Gas leakage alarm method and system based on self-healing network

Abstract

The invention discloses a gas leakage alarm method and system based on a self-healing network, and the method comprises the steps: constructing the self-healing network composed of a terminal node, routing nodes and an aggregation node in an underground pipe gallery, the terminal node registering at least K routing nodes as father nodes, K > = 2, and K belongs to N; when any terminal node detects a gas leakage event, an alarm frame is constructed; transmitting the alarm frame copies carrying different path labels to corresponding routing nodes through a terminal node by adopting a parallel multi-path mode; performing de-duplication processing on the received alarm frame copy through a routing node, and sending the alarm frame copy after de-duplication processing to a sink node; and sending an end-to-end acknowledgement frame to the terminal node through the sink node based on the received alarm frame copy. By using the scheme of the invention, network resource waste and processing of redundant information by a back-end system are avoided, reliable closed-loop communication is constructed, and successful delivery and integrity of alarm information are guaranteed.

Description

Technical Field

[0001] This application generally relates to the field of wireless sensor network technology. More specifically, this application relates to a gas leak alarm method and system based on a self-healing network. Background Technology

[0002] Underground utility tunnels are a vital infrastructure component of modern cities, with the safe operation of gas pipelines being of paramount importance. Real-time, reliable monitoring, alarm systems, and initial location assessment of gas leaks are crucial for ensuring tunnel safety and preventing major accidents.

[0003] Currently, monitoring methods based on wireless sensor networks (WSNs) are widely studied, but their application in the unique environment of underground utility tunnels faces numerous challenges. First, the complex and elongated structure of underground utility tunnels leads to severe attenuation of wireless signals, significant multipath effects, and substantial external interference. This results in a substantial decrease in the communication quality of traditional wireless sensor networks, with high transmission delays and packet loss rates for alarm information. Second, monitoring nodes within utility tunnels are typically battery-powered, requiring strict power consumption control. Existing network protocols struggle to achieve rapid response to emergencies such as gas leaks while maintaining low power consumption and low duty cycle operation.

[0004] More importantly, due to harsh environments and node aging, sensor nodes or communication links in the network are prone to failure. Traditional wireless network structures and transmission protocols lack effective self-healing and fault-tolerance mechanisms. Once a critical node or link fails, it can easily cause partial or even complete network paralysis, creating monitoring blind spots and failing to meet the "always online" and high reliability requirements of gas monitoring. In addition, existing network construction methods are mostly general-purpose designs that are not optimized for the special topology of underground pipe corridors, which are long, narrow, and linear. This makes it difficult to achieve dense deployment of monitoring nodes and efficient and robust transmission of alarm signals.

[0005] In view of this, there is an urgent need to provide a solution for underground gas pipeline leakage alarm based on self-healing network, which can adapt to the strong interference and high dynamic environment of underground pipe gallery, and take into account low power consumption and fast response, so as to achieve low latency and high reliability transmission of gas leakage alarm signal. Summary of the Invention

[0006] In order to at least solve one or more of the technical problems mentioned above, this application proposes a gas leak monitoring and alarm scheme based on self-healing networks in several aspects.

[0007] In a first aspect, this application provides a gas leak alarm method based on a self-healing network, comprising: constructing a self-healing network consisting of terminal nodes, routing nodes, and aggregation nodes within an underground utility tunnel, wherein each terminal node registers at least K routing nodes as parent nodes, where K ≥ 2, K ∈ N; when any terminal node detects a gas leak event, constructing an alarm frame, wherein the alarm frame includes an alarm ID, sequence number, priority, expiration time, lifetime, path label, source node ID, sensor location information, digital signature, and message integrity check code; transmitting copies of the alarm frame carrying different path labels to the corresponding routing nodes via parallel multipathing by the terminal nodes; deduplicating the received alarm frame copies via the routing nodes and sending the deduplicated alarm frame copies to the aggregation nodes; and sending an end-to-end acknowledgment frame to the terminal nodes based on the received alarm frame copies via the aggregation nodes.

[0008] In some embodiments, during the construction of a self-healing network consisting of terminal nodes, routing nodes, and aggregation nodes, the following steps are performed: Each parent node periodically maintains a neighbor table, recording information including link quality indicators, expected transmission counts, round-trip time, queue level, remaining energy, and channel ID; based on the recorded information, a weighted score for each parent node is calculated, wherein the formula for calculating the weighted score of the parent node is: S = w1LQI + w2(1 / ETX) + w3(1 / RTT) + w4(1 / Q) + w5E, where LQI is the link quality indicator, w1 is the link quality index, and w2 is the link quality index. The weights are as follows: ETX is the expected transmission count, w2 is the weight of the expected transmission count, RTT is the round-trip time, w3 is the weight of the round-trip time, Q is the queue level, w4 is the weight of the queue level, E is the remaining energy, and w5 is the weight of the remaining energy. The system determines whether the communication link between the terminal node or routing node and its corresponding parent node meets the self-healing trigger condition. If the self-healing trigger condition is met, a parent node handover and / or channel handover is performed based on the weighted score of the remaining parent nodes other than the current parent node. If the self-healing trigger condition is not met, the system returns to the step of each parent node periodically maintaining its neighbor table.

[0009] In some embodiments, the self-healing triggering conditions include: heartbeat loss, ACK loss, RTT surge, and CCA failure rate increase; when one of the heartbeat loss, ACK loss, and RTT surge triggering conditions is met, it is determined whether the highest value among the weighted scores of the remaining parent nodes other than the current parent node exceeds a scoring threshold; in response to the highest value among the weighted scores of the remaining parent nodes other than the current parent node exceeding the scoring threshold, the current parent node is switched to the parent node corresponding to the highest value among the weighted scores; in response to the highest value among the weighted scores of the remaining parent nodes other than the current parent node not exceeding the scoring threshold, the channel is switched from the current channel to a candidate channel set. The next channel is selected, and the current channel is removed from the candidate channel set and added to the channel blacklist. When the CCA failure rate increases, the current channel is switched to the next channel in the candidate channel set, and it is determined whether there is a parent node on the switched channel whose highest weighted score exceeds the scoring threshold. In response to the existence of a parent node on the switched channel whose highest weighted score exceeds the scoring threshold, it is designated as the current parent node. In response to the existence of a parent node on the switched channel whose highest weighted score exceeds the scoring threshold, the process returns to the step of switching from the current channel to the next channel in the candidate channel set and performs channel switching again.

[0010] In some embodiments, during the process of transmitting copies of alarm frames carrying different path labels to the corresponding routing nodes via the terminal node using a parallel multipath method, the terminal node selects the first M parent nodes from its set of parent nodes and sends copies of alarm frames carrying different path labels to them in parallel.

[0011] In some embodiments, during the process of transmitting alarm frame copies carrying different path labels to the corresponding routing nodes via parallel multipathing by the terminal node, a deadline-aware retransmission strategy is adopted. This deadline-aware retransmission strategy includes the following steps: the terminal node calculates the remaining margin based on the deadline, round-trip time, and current time carried in the alarm frame copy, wherein the formula for calculating the remaining margin is: Slack represents the remaining margin, DL represents the cutoff time in the alarm frame replica, now represents the current time, and RTT represents the round-trip time in the alarm frame replica. The retransmission count and parallelism are adaptively adjusted based on the remaining margin value. It is determined whether the current remaining margin has decreased compared to the previous time step. If the current remaining margin has not decreased compared to the previous time step, no action is taken. If the current remaining margin has decreased compared to the previous time step, the terminal node reduces the retransmission interval. The retransmission interval is calculated using the formula: Interval_n = Initial_Interval × (1 / 2...). n-1), where Interval_n is the retransmission interval, Initial_Interval is the initial retransmission interval, and n is the number of retransmissions; wherein, in the process of adaptively adjusting the number of retransmissions and parallelism based on the value of the remaining margin, the following steps are performed: when the remaining margin is greater than the first preset value, the parallelism is set to the first threshold; when the remaining margin is less than or equal to the first preset value and greater than the second preset value, the number of retransmissions is increased by the second threshold; When the remaining margin is less than the first preset value but greater than or equal to the third preset value, the parallelism is increased by a third threshold; when the remaining margin is less than the third preset value, the number of retransmissions is decreased by a fourth threshold.

[0012] In some embodiments, during the deduplication process of the received alarm frame copy by the routing node, the following steps are performed: the routing node calculates the (alarm ID, sequence number) key corresponding to the received alarm frame copy; determines whether the (alarm ID, sequence number) key corresponding to the alarm frame copy exists in the deduplication table; in response to the (alarm ID, sequence number) key corresponding to the alarm frame copy existing in the deduplication table, determines that the alarm frame copy is a duplicate frame and discards it; in response to the (alarm ID, sequence number) key corresponding to the alarm frame copy not existing in the deduplication table, inserts the (alarm ID, sequence number) key corresponding to the alarm frame copy into the deduplication table.

[0013] In some embodiments, after the terminal node transmits copies of alarm frames carrying different path labels to the corresponding routing nodes using a parallel multipath approach, the terminal node performs the following steps: starting a timer to wait for an end-to-end acknowledgment frame sent by the aggregation node; determining whether an end-to-end acknowledgment frame has been received within a preset time set by the timer; in response to receiving an end-to-end acknowledgment frame within the preset time set by the timer, verifying the digital signature and message integrity check code corresponding to the alarm frame copy, and after successful verification, placing the terminal node in an idle state; in response to not receiving an end-to-end acknowledgment frame within the preset time set by the timer, determining whether the remaining margin is greater than 0, wherein the formula for calculating the remaining margin is: Slack is the remaining margin, DL is the deadline in the alarm frame replica, now is the current time, and RTT is the round-trip time in the alarm frame replica. In response to a remaining margin greater than 0, the terminal node retransmits the alarm frame by increasing parallelism, switching channels, increasing the number of retransmissions, and using exponential backoff to reduce the retransmission interval. In response to a remaining margin not greater than 0, the terminal node terminates the current alarm transmission and records the failure.

[0014] In some embodiments, the self-healing network employs a congestion and backpressure control mechanism. During this mechanism, the following steps are performed: the routing node determines whether it is in a congested state based on its own packet queue level and packet loss rate; if not in a congested state, no action is taken; if in a congested state, the routing node uploads congestion status information to the terminal node, and the terminal node performs a congestion response. During the congestion response by the terminal node, at least one of the following steps is performed: reducing the sampling and reporting frequency of non-alarm service data; aggregating multiple non-alarm service data packets; identifying the highest-priority data frame in its own queue and discarding data frames with lower priority than the highest priority.

[0015] In some embodiments, the self-healing network employs a low-power and fast-response operation mechanism. During this mechanism, the following steps are performed: When the terminal node does not detect a gas leak event, it operates in a first duty cycle mode and listens for information using a first listening time window; when the terminal node detects a gas leak event, it operates in a second duty cycle mode and listens for information using a second listening time window, and generates and sends an alarm activation message to the corresponding routing node. The alarm activation message includes at least an alarm type, a timestamp, and an initial path identifier, wherein the second duty cycle is greater than the first duty cycle, and the second listening time window is greater than the first listening time window; the corresponding routing nodes cascade their own duty cycles to be the same as the terminal node's, and select the optimal next-hop path for message forwarding based on the weighted score of their neighboring nodes; wherein all nodes on the selected optimal next-hop path synchronously activate a temporary coordinated forwarding time slot based on time-division multiple access according to the request in the alarm activation message.

[0016] In a second aspect, this application provides a gas leak alarm system based on a self-healing network, employing the gas leak alarm method based on a self-healing network as described in any embodiment of the first aspect. The system includes: a self-healing network construction module, used to construct a self-healing network composed of terminal nodes, routing nodes, and aggregation nodes within an underground utility tunnel, wherein each terminal node registers at least K routing nodes as parent nodes, where K≥2, K∈N; an alarm frame construction module, used to construct an alarm frame when any terminal node detects a gas leak event, wherein the alarm frame includes an alarm ID, sequence number, priority, expiration time, lifetime, path label, source node ID, sensor location information, digital signature, and message integrity check code; an alarm frame copying module, used to transmit alarm frame copies carrying different path labels to the corresponding routing nodes via the terminal nodes using a parallel multipath approach; a deduplication processing module, used to deduplicate the received alarm frame copies via the routing nodes and send the deduplicated alarm frame copies to the aggregation node; and an end-to-end confirmation frame sending module, used to send an end-to-end confirmation frame to the terminal nodes via the aggregation node based on the received alarm frame copies.

[0017] By employing the self-healing network-based gas leak alarm scheme described above, this embodiment significantly improves the reliability and resilience of gas leak alarms in complex environments such as underground utility tunnels by registering at least two parent nodes at the terminal node and transmitting alarm frame copies with detailed information using a parallel multi-path approach. This redundancy mechanism ensures that even if some paths or nodes fail, alarm information can still be quickly delivered through other paths, thereby greatly shortening the response time. Simultaneously, the deduplication process at the routing nodes avoids wasting network resources and redundant information processing in the backend system, while the sending of end-to-end acknowledgment frames from the aggregation node to the terminal node establishes reliable closed-loop communication, further guaranteeing the successful delivery and integrity of alarm information.

[0018] Furthermore, in some embodiments, by periodically collecting multi-dimensional key indicators including link quality, transmission latency, node load, and remaining energy, and using a weighted scoring formula to quantitatively evaluate each potential communication link, precise perception of network health status is achieved. This not only enables rapid switching to the highest-scoring backup parent node to restore communication after link interruption events such as lost heartbeats or missing ACKs, but also allows for proactive parent node switching or channel switching by monitoring early warning signals of performance degradation, such as sudden increases in round-trip latency or rising CCA failure rates. This hierarchical and orderly response strategy not only greatly improves the network's robustness and adaptability but also ensures efficient fault repair with minimal resource overhead. This allows the entire alarm network to automatically and quickly self-repair when facing complex challenges such as single-point failures, signal interference, or network congestion, ensuring the continuous smooth operation of the alarm path.

[0019] Furthermore, in some embodiments, a deadline-aware retransmission strategy optimizes the retransmission behavior of terminal nodes when transmitting alarm frame copies in parallel multipath transmission, ensuring that highly time-sensitive alarm information arrives reliably and on time. By calculating the remaining margin in real time, it can dynamically and adaptively adjust the number of retransmissions and the degree of parallelism. This means that when the deadline for the alarm frame is sufficient, the system will transmit efficiently; while when the deadline approaches and the remaining margin decreases, the system will strategically shorten the retransmission interval and increase the degree of parallelism or the number of retransmissions according to different preset thresholds, thereby maximizing the probability of successful alarm information transmission under time pressure. This intelligent retransmission mechanism avoids the occupation of network resources by invalid retransmissions, while significantly improving the real-time transmission success rate and response efficiency of critical alarm information in complex and dynamic network environments, ensuring the timeliness and reliability of alarm information.

[0020] Furthermore, in some embodiments, by setting up a closed-loop alarm transmission confirmation and adaptive retransmission mechanism, it is ensured that gas leak alarm information in underground utility tunnels can not only be sent, but also confirmed to have arrived safely and completely, and that intelligent recovery can be performed in the event of an initial transmission failure. The terminal node establishes a complete communication loop by starting a timer to wait for the end-to-end confirmation frame from the aggregation node, and ensures the authenticity and validity of the received confirmation by verifying the digital signature and message integrity check code. If no confirmation is received, the system calculates the remaining margin in real time and adopts a highly adaptive retransmission strategy based on the margin size: when there is still time margin, the terminal node dynamically increases parallelism, switches channels, increases the number of retransmissions, and uses exponential backoff to reduce the retransmission interval, maximizing the probability of successful alarm information delivery and demonstrating strong fault tolerance and recovery capabilities. When the time margin is exhausted, transmission is decisively terminated and the failure is recorded, effectively avoiding unnecessary consumption of network resources. This ensures the timeliness, security, and eventual reachability of critical alarm information, while also considering the efficiency of system operation. Attached Figure Description

[0021] The above and other objects, features, and advantages of exemplary embodiments of this application will become readily understood by reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of this application are illustrated by way of example and not limitation, and the same or corresponding reference numerals denote the same or corresponding parts, wherein: Figure 1 An exemplary flowchart of a gas leak alarm method based on a self-healing network according to an embodiment of this application is shown; Figure 2 A schematic diagram illustrating the composition of a self-healing network according to some embodiments of this application is shown; Figure 3A schematic diagram of the deployment of sensors along a natural gas pipeline according to an embodiment of this application is shown; Figure 4 An exemplary flowchart illustrating the construction of a self-healing network consisting of terminal nodes, routing nodes, and aggregation nodes according to an embodiment of this application is shown. Figure 5 An exemplary flowchart of the deadline-aware retransmission strategy according to an embodiment of this application is shown; Figure 6 This paper presents an exemplary flowchart of a routing node performing deduplication on a received copy of an alarm frame, according to an embodiment of this application. Figure 7 A timing diagram illustrating the working process of a terminal node according to an embodiment of this application is shown; Figure 8 An exemplary flowchart illustrating the congestion and back pressure control mechanism in an embodiment of this application is shown; Figure 9 An exemplary structural block diagram of a gas leak alarm system based on a self-healing network according to an embodiment of this application is shown. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] It should be understood that the terms "comprising" and "including" used in the specification and claims of this application indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0024] It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application. As used in this specification and claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used in this specification and claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations.

[0025] Figure 1 An exemplary flowchart of a gas leak alarm method 100 based on a self-healing network according to an embodiment of this application is shown.

[0026] like Figure 1 As shown, in step S110, a self-healing network consisting of terminal nodes, routing nodes, and aggregation nodes is constructed in the underground utility tunnel. The terminal nodes register at least K routing nodes as parent nodes, where K≥2 and K∈N.

[0027] In some embodiments of this application, the constructed self-healing network can be found in [reference needed]. Figure 2 .

[0028] like Figure 2 As shown, terminal node E registers two routing nodes as parent nodes, and routing node R supports forwarding and congestion reporting. Coordinator C is used as the aggregation node. There are two links between terminal node E and coordinator C, which can maintain transmission even if the links are interrupted. Specifically, terminal node E includes a GasSensor, AlarmStateMachine, NetworkModule, AckHandler, ultra-low power MCU, IEEE 802.15.4 RF, and low-noise power supply. It supports low duty cycle and event-triggered wake-up. Routing node R is used for enhanced storage and forwarding scheduling, congestion detection and backpressure mechanisms, and channel switching coordination. Coordinator C is used for end-to-end acknowledgment frame generation and multipath feedback, statistical learning weights w, blacklist B, candidate set H maintenance, and interface with the upper-level platform.

[0029] In the embodiments of this application, the deployment of sensors in the terminal node E within the natural gas pipeline can be found in [reference needed]. Figure 3 .

[0030] exist Figure 3 In this diagram, sensors are labeled using a simplified view. The reference information for the circular sensor layout on the surface of a simulated natural gas pipeline is provided. The pipeline is assumed to be an ideal cylinder with its central axis coinciding with the Z-axis of the global coordinate system. The cylinder radius is r, and the coordinate along the pipeline axis is z (relative to the reference point z0). The circumferential angle is represented by θ (0° is set to true north of the pipeline, increasing clockwise). The sensor position formula is: Location = {SensorSeq, θ, z}, where SensorSeq is the sensor serial number (uniquely identifying a sensor on the pipeline surface). The formula for calculating the three-dimensional rectangular coordinates of the sensors distributed on the pipeline is as follows: Where (x0, y0, z0) are the coordinates of the reference point at the center of the cylinder axis, r is the outer radius of the pipe, h is the axial offset relative to the reference point, and θ is the sensor orientation angle, which is consistent with the reference direction of the (x0, y0) plane.

[0031] In the embodiments of this application, the specific process of constructing a self-healing network consisting of terminal nodes, routing nodes, and aggregation nodes can be found in [reference needed]. Figure 4 .

[0032] Figure 4 An exemplary flowchart illustrating the construction of a self-healing network consisting of terminal nodes, routing nodes, and aggregation nodes is shown in an embodiment of this application.

[0033] like Figure 4 As shown, in step S410, each parent node periodically maintains a neighbor table, recording information including link quality indication, expected transmission count, round-trip time, queue level, remaining energy, and channel ID. In step S420, a weighted score for each parent node is calculated based on the recorded information. In step S430, it is determined whether the communication link between the terminal node or routing node and the corresponding parent node meets the self-healing trigger condition. In response to meeting the self-healing trigger condition, in step S440, parent node switching and / or channel switching are performed based on the weighted scores of the remaining parent nodes other than the current parent node. In response to not meeting the self-healing trigger condition, the process returns to step S410, that is, returns to the step of each parent node periodically maintaining its neighbor table.

[0034] Specifically, in calculating the weighted score of each parent node, the weighted score calculation formula for the parent node is adopted. The weighted score calculation formula for the parent node is: S=w1LQI+w2(1 / ETX)+w3(1 / RTT)+w4(1 / Q)+w5E, where LQI is the link quality indicator, w1 is the weight of the link quality indicator, ETX is the expected transmission count, w2 is the weight of the expected transmission count, RTT is the round-trip time, w3 is the weight of the round-trip time, Q is the queue level, w4 is the weight of the queue level, E is the remaining energy, and w5 is the weight of the remaining energy.

[0035] In the embodiments of this application, the weights w1-w5 are dynamically adjusted based on performance feedback (e.g., transmission success rate ≥99%, latency ≤200ms, and energy consumption). Initially, the weights are set to equal values ​​(e.g., 0.2 each, summing to 1), or adjusted based on prior knowledge (e.g., increasing w1 and w2 to prioritize link quality) to accelerate convergence. The learning process employs a progressive design, evaluating metrics after every 10 transmissions. A reward function is used to maximize transmission rate and minimize latency and energy consumption. Weights are updated via gradient descent (e.g., when w1 increases by 0.1, other weights decrease accordingly), ensuring low computational overhead and network self-healing robustness, thereby achieving efficient alarm transmission in interference environments.

[0036] In the embodiments of this application, the self-healing triggering conditions include: heartbeat loss, ACK absence, RTT surge, and CCA failure rate increase.

[0037] In the embodiments of this application, the specific details of the self-healing triggering conditions are shown in Table 1: Table 1 Self-Healing Triggering Conditions Specifically, when one of the following trigger conditions is met—heartbeat loss, ACK loss, or RTT surge—it is determined whether the highest value among the weighted scores of the remaining parent nodes (excluding the current parent node) exceeds a scoring threshold. If the highest value among the weighted scores of the remaining parent nodes exceeds the scoring threshold, the current parent node is switched to the parent node corresponding to the highest weighted score. If the highest value among the weighted scores of the remaining parent nodes does not exceed the scoring threshold, the current channel is switched to the next channel in the candidate channel set, and the current channel is removed from the candidate channel set and added to the channel blacklist.

[0038] Specifically, when the CCA failure rate increases, the system switches from the current channel to the next channel in the candidate channel set, and determines whether there is a parent node on the switched channel whose highest weighted score exceeds the scoring threshold. If a parent node with the highest weighted score exceeding the scoring threshold exists on the switched channel, it is designated as the current parent node. If a parent node with the highest weighted score exceeding the scoring threshold exists on the switched channel, the system returns to the step of switching from the current channel to the next channel in the candidate channel set, and the channel switching is performed again.

[0039] In the embodiments of this application, the scoring threshold is set according to actual needs and historical experience, and this application does not impose any restrictions on it.

[0040] After step S110 is completed, in step S120, when any terminal node detects a gas leak event, an alarm frame is constructed.

[0041] In the embodiments of this application, the aforementioned alarm frame includes an alarm ID, sequence number, priority, deadline, lifespan, path label, source node ID, sensor location information, digital signature, and message integrity check code.

[0042] Specifically, the data structure of the alarm frame is: AlarmFrame={AID, Seq, Pri, Deadline DL, TTL, PathTag, OriginID, Location: {SensorSeq, Angle, z}, Sig, MIC} For a detailed explanation of the data structure of the alarm frame, please refer to Table 2: Table 2. Detailed Explanation of the Data Structure of Alarm Frames After step S120 is completed, in step S130, the terminal node transmits copies of alarm frames carrying different path labels to the corresponding routing node in a parallel multipath manner.

[0043] In an embodiment of this application, during step S130, the terminal node selects the first M parent nodes from its set of parent nodes and sends copies of alarm frames carrying different path labels to them in parallel. Specifically, 2 ≤ M ≤ 4.

[0044] By carrying a different PathTag (path label, such as Path_A, Path_B, etc.) on each copy of the alarm frame to identify independent transmission paths, self-healing and redundancy are achieved, improving the transmission success rate to ≥99%.

[0045] In the embodiments of this application, a deadline-aware retransmission strategy is adopted during the execution of step S130.

[0046] The specific process involved in the deadline-aware retransmission strategy in the embodiments of this application can be found in [reference needed]. Figure 5 .

[0047] Figure 5 An exemplary flowchart of the deadline-aware retransmission strategy according to an embodiment of this application is shown.

[0048] like Figure 5 As shown, in step S510, the terminal node calculates the remaining margin based on the deadline, round-trip time, and current time carried in the alarm frame copy. In step S520, the retransmission count and parallelism are adaptively adjusted based on the remaining margin value. In step S530, it is determined whether the current remaining margin has decreased compared to the remaining margin at the previous time. If the current remaining margin has not decreased compared to the remaining margin at the previous time, no action is performed in step S540. If the current remaining margin has decreased compared to the remaining margin at the previous time, the terminal node reduces the retransmission interval in step S550.

[0049] In the embodiments of this application, the formula for calculating the residual margin is as follows: Slack is the remaining margin, DL is the cutoff time in the alarm frame copy, now is the current time, and RTT is the round-trip time in the alarm frame copy.

[0050] In the embodiments of this application, during the process of adaptively adjusting the number of retransmissions and the parallelism based on the value of the remaining margin, the following steps are performed: when the remaining margin is greater than a first preset value, the parallelism is set to a first threshold; when the remaining margin is less than or equal to the first preset value and greater than a second preset value, the number of retransmissions is increased by a second threshold; when the remaining margin is less than the first preset value and greater than or equal to a third preset value, the parallelism is increased by a third threshold; when the remaining margin is less than the third preset value, the number of retransmissions is decreased by a fourth threshold.

[0051] In some embodiments of this application, the first preset value is 150ms, the second preset value is 100ms, the third preset value is 50ms, the first threshold is 2, the second threshold ranges from 3 to 5, the third threshold ranges from 3 to 4, and the fourth threshold ranges from 1 to 2.

[0052] In the embodiments of this application, the retransmission interval is calculated using the formula: Interval_n = Initial_Interval × (1 / 2 n-1 ), where Interval_n is the retransmission interval, Initial_Interval is the initial retransmission interval, and n is the number of retransmissions.

[0053] In some embodiments of this application, the initial retransmission interval is 50ms.

[0054] Based on step S130, the terminal node selects M parent nodes from multiple parent nodes for parallel transmission and assigns a different path label to each alarm frame copy. This inherent multi-path redundancy mechanism ensures that even if some paths fail, the alarm information can still be successfully delivered through other paths, thereby increasing the transmission success rate to over 99% and significantly enhancing the network's self-healing capability and resilience. By calculating the remaining margin of alarm frame copies in real time, the urgency of the alarm information can be dynamically perceived, and the number of retransmissions and parallelism can be adaptively adjusted according to the size of the remaining margin. When time is ample, the retransmission behavior may be more conservative. However, when the remaining margin decreases, the system strategically shortens the retransmission interval and increases the parallelism or the number of retransmissions according to a preset threshold, thereby maximizing the probability of successful alarm information transmission under time pressure.

[0055] After step S130 is completed, in step S140, the received alarm frame copy is deduplicated by the routing node, and the deduplicated alarm frame copy is sent to the aggregation node.

[0056] In the embodiments of this application, the specific process of deduplicating received alarm frame copies through routing nodes can be found in [reference needed]. Figure 6 .

[0057] Figure 6An exemplary flowchart illustrating the deduplication process of received alarm frame copies via a routing node, according to an embodiment of this application, is shown.

[0058] like Figure 6 As shown, in step S610, the routing node calculates the (alarm ID, sequence number) key corresponding to the received alarm frame copy. In step S620, it is determined whether the (alarm ID, sequence number) key corresponding to the alarm frame copy exists in the deduplication table. If the (alarm ID, sequence number) key corresponding to the alarm frame copy exists in the deduplication table, in step S630, the alarm frame copy is determined to be a duplicate frame and discarded. If the (alarm ID, sequence number) key corresponding to the alarm frame copy does not exist in the deduplication table, in step S640, the (alarm ID, sequence number) key corresponding to the alarm frame copy is inserted into the deduplication table.

[0059] In the embodiments of this application, during the process of inserting the (alarm ID, sequence number) key corresponding to the alarm frame copy into the deduplication table, the digital signature and message integrity check code corresponding to the alarm frame copy are verified. Upon successful verification, the (alarm ID, sequence number) key corresponding to the alarm frame copy and its associated structured metadata (including but not limited to timestamps and processing status) are inserted into the deduplication table to mark that the alarm frame has been effectively received and processed. If verification fails, the alarm frame is determined to be an illegal or tampered message and is discarded without further processing or forwarding.

[0060] Based on step S140, the deduplication mechanism uniquely identifies each alarm frame using a (alarm ID, sequence number) key and quickly identifies and discards duplicate frames using a deduplication table. This significantly reduces the amount of invalid data transmitted in the network, optimizes network bandwidth and the processing burden on routing nodes, and improves the overall system efficiency. Before inserting an alarm frame into the deduplication table, the routing node performs digital signature and message integrity check code verification. This ensures that only legitimate and tamper-proof alarm frames are received and processed. Any illegal or tampered messages are immediately discarded, thereby enhancing the security of alarm transmission and preventing malicious attacks or data corruption.

[0061] In the embodiments of this application, the deduplication table (DedupTable) is a custom data structure specifically designed for alarm deduplication, aiming to efficiently filter duplicate alarm frame messages. It is implemented as a hash table to support fast lookup and insertion operations.

[0062] For a detailed explanation of the structure of the deduplication table in the embodiments of this application, please refer to Table 3: Table 3. Detailed Explanation of the Structure of the Deduplication Table After step S140 is completed, in step S150, the aggregation node sends an end-to-end confirmation frame to the terminal node based on the received copy of the alarm frame.

[0063] The working process of the terminal node in the embodiments of this application can be found in [reference]. Figure 7 .

[0064] like Figure 7 As shown, in the Idle state, the GasSensor on the terminal node continuously monitors the gas concentration. When the concentration exceeds a threshold, the GasSensor triggers the AlarmStateMachine to start. The AlarmStateMachine transitions from the Idle state to the Detect state and begins constructing an alarm frame, which includes key information such as Alarm ID (AID), Sequence Number (Seq), Priority (Pri), Time-to-Live (TTL), and PathTag. In the Detect state, the AlarmStateMachine completes the construction of the alarm frame. Subsequently, the alarm frame is added to the highest priority queue. The AlarmStateMachine then transitions from the Detect state to the Schedule state. In the Schedule state, the AlarmStateMachine sends a command to the NetworkModule, requesting the transmission of the alarm frame. After completing the transmission, the NetworkModule returns a confirmation of completion to the AlarmStateMachine. The AlarmStateMachine then transitions from the Schedule state to the Dispatch state. Next, in the Dispatch state, the AlarmStateMachine instructs the AckHandler (acknowledgment processor) to wait for an ACK (acknowledgment signal). The AckHandler is responsible for receiving the ACK signal, or determining a timeout if no ACK is received within a preset time. Whether an ACK is received or a timeout occurs, the AckHandler notifies the AlarmStateMachine. At this point, the AlarmStateMachine transitions from the Dispatch state to the AwaitAck state (awaiting acknowledgment).

[0065] Then, in the AwaitAck state, the AlarmStateMachine performs resource release operations, such as clearing copies of alarm frames in the queue and releasing memory. The AlarmStateMachine then transitions from the AwaitAck state to the Terminate state. In the Terminate state, the alarm processing flow ends, and the AlarmStateMachine transitions back to the Idle state, entering a loop to wait for the next trigger, preparing to process the next potential alarm event.

[0066] In the embodiments of this application, the detailed state description of the alarm state machine can be found in Table 4: Table 4. Detailed Explanation of Alarm State Machine States according to Figure 7 After the terminal node transmits copies of alarm frames carrying different path labels to the corresponding routing nodes using a parallel multipath approach, the terminal node first starts a timer to wait for the end-to-end acknowledgment frame sent by the aggregation node. Next, it checks whether an end-to-end acknowledgment frame has been received within the preset time set by the timer. If an end-to-end acknowledgment frame is received within the preset time set by the timer, the digital signature and message integrity check code corresponding to the alarm frame copy are verified. Upon successful verification, the terminal node enters an idle state. If no end-to-end acknowledgment frame is received within the preset time set by the timer, it checks whether the remaining margin is greater than 0. If the remaining margin is greater than 0, the terminal node retransmits the alarm frame by increasing parallelism, switching channels, increasing the number of retransmissions, and using exponential backoff to reduce the retransmission interval. If the remaining margin is not greater than 0, the terminal node terminates the current alarm transmission and records the failure.

[0067] The terminal node waits for the end-to-end acknowledgment (ACK) frame from the aggregation node by starting a timer. Only after receiving and verifying the digital signature and message integrity of the ACK is the alarm transmission considered successful. This fundamentally ensures that the alarm information is not only sent but also securely and completely received by the target. If no ACK is received, the system does not simply give up but intelligently assesses the remaining margin of the alarm (i.e., the urgency of the alarm and the remaining time). When time permits (remaining margin is greater than 0), the terminal node actively takes a series of enhancement measures, including increasing parallelism, switching channels, increasing the number of retransmissions, and using exponential backoff to reduce the retransmission interval, to maximize the success rate of alarm frame retransmission.

[0068] In the embodiments of this application, during the execution of steps S120-S150, the self-healing network employs a congestion and back pressure control mechanism.

[0069] For details regarding the specific processes involved in employing the congestion and backpressure control mechanism in the embodiments of this application, please refer to [link / reference needed]. Figure 8 .

[0070] Figure 8 An exemplary flowchart illustrating the congestion and backpressure control mechanism in an embodiment of this application is shown.

[0071] like Figure 8 As shown, in step S810, the routing node determines whether it is in a congested state based on its own packet queue level and packet loss rate. If it is not in a congested state, no action is taken in step S820. If it is in a congested state, in step S820, the routing node uploads congestion status information to the terminal node, and the terminal node responds to the congestion.

[0072] In the embodiments of this application, during the congestion response process through the terminal node, at least one of the following steps is performed: reducing the sampling and reporting frequency of non-alarm service data; aggregating multiple non-alarm service data packets; identifying the highest priority data frame in its own queue and discarding data frames with a priority lower than the highest priority.

[0073] Specifically, during congestion response, terminal nodes reduce sampling frequency (e.g., from 1Hz to 0.1Hz), combine non-alarm service data (e.g., batch-pack sensor readings to reduce transmission volume), and discard low-priority data (e.g., frames with priority < alarm level) at routing or aggregation nodes when necessary, ensuring clear response from alarm channels. This seamlessly integrates with state machines and end-to-end acknowledgments, achieving resource optimization and network reliability.

[0074] In the embodiments of this application, during the execution of steps S120-S150, the self-healing network adopts a low-power and fast-response operation mechanism.

[0075] In the embodiments of this application, during the low-power and fast-response operation mechanism, when the terminal node does not detect a gas leak event, it operates in a first duty cycle mode and listens for information using a first listening time window. When the terminal node detects a gas leak event, it operates in a second duty cycle mode and listens for information using a second listening time window, and generates and sends an alarm activation message to the corresponding routing node. The alarm activation message includes at least the alarm type, timestamp, and initial path identifier, wherein the second duty cycle is greater than the first duty cycle, and the second listening time window is greater than the first listening time window. Then, the corresponding routing nodes cascade their own duty cycles to be the same as the terminal node's, and select the optimal next-hop path for message forwarding based on the weighted score of their neighboring nodes.

[0076] Specifically, for all nodes on the selected optimal next-hop path, a temporary coordinated forwarding time slot based on time division multiple access is synchronously activated according to the request in the alarm activation message.

[0077] In the embodiments of this application, the triggering node embeds a slot activation request in the alarm activation message, indicating the need to activate a temporary time-division multiple access (TDMA) based coordinated forwarding slot for priority transmission of alarm data. Nodes receiving the alarm activation message containing the slot activation request (i.e., nodes on the alarm path) will acknowledge it. Once acknowledged, these nodes will synchronously activate the TDMA-based coordinated forwarding slot. This means they will allocate slots specifically for priority transmission of alarm data within a predetermined time period (e.g., slot length of 100-200 milliseconds, period of 1 second). To ensure slot synchronization of all relevant nodes, the system uses a heartbeat signal to maintain precise clock synchronization. Through this synchronization mechanism, the communication channel is dynamically divided into dedicated slots, forming a temporary coordination chain. This chain will cover all nodes on the optimal transmission path from the triggering terminal node to the aggregation node. This temporary coordination chain particularly supports multipath transmission, further enhancing the reliability of alarm information. During slot activation, if a node detects channel interference (e.g., increased failure rate via CCA), the system, using a self-healing mechanism, switches to an available channel and restarts and synchronizes the temporary coordinated time slot on this new channel to ensure transmission continuity. Once the alarm is cleared (e.g., via a "network activation confirmation" instruction broadcast by the coordinator, or automatically after 5-10 minutes, or by manual confirmation), the relevant nodes are notified via a clearance message. Nodes receiving the clearance message will close the temporary coordinated forwarding time slot and fall back to a low duty cycle normal operating mode, thereby saving energy.

[0078] In some embodiments of this application, the first duty cycle is 1%-5%, the second duty cycle is 50%-100%, the first listening time window is 50ms-100ms, and the second listening time window is 1-5 seconds.

[0079] In summary, the gas leak alarm scheme based on a self-healing network, as described above, significantly improves the reliability and resilience of gas leak alarms in complex environments such as underground utility tunnels by forcibly registering at least two parent nodes at the terminal node and employing a parallel multi-path approach to transmit alarm frame copies with detailed information. This redundancy mechanism ensures that even if some paths or nodes fail, alarm information can still be quickly delivered through other paths, thereby greatly shortening the response time. Simultaneously, the deduplication process at the routing nodes avoids wasting network resources and redundant information processing in the backend system, while the sending of end-to-end acknowledgment frames from the aggregation node to the terminal node establishes a reliable closed-loop communication, further guaranteeing the successful delivery and integrity of alarm information.

[0080] Furthermore, in some embodiments, by periodically collecting multi-dimensional key indicators including link quality, transmission latency, node load, and remaining energy, and using a weighted scoring formula to quantitatively evaluate each potential communication link, precise perception of network health status is achieved. This not only enables rapid switching to the highest-scoring backup parent node to restore communication after link interruption events such as lost heartbeats or missing ACKs, but also allows for proactive parent node switching or channel switching by monitoring early warning signals of performance degradation, such as sudden increases in round-trip latency or rising CCA failure rates. This hierarchical and orderly response strategy not only greatly improves the network's robustness and adaptability but also ensures efficient fault repair with minimal resource overhead. This allows the entire alarm network to automatically and quickly self-repair when facing complex challenges such as single-point failures, signal interference, or network congestion, ensuring the continuous smooth operation of the alarm path.

[0081] Furthermore, in some embodiments, a deadline-aware retransmission strategy optimizes the retransmission behavior of terminal nodes when transmitting alarm frame copies in parallel multipath transmission, ensuring that highly time-sensitive alarm information arrives reliably and on time. By calculating the remaining margin in real time, it can dynamically and adaptively adjust the number of retransmissions and the degree of parallelism. This means that when the deadline for the alarm frame is sufficient, the system will transmit efficiently; while when the deadline approaches and the remaining margin decreases, the system will strategically shorten the retransmission interval and increase the degree of parallelism or the number of retransmissions according to different preset thresholds, thereby maximizing the probability of successful alarm information transmission under time pressure. This intelligent retransmission mechanism avoids the occupation of network resources by invalid retransmissions, while significantly improving the real-time transmission success rate and response efficiency of critical alarm information in complex and dynamic network environments, ensuring the timeliness and reliability of alarm information.

[0082] Furthermore, in some embodiments, by setting up a closed-loop alarm transmission confirmation and adaptive retransmission mechanism, it is ensured that gas leak alarm information in underground utility tunnels can not only be sent, but also confirmed to have arrived safely and completely, and that intelligent recovery can be performed in the event of an initial transmission failure. The terminal node establishes a complete communication loop by starting a timer to wait for the end-to-end confirmation frame from the aggregation node, and ensures the authenticity and validity of the received confirmation by verifying the digital signature and message integrity check code. If no confirmation is received, the system calculates the remaining margin in real time and adopts a highly adaptive retransmission strategy based on the margin size: when there is still time margin, the terminal node dynamically increases parallelism, switches channels, increases the number of retransmissions, and uses exponential backoff to reduce the retransmission interval, maximizing the probability of successful alarm information delivery and demonstrating strong fault tolerance and recovery capabilities. When the time margin is exhausted, transmission is decisively terminated and the failure is recorded, effectively avoiding unnecessary consumption of network resources. This ensures the timeliness, security, and eventual reachability of critical alarm information, while also considering the efficiency of system operation.

[0083] This application also provides a gas leak alarm system based on a self-healing network, which can use the aforementioned gas leak alarm method 100 based on a self-healing network to trigger an alarm, or it can use other methods to trigger an alarm. This application does not limit the methods used here.

[0084] Figure 9 An exemplary structural block diagram of a gas leak alarm system based on a self-healing network according to an embodiment of this application is shown.

[0085] like Figure 9 As shown, the system 900 includes a self-healing network construction module 910, an alarm frame construction module 920, an alarm frame copy module 930, a deduplication processing module 940, and an end-to-end acknowledgment frame sending module 950. In the embodiments of this application, the self-healing network construction module 910, the alarm frame construction module 920, the alarm frame copy module 930, the deduplication processing module 940, and the end-to-end acknowledgment frame sending module 950 may be separate units or integrated into the same controller; this application does not impose any restrictions here.

[0086] Specifically, the self-healing network construction module 910 is used to construct a self-healing network consisting of terminal nodes, routing nodes, and aggregation nodes in the underground utility tunnel. The terminal nodes register at least K routing nodes as parent nodes, where K≥2 and K∈N.

[0087] Specifically, the alarm frame construction module 920 is used to construct an alarm frame when any terminal node detects a gas leak event. The alarm frame includes an alarm ID, serial number, priority, expiration time, lifespan, path label, source node ID, sensor location information, digital signature, and message integrity check code.

[0088] Specifically, the alarm frame copy module 930 is used to transmit alarm frame copies carrying different path labels to the corresponding routing nodes through the terminal node using a parallel multipath method.

[0089] Specifically, the deduplication module 940 is used to deduplicatize the received alarm frame copies through the routing node, and then send the deduplicated alarm frame copies to the aggregation node. Specifically, the end-to-end acknowledgment frame sending module 950 is used by the aggregation node to send an end-to-end acknowledgment frame to the terminal node based on the received copy of the alarm frame.

[0090] When system 900 uses the aforementioned gas leak alarm method 100 based on a self-healing network to trigger an alarm, the self-healing network construction module 910 executes step S110, the alarm frame construction module 920 executes step S120, the alarm frame copy module 930 executes step S130, the deduplication module 940 executes step S140, and the end-to-end confirmation frame sending module 950 executes step S150. The specific execution process can be found above and will not be repeated here.

[0091] While numerous embodiments of this application have been shown and described herein, it will be apparent to those skilled in the art that such embodiments are provided by way of example only. Many modifications, alterations, and alternatives will arise for those skilled in the art without departing from the spirit and intent of this application. It should be understood that various alternatives to the embodiments of this application described herein may be employed in the practice of this application. The appended claims are intended to define the scope of protection of this application and therefore cover equivalents or alternatives within the scope of these claims.

Claims

1. A gas leak alarm method based on a self-healing network, characterized in that, include: A self-healing network consisting of terminal nodes, routing nodes, and aggregation nodes is constructed within the underground utility tunnel. Each terminal node registers at least K routing nodes as parent nodes, where K ≥ 2 and K ∈ N. When any of the terminal nodes detects a gas leak event, an alarm frame is constructed. The alarm frame includes an alarm ID, serial number, priority, deadline, lifespan, path label, source node ID, sensor location information, digital signature, and message integrity check code. The terminal node uses a parallel multipath method to transmit copies of alarm frames carrying different path labels to the corresponding routing nodes. The receiving alarm frame copies are deduplicated by the routing node, and the deduplicated alarm frame copies are sent to the aggregation node. The aggregation node sends an end-to-end confirmation frame to the terminal node based on a copy of the received alarm frame.

2. The gas leak alarm method based on a self-healing network according to claim 1, characterized in that, In constructing a self-healing network consisting of endpoint nodes, routing nodes, and aggregation nodes, the following steps are performed: Each parent node periodically maintains a neighbor table, recording information including link quality indicators, expected transmission counts, round-trip time, queue level, remaining energy, and channel ID; Based on the recorded information, a weighted score for each parent node is calculated. The formula for calculating the weighted score of a parent node is: S = w1LQI + w2(1 / ETX) + w3(1 / RTT) + w4(1 / Q) + w5E, where LQI is the link quality indicator, w1 is the weight of the link quality indicator, ETX is the expected transmission count, w2 is the weight of the expected transmission count, RTT is the round-trip time, w3 is the weight of the round-trip time, Q is the queue level, w4 is the weight of the queue level, E is the remaining energy, and w5 is the weight of the remaining energy. Determine whether the communication link between the terminal node or routing node and the corresponding parent node meets the self-healing trigger condition; In response to the fulfillment of the self-healing trigger condition, a parent node switch and / or channel switch is performed based on the weighted score of the remaining parent nodes other than the current parent node; If the self-healing trigger condition is not met, return to the step of periodically maintaining the neighbor table for each parent node.

3. The gas leak alarm method based on a self-healing network according to claim 2, characterized in that, The self-healing triggering conditions include: heartbeat loss, missing ACK, sudden increase in RTT, and increased CCA failure rate; When one of the following trigger conditions is met—heartbeat loss, ACK missing, or RTT surge—it is determined whether the highest value among the weighted scores of the remaining parent nodes (excluding the current parent node) exceeds the scoring threshold. If the highest value among the weighted scores of the remaining parent nodes (excluding the current parent node) exceeds the scoring threshold, the current parent node is switched to the parent node corresponding to the highest value among the weighted scores. If the highest value among the weighted scores of the remaining parent nodes other than the current parent node does not exceed the scoring threshold, switch from the current channel to the next channel in the candidate channel set, remove the current channel from the candidate channel set, and add it to the channel blacklist. When the CCA failure rate increases, switch from the current channel to the next channel in the candidate channel set, and determine whether there is a parent node on the switched channel whose highest value in the weighted score exceeds the score threshold. If a parent node with the highest weighted score exceeding the score threshold exists on the channel after the handover, it is designated as the current parent node. If a parent node has a weighted score that exceeds the score threshold on the switched channel, the process returns to the step of switching from the current channel to the next channel in the candidate channel set, and the channel switching is performed again.

4. The gas leak alarm method based on a self-healing network according to claim 1, characterized in that, In the process of transmitting alarm frame copies carrying different path labels to the corresponding routing nodes through the terminal node using a parallel multipath method, the terminal node selects the first M parent nodes from its set of parent nodes and sends alarm frame copies carrying different path labels to them in parallel.

5. The gas leak alarm method based on a self-healing network according to claim 1 or 4, characterized in that, During the process of transmitting alarm frame copies carrying different path labels to the corresponding routing nodes through the terminal node using a parallel multipath method, a deadline-aware retransmission strategy is adopted, which includes the following steps: The terminal node calculates the remaining margin based on the deadline, round-trip time, and current time carried in the alarm frame copy. The formula for calculating the remaining margin is as follows: Slack is the remaining margin, DL is the deadline in the alarm frame copy, now is the current time, and RTT is the round-trip time in the alarm frame copy. The number of retransmissions and the degree of parallelism are adaptively adjusted based on the value of the remaining margin. Determine whether the current residual margin has decreased compared to the residual margin at the previous time step; Since the current margin of margin has not decreased compared to the previous margin of margin, no action is taken; In response to the decrease in remaining margin compared to the previous time step, the terminal node reduces the retransmission interval. The retransmission interval is calculated using the formula: Interval_n = Initial_Interval × (1 / 2 n-1 ), where Interval_n is the retransmission interval, Initial_Interval is the initial retransmission interval, and n is the number of retransmissions; In the process of adaptively adjusting the number of retransmissions and the degree of parallelism based on the value of the remaining margin, the following steps are performed: When the remaining margin is greater than the first preset value, the parallelism is set to the first threshold. When the remaining margin is less than or equal to the first preset value and greater than the second preset value, the second threshold is increased for the number of retransmissions. When the remaining margin is less than the first preset value but greater than or equal to the third preset value, the parallelism is increased by a third threshold. When the remaining margin is less than the third preset value, the number of retransmissions is reduced by the fourth threshold.

6. The gas leak alarm method based on a self-healing network according to claim 1, characterized in that, During the deduplication process of the received alarm frame copies through the routing node, the following steps are performed: The routing node calculates the (alarm ID, sequence number) key corresponding to the received alarm frame copy; Determine if the (alarm ID, sequence number) key corresponding to the alarm frame copy exists in the deduplication table; If the (alarm ID, sequence number) key corresponding to the alarm frame copy exists in the deduplication table, the alarm frame copy is determined to be a duplicate frame and discarded. If the (alarm ID, serial number) key corresponding to the alarm frame copy does not exist in the deduplication table, the (alarm ID, serial number) key corresponding to the alarm frame copy is inserted into the deduplication table.

7. The gas leak alarm method based on a self-healing network according to claim 1, characterized in that, After the terminal node transmits copies of alarm frames carrying different path labels to the corresponding routing nodes using a parallel multipath approach, the terminal node performs the following steps: Start a timer to wait for the end-to-end acknowledgment frame sent by the aggregation node; Determine whether an end-to-end acknowledgment frame has been received within the preset time set by the timer; In response to receiving an end-to-end confirmation frame within a preset time set by the timer, the digital signature and message integrity check code corresponding to the copy of the alarm frame are verified, and the terminal node is put into an idle state after the verification is successful. In response to the failure to receive an end-to-end acknowledgment frame within a preset time set by the timer, it is determined whether the remaining margin is greater than 0. The formula for calculating the remaining margin is as follows: Slack is the remaining margin, DL is the deadline in the alarm frame copy, now is the current time, and RTT is the round-trip time in the alarm frame copy. In response to a remaining margin greater than 0, the terminal node retransmits the alarm frame by increasing parallelism, switching channels, increasing the number of retransmissions, and using exponential backoff to reduce the retransmission interval. If the remaining margin is not greater than 0, the terminal node terminates the alarm transmission and records the failure.

8. The gas leak alarm method based on a self-healing network according to claim 1, characterized in that, The self-healing network employs a congestion and backpressure control mechanism. During the implementation of this mechanism, the following steps are performed: The routing node determines whether it is in a congested state based on its own data packet queue level and packet loss rate. If the system is not in a congested state, no action is taken. In response to being in a congested state, the congestion status information is uploaded to the terminal node through the routing node, and the terminal node performs a congestion response. During the congestion response process via the terminal node, at least one of the following steps is performed: Reduce the sampling and reporting frequency of non-alarm service data; Aggregate multiple non-alarm service data packets; The system identifies the highest priority data frame in its own queue and discards data frames with a lower priority than the highest priority.

9. The gas leak alarm method based on a self-healing network according to claim 1 or 8, characterized in that, The self-healing network employs a low-power and fast-response operating mechanism. During this process, the following steps are performed: When the terminal node does not detect a gas leak event, the terminal node operates in a first duty cycle mode and uses a first listening time window to listen for information; When the terminal node detects a gas leak event, the terminal node operates in a second duty cycle mode and listens for information using a second listening time window, and generates and sends an alarm activation message to the corresponding routing node. The alarm activation message includes at least the alarm type, timestamp, and initial path identifier, wherein the second duty cycle is greater than the first duty cycle, and the second listening time window is greater than the first listening time window. The corresponding routing nodes cascade their own duty cycles to be the same as the terminal nodes, and select the optimal next-hop path for message forwarding based on the weighted scores of their neighboring nodes. Specifically, all nodes on the selected optimal next-hop path synchronously activate a temporary coordinated forwarding time slot based on time division multiple access, according to the request in the alarm activation message.

10. A gas leak alarm system based on a self-healing network, characterized in that, The gas leak alarm method based on a self-healing network as described in any one of claims 1-9 is used for alarm purposes, and the system includes: The self-healing network construction module is used to construct a self-healing network consisting of terminal nodes, routing nodes, and aggregation nodes in an underground utility tunnel. The terminal nodes register at least K routing nodes as parent nodes, where K≥2 and K∈N. An alarm frame construction module is used to construct an alarm frame when any of the terminal nodes detects a gas leak event. The alarm frame includes an alarm ID, serial number, priority, expiration time, lifespan, path label, source node ID, sensor location information, digital signature, and message integrity check code. The alarm frame copy module is used to transmit alarm frame copies carrying different path labels to the corresponding routing nodes through the terminal node in a parallel multipath manner. The deduplication module is used to deduplicatize the received alarm frame copies through the routing node and send the deduplicated alarm frame copies to the aggregation node. The end-to-end acknowledgment frame sending module is used to send an end-to-end acknowledgment frame to the terminal node through the aggregation node based on a copy of the received alarm frame.

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