A fast cooperative ranging method for self-localization of underwater acoustic sensor network nodes

Abstract

This invention provides a rapid collaborative ranging method for self-localization of nodes in an underwater acoustic sensor network. By slightly modifying Time Division Multiple Access (TDMA) and utilizing the characteristics of acoustic broadcasting, the transmission time of the ranging frame acoustic signal is controlled. Distance is calculated by recording the arrival time difference of different broadcast ranging frames and the arrival time difference information carried by the ranging frames, relying solely on observations of the node's local clock. This enables collaborative ranging among nodes in the network, achieving the ranging process for all nodes with fewer communication attempts. It facilitates rapid ranging during the network deployment phase, reducing time and energy consumption and extending network lifetime. This invention also helps in the effective scheduling of channels, avoiding collisions between multiple communication frames and ensuring the timing relationship during the ranging process.

Description

Technical Field

[0001] This invention relates to the field of underwater acoustic wireless sensor network technology, and is applicable to the autonomous ranging process in the self-localization of multi-node networks with underwater acoustic broadcast communication capabilities and no anchor nodes. Background Technology

[0002] Sound waves are currently the most effective means of long-distance underwater communication. Underwater acoustic communication networks play a vital role in underwater environmental monitoring, marine exploration, and resource development. For effective network deployment, nodes within the network need to determine their distances to each other, providing a basis for node positioning and support for data transmission.

[0003] Underwater acoustic communication has the characteristic of omnidirectional broadcasting, but its propagation time is long and its bandwidth is narrow. Time division multiple access (TDMA) is simple to implement, effectively avoids channel contention by pre-allocating time slots, thereby reducing the probability of collisions between different data frames and the bit error rate of data packets, and allows multiple users to use all available frequency resources in different time slots, thus improving the data rate. Therefore, TDMA is more commonly used in underwater networking than other multiple access technologies.

[0004] In underwater environments where GPS, anchorless nodes, or positioning base stations cannot be directly used, distance measurement between nodes is an essential process for the network. Currently, some mature commercial acoustic communication devices use TOA (Time of Arrival) technology to estimate the distance between nodes. The distance between each pair of communicating devices is estimated based on the round-trip time delay of the ranging frames. Therefore, the minimum distance data required to complete a typical positioning task (the distance between each node, total distance between nodes) is... (data points), at least the required This is a single-way communication, where n is the number of network nodes to be located. Underwater acoustic communication is time-consuming, and nodes have limited energy capacity; excessive communication interactions prolong network initialization time and reduce network lifespan. Furthermore, TDOA (Time Difference of Arrival) technology uses time difference for positioning. It determines the distance difference between the signal source and different anchored nodes by measuring the time difference between the arrival of ranging frames at different anchored nodes, and calculates the location based on the distance difference information. This method requires knowledge of the locations of multiple anchored nodes and time synchronization between them. When multiple nodes have unknown locations, this method cannot directly determine the distances between them.

[0005] The above technologies do not fully utilize the broadcast characteristics of sound waves and the time difference information of broadcast frames arriving at different locations. Within the communication distance, all underwater nodes can sense the time difference of arrival of different ranging frames by listening to the channel. In addition, the underwater environment is complex and variable, and the speed of sound changes nonlinearly, so the method of ranging using time delay will inevitably have errors. Therefore, this patent explores a broadcast collaborative ranging method that is suitable for underwater scenarios, requires less communication interaction, and can quickly perform ranging. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides a rapid collaborative ranging method for self-localization of underwater acoustic sensor network nodes. This invention focuses on efficient collaborative ranging of underwater acoustic sensor network nodes. By slightly modifying Time Division Multiple Access (TDMA) and utilizing the characteristics of acoustic wave broadcasting, the transmission time of the ranging frame acoustic signal is controlled. Distance is calculated by recording the arrival time difference of different broadcast ranging frames and the arrival time difference information carried by the ranging frames, relying solely on observations of the node's local clock. This enables collaborative ranging among nodes in the network, achieving the ranging process for all nodes with fewer communication attempts. It facilitates rapid ranging during the network setup phase, reduces time and energy consumption, and extends network lifespan.

[0007] This invention is based on a time-division multiple access (TDMA) mechanism: time is divided into time slots with a maximum length but which can end early. Different time slots are assigned to different nodes. Before the maximum length of a time slot is reached and in the absence of abnormalities, the start of the next sequential time slot is triggered by the completed state of events in the previous sequential time slot. That is, when a time slot starts is determined by when the previous time slot ends. This helps to effectively schedule the channel, avoid collisions between multiple communication frames in the channel, and also ensure the timing relationship in the ranging process. In addition, considering that the transmission and processing delays of actual underwater acoustic communication devices cannot be ignored, a fixed guard interval Δt is added between each time slot in this invention.

[0008] The underwater acoustic sensor network node collaborative ranging method proposed in this invention includes the following implementation steps: topology discovery and time slot allocation, node 0 broadcasting ranging frames, all nodes recording the arrival time of ranging signals, ordinary nodes broadcasting ranging frames, and node 0 calculating based on the broadcast of ranging frames.

[0009] The steps of the technical solution adopted by this invention to solve its technical problem are as follows:

[0010] Step 1: Topology discovery and time slot allocation;

[0011] After network nodes are deployed, topology discovery and time slot allocation are performed to determine the total number of nodes participating in the self-localization ranging process and the time slot order of the nodes broadcasting ranging frames. All nodes are numbered i, where i = 0, 1, 2, ..., n-1, and n is the number of nodes participating in the ranging process. Node 0 is the initiating node for ranging, and the other nodes numbered 1, 2, ..., n-1 are called ordinary nodes.

[0012] Step 2: Node 0 broadcasts the ranging frame;

[0013] Node 0 first broadcasts a ranging frame and records the time of its broadcast. time This also marks the start of the 0th time slot in the network. Subsequent time slots are numbered sequentially from 1, 2, ..., n-1. The start time of the ranging time slot for ordinary node i is determined by the arrival time of the ranging frame broadcast from node 0. And record, This represents the time when the ranging frame broadcast from node j, observed at node i, arrives at node i; if j = i, then it represents the time when the ranging frame broadcast from ordinary node i, observed at the i-th ordinary node, is sent by ordinary node i. The time is the local clock value at the observation node, given by the hardware clock system.

[0014] Step 3: All nodes record the arrival time of the ranging frame broadcast locally;

[0015] The i-th ordinary node continuously records the arrival times of other ranging frames broadcast before the time slot sequence allocated in the first step. Node 0 continuously records the arrival times of other ranging frames broadcast before the end of the last time slot.

[0016] Step 4: Ordinary nodes broadcast ranging frames;

[0017] When the i-th ordinary node receives the ranging frame broadcast from the (i-1)-th ordinary node, after a delay protection interval Δt, starting from the i-th time slot, the i-th ordinary node calculates the relative time difference for all the times recorded in step three, loads the resulting relative time difference information as the data part into the ranging frame, and broadcasts the ranging frame. Considering energy saving and minimizing the number of valid data points required for calculation, the data part of the ranging frame broadcast by the i-th ordinary node consists of i-1 relative time difference values, which are represented by... Let k = 1, ..., i-1; where, This represents the time difference between the arrival time of the ranging frame broadcast from the k-th ordinary node and the arrival time of the ranging frame broadcast from the j-th ordinary node, as observed from the i-th ordinary node. Calculated;

[0018] Step 5: Node 0 performs calculations based on the broadcast information of the ranging frame;

[0019] After the nth time slot ends, node 0 receives n-1 ranging frame broadcasts from all n-1 ordinary nodes, along with the time difference information carried in the data portion of the n-1 ordinary nodes' ranging frame broadcasts, and the time when node 0 sends its first ranging frame broadcast. The relative time difference information is converted into the one-way propagation delay between nodes. Then, the distance between nodes is calculated based on the one-way propagation delay between nodes. The distance data between nodes is then applied to the node self-localization process.

[0020] In the first step, during the ranging process, the maximum length of the time slot is set to an empirical value that is sufficient for all nodes to communicate one way. The order of the time slots occupied by all nodes is consistent with the node number, that is, node i uses the i-th ranging time slot. After receiving the time slot allocation frame, ordinary nodes other than node 0 wait for node 0 to broadcast the ranging frame.

[0021] In the fifth step, the calculation steps for the distance between nodes are as follows:

[0022] Let the one-way propagation delay between two ordinary nodes a and b be t. ab Based on the conditions and order in which the ranging frame broadcasts of each node are triggered, as listed in steps one through four, there exists a mathematical relationship between the ranging frame broadcasts emitted by each node during their propagation in the underwater acoustic channel. Therefore, the following is listed at node 0: One relation:

[0023]

[0024] Transform into the form Ax = b, where:

[0025]

[0026] Vector x represents the point-to-point communication delay:

[0027]

[0028] Vector b consists of known relative time differences:

[0029]

[0030] Given the total number of nodes n participating in the self-localization ranging process as determined in the first step, node 0 determines and initializes the size and elements of matrix A and vector x, and determines the size of vector b. Based on the arrival times of n-1 ranging frames broadcast from n-1 ordinary nodes recorded by node 0 in steps two to four, and the time difference information carried in their data portions, the data is extracted, organized, and assigned to vector b. The rank of matrix A can then be verified. The equation has a solution;

[0031] Within the underwater node, the point-to-point communication delay vector x is solved by solving matrix equations or other methods, depending on the computing power supported by the actual hardware. Finally, the distance vector d between nodes is:

[0032]

[0033] The distance between nodes is obtained by cx = d, where c is the speed of sound. From this, the distance matrix d between nodes is obtained, and the distance measurement results between all nodes in the network are obtained.

[0034] An electronic device includes one or more processors; a memory; and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs are configured to perform the methods described above.

[0035] A computer-readable storage medium storing program code that can be invoked by a processor to perform the method described above.

[0036] The beneficial effect of this invention lies in the proposed method for collaborative ranging among nodes in an underwater acoustic sensor network. Utilizing the characteristics of acoustic wave broadcasting, by controlling the transmission time of the ranging frame acoustic signal, nodes at different locations in the network rely on their local clocks to observe and record the arrival time difference of different broadcast ranging frames and the arrival time difference information carried by the ranging frames to calculate the distance, thus achieving collaborative ranging among nodes. This invention does not rely on anchored nodes or base stations and does not require absolute time synchronization between nodes. This invention can be applied in underwater acoustic communication networks with high requirements for initialization time. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of an underwater acoustic network scenario according to the present invention.

[0038] Figure 2a This is a flowchart of the distance measurement process at node 0 of the present invention. Figure 2b The flowchart below shows the distance measurement process for the remaining ordinary nodes in this invention.

[0039] Figure 3 This is a schematic diagram of the broadcast ranging process of the present invention.

[0040] Figure 4 This is a comparison chart showing the minimum number of distance measurements required for this invention.

[0041] Among them, there are nodes 0-0, 1-1, 2-2, 3-3, and 4-4. Detailed Implementation

[0042] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0043] The following example uses a 5-node underwater acoustic sensor network to illustrate the implementation scheme of a broadcast cooperative ranging method for the network nodes. The network node scenario is as follows: Figure 1 As shown, the nodes are numbered 0, 1, 2, 3, and 4. Node 0 is the initiating node for ranging, and the remaining nodes are ordinary nodes. Nodes transmit information using acoustic signals, and are deployed at different locations on the same horizontal plane underwater according to the mission requirements of the underwater sensor network.

[0044] The frame formats used in this invention are shown in Table 1:

[0045] Table 1 Frame Format Diagram

[0046]

[0047] The frame types used in this invention are shown in Figure 2.

[0048] Table 2 Frame Type Description

[0049]

[0050] The symbols involved in this invention are explained in Table 3:

[0051] Table 3. Explanation of Symbols

[0052]

[0053] The specific implementation steps are as follows:

[0054] Step 1: Topology Discovery and Time Slot Allocation. After the underwater acoustic network nodes are deployed, a topology discovery and time slot allocation process is performed to determine the total number of nodes participating in the ranging and positioning process and the time slot order in which nodes send broadcast ranging frames. The control node sends a start signal frame to initiate topology discovery. After the topology discovery process is completed, the control node broadcasts the time slot allocation results. The maximum length of the time slot is set to an empirical value greater than the time required for one-way communication between nodes. In this invention, the time slot order occupied by all nodes is consistent with the node ID number, that is, node i uses the i-th ranging time slot, and the numbering starts from 0. After receiving the time slot allocation frame, ordinary nodes other than node 0 wait for node 0 to broadcast its ranging frame.

[0055] Step 2: Node 0 broadcasts the ranging frame. Node 0 first broadcasts the ranging frame and records the time when it broadcasts the ranging frame. This moment also marks the start of the 0th time slot in the network. Other nodes (node ​​i) use the arrival time of the ranging frame broadcast by node 0 as the start time of their own ranging time slot. And record it.

[0056] Step 3: All nodes record the arrival time of the ranging frame broadcast. Ordinary nodes, prior to the time slots allocated in Step 1, continuously record the arrival times of other ranging frame broadcasts. The node records are as follows:

[0057] Before the first time slot, node 1 records the time when the ranging frame broadcast by node 0 arrives locally.

[0058] Node 2 records the arrival times of the ranging frames broadcast by nodes 0 and 1 before the second time slot. and

[0059] Node 3 records the arrival times of the ranging frames broadcast by nodes 0, 1, and 2 before the third time slot. and

[0060] Node 4 records the arrival times of the ranging frames broadcast by nodes 0, 1, 2, and 3 before the 4th time slot. and

[0061] Node 0 continuously records the arrival times of other ranging frames broadcast before the end of the 4th time slot. and

[0062] Step 4: Ordinary nodes broadcast the ranging frame. Within the time slot allocated in Step 1, ordinary nodes calculate the relative time differences for all moments recorded in Step 3, and according to the agreed format, load this as part of the data payload into the ranging frame, then broadcast the ranging frame. The behavior of each node in this step is as follows:

[0063] After receiving the ranging frame broadcast from node 0, node 1 ends the 0th time slot, delays by Δt, and then sends out a no-load ranging broadcast in the 1st time slot.

[0064] After receiving the ranging frame broadcast by node 1, node 2 ends its first time slot, delays by Δt, and then transmits the time difference information that was waited for and recorded in the third step during the second time slot. As the data payload of the ranging frame, a ranging broadcast is emitted, in which...

[0065] After receiving the ranging frame broadcast by node 2, node 3 ends the second time slot, delays by Δt, and then transmits the time difference information that was waited for and recorded in the third time slot. and As the data payload of the ranging frame, a ranging broadcast is emitted, in which...

[0066] After receiving the ranging frame broadcast by node 3, node 4 ends its third time slot, delays by Δt, and then transmits the time difference information that was waited for and recorded in the third step in the fourth time slot. and As the data payload of the ranging frame, a ranging broadcast is emitted, in which...

[0067] Step 5: Node 0 performs calculations based on the broadcast of the ranging frames. The fourth time slot ends after Node 0 receives the ranging frame broadcast from Node 4. Node 0 receives a total of four ranging frames from the four nodes and extracts the time difference information carried in the data portion; this is combined with the time slot start time recorded at Node 0. The time when all node moment measurement frames arrive at node 0. The conditions and order for triggering ranging frame broadcasts, as listed in steps one through four above, and the mathematical relationships involved in the propagation of ranging frame broadcasts in the channel, are listed at node 0:

[0068]

[0069] Transform it into the form AX = b, where:

[0070]

[0071] Point-to-point propagation delay vector x:

[0072] x 10×1 =[t 01 t 02 t 03 t 04 t 12 t 13 t 14 t 23 t 24 t 34 ] T

[0073] Relative time difference vector b:

[0074]

[0075] Verify the rank of matrix A The equation has a solution.

[0076] Within the underwater nodes, the solution is obtained by solving matrix equations or other methods, depending on the computing power supported by the actual hardware. Ultimately, the distance vector d between nodes is:

[0077] d 10×1 =[d 01 d 02 d 03 d 04 d 12 d 13 d 14 d 23 d 24 d 34 ] T

[0078] The distance between nodes is obtained by cx = d, where c is the speed of sound. From this, the distance matrix d between nodes is obtained, and the distance measurement results between all nodes in the network are obtained. The distance data between nodes can be applied to the node self-localization process.

[0079] The broadcast ranging process involved in this invention is as follows: Figure 3 As shown, the distance measurement method proposed in this invention requires a number of measurements compared to the point-to-point distance measurement method. Figure 4 As shown. Compared with existing methods, this invention obtains the distance between nodes by utilizing the propagation distance difference inherent in the arrival time difference of broadcasts from different nodes. The number of broadcasts required to complete the distance measurement between n nodes is n, compared to the number of communication calls required for point-to-point distance measurement between nodes. It significantly reduces the time and energy consumption required for network nodes to self-locate. Figure 4 A comparison chart of the required number of distance measurements is provided.

Claims

1. A rapid collaborative ranging method for self-localization of underwater acoustic sensor network nodes, characterized in that... Includes the following steps: Step 1: Topology discovery and time slot allocation; After network nodes are deployed, topology discovery and time slot allocation are performed to determine the total number of nodes participating in the self-localization ranging process and the time slot order of the nodes broadcasting ranging frames. All nodes are numbered i, where i = 0, 1, 2, ..., n-1, and n is the number of nodes participating in the ranging process. Node 0 is the initiating node for ranging, and the other nodes numbered 1, 2, ..., n-1 are called ordinary nodes. Step 2: Node 0 broadcasts the ranging frame; Node 0 first broadcasts a ranging frame and records the time of its broadcast. time This also marks the start of the 0th time slot in the network. Subsequent time slots are numbered sequentially from 1, 2, ..., n-1. The start time of the ranging time slot for ordinary node i is determined by the arrival time of the ranging frame broadcast from node 0. And record, This represents the time when the ranging frame broadcast from node j, observed at node i, arrives at node i; if j = i, then it represents the time when the ranging frame broadcast from ordinary node i, observed at the i-th ordinary node, is sent by ordinary node i. The time is the local clock value at the observation node, given by the hardware clock system. Step 3: All nodes record the arrival time of the ranging frame broadcast locally; The i-th ordinary node continuously records the arrival times of other ranging frames broadcast before the time slot sequence allocated in the first step. Node 0 continuously records the arrival times of other ranging frames broadcast before the end of the last time slot. Step 4: Ordinary nodes broadcast ranging frames; When the i-th ordinary node receives the ranging frame broadcast from the (i-1)-th ordinary node, after a delay protection interval Δt, starting from the i-th time slot, the i-th ordinary node calculates the relative time difference for all the times recorded in step three, loads the resulting relative time difference information as the data part into the ranging frame, and broadcasts the ranging frame. Considering energy saving and minimizing the number of valid data points required for calculation, the data part of the ranging frame broadcast by the i-th ordinary node consists of i-1 relative time difference values, which are represented by... Let k = 1, ..., i-1; where, This represents the time difference between the arrival time of the ranging frame broadcast from the k-th ordinary node and the arrival time of the ranging frame broadcast from the j-th ordinary node, as observed from the i-th ordinary node. Calculated; Step 5: Node 0 performs calculations based on the broadcast information of the ranging frame; After the nth time slot ends, node 0 receives n-1 ranging frame broadcasts from all n-1 ordinary nodes, along with the time difference information carried in the data portion of the n-1 ordinary nodes' ranging frame broadcasts, and the time when node 0 sends its first ranging frame broadcast. The relative time difference information is converted into the one-way propagation delay between nodes. Then, the distance between nodes is calculated based on the one-way propagation delay between nodes. The distance data between nodes is then applied to the node self-localization process.

2. The rapid collaborative ranging method for self-localization of underwater acoustic sensor network nodes according to claim 1, characterized in that: In the first step, during the ranging process, the maximum length of the time slot is set to an empirical value that is sufficient for all nodes to communicate one way. The order of the time slots occupied by all nodes is consistent with the node number, that is, node i uses the i-th ranging time slot. After receiving the time slot allocation frame, ordinary nodes other than node 0 wait for node 0 to broadcast the ranging frame.

3. The rapid cooperative ranging method for self-localization of underwater acoustic sensor network nodes according to claim 1, characterized in that: In the fifth step, the calculation steps for the distance between nodes are as follows: Let the one-way propagation delay between two ordinary nodes a and b be t. ab Based on the conditions and order in which the ranging frame broadcasts of each node are triggered, as listed in steps one through four, there exists a mathematical relationship between the ranging frame broadcasts emitted by each node during their propagation in the underwater acoustic channel. Therefore, the following is listed at node 0: One relation: Transform into the form Ax = b, where: Vector x represents the point-to-point communication delay: Vector b consists of known relative time differences: Given the total number of nodes n participating in the self-localization ranging process as determined in the first step, node 0 determines and initializes the size and elements of matrix A and vector x, and determines the size of vector b. Based on the arrival times of n-1 ranging frames broadcast from n-1 ordinary nodes recorded by node 0 in steps two to four, and the time difference information carried in their data portions, the data is extracted, organized, and assigned to vector b. The rank of matrix A can then be verified. The equation has a solution; Within the underwater node, the point-to-point communication delay vector x is solved by solving matrix equations or other methods, depending on the computing power supported by the actual hardware. Finally, the distance vector d between nodes is: The distance between nodes is obtained by cx = d, where c is the speed of sound. From this, the distance matrix d between nodes is obtained, and the distance measurement results between all nodes in the network are obtained.

4. An electronic device, characterized in that, include: One or more processors; Memory; One or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, the one or more programs being configured to perform the method as described in any one of claims 1-3.

5. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores program code that can be invoked by a processor to execute the method as described in any one of claims 1-3.

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