Wireless Power and Data Transmission System of Submarine Cable-Inspecting Robot Fish and Its Time-Sharing Multiplexing Method

In this paper, a hybrid system topology with one-way wireless charging function and the function of the bi-directional data communication is proposed for the problem of electric energy replenishment and data transmission faced by robot fish in the implementation of autonomous submarine cable inspection. Three working modes of the system and the time-sharing multiplexing method are studied. In the power transmission mode, high-efficiency wireless charging is realized by utilizing the transmission characteristics of a series–series (SS)-type resonant network which involves series resonant networks in both the primary side and the secondary side. In the alignment detection and handshake communication mode, the charging platform distance recognition and the handshake signal transmission are implemented through a series–parallel (SP)-type resonant network based on the ASK (amplitude shift keying) modulation method. In the high-speed data transmission mode, the reverse (secondary to primary) high-speed transmission of the inspection data is achieved through a SP-type resonant network based on the OFDM (orthogonal frequency division multiplexing) modulation method. The three modes share the same coupled coils via a reconfigurable resonant network. The working principle of the system is expounded, the system characteristics under each working mode are analyzed, and the time-division multiplexing control strategy is given. The rationality and effectiveness of the scheme are verified by experiments.


Introduction
With the further development of the 21st Century Maritime Silk Road, the marine economy and energy interconnection have become of key interest, which puts higher demands on energy security and power supply reliability. Compared with the mainland power supply, the special coastal environment of the coast makes the overhead lines subject to many restrictions, as a result, the submarine cable becomes the first choice for island power supply. Due to the special and complex marine environment, the safety operation and maintenance of submarine cables confronts great challenges. Due to the special and complex nature of the marine environment, the safety operation and maintenance of submarine cables is facing severe challenges. Setting warning signs, submarine cable monitoring and alarming, and improving the submarine cable manufacturing process are the main means of strengthening the protection of submarine cables. However, these methods are limited to monitoring and protection in areas above the sea surface. It is impossible to monitor the complex seabed conditions where the submarine cables are located [1]. Aiming at this practical problem, an ideal solution is taking use of underwater robots to monitor the submarine cable and the seabed environment to achieve the It is docked on the platform of underwater wireless charging and data transmission after inspection of robot fish. The platform identifies the load by the resonant coil current magnitude, and sends a handshake command after identifying the load. The robot fish responds to the command and sends battery status information to the platform. After the platform and the robot fish shake hands successfully, the platform wirelessly charges them and the robot fish transmits the inspection data to the monitoring center on the shore through the platform after the charging is completed.
According to the wireless charging requirements of sea cable-inspection robot fish and its forward and reverse data transmission requirements, the structure of the energy and signal time division transmission system, as shown in Figure 2, is proposed. As we can see in Figure 2, the main topology consists of a BUCK converter, a full bridge inverter, a coupled reconfigurable resonant network, a rectifier, and the load. The BUCK converter regulates the transferred power by adjusting the input voltage of the inverter. The inverter converts the dc voltage into high frequency square wave ac voltage and stimulates wireless power transmission via the coupled resonant network. Then the rectifier converts the induced ac voltage into dc voltage and output to power the load. The coupled reconfigurable resonant network consists of a series-series (SS)-type network for power transfer (labeled by the red lines in Figure 2), a series-parallel (SP)-type for distance detection and handshake communication (labeled by the green lines in Figure 2), a SP-type network for high speed signal transmitting (labeled by the blue lines in Figure 2), and the three networks can be configured by the switches S5   In the scheme shown in Figure 2, there are three modes of operation: Mode 1 is the energy transmission mode, which is to achieve the wireless charging function of the charging platform to the robot fish. In this mode, the main circuit topology of the system is: It is docked on the platform of underwater wireless charging and data transmission after inspection of robot fish. The platform identifies the load by the resonant coil current magnitude, and sends a handshake command after identifying the load. The robot fish responds to the command and sends battery status information to the platform. After the platform and the robot fish shake hands successfully, the platform wirelessly charges them and the robot fish transmits the inspection data to the monitoring center on the shore through the platform after the charging is completed.
According to the wireless charging requirements of sea cable-inspection robot fish and its forward and reverse data transmission requirements, the structure of the energy and signal time division transmission system, as shown in Figure 2, is proposed. As we can see in Figure 2, the main topology consists of a BUCK converter, a full bridge inverter, a coupled reconfigurable resonant network, a rectifier, and the load. The BUCK converter regulates the transferred power by adjusting the input voltage of the inverter. The inverter converts the dc voltage into high frequency square wave ac voltage and stimulates wireless power transmission via the coupled resonant network. Then the rectifier converts the induced ac voltage into dc voltage and output to power the load. The coupled reconfigurable resonant network consists of a series-series (SS)-type network for power transfer (labeled by the red lines in Figure 2), a series-parallel (SP)-type for distance detection and handshake communication (labeled by the green lines in Figure 2), a SP-type network for high speed signal transmitting (labeled by the blue lines in Figure 2), and the three networks can be configured by the switches S 5 and S 6 . It is docked on the platform of underwater wireless charging and data transmission after inspection of robot fish. The platform identifies the load by the resonant coil current magnitude, and sends a handshake command after identifying the load. The robot fish responds to the command and sends battery status information to the platform. After the platform and the robot fish shake hands successfully, the platform wirelessly charges them and the robot fish transmits the inspection data to the monitoring center on the shore through the platform after the charging is completed.
According to the wireless charging requirements of sea cable-inspection robot fish and its forward and reverse data transmission requirements, the structure of the energy and signal time division transmission system, as shown in Figure 2, is proposed. As we can see in Figure 2, the main topology consists of a BUCK converter, a full bridge inverter, a coupled reconfigurable resonant network, a rectifier, and the load. The BUCK converter regulates the transferred power by adjusting the input voltage of the inverter. The inverter converts the dc voltage into high frequency square wave ac voltage and stimulates wireless power transmission via the coupled resonant network. Then the rectifier converts the induced ac voltage into dc voltage and output to power the load. The coupled reconfigurable resonant network consists of a series-series (SS)-type network for power transfer (labeled by the red lines in Figure 2), a series-parallel (SP)-type for distance detection and handshake communication (labeled by the green lines in Figure 2), a SP-type network for high speed signal transmitting (labeled by the blue lines in Figure 2), and the three networks can be configured by the switches S5 and S6.  In the scheme shown in Figure 2, there are three modes of operation: Mode 1 is the energy transmission mode, which is to achieve the wireless charging function of the charging platform to the robot fish. In this mode, the main circuit topology of the system is: In the scheme shown in Figure 2, there are three modes of operation: Mode 1 is the energy transmission mode, which is to achieve the wireless charging function of the charging platform to the robot fish. In this mode, the main circuit topology of the system is: BUCK + full bridge inverter + SS (primary side series compensation, secondary side series compensation) resonant network + rectifier + load (robot fish battery). The reconfigurable resonant network is configured as SS-type by turning off S 5 and S 6 . Battery charging power is regulated by adjusting the duty cycle of the BUCK link switch S a . The switching frequency of the full-bridge inverter link is the same as the resonant frequency f 0 of the SS resonant network, which can reduce switching losses and reduce EMI (electromagnetic interference) [16,17] in the soft-switching operation mode of the inverter switches.
Mode 2 is an alignment detection and handshake communication mode, which is to complete the transmission and reception of the handshake signal from the charging platform to the robot fish, and the robot fish calculates the distance to the platform by recognizing the signal strength. The reconfigurable resonant network is configured as SP-type by turning off S 5 and turning on S 6 . This mode uses ASK (amplitude shift keying) modulation to transmit data. The primary-to-secondary signal transmission modulates the digital signal with the inverter bridge control frequency f 1 (f 1 >>f 0 ), because the control frequency of the inverter bridge is much larger than the resonant soft switching frequency f 0 of the resonant network, the system operates in a non-resonant state. Therefore, the transmission power is greatly reduced with a large loop impedance and achieves low-power data transmission. Because the resonant frequency (f 0 ) of secondary side's power transmission channel is much lower than the primary modulation frequency (f 1 ), the pickup voltage will not be able to charge the battery after rectification and filtering, so that the series resonant circuit is in an open state and does not consume power. When the switch S 6 of the signal receiving module is closed, the capacitor C 2 and the inductance L s of the pickup coil constitute a parallel resonant circuit, whose frequency is close to f 1 , so that a high signal voltage can be picked up. During the process of the robot fish approaching the charging platform, the amplitude of the picked-up signal gradually increases, and the robot fish can determine the offset distance to the platform based on the amplitude of the picked-up signal. When the amplitude of the picked-up signal reaches the maximum value, it indicates that the robot fish is directly above the charging platform, and then the robot fish can be controlled to park at the point. At the same time, the voltage can be demodulated by the signal demodulation circuit to demodulate the handshake signal sent by the charging platform. The robot fish can transmit a feedback signal to the platform by controlling the switch S 6 to be on or off, and the platform demodulates the handshake signal from the envelope of the output current.
Mode 3 is a high-speed signal transmission mode, which is to complete the inspection data transmission from the robot fish to the charging platform. The reconfigurable resonant network is configured as SP-type by turning on S 5 and turning off S 6 . Because the amount of inspection data is large, it is designed as a high-speed signal transmission channel based on OFDM (orthogonal frequency division multiplexing) mode. The data to be transmitted is loaded into the SP-type resonant transmission network composed of L S , C 3 , L P , and C 1 through the signal modulation transmitting module. The signal secondary side demodulates the transmitted inspection data from the capacitance voltage signal of the P-type (parallel-type) pickup network.
As described above, the three working modes share the same coupled transmitting and receiving coils L p and L s . The system runs among the three working modes through a time-sharing multiplexing method to achieve accurate parking, high-efficiency wireless charging, and high-speed data transmission. Next, the characteristics of the three working modes will be analyzed and then the time-sharing multiplexing method for mode switching will be given.

Characteristics of Energy Transmission Mode
In the energy transfer mode, the equivalent circuit of the system is shown in Figure 3. The energy wireless transmission is realized by the SS resonance network, and the received electric energy is rectified and filtered, and then output to the battery for charging, and the input voltage is adjusted through the BUCK link.  The voltage equation of the secondary resonant circuit can be obtained as follows: In the continuous state of charge of the current, the battery charging voltage can be approximated as follows: When the operating frequency is consistent with the secondary side resonant frequency, the following Equation (3) can be established: During the charging process, the battery voltage rises slowly and steadily. Therefore, it can be known from the above equation that the primary side resonant current IP also follows the battery voltage slowly changing. In the case of ignoring the secondary side internal resistance, the magnitude of IP can be approximated by the following formula: The primary resonant loop voltage can be expressed by Equation (5).
When the operating frequency is consistent with the primary side resonant frequency and the primary internal resistance RP is ignored, it is known from Equation (5) that the amplitude of the secondary current Is is approximately determined by Equation (6): Therefore, from Equations (4) and (6), the topology in which the primary and secondary sides are series resonant is used. In battery charging, the system main circuit topology has the following energy transmission characteristics: The amplitude of the primary side resonant current IP is approximately determined by the output voltage Uop, and the charging power is determined by the input voltage UP. When designing the parameters, it is necessary to meet the same resonance parameters of the primary and secondary sides, as follows: The voltage equation of the secondary resonant circuit can be obtained as follows:

Characteristics of Alignment Detection and Handshake Communication Mode
In the continuous state of charge of the current, the battery charging voltage can be approximated as follows: When the operating frequency is consistent with the secondary side resonant frequency, the following Equation (3) can be established: During the charging process, the battery voltage rises slowly and steadily. Therefore, it can be known from the above equation that the primary side resonant current I P also follows the battery voltage slowly changing. In the case of ignoring the secondary side internal resistance, the magnitude of I P can be approximated by the following formula: The primary resonant loop voltage can be expressed by Equation (5).
When the operating frequency is consistent with the primary side resonant frequency and the primary internal resistance R P is ignored, it is known from Equation (5) that the amplitude of the secondary current I s is approximately determined by Equation (6): Therefore, from Equations (4) and (6), the topology in which the primary and secondary sides are series resonant is used. In battery charging, the system main circuit topology has the following energy transmission characteristics: The amplitude of the primary side resonant current I P is approximately determined by the output voltage U op , and the charging power is determined by the input voltage U P . When designing the parameters, it is necessary to meet the same resonance parameters of the primary and secondary sides, as follows:

Characteristics of Alignment Detection and Handshake Communication Mode
The equivalent topology of the handshake communication signal transmission is shown in Figure 4. When the handshake communication signal is transmitted, the secondary side switch S 6 is closed, so that C 2 is connected in parallel with the resonant coil. The primary side modulates the signal in the ASK mode, and the signal received by the secondary side is reflected as the amplitude change of the C 2 terminal voltage, and the control command signal can be obtained by demodulating the voltage characteristic. The equivalent topology of the handshake communication signal transmission is shown in Figure 4. When the handshake communication signal is transmitted, the secondary side switch S6 is closed, so that C2 is connected in parallel with the resonant coil. The primary side modulates the signal in the ASK mode, and the signal received by the secondary side is reflected as the amplitude change of the C2 terminal voltage, and the control command signal can be obtained by demodulating the voltage characteristic.  It can be seen from Figure 4 that when the handshake communication signal is transmitted, the resonant network topology is equivalent to the SP topology. The total impedance of the secondary side resonant circuit can be expressed as Equation (8): where RL is the input impedance of the positive signal receiving module, and its resistance is large.
According to Ohm's law, the resonant current of the pick-up loop can be calculated at this time.
Where IP is the primary side transmitting coil current, and when the resonant network input voltage is UP, the primary side current IP is represented by Equation (10).
The equivalent impedance ZP is established by the following equation: The parallel Equations (9) and (10) can obtain the secondary side resonance voltage, that is, the input voltage of the handshake communication signal receiving module is expressed as Equation (12): From Equation (12), the voltage gain of the signal transmission channel is established by Equation (13): It can be seen from Figure 4 that when the handshake communication signal is transmitted, the resonant network topology is equivalent to the SP topology. The total impedance of the secondary side resonant circuit can be expressed as Equation (8): where R L is the input impedance of the positive signal receiving module, and its resistance is large. According to Ohm's law, the resonant current of the pick-up loop can be calculated at this time.
where I P is the primary side transmitting coil current, and when the resonant network input voltage is U P , the primary side current I P is represented by Equation (10).
The equivalent impedance Z P is established by the following equation: The parallel Equations (9) and (10) can obtain the secondary side resonance voltage, that is, the input voltage of the handshake communication signal receiving module is expressed as Equation (12): From Equation (12), the voltage gain of the signal transmission channel is established by Equation (13): The frequency response function of the forward data transmission channel is obtained by the following equation: Under the parameters shown in Table 1, the frequency response characteristic curve is shown in Figure 5 below. According to the frequency response characteristic curve, 200 kHz with a gain of about −37 dB is selected as the communication frequency, which not only ensures the signal strength, but also makes the power consumption reach a relatively low level. The frequency response function of the forward data transmission channel is obtained by the following equation: Under the parameters shown in Table 1, the frequency response characteristic curve is shown in Figure 5 below. According to the frequency response characteristic curve, 200 kHz with a gain of about −37 dB is selected as the communication frequency, which not only ensures the signal strength, but also makes the power consumption reach a relatively low level.

Characteristics of High-Speed Signal Transmission Mode
Through the SP high-frequency resonant network built on the coupled coil, high-speed signal transmission is achieved from robot fish to charging platform based on OFDM [18].
In the high-speed signal transmission mode, the equivalent circuit of the system is shown in Figure 6.

Characteristics of High-Speed Signal Transmission Mode
Through the SP high-frequency resonant network built on the coupled coil, high-speed signal transmission is achieved from robot fish to charging platform based on OFDM [18].
In the high-speed signal transmission mode, the equivalent circuit of the system is shown in Figure 6.

Characteristics of High-Speed Signal Transmission Mode
Through the SP high-frequency resonant network built on the coupled coil, high-speed signal transmission is achieved from robot fish to charging platform based on OFDM [18].
In the high-speed signal transmission mode, the equivalent circuit of the system is shown in Figure 6. During data transmission, it is loaded into the SP resonance network by high-frequency modulation. In order to meet the high-speed data transmission requirements, the communication band of OFDM is selected in the frequency band of 2 to 30 MHz. The resonant frequency is set to 10 MHz, and the frequency response curve of the reverse data transmission channel is as shown in Figure 7. During data transmission, it is loaded into the SP resonance network by high-frequency modulation. In order to meet the high-speed data transmission requirements, the communication band of OFDM is selected in the frequency band of 2 to 30 MHz. The resonant frequency is set to 10 MHz, and the frequency response curve of the reverse data transmission channel is as shown in Figure 7. As shown in Figure 7, the signal transmission characteristic of the SP resonant network has a small attenuation in the frequency range of 2 to 28 MHz, and is suitable for OFDM carrier communication.

Time-Sharing Multiplexing Strategy for Mode Switching
When the inspection robot fish returns to the charging platform, in order to carry out efficient and reliable power supply and data transmission, the time-sharing multiplexing strategy for mode switching between the three working modes is shown in Figure 8. In the stage of standby, the charging platform periodically adjusts the handshake signal with the robot fish by inverter bridge in the modulation mode of AFK, and waits for the robot fish to respond. During the process of the robot fish approaching the platform, the robot fish reaches the top of the charging platform and performs a berth at the maximum point of the signal amplitude by detecting the amplitude of the received signal to determine the alignment between the platform and the robot fish. After the robot fish's berth is completed, the handshake signal sent by the platform is received and the feedback signal is modulated by the switching of switch S6. The charging platform demodulates the signal returned by the robot fish by detecting the change of the coil current, and As shown in Figure 7, the signal transmission characteristic of the SP resonant network has a small attenuation in the frequency range of 2 to 28 MHz, and is suitable for OFDM carrier communication.

Time-Sharing Multiplexing Strategy for Mode Switching
When the inspection robot fish returns to the charging platform, in order to carry out efficient and reliable power supply and data transmission, the time-sharing multiplexing strategy for mode switching between the three working modes is shown in Figure 8. As shown in Figure 7, the signal transmission characteristic of the SP resonant network has a small attenuation in the frequency range of 2 to 28 MHz, and is suitable for OFDM carrier communication. In the stage of standby, the charging platform periodically adjusts the handshake signal with the robot fish by inverter bridge in the modulation mode of AFK, and waits for the robot fish to respond. During the process of the robot fish approaching the platform, the robot fish reaches the top of the charging platform and performs a berth at the maximum point of the signal amplitude by detecting the amplitude of the received signal to determine the alignment between the platform and the robot fish. After the robot fish's berth is completed, the handshake signal sent by the platform is received and the feedback signal is modulated by the switching of switch S6. The charging platform demodulates the signal returned by the robot fish by detecting the change of the coil current, and enters the charging mode if the feedback signal is correct. During the charging process, the primary In the stage of standby, the charging platform periodically adjusts the handshake signal with the robot fish by inverter bridge in the modulation mode of AFK, and waits for the robot fish to respond. During the process of the robot fish approaching the platform, the robot fish reaches the top of the charging platform and performs a berth at the maximum point of the signal amplitude by detecting the amplitude of the received signal to determine the alignment between the platform and the robot fish. After the robot fish's berth is completed, the handshake signal sent by the platform is received and the feedback signal is modulated by the switching of switch S 6 . The charging platform demodulates the signal returned by the robot fish by detecting the change of the coil current, and enters the charging mode if the feedback signal is correct. During the charging process, the primary side collects current and voltage on the coil, and judges whether the charging is completed by calculating the equivalent impedance. After charging is completed, the robot fish enters the high-speed data transmission mode and transmits the submarine cable-inspection data packet. When all the data is sent, the charging platform checks whether the data is complete and sends a response. If the data is sent correctly, the robot fish enters the inspection state again, and the charging platform enters standby state.
The system workflow is shown in Figure 9.

Experimental Study
In order to verify the feasibility of the wireless power and data transmission scheme of the shared channel mentioned above, the experimental device is built according to the system topology diagram shown in Figure 2, and the system parameters are designed as shown in Table 1 according to the parameter design method proposed in [19,20]. The power and data transmission performance and various indicators of the system are further verified by experiments.

Experimental Study
In order to verify the feasibility of the wireless power and data transmission scheme of the shared channel mentioned above, the experimental device is built according to the system topology diagram shown in Figure 2, and the system parameters are designed as shown in Table 1 according to the parameter design method proposed in [19,20]. The power and data transmission performance and various indicators of the system are further verified by experiments.
The experimental prototype diagram is shown in Figure 10. The prototype includes power conversion, signal modulation and demodulation, coupling mechanism, and load composition. The power conversion part performs high-frequency inversion on the direct current and necessary overcurrent and overvoltage protection, realizes amplitude amplification by compensating the network, generates an alternating magnetic field on the resonant network, and transmits to the secondary side of the electric energy. The signal modulation and demodulation section complete the carrier signal modulation, the power amplification and the amplitude change of the carrier signal are shaped and restored to a digital signal to communicate with the host computer. The secondary side power conversion section provides rectification and voltage regulation functions to provide the DC power required for charging to the load. the carrier signal modulation, the power amplification and the amplitude change of the carrier signal are shaped and restored to a digital signal to communicate with the host computer. The secondary side power conversion section provides rectification and voltage regulation functions to provide the DC power required for charging to the load. The experimental device handshake communication signal transmission part adopts halfduplex communication, and performs modulation and demodulation in ASK mode, the carrier frequency of the transmitted signal is 200 kHz. In order to make the working frequency and the signal carrier frequency of the power transmission mode far away from each other, the working frequency of the power transmission is designed to be a frequency of 85 kHz, which not only ensures the power transmission but also does not affect the communication effect. High-speed signal transmission uses a 2 to 28 MHz carrier OFDM module for high-speed data transmission from the robotic fish to the charging pile. The energy and signal transmission experimental waveforms are shown in Figures 11-13, where Figure 11 shows the working waveform of the coil voltage and current at the time of power transmission. Figure 12 is a waveform diagram of a signal secondary side carrier signal and a demodulated signal during signal transmission. Figure 13 is a spectrum waveform obtained by fast Fourier transform of a picked-up signal in a high-speed signal transmission mode, which reflects the gain of each subcarrier in the OFDM modulation mode.  As it can be seen from Figure 11, since the power transmission portion operates at the resonance frequency point of the system, the system operates in a resonance state. At the same time, the experimental device was used to test different loads. The system works stably, the transmission The experimental device handshake communication signal transmission part adopts half-duplex communication, and performs modulation and demodulation in ASK mode, the carrier frequency of the transmitted signal is 200 kHz. In order to make the working frequency and the signal carrier frequency of the power transmission mode far away from each other, the working frequency of the power transmission is designed to be a frequency of 85 kHz, which not only ensures the power transmission but also does not affect the communication effect. High-speed signal transmission uses a 2 to 28 MHz carrier OFDM module for high-speed data transmission from the robotic fish to the charging pile. The energy and signal transmission experimental waveforms are shown in Figures 11-13, where Figure 11 shows the working waveform of the coil voltage and current at the time of power transmission. Figure 12 is a waveform diagram of a signal secondary side carrier signal and a demodulated signal during signal transmission. Figure 13 is a spectrum waveform obtained by fast Fourier transform of a picked-up signal in a high-speed signal transmission mode, which reflects the gain of each subcarrier in the OFDM modulation mode. the carrier signal modulation, the power amplification and the amplitude change of the carrier signal are shaped and restored to a digital signal to communicate with the host computer. The secondary side power conversion section provides rectification and voltage regulation functions to provide the DC power required for charging to the load. The experimental device handshake communication signal transmission part adopts halfduplex communication, and performs modulation and demodulation in ASK mode, the carrier frequency of the transmitted signal is 200 kHz. In order to make the working frequency and the signal carrier frequency of the power transmission mode far away from each other, the working frequency of the power transmission is designed to be a frequency of 85 kHz, which not only ensures the power transmission but also does not affect the communication effect. High-speed signal transmission uses a 2 to 28 MHz carrier OFDM module for high-speed data transmission from the robotic fish to the charging pile. The energy and signal transmission experimental waveforms are shown in Figures 11-13, where Figure 11 shows the working waveform of the coil voltage and current at the time of power transmission. Figure 12 is a waveform diagram of a signal secondary side carrier signal and a demodulated signal during signal transmission. Figure 13 is a spectrum waveform obtained by fast Fourier transform of a picked-up signal in a high-speed signal transmission mode, which reflects the gain of each subcarrier in the OFDM modulation mode.  As it can be seen from Figure 11, since the power transmission portion operates at the resonance frequency point of the system, the system operates in a resonance state. At the same time, the experimental device was used to test different loads. The system works stably, the transmission power reaches 300 W, and the efficiency is above 80%, which satisfies the wireless charging demand of the submarine patrol robot fish. From Figure 12, the ASK method can demodulate the digital signal very well. In the handshake communication signal transmission mode, the charging pile sends a control signal to the robot fish, the baud rate reaches 41 kbps, and the error rate of the system signal transmission is less than one ten thousandth. In practical applications, measures such as adding verification to signal transmission can ensure stable and reliable transmission of system signals, which can meet actual needs.
The high-speed signal transmission mode signal spectrum is shown in Figure 13. The data carrier has a frequency band of 2 to 28 MHz and a frequency band of 26 MHz, which contains many subcarriers. The data transmission can be carried out steadily, and the transmission rate is maintained at 10 Mbps or more, which satisfies the need for high-speed transmission of patrol data.

Conclusion
This article starts from the application requirements of the cable-inspection robotic fish wireless-charging system, based on the existing power and signal transmission methods, the twoway time-sharing transmission of power and signals in shared channels is studied. The electric energy coupling coils are used as the transmission channel of the signal, and the one-way transmission of electric energy and the bidirectional transmission of the signal are realized without interference between the electric energy and the signal. The transmission characteristics of the  From Figure 12, the ASK method can demodulate the digital signal very well. In the handshake communication signal transmission mode, the charging pile sends a control signal to the robot fish, the baud rate reaches 41 kbps, and the error rate of the system signal transmission is less than one ten thousandth. In practical applications, measures such as adding verification to signal transmission can ensure stable and reliable transmission of system signals, which can meet actual needs.
The high-speed signal transmission mode signal spectrum is shown in Figure 13. The data carrier has a frequency band of 2 to 28 MHz and a frequency band of 26 MHz, which contains many subcarriers. The data transmission can be carried out steadily, and the transmission rate is maintained at 10 Mbps or more, which satisfies the need for high-speed transmission of patrol data.

Conclusion
This article starts from the application requirements of the cable-inspection robotic fish wireless-charging system, based on the existing power and signal transmission methods, the twoway time-sharing transmission of power and signals in shared channels is studied. The electric energy coupling coils are used as the transmission channel of the signal, and the one-way transmission of electric energy and the bidirectional transmission of the signal are realized without interference between the electric energy and the signal. The transmission characteristics of the As it can be seen from Figure 11, since the power transmission portion operates at the resonance frequency point of the system, the system operates in a resonance state. At the same time, the experimental device was used to test different loads. The system works stably, the transmission power reaches 300 W, and the efficiency is above 80%, which satisfies the wireless charging demand of the submarine patrol robot fish.
From Figure 12, the ASK method can demodulate the digital signal very well. In the handshake communication signal transmission mode, the charging pile sends a control signal to the robot fish, the baud rate reaches 41 kbps, and the error rate of the system signal transmission is less than one ten thousandth. In practical applications, measures such as adding verification to signal transmission can ensure stable and reliable transmission of system signals, which can meet actual needs.
The high-speed signal transmission mode signal spectrum is shown in Figure 13. The data carrier has a frequency band of 2 to 28 MHz and a frequency band of 26 MHz, which contains many subcarriers. The data transmission can be carried out steadily, and the transmission rate is maintained at 10 Mbps or more, which satisfies the need for high-speed transmission of patrol data.

Conclusions
This article starts from the application requirements of the cable-inspection robotic fish wireless-charging system, based on the existing power and signal transmission methods, the two-way time-sharing transmission of power and signals in shared channels is studied. The electric energy coupling coils are used as the transmission channel of the signal, and the one-way transmission of electric energy and the bidirectional transmission of the signal are realized without interference between the electric energy and the signal. The transmission characteristics of the energy channel, the characteristics of alignment detection and low-speed handshake signal transmission, and the transmission characteristics of a high-speed signal are analyzed theoretically, and the corresponding channel switching control strategy is presented. The experimental device was built to verify the feasibility of the method, which gave an effective reference for the wireless charging, control and data transmission of the robot fish in the submarine cable-inspection system, and provided a solution for similar underwater robot wireless charging. This paper only explores the feasibility of the wireless energy and data transmission system and its time division multiplexing method; further exploration of output control and maximum efficiency tracking will be done soon.