Wireless ad hoc network synchronization method and device and medium

Abstract

The invention relates to the technical field of network communication, in particular to a wireless ad hoc network synchronization method, a wireless ad hoc network synchronization device and a medium, a root node periodically sends a system message at a specified time slot as an initial synchronization source of the whole network, and a non-network-access node searches and demodulates the system message through a full frequency point, selecting a superior synchronization source according to the demodulation energy, accessing the leaf node which has accessed the network, monitoring the signal strength of the system message of the superior synchronization source, and when the signal strength is lower than a first threshold value, upgrading the leaf node into a forwarding node, and sending the system message according to the allocated time-frequency resource, monitoring the signal strength of the system message of the superior synchronization source by the forwarding node accessed to the network, and when the signal strength is higher than a second threshold value, degrading the forwarding node into a leaf node and stopping sending the system message. According to the method and the device, the dynamic mutual conversion between the leaf and the forwarding node is realized based on the first threshold value / the second threshold value, resources are staggered in the time domain by utilizing the forwarding level, the same-frequency interference is physically isolated, and efficient information forwarding coverage can be realized.

Description

Technical Field

[0001] This invention relates to the field of network communication technology, and in particular to a wireless ad hoc network synchronization method, apparatus, and medium. Background Technology

[0002] With the rapid development of applications such as the Internet of Things (IoT), smart homes, industrial control, and emergency communications, mesh network technology is widely used in low-power, low-cost, and nodeless communication scenarios. In these networks, multiple nodes form a multi-hop communication topology through self-discovery and self-connection, thereby achieving wide-area data transmission and coverage without relying on a centralized base station.

[0003] In practical deployments, wireless ad hoc network nodes generally face challenges such as limited hardware resources, scarce available spectrum resources, and low link capacity. These limitations make the time synchronization process between nodes highly susceptible to interference, and the reliable propagation of system messages is difficult to guarantee. Existing technologies typically employ a fixed role allocation strategy, requiring all intermediate nodes to forward system messages indiscriminately. This approach not only causes signal collisions but also fails to efficiently support large-scale, multi-hop wireless ad hoc network applications in low-power, low-bandwidth scenarios, resulting in poor overall network stability. Therefore, achieving efficient information forwarding coverage while reducing overall network power consumption and interference is a pressing technical problem that needs to be solved. Summary of the Invention

[0004] Therefore, in order to address the above-mentioned technical problems, this invention provides a wireless ad hoc network synchronization method, apparatus, and medium, which can achieve efficient information forwarding coverage, reduce overall network power consumption and interference, and improve overall network stability.

[0005] A first aspect of this application provides a synchronization method for a wireless ad hoc network, wherein the wireless ad hoc network includes a root node, a forwarding node, and leaf nodes. The method employs Time Division Multiple Access (TDMA) to divide time into periodic frames, with each frame further divided into multiple time slots. The method includes: The root node periodically sends system messages in the specified time slot as the initial synchronization source for the entire network; Unconnected nodes search for demodulation system messages across all frequencies, select an upstream synchronization source based on demodulation energy, and connect to the network. The leaf nodes that have joined the network monitor the signal strength of system messages from the upper-level synchronization source. When the signal strength is lower than the first threshold, the leaf node is upgraded to a forwarding node and sends system messages according to the allocated time and frequency resources. The forwarding node that has joined the network monitors the signal strength of the system messages from the upper-level synchronization source. When the signal strength is higher than the second threshold, the forwarding node is downgraded to a leaf node and stops sending system messages. The time-frequency resources for the forwarding node to send system messages are determined based on the forwarding level of the forwarding node in the network topology, and forwarding nodes with adjacent forwarding levels send messages at different times in the time domain.

[0006] A second aspect of this application provides a wireless ad hoc network synchronization device. The wireless ad hoc network synchronization device includes a wireless ad hoc network, which includes a root node, a forwarding node, and leaf nodes. The device employs Time Division Multiple Access (TDMA) to divide time into periodic frames, with each frame divided into multiple time slots. The wireless ad hoc network synchronization device is used for: The root node periodically sends system messages in the specified time slot as the initial synchronization source for the entire network; Unconnected nodes search for demodulation system messages across all frequencies, select an upstream synchronization source based on demodulation energy, and connect to the network. The leaf nodes that have joined the network monitor the signal strength of system messages from the upper-level synchronization source. When the signal strength is lower than the first threshold, the leaf node is upgraded to a forwarding node and sends system messages according to the allocated time and frequency resources. The forwarding node that has joined the network monitors the signal strength of the system messages from the upper-level synchronization source. When the signal strength is higher than the second threshold, the forwarding node is downgraded to a leaf node and stops sending system messages. The time-frequency resources for the forwarding node to send system messages are determined based on the forwarding level of the forwarding node in the network topology, and forwarding nodes with adjacent forwarding levels send messages at different times in the time domain.

[0007] Thirdly, a computer-readable storage medium is provided, the computer-readable storage medium storing a computer program that, when executed by a processor, implements the wireless ad hoc network synchronization method as described in the first aspect.

[0008] In summary, this invention provides a wireless ad hoc network synchronization method, apparatus, and medium. The wireless ad hoc network includes a root node, forwarding nodes, and leaf nodes. By employing Time Division Multiple Access (TDMA), time is divided into periodic frames, with multiple time slots within each frame. The root node periodically transmits system messages in designated time slots as the initial synchronization source for the entire network. Nodes not yet connected to the network demodulate system messages through a full-frequency search and select a superior synchronization source based on demodulation energy. Already connected leaf nodes monitor the signal strength of the superior synchronization source's system messages. When the signal strength is below a first threshold, the leaf node is upgraded to a forwarding node and transmits system messages according to the allocated time-frequency resources. Already connected forwarding nodes monitor the signal strength of the superior synchronization source's system messages. When the signal strength is above a second threshold, the forwarding node is downgraded to a leaf node and stops transmitting system messages. The time-frequency resources for forwarding nodes to transmit system messages are determined based on the forwarding level of the forwarding node in the network topology, with forwarding nodes of adjacent forwarding levels transmitting messages at staggered times in the time domain. As can be seen, this application defines a root / forwarding / leaf node architecture, adopts a TDMA frame structure, utilizes forwarding levels to plan resources, and realizes dynamic mutual switching between leaf and forwarding nodes based on a first threshold / second threshold. Nodes are upgraded for forwarding only when the signal is weak (needing to fill blind spots), and forwarding is automatically canceled when the signal is strong. At the same time, by using forwarding levels to stagger resources in the time domain, co-channel interference is physically isolated, which can achieve efficient information forwarding coverage, avoid broadcast storms, reduce overall network power consumption and interference, and improve the overall stability of the network. Attached Figure Description

[0009] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0010] Figure 1 This is a flowchart illustrating a wireless ad hoc network synchronization method according to an embodiment of the present invention; Figure 2 This is a schematic diagram of a wireless ad hoc network in a wireless ad hoc network synchronization method provided in an embodiment of the present invention; Figure 3 This is a time slot diagram of a wireless ad hoc network synchronization method provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the forwarding topology in a wireless ad hoc network synchronization method provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of another time slot in a wireless ad hoc network synchronization method provided in an embodiment of the present invention; Figure 6 This is an upgraded schematic diagram of a wireless ad hoc network synchronization method provided in an embodiment of the present invention; Figure 7 This is a downgraded schematic diagram of a wireless ad hoc network synchronization method provided in an embodiment of the present invention; Figure 8 This is another downgraded schematic diagram of a wireless ad hoc network synchronization method provided in an embodiment of the present invention; Figure 9 This is a schematic diagram of a forwarding node conflict in a wireless ad hoc network synchronization method provided by an embodiment of the present invention; Figure 10 This is a schematic diagram of another time slot in a wireless ad hoc network synchronization method provided in an embodiment of the present invention; Figure 11 This is a schematic diagram of the structure of a wireless self-organizing network synchronization device provided in an embodiment of the present invention. Detailed Implementation

[0011] The technical solutions of the embodiments of the present invention 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 the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0012] References to one or more embodiments described in this specification mean that a particular feature, structure, or characteristic described in connection with that embodiment is included in one or more embodiments of the invention. Therefore, phrases appearing in different parts of this specification as referring to one embodiment, some embodiments, some other embodiments, and others do not necessarily refer to the same embodiment, but rather mean one or more, but not all, embodiments, unless otherwise specifically emphasized. The terms include, comprise, have, and variations thereof mean including but not limited to, unless otherwise specifically emphasized.

[0013] It should be understood that the sequence number of each step in the following embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0014] To illustrate the technical solution of the present invention, specific embodiments are described below.

[0015] See Figure 1 This is a flowchart illustrating a wireless ad hoc network synchronization method according to an embodiment of the present invention, as shown below. Figure 1As shown, the wireless ad hoc network synchronization method includes a root node, a forwarding node, and leaf nodes. By adopting the time division multiple access (TDMA) method, time is divided into periodic frames, and each frame is divided into multiple time slots. This can be achieved through the following steps.

[0016] S101: The root node periodically sends system messages in the specified time slot as the initial synchronization source for the entire network; S102: Unconnected nodes search for demodulation system messages across all frequencies, select an upstream synchronization source based on demodulation energy, and connect to the network. S103: The leaf node that has joined the network monitors the signal strength of the system message from the upper-level synchronization source. When the signal strength is lower than the first threshold, the leaf node is upgraded to a forwarding node and sends the system message according to the allocated time and frequency resources. S104: The forwarding node that has joined the network monitors the signal strength of the system message from the upper-level synchronization source. When the signal strength is higher than the second threshold, the forwarding node is downgraded to a leaf node and stops sending system messages. The time-frequency resources for the forwarding node to send system messages are determined according to the forwarding level of the forwarding node in the network topology. Forwarding nodes with adjacent forwarding levels send messages at different times in the time domain.

[0017] In one implementation, the wireless ad hoc network includes a root node, forwarding nodes, and leaf nodes. The root node (RootNode) is the starting node of the tree-like network structure, serving as the entry point for data access. It has no parent node and is unique. Its child nodes constitute the branch hierarchy of the entire network. It is the unique initial synchronization source, responsible for broadcasting System Messages (SI) during the network initialization phase and providing time references and system information to lower-level nodes. It typically acts as an initial synchronization source or routing coordinator. The forwarding node (RelayNode) is a node that undertakes the function of forwarding System Messages (SI) and can be downgraded to a leaf node. The leaf node (LeafNode) is an ordinary terminal node that only receives System Messages (SI) and does not forward them. It can be upgraded to a forwarding node (RelayNode) to receive System Messages (SI) without forwarding them, thereby achieving efficient time synchronization and information propagation among network nodes. As shown in Figure 2, this wireless ad hoc network consists of a root node, forwarding nodes with a forwarding level of 1, forwarding nodes with a forwarding level of 2, and multiple leaf nodes. In this figure, node 0 is the root node, i.e., an unsynchronized node, nodes 3 / 7 are forwarding nodes, and nodes 1 / 2 / 4 / 6 are leaf nodes. The parent synchronization source of nodes 1 / 4 / 7 is node 0, the parent synchronization source of nodes 3 / 6 is node 7, and the parent synchronization source of node 2 is node 3. The subnets where the nodes are located are classified into levels according to the number of hops from the root node. Node 0 and its leaf nodes are level 0; node 7 and its leaf nodes are level 1; and node 3 and its leaf nodes are level 2.

[0018] Furthermore, by employing Time Division Multiple Access (TDMA), time is divided into periodic frames, with multiple time slots within each frame, to achieve efficient time synchronization and information propagation between network nodes. For example... Figure 3 As shown, time is divided into periodic frames, each containing 10 time slots. The root node periodically sends system messages in time slot 0, and all nodes in the network can move. Nodes send and receive data in half-duplex mode, with 5 time slots used for sending and 5 time slots used for receiving. If the upstream synchronization source is a forward-receiver-backwards-transmitter, then this node is a forward-transmitter-backwards-receiver. Figure 3 For example, if node 5 synchronizes with node 0, then the transmit and receive time slots of node 5 are opposite to those of node 0. Since it is a TDMA signal, the air interface resources are only divided according to the time domain.

[0019] In the embodiments of this application, the root node periodically sends system messages in the specified time slots as the initial synchronization source for the entire network, providing a unified time reference for all nodes, avoiding synchronization chaos caused by the lack of a central node. Un入网 nodes search and demodulate system messages across all frequency points and select the superior synchronization source with the best signal quality for network access based on the demodulation energy. This mechanism is based on the real-time evaluation of signal strength, ensuring that nodes can quickly identify and access stable links, thereby improving the network self-organization efficiency. Further, the already入网 leaf nodes continuously monitor the signal strength of the system messages of the superior synchronization source. When the signal strength is lower than the first threshold, they are upgraded to forwarding nodes and send system messages according to the allocated time-frequency resources. This upgrade operation can timely expand the network coverage when the link quality deteriorates, preventing synchronization interruption. At the same time, the allocation of time-frequency resources matches the network topology structure, avoiding resource waste caused by blind forwarding. Finally, the already入网 forwarding nodes monitor the signal strength of the system messages of the superior synchronization source. When the signal strength is higher than the second threshold, they are downgraded to leaf nodes and stop sending system messages. This downgrade operation can actively reduce redundant forwarding behavior when the link quality improves, significantly reducing the network power consumption.

[0020] Furthermore, it is necessary to select appropriate nodes among the already入网 leaf nodes to be upgraded to forwarding nodes, and establish a system message bearer SIC to send system messages SI according to established rules to expand the network coverage. If all nodes forward the system message bearer SIC, in essence, the system message SI floods from the root node to the entire network, which is not considered. If the node is very close to the superior synchronization source, the effect of expanding the coverage after upgrading is limited, and forwarding nodes will densely appear in the network, making it difficult to solve the resource collision of the system message bearer SIC / DC in each subnet. Therefore, the demodulation energy at the coverage distance S1 is taken as the upgrade threshold RSSIU (the first threshold), which is the system message SI demodulation energy threshold required for a leaf node to be upgraded to a forwarding node. If the demodulation energy of the system message SI of a certain leaf node from the superior synchronization source is lower than this threshold, it is upgraded to a forwarding node to send the system message SI. The demodulation energy at the coverage distance S2 is taken as the downgrade threshold RSSID (the second threshold), that is, the system message SI demodulation energy threshold required for a forwarding node to be downgraded to a leaf node (S2 < S1). If the demodulation energy of the system message SI of a certain forwarding node from the superior synchronization source is higher than this threshold, it is downgraded to a leaf node and the system message bearer SIC is cancelled. As Figure 4 shown, in this figure, the demodulation energy RSSI0_2 of the system message SI of node 2 from node 0 is lower than RSSIU, so it is upgraded to a forwarding node; the demodulation energy of the system message SI of node 3 from node 0 is higher than RSSIU, so it maintains its leaf node identity.

[0021] Specifically, the time-frequency resources for forwarding nodes to send system messages are determined based on their forwarding level in the network topology. Forwarding nodes with adjacent forwarding levels send messages at staggered times in the time domain. This resource allocation strategy naturally disperses the sending opportunities of nodes with different hop counts, effectively solving the problems of low time synchronization efficiency, insufficient network coverage, and high interference caused by limited node hardware resources and limited available frequency points in wireless ad hoc networks. The dynamic node role adjustment mechanism expands network coverage when link quality deteriorates and reduces redundant forwarding when link quality improves, thereby reducing overall network power consumption. The time-frequency resource allocation strategy based on forwarding level ensures that system messages propagate in an orderly manner in multi-hop networks without mutual interference, improving spectrum utilization efficiency. The design of a second threshold higher than the first threshold ensures network stability and avoids oscillations caused by frequent role switching, thus achieving efficient partial forwarding coverage and enhancing overall network stability. Full-frequency search refers to the process by which nodes scan all available frequency points to detect system messages. This can be done by sequentially scanning all frequency points or by polling multiple frequency points using a predefined frequency hopping sequence. Selecting a superior synchronization source based on demodulation energy refers to choosing a synchronization source based on received signal strength or demodulation quality indicators. For example, this can be done by measuring the received signal strength and selecting the synchronization source with the highest strength, or by evaluating demodulation quality through bit error rate. Forwarding class refers to the number of hops a node is in from the root node in the network topology. This can be achieved by including a hop count field in the system message, and the node determines its forwarding class by incrementing this field. Therefore, determining time-frequency resources based on forwarding class means allocating different transmission opportunities to nodes with different forwarding classes.

[0022] For example, nodes in forwarding level 1 are assigned to send system messages in time slot 2, and nodes in forwarding level 2 are assigned to send system messages in time slot 4, ensuring that the sending times of adjacent forwarding level nodes are staggered. The first threshold is set to -85dBm, and the second threshold is set to -80dBm. When a leaf node detects that the signal strength of its superior synchronization source is below -85dBm, it upgrades to a forwarding node and begins sending system messages in the designated time slot; when a forwarding node detects that the signal strength of its superior synchronization source is above -80dBm, it downgrades to a leaf node and stops sending system messages. In this example, the setting of the signal strength threshold introduces a hysteresis interval to prevent nodes from frequently switching roles at threshold critical points.

[0023] As a preferred implementation, a lookup table can be used to map forwarding levels to specific frames and time slots, or a time slot offset can be calculated based on the forwarding level. Staggered transmission in the time domain by forwarding nodes of adjacent forwarding levels means that nodes with different hop counts send system messages at different times; for example, nodes with odd-numbered forwarding levels send messages in odd-numbered time slots of a frame, and nodes with even-numbered forwarding levels send messages in even-numbered time slots of a frame. This application achieves partial forwarding coverage by dynamically adjusting node roles and allocating time-frequency resources based on forwarding levels, thereby reducing overall network power consumption and improving stability.

[0024] In summary, this invention provides a wireless ad hoc network synchronization method, apparatus, and medium. The wireless ad hoc network includes a root node, forwarding nodes, and leaf nodes. By employing Time Division Multiple Access (TDMA), time is divided into periodic frames, with multiple time slots within each frame. The root node periodically transmits system messages in designated time slots as the initial synchronization source for the entire network. Nodes not yet connected to the network demodulate system messages through a full-frequency search and select a superior synchronization source based on demodulation energy. Already connected leaf nodes monitor the signal strength of the superior synchronization source's system messages. When the signal strength is below a first threshold, the leaf node is upgraded to a forwarding node and transmits system messages according to the allocated time-frequency resources. Already connected forwarding nodes monitor the signal strength of the superior synchronization source's system messages. When the signal strength is above a second threshold, the forwarding node is downgraded to a leaf node and stops transmitting system messages. The time-frequency resources for forwarding nodes to transmit system messages are determined based on the forwarding level of the forwarding node in the network topology, with forwarding nodes of adjacent forwarding levels transmitting messages at staggered times in the time domain. As can be seen, this application defines a root / forwarding / leaf node architecture, adopts a TDMA frame structure, utilizes forwarding levels to plan resources, and realizes dynamic mutual switching between leaf and forwarding nodes based on a first threshold / second threshold. Nodes are upgraded for forwarding only when the signal is weak (needing to fill blind spots), and forwarding is automatically canceled when the signal is strong. At the same time, by using forwarding levels to stagger resources in the time domain, co-channel interference is physically isolated, which can achieve efficient information forwarding coverage, avoid broadcast storms, reduce overall network power consumption and interference, and improve the overall stability of the network.

[0025] In one embodiment, the time-frequency resource determination rule for forwarding nodes sending system messages includes the following steps: The timing of sending system messages by the forwarding node is hashed in the frame dimension, and a system message is sent once every N frames. The specific frame number for sending the system message is determined based on the result of the modulo operation between the forwarding level and N. The time slot position in which the forwarding node sends system messages within a frame is determined based on the parity of the forwarding level; where N is an integer greater than 1, and the forwarding level represents the number of hops from the root node.

[0026] In one implementation, the timing of system message transmission by forwarding nodes is staggered in both the frame period and intra-frame time slot dimensions through the coordinated design of frame-dimensional hashing and time slot parity rules. Frame-dimensional hashing refers to discontinuously distributing the system message transmission period on the time axis, which can be achieved by a periodic frame skipping scheduling strategy. Its purpose is to reduce channel occupancy density and disperse potential interference sources. Specifically, frame-dimensional hashing uses modular arithmetic to map nodes of different forwarding levels to different frame offset positions. Due to the periodicity of modular arithmetic, nodes of the same forwarding level maintain the same frame number every N frames, while nodes of adjacent forwarding levels automatically stagger their frame transmissions due to differences in modular arithmetic results, thus forming distributed temporal separation on the time axis. Sending a system message once every N frames means that the node triggers the transmission behavior only within a preset frame period, which can be achieved by using a dynamic adjustment interval control mechanism for the N value. Its purpose is to flexibly adjust the transmission frequency according to the network scale to balance resource consumption and synchronization requirements. At the same time, the time slot position parity rule divides the forwarding levels into two groups according to parity. Nodes of odd-numbered levels are fixed to use odd-numbered time slots, and nodes of even-numbered levels are fixed to use even-numbered time slots. This rule further refines the resource allocation within the frame, ensuring that even adjacent level nodes in the same frame will not have time slot overlap. The above mechanism can automatically coordinate the transmission timing between nodes without centralized scheduling. It effectively avoids signal conflicts caused by concurrent transmission of multiple nodes through dual-dimensional resource misalignment. Specifically, determining the frame number by modulo operation means establishing a mapping relationship between forwarding level and frame offset through mathematical operations. This can be achieved by generating offsets using modulo operations or hash functions. Its purpose is to automatically align the transmission timing of nodes with the same forwarding level, while nodes with adjacent levels are naturally offset in the frame dimension. Determining the time slot position based on parity means dividing the transmission time slot groups according to the parity attribute of the forwarding level value. This can be achieved by classifying time slots using binary bit judgment or modulo 2 operations. Its purpose is to divide the nodes into two groups and allocate mutually exclusive time slot resources to avoid intra-frame time slot overlap. Forwarding level, as a quantitative indicator of node topology position, can be understood as the shortest path hop count statistics starting from the root node. Its purpose is to directly link time-frequency resource allocation with network topology structure to ensure that resource allocation strategy adapts to dynamic network changes.

[0027] Furthermore, the root node and forwarding nodes periodically send System Messages (SI) to provide synchronization opportunities for nodes not yet connected to the network. Nodes already connected to the network need to continuously demodulate the System Messages (SI) from the upstream synchronization source to continuously adjust their Time Acquisition (TA) to counteract time-domain errors caused by crystal oscillator drift in different devices, maintain accurate synchronization with the upstream synchronization source, and also obtain the latest system information. The root node (node ​​0) and its downstream forwarding nodes establish a System Message Bearer (SIC) in the first TX time slot of each frame to send System Messages (SI). For example... Figure 5As shown in the figure, the System Message Carriers (SICs) of adjacent forwarding nodes are staggered in the time domain, but forwarding nodes separated by one level (e.g., node 1 / 3) create the same time slot for their SICs. This invention distributes the SIC transmission timing by frame, sending a SIC once every N frames, significantly reducing frequency planning pressure. The larger N is, the lower the probability of time-frequency resource collisions for the SICs of forwarding nodes (resource conflicts can be resolved using the 3.2.5 random silencing mechanism). An appropriate value can be chosen based on hardware conditions and relevant protocols that depend on the real-time nature of system messages. For example, if N is set to 3, the root node of forwarding level 0 sends system messages in odd-numbered time slots (frame numbers 0, 3, 6…); nodes of forwarding level 1 send system messages in even-numbered time slots (frame numbers 1, 4, 7…); and nodes of forwarding level 2 send system messages in odd-numbered time slots (frame numbers 2, 5, 8…). In this configuration, nodes of adjacent forwarding levels do not transmit within the same frame, nor in overlapping time slots of the same frame. For example, a level 1 node transmits in an even-numbered time slot of frame 1, a level 0 node transmits in frame 0 or frame 3, and a level 2 node transmits in frame 2. The transmission timings of these three levels are completely separated in the time domain. When network topology changes lead to adjustments in forwarding levels, nodes automatically recalculate the frame number offset and switch time slot groups according to the new level, maintaining dynamic adaptability in resource allocation. It is evident that by distributing transmission timings across different frames (the larger N is, the more dispersed) and different time slots (odd and even shifts) through modulo operations, even physically adjacent nodes, as long as they are at different levels or have different frame counts, can avoid resource conflicts and signal interference caused by nodes of different forwarding levels transmitting system messages at the same time. This significantly reduces the probability of resource collisions between adjacent or near-adjacent forwarding nodes, improves the demodulation success rate of system messages, and thus enhances the overall stability of wireless ad hoc networks in low-power, low-bandwidth scenarios.

[0028] In one embodiment, the process of upgrading a leaf node to a forwarding node includes the following steps: When the leaf node detects that the signal strength of the current upper-level synchronization source is lower than the first threshold, it starts an upgrade timer, the duration of which is a random value; During the upgrade timer's operation, the leaf node retains its identity and continues to listen for system messages; If a system message with a signal strength higher than the first threshold is detected during the operation of the upgrade timer, the upgrade timer is cleared and the upgrade is canceled. If the upgrade timer overflows, the leaf node switches to a forwarding node and establishes a system message bearer.

[0029] In one implementation, an upgrade timer mechanism is designed to address signal fluctuation issues. When a leaf node detects that the signal strength of its upstream synchronization source is below a first threshold, it initiates an upgrade timer, providing a decision-making buffer period for the node. The upgrade timer uses a random duration to distribute the upgrade opportunities among different nodes. During the timer's operation, the node maintains its original identity and continuously listens for system messages, allowing verification of signal quality continuity. If a system message with a signal strength above the first threshold is detected, the timer is cleared and the upgrade is canceled. The decision is dynamically adjusted based on real-time listening results. Only when the upgrade timer overflows does the node switch to a forwarding node and establish a system message bearer. This mechanism, based on the dynamic characteristics of signal quality changes, maintains coverage expansion functionality while avoiding the additional overhead of frequent switching, thereby achieving more reliable self-organizing network synchronization in complex wireless environments. Among them, the upgrade timer refers to a timing mechanism used to provide a decision-making buffer period. It can be implemented using a hardware timer or a software task scheduling module, aiming to avoid an immediate response to a sudden drop in signal strength. The random value duration can be understood as a timing parameter determined based on a pseudo-random number generation algorithm. Its purpose is to distribute the upgrade timing of different nodes across the timeline, avoiding resource contention caused by synchronous upgrades. Maintaining identity and continuous listening specifically refers to a node maintaining its current network identity while continuously receiving system messages. This can be achieved by using physical layer radio frequency circuits to maintain the receiving state and synchronously update network layer routing table entries, aiming to verify the continuity of signal quality. Clearing the upgrade timer refers to the operation of terminating the timing process. It can be achieved by triggering a reset command based on a signal strength threshold, aiming to dynamically adjust the decision. Switching to a forwarding node and establishing a system message bearer refers to the node identity transformation and communication resource configuration process. It can be understood as allocating time-frequency resources at the physical layer and updating routing information at the network layer, aiming to ensure the necessity and stability of network topology changes.

[0030] Furthermore, when a leaf node detects that the signal strength of its parent synchronization source is lower than a first threshold, it starts an upgrade timer with a random duration, generated by a random number generator built into the chip. During this period, the node continues to maintain its leaf node identity, and its RF front-end continuously scans for system messages. If a system message with a signal strength higher than the first threshold is detected during the timer's operation, the timer is cleared and the current state is maintained. If a sufficiently strong signal is not detected after the timer overflows, the node switches to a forwarding node and configures its transmission circuit to send system messages. In this embodiment, the node can use a low-power microcontroller to implement the timer function, dynamically adjust the random duration range through software algorithms, and continuously listen for system messages using existing receiving channels, such as... Figure 6As shown, node 2 moves towards node 0 until RSSI0_2 is higher than RSSID, at which point node 2 is demoted to a leaf node. The system message SI signals demodulated by Node 1 / 4 to Node 0 are resynchronized to node 0. Since the demodulated system message SI energy is lower than RSSIU, a new forwarding node should compete for it to continuously expand network coverage.

[0031] At this point, the competitive upgrade scheme becomes crucial. If nodes 1 and 4 are simultaneously upgraded to forwarding nodes, the final result must be determined by a collision mechanism among forwarding nodes, which takes longer and significantly impacts the normal demodulation of other nodes in the network. As the topology changes, if the demodulation energy of the system message SI from the strongest synchronization source in the synchronization source list of leaf node X1 is lower than RSSIU, the upgrade condition must be met. Node X1 starts a timer T1 = M frames (M is a random value). During T1, node X1 maintains its leaf node status and continuously listens for the system message SI signal. If the demodulation energy of the system message SI is higher than RSSIU, the T1 timer is cleared, the upgrade is canceled, T1 overflows, node X1 switches to a forwarding node, establishes a system message bearer SIC, and completes the upgrade. When a leaf node triggers an upgrade, it starts a timer T1 of random duration. If other strong signals are heard during this period, the upgrade is canceled. Figure 6 As shown, node 1 and 4 simultaneously start T1. At this time, node 1 has the shortest random timeout and successfully upgrades to a forwarding node. Subsequently, node 4 demodulates the system message SI signal from node 1, and its strength is higher than RSSIU. It then clears T1 and cancels the upgrade. If adjacent nodes randomly obtain the same M, a unique forwarding node can be converged through the random silence mechanism in 3.2.5. Through the above scheme, this application effectively solves the problem of frequent node identity switching caused by instantaneous fluctuations in wireless signal, reduces network topology oscillation. When multiple leaf nodes at the coverage edge simultaneously detect a weakening signal, the random timer breaks the symmetry. The node that times out the upgrade earliest will send a strong signal. Other nodes that are currently timing will hear this signal and cancel their upgrades, thus automatically converging to a unique optimal forwarding node. This avoids resource conflicts caused by multiple nodes upgrading simultaneously, thereby improving the overall stability and reliability of the wireless ad hoc network in complex environments.

[0032] In one embodiment, the process of a forwarding node being downgraded to a leaf node includes the following steps: When the forwarding node detects that the signal strength of the upper-level synchronization source is higher than the second threshold and the degradation condition is met, the degradation timer is started. During the operation of the degradation timer, the forwarding node sends a system message carrying a degradation flag to notify its lower-level leaf nodes; If the degradation timer overflows, the forwarding node switches to a leaf node and stops sending system messages.

[0033] In one implementation, a degradation timer is started when the strength of the upper-level synchronization source signal is detected to be higher than a second threshold and the degradation condition is met, thus reserving a buffer time window for the lower-level nodes. During this period, the forwarding node continuously sends system messages carrying degradation flags, enabling the lower-level leaf nodes to accurately identify topology changes and actively initiate the synchronization source switching process. When the degradation timer overflows, the forwarding node performs a role switch and stops sending system messages, thereby ensuring that the degradation process proceeds in an orderly manner and avoiding network instability caused by the sudden disappearance of the synchronization source. Among them, the degradation timer refers to the timing unit used to manage the time window of the degradation process. It can be implemented using a programmable hardware timer or a software timer in the operating system. Its purpose is to provide a buffer period for lower-level nodes to respond to topology changes. The system message carrying the degradation flag can be understood as a message format that embeds a specific identifier in a regular system message. It can be implemented by reserving message header fields or extending message type fields. Its purpose is to clearly indicate the degradation intention to trigger the switching logic of lower-level nodes. The degradation timer overflow refers to the state of the timer reaching a preset time threshold. It can be detected by hardware interrupt signals or software polling mechanisms. Its purpose is to ensure that the degradation operation is performed only under safe conditions. The switching of a forwarding node to a leaf node refers to the state transition of a node's role from forwarding function to receiving function only. It can be implemented by updating the node status register or configuration table. Its purpose is to optimize the network topology and reduce overall power consumption.

[0034] Furthermore, the forwarding node uses a microcontroller to implement a degradation timer function, with the degradation timer configured for a random duration; the degradation flag is indicated by setting the 5th bit of the message header to 1 in the system message; after the lower-level leaf node demodulates this flag, it immediately polls the synchronization source list and switches to the candidate synchronization source with a higher signal strength, such as... Figure 7As shown, if nodes 1 and 4 move successively towards node 0, the degradation condition is triggered after the distance shrinks to a certain range. At this time, the MESH network shrinks to a one-hop communication distance centered on node 0, and node 5 becomes an isolated node. That is, with the topology change, if the synchronization source list of the forwarding node node X1 contains a synchronization source node X2 with a system message SI demodulation energy higher than the RSSID, and if node X2 -> relay level > node X1 -> relay level m, no action is taken; otherwise, node X1 triggers the degradation condition, and then node X1 starts a timer T2 = L frames. If T2 <= L, the SI sent by node X1 carries a degradation flag, which then notifies its lower-level leaf nodes. When the degradation timer T2 overflows, node X1 switches to a leaf node, cancels the SIC, and completes the degradation. That is, the forwarding node switches to a leaf node and stops sending system messages. Through the above scheme, a reaction time (L frames) is given to the lower-level nodes, allowing them to perceive the topology change in advance and prepare for switching or initiating retention, thus ensuring the continuity of the link. It effectively avoids network interruptions caused by the sudden disappearance of the synchronization source of the lower-level nodes, achieves smooth network topology contraction, and avoids the instantaneous loss of synchronization of the lower-level nodes caused by the sudden disappearance of the forwarding node.

[0035] In one embodiment, after the forwarding node sends a system message carrying a degradation flag, the following steps are included: The lower-level leaf node demodulates the degradation flag; If the lower-level leaf node determines that the forwarding node is its only synchronization source, it sends a stop degradation request to the forwarding node. After receiving the stop downgrade request, the forwarding node resets the downgrade timer to extend the time for maintaining the forwarding node's identity; If the lower-level leaf node has other available synchronization sources, then switch to the other synchronization source and prohibit sending stop-degradation requests.

[0036] In one implementation, intelligent control of the degradation process is achieved through a dynamic interaction mechanism between lower-level leaf nodes and forwarding nodes. After a forwarding node sends a system message carrying a degradation flag, the lower-level leaf node demodulates the flag in real time to obtain degradation intention information. The leaf node determines whether the forwarding node is its only synchronization source based on the synchronization source list. If it is determined to be the only synchronization source, it triggers the sending of a stop degradation request; otherwise, it autonomously switches to other available synchronization sources and suppresses invalid requests. Upon receiving a stop degradation request, the forwarding node immediately resets the degradation timer, extending the retention time of its forwarding node identity, thereby maintaining the continuity of synchronization coverage in the edge area. This mechanism, through a closed-loop process of information perception, condition judgment, request feedback, and state adjustment, ensures that the degradation operation is performed only under conditions that do not affect network topology connectivity, effectively avoiding the coverage hole problem caused by lower-level nodes relying on a single synchronization source.

[0037] Specifically, a degradation flag refers to a specific information unit in a system message used to identify that a node is about to perform a degradation operation. It can be implemented by reserving a dedicated bit field in the system message frame header or embedding a predefined identifier in the message payload. The purpose is to promptly transmit the degradation intention to lower-level nodes and avoid passive disconnection caused by information lag. A stop degradation request refers to a control signal sent by a lower-level leaf node to a higher-level forwarding node to request a delayed degradation. It can be implemented by using a dedicated signaling message or by carrying a request flag in the service data packet. The purpose is to trigger intervention only when the leaf node has no other synchronization options to prevent unexpected interruption of critical links. Resetting the degradation timer refers to the operation of restoring the degradation timer's count value to its initial state. It can be implemented by resetting the timer count value to a preset duration or extending the remaining count period. The purpose is to dynamically adjust the degradation timing based on the real-time feedback from lower-level nodes. Other available synchronization sources refer to alternative upper-level nodes that leaf nodes can switch between. They can be implemented based on candidate nodes whose signal strength is higher than a first threshold recorded in the synchronization source list. The purpose is to provide multi-path selection to reduce dependence on a single node.

[0038] Furthermore, when forwarding node A sends system messages to its subordinate leaf node B, it embeds a degradation flag. After leaf node B demodulates this flag, it checks its synchronization source list and finds that node A is the only valid synchronization source. If it does, it generates a stop degradation request and sends it to node A via the control channel. Upon receiving this request, node A resets the degradation timer to its initial duration, continues to maintain its forwarding node identity, and sends system messages. Simultaneously, leaf node B continuously monitors the synchronization source list. When it detects other candidate synchronization sources with signal strengths exceeding a first threshold, it automatically switches to the new synchronization source and stops sending subsequent stop degradation requests. Figure 8As shown, node Y1, a leaf node under Node X1, demodulates the SI and identifies the degradation flag. If node X1 is its only synchronization source, node Y1 sends a stop degradation request to node X1. Upon receiving the stop degradation request, Node X1 resets T2 to L + K frames. As T2 continues to run, the above process is retried when T2 equals L frames. Otherwise, node Y1 searches for the strongest synchronization source other than node X1 in the synchronization source list, performs a switchover, and prohibits sending stop degradation requests. Through the above technical solution, a handshake mechanism between upper and lower levels is established. Even if the forwarding node's own signal is good (meeting the degradation conditions), as long as it is still the only reliance of a certain lower-level node, it is forcibly retained. This prioritizes network connectivity over resource conservation, ensuring that degradation is only completed when there is a backup synchronization source at the leaf node, eliminating the risk of orphan nodes and guaranteeing the connection reliability of network edges or single-link areas.

[0039] In one embodiment, satisfying the degradation conditions includes the following steps: The forwarding node checks whether there is a candidate synchronization source in its synchronization source list with a signal strength higher than the second threshold; if the candidate synchronization source exists and the forwarding level of the candidate synchronization source is not greater than the forwarding level of this node, then it is determined that the downgrade condition is met.

[0040] In one implementation, a dual-condition decision-making mechanism is used to precisely control degradation decisions. First, a forwarding node filters candidate synchronization sources based on a list of synchronization sources, selecting those with signal strength exceeding a second threshold to ensure reliable link quality for candidate nodes. Then, by comparing the forwarding levels of the candidate synchronization sources with its own, the node determines that the degradation condition is met only if the forwarding level of the candidate synchronization source is not greater than that of its own. This step-by-step verification logic closely links the degradation operation to the actual network topology, preventing invalid degradation when no suitable replacement node is available, and allowing nodes to release forwarding resources promptly when signal quality improves. This optimizes overall energy efficiency and anti-interference capabilities while maintaining network connectivity. The synchronization source list refers to a data structure maintained by non-root nodes during service transmission, recording information on multiple candidate synchronization sources. It can be implemented using general data structures such as linked lists, arrays, or hash tables. Its purpose is to store key information such as the signal strength, forwarding level, and node identifier of successfully demodulated synchronization sources. A signal strength exceeding a second threshold can be understood as the signal strength of the received system message exceeding a preset reliable communication threshold. This threshold corresponds to a critical point for stable link quality, aiming to eliminate weak signal interference sources and ensure sufficient communication reliability for candidate synchronization sources. Candidate synchronization sources specifically refer to candidate nodes in the synchronization source list that meet the signal strength condition. These can be any parent node with a signal strength exceeding the second threshold, providing potential alternative synchronization paths. The forwarding level represents the number of hops a node has from the root node in the network topology. It can be determined based on the path hop count information recorded when the node joins the network, quantifying the node's position in the network hierarchy. A forwarding level not greater than the current node's can be understood as the forwarding level of a candidate synchronization source being less than or equal to the current node's forwarding level. Its purpose is to constrain the direction of topology optimization, avoiding the selection of nodes with higher hop counts that could lead to path redundancy or increased latency.

[0041] For example, consider a forwarding node A. If the signal strength of its current upstream synchronization source is higher than a second threshold, a degradation check process is triggered. Node A checks its synchronization source list and finds two candidates: node B (signal strength higher than the second threshold, forwarding level 2) and node C (signal strength lower than the second threshold). Node A's forwarding level is 3. Since node B meets the signal strength condition and forwarding level 2 is not greater than 3, node A determines that the degradation condition is met, starts a degradation timer, and sends a system message carrying a degradation flag. Node C, however, is automatically excluded due to insufficient signal strength and does not participate in the degradation determination process. Through this scheme, this application effectively avoids forwarding nodes performing degradation operations when there are no reliable alternative synchronization sources. Degradation is only safe when a strong signal from an upstream or peer is heard. Degrading upon hearing a strong signal from a downstream node would lead to clock source backflow, disrupting the tree-like synchronization structure. This prevents routing loops and erroneous hierarchical inversions, maintains the health of the tree topology, and thus prevents the loss of synchronization sources for downstream leaf nodes and network coverage interruptions, improving the stability of the network topology.

[0042] In one embodiment, the wireless ad hoc network synchronization method further includes random silent listening, the steps of which are as follows: The forwarding node periodically starts a silent timer, and cancels the sending of the current system message when the silent timer overflows; During the time slot where transmission is cancelled, the forwarding node listens to the channel to detect system message signals indicating whether there is a resource conflict. If a system message signal indicating a resource conflict is detected during the silent period, a downgrade operation or a switch of the system message transmission frequency will be performed based on the signal strength of the conflict signal and the forwarding level of the source node.

[0043] In one implementation, a forwarding node periodically starts a silent timer, causing the node to pause transmission and switch to receive mode at randomized time points, thereby listening to the channel during the time slot originally intended for transmission. When the timer overflows, the node cancels the transmission of the current system message, converting the transmission opportunity into a listening opportunity, avoiding the problem of potential conflicts being masked by continuous transmission. During this time slot, the node actively detects whether there are system message signals transmitted by other nodes on the same resource, promptly identifying co-channel interference sources. If a conflict signal is detected, intelligent decisions are made based on the signal strength and the forwarding level of the source node: when the signal strength is high and the forwarding level of the source node is low, the node triggers a degradation process, because the source node is closer to the root node and its signal priority is higher, allowing the degradation operation to give way to key nodes to reduce interference; when the signal strength is low, the node switches its transmission frequency to avoid continuous interference in weak signal areas; when the forwarding level of the source node is high, the node maintains its current state and waits for the other party to adjust, because nodes with high forwarding levels have a wider coverage area, and their proactive handling of conflicts is more conducive to network topology stability. This mechanism, through random silencing and conditional decision-making, achieves dynamic perception and intelligent response to conflicts without increasing additional resource overhead, effectively alleviating resource conflict problems in multi-hop networks.

[0044] Specifically, random silent listening is a mechanism for actively detecting resource conflicts. It can be implemented by periodically interrupting the transmission process, aiming to provide a window of opportunity for conflict detection and prevent potential interference from being masked by continuous transmission. The silent timer can be understood as a timing device, specifically a hardware timer or a software counter. Its purpose is to distribute node behavior by randomizing the start time, ensuring that the silent actions of different nodes are staggered in time, preventing conflicts from occurring in a concentrated manner. Specifically, canceling the transmission of the current system message means stopping the transmission operation in a predetermined transmission time slot. This can be achieved by switching the RF module to receive mode, aiming to convert the time slot resources originally used for transmission into listening resources, making full use of the idle time slots in the TDMA frame structure. Furthermore, channel listening can be understood as using a receiver to perform energy detection or signal demodulation on the channel, specifically wideband scanning or narrowband monitoring, aiming to identify the presence of co-channel interference sources in real time. Performing a downgrade operation or switching the sending frequency of system messages can be understood as a response measure taken based on conflict conditions. Specifically, it may involve reducing the role of a node or changing its operating frequency. The purpose is to dynamically adjust node behavior to reduce interference while maintaining the stability of the network topology.

[0045] Furthermore, such as Figure 9As shown, nodes 2 and 3, along with relay level 1 forwarding nodes, become increasingly closer during their movement. Since both nodes 2 and 3 need to send system messages (SI) in slot 5, they have no opportunity to listen to each other, preventing them from triggering degradation, resulting in a dense cluster of forwarding nodes. Meanwhile, node 1 needs to listen for system messages (SI) from its parent synchronization source (node ​​2) in slot 5, and therefore has no opportunity to listen to node 3, thus preventing it from being added to the synchronization source list. This involves introducing a random silencing mechanism to randomly silence system message (SI) transmissions, thereby gaining more listening opportunities. Specifically, every G frames, a forwarding node starts a timer T3 = K frames. Each time, K is randomly selected, and G>= K. The forwarding node then publishes the K value of T3 in the SI. When T3 overflows, the forwarding node cancels the next SI transmission. All nodes in the subnet listen for other nodes' SI signals in that time slot, waiting for the next T3 to start. If a forwarding node detects a system message SI signal on the same frequency as its own during the SI silence period (resource conflict), it performs a downgrade operation or switches the transmission frequency of the system message based on the signal strength of the conflicting signal and the forwarding level of the source node. This scheme creates a receiving window using the random silencing mechanism, enabling nodes to detect conflicting signals on the same frequency in the environment and discover hidden resource conflicts. This reduces co-channel interference caused by resource conflicts and improves the stability and coverage efficiency of network synchronization.

[0046] In one embodiment, the process of performing a downgrade operation or switching the transmission frequency of system messages based on the signal strength of the conflicting signal and the forwarding level of the source node includes the following steps: If the signal strength of the conflict signal is higher than the second threshold, and the forwarding level of the source node is less than or equal to the forwarding level of this node, then this node triggers a degradation process. If the signal strength of the conflict signal is lower than the second threshold, the node switches the frequency of sending system messages. If the forwarding level of the source node is higher than that of this node, this node will maintain its current state and wait for the source node to perform conflict resolution.

[0047] In one implementation, a decision-making framework is constructed through a collaborative evaluation of signal strength and forwarding level. When a node detects a conflict signal during random silent listening, it first determines whether the signal strength is higher than a second threshold. If it is higher and the source node's forwarding level is less than or equal to the node's level, a degradation process is triggered. This leverages the characteristic that a high-strength signal reflects better synchronization quality from the source node, combined with the logic that the forwarding level indicates a topology position closer to the root node, enabling the node to proactively degrade to avoid resource contention. If the signal strength is lower than the second threshold, the transmission frequency is switched. This mechanism is based on the judgment that weak signals usually originate from edge nodes or long-distance links, eliminating local interference through frequency adjustment. If the source node's forwarding level is higher than the node's level, the current state is maintained and the node waits. This strategy relies on the topology characteristic that higher-level nodes are more likely to perform degradation operations, preventing multi-node decision conflicts. Overall, this scheme transforms conflict handling into predictable behavioral rules through multi-dimensional conditional judgments, ensuring that nodes intelligently distinguish conflict types and take targeted measures. Among these, the signal strength of the collision signal refers to the power level of the received collision signal, which can be implemented using a Received Signal Strength Indicator (RSSI) measurement circuit. Its purpose is to quantify signal quality to distinguish the reliability and distance of the signal source. The forwarding level of the source node refers to the number of hops the node has from the root node in the network topology. This can be achieved by parsing the level identifier field carried in the system message, and its purpose is to identify the node's hierarchical position in the synchronization tree. Degradation operation refers to the process of a node being downgraded from a forwarding node to a leaf node. This can be implemented using a state machine switching mechanism, and its purpose is to reduce interference caused by redundant transmissions and optimize network coverage. Switching the transmission frequency of system messages refers to changing the carrier frequency used to transmit system messages. This can be achieved using a frequency synthesizer for dynamic adjustment, and its purpose is to avoid co-channel interference without affecting the network topology.

[0048] Furthermore, consider a forwarding node detecting a conflict signal during a silent listening slot. If the signal strength of the conflict signal is higher than a second threshold, and the forwarding level of the source node is less than or equal to the forwarding level of this node, then this node triggers a degradation process; if the signal strength of the conflict signal is lower than the second threshold, then this node switches the frequency point for sending system messages; if the forwarding level of the source node is higher than the forwarding level of this node, then this node maintains its current state and waits for the source node to perform conflict resolution operations. That is, if a forwarding node detects a system message SI signal (resource conflict) at the same frequency as itself while the system message SI is silent, it needs to resolve the conflict according to the following rules: if the demodulation energy of the system message SI is higher than the RSSID, and the relay level of the other party is less than or equal to the local relay level, this node triggers a degradation process; otherwise, if the demodulation energy of SI is lower than the RSSID, this node switches the frequency point for SIC. For system message SI signals with resource conflicts but higher relay levels, this forwarding node can do nothing and wait for the other party to enter silence before detecting this node's system message SI and actively performing the above conflict resolution actions. Through the above technical solution, when a node detects a resource conflict, it can perform corresponding operations according to clear avoidance rules, so that weaker nodes (low strength or suboptimal level) can actively give up resources (downgrade or frequency switching), ensuring the preservation of high-quality backbone links, enabling the network structure to automatically evolve to a more orderly state, realizing the self-organization optimization and interference elimination of the network topology, without the need for central node intervention, avoiding inconsistent behavior and erroneous operations, and effectively reducing network instability.

[0049] In one embodiment, the wireless ad hoc network synchronization method further includes the following steps: During service transmission, non-root nodes maintain a synchronization source list, which records information on multiple candidate synchronization sources that have been successfully demodulated. The non-root nodes include non-root nodes that have not joined the network and non-root nodes that have joined the network. Non-root nodes that have not joined the network configure all time slots to receive and attempt to demodulate system information. Non-root nodes that have joined the network configure the system message time slots in the preset receiving time slots to demodulate the system messages of the current superior synchronization source, and poll other frequency points in the idle time slots to demodulate the system messages of potential synchronization sources, and update the demodulation results to the synchronization source list. When a non-root node detects that the link quality with the current upper-level synchronization source meets the switching conditions, it selects the candidate synchronization source with the highest signal strength from the synchronization source list as the new upper-level synchronization source. The switching conditions include: the signal strength of the current upper-level synchronization source is lower than the first threshold, and the signal strength of the candidate synchronization source is higher than the signal strength of the current upper-level synchronization source by a third threshold.

[0050] In one implementation, non-root nodes continuously maintain a synchronization source list during service transmission, enabling nodes to accumulate real-time information from multiple candidate synchronization sources. Non-root nodes include those not yet connected to the network and those already connected. Non-root nodes not yet connected to the network, lacking any synchronization information, must configure all time slots to receive and attempt to demodulate system information. Conversely, non-root nodes already connected to the network are only configured to demodulate system messages from the current upstream synchronization source within a preset receiving time slot, ensuring the reliability of the main link communication. Simultaneously, they poll other frequency points in idle time slots to demodulate system messages from potential synchronization sources, updating the demodulation results to the synchronization source list to ensure the list always reflects the latest status of available synchronization sources in the network. When a node detects that the signal strength of the current upstream synchronization source is below a first threshold and that the signal strength of a candidate synchronization source is above a third threshold, a handover process is triggered, selecting the candidate synchronization source with the highest signal strength from the synchronization source list as the new upstream synchronization source. This mechanism organically combines synchronization source monitoring with service transmission, avoiding delays caused by passive searching during link degradation. The dual threshold design effectively prevents frequent erroneous handovers caused by brief signal fluctuations. The synchronization source list is a data structure that dynamically stores the real-time status information of multiple candidate synchronization sources. It can be implemented using a linked list or hash table. Each entry contains a node identifier, signal strength measurement, and timestamp, aiming to provide a basis for synchronization source handover decisions. Idle time slot polling can be understood as actively scanning other frequency points during time slots when nodes are not assigned service transmission tasks. It can be implemented using periodic frequency hopping scanning or random frequency point scanning, aiming to utilize idle time slot resources for network environment awareness without increasing additional power consumption. The dual threshold mechanism in the handover conditions refers to a combined judgment logic that simultaneously satisfies a signal strength below the first threshold and a candidate source signal strength above the third threshold. It can dynamically adjust the threshold parameter range based on network load, aiming to filter brief signal fluctuations and ensure that the benefits of the handover operation outweigh the overhead.

[0051] Specifically, non-root nodes are implemented using embedded microcontrollers with integrated RF transceivers, and the synchronization source list is stored in on-chip non-volatile memory in the form of a linked list. In the TDMA frame structure, the node demodulates the current superior synchronization source message in the time slot allocated for reception. In idle time slots not occupied by service transmission, it controls the RF front-end to switch to other preset frequency points for scanning. For example, after receiving the primary synchronization source message in the 2.4GHz band, it switches to the 5GHz band to scan for potential synchronization sources in idle time slots. The signal strength information in the demodulation results is updated to the synchronization source list. When the primary synchronization source signal strength is detected to be continuously below the threshold and there is a candidate source with a significantly higher signal strength in the list, it automatically switches to that candidate source. That is, after powering on, the non-root node enters a continuous search phase, attempting to demodulate the system message SI signal at various frequency points. If the node is located in the network center, it is highly likely to demodulate the system message SI sent by multiple forwarding nodes. This invention stipulates that after a node powers on, it must demodulate all frequency points, save the successfully demodulated system message SI information to form a synchronization source list, and select the node with the highest RSSI as the superior synchronization source.

[0052] However, since all nodes in the network are mobile, the demodulation of the System Message (SI) from the upstream synchronization source gradually becomes unstable as the topology changes. If synchronization can be switched to a forwarding node with a higher RSSI and more stable demodulation in advance, the process of connection instability leading to eventual disconnection and re-searching can be avoided. Therefore, nodes need to demodulate as many System Message (SI) signals as possible to update the synchronization source list while performing normal business operations, so that they can select a new synchronization source at any time to seek stable synchronization. Therefore, if Figure 10As shown in the diagram, the leaf node's receive time slot is extended by one slot. The parent synchronization source of leaf node 2 is node 0, and the system message SI signal of node 0 is continuously demodulated in slot 0. Meanwhile, since slot 5 is also a receive time slot, demodulation of the system message SI signal across all frequency points can be attempted. Therefore, this invention proposes the following scheme for synchronization source switching during movement: Node x uses a forward-receive-backward-transmit frame format, and its superior synchronization source is node y; Node y transmits system message SI in slot 0 of frame n / n+m / n+2m / n+3m / … (hereinafter referred to as frame_y_system message SI); Node x demodulates system message SI in slot 0. If current_frame == frame_y_system message SI, node x demodulates the system message SI signal of node y in slot 0; otherwise, node x polls the entire frequency range in slot 0 to attempt to demodulate the system message SI signal; Node x polls the entire frequency range in slot 5 to attempt to demodulate the system message SI signal; Node x successfully demodulates the system message SI signal of node z1 / z2 / z3 and saves its relevant information in the synchronization source list; Node x deletes synchronization sources in the synchronization source list that have been written for more than X frames since the last time (to maintain the real-time performance of synchronization source information). It can be seen that as the topology changes, Node x and node… As the distance increases, the demodulated energy of system message SI falls below the threshold S1. Node x queries the strongest synchronization source in the synchronization source list, node z2. If the demodulated energy of node z2 (S2 – S1) > the threshold S3, node x switches its parent synchronization source to node z2; otherwise, no switch is performed. This scheme, by pre-demodulating backup synchronization sources (SyncList), eliminates the need for a full network search when the main link is disconnected or deteriorates, allowing for immediate switching. It ensures that switching only occurs when the new signal is significantly superior to the old one, preventing repeated jumps between similar signals and achieving rapid switching. This adapts to highly dynamic mobile scenarios, avoids network topology oscillations caused by fluctuations in a single synchronization source link, thereby reducing overall network power consumption and improving synchronization stability.

[0053] In one embodiment, the signal strength corresponding to the second threshold is greater than the signal strength corresponding to the first threshold; The leaf nodes in the wireless ad hoc network adopt a half-duplex mode, and the frame structure is configured with the first half of the time slots for receiving and the second half of the time slots for transmitting, or the first half of the time slots for transmitting and the second half of the time slots for receiving. When selecting a parent synchronization source, a leaf node configures its own transmit and receive time slots to be opposite to those of the parent synchronization source.

[0054] In one implementation, by precisely setting a second threshold greater than the first threshold, the signal strength fluctuations within the threshold range will not trigger false state switching, thus maintaining the stability of the network topology. Simultaneously, by standardizing the half-duplex frame structure, frames are divided into ordered reception and transmission periods, ensuring that nodes focus on performing a single operation within a specified time slot, reducing the probability of channel collisions caused by timing irregularities. Furthermore, by dynamically coordinating the transmission and reception time slot configuration when selecting a higher-level synchronization source, the timing of this node and the higher-level synchronization source becomes complementary; for example, this node receives when the higher-level source transmits, and the higher-level source receives when this node transmits, achieving reliable transmission of system messages and significantly improving the efficiency of network-wide synchronization. Half-duplex mode can be understood as a node being able to perform only one of the two operations at a time: sending or receiving. It can be configured using time-division multiplexing to achieve the frame structure configuration. Specifically, it can be configured so that the first half of the time slot is used for receiving and the second half for sending, or vice versa. The purpose is to adapt to hardware limitations and avoid self-interference caused by simultaneous sending and receiving. When selecting a parent synchronization source, the leaf node configures its send and receive time slots to be opposite to those of the parent synchronization source. This means that the receiving time slot of the leaf node is aligned with the sending time slot of the parent, and the sending time slot of the leaf node is aligned with the receiving time slot of the parent. This can be achieved using an automatic negotiation mechanism or predefined rules. The purpose is to ensure bidirectional communication timing matching and reduce message collisions.

[0055] Furthermore, the wireless ad hoc network nodes employ general-purpose microcontrollers for processing. The frame structure is configured such that the first half of the time slot is used for reception and the second half for transmission. When a node detects that its upstream synchronization source uses a configuration of receiving in the first half and transmitting in the second half, the node automatically configures itself to transmit in the first half and receive in the second half. This scheme effectively avoids frequent changes in network topology and prevents nodes from frequently triggering upgrade / degrade oscillations at critical points. The opposite transmit and receive time slots are a physical prerequisite for TDMA multi-hop synchronization, enhancing system stability and establishing the physical basis for upstream and downstream synchronization.

[0056] Please see Figure 11 , Figure 11 This is a schematic diagram of the wireless ad hoc network synchronization device provided in an embodiment of the present invention. This wireless ad hoc network synchronization device corresponds one-to-one with the wireless ad hoc network synchronization method in the above embodiments. Please refer to [link / reference] for details. Figure 1 as well as Figure 1 The relevant descriptions in the corresponding embodiments are shown below. For ease of explanation, only the parts relevant to this embodiment are shown. See also... Figure 11 The wireless ad hoc network synchronization device 11 includes a wireless ad hoc network, which includes a root node, a forwarding node, and leaf nodes. The device uses Time Division Multiple Access (TDMA) to divide time into periodic frames, with each frame divided into multiple time slots. Specifically, the wireless ad hoc network synchronization device 11 is used for: The root node periodically sends system messages in the specified time slot as the initial synchronization source for the entire network; Unconnected nodes search for demodulation system messages across all frequencies, select an upstream synchronization source based on demodulation energy, and connect to the network. The leaf nodes that have joined the network monitor the signal strength of system messages from the upper-level synchronization source. When the signal strength is lower than the first threshold, the leaf node is upgraded to a forwarding node and sends system messages according to the allocated time and frequency resources. The forwarding node that has joined the network monitors the signal strength of the system messages from the upper-level synchronization source. When the signal strength is higher than the second threshold, the forwarding node is downgraded to a leaf node and stops sending system messages. The time-frequency resources for the forwarding node to send system messages are determined based on the forwarding level of the forwarding node in the network topology, and forwarding nodes with adjacent forwarding levels send messages at different times in the time domain.

[0057] Optionally, the rules for determining the time-frequency resources for forwarding nodes to send system messages include: The timing of sending system messages by the forwarding node is hashed in the frame dimension, and a system message is sent once every N frames. The specific frame number for sending the system message is determined based on the result of the modulo operation between the forwarding level and N. The time slot position in which the forwarding node sends system messages within a frame is determined based on the parity of the forwarding level; where N is an integer greater than 1, and the forwarding level represents the number of hops from the root node.

[0058] Optionally, leaf nodes are upgraded to forwarding nodes, including: When the leaf node detects that the signal strength of the current upper-level synchronization source is lower than the first threshold, it starts an upgrade timer, the duration of which is a random value; During the upgrade timer's operation, the leaf node retains its identity and continues to listen for system messages; If a system message with a signal strength higher than the first threshold is detected during the operation of the upgrade timer, the upgrade timer is cleared and the upgrade is canceled. If the upgrade timer overflows, the leaf node switches to a forwarding node and establishes a system message bearer.

[0059] Optionally, a forwarding node may be downgraded to a leaf node, including: When the forwarding node detects that the signal strength of the upper-level synchronization source is higher than the second threshold and the degradation condition is met, the degradation timer is started. During the operation of the degradation timer, the forwarding node sends a system message carrying a degradation flag to notify its lower-level leaf nodes; If the degradation timer overflows, the forwarding node switches to a leaf node and stops sending system messages.

[0060] Optionally, after the forwarding node sends a system message carrying a degradation flag, the method further includes: The lower-level leaf node demodulates the degradation flag; If the lower-level leaf node determines that the forwarding node is its only synchronization source, it sends a stop degradation request to the forwarding node. After receiving the stop downgrade request, the forwarding node resets the downgrade timer to extend the time for maintaining the forwarding node's identity; If the lower-level leaf node has other available synchronization sources, then switch to the other synchronization source and prohibit sending stop-degradation requests.

[0061] Optionally, the aforementioned wireless ad hoc network synchronization device 11 is also used for: The forwarding node periodically starts a silent timer, and cancels the sending of the current system message when the silent timer overflows; During the time slot where transmission is cancelled, the forwarding node listens to the channel to detect system message signals indicating whether there is a resource conflict. If a system message signal indicating a resource conflict is detected during the silent period, a downgrade operation or a switch of the system message transmission frequency will be performed based on the signal strength of the conflict signal and the forwarding level of the source node.

[0062] Optionally, based on the signal strength of the conflicting signal and the forwarding level of the source node, a downgrade operation or a switch of the system message transmission frequency may be performed, including: If the signal strength of the conflict signal is higher than the second threshold, and the forwarding level of the source node is less than or equal to the forwarding level of this node, then this node triggers a degradation process. If the signal strength of the conflict signal is lower than the second threshold, the node switches the frequency of sending system messages. If the forwarding level of the source node is higher than that of this node, this node will maintain its current state and wait for the source node to perform conflict resolution.

[0063] Optionally, the aforementioned wireless ad hoc network synchronization device 11 is also used for: During service transmission, non-root nodes maintain a synchronization source list, which records information on multiple candidate synchronization sources that have been successfully demodulated. The non-root nodes include non-root nodes that have not joined the network and non-root nodes that have joined the network. Non-root nodes that have not joined the network configure all time slots to receive and attempt to demodulate system information. Non-root nodes that have joined the network configure the system message time slots in the preset receiving time slots to demodulate the system messages of the current superior synchronization source, and poll other frequency points in the idle time slots to demodulate the system messages of potential synchronization sources, and update the demodulation results to the synchronization source list. When a non-root node detects that the link quality with the current upper-level synchronization source meets the switching conditions, it selects the candidate synchronization source with the highest signal strength from the synchronization source list as the new upper-level synchronization source. The switching conditions include: the signal strength of the current upper-level synchronization source is lower than the first threshold, and the signal strength of the candidate synchronization source is higher than the signal strength of the current upper-level synchronization source by a third threshold.

[0064] Optionally, the signal strength corresponding to the second threshold is greater than the signal strength corresponding to the first threshold; The leaf nodes in the wireless ad hoc network adopt a half-duplex mode, and the frame structure is configured with the first half of the time slots for receiving and the second half of the time slots for transmitting, or the first half of the time slots for transmitting and the second half of the time slots for receiving. When selecting a parent synchronization source, a leaf node configures its own transmit and receive time slots to be opposite to those of the parent synchronization source.

[0065] It should be noted that the information interaction and execution process between the above-mentioned units are based on the same concept as the method embodiments of the present invention. For details on their specific functions and technical effects, please refer to the method embodiments section, which will not be repeated here.

[0066] In one embodiment, a computer-readable storage medium is provided that, when the instructions in the computer-readable storage medium are executed by a processor in a computer device, enables the computer device to perform the steps of any embodiment of the wireless ad hoc network synchronization method disclosed in this invention, which will not be repeated here. The computer-readable storage medium may be non-volatile or volatile.

[0067] The processor referred to can be a CPU, but it can also be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor can be a microprocessor or any conventional processor.

[0068] Memory includes readable storage media, internal memory, etc., wherein internal memory can be the RAM of a computer device, providing an environment for the operation of the operating system and computer-readable instructions stored in the readable storage media. The readable storage media can be the hard drive of the computer device, or in other embodiments, it can be an external storage device of the computer device, such as a plug-in hard drive, SmartMediaCard (SMC), SecureDigital (SD) card, or FlashCard. Furthermore, memory can include both internal storage units and external storage devices of the computer device. Memory is used to store the operating system, cooperative applications, bootloader, data, and other programs, such as program code of computer programs. Memory can also be used to temporarily store data that has been output or will be output.

[0069] Those skilled in the art will understand that implementing all or part of the processes in the above embodiments can be accomplished by a computer program instructing related hardware. This computer program can be stored in a non-volatile computer-readable storage medium. When executed, the computer program can include the processes of the embodiments described above. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory may include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory may include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in a variety of forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), RAMbus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM).

[0070] Those familiar with the technical field will understand that, for ease of description and brevity, the above-described division of functional units and modules is used as an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the system can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this invention. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here. If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium.

[0071] The above-described 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 foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A wireless ad hoc network synchronization method, characterized in that, The wireless ad hoc network includes a root node, forwarding nodes, and leaf nodes. The method employs Time Division Multiple Access (TDMA), dividing time into periodic frames, with each frame further divided into multiple time slots. The method includes: The root node periodically sends system messages in the specified time slot as the initial synchronization source for the entire network; Unconnected nodes search for demodulation system messages across all frequencies, select an upstream synchronization source based on demodulation energy, and connect to the network. The leaf nodes that have joined the network monitor the signal strength of system messages from the upper-level synchronization source. When the signal strength is lower than the first threshold, the leaf node is upgraded to a forwarding node and sends system messages according to the allocated time and frequency resources. The forwarding node that has joined the network monitors the signal strength of the system messages from the upper-level synchronization source. When the signal strength is higher than the second threshold, the forwarding node is downgraded to a leaf node and stops sending system messages. The time-frequency resources for the forwarding node to send system messages are determined based on the forwarding level of the forwarding node in the network topology, and forwarding nodes with adjacent forwarding levels send messages at different times in the time domain.

2. The wireless ad hoc network synchronization method as described in claim 1, characterized in that, The time-frequency resource determination rules for the forwarding node to send system messages include: The timing of sending system messages by the forwarding node is hashed in the frame dimension, and a system message is sent once every N frames. The specific frame number for sending the system message is determined based on the result of the modulo operation between the forwarding level and N. The time slot position in which the forwarding node sends system messages within a frame is determined based on the parity of the forwarding level, where N is an integer greater than 1, and the forwarding level represents the number of hops from the root node.

3. The wireless ad hoc network synchronization method as described in claim 1, characterized in that, The leaf node is upgraded to a forwarding node, including: When the leaf node detects that the signal strength of the current upper-level synchronization source is lower than the first threshold, it starts an upgrade timer, the duration of which is a random value; During the upgrade timer's operation, the leaf node retains its identity and continues to listen for system messages; If a system message with a signal strength higher than the first threshold is detected during the operation of the upgrade timer, the upgrade timer is cleared and the upgrade is canceled. If the upgrade timer overflows, the leaf node switches to a forwarding node and establishes a system message bearer.

4. The wireless ad hoc network synchronization method as described in claim 1, characterized in that, The forwarding node is downgraded to a leaf node, including: When the forwarding node detects that the signal strength of the upper-level synchronization source is higher than the second threshold and the degradation condition is met, the degradation timer is started. During the operation of the degradation timer, the forwarding node sends a system message carrying a degradation flag to notify its lower-level leaf nodes; If the degradation timer overflows, the forwarding node switches to a leaf node and stops sending system messages.

5. The wireless ad hoc network synchronization method as described in claim 4, characterized in that, After the forwarding node sends a system message carrying a degradation flag, the method further includes: The lower-level leaf node demodulates the degradation flag; If the lower-level leaf node determines that the forwarding node is its only synchronization source, it sends a stop degradation request to the forwarding node. After receiving the stop downgrade request, the forwarding node resets the downgrade timer to extend the time for maintaining the forwarding node's identity; If the lower-level leaf node has other available synchronization sources, then switch to the other synchronization source and prohibit sending stop-degradation requests.

6. The wireless ad hoc network synchronization method as described in claim 1, characterized in that, The method also includes random silent listening, including: The forwarding node periodically starts a silent timer, and cancels the sending of the current system message when the silent timer overflows; During the time slot where transmission is cancelled, the forwarding node listens to the channel to detect system message signals indicating whether there is a resource conflict. If a system message signal indicating a resource conflict is detected during the silent period, a downgrade operation or a switch of the system message transmission frequency will be performed based on the signal strength of the conflict signal and the forwarding level of the source node.

7. The wireless ad hoc network synchronization method as described in claim 6, characterized in that, The step of performing a downgrade operation or switching the transmission frequency of system messages based on the signal strength of the conflict signal and the forwarding level of the source node includes: If the signal strength of the conflict signal is higher than the second threshold, and the forwarding level of the source node is less than or equal to the forwarding level of this node, then this node triggers a degradation process. If the signal strength of the conflict signal is lower than the second threshold, the node switches the frequency of sending system messages. If the forwarding level of the source node is higher than that of this node, this node will maintain its current state and wait for the source node to perform conflict resolution.

8. The wireless ad hoc network synchronization method as described in claim 1, characterized in that, The method further includes: During service transmission, non-root nodes maintain a synchronization source list, which records information on multiple candidate synchronization sources that have been successfully demodulated. The non-root nodes include non-root nodes that have not joined the network and non-root nodes that have joined the network. Non-root nodes that have not joined the network configure all time slots to receive and attempt to demodulate system information. Non-root nodes that have joined the network configure the system message time slots in the preset receiving time slots to demodulate the system messages of the current superior synchronization source, and poll other frequency points in the idle time slots to demodulate the system messages of potential synchronization sources, and update the demodulation results to the synchronization source list. When a non-root node detects that the link quality with the current upper-level synchronization source meets the switching conditions, it selects the candidate synchronization source with the highest signal strength from the synchronization source list as the new upper-level synchronization source. The switching conditions include: the signal strength of the current upper-level synchronization source is lower than the first threshold, and the signal strength of the candidate synchronization source is higher than the signal strength of the current upper-level synchronization source by a third threshold.

9. The wireless ad hoc network synchronization method as described in claim 1, characterized in that, The signal strength corresponding to the second threshold is greater than the signal strength corresponding to the first threshold; The leaf nodes in the wireless ad hoc network adopt a half-duplex mode, and the frame structure is configured with the first half of the time slots for receiving and the second half of the time slots for transmitting, or the first half of the time slots for transmitting and the second half of the time slots for receiving. When selecting a parent synchronization source, a leaf node configures its own transmit and receive time slots to be opposite to those of the parent synchronization source.

10. A wireless self-organizing network synchronization device, characterized in that, The wireless ad hoc network synchronization device includes a wireless ad hoc network, which includes a root node, a forwarding node, and leaf nodes. The device employs Time Division Multiple Access (TDMA) to divide time into periodic frames, with each frame further divided into multiple time slots. The device is used for: The root node periodically sends system messages in the specified time slot as the initial synchronization source for the entire network; Unconnected nodes search for demodulation system messages across all frequencies, select an upstream synchronization source based on demodulation energy, and connect to the network. The leaf nodes that have joined the network monitor the signal strength of system messages from the upper-level synchronization source. When the signal strength is lower than the first threshold, the leaf node is upgraded to a forwarding node and sends system messages according to the allocated time and frequency resources. The forwarding node that has joined the network monitors the signal strength of the system messages from the upper-level synchronization source. When the signal strength is higher than the second threshold, the forwarding node is downgraded to a leaf node and stops sending system messages. The time-frequency resources for the forwarding node to send system messages are determined based on the forwarding level of the forwarding node in the network topology, and forwarding nodes with adjacent forwarding levels send messages at different times in the time domain.

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