A long-service underwater OTN system for an ocean bottom observation network

Abstract

The application relates to the technical field of seabed observation communication systems and underwater optical transmission network equipment, and discloses a long-term service type underwater OTN system for a seabed observation network. The system comprises a shore-based station OTN communication main control unit, a time server, a seabed optical cable and at least one underwater node. The underwater node adopts a static optical transmission architecture of fixed wavelength mapping, and does not set ROADM, optical switches, wavelength tuners and other optical layer dynamic scheduling devices; at least two independent OTN single wave processing branches are arranged in the node. Only one branch is powered on for work in normal operation, and the remaining branches are powered off for cold standby, and the standby branch is powered on and the service and time synchronization configuration are inherited under the control of a main control switching control module in case of failure. The system also reduces power consumption and thermal load and improves long-term reliability under deep-sea closed unattended conditions through main control and frame integrator integrated card, hardware time stamp synchronization, temperature-time delay compensation and multi-stage conduction heat dissipation structure.

Description

Technical Field

[0001] This invention relates to the technical field of seabed observation and communication systems and underwater optical transmission network equipment, and particularly to a long-term service underwater OTN system for seabed observation networks. This system is mainly designed for long-term unattended environments. Background Technology

[0002] Submarine observation networks are crucial infrastructure for long-term, continuous, in-situ observations of the marine environment, earthquakes and tsunamis, seabed geological processes, marine acoustics, and the ecological environment. Underwater optical transmission equipment operates in environments with high hydrostatic pressure, sealed pressure chambers, no active cooling, long maintenance cycles, and high failure repair costs. Its engineering constraints differ from those of terrestrial OTN equipment under maintainable conditions in data centers. Terrestrial OTN systems typically emphasize dynamic wavelength scheduling, flexible protection switching, and maintainable expansion capabilities, thus requiring reconfigurable optical add-drop multiplexers, optical switches, wavelength tuners, complex backplanes, and hot backup modules, resulting in high system power consumption, size, and heat dissipation requirements. Directly transplanting this architecture to underwater pressure chambers would face challenges such as long-term heat accumulation, unavailability of active cooling, continuous power consumption and heat generation in backup systems, and an increase in connector and backplane failure points.

[0003] Unlike terrestrial telecommunications networks, the underwater node locations, service types, wavelength planning, and connection topologies of submarine observation networks remain relatively stable long-term after construction, and service capacity changes are typically less pronounced than in terrestrial operator networks. Therefore, underwater OTN equipment for submarine observation networks requires system reconfiguration geared towards fixed topologies, long-term unattended operation, and low heat dissipation, rather than pursuing the full-featured optical layer dynamic scheduling capabilities of terrestrial OTN equipment. While existing technologies have proposed a general concept for using OTN in submarine observation networks, they largely remain at the functional division level of shore stations and underwater junction boxes, failing to provide specific implementations of low-power redundancy, state inheritance switching, high-precision time synchronization, and passive heat dissipation structures within underwater nodes.

[0004] Submarine observation networks are critical infrastructure for long-term, continuous, and in-situ monitoring of the marine environment. Underwater optical transmission equipment is the core equipment of these networks, facing extreme conditions such as ultra-high pressure sealing, passive heat dissipation, difficult routine maintenance, and unattended continuous operation. Therefore, traditional submarine observation underwater optical transmission systems mostly employ 10G and below intensity modulation / direct detection (IM-DD) technology. However, these systems suffer from drawbacks such as small communication capacity, short transmission distance, low dispersion tolerance, low spectral efficiency, and poor receiving sensitivity, hindering the extension of submarine observation networks to the deep sea and open ocean, and limiting the access requirements of a large number of submarine observation devices. Therefore, the construction of a submarine observation network based on OTN technology is essential.

[0005] Existing terrestrial OTN systems are primarily designed for maintainable environments with computer rooms. They feature dynamically scheduled wavelengths, complex protection mechanisms, large size and power consumption, combined cooling designs with air conditioning and fans, short mean time between failures (MTBF), and require regular maintenance. They are not suitable for long-term unattended scenarios in deep-sea environments. The OTN mentioned here stands for Optical Transport Network.

[0006] To solve the technical problems of long-term underwater operation of OTN systems, it is necessary to overcome the challenges of efficient passive heat dissipation of optoelectronic devices packaged inside a metal pressure-resistant hull, high power consumption and heat generation control, and high reliability requirements. It is necessary to reconstruct a low-power, high-reliability underwater OTN technology system specifically for the seabed environment.

[0007] The invention described in application number "202110118919.0" is an optical transmission system and method applied to a submarine observation network: a shore-based OTN service layer processing module for converting different service electrical signals into optical signals of different wavelengths; a shore-based OTN optical path layer processing module for aggregating optical signals of different wavelengths and outputting them to the backbone optical cable; an underwater junction box OTN optical path layer module for converting the aggregated optical signals input from the backbone optical cable into optical signals of different wavelengths; and an underwater junction box OTN service layer processing module for converting optical signals of different wavelengths into electrical signals for output. This invention provides an optical transmission system and method for a submarine observation network that uses OTN equipment to achieve optical path communication management, realizing ultra-high capacity broadband transmission. Different services are independently separated, allowing for flexible scheduling of channel resources, strong stability, automatic error correction and fault recovery, and improved reliability through ring network construction.

[0008] The invention has the following drawbacks: (1) The solution is too macroscopic and does not address the core problems of underwater engineering: The invention only describes the OTN interaction between the shore station and the underwater docking box from the functional module level, which is essentially an underwater mapping of the functions of the land-based OTN system. It does not disclose the specific implementation method of the underwater node, and in particular, it does not solve the fundamental contradiction between the high power consumption, high heat generation and passive heat dissipation limit of OTN equipment in the high-pressure closed environment of the deep sea. If its implicit land-based OTN architecture (including hot backup, optical layer scheduling, etc.) is directly adopted, its power consumption and heat dissipation will far exceed the passive heat dissipation capacity of the underwater pressure tank, resulting in system thermal failure.

[0009] (2) No underwater high-precision time synchronization scheme is provided: The seabed observation network has strict time synchronization requirements for multi-node data fusion, but this invention does not involve any specific method for realizing high-precision (sub-microsecond) time synchronization of underwater nodes using OTN network, nor does it consider the impact of deep-sea temperature changes on synchronization accuracy.

[0010] (3) No reliable redundancy mechanism is provided for unattended underwater scenarios: This invention does not address the implementation of a primary / backup OTN system. The hot backup mechanism commonly used in land-based OTN systems would cause the backup system to continuously consume power and generate heat underwater, wasting valuable power and heat dissipation budget. Simple cold backup, on the other hand, cannot achieve rapid service recovery and seamless inheritance of clock parameters.

[0011] (4) The invention does not consider the reliability design for long-term underwater service: The invention is essentially a land-based operational product for underwater application. It does not involve systematic reliability design such as redundancy backup strategy, power consumption control, low thermal resistance heat dissipation structure, and device derating selection for unattended scenarios of more than 15 years. Therefore, it cannot truly meet the long-term application needs of the seabed observation network.

[0012] To address the problems of existing terrestrial OTN systems, such as complex design, high power consumption, reliance on active air cooling, insufficient long-term reliability, and lack of engineering feasibility in existing underwater application concepts, this invention proposes an underwater OTN system truly designed for long-term unattended environments of seabed observation networks.

[0013] This invention leverages the characteristics of long-term fixed communication topology and minimal changes in service capacity of seabed observation networks. It abandons the complex terrestrial OTN architecture that relies on dynamic scheduling at the optical layer and proposes a simplified OTN architecture based on static wavelengths. Building upon this, it systematically solves the power consumption, heat dissipation, and reliability challenges in the high-pressure, enclosed environment of the deep sea by combining low-power design with redundant cold backup, long-term low thermal resistance conduction heat dissipation technology, high-precision time synchronization methods, and long-life derating design, thus achieving long-term stable operation of the deep-sea OTN communication system. Summary of the Invention

[0014] The purpose of this invention is to provide a long-term service underwater OTN system for long-term unattended environments of seabed observation networks, in order to solve the problems of existing land-based OTN systems, such as high complexity, high power consumption and heat dissipation burden, reliance on active heat dissipation and regular maintenance, and difficulty in adapting to long-term service in sealed pressure chambers in deep seas.

[0015] In view of this, the present invention provides a long-term service underwater OTN system for seabed observation networks. The long-term service underwater OTN system for seabed observation networks includes: an OTN communication main control unit and a time server located at a shore base station connected in series via submarine cables, and at least one underwater node. The underwater node adopts a static optical transmission architecture with a fixed wavelength mapping relationship, and realizes optical transmission through electrical layer OTN frame processing and a fixed wavelength division multiplexer. The underwater node includes: an observation data optical interface, a main control switching control module, at least two independent OTN single-wavelength processing branches, and a passive optical combiner. Multiple OTN single-wavelength processing branches are used for cold backup redundancy. The OTN single-wavelength processing branch includes: a passive optical splitter and a main control and framing integrated board, each corresponding to one of the observation data optical interfaces. Each passive optical splitter is used to distribute the observation data optical signal input from the corresponding observation data optical interface to the input optical interface of each OTN single-wavelength processing branch. The passive optical combiner is used to pre-connect the output optical interface of each OTN single-wavelength processing branch to the corresponding transmission optical fiber in the submarine optical cable. Each OTN single-wavelength processing branch maintains optical path connection with the corresponding passive optical splitter and passive optical combiner, regardless of whether it is in a powered-on working state.

[0016] As an improvement to the above system, the main control and framing integrated board is used to realize the framing of multi-channel observation data, high-precision time synchronization and status monitoring. The status monitoring is specifically as follows: when the main control and framing integrated board detects that the optical power, packet loss rate and bit error rate exceed the threshold for more than a set number of consecutive times and the alarm duration exceeds the threshold, it is determined that the main control and framing integrated board has failed. The main control switching control module controls the backup main control and framing integrated board to power on and writes the configuration information into the backup main control and framing integrated board to realize the inheritance and switching of service and time synchronization status.

[0017] As an improvement to the above system, the main control MCU and OTN framer are integrated on the same circuit board in the main control and framer integrated board. The main control MCU and OTN framer are directly interconnected through the signal channel in the board to reduce the high-speed serial connection on the backplane. The main control and framer integrated board includes: main control MCU, OTN framer, high-stability constant temperature crystal oscillator, hardware timestamp synchronization unit, temperature sensor and power management chip. The main control MCU is used for high-precision time analysis, OTN status monitoring, master-slave switching control, and communication with the master switching control module to report information such as optical power, packet loss rate, and bit error rate. The OTN framer contains multiple optical interfaces. The input side consists of multiple adaptive optical interfaces for receiving seabed observation data. The output side has a fixed wavelength optical interface for transmitting the data collected from the input side to the OTN communication main control unit via a submarine optical-electric composite cable. High-stability temperature-controlled crystal oscillators are used to provide high-precision clocks. The hardware timestamp synchronization unit is used to timestamp the time synchronization information sent by the time server of the OTN communication master control unit and send it to the master control MCU for time parsing; Temperature sensor is used to provide temperature information and calculate time accuracy deviation; Power management chips are used to supply power to modules such as high-stability constant-temperature crystal oscillators and OTN framers.

[0018] As an improvement to the above system, the main control switching control module consists of a current sensor, a power supply control module, a power supply control circuit, and a power supply control switch; wherein, Current sensors are used to monitor the power supply status of each main control and framer integrated board; The power supply control module communicates with the primary and backup integrated control and framer boards respectively to obtain real-time status information such as optical power, packet loss rate, and bit error rate. When the optical power of the primary integrated control and framer board is detected to be lower than the threshold for more than a set number of consecutive times and the alarm continues to exceed the threshold, or the packet loss rate and bit error rate exceed the threshold, the primary integrated control and framer board is determined to be faulty. The power supply control circuit controls the power supply control switch to realize the power-on of the backup integrated control and framer board and the power-off of the primary integrated control and framer board.

[0019] As an improvement to the above system, the execution steps of the underwater node switching between the primary and backup main control and framer integrated board include: Step 1: When the system is running, the first main control and framer integrated board is powered on. The board collects optical power, bit error rate and packet loss rate status data in real time and sends them to the main control switching control module. Step 2: The main control switching control module continuously monitors the status data. If the optical power, packet loss rate, and bit error rate exceed the threshold for more than a set number of consecutive times and the alarm continues to exceed the threshold, a switching command is generated and sent to the power supply control circuit; otherwise, proceed to step 1. Step 3: After receiving the switching command, the power supply control circuit turns on the power supply control switch of the second main control and framer integrated board, and the second main control and framer integrated board, which is in a power-off cold backup state, is powered on. Step 4: The laser on the second main control and framer integrated board is activated, and the service is sent to the submarine cable through the passive optical combiner. Step 5: The master control switching control module sends the configuration information of the first master control and framer integrated board to the second master control and framer integrated board. The configuration information includes the master-slave status of the PTP clock parameters, the offset, and the path delay parameters. Step 6: The main control switching control module shuts off the power supply to the integrated board of the first main control and framer.

[0020] As an improvement to the aforementioned system, the high-precision time synchronization of the integrated control and framing board is achieved through the cooperation of the OTN framing unit, hardware timestamp synchronization unit, high-stability constant-temperature crystal oscillator, main control MCU, and temperature sensor. The time server sends time synchronization messages to the OTN framing unit via submarine optical cable through the OTN communication main control unit. The OTN framing unit parses the time synchronization messages and sends them to the hardware timestamp synchronization unit. The hardware timestamp synchronization unit timestamps the messages and then sends them to the PTP slave clock inside the main control MCU. The PTP slave clock performs final parsing of the messages and uses a time delay-temperature compensation model for correction, thereby eliminating synchronization errors caused by temperature drift. The time delay-temperature compensation model is as follows: Δdelay = k1·ΔT + k2·(ΔT) 2 ; Where Δdelay is the time delay caused by relative temperature change, k1 is the primary temperature delay coefficient, k2 is the secondary temperature delay coefficient, and ΔT is the temperature change value.

[0021] As an improvement to the above system, the underwater node adopts a heat dissipation structure based on conduction heat dissipation, including: The heat-generating devices on the main control and framing integrated board are mounted to the communication unit fixing structure through close contact with the flexible thermal conductive pad. The communication unit fixing structure is in close contact with the inner wall of the cabin through a high thermal conductivity interface material, and is then fixed to the inner wall of the cabin by a locking mechanism. The heat from the heat-generating devices is conducted into the seawater through the flexible thermal conductive pad, the communication unit fixing structure, the high thermal conductivity interface material, and the pressure-resistant inner wall of the cabin.

[0022] As an improvement to the above system, the active devices in the underwater node adopt a triple derating design of voltage, current and junction temperature, and are selected as automotive-grade or aerospace-grade. The active devices include: power management chip, clock buffer, main control MCU and optical module driver chip.

[0023] As an improvement to the above system, high-power, complex optical layer reconfiguration devices that require dynamic scheduling are not set up in order to reduce heat generation. The optical layer reconfiguration devices include: a reconfigurable optical add-drop multiplexer, an optical switch, and a wavelength tuner.

[0024] As an improvement to the above system, the underwater node further includes: The business performance monitoring module is used to report error seconds, critical error seconds, and unavailable seconds in OTN overhead in real time. The built-in instrumentation module is used to send test frames and measure latency and jitter before service activation; the multi-level loopback module supports OTN-level loopback, port loopback and optical module loopback. The online upgrade module is used to support receiving upgrade packages via the optical monitoring channel or OTN overhead channel, enabling online upgrades of FPGA logic and embedded software, and supporting rollback.

[0025] Compared with the prior art, the advantages of the present invention are: This invention replaces the complex dynamic scheduling of the optical layer in terrestrial OTN with fixed wavelength static mapping, reducing high-power or high-complexity devices such as ROADM, optical switches, and wavelength tuners, which helps to reduce underwater node failure points and heat dissipation pressure.

[0026] This invention achieves underwater OTN primary / backup redundancy without introducing an underwater dynamic optical switch by combining a "passive optical path pre-connection + single branch power-on operation + other branches power-off cold standby + state inheritance switching" structure, while taking into account long-term low power consumption and recoverability after failure.

[0027] This invention uses an integrated board for the main control and framer, reducing high-speed serial connections on the backplane and inter-board connectors, thereby reducing power consumption and structural complexity, making it suitable for long-term unattended operation inside pressure chambers.

[0028] This invention achieves underwater node time synchronization correction through a hardware timestamp synchronization unit, a high-stability isothermal crystal oscillator, and a temperature-delay compensation model, which can meet the requirement of a unified time reference for the fusion of multi-node seabed observation data.

[0029] This invention maintains heat dissipation contact pressure through a multi-stage conductive heat dissipation structure and a double tension bar and inclined locking mechanism, which can improve thermal stability and long-term reliability in underwater pressure tank environments without fans or active cooling. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the overall architecture of a seabed observation network system using the OTN system; Figure 2 This is a block diagram of the internal functional modules of the underwater node; Figure 3 This is a block diagram of the integrated board consisting of the main control unit and the framer; Figure 4 This is a flowchart of the hardware time synchronization implementation method for 1588v2; Figure 5 This is a schematic diagram of the backup protection architecture for a primary and backup OTN system; Figure 6 This is the control flowchart for switching between primary and backup OTN systems; Figure 7 This is a block diagram of the multi-stage conductive heat dissipation implementation of the OTN system. Detailed Implementation

[0031] To achieve the above objectives, this invention provides a long-term service underwater OTN system for seabed observation networks, comprising an OTN communication main control unit and a time server located at a shore base station connected in series via submarine cables, and at least one underwater node. It employs a static optical transmission architecture with a fixed wavelength mapping relationship. Each underwater node includes multiple observation data optical interfaces, at least two independent OTN single-wavelength processing branches, a main control switching module, passive optical splitters corresponding one-to-one with the observation data optical interfaces, and passive optical combiners connecting the outputs of each branch. Each OTN single-wavelength processing branch maintains pre-connection to the passive optical splitter and passive optical combiner regardless of whether it is in a powered-on or powered-off standby state; during normal operation, only one branch is powered on, while the other branches consume no power and generate no heat.

[0032] When an abnormal optical power, packet loss rate, bit error rate, or persistent OTN alarm occurs in the currently operating OTN single-wavelength processing branch, the master control switching module powers on the backup branch and writes configuration information such as the current branch's ODUk mapping relationship, fixed wavelength parameters, PTP clock master-slave status, clock offset, and path delay parameters into the backup branch. This allows the backup branch to inherit the service and time synchronization status after a cold start. Since the input and output optical paths are pre-connected via passive devices, the switching process does not require underwater optical switch operation or underwater plugging / unplugging.

[0033] Preferably, the OTN single-wavelength processing branch adopts an integrated control and framing board, integrating the main control unit and the OTN framing unit on the same circuit board and interconnecting them through an internal signal channel, thereby reducing the need for high-speed serial links on the backplane, inter-board connectors, and related power consumption. This integrated board may include a hardware timestamp synchronization unit, a high-stability, temperature-controlled crystal oscillator, a temperature sensor, and a power management chip, and can achieve high-precision time synchronization of underwater nodes via 1588v2 / PTP.

[0034] Preferably, the underwater node adopts a multi-stage conductive heat dissipation structure, which conducts the heat generated by the heat-generating device to the external seawater through a flexible thermal conductive pad, a communication unit fixing structure, a heat sink, a high thermal conductivity interface material, an internal heat dissipation structure, and the inner wall of the pressure-resistant cabin; the double tensioning strip and the inclined locking mechanism cooperate to generate radial clamping force to maintain low thermal resistance contact between the heat dissipation structure and the inner wall of the pressure-resistant cabin during long-term service.

[0035] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0036] In this invention, the main control and framer integrated board 1 refers to the same board as the first main control and framer integrated board and the primary main control and framer integrated board; the main control and framer integrated board 2 refers to the same board as the second main control and framer integrated board and the backup main control and framer integrated board.

[0037] The hardware timestamp synchronization unit of this invention is preferably a 1588v2 hardware timestamp engine.

[0038] Example 1 Embodiment 1 of the present invention provides a deep-sea observation system with a depth of 3000 meters, a submarine cable length of 1000 km, a pressure-resistant chamber made of titanium alloy, and a network of 3 nodes, as detailed below: Appendix Figure 1 This is a schematic diagram of the overall architecture of the seabed observation network system using the OTN system of this invention.

[0039] like Figure 1 As shown, the communication of this observation network consists of an OTN communication master control unit at the shore base station, a time server, submarine optical cables, and OTN communication units within multiple underwater nodes. The distance between each underwater OTN communication unit ranges from tens to hundreds of kilometers, and different optical wavelengths, λ1, λ2, and λ3, are selected to communicate with the OTN communication master control unit via submarine optical cables using these wavelengths. The time server is used for remote time synchronization of the OTN communication units at the underwater nodes.

[0040] Appendix Figure 2 This is a block diagram showing the internal functional modules of an underwater node. (Example:) Figure 2 As shown, the underwater node internally includes a passive optical splitter, a first OTN single-wavelength processing branch, a second OTN single-wavelength processing branch, a main control switching module, and a passive optical combiner. Each observation data optical interface corresponds to one passive optical splitter. The input end of the passive optical splitter connects to the observation data optical interface of the corresponding observation equipment or lower-level access unit, and its multiple output ends connect to the input optical interfaces of the first and second OTN single-wavelength processing branches, respectively. The multiple input ends of the passive optical combiner connect to the output optical interfaces of the first and second OTN single-wavelength processing branches, respectively, and the output ends connect to the corresponding transmission optical fibers in the submarine optical cable.

[0041] The first and second OTN single-wavelength processing branches adopt the same or equivalent fixed wavelength configuration. Both include a main control and framing integrated board, a fixed wavelength optical module or laser, a power management circuit, and corresponding input / output optical interfaces. During normal operation, the first OTN single-wavelength processing branch is powered on and working, while the second OTN single-wavelength processing branch is powered off and in cold standby mode. Although the second OTN single-wavelength processing branch is powered off, its input terminal is still connected to each passive optical splitter, and its output terminal is still connected to the passive optical combiner.

[0042] Appendix Figure 3 This is a block diagram of the integrated board consisting of the main control unit and the framer. (Example:) Figure 3As shown, the integrated control and framing board includes a main control unit, an OTN framing unit, a hardware timestamp synchronization unit, a high-stability, temperature-controlled crystal oscillator, a temperature sensor, and a power management chip. The OTN framing unit has multiple 1G / 10G adaptive optical interfaces on its input side for accessing data from different observation devices; its output side has a 100G fixed-wavelength OTN optical interface for transmitting the aggregated observation data via submarine optical cable to the shore base station's OTN communication main control unit. The main control unit is used for OTN status monitoring, time synchronization parsing, primary / backup switchover configuration information management, and communication with the main control switchover control module. The 1588v2 hardware timestamp engine timestamps the time synchronization information sent by the shore base station time server and sends it to the main controller for time parsing. The temperature sensor provides temperature information for time accuracy deviation calculation. The high-stability constant temperature crystal oscillator provides a high-precision clock. Power management provides power to modules such as high-stability constant-temperature crystal oscillators and OTN framers; Appendix Figure 4 This is a flowchart illustrating the implementation method for hardware time synchronization in the 1588v2. Figure 4 As shown, the shore-based base station time server acts as the PTP master clock, sending PTP time synchronization messages to the underwater nodes via the OTN communication master control unit. The OTN framer parses the PTP time synchronization messages from the OTN frame or overhead channel and sends them to the 1588v2 hardware timestamp engine for hardware timestamp marking. The master control unit performs PTP slave clock parsing based on the hardware timestamp, the high-stability constant-temperature crystal oscillator, and the cabin temperature collected by the temperature sensor, and uses a time delay-temperature compensation model to correct the transmission delay drift caused by temperature changes.

[0043] The time delay-temperature compensation model can be expressed as: Δdelay = k1·ΔT + k2·(ΔT) 2 In one embodiment, the temperature sensor has a measurement accuracy of ±0.5℃ and a temperature sampling range of 0℃ to 40℃; after calibration and compensation, the 24-hour synchronization drift is less than 50ns, and the overall synchronization accuracy of the underwater node can reach ±300ns.

[0044] Primary / standby switchover process.

[0045] like Figure 5 and Figure 6 As shown, the main control switching control module includes a power supply control module, a power supply control circuit, a power supply control switch, and a current sensor. The power supply control module communicates with the currently operating OTN single-wavelength processing branch to acquire optical power, bit error rate, and OTN alarm status in real time. If the optical power is detected to be lower than a preset threshold, the bit error rate is detected to be higher than a preset threshold, the packet loss rate is detected to be higher than a preset threshold, or the OTN alarm persists for more than a preset time for N consecutive times, the currently operating OTN single-wavelength processing branch is determined to have failed. In one embodiment, N is 5, and the preset alarm duration is 1 second.

[0046] Upon failure detection, the power supply control module closes the power supply control switch of the backup branch via the power supply control circuit, powering the backup branch and activating the fixed-wavelength optical module or laser. Subsequently, it writes the configuration information stored in the current branch, including the ODUk mapping relationship, fixed-wavelength parameters, PTP master-slave status, clock offset, and path delay parameters, into the backup branch. After the backup branch enters the working state, its service optical signal is transmitted to the submarine optical cable via a pre-connected passive optical combiner. The power supply control module then shuts off the power supply to the original working branch, causing it to exit the working state.

[0047] Appendix Figure 7 A block diagram illustrating the multi-stage conductive heat dissipation implementation of an OTN system. (Example:) Figure 7 As shown, the heat-generating components of the underwater node include FPGAs, OTN framers, optical modules or lasers, and power management chips. These heat-generating components are bonded to flexible thermal pads, which in turn are bonded to the communication unit's mounting structure or its heat sink. A high thermal conductivity interface material is placed between the heat sink and the internal heat dissipation structure; this material fills the contact gaps and reduces contact thermal resistance. The internal heat dissipation structure is bonded to the inner wall of the pressure tank, ultimately conducting heat through the pressure tank to the external seawater.

[0048] Double tensioning strips are positioned on both sides of the heat dissipation plate, and the inclined locking mechanism forms a wedge-shaped fit with the double tensioning strips. During assembly, the radial clamping force is generated by the locking inclined mechanism, causing the internal heat dissipation structural components to continuously press against the inner wall of the pressure-resistant chamber, thereby improving thermal conductivity stability. Unlike "high thermal conductivity composite materials," the internal heat dissipation structural components are structural components that bear heat transfer and mechanical support, and the high thermal conductivity interface material is a gap-filling material used to reduce contact thermal resistance.

[0049] Example 2 Embodiment 2 of the present invention provides a long-term service underwater OTN system for seabed observation networks: A long-term service underwater OTN system for seabed observation networks includes: an OTN communication master control unit located at a shore base station, a time server, a submarine optical cable, and at least one underwater node. The underwater node is communicatively connected to the OTN communication master control unit via the submarine optical cable, and is used to aggregate and transmit seabed observation data and receive shore-based control information and time synchronization information. The underwater node adopts a static optical transmission architecture based on a fixed wavelength mapping relationship. Each underwater node includes multiple observation data optical interfaces, at least two independent OTN single-wavelength processing branches, a master control switching module, passive optical splitters corresponding to the observation data optical interfaces, and passive optical combiners connecting the outputs of each OTN single-wavelength processing branch. Each OTN single-wavelength processing branch includes a master control and framing integrated board, a fixed-wavelength optical module or laser, a power management circuit, and corresponding input / output optical interfaces. Each passive optical splitter is used to transfer the observation data input from the corresponding observation data optical interface. The data optical signals are distributed to the input optical interfaces of each OTN single-wavelength processing branch. The passive optical combiner is used to pre-connect the output optical interfaces of each OTN single-wavelength processing branch to the corresponding transmission optical fibers in the submarine optical cable. Each OTN single-wavelength processing branch maintains optical path connection with the corresponding passive optical splitter and passive optical combiner, regardless of whether it is in a powered-on or powered-off standby state. During normal operation, only one OTN single-wavelength processing branch is in a powered-on state, while the others are in a powered-off standby state. The master control switching control module is configured to, when it determines that the currently working OTN single-wavelength processing branch has failed, control the other OTN single-wavelength processing branch in the powered-off standby state to be powered on, and write the configuration information of the currently working branch into the other OTN single-wavelength processing branch to achieve the inheritance switching of service and time synchronization states. The underwater node does not have optical layer dynamic scheduling devices, including reconfigurable optical add-drop multiplexers, optical switches, and wavelength tuners.

[0050] The integrated control and framing board integrates the main control unit and the OTN framing unit on the same circuit board. The main control unit and the OTN framing unit are directly interconnected through the on-board signal channel to reduce high-speed serial connections on the backplane. The integrated control and framing board also includes a hardware timestamp synchronization unit, a high-stability constant-temperature crystal oscillator, a temperature sensor, and a power management chip. The input side of the OTN framing unit includes multiple adaptive optical interfaces for receiving seabed observation data, and the output side includes a fixed-wavelength OTN optical interface for transmitting the aggregated observation data to the OTN communication main control unit via a submarine optical cable.

[0051] The main control switching module includes a power supply control module, a power supply control circuit, a power supply control switch, and a current sensor. The current sensor is used to monitor the power supply status of each OTN single-wavelength processing branch. The power supply control module is used to communicate with the currently operating OTN single-wavelength processing branch to obtain optical power, bit error rate, and OTN alarm status information. When at least one of the following abnormal conditions is detected N times consecutively: optical power is lower than a preset optical power threshold, bit error rate is higher than a preset bit error rate threshold, or OTN alarm persists for more than a preset time, the power supply control module determines that the currently operating OTN single-wavelength processing branch has failed and controls the power supply control switch through the power supply control circuit to power on the OTN single-wavelength processing branch that is in a power-off cold standby state.

[0052] The master control switching module is configured to perform master-slave switching according to the following steps: S1, the currently operating first OTN single-wavelength processing branch collects optical power, bit error rate, and OTN alarm status in real time and sends them to the master control switching module; S2, the master control switching module determines whether the status meets preset abnormal conditions. If not, it continues monitoring; if it does, it generates a switching command; S3, the master control switching module controls the second OTN single-wavelength processing branch to power on, enabling its fixed wavelength optical module or laser to start; S4, the master control switching module writes the configuration information of the first OTN single-wavelength processing branch into the second OTN single-wavelength processing branch. The configuration information includes at least one of ODUk mapping relationship, fixed wavelength parameters, PTP clock master-slave status, clock offset, and path delay parameters; S5, the second OTN single-wavelength processing branch sends service optical signals to the submarine optical cable via a passive optical combiner; S6, the master control switching module shuts off the power supply to the first OTN single-wavelength processing branch.

[0053] The hardware timestamp synchronization unit is a 1588v2 hardware timestamp engine. The time server sends PTP time synchronization messages to the underwater node via the OTN communication master control unit. The OTN framer parses the PTP time synchronization messages and sends them to the 1588v2 hardware timestamp engine for hardware timestamp marking. The master control unit performs PTP clock parsing based on the hardware timestamp, the high-stability constant-temperature crystal oscillator, and the cabin temperature collected by the temperature sensor, and corrects the time synchronization result according to the delay-temperature compensation model. The delay-temperature compensation model is: Δdelay = k1·ΔT + k2·(ΔT) 2 Where Δdelay is the transmission delay correction relative to the reference temperature, ΔT is the difference between the current temperature and the reference temperature, and k1 and k2 are temperature-delay compensation coefficients obtained through calibration.

[0054] The underwater node employs a heat dissipation structure based on conductive heat dissipation. This structure includes a flexible thermally conductive pad attached to the heat-generating device, a communication unit fixing structure, a heat dissipation plate mounted on the communication unit fixing structure, a high thermal conductivity interface material, an internal heat dissipation structure, double tensioning strips, and a beveled locking mechanism. The heat generated by the heat-generating device is sequentially conducted to the external seawater through the flexible thermally conductive pad, the communication unit fixing structure, the heat dissipation plate, the high thermal conductivity interface material, the internal heat dissipation structure, and the inner wall of the pressure-resistant chamber. The double tensioning strips are located on both sides of the heat dissipation plate, and the beveled locking mechanism forms a wedge-shaped fit with the double tensioning strips, which generates a radial clamping force after locking, causing the internal heat dissipation structure to press against the inner wall of the pressure-resistant chamber.

[0055] This embodiment has completed comprehensive tests of hydrostatic pressure, circulating temperature, and mechanical vibration, and works normally after deep-sea deployment, with all indicators meeting the design requirements.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A long-term service underwater OTN system for seabed observation networks, comprising: The system comprises an OTN communication main control unit and a time server connected in series via a submarine cable at a shore-based base station, and at least one underwater node. The underwater node employs a static optical transmission architecture with a fixed wavelength mapping relationship, and optical transmission is achieved through electrical layer OTN frame processing and a fixed wavelength division multiplexer. The underwater node includes: an observation data optical interface, a main control switching module, at least two independent OTN single-wavelength processing branches, and a passive optical combiner. Multiple OTN single-wavelength processing branches are used for cold backup redundancy. The OTN single-wavelength processing branch includes: a passive optical splitter and a main control and framing integrated board, each corresponding to one of the observation data optical interfaces. Each passive optical splitter is used to distribute the observation data optical signal input from the corresponding observation data optical interface to the input optical interface of each OTN single-wavelength processing branch. The passive optical combiner is used to pre-connect the output optical interface of each OTN single-wavelength processing branch to the corresponding transmission optical fiber in the submarine optical cable. Each OTN single-wavelength processing branch maintains optical path connection with the corresponding passive optical splitter and passive optical combiner, regardless of whether it is in a powered-on working state.

2. The long-term service underwater OTN system for seabed observation networks as described in claim 1, characterized in that, The integrated main control and framing board is used to achieve framing of multi-channel observation data, high-precision time synchronization, and status monitoring. The status monitoring specifically involves the following: if the primary main control and framing board detects that the optical power, packet loss rate, and bit error rate exceed the threshold for more than a set number of consecutive times, and the alarm duration exceeds the threshold, then the primary main control and framing board is deemed to have failed. The main control switching control module controls the backup main control and framing board to power on and writes the configuration information to the backup main control and framing board to achieve the inheritance and switching of service and time synchronization status.

3. The long-term service underwater OTN system for seabed observation networks as described in claim 2, characterized in that, The integrated board for the main control and framer includes: a main control MCU, an OTN framer, a high-stability constant-temperature crystal oscillator, a hardware timestamp synchronization unit, a temperature sensor, and a power management chip; wherein, the main control MCU and the OTN framer are integrated on the same circuit board and directly interconnected through the on-board signal channel to reduce high-speed serial connections on the backplane. The main control MCU is used for high-precision time analysis, OTN status monitoring, master-slave switching control, and communication with the master switching control module, reporting information such as optical power, packet loss rate, and bit error rate; The OTN framer contains multiple optical interfaces. The input side consists of multiple adaptive optical interfaces for receiving seabed observation data. The output side has a fixed wavelength optical interface for transmitting the data collected from the input side to the OTN communication main control unit via a submarine optical-electric composite cable. High-stability temperature-controlled crystal oscillators are used to provide high-precision clocks. The hardware timestamp synchronization unit is used to timestamp the time synchronization information sent by the OTN communication master control unit time server and send it to the master control MCU for time parsing; Temperature sensor is used to provide temperature information and calculate time accuracy deviation; Power management chips are used to supply power to modules such as high-stability constant-temperature crystal oscillators and OTN framers.

4. The long-term service underwater OTN system for seabed observation networks as described in claim 1, characterized in that, The main control switching control module consists of a current sensor, a power supply control module, a power supply control circuit, and a power supply control switch; wherein, Current sensors are used to monitor the power supply status of each main control and framer integrated board; The power supply control module communicates with the primary and backup integrated control and framer boards respectively to obtain real-time status information on optical power, packet loss rate, and bit error rate. When the optical power of the primary integrated control and framer board is lower than the threshold for more than a set number of consecutive detections and the alarm continues to exceed the threshold, or the packet loss rate or bit error rate exceeds the threshold, the primary integrated control and framer board is determined to be faulty. The power supply control circuit controls the power supply control switch to power on the backup integrated control and framer board and power off the primary integrated control and framer board.

5. The long-term service underwater OTN system for seabed observation networks as described in claim 2, characterized in that, The execution steps for switching the primary and backup main control and framer integrated board at the underwater node include: Step 1: When the system is running, the first main control and framer integrated board is powered on. The board collects optical power, bit error rate and packet loss rate status data in real time and sends them to the main control switching control module. Step 2: The main control switching control module continuously monitors the status data. If the optical power, packet loss rate, and bit error rate exceed the threshold for more than a set number of consecutive times and the alarm duration exceeds the threshold, a switching command is generated and sent to the power supply control circuit; otherwise, proceed to step 1. Step 3: After receiving the switching command, the power supply control circuit turns on the power supply control switch of the second main control and framer integrated board, and the second main control and framer integrated board, which is in a power-off cold backup state, is powered on. Step 4: The laser on the second main control and framer integrated board is activated, and the service is sent to the submarine cable through the passive optical combiner. Step 5: The master control switching control module sends the configuration information of the first master control and framer integrated board to the second master control and framer integrated board. The configuration information includes the master-slave status of the PTP clock parameters, the offset, and the path delay parameters. Step 6: The main control switching control module shuts off the power supply to the integrated board of the first main control and framer.

6. The long-term service underwater OTN system for seabed observation networks as described in claim 3, characterized in that, The high-precision time synchronization of the integrated board between the main control unit and the framer is achieved through the cooperation of the OTN framer, the hardware timestamp synchronization unit, the high-stability constant-temperature crystal oscillator, the main control MCU, and the temperature sensor. The time server sends the time synchronization message to the OTN framer via the submarine optical cable through the OTN communication main control unit. The OTN framer parses the time synchronization message and sends it to the hardware timestamp synchronization unit. The hardware timestamp synchronization unit timestamps the message and then sends it to the PTP slave clock inside the main control MCU. The PTP slave clock performs the final parsing of the message and uses a time delay-temperature compensation model for correction, thereby eliminating the synchronization error caused by temperature drift. The time delay-temperature compensation model is as follows: Δdelay = k1·ΔT + k2·(ΔT) 2 ; Where Δdelay is the time delay caused by relative temperature change, k1 is the primary temperature delay coefficient, k2 is the secondary temperature delay coefficient, and ΔT is the temperature change value.

7. The long-term service underwater OTN system for seabed observation networks as described in claim 1, characterized in that, The underwater node employs a heat dissipation structure based on conduction, including: The heat-generating devices on the main control and framing integrated board are mounted to the communication unit fixing structure through close contact with the flexible thermal conductive pad. The communication unit fixing structure is in close contact with the inner wall of the cabin through a high thermal conductivity interface material, and is then fixed to the inner wall of the cabin by a locking mechanism. The heat from the heat-generating devices is conducted into the seawater through the flexible thermal conductive pad, the communication unit fixing structure, the high thermal conductivity interface material, and the pressure-resistant inner wall of the cabin.

8. The long-term service underwater OTN system for seabed observation networks as described in claim 1, characterized in that, The active devices in the underwater node adopt a triple derating design of voltage, current, and junction temperature, and are selected as automotive-grade or aerospace-grade. The active devices include: power management chip, clock buffer, main control MCU, and optical module driver chip.

9. The long-term service underwater OTN system for seabed observation networks as described in claim 1, characterized in that, To reduce heat generation, high-power, complex, and dynamically scheduled optical layer reconfiguration devices are not used. The optical layer reconfiguration devices include: a reconfigurable optical add-drop multiplexer, an optical switch, and a wavelength tuner.

10. The long-term service underwater OTN system for seabed observation networks as described in claim 1, characterized in that, The underwater node also includes: The business performance monitoring module is used to report error seconds, critical error seconds, and unavailable seconds in OTN overhead in real time. The built-in instrumentation module is used to send test frames and measure latency and jitter before service activation; the multi-level loopback module supports OTN-level loopback, port loopback and optical module loopback. The online upgrade module is used to support receiving upgrade packages via the optical monitoring channel or OTN overhead channel, enabling online upgrades of FPGA logic and embedded software, and supporting rollback.

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