An underwater cross-layer transmission method based on acousto-optic hybrid optimization design

Abstract

The application provides an underwater cross-layer transmission method with sound-light mixed optimization design, position information is comprehensively and effectively shared by a sound transmitter to assist selection of a candidate area and alignment of a light link, a transmission node selects an optimal candidate area for the purpose of ensuring a delivery rate by calculating a candidate area factor based on the number of nodes in the area and position information of neighbor nodes, and uses a light transmitter to quickly send a data packet, and a node in the candidate area calculates a forwarding factor with high timeliness based on local information, informs neighbor nodes by omnidirectional sound transmitter, synchronously competes for the qualification of forwarding the data packet, and efficiently selects each hop node. The application realizes efficient delivery of DATA data packets, greatly reduces network overhead, assists alignment of the light link, reduces time delay, improves transmission efficiency of the underwater network, efficiently suppresses redundant transmission of data packets by the network, and reduces more time delay.

Description

Technical Field

[0001] This invention relates to the field of underwater communication networks, specifically to underwater optical wireless communication, underwater acoustic communication, etc., and more specifically to an underwater acoustic-optical hybrid cross-layer transmission method. Background Technology

[0002] Ocean observation and monitoring are crucial for environmental protection and marine exploration. Deploying underwater sensor nodes in specific sea areas and utilizing their self-organizing capabilities to transmit data, forming an underwater wireless sensor network, is currently a feasible solution for this task. Routing is a critical issue in wireless sensor networks, ensuring data is transmitted from source nodes to destination nodes within the network.

[0003] Routing protocols are designed to transmit data to the destination node efficiently and securely. Underwater acoustic communication-based routing protocols are widely studied and applied due to the advantages of sound waves' longest communication distance and high reliability underwater. However, due to the propagation characteristics of sound waves in water, many problems remain: 1) The low propagation speed and long transmission distance of sound waves in water cause significant delays, reducing communication efficiency for dynamic topology networks; 2) Underwater acoustic channels have narrow bandwidth, resulting in small data transmission capacity; 3) High energy consumption and short lifespan. Underwater optical wireless communication (UOWC)-based routing protocols offer the possibility of implementing many real-time applications due to their high speed and high bandwidth. Despite significant progress, the complexity of the underwater environment still presents many challenges to underwater wireless optical networks: 1) Short communication distance is one of the main obstacles to UOWC development, stemming from severe absorption and scattering of optical signals underwater, ultimately leading to small coverage and affecting application scenarios; 2) Link alignment issues. Since optical communication takes two forms—light-emitting diode (LED) and laser (LD)—both have a limited field of view and are not omnidirectional, link alignment must be considered during communication. Underwater routing protocols based on either of these two communication methods cannot achieve the design goals of high speed, high capacity, and reliability on their own. However, a hybrid approach that leverages the complementary advantages of both offers a possibility. Therefore, underwater acoustic-optical hybrid routing protocols have become an important research direction.

[0004] A patent application published on April 24, 2020, entitled "An Underwater Distributed Opportunistic Routing Based on Optical-Acoustic Fusion" [CN 111065144 A], divides a three-dimensional space into several transmit / receive intervals. Transmitting nodes, pointing towards the sink node, continuously transmit test data packets and expand the transmit / receive intervals using optical communication until a response is received, confirming the working transmit / receive interval. Candidate nodes within the working transmit / receive interval that receive test data packets calculate their information metrics (distance to the sink node, single-hop error rate, and remaining energy) and broadcast them back to the transmitting node via acoustic communication. The transmitting node prioritizes the received information metrics and, together with the data to be sent, forms a data packet, which is then transmitted to the working transmit / receive interval via optical communication. Nodes that successfully receive data packets traverse the waiting time according to priority to determine the forwarding node. Although this protocol provides a new approach for optical-acoustic fusion, it still has some problems: (1) By continuously expanding the working transmission and reception interval and sending test data packets multiple times, it brings huge latency and high energy consumption; (2) Since the nodes are constantly moving under the influence of ocean currents, their location information is dynamically changing. Therefore, the location information in the information metric value obtained by the test data packet cannot represent the location information when the data packet is actually received. That is, the calculated node priority is not timely, which will cause the selected routing information to fail and thus cause packet loss; (3) The method of nodes traversing the waiting time according to priority greatly increases the network latency. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides an underwater cross-layer transmission method with hybrid acoustic-optical design. To ensure reliable, fast, efficient, low-latency, low-power, and secure transmission of monitored data to the destination node in harsh underwater environments, this invention proposes a hybrid acoustic-optical underwater wireless network routing protocol. This method leverages the omnidirectional, long-distance communication advantages of underwater acoustic links and the high-bandwidth, high-speed data transmission advantages of underwater optical links, combining the two to achieve a fast, high-capacity, and reliable data transmission scheme.

[0006] This invention provides an underwater cross-layer transmission method with hybrid acoustic-optical optimization design. Nodes share location information comprehensively and effectively through acoustic broadcasting, thereby assisting in the selection of candidate areas and the alignment of optical links. The transmitting node calculates the candidate area factor based on the number of regional aggregation nodes by acquiring the locations of neighboring nodes, ensuring a high delivery rate. The optimal candidate area is selected and data packets are quickly sent using an optical broadcasting device. Nodes receiving data packets within the candidate area calculate a highly timely forwarding factor based on local information and omnidirectionally notify neighboring nodes via acoustic broadcasting devices, synchronously competing for the right to forward data packets, thus efficiently completing the selection of each hop node.

[0007] The technical solution adopted by this invention to solve its technical problem includes the following steps:

[0008] Step 1: There are several underwater nodes, one of which is a sink node. Each node is equipped with both acoustic and optical transmission methods and knows its own position l and the position of the sink node.

[0009] After the network is deployed, each node uses a voice communication device based on the TDMA mechanism to broadcast its own "hello" packet in its corresponding time slot;

[0010] Step 2: Since the transmission radius of the underwater acoustic communication device is larger than the network radius and covers the entire network, after all nodes complete the transmission of a "hello" packet, the nodes in the network obtain the location information of all nodes in the network; any node with a DATA data packet to be sent first checks whether the data packet is a new packet. If the data packet is a new packet, proceed to step 3; if the data packet is not a new packet, proceed to step 9.

[0011] Step 3: Point the node to the sink node ( Figure 1 Centered on (d), the region is divided into three candidate regions, such as... Figure 1 As shown, the middle candidate area is a sector-shaped area with a beam angle of θ centered on the sink node. The two side candidate areas are adjacent to the middle candidate area with the same beam angle. The coverage area is determined according to the communication radius r and beam angle θ of the optical communication device. The nodes belonging to the three candidate areas are determined based on the obtained location information of the neighbor nodes. The node is located within the candidate area, and the distance factor of each node in the candidate area is calculated.

[0012] Step 4: Based on the distance factors of the nodes in the candidate regions, calculate a candidate region factor CS for each of the three candidate regions;

[0013] Each candidate region sums up the distance factors of all nodes within the candidate region to obtain the candidate region factor. That is, the selection of candidate regions takes into account both the position of the nodes and the number of nodes in the candidate region. The candidate region corresponding to the maximum value of the candidate region factor has the highest priority.

[0014] Step 5: Select the candidate area with the highest priority and use optical beam direction to send the DATA data packet to the candidate area. The DATA data packet includes the data packet type, source node ID, data packet number and payload.

[0015] Step 6: After receiving the DATA data packet, the node in the candidate area calculates its own forwarding factor according to the following formula;

[0016] Step 7: The node that receives the DATA data packet continues to calculate a hold interval T based on its own forwarding factor. iThe node will save the DATA data packet at a time interval T. i If no ACK message is received from other nodes, the ACK packet is broadcast in the network using a voice transmitter to suppress forwarding by low-priority competing nodes; after the ACK packet is sent, the node becomes a forwarding node.

[0017] Step 8: The forwarding node checks whether it is a sink node. If it is a sink node, proceed to step 9; otherwise, return to step 3.

[0018] Step 9: End.

[0019] The “hello” packet includes three parts: data packet type, node number (ID), and node location. The TDMA mechanism aims to ensure that “hello” packets sent by different nodes in the network do not conflict.

[0020] The distance factor is calculated using the following formula:

[0021]

[0022] Among them l d The position of the sink node, l s For the location of the sending node, l i Let r be the location of the node whose distance factor needs to be calculated within the i-th candidate region, and r be the optical communication radius.

[0023] The candidate region factor CS is:

[0024]

[0025] The node is located in the i-th candidate region, and the candidate factors of the corresponding candidate region are summed.

[0026] The forwarding factor is:

[0027]

[0028] Where E is the initial energy, e i For the remaining energy, n i α represents the number of candidate nodes for the next hop, N represents the maximum number of candidate nodes, and α, β, and γ represent their respective weights. The smaller the calculated forwarding factor, the higher the priority of the node that receives the DATA data packet.

[0029] The holding interval is:

[0030]

[0031] Where ξ is a positive integer representing the adjustment of the hold interval, and v is the propagation speed of the sound signal in water, this formula shows that nodes with higher priority need to wait for a shorter time.

[0032] The beneficial effects of this invention are as follows:

[0033] 1. Based on the design method of free switching between acoustic and optical links, the acoustic link utilizes the omnidirectional and long-distance transmission characteristics to be responsible for broadcasting "hello" packets in the network. It can obtain the location information of all nodes in one broadcast, reduce latency, and be robust and reliable. The acoustic link is also responsible for broadcasting ACK packets, omnidirectionally notifying neighboring nodes to compete for forwarding rights. The optical link utilizes the characteristics of speed and high capacity to achieve efficient delivery of DATA data packets, which greatly reduces network overhead.

[0034] 2. The candidate area factor design method based on location distance and the number of neighbors can select the optimal transmission candidate area by obtaining the location and number of neighbor nodes during the network node broadcast phase. This not only assists in the alignment of optical links and ensures the successful transmission of data packets to the next hop, but also reduces latency and improves the transmission efficiency of underwater networks.

[0035] 3. The forwarding factor and hold interval design method based on local information allows nodes to calculate the forwarding factor and hold interval based on their local information after receiving the DATA data packet. The calculation result has high timeliness, which is more conducive to the accuracy of priority calculation and also takes into account the mobility of underwater nodes. Each node holds interval independently. Compared with waiting time based on priority, the result can effectively suppress redundant transmission of data packets in the network and reduce the generation of more latency. Attached Figure Description

[0036] Figure 1 This is the network structure diagram of the present invention.

[0037] Figure 2 This is the overall flowchart of the present invention.

[0038] Figure 3 This is a simulation result diagram. Figure 3 (a) is a simulation result graph of the data packet delivery rate. Figure 3 (b) is a simulation result diagram of the average end-to-end delay. Figure 3 (c) is a simulation result of energy consumption. Detailed Implementation

[0039] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0040] Figure 1This is a network structure diagram of the present invention. More specifically, a network is constructed within a 500m × 500m underwater area, where nodes are randomly distributed. 's' is the source node, and 'd' is the destination node. The optical communication of the nodes uses LED communication, with the transmission field of view θ set to 30 degrees to achieve wider coverage and practical operation. Each node has three 30-degree fan-shaped candidate areas centered on the sink node. When 's' wants to transmit a data packet, it will be forwarded to 'd' via multi-hop relay according to routing rules.

[0041] Figure 2 This is the overall flowchart of the present invention. Figure 2 As shown in the figure, this embodiment of the invention provides an underwater acoustic-optical hybrid cross-layer transmission mechanism, the steps of which are as follows:

[0042] Step 1: After the network deployment is complete, each node broadcasts its "hello" packet in its corresponding time slot using a voice transmitter based on the TDMA mechanism. This packet consists of three parts: data packet type, node number (ID), and node location. Using a voice transmitter ensures successful reception by other nodes in the network. The TDMA mechanism aims to ensure that "hello" packets sent by different nodes in the network do not conflict.

[0043] The location information of the nodes is obtained through a localization method based on the time difference of arrival (TDOA) estimation of acoustic waves.

[0044] Step 2: Since the transmission radius of the underwater acoustic communication device is larger than the network radius and can cover the entire network, once all nodes have completed sending a "hello" packet, the nodes in the network can obtain the location information of all nodes in the entire network. When the source node needs to send a DATA data packet, proceed to Step 3.

[0045] Step 3: The sending node, based on the received position information from other nodes, divides the target node into three candidate regions (e.g., the region pointing to the sink node). Figure 1 As shown), based on the obtained location information of other nodes, the nodes in each candidate area are determined according to the communication radius and beam angle of the optical communication device, and the distance factor of all nodes in the candidate areas is calculated:

[0046]

[0047] Among them l s For the location of the sending node, l d The position of the sink node, l i Here, r represents the location of the node within the candidate region for which the distance factor is to be calculated, and r is the optical communication radius, set to 100 meters. That is, the closer the node is to the sink node, the larger the calculated distance factor.

[0048] Step 4: Based on the distance factors of the nodes within the candidate regions, calculate a candidate region factor for each of the three candidate regions:

[0049]

[0050] The candidate region factor takes into account both the location of the node and the number of nodes within the candidate region. The larger the candidate region factor, the higher the priority, meaning a higher probability of successful delivery of subsequent data packets.

[0051] Step 5: The node selects the candidate area with the highest priority and sends a DATA data packet quickly to the center of the candidate area using light waves. The DATA data packet consists of the following parts: data packet type, source node ID, data packet number, sending node ID, and payload.

[0052] Step 6: After a node in the selected candidate area receives a data packet, it calculates a metric (forwarding factor) based on its local information.

[0053]

[0054] The local information includes:

[0055] The distance parameter is the distance between the candidate node and the sink node;

[0056] Node energy, which is the remaining energy of the candidate node;

[0057] The number of next-hop candidate nodes is the number of nodes within the optical communication range, calculated as the 90-degree angle between the candidate node and the sink node. Where e... i The remaining energy is E, and the initial energy is set to 100 J; n i The forwarding factor represents the number of candidate nodes within 90 degrees of the next hop, where N is the maximum number of candidate nodes, set to 10. α, β, and γ represent their respective weights, set to 1 / 3, 1 / 3, and 1 / 3 respectively. The smaller the calculated forwarding factor, the higher the priority, which is most beneficial to the overall packet delivery rate, latency, and energy consumption of the network.

[0058] Step 7: Calculate the hold interval based on its own forwarding factor:

[0059]

[0060] Where ξ is an integer representing the hold interval, set to 2; v is the speed of sound in water, taken as 1500 m / s. This formula indicates that nodes with higher priority have shorter hold intervals, and the node most advantageous to the network responds with an ACK and forwards the data packet first. After a node holds the data packet for a period of time (i.e., the hold interval), if it does not receive an ACK message from other nodes, it broadcasts an ACK packet in the network using a sound transmitter, aiming to suppress forwarding by low-priority competing nodes. At this moment, the node becomes the forwarding node. This ACK message consists of the following parts: data packet type, source node ID, data packet number, and priority factor. After receiving the ACK message, other candidate nodes compare the priority factor. If the priority factor is greater than the received priority factor, they stop timing, abandon forwarding the data packet, and discard it.

[0061] The ACK message is sent using sound waves for omnidirectional broadcasting within a radius of r. This is because sound waves, compared to light waves, can notify other candidate nodes at once, and have a shorter transmission distance and smaller data packets, so they do not cause much delay.

[0062] Step 8: The forwarding node checks if it is a sink node. If it is, proceed to step 9; otherwise, return to step 3.

[0063] Step 9: End.

[0064] The underwater communication network constructed using this method was simulated using OPNET software. 15, 30, 45, 60, and 75 nodes were deployed in a 500m × 500m network space, respectively. Simulations were performed on packet delivery rate, average end-to-end latency, and energy consumption under different packet error rates (per = 0, 0.1, 0.2). Assuming the source node sends 100 packets, the simulation results are as follows: Figure 3 As shown, with increasing network density, the candidate set of each node increases, thus increasing the successful delivery rate of data packets. Due to the small network range and the fixed optical communication distance, the distance from the source node to the destination node is fixed, and the number of hops for data packets is between 6 and 7, so the end-to-end delay is not significantly different. However, with the increase in the number of nodes, more nodes participate in data packet forwarding, leading to an increase in overall energy consumption. Compared with the omnidirectional underwater acoustic routing method, this acoustic-optical hybrid cross-layer transmission mechanism can improve the data transmission rate and reduce network overhead while ensuring a high delivery rate. Compared with underwater optical wireless communication networks, the addition of acoustics ensures the effectiveness of the protocol's contention mechanism, suppresses redundant data packet transmission, and reduces network overhead.

[0065] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. An underwater interlayer transmission method with acoustic-optical hybrid optimization design, characterized in that... Includes the following steps: Step 1: There are several underwater nodes, one of which is a sink node. Each node is equipped with both acoustic and optical transmission methods and knows its own position l and the position of the sink node. After the network is deployed, each node uses a voice communication device based on the TDMA mechanism to broadcast its own "hello" packet in its corresponding time slot; Step 2: Since the transmission radius of the underwater acoustic communication device is larger than the network radius and covers the entire network, after all nodes complete the transmission of a "hello" packet, the nodes in the network obtain the location information of all nodes in the network; any node with a DATA data packet to be sent first checks whether the data packet is a new packet. If the data packet is a new packet, proceed to step 3; if the data packet is not a new packet, proceed to step 9. Step 3: The node is divided into three candidate areas centered on the sink node. The middle candidate area is a sector-shaped area with a beam angle of θ centered on the sink node. The two outer candidate areas are adjacent to the middle candidate area with the same beam angle. The coverage area is determined according to the communication radius r and beam angle θ of the optical communication device. The nodes belonging to the three candidate areas are determined according to the obtained location information of the neighboring nodes. The node is located within the candidate area, and the distance factor of each node in the candidate area is calculated. Step 4: Based on the distance factors of the nodes in the candidate regions, calculate a candidate region factor CS for each of the three candidate regions; For each candidate region, the distance factors of all nodes within the candidate region are summed to obtain the candidate region factor. The candidate region corresponding to the maximum value of the candidate region factor has the highest priority. Step 5: Select the candidate area with the highest priority, and use optical beam direction to send the DATA data packet to the candidate area. The DATA data packet includes the data packet type, source node ID, data packet number and payload. Step 6: After receiving the DATA data packet, the node in the candidate area calculates its own forwarding factor according to the following formula; Step 7: The node that receives the DATA data packet continues to calculate a hold interval T based on its own forwarding factor. i The node will save the DATA data packet at a time interval T. i If no ACK message is received from other nodes, the ACK packet is broadcast in the network using a voice transmitter to suppress forwarding by low-priority competing nodes; after the ACK packet is sent, the node becomes a forwarding node. Step 8: The forwarding node checks whether it is a sink node. If it is a sink node, proceed to step 9; otherwise, return to step 3. Step 9: End.

2. The underwater interlayer transmission method with acoustic-optical hybrid optimization design according to claim 1, characterized in that: The "hello" packet includes three parts: data packet type, node number, and node location. The TDMA mechanism aims to ensure that "hello" packets sent by different nodes in the network do not conflict.

3. The underwater interlayer transmission method with acoustic-optical hybrid optimization design according to claim 1, characterized in that: The distance factor calculation formula is as follows: Among them l d The position of the sink node, l s For the location of the sending node, l i Let r be the location of the node whose distance factor needs to be calculated within the i-th candidate region, and r be the optical communication radius.

4. The underwater interlayer transmission method with acoustic-optical hybrid optimization design according to claim 1, characterized in that: The candidate region factor CS is: The node is located in the i-th candidate region, and the candidate factors of the corresponding candidate region are summed.

5. The underwater interlayer transmission method with acoustic-optical hybrid optimization design according to claim 1, characterized in that: The forwarding factor is: Where E is the initial energy, e i For the remaining energy, n i α represents the number of candidate nodes for the next hop, N represents the maximum number of candidate nodes, and α, β, and γ represent their respective weights. The smaller the calculated forwarding factor, the higher the priority of the node that receives the DATA data packet.

6. The underwater interlayer transmission method with acoustic-optical hybrid optimization design according to claim 1, characterized in that: The holding interval is: Where ξ is a positive integer representing the adjustment of the hold interval, and v is the propagation speed of the sound signal in water, this formula shows that nodes with higher priority need to wait for a shorter time.

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