An improved tdma protocol-based centralized communication method for underwater acoustic networks

Abstract

The application discloses a centralized communication method of underwater acoustic network based on improved TDMA protocol, which comprises the following steps: obtaining a full-link set and a link conflict matrix; calculating a final routing link set of each underwater node; dividing continuous time into equal-length frames, and then dividing each frame into equal-length time slots, and setting an inherent node with the highest transmission priority in each time slot; calculating a maximum interference-free routing link set capable of transmitting in each time slot according to a candidate routing link set which does not conflict with the inherent node in each time slot, obtaining a transmission time slot set of each routing link according to the maximum interference-free routing link set, and synchronizing with all underwater nodes in the network through broadcasting; determining the transmission time of each data packet, and performing node data transmission. The application can reduce the transmission delay of underwater acoustic multi-hop communication network and improve the network throughput.

Description

Technical Field

[0001] This invention relates to the field of underwater acoustic communication, and more particularly to a centralized communication method for underwater acoustic networks based on an improved TDMA protocol. Background Technology

[0002] Due to the unique characteristics of underwater acoustic channels, such as high propagation loss and long propagation delay, providing reliable data transmission in underwater acoustic communication networks is challenging. Traditional underwater acoustic MAC protocols perform poorly, with large packet transmission delays and low throughput. Traditional Time Division Multiple Access (TDMA) methods divide time into multiple discrete time slots. To avoid interference with other nodes, only one node is allowed to transmit in each time slot, which significantly limits the performance of underwater acoustic communication networks. Furthermore, most existing improved methods are based on a distributed network structure, meaning that underwater nodes make MAC decisions and calculate the set of nodes that can transmit within a time slot, rather than calculating the set of links that can transmit within a time slot. This introduces a huge MAC information update overhead for underwater acoustic multi-hop communication networks, further limiting network performance. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention proposes a centralized communication method for underwater acoustic networks based on an improved TDMA protocol, which enhances the network performance of underwater acoustic multi-hop sensor networks and reduces network transmission latency.

[0004] The specific technical solution is as follows:

[0005] A centralized communication method for underwater acoustic networks based on an improved TDMA protocol includes the following steps:

[0006] S1: Based on the location of the underwater node, the maximum communication distance, and the maximum interference distance, obtain the full link set and the link conflict matrix;

[0007] S2: Calculate the shortest hop count and least energy-consuming path for the underwater node to transmit data packets to the sink node as the final route, and the links contained therein are the routing links; sum up all the routing links to obtain the routing link set;

[0008] S3: Divide continuous time into several time frames of equal length, each frame into several time slots of equal length, and set an inherent node with the highest transmission priority for each time slot;

[0009] S4. Determine the transmission time slot set for each routing link: Calculate the set S of candidate routing links that do not conflict with the links of its inherent nodes within each time slot. Based on the number of routing links in set S, calculate the maximum set of interference-free routing links that can be transmitted in each time slot, and thus obtain the transmission time slot set for each routing link.

[0010] S5: Synchronize the final routes of all underwater nodes in the network and the set of transmission time slots for each route link via broadcast;

[0011] S6: When there are data packets to be sent, determine the sending time of each data packet, aggregate and compress multiple data packets, and then transmit node data through multicast.

[0012] Furthermore, S1 is specifically implemented through the following sub-steps:

[0013] (S1.1) Set the maximum communication distance and the maximum interference distance; the maximum communication distance and the maximum interference distance are the same for all nodes;

[0014] (S1.2) Define a link conflict matrix to record whether there is a conflict between any two links; for any two links, determine whether the distance between the sending node of one link and the receiving node of the other link is within the maximum interference distance. If so, it means that there is a conflict between the two links, and mark the corresponding element in the link conflict matrix as 1; otherwise, mark it as 0.

[0015] (S1.3) The aggregation node traverses all possible node pairs, calculates the actual distance between nodes, and if it does not exceed the maximum communication distance, the node pair is recorded as a valid link; otherwise, it is recorded as an invalid link. All valid links are summarized to obtain the full link set.

[0016] Furthermore, S2 is specifically implemented through the following sub-steps:

[0017] (S2.1) The sink node calculates the shortest hop path for each underwater node to transmit data packets to the sink node; if there are multiple shortest hop paths, calculate the average remaining energy of the underwater nodes related to each shortest hop path, and select the shortest hop path with the highest average remaining energy as the final route.

[0018] (S2.2) Extract the routing links contained in the final route of all underwater nodes, remove duplicate links to form a routing link set; establish the mapping relationship between the routing link set and the full link set, and clarify the position of each routing link in the full link set.

[0019] Furthermore, the sink node uses the Dijkstra algorithm to calculate the shortest hop path for the underwater nodes to transmit data packets to the sink node.

[0020] Furthermore, in S4, the calculation of the maximum set of interference-free links that can be transmitted in each time slot based on the number of routing links in set S is specifically as follows: when the number of routing links is less than the link number threshold, a recursive method is used to exhaust all link combinations through a divide-and-conquer strategy to obtain the maximum set of interference-free links that can be transmitted in each time slot; otherwise, a heuristic algorithm is used to sort the links according to the existing order of conflict degree and link priority, and then iteratively selects links that do not conflict with the selected links to obtain the maximum set of interference-free links that can be transmitted in each time slot.

[0021] Furthermore, the recursive method is based on a divide-and-conquer strategy, specifically: A link g is randomly selected from set S, and set S is split into subsets S1 and S2. Subset S1 is the set of links remaining after excluding link g, and subset S2 is the set of all links in set S that do not conflict with link g. The size of the largest non-interference subset that can be formed by S1 and S2 is calculated respectively. If the size of the largest non-interference subset formed by S1 is... The size of the largest undisturbed subset formed by S2 is greater than or equal to that of S2. If the maximum undisturbed subset MTS(S) of set S is equal to the maximum undisturbed subset MTS(S1) of subset S1, then the recursive operation continues on S1; otherwise, let... And recursively on subset S2; repeat the recursion until S is an empty set, to obtain the maximum set of interference-free links in this time slot;

[0022] The heuristic algorithm is as follows: Calculate the number of collisions between a given link and other links in set S to obtain the collision degree of the link; calculate the link priority of the link, first sort the links according to the collision degree, and if the collision degrees are the same, sort them according to the link priority, and traverse each link in the order of the newly obtained links; for the link currently being processed, determine whether it has a collision with the already selected links through the link collision matrix. If it does, skip the link; if it does not, select the link; after traversing all links, obtain the set of all links that can be transmitted simultaneously in the time slot based on the selection results, that is, the maximum set of interference-free links in the time slot.

[0023] Further, S5 is specifically implemented through the following operations: the aggregation node generates an information broadcast packet containing the final routes of all underwater nodes and the transmission time slot set of each route link, and broadcasts the information broadcast packet to surrounding underwater nodes through the underwater acoustic channel; after receiving the broadcast packet, the underwater node verifies the integrity of the information. If the routing and time slot information stored by the current underwater node has not been updated, it updates its local final route and transmission time slot set, and broadcasts the information broadcast packet to neighboring underwater nodes that have not sent an acknowledgment signal to the previous hop node in the next time slot where interference-free transmission can be performed; this process is repeated until all underwater nodes have reported the completion of information updates to the aggregation node, and the aggregation node stops broadcasting.

[0024] Furthermore, S6 is specifically implemented through the following sub-steps:

[0025] (S6.1) When multiple data packets to be transmitted are detected in the local cache of the underwater node, the data packet aggregation and compression algorithm is called to aggregate and compress these data packets into a single aggregate packet;

[0026] (S6.2) Calculate the amount of data in the aggregation packet, and at the same time query the routing link information stored locally to determine the routing link corresponding to the current underwater node and the set of transmission time slots of the link;

[0027] (S6.3) Select available time slots belonging to the current frame from the transmission time slot set;

[0028] (S6.4) The underwater node transmits data packets sequentially along the routing link to the aggregation node within the available time slots and uses multicast to transmit the data packets; if the amount of compressed data does not exceed the maximum amount of data that can be transmitted in a single time slot, the earliest available time slot of the current frame is selected to send the aggregated packet, and the corresponding data packet in the local buffer is cleared after the transmission is completed; if the amount of compressed data exceeds the maximum amount of data that can be transmitted in a single time slot, part of the data is sent in the earliest available time slot of the current frame, and the corresponding data packet is cleared in the local buffer, and the remaining data is temporarily stored in the buffer; after the next available time slot begins, the remaining data is aggregated and compressed again, and transmission continues in the new available time slot until all data transmission is completed; if there is no new available time slot in the current frame, the next frame is entered and steps (S6.1)-(S6.4) are repeated until all data is transmitted.

[0029] During this process, if the sending node does not receive an acknowledgment signal from the receiving node within the transmission time slot, it will retransmit the data in the next time slot belonging to that link, with a maximum of N retransmissions. If all N retransmissions fail, it will report a link failure to the aggregation node, and the aggregation node will re-execute the routing link determination step to allocate a new routing link for the node, ensuring that the data can be transmitted smoothly.

[0030] Furthermore, the aggregation node periodically updates the link conflict matrix and re-makes routing decisions, i.e., repeats S1-S6, to ensure that the underwater acoustic multi-hop communication network can continuously optimize the communication scheduling of the underwater acoustic multi-hop communication network according to state changes during operation.

[0031] Furthermore, the underwater acoustic multi-hop communication network includes a convergence node and multiple underwater nodes, each node having a fixed sequence number, and all nodes having the same maximum communication distance and maximum interference distance. The underwater nodes in the underwater acoustic multi-hop communication network periodically send data packets to the convergence node according to the allocated time slots through an underwater acoustic modem, wherein the underwater acoustic modem is in half-duplex mode.

[0032] The beneficial effects of this invention are:

[0033] The communication method proposed in this invention calculates the maximum set of interference-free links that can be transmitted in each time slot through a convergence node, and then broadcasts the result to the entire network. This allows underwater nodes to transmit data via multicast after aggregating and compressing data packets. Within a single time frame, data can be transmitted in multiple time slots, effectively reducing data transmission latency, increasing network throughput, and improving network performance. Attached Figure Description

[0034] Figure 1 This is a flowchart of a centralized communication method for underwater acoustic networks based on an improved TDMA protocol, as described in an embodiment of the present invention.

[0035] Figure 2 This is a flowchart for determining the link conflict matrix in an embodiment of the present invention.

[0036] Figure 3 This is a schematic diagram of time slot division in an embodiment of the present invention.

[0037] Figure 4 This is a flowchart illustrating the process of determining the set of transmission time slots for each routing link in an embodiment of the present invention. Detailed Implementation

[0038] The present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. The objectives and effects of the present invention will become clearer as a result. The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0039] This embodiment proposes a centralized communication method for underwater acoustic networks based on an improved TDMA protocol. The scenario discussed is a multi-hop underwater acoustic communication network with multiple nodes. The network consists of a sink node (typically a node deployed on an underwater acoustic test vessel, but could also be a specific underwater node) and multiple underwater nodes. Each node has a fixed sequence number, and all nodes have the same maximum communication distance and maximum interference distance. Underwater nodes in the network send data packets to the sink node via underwater acoustic modems. The underwater acoustic modems of each node are half-duplex, meaning a node cannot simultaneously receive and send data packets. This method employs a centralized communication approach, with unified scheduling by the network sink node. However, the application scenarios of this method are not limited to this; it can also be used for data transmission between nodes in the network (i.e., underwater nodes can also make routing decisions and then broadcast to other nodes). Figure 1 As shown, the method includes the following steps:

[0040] S1: Based on the location of the underwater node, the maximum communication distance, and the maximum interference distance, calculate the full link set and link collision matrix of all transmission links. This is achieved through the following sub-steps:

[0041] (S1.1) Set the maximum communication distance and maximum interference distance Maximum communication distance The maximum distance at which effective data transmission can be achieved between underwater nodes via an underwater acoustic channel, and the maximum interference distance. This refers to the furthest distance at which a signal transmitted by one node can interfere with the signal received by another node.

[0042] (S1.2) Define a link collision matrix to record whether there is a collision between any two links. After generating the complete link collision matrix, store it in the local database of the aggregation node to lay the foundation for subsequent collision-free transmission.

[0043] Specifically, such as Figure 2 As shown, for any two links, determine whether the distance between the sending node of one link (link i) and the receiving node of the other link (link j) is within the maximum interference distance (i.e., determine whether the receiving node of one communication link is within the interference range of the sending node of the other link). If so, it means that there is a conflict between the two links, and the corresponding element in the link conflict matrix is ​​marked as 1; otherwise, it is marked as 0.

[0044] (S1.3) The aggregation node traverses all possible node pairs and calculates the actual distance between nodes using the three-dimensional spatial distance formula. If this distance does not exceed the set maximum communication distance, the corresponding node pair is recorded as a valid link; otherwise, it is recorded as an invalid link. All valid links are aggregated to form a full link set.

[0045] S2: Determining the set of routing links. The sink node makes routing decisions, calculating the shortest hop count and least energy-consuming path for underwater nodes to transmit data packets to the sink node as the final route. The links contained in the final route are recorded as routing links, and all routing links are aggregated to form the set of routing links. S2 is implemented through the following sub-steps:

[0046] (S2.1) The sink node calls Dijkstra's algorithm to calculate the shortest hop count path from each underwater node to the sink node, thereby obtaining the final route and generating a routing table. The hop count refers to the number of intermediate nodes that data passes through from the source node to the destination node. The fewer the hop count, the shorter the path. The algorithm uses this algorithm to filter out the set of paths with the smallest hop count (i.e., the shortest hop count path).

[0047] If a node has multiple shortest hop paths, a secondary decision is needed based on the average remaining energy of the underwater nodes involved in the path to obtain the final route:

[0048] In the early stages of network startup, nodes have not yet transmitted data packets and there is no real-time energy feedback data. Since nodes have not generated transmission behavior, they cannot synchronize energy information through data interaction. Therefore, one of the multiple shortest hop paths is randomly selected as the final route.

[0049] Once the network enters a stable operating phase, nodes begin periodically transmitting data packets. After each data packet transmission or reception operation, the underwater node immediately collects the current real-time remaining energy through its built-in energy monitoring module. The timing of this collection is chosen during transmission gaps to avoid conflicts with the data transmission and reception process, ensuring that the collected energy data reflects the node's true energy consumption status after transmission. Subsequently, the underwater node embeds the real-time remaining energy information into the next data packet to be transmitted. Upon receiving the data packet, the next-hop node first parses the real-time remaining energy field, updates its locally stored neighbor node energy table, and then forwards the data packet (including the current node's remaining energy) to subsequent nodes. Finally, when the aggregation node receives all data packets, it extracts the real-time remaining energy data of each node and updates the global energy table (overwriting the initial energy data), ensuring the real-time nature and accuracy of the energy information. Using the global energy table, the aggregation node calculates the average remaining energy of the underwater nodes associated with each shortest hop path and selects the shortest hop path with the highest average remaining energy as the node's final route, thereby balancing the energy consumption of nodes in the network and extending the network's lifespan.

[0050] (S2.2) Extract the links contained in the final route of all underwater nodes (denoted as routing links), remove duplicate links to form a set of routing links, and establish a mapping relationship between this set and the previously formed full link set to clarify the position of each routing link in the full link set.

[0051] S3: Time slot allocation. For example... Figure 3 As shown, continuous time is divided into several time frames of equal length (hereinafter referred to as frames), and each frame is divided into several time slots of equal length, forming a time slot sequence. Each time slot is assigned a unique node (i.e., a one-to-one correspondence between "time slot" and "unique node" is established). This unique node has the highest transmission priority in the time slot, ensuring that each time slot has a unique highest transmission node priority point. When other links need to transmit data in the time slot, they must transmit data without interfering with the transmission of the unique node link.

[0052] Furthermore, the time frame period is set based on the total amount of data generated by nodes in the network and the number of nodes.

[0053] Furthermore, the number of discrete time slots divided into each time frame is equal to the number of nodes in the network.

[0054] S4: The set of transmission time slots for each route link is determined. For example... Figure 4 As shown, this is achieved through the following sub-steps:

[0055] (S4.1) Through the link conflict matrix (K is the total number of links in the routing link set, matrix element) This indicates that there is a conflict between link i and link j. (This indicates no conflict) Calculate the set S of candidate links that do not conflict with the links of the inherent nodes in each time slot; that is, for each link i in the routing link set, if link i does not interfere with any transmission links of the inherent nodes, then link i is included in the candidate link set S.

[0056] (S4.2) Since there may be mutual interference between the routing links in set S, different algorithms are used to obtain the maximum set of interference-free links L that can be transmitted in each time slot, depending on the number of routing links in set S and the size of the link set. max The details are as follows:

[0057] When the number of routing links in the candidate link set S is less than the link number threshold M th (Right now If the number of links in set S is considered small, then a recursive method is used to obtain the maximum set of interference-free links L that can be transmitted in that time slot. maxThe recursive function works based on a divide-and-conquer strategy: It randomly selects a link g from the candidate link set S, then splits S into two subsets, S1 = S{g} (the set of links remaining after excluding link g) and S2 = S{g}. (The set of links in set S that do not conflict with link g). Then, calculate the size of the largest interference-free subset that S1 and S2 can form respectively; here, we use... This represents the largest undisturbed subset. If So let And continue the recursive operation on S1; otherwise, let This process is repeated on S2. This is continued until S is an empty set, ultimately yielding the maximum set of interference-free links L for that time slot. max .

[0058] When the number of routing links in the candidate link set S is greater than or equal to the link number threshold M th (Right now If the set S contains a large number of links, then a heuristic algorithm is used to obtain the maximum set of interference-free links L that can be transmitted in that time slot. max Specifically, firstly, the number of collisions between link j and other links in set S is calculated, i.e., the collision degree Deg[j] of link j. Simultaneously, the link priority of link j is calculated. Then, based on the conflict degree Deg[j] and link priority... The links are sorted (first by conflict severity from lowest to highest; if the conflict severity is the same, then by link priority) to obtain a new link order. Then, traverse each link in this order. For the link currently being processed... It is necessary to check whether it conflicts with the already selected links, using a link conflict matrix. The process involves making a judgment; if a conflict exists, the link is skipped; if no conflict exists, the link is selected. After traversing all links, the set of all links that can transmit simultaneously in that time slot is obtained based on the selection results, i.e., the maximum set of interference-free links L. max .

[0059] The conflict degree Deg[j] is calculated as follows:

[0060]

[0061] Link priority of link j The expression is:

[0062]

[0063] In the formula, d j It is the distance between link j and the sink node, c jIt is the number of time slots that link j is allowed to transmit within a time frame.

[0064] (S4.3) Traverse each link in the set of routing links and count the largest set of interference-free links L that contains link j. max The corresponding time slots are identified, and these time slots are aggregated to form the transmission time slot set for link j, thus determining in which time slots link j can transmit data. This yields the transmission time slot set for each routing link.

[0065] S5: Network-wide routing and timeslot information synchronization. The aggregation node generates a broadcast packet containing the final routes of all underwater nodes and the transmission timeslot set for each route link, and broadcasts this packet to surrounding underwater nodes via the underwater acoustic channel. Upon receiving the broadcast packet, the underwater nodes first verify the integrity of the information, such as checking whether the route path is reasonable and whether the timeslot information is within the valid range. If the routing and timeslot information stored by the current underwater node has not been updated, it updates its local routing table and timeslot table (i.e., the transmission timeslot set), and broadcasts the packet to neighboring underwater nodes that have not sent an acknowledgment signal to the previous hop node in the next timeslot where interference-free transmission is possible. This process is repeated until all underwater nodes have reported the completion of information updates to the aggregation node (i.e., the routing and timeslot information of all nodes in the network has been updated), at which point the aggregation node stops broadcasting.

[0066] S6: Node Data Transmission. In the underwater acoustic multi-hop communication network, underwater nodes determine the transmission time of each data packet when it needs to be sent, based on routing decisions and the set of time slots that each routing link can transmit. Multiple nodes are allowed to send data packets simultaneously within the same time slot, and a single node can send data packets within multiple time slots of a single frame. This is specifically achieved through the following sub-steps:

[0067] (S6.1) The underwater node monitors the local buffer in real time. When there are multiple data packets to be transmitted, it calls the data packet aggregation and compression algorithm to aggregate and compress these data packets into one aggregate packet, thereby reducing the number of transmissions and improving transmission efficiency.

[0068] (S6.2) Calculate the amount of data after aggregation and compression, and at the same time query the routing link information stored locally to determine the corresponding routing link and the set of transmission time slots of the link.

[0069] (S6.3) Calculate the time slot range within the current frame and filter out the available time slots belonging to the current frame from the transmission time slot set.

[0070] (S6.4) The underwater node transmits data packets sequentially along the route link to the aggregation node within the available time slots, and uses multicast to transmit the data packets. If the amount of compressed data does not exceed the maximum amount of data that can be transmitted in a single time slot, the earliest available time slot of the current frame is selected to send the aggregated packet, and the corresponding data packet in the buffer is cleared after the transmission is completed. If the amount of compressed data exceeds the maximum transmission capacity of a single time slot, part of the data is sent in the earliest available time slot of the current frame, and the corresponding data packet is cleared from the local buffer. The remaining data is temporarily stored in the buffer. After the next available time slot begins, the remaining data is aggregated and compressed again, and transmission continues in the new available time slot until all data transmission is completed. In particular, if there is no new available time slot in the current frame, processing is required in the next frame. At this time, the remaining data is aggregated and compressed again, and the available time slots of the link in the new frame are recalculated. Transmission continues in the new available time slot, that is, steps (S6.1)-(S6.4) are repeated until all data is transmitted.

[0071] During this process, if the sending node does not receive an acknowledgment signal from the receiving node within the transmission time slot, it will retransmit the data in the next time slot belonging to that link, with a maximum of N retransmissions. If all N retransmissions fail, it will report a link failure to the aggregation node, and the aggregation node will re-execute the routing link determination step (i.e., repeat S2) to allocate a new routing link for the node, ensuring that the data can be transmitted smoothly.

[0072] Furthermore, the aggregation node will periodically update the link conflict matrix and re-make routing decisions, i.e., repeat S1-S6, to ensure that the network can continuously optimize the communication scheduling of the underwater acoustic multi-hop communication network according to state changes during operation.

[0073] The communication method proposed in this invention calculates the maximum set of interference-free links that can be transmitted in each time slot through a convergence node, and then broadcasts the result to the entire network. Furthermore, it allows nodes to transmit data via multicast after aggregating and compressing data packets. Within a single time frame, nodes can transmit data in multiple time slots, effectively reducing data transmission latency, increasing network throughput, and improving network performance.

[0074] This invention presents an improved communication method that addresses the unique challenges of centralized underwater acoustic multi-hop communication networks, including half-duplex modems, frequent link collisions, and high transmission latency. Through an innovative design combining "collision-free link scheduling + network-wide synchronization + data aggregation multicast," it effectively overcomes the limitations of traditional TDMA solutions. For collision-free link scheduling, a link collision matrix is ​​used to filter candidate links that are collision-free with the inherent node links in the time slots. Then, a recursive algorithm (for small-scale global collision-free implementation) or a heuristic algorithm (for centralized fast filtering) is flexibly selected based on the link size, avoiding the "listen-backoff" overhead and data retransmissions inherent in traditional random access mechanisms. For network-wide synchronization, the aggregation node packages "routing link + time slot allocation" information into a broadcast packet for periodic broadcasting. Receiving nodes relay and forward this packet to achieve synchronization. Furthermore, in the event of a link failure, the scheduling information is updated and the entire network is synchronized, ensuring scheduling consistency. For data transmission, underwater nodes aggregate and compress multiple data packets before multicasting, reducing the frequency of transmission per node and redundant transmissions, thus improving transmission resource utilization. These designs ultimately bring significant improvements in network performance: greatly reducing data transmission latency, aggregated transmission reduces the transmission cycle of a single packet, and collision-free and synchronous scheduling avoids retransmission and waiting time; a single time slot can support parallel transmission of multiple collision-free links, significantly improving network throughput; comprehensively improving overall network performance, and can also switch between different node sizes through algorithms, adapting to diverse scenario requirements from small to large underwater acoustic multi-hop networks.

[0075] It will be understood by those skilled in the art that the above descriptions are merely preferred examples of the invention and are not intended to limit the invention. Although the invention has been described in detail with reference to the foregoing examples, those skilled in the art can still modify the technical solutions described in the foregoing examples or make equivalent substitutions for some of the technical features. All modifications and equivalent substitutions made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A centralized communication method for underwater acoustic networks based on an improved TDMA protocol, characterized in that, Includes the following steps: S1: Based on the location of the underwater node, the maximum communication distance, and the maximum interference distance, obtain the full link set and the link conflict matrix; S2: Calculate the shortest hop count and least energy-consuming path for the underwater node to transmit data packets to the sink node as the final route, and the links contained therein are the routing links; sum up all the routing links to obtain the routing link set; S3: Divide continuous time into several time frames of equal length, each frame into several time slots of equal length, and set an inherent node with the highest transmission priority for each time slot; S4. Determine the transmission time slot set for each routing link: Calculate the set S of candidate routing links that do not conflict with the links of its inherent nodes within each time slot. Based on the number of routing links in set S, calculate the maximum set of interference-free routing links that can be transmitted in each time slot, and thus obtain the transmission time slot set for each routing link. In S4, the calculation of the maximum set of interference-free links that can be transmitted in each time slot based on the number of routing links in set S is as follows: when the number of routing links is less than the link number threshold, a recursive method is used to exhaust all link combinations through a divide-and-conquer strategy to obtain the maximum set of interference-free links that can be transmitted in each time slot; otherwise, a heuristic algorithm is used to sort the links according to the existing order of conflict degree and link priority, and then iteratively selects links that do not conflict with the selected links to obtain the maximum set of interference-free links that can be transmitted in each time slot. S5: Synchronize the final routes of all underwater nodes in the network and the set of transmission time slots for each route link via broadcast; S5 is specifically implemented through the following operations: The aggregation node generates an information broadcast packet containing the final routes of all underwater nodes and the transmission time slot set of each route link, and broadcasts the information broadcast packet to surrounding underwater nodes through the underwater acoustic channel; After receiving the broadcast packet, the underwater node verifies the integrity of the information. If the routing and time slot information stored by the current underwater node has not been updated, it updates its local final route and transmission time slot set, and broadcasts the information broadcast packet to neighboring underwater nodes that have not sent an acknowledgment signal to the previous hop node in the next time slot where interference-free transmission can be performed; This process is repeated until all underwater nodes have reported the completion of information updates to the aggregation node, and the aggregation node stops broadcasting; S6: When there are data packets to be sent, determine the sending time of each data packet, aggregate and compress multiple data packets, and then transmit node data through multicast.

2. The centralized communication method for underwater acoustic networks based on the improved TDMA protocol according to claim 1, characterized in that, S1 is specifically implemented through the following sub-steps: (S1.1) Set the maximum communication distance and the maximum interference distance; the maximum communication distance and the maximum interference distance are the same for all nodes; (S1.2) Define a link conflict matrix to record whether there is a conflict between any two links; for any two links, determine whether the distance between the sending node of one link and the receiving node of the other link is within the maximum interference distance. If so, it means that there is a conflict between the two links, and mark the corresponding element in the link conflict matrix as 1; otherwise, mark it as 0. (S1.3) The aggregation node traverses all possible node pairs, calculates the actual distance between nodes, and if it does not exceed the maximum communication distance, the node pair is recorded as a valid link; otherwise, it is recorded as an invalid link. All valid links are summarized to obtain the full link set.

3. The centralized communication method for underwater acoustic networks based on the improved TDMA protocol according to claim 1, characterized in that, S2 is specifically implemented through the following sub-steps: (S2.1) The sink node calculates the shortest hop path for each underwater node to transmit data packets to the sink node; if there are multiple shortest hop paths, calculate the average remaining energy of the underwater nodes related to each shortest hop path, and select the shortest hop path with the highest average remaining energy as the final route. (S2.2) Extract the routing links contained in the final route of all underwater nodes, remove duplicate links to form a routing link set; establish the mapping relationship between the routing link set and the full link set, and clarify the position of each routing link in the full link set.

4. The centralized communication method for underwater acoustic networks based on the improved TDMA protocol according to claim 1, characterized in that, The sink node uses Dijkstra's algorithm to calculate the shortest hop path for underwater nodes to transmit data packets to the sink node.

5. The centralized communication method for underwater acoustic networks based on the improved TDMA protocol according to claim 1, characterized in that, The recursive method is based on a divide-and-conquer strategy, specifically: A link g is randomly selected from set S, and set S is split into subsets S1 and S2. Subset S1 is the set of links remaining after excluding link g, and subset S2 is the set of all links in set S that do not conflict with link g. The size of the largest non-interference subset that can be formed by S1 and S2 is calculated respectively. If the size of the largest non-interference subset formed by S1 is... The size of the largest undisturbed subset formed by S2 is greater than or equal to that of S2. If the maximum undisturbed subset MTS(S) of set S is equal to the maximum undisturbed subset MTS(S1) of subset S1, then the recursive operation continues on S1; otherwise, let... And recursively on subset S2; repeat the recursion until S is an empty set, to obtain the maximum set of interference-free links in this time slot; The heuristic algorithm is as follows: calculate the number of times a certain link conflicts with other links in set S to obtain the conflict degree of the link; calculate the link priority of the link, first sort the links according to the conflict degree, if the conflict degrees are the same, sort them according to the link priority, and traverse each link in the order of the newly obtained links. For the currently processed link, the link conflict matrix is ​​used to determine whether it conflicts with the already selected link. If it does, the link is skipped; if it does not, the link is selected. After traversing all links, the set of all links that can be transmitted simultaneously in this time slot is obtained based on the selection results, which is the maximum set of interference-free links in this time slot.

6. The centralized communication method for underwater acoustic networks based on the improved TDMA protocol according to claim 1, characterized in that, S6 is specifically implemented through the following sub-steps: (S6.1) When multiple data packets to be transmitted are detected in the local cache of the underwater node, the data packet aggregation and compression algorithm is called to aggregate and compress these data packets into a single aggregate packet; (S6.2) Calculate the amount of data in the aggregation packet, and at the same time query the routing link information stored locally to determine the routing link corresponding to the current underwater node and the set of transmission time slots of the link; (S6.3) Select available time slots belonging to the current frame from the transmission time slot set; (S6.4) The underwater node transmits data packets sequentially along the routing link to the aggregation node within the available time slots and uses multicast to transmit the data packets; if the amount of compressed data does not exceed the maximum amount of data that can be transmitted in a single time slot, the earliest available time slot of the current frame is selected to send the aggregated packet, and the corresponding data packet in the local buffer is cleared after the transmission is completed; if the amount of compressed data exceeds the maximum amount of data that can be transmitted in a single time slot, part of the data is sent in the earliest available time slot of the current frame, and the corresponding data packet is cleared in the local buffer, and the remaining data is temporarily stored in the buffer; after the next available time slot begins, the remaining data is aggregated and compressed again, and transmission continues in the new available time slot until all data transmission is completed; if there is no new available time slot in the current frame, the next frame is entered and steps (S6.1)-(S6.4) are repeated until all data is transmitted. During this process, if the sending node does not receive an acknowledgment signal from the receiving node within the transmission time slot, it will retransmit the data in the next time slot belonging to that link, with a maximum of N retransmissions. If all N retransmissions fail, it will report a link failure to the aggregation node, and the aggregation node will re-execute the routing link determination step to allocate a new routing link for the node, ensuring that the data can be transmitted smoothly.

7. The centralized communication method for underwater acoustic networks based on the improved TDMA protocol according to claim 1, characterized in that, The aggregation node periodically updates the link conflict matrix and re-makes routing decisions, i.e., repeats S1-S6, to ensure that the underwater acoustic multi-hop communication network can continuously optimize the communication scheduling of the underwater acoustic multi-hop communication network according to the state changes during operation.

8. The centralized communication method for underwater acoustic networks based on the improved TDMA protocol according to claim 1, characterized in that, The underwater acoustic multi-hop communication network includes a sink node and multiple underwater nodes. Each node has a fixed sequence number, and all nodes have the same maximum communication distance and maximum interference distance. The underwater nodes in the underwater acoustic multi-hop communication network periodically send data packets to the sink node according to the allocated time slots through an underwater acoustic modem. The underwater acoustic modem is in half-duplex mode.

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