] Based on the comparison in step St24, the t-PLC6 determines the t-PLC4 with the smallest total link cost (i.e., the best connection status) as the data communication partner for multi-hop transmission (St24). Then, the authentication process described with reference to Fig. 6 is executed between the t-PLC6 and the M-PLC via the t-PLC1 and t-PLC4 (St24). This enables data communication between the M-PLC and the t-PLC6 via the t-PLC1 and t-PLC4.

[0092] As described above, the wireless data transmission system 100 according to the first embodiment includes N (N: an integer of 2 or more) transmission coils CL1 to CL7, each having an aperture and arranged in water with the aperture facing vertically upward, and N communication devices (e.g., PLC adapters P1 to P7) that are connected one-to-one to a connection transmission coil that is one of the N transmission coils and perform data communication via the connection transmission coil. The communication devices perform multi-hop transmission of data acquired by a data acquisition device (e.g., AUV 30) that can move underwater, based on a previously generated topology indicating the connection form between the N communication devices and on magnetic field coupling occurring between the connection transmission coil and at least one other adjacent connection transmission coil.

[0093] As a result, the wireless data transmission system 100 can perform multi-hop transmission of data acquired by the AUV 30 during marine exploration with N transmission coils arranged horizontally over a wide area of the environment to be explored (e.g., underwater or on the seabed), thereby enabling high-capacity data communication to be performed quickly and stably.

[0094] Furthermore, the communication device performs a topology generation process based on the transmission of a predetermined packet (e.g., an H packet) to at least one other communication device and a reception response to the transmitted predetermined packet. This allows a topology that defines the packet destination and source to be efficiently generated while taking into account the potentially fluid communication state between transmission coils placed underwater, where ocean currents or marine life may cause interference, thereby improving the data communication quality of the wireless data transmission system 100.

[0095] Furthermore, when the communication device receives data sent from another connected transmission coil that is a source defined by the topology, it controls the transmission power of the received data to a predetermined value and transmits the data in a multi-hop manner to another connected transmission coil that is a destination defined by the topology. This makes it possible to suppress deterioration in the received signal level of data acquired by the AUV 30 during ocean exploration or the like each time the data is transmitted between transmission coils, enabling the wireless data transmission system 100 to perform stable data communication.

[0096] The wireless data transmission system 100 further includes a master communication device (e.g., a PLC adapter P0) that serves as a master device for the N communication devices and is connected to enable data communication with each of the N communication devices. When a communication device receives a predetermined packet from each of at least two adjacent relay devices (e.g., t-PLC2 and t-PLC4 for t-PLC3), the communication device determines a relay device to which the data communication will be performed based on the sum of a first cost indicating the reception quality of the predetermined packet received from each relay device (e.g., the link cost of an H packet received by t-PLC3 from t-PLC2 or t-PLC4) and a second cost indicating the reception quality of the predetermined packet from each relay device to the master communication device (e.g., the sum of the link costs from t-PLC2 to M-PLC or the sum of the link costs from t-PLC4 to M-PLC). This allows the wireless data transmission system 100 to select a PLC adapter that is less likely to be disconnected (in other words, that facilitates data communication) even if the communication environment may fluctuate depending on the underwater environment, which may cause interference from ocean currents or marine life, thereby ensuring stable data communication.

[0097] Furthermore, each of the N communication devices is placed underwater, which allows the wireless data transmission system 100 to perform high-volume data communication at high speed and stably even underwater (for example, under the sea).

[0098] The master communication device is installed on a surface facility (e.g., ship SH1). The communication devices transmit data to the master communication device through multi-hop transmission. This allows the wireless data transmission system 100 to efficiently collect data acquired by the AUV 30 during ocean exploration or the like in a management device such as PC1 installed on the surface facility such as ship SH1.

[0099] Although various embodiments have been described above with reference to the drawings, it goes without saying that the present disclosure is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications, alterations, substitutions, additions, deletions, and equivalents within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present disclosure. Furthermore, the components of the various embodiments described above may be combined in any manner without departing from the spirit of the invention. [Industrial Applicability]

[0100] The present disclosure is useful for a data transmission system and a data transmission method that perform high-speed, stable, and large-capacity data communication over a wide area, such as underwater. [Explanation of symbols]

[0101] 1 PC 10 Controller 11 CPU 12 PLC_PHY blocks 13 PLC_MAC Block 14 CLK 15 GPIO 16 UART 17 Flash memory interface 18 SDRAM controller 19 Wired LAN_MAC Block 20 memory 21. Flash Memory 22 SDRAM 23 Wired LAN PHY Block 24 AFE 25 OSC 30 AUV 70 Power equipment 100 Wireless Data Transmission System 101 Packet Analysis Unit 102 Authentication processing section 103 Link cost calculation unit 104 Topology Management Unit 105 Packet Generation Unit CL1, CL2, CL3, CL4, CL5, CL6, CL7, CL8 transmission coils P0, P1, P2, P3, P4, P5, P6, P7, P8 PLC adapter

Claims

1. N (N: integer equal to or greater than 2) transmission coils each having an open surface and disposed in water with the open surface facing vertically upward; N communication devices that are connected one-to-one to a connection transmission coil that is any one of the N transmission coils and perform data communication via the connection transmission coil, the communication device performs multi-hop transmission of data acquired by the underwater mobile data acquisition device based on a topology indicating a connection form between the N communication devices generated in advance and on magnetic field coupling occurring between the connection transmission coil and at least one other adjacent connection transmission coil; Wireless data transmission system.

2. the communication device performs a process of generating the topology based on transmission of a predetermined packet to at least one other communication device and a reception response to the transmitted predetermined packet; 2. The wireless data transmission system according to claim 1.

3. When the communication device receives the data transmitted from the other connected transmission coil that is a transmission source defined in the topology, the communication device controls transmission power of the received data to a predetermined value and transmits the data in a multi-hop manner to the other connected transmission coil that is a transmission destination defined in the topology.

2. The wireless data transmission system according to claim 1.

4. a master communication device that serves as a parent device for the N communication devices and is connected to each of the N communication devices so as to be able to perform data communication with the master communication device; When the communication device receives the predetermined packet from each of at least two adjacent relay devices that are the communication devices, the communication device determines the relay device to which the data communication will be performed based on the sum of a first cost indicating the reception quality of the predetermined packet received from each of the relay devices and a second cost indicating the reception quality of the predetermined packet from each of the relay devices to the master communication device.

3. The wireless data transmission system according to claim 2.

5. Each of the N communication devices is disposed underwater.

2. The wireless data transmission system according to claim 1.

6. the master communication device is located at a floating facility; the communication device transmits the data to the master communication device through the multi-hop transmission; 5. The wireless data transmission system according to claim 4.

7. N (N: an integer of 2 or more) transmission coils each having an opening and disposed in water with the opening facing vertically upward, and N communication devices each connected one-to-one to a connection transmission coil that is any one of the N transmission coils and performing data communication via the connection transmission coil, transmitting data acquired by the underwater mobile data acquisition device in a multi-hop manner based on a topology indicating a connection form between the N communication devices and magnetic field coupling occurring between the connection transmission coil and at least one other adjacent connection transmission coil; Wireless data transmission method.

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