A VDES-based networking and communication method and system for water internet of things

Abstract

The application relates to the technical field of water radio communication and Internet of Things, and provides a water Internet of Things networking and communication method and system based on VDES, which comprises the following steps: dividing a time axis into equal-length time slots; dividing a sea area into multiple geographical grids, counting terminal density in each grid, and issuing a mode switching instruction when the terminal density exceeds a preset threshold, switching the terminal from random access to assignment mode and allocating a main transmission time slot and a backup transmission time slot; calculating an included angle between an antenna and a horizontal plane, and sending data in the allocated time slot when the included angle meets a condition; forwarding the data to a network server via a base station after protocol conversion; encapsulating the data into different types of messages according to preset service rules and pushing the messages to a ship terminal; and starting a receiver to receive a downlink instruction in a preset receiving time slot. The application effectively reduces a channel collision rate, realizes bidirectional controllable communication under low power consumption, and avoids occupation of an AIS collision avoidance channel by Internet of Things data.

Description

Technical Field

[0001] This application relates to the fields of maritime radio communication and Internet of Things (IoT) technology, specifically to a maritime IoT networking and communication method and system based on VDES. Background Technology

[0002] The Automatic Identification System (AIS) is a maritime communication system applied to ship-to-shore and ship-to-ship communication. AIS broadcasts its own name, identification number, latitude and longitude, speed, and heading in real time through a dedicated VHF channel, and receives data broadcast by other ships, thus building a ship-to-ship and ship-to-shore communication network to achieve collision avoidance, monitoring, and improve navigation safety.

[0003] With the increasing frequency of maritime economic activities, AIS applications are becoming more widespread. Besides ship monitoring and collision avoidance, it is also extensively used in areas such as personal overboard positioning, navigation aids, fishing net marking, and floating object marking. Existing AIS systems have low communication rates and limited capacity, which can no longer meet the rapidly growing application demands. Therefore, organizations such as the International Telecommunication Union (ITU) and the International Maritime Organization (IMO) have proposed a VHF data exchange system as an upgrade to AIS. VDES, while retaining the functions of the Automatic Identification System (AIS), adds special application messages and a VHF data exchange module. By allocating dedicated channels, it alleviates congestion in the traditional VHF band, improves transmission efficiency and coverage, and supports two-way data exchange between ships, between ships and shore, and between ships and satellites. Simultaneously, the ITU has also proposed a new "Autonomous Maritime Radio Equipment" standard for IoT applications such as fishing net marking and floating object marking. This standard reduces the occupancy of the VDES channel by transmitting information on newly allocated dedicated frequencies different from the VDES channel.

[0004] According to the AMRD standard, devices used for fishing net marking, floating object marking, and other similar applications operate autonomously on a single frequency point in the VHF band, determining and scheduling their own message transmissions based on randomly selected transmission time slots. However, this model suffers from the following problems when deployed at scale: 1) Severe channel collisions and limited system capacity: In densely populated fishing areas or port waters, hundreds or thousands of terminal devices randomly and disorderly send data packets. Due to the lack of coordination mechanisms, data packets severely overlap in the time and frequency domains, resulting in a high channel collision rate, affecting communication success rate, and failing to meet the reliability requirements of real-time monitoring.

[0005] 2) Unidirectional operation and lack of controllability: The vast majority of existing devices only have transmission capabilities and do not include a receiving channel. The monitoring center cannot perform downlink control on the devices according to actual needs. Once deployed, the device behavior is completely fixed and cannot be adjusted as needed.

[0006] 3) The communication link is fragile and greatly affected by sea conditions: AMRD's antenna uses vertical polarization. Generally, the communication effect is best when the antenna is perpendicular to the horizontal plane and worst when the antenna is parallel to the horizontal plane. The antenna is installed at a height of less than 1 meter. Wave fluctuations and the tilt of the float can cause changes in the antenna attitude, thus affecting the communication success rate.

[0007] 4) The contradiction between power consumption and performance: If a receiving function is added to the device to achieve controllability, continuous monitoring of the receiving channel will lead to increased power consumption, which will affect the service life of battery-powered terminals.

[0008] 5) Information transmission issues between heterogeneous networks: On the one hand, AMRD devices operate on dedicated IoT frequencies, which differ from the VDES system's operating frequencies. This frequency isolation prevents shipborne VDES devices from directly receiving AMRD signals, and most ships are not equipped with AMRD receiving devices. When AMRD is used to identify floating objects (such as fishing nets), its identification information is difficult for passing ships to obtain, rendering the collision avoidance warning function ineffective. On the other hand, if AMRD data is simply converted into AIS messages and forwarded through shore-based systems, each floating object identification will occupy valuable AIS channel time slots. This severely impacts the already fragile channel capacity of the AIS system, potentially interfering with normal ship collision avoidance communication and posing a navigational safety hazard. Summary of the Invention

[0009] To help solve the above-mentioned technical problems, this application provides a method and system for networking and communicating on waterborne IoT based on VDES.

[0010] In a first aspect, this application provides a method for networking and communication control of a maritime Internet of Things (IoT) system based on VDES, wherein the method is applied to a communication system including a maritime IoT terminal, a converged gateway, a base station, a network server, and an application server, and the method includes the following steps: Before preparing to transmit data, the waterborne IoT terminal calculates the angle between its antenna and the horizontal plane in real time using its built-in three-axis accelerometer. If the included angle is greater than or equal to a preset attitude threshold, the communication conditions are determined to be good, and the waterborne IoT terminal transmits data in the allocated main transmission time slot; If the included angle is less than the attitude threshold, it is determined that the waterborne IoT terminal is affected by wave obstruction or capsizing. The terminal abandons the main transmission time slot and automatically postpones the transmission to one of the multiple alternative transmission time slots allocated later. Data transmission is then performed in the first time slot that meets the attitude threshold requirement.

[0011] The method further includes: All waterborne IoT terminals use the clock signal output by the GNSS positioning module to achieve time synchronization, dividing the time axis into equal-length time slots; The network server divides the sea area into multiple geographic grids and calculates the terminal density in each geographic grid based on the coordinates of the maritime IoT terminals reported by each fusion gateway. When the terminal density of any geographic grid exceeds a preset density threshold, the network server generates a mode switching instruction and sends it through the base station and the fusion gateway located in that geographic grid. This instruction switches the transmission mode of the maritime IoT terminals in the corresponding grid from random access to assigned mode and allocates the main transmission time slot and one or more alternative transmission time slots to each maritime IoT terminal.

[0012] In the random access mode, the waterborne IoT terminal autonomously and randomly selects a transmission time slot within each working cycle, and repeatedly transmits the same data M times at fixed time intervals through its built-in VHF transmitter, where M is a positive integer.

[0013] The network server also dynamically adjusts the working cycle of the waterborne IoT terminals within each geographic grid based on the load pressure of each geographic grid.

[0014] The method further includes: The converged gateway converts the data received from the waterborne IoT terminal into a protocol and then forwards it to the network server via the base station. Specifically, the convergence gateway receives data sent by the waterborne IoT terminal in the first frequency band, converts the protocol of the received data from the first frequency band protocol to the second frequency band protocol, and then forwards it to the network server through the base station; and the convergence gateway aggregates the data packets received from multiple waterborne IoT terminals and then forwards them to the network server through the base station.

[0015] The first frequency band is 160.900MHz, and the second frequency band includes 157.200MHz to 157.350MHz and 161.800MHz to 162.050MHz.

[0016] The method further includes: The application server encapsulates the data forwarded by the network server into different types of messages according to preset business rules and pushes them to the ship terminal through the base station. Specifically, IoT data is preferentially transmitted via a dedicated data channel of the VHF data exchange system in the form of ASM messages or VDE messages; Automatic Identification System (AIS) messages are generated only when broadcasting to ships equipped only with AIS receivers, and the AIS message rate and time slot occupancy rules are followed when generating the AIS messages; wherein, the AIS messages include AIS message 8 or AIS message 28.

[0017] The method further includes: The waterborne IoT terminal activates its receiver during a preset receiving time slot in each working cycle to receive downlink commands from the converged gateway. The preset receiving time slots are N consecutive time slots; the fusion gateway will repeatedly send the same instruction to be sent to the target waterborne IoT terminal within the N consecutive time slots; the waterborne IoT terminal will continuously receive from its built-in VHF receiver after the first receiving time slot is turned on, and if the instruction is fully received, the VHF receiver will be turned off immediately.

[0018] When data sent by a floating IoT terminal is simultaneously received by multiple converged gateways, the network server collects the signal-to-noise-plus-interference ratio reported by each converged gateway and assigns the converged gateway with the highest ratio as the downlink command proxy gateway for the floating IoT terminal. If the difference between the ratios of two or more converged gateways is less than a preset threshold, the current channel load of these converged gateways is further compared, the converged gateway with the lowest channel load is selected as the proxy gateway, and the remaining converged gateways are controlled to suppress the sending of downlink commands to the floating IoT terminal.

[0019] In a second aspect, this application provides a VDES-based waterborne IoT networking and communication control system, wherein the system is used to execute the VDES-based waterborne IoT networking and communication control method as described in any one of the first aspects, wherein the system includes a waterborne IoT terminal, a converged gateway, a base station, a network server, and an application server. The aquatic IoT terminal includes a three-axis accelerometer, a main control MCU, and a VHF transmitter. The three-axis accelerometer is used to detect acceleration along three axes. Before preparing to transmit data, the main control MCU calculates the angle between the antenna and the horizontal plane in real time based on the detection data from the three-axis accelerometer. When the angle is greater than or equal to a preset attitude threshold, it determines that the communication conditions are good and controls the VHF transmitter to transmit data in the allocated main transmission time slot. When the angle is less than the attitude threshold, it determines that the transmission is affected by wave obstruction or capsizing, abandons the main transmission time slot, and automatically postpones the transmission to one of the subsequently allocated alternative transmission time slots. The main control MCU controls the VHF transmitter to transmit data in the first time slot that meets the attitude threshold requirement. The network server is used to allocate the main transmission time slot and the alternative transmission time slot to the waterborne IoT terminal; The converged gateway is used to convert and forward data and protocols between the waterborne IoT terminal and the base station; The base station is used to forward data between the converged gateway and the network server and / or application server; The application server is used to selectively encapsulate data into different types of messages according to business needs and push them to the ship terminal via base station.

[0020] In summary, compared with the prior art, this application has the following beneficial effects: 1) By using dynamic time slot allocation and conflict avoidance, the channel collision rate can be effectively reduced and the communication success rate can be improved under the same spectrum resources.

[0021] 2) By adopting time-synchronized short-time reception technology, controlled network management is achieved while ensuring low power consumption.

[0022] 3) Improve the success rate of IoT terminal data transmission through attitude-aware alternative time slot mechanism; improve the success rate of IoT terminal data reception through redundant downlink mechanism.

[0023] 4) By integrating the protocol conversion of the gateway and the dedicated data channel of VDES, a bridge is established between the dedicated frequency band for maritime IoT and the AIS / VDES broadcast frequency band. Ships can indirectly obtain floating object identification information through VDES base stations or gateways without modifying their existing AIS receiving equipment. At the same time, since IoT data is mainly transmitted in the VDES data channel, the application server only generates a small number of AIS broadcast messages according to rules when necessary, effectively reducing the encroachment of IoT data on the AIS collision avoidance channel and ensuring the reliability of core maritime navigation safety services.

[0024] 5) It has connected the entire chain from sensing terminals to converged gateways to VDES backbone to ship applications, enabling real-time monitoring and data interaction of widely distributed small-scale maritime IoT devices, supporting advanced applications such as smart ocean, precision fisheries, and waterway safety. Attached Figure Description

[0025] Figure 1 This is a schematic block diagram of the VHF data switching system of this application; Figure 2 for Figure 1 A schematic block diagram of the IoT terminal in the illustrated embodiment; Figure 3 This is a flowchart of the launch process for this application. Detailed Implementation

[0026] The present application will be further described below with reference to the accompanying drawings. The principles of the present application are very clear to those skilled in the art. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

[0027] To facilitate understanding of this application, the following explanations are provided for the English abbreviations used in this application: GNSS (Global Navigation Satellite System) VHF (Very High Frequency): Very high frequency; VDES (VHF Data Exchange System): Very High Frequency Data Exchange System; AIS (Automatic Identification System): Automatic Identification System for Ships; ASM (Application Specific Message): Application-specific message; VDE (VHF Data Exchange): Very High Frequency Data Exchange; AMRD (Autonomous Maritime Radio Device): Autonomous Maritime Radio Device; MCU (Microcontroller Unit): Microcontroller unit; SINR (Signal to Interference plus Noise Ratio): The ratio of signal to noise plus interference. ITU (International Telecommunication Union): The International Telecommunication Union; IMO (International Maritime Organization): The International Maritime Organization.

[0028] This application provides a highly reliable, low-power waterborne IoT networking system and control method based on VDES architecture, integrating attitude perception and precise time slot alignment technology, and solves the channel encroachment problem in heterogeneous network interconnection. Figure 1 This is a schematic block diagram of the VHF data exchange system of this application, which consists of an IoT terminal, a converged gateway, a base station, a network server, and an application server. Figure 2 for Figure 1 A schematic block diagram of the IoT terminal in the illustrated embodiment.

[0029] a) System composition.

[0030] 1) Waterborne Internet of Things (IoT) terminal.

[0031] The maritime IoT terminal consists of a VHF transmitter, a VHF receiver, a transceiver conversion circuit, a VHF antenna, a main control MCU, a GNSS positioning module, an accelerometer, an interface and power management module, and a battery. The VHF transmitter modulates the data to be transmitted onto a first-band (160.900MHz) carrier and amplifies the signal power. The VHF receiver amplifies, filters, and demodulates the first-band signal received by the VHF antenna. The VHF antenna radiates and receives VHF signals from space. The transceiver conversion circuit switches the connection between the VHF antenna and the VHF transmitter and receiver. The GNSS positioning module receives navigation satellite signals and calculates positioning and timing data. The accelerometer detects acceleration along three axes. The main processor controls the overall operation and calculates the angle between the VHF antenna and the horizontal plane. The interface and power management module provides external data interfaces and converts external power or battery voltage to internal circuit power, and, under the control of the main processor, selects to turn the power supply to each module on or off. The terminal can be set to different working modes depending on whether it is battery powered, and can be set to turn the receiver on and off at regular intervals or to keep the receiver on all the time.

[0032] 2) Converged gateway.

[0033] Deployed on ships, buoys, or shore-based platforms, it possesses dual-mode physical layer transceiver capabilities in a first frequency band (160.900MHz) and a second frequency band (157.200MHz to 157.350MHz and 161.800MHz to 162.050MHz). The first frequency band is a dedicated narrowband band for maritime IoT, while the second frequency band is a broadband maritime data exchange band. The core function of the converged gateway is protocol conversion and transparent forwarding. Uplink direction: Receive terminal data packets on the first frequency band, convert the terminal data packets on the first frequency band into data packets of the second frequency band standard protocol, and aggregate the received data packets from multiple waterborne IoT terminals into a large data packet, which is then transparently forwarded to the network server and application server through the base station; The aggregation process can be as follows: the converged gateway collects data packets from different IoT terminals within a preset time window, merges these data packets into an aggregated data packet containing multiple terminal identifiers and corresponding payload data, adds a unified second-band protocol header, and then sends it. Aggregation effectively reduces signaling overhead and transmission frequency at the air interface, further improving uplink spectrum efficiency.

[0034] Downlink direction: Receive downlink commands from the base station, convert them into the first frequency band protocol format, and transparently forward them to the target IoT terminal.

[0035] 3) Base station.

[0036] Base stations have the following functions: It receives data packets sent by the converged gateway via the second frequency band and sends the data packets to the network server and application server via the Internet or private network; Receive data from a network server or application server via the Internet or private network, convert the data into second-band data packets, and send them to the converged gateway; Data is transmitted and received between the shipborne VDES terminal.

[0037] 4) Web server.

[0038] Deployed in the cloud. Functions include: IoT terminal device registration and authentication, geographic grid-based marine channel load monitoring, dynamic time slot resource management, IoT terminal access mode decision-making, downlink command queue scheduling, and data deduplication.

[0039] 5) Application server.

[0040] Deployed in the cloud, it is responsible for business logic processing. Its main functions include: Receive uplink data forwarded by the network server; Based on data type and business needs, execute differentiated message conversion and distribution decisions: convert data into ASM message, VDE message or AIS message format, and push it to the ship terminal through VDES base station; The downlink control commands (such as adjusting the reporting cycle, attitude threshold configuration, etc.) are generated and sent to the target IoT terminal via the network server, VDES base station, and converged gateway. When generating AIS messages, strictly adhere to the AIS message rate and time slot occupancy rules to ensure that collision avoidance communication between ships is not affected.

[0041] b) Control methods.

[0042] 1) All IoT terminals use the clock signal output by the GNSS module to achieve time synchronization, dividing the time axis into 2250 equal-length time slots per minute. The terminals send data periodically according to the set working cycle.

[0043] 2) IoT terminals operate in random access mode by default, autonomously and randomly selecting a transmission time slot to send data in each working cycle. To improve communication success rate, the same data is repeatedly transmitted four times at fixed time intervals in each working cycle.

[0044] 3) The network server divides the sea area into multiple geographic grids. Based on the coordinates of IoT terminals reported by each converged gateway, it calculates the IoT terminal density within each geographic grid. When the terminal density of a grid exceeds a preset threshold, the server sends control commands to all terminals within that grid through base stations and gateways, switching the transmission mode of the IoT terminals from random access to assigned mode. It allocates a primary transmission time slot and a backup transmission time slot to each terminal, ensuring that the IoT terminals only transmit data in the designated time slots to avoid conflicts. Simultaneously, the server can dynamically adjust the terminal reporting cycle based on load pressure.

[0045] 4) During each work cycle, the IoT terminal only activates its receiver or transmitter in a few designated time slots; the remaining time, the terminal operates in sleep mode to reduce power consumption. IoT terminals within the same network share the same default receive time slot. The IoT terminal activates its receiver during the receive time slot to receive instructions from the gateway.

[0046] 5) Figure 3 This is a flowchart illustrating the launch process of this application. Figure 3 In this process, the IoT terminal first prepares the data to be transmitted and reads the main transmission time slot value allocated by the network server in each working cycle, and then starts timing. When the time to the main transmission time slot is less than a preset threshold, it reads the built-in accelerometer data to calculate the angle between the antenna and the horizontal plane. If the angle is greater than the preset angle threshold, the data is transmitted in the main transmission time slot. If the angle is less than or equal to the angle threshold, the next backup transmission time slot is read in sequence, and the above angle judgment is repeated for each backup transmission time slot. Once the angle corresponding to a backup transmission time slot is greater than the angle threshold, the data is transmitted in that backup transmission time slot. If no time slot that meets the angle condition is found after traversing all backup transmission time slots, the transmission is abandoned.

[0047] In each working cycle, before transmission, the IoT terminal calculates the angle between the antenna and the horizontal plane using a three-axis accelerometer. If the angle is greater than a set threshold, the communication conditions are considered good, and transmission occurs in the main time slot. If the angle is less than the threshold, it is determined that the transmission is affected by wave obstruction or overturning, and the main time slot is abandoned, automatically postponed to the first time slot among several subsequently allocated alternative time slots where the attitude meets the requirements. During reception, to improve communication success rate and reduce power consumption, the IoT terminal uses four consecutive time slots for reception. The gateway repeatedly transmits the same command in four consecutive time slots. The IoT terminal starts receiving from the first time slot and continues to receive. Once a complete command is received, reception stops, effectively combating momentary wave obstruction.

[0048] It is understandable that the number of receive time slots N is not limited to 4. It can be configured with other integer values, such as 2, 3, 5, 6, 8, etc., depending on the needs of the actual application scenario. The larger the value of N, the higher the success rate of receiving downlink commands, but the corresponding power consumption is also greater; the smaller the value of N, the lower the power consumption, but the weaker the resistance to transient blockage. In actual deployment, the value of N can be flexibly set according to factors such as the sea state environment where the terminal is located, the service reliability requirements, and battery capacity constraints.

[0049] 6) When data sent by an IoT terminal is simultaneously received by multiple converged gateways, the network server collects the signal-to-noise-plus-interference ratio (SNR) of all reporting gateways. The gateway with the highest SNR is assigned as the downlink command proxy for that IoT terminal. If the difference in SNR between two gateways is very small, the current channel load of the two gateways is further compared, and the gateway with the lower load is selected as the proxy. The remaining gateways automatically suppress downlink transmissions to that IoT terminal. This mechanism avoids channel waste and potential conflicts caused by multiple gateways simultaneously sending downlink commands to the same IoT terminal.

[0050] It is understandable that the aforementioned signal-to-noise-plus-interference ratio (SINR) comparison and gateway proxy selection mechanism can be implemented independently or in conjunction with the data aggregation mechanism. When the converged gateway simultaneously undertakes uplink data aggregation and downlink command proxy functions, the network server can allocate uplink reception and downlink transmission time slot resources to the converged gateway after comprehensively evaluating SINR and load, in order to further optimize the overall system efficiency.

[0051] 7) The converged gateway only performs physical / link layer protocol conversion and does not involve business message types. The application server flexibly selects to convert data into ASM, VDE, or AIS messages based on data type and business requirements, sending them to designated vessels or broadcasting them to all vessels. IoT data is preferentially transmitted through the VDES dedicated data channel (ASM / VDE), generating only a small number of AIS messages when necessary, fundamentally avoiding encroachment on the AIS collision avoidance channel.

[0052] For example, an IoT terminal connects to a weather sensor to collect environmental data such as temperature (°C), humidity, wind speed (m / s), wind direction, and air pressure (hPa). After being converted and transparently forwarded by the converged gateway protocol, the data reaches the application server. The application server can choose one or more of the following distribution methods based on the business configuration: Method 1: Encapsulate the data into ASM or VDE messages and broadcast them through VDES base stations. Only ships equipped with VDES receivers can receive the data; this does not occupy AIS channels.

[0053] Method 2: If it is necessary to broadcast to traditional ships equipped only with AIS receivers, the application server encodes the data into AIS message 8 and broadcasts it to surrounding ships through VDES base stations or AIS base stations.

[0054] Simultaneously, the IoT terminal reports latitude, longitude, speed, and heading data. The application server selects the appropriate server based on business needs. Method 1: Encapsulate the latitude, longitude, speed, and heading data of each IoT terminal into a VDE message and send it to a specific ship through the VDES base station.

[0055] Method 2: If a collision avoidance warning needs to be broadcast to all nearby vessels, the application server encapsulates the data into an AIS message 28 and sends the coordinates and area range of the IoT terminal's location to surrounding vessels via the VDES base station. Upon receiving the message, surrounding vessels can display the coordinates and size of the IoT terminal's location on their screens, aiding in navigation and preventing collisions.

[0056] In the aforementioned service distribution rules, "ships equipped only with AIS receivers" refers to ships that are not equipped with VDES receiving equipment and can only receive messages through traditional AIS channels. In practical applications, the application server can determine the equipment type of the target ship by querying the ship's registration information or obtaining the ship's capability identifier from the base station. When the target ship is a VDES ship, IoT data is transmitted preferentially through ASM or VDE messages, without occupying AIS channel resources at all. Only when it is confirmed that the target ship is a traditional ship equipped only with an AIS receiver and there is a service requirement to transmit information to it, will the application server trigger the generation and transmission of AIS messages, strictly adhering to the AIS message rate and time slot occupancy rules to ensure that it does not interfere with ship collision avoidance communication.

[0057] This application also proposes a VDES-based waterborne Internet of Things (IoT) networking and communication control system.

[0058] The system includes a maritime IoT terminal, a converged gateway, a base station, a network server, and an application server. The maritime IoT terminal includes a three-axis accelerometer, a main control MCU, and a VHF transmitter. The network server allocates primary and alternative transmission time slots to the maritime IoT terminal. The converged gateway performs data and protocol conversion and forwarding between the maritime IoT terminal and the base station. The base station forwards data between the converged gateway and the network server and / or application server. The application server selectively encapsulates data into different message types according to business needs and pushes them to the ship terminal via the base station.

[0059] The technical scope of this application is not limited to the contents of the above specification. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this application, and all such modifications and variations should fall within the scope of this application.

Claims

1. A method for networking and communication control of aquatic IoT based on VDES, characterized in that, The method, applicable to a communication system including aquatic IoT terminals, converged gateways, base stations, network servers, and application servers, includes the following steps: Before preparing to transmit data, the waterborne IoT terminal calculates the angle between its antenna and the horizontal plane in real time using its built-in three-axis accelerometer. If the included angle is greater than or equal to a preset attitude threshold, the communication conditions are determined to be good, and the waterborne IoT terminal transmits data in the allocated main transmission time slot; If the included angle is less than the attitude threshold, it is determined that the waterborne IoT terminal is affected by wave obstruction or capsizing. The terminal abandons the main transmission time slot and automatically postpones the transmission to one of the multiple alternative transmission time slots allocated later. Data transmission is then performed in the first time slot that meets the attitude threshold requirement.

2. The method according to claim 1, characterized in that, The method further includes: All waterborne IoT terminals use the clock signal output by the GNSS positioning module to achieve time synchronization, dividing the time axis into equal-length time slots; The network server divides the sea area into multiple geographic grids and calculates the terminal density in each geographic grid based on the coordinates of the maritime IoT terminals reported by each fusion gateway. When the terminal density of any geographic grid exceeds a preset density threshold, the network server generates a mode switching instruction and sends it through the base station and the fusion gateway located in that geographic grid. This instruction switches the transmission mode of the maritime IoT terminals in the corresponding grid from random access to assigned mode and allocates the main transmission time slot and one or more alternative transmission time slots to each maritime IoT terminal.

3. The method according to claim 2, characterized in that, In the random access mode, the waterborne IoT terminal autonomously and randomly selects a transmission time slot within each working cycle, and repeatedly transmits the same data M times at fixed time intervals through its built-in VHF transmitter, where M is a positive integer.

4. The method according to claim 2, characterized in that, The network server also dynamically adjusts the working cycle of the waterborne IoT terminals within each geographic grid based on the load pressure of each geographic grid.

5. The method according to claim 1, characterized in that, The method further includes: The converged gateway converts the data received from the waterborne IoT terminal into a protocol and then forwards it to the network server via the base station. Specifically, the convergence gateway receives data sent by the waterborne IoT terminal in the first frequency band, converts the protocol of the received data from the first frequency band protocol to the second frequency band protocol, and then forwards it to the network server through the base station; and the convergence gateway aggregates the data packets received from multiple waterborne IoT terminals and then forwards them to the network server through the base station.

6. The method according to claim 5, characterized in that, The first frequency band is 160.900MHz, and the second frequency band includes 157.200MHz to 157.350MHz and 161.800MHz to 162.050MHz.

7. The method according to claim 1 or 5, characterized in that, The method further includes: The application server encapsulates the data forwarded by the network server into different types of messages according to preset business rules and pushes them to the ship terminal through the base station. Specifically, IoT data is preferentially transmitted via a dedicated data channel of the VHF data exchange system in the form of ASM messages or VDE messages; Automatic Identification System (AIS) messages are generated only when broadcasting to ships equipped only with AIS receivers, and the AIS message rate and time slot occupancy rules are followed when generating the AIS messages; wherein, the AIS messages include AIS message 8 or AIS message 28.

8. The method according to claim 1, characterized in that, The method further includes: The waterborne IoT terminal activates its receiver during a preset receiving time slot in each working cycle to receive downlink commands from the converged gateway. The preset receiving time slots are N consecutive time slots; the fusion gateway will repeatedly send the same instruction to be sent to the target waterborne IoT terminal within the N consecutive time slots; the waterborne IoT terminal will continuously receive from its built-in VHF receiver after the first receiving time slot is turned on, and if the instruction is fully received, the VHF receiver will be turned off immediately.

9. The method according to claim 1 or 5, characterized in that, When data sent by a floating IoT terminal is simultaneously received by multiple converged gateways, the network server collects the signal-to-noise-plus-interference ratio reported by each converged gateway and assigns the converged gateway with the highest ratio as the downlink command proxy gateway for the floating IoT terminal. If the difference between the ratios of two or more converged gateways is less than a preset threshold, the current channel load of these converged gateways is further compared, the converged gateway with the lowest channel load is selected as the proxy gateway, and the remaining converged gateways are controlled to suppress the sending of downlink commands to the floating IoT terminal.

10. A VDES-based maritime Internet of Things (IoT) networking and communication control system, characterized in that, The system is used to execute the VDES-based waterborne IoT networking and communication control method as described in any one of claims 1-9, and the system includes a waterborne IoT terminal, a converged gateway, a base station, a network server, and an application server. The waterborne IoT terminal includes a three-axis accelerometer, a main control MCU, and a VHF transmitter; the three-axis accelerometer is used to detect acceleration in three axes. Before preparing to transmit data, the main control MCU calculates the angle between the antenna and the horizontal plane in real time based on the detection data of the triaxial accelerometer. When the angle is greater than or equal to a preset attitude threshold, it determines that the communication conditions are good and controls the VHF transmitter to transmit data in the allocated main transmission time slot. When the angle is less than the attitude threshold, it determines that the transmission is affected by wave obstruction or overturning, abandons the main transmission time slot, and automatically postpones the transmission to one of the multiple alternative transmission time slots allocated later. The MCU controls the VHF transmitter to transmit data in the first time slot that meets the attitude threshold requirement. The network server is used to allocate the main transmission time slot and the alternative transmission time slot to the waterborne IoT terminal; The converged gateway is used to convert and forward data and protocols between the waterborne IoT terminal and the base station; The base station is used to forward data between the converged gateway and the network server and / or application server; The application server is used to selectively encapsulate data into different types of messages according to business needs and push them to the ship terminal via base station.

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