Fast collaborative ranging method for self-positioning of underwater acoustic sensor network nodes

Abstract

The invention provides a rapid cooperative ranging method for underwater acoustic sensor network node self-positioning, which slightly changes time division multiple access, controls the sending time of ranging frame sound wave signals by utilizing the characteristics of sound wave broadcast, and realizes the ranging frame sound wave signal self-positioning through observation only depending on a node local clock. And recording the time difference of arrival of different broadcast ranging frames and the time difference of arrival information carried by the ranging frames to calculate the distance. Cooperative ranging of the nodes in the network is realized, ranging processes of all the nodes are completed with fewer communication times, fast ranging in a networking stage is realized, time and energy consumption is reduced, and the service life of the network is prolonged. According to the invention, effective scheduling of the channel is facilitated, collision of a plurality of communication frames in the channel is avoided, and a time sequence relation in a distance measurement process is ensured at the same time.

Description

Technical Field

[0001] The invention relates to the technical field of underwater acoustic wireless sensor networks, and is applicable to an autonomous ranging process in self-positioning of multi-node networks with underwater acoustic broadcast communication capability and no anchor nodes. Background Art

[0002] Sound waves are currently the most effective means of underwater long-distance communication. Underwater acoustic communication networks play an important role in underwater environmental monitoring, ocean exploration, and resource development. In order to achieve effective network deployment, nodes in the network need to determine the distance between each other, provide a basis for node positioning, and provide support for data transmission.

[0003] Underwater acoustic communication has the characteristics of omnidirectional broadcasting, but its propagation time is long and the bandwidth is narrow; time division multiple access is simple to implement, and it effectively avoids channel competition by pre-allocating time slots, thereby reducing the collision probability of different data frames and the error rate of data packets, allowing multiple users to use all available frequency resources in different time slots, thereby increasing the data rate. Therefore, time division multiple access 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 used directly, it is an essential process for the network to complete the distance measurement between nodes. At present, some mature commercial acoustic communication devices use TOA (Time of Arrival) technology to estimate the distance between each node. The distance between two communication devices is estimated based on the round-trip delay of the ranging frame. Therefore, the minimum distance data required to complete a typical positioning task (the distance between each node, the total distance) is data), at least One-way communication, where n is the number of network nodes that need to be located. Underwater acoustic communication takes a long time, and the nodes carry limited energy. Too many communication interactions will prolong the time of the network initialization process and reduce the life of the network. In addition, TDOA (Time Difference of Arrival) technology uses time difference for positioning. It measures the time difference between the arrival of the ranging frame at different anchored nodes to determine the distance difference between the signal source and different anchored nodes, and calculates its position based on the distance difference information. It requires the known positions of multiple anchored nodes and the realization of time synchronization between nodes. In the case of multiple nodes with unknown positions, this method cannot be directly applied to obtain the distances between multiple nodes.

[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 perceive the arrival time difference of different ranging frames by monitoring the channel. In addition, the underwater environment is complex and changeable, and the speed of sound changes nonlinearly. The method of using time delay ranging is bound to have errors. Therefore, this patent explores a broadcast collaborative ranging method that is suitable for underwater scenes, has less communication interaction, and can quickly perform ranging. Summary of the invention

[0006] In order to overcome the deficiencies of the prior art, the present invention provides a rapid collaborative ranging method for self-positioning of underwater acoustic sensor network nodes. The present invention is directed to efficient collaborative ranging of underwater acoustic sensor network nodes. The time division multiple access is slightly changed, and the characteristics of acoustic wave broadcasting are used to control the sending time of the ranging frame acoustic wave signal. By relying only on the observation of the node local clock, the arrival time difference of different broadcast ranging frames and the arrival time difference information carried by the ranging frame are recorded to calculate the distance. Collaborative ranging of nodes in the network is achieved, so that the ranging process of all nodes can be completed with fewer communications, and rapid ranging can be achieved in the networking stage, reducing time and energy consumption and extending the network life.

[0007] The present invention is based on a time division multiple access mechanism: time is divided into time slots with a maximum length but can end early. Different time slots are assigned to different nodes. Before the maximum length of the time slot is reached and there are no abnormalities, the start of the next sequential time slot is triggered by the completed state of the event in the previous sequential time slot. That is, when the time slot starts is determined by when the previous time slot ends. This helps to effectively schedule the channel and avoid collisions of multiple communication frames in the channel, while also ensuring the timing relationship during the ranging process. In addition, considering that the transmission process and processing delay of the actual underwater acoustic communication machine cannot be ignored, a fixed protection interval Δt is added between each time slot in the present invention.

[0008] The cooperative ranging method of underwater acoustic sensor network nodes proposed in the present invention includes the following implementation steps: topology discovery and time slot allocation, node 0 broadcasts ranging frames, all nodes record the arrival time of ranging signals, ordinary nodes broadcast ranging frames, and node 0 calculates according to the broadcasting situation of ranging frames.

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

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

[0011] After the network nodes are deployed, topology discovery and time slot allocation are performed to determine the total number of nodes participating in the self-positioning 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 of 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 sends out a ranging frame broadcast and records the time when this node sends out the ranging frame. time It also serves as the start of the 0th time slot in the network. After that, the time slots are numbered in sequence from 1, 2, ..., n-1. The time when the ranging frame broadcast sent by node 0 arrives locally is used as the starting time of the ranging time slot of this node. And record, It indicates the time when the ranging frame broadcast sent by node j arrives at node i as observed at node i; if j=i, it indicates the time when ordinary node i sends the ranging frame broadcast as observed at the i-th ordinary node. The time is the local clock value at the observation node and is given by the hardware clock system;

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

[0015] The i-th ordinary node keeps recording the time when other ranging frames are broadcast and arrive at the local time before the time slot sequence allocated in the first step. Node 0 keeps recording the time when other ranging frames are broadcast and arrive at the local time before the end of the last time slot.

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

[0017] When the ith ordinary node receives the ranging frame broadcast of the i-1th ordinary node, the ith time slot starts after the delay protection interval Δt. The ith ordinary node calculates the relative time difference of all the moments recorded in the third step, and loads the obtained relative time difference information as the data part in the ranging frame, and sends out the ranging frame broadcast; considering energy saving and the minimum number of valid data required for calculation, the data part of the ranging frame broadcast sent by the ith ordinary node consists of i-1 relative time difference values, and the relative time difference is expressed as represents, k = 1,…,i-1; where, It represents the time difference between the arrival time of the ranging frame broadcast sent by the kth ordinary node and the arrival time of the ranging frame broadcast sent by the jth ordinary node observed at the ith ordinary node, and is represented by Calculated;

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

[0019] After the end of the nth time slot, node 0 receives the time when the n-1 ranging frames broadcast from all n-1 common nodes reach node 0, the time difference information carried in the data part of the ranging frames broadcast by n-1 common nodes, and the time when node 0 sends the first ranging frame broadcast. The relative time difference information is converted into the one-way propagation delay between nodes, and then the distance between nodes is calculated based on the one-way propagation delay of the nodes. The distance data between nodes is used in the node self-positioning 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 the time required for one-way communication of all nodes; 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, and ordinary nodes except node 0 wait for the ranging frame broadcast of node 0 after receiving the time slot allocation frame.

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

[0022] Assume that the one-way propagation delay between two common nodes a and b is t ab ,According to the conditions and order of triggering the ranging frame broadcast of each node listed in the first to fourth steps, there is a mathematical relationship between the ranging frame broadcasts sent by each node in the propagation process in the underwater acoustic channel. Then, the number of nodes listed at node 0 is The relations:

[0023]

[0024] It is transformed into the form of Ax=b, where:

[0025]

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

[0027]

[0028] The vector b is composed of the known relative time differences:

[0029]

[0030] Based on the total number of nodes n involved in the self-positioning and ranging process determined in the first step, node 0 determines and initializes the size and elements of matrix A and vector x, determines the size of vector b, and extracts and sorts the time when the n-1 ranging frames broadcast from a total of n-1 common nodes reach node 0 and the time difference information carried in the data part, and assigns them to vector b to verify the rank of matrix A. The equation has a solution;

[0031] In the underwater node, the point-to-point communication delay vector x is solved by solving matrix equations or other methods according to 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, thereby obtaining the distance matrix d between nodes and obtaining the distance measurement results between all nodes in the network.

[0034] An electronic device comprises 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 execute the method as described above.

[0035] A computer-readable storage medium stores program codes, and the program codes can be called by a processor to execute the method as described above.

[0036] The beneficial effect of the present invention lies in the method of cooperative ranging of underwater acoustic sensor network nodes broadcast proposed by the present invention, which utilizes the characteristics of sound wave broadcasting and controls the sending time of the ranging frame sound wave signal. Nodes at different locations in the network rely on the node local clock to observe and record the arrival time difference of different broadcast ranging frames and the arrival time difference information carried by the ranging frame to calculate the distance, thereby realizing node cooperative ranging. The present invention does not rely on anchored nodes or base stations, and does not need to realize absolute synchronization of time between nodes. The present invention can be applied in underwater acoustic communication networks that have high requirements for initialization time. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0038] Figure 2a This is the flow chart of the distance measurement of node 0 of the present invention. Figure 2b This is the flow chart of the ranging of other common nodes in the present invention.

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

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

[0041] Among them, node 0-0, node 1-1, node 2-2, node 3-3, and node 4-4. DETAILED DESCRIPTION

[0042] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0043] Taking a 5-node underwater acoustic sensor network as an example, the following implementation plan of the corresponding underwater acoustic sensor network node broadcast cooperative ranging method is given. Figure 1 As shown in the figure, the nodes are numbered 0, 1, 2, 3, and 4. Node 0 is the initiating node of ranging, and the other nodes are common nodes. The nodes use acoustic signals to transmit information, and the nodes are deployed at different positions on the same horizontal plane underwater according to the task requirements of the underwater sensor network.

[0044] The frame format used in the present invention is shown in Table 1:

[0045] Table 1 Frame format diagram

[0046]

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

[0048] Table 2 Frame type description

[0049]

[0050] The symbols involved in the present invention are shown in Table 3:

[0051] Table 3 Symbols

[0052]

[0053] The specific implementation steps are:

[0054] Step 1: topology discovery and time slot allocation. After the deployment of the underwater acoustic network nodes, the topology discovery and time slot allocation process is carried out to determine the total number of nodes involved in the ranging and positioning process and the time slot order in which the nodes send broadcast ranging frames. The control node sends a start signal frame to start topology discovery. After the topology discovery process is completed, the control node broadcasts the time slot allocation result. The maximum length of the time slot is set to an empirical value that is greater than the time required for one-way communication between nodes. In the present invention, the order of time slots 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 except node 0 wait for the ranging frame broadcast of node 0.

[0055] Step 2: Node 0 broadcasts the ranging frame. Node 0 first broadcasts the ranging frame and records the time when this node sends the ranging frame broadcast as This time is also the beginning of the 0th time slot in the network. Other nodes i use the time when the ranging frame broadcast of node 0 arrives locally as the starting time of the ranging time slot of this node. And record.

[0056] Step 3: All nodes record the time when the ranging frame broadcast arrives locally. Ordinary nodes always record the time when other ranging frame broadcasts arrive locally before the time slot sequence allocated in the first step. The node records are as follows:

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

[0058] Node 2 records the time when the ranging frame broadcast sent by nodes 0 and 1 arrives locally before the second time slot. and

[0059] Node 3 records the time when the ranging frame broadcast sent by nodes 0, 1, and 2 arrives locally before the third time slot. and

[0060] Node 4 records the time when the ranging frame broadcast sent by nodes 0, 1, 2, and 3 arrives locally before the 4th time slot. and

[0061] Node 0 keeps recording the time when other ranging frames arrive at the local time before the end of the fourth time slot. and

[0062] Step 4: Ordinary nodes broadcast ranging frames. In the time slots allocated in the first step, ordinary nodes calculate the relative time difference of all the moments recorded in the third step, load them into the ranging frame as the data payload according to the agreed format, and broadcast the ranging frame. The behavior of each node in this step is as follows:

[0063] After node 1 receives the ranging frame broadcast from node 0, the 0th time slot ends, and after a delay of Δt, a load-free ranging broadcast is sent out in the 1st time slot;

[0064] After node 2 receives the ranging frame broadcast from node 1, the first time slot ends, and the delay is Δt. In the second time slot, the time difference information recorded in the third step is recorded. As the data payload of the ranging frame, a ranging broadcast is sent, wherein:

[0065] After node 3 receives the ranging frame broadcast from node 2, the second time slot ends, and the delay is Δt. In the third time slot, the time difference information recorded in the third step is recorded. and As the data payload of the ranging frame, a ranging broadcast is sent, wherein:

[0066] After node 4 receives the ranging frame broadcast from node 3, the third time slot ends, and the delay is Δt. In the fourth time slot, the time difference information recorded in the third step is recorded. and As the ranging frame data payload, a ranging broadcast is sent out, where:

[0067] Step 5: Node 0 performs calculations based on the broadcast of the ranging frame. After node 0 receives the ranging frame broadcast from node 4, the 4th time slot ends. Node 0 receives a total of 4 ranging frames from 4 nodes, extracts the time difference information carried in the data part, and combines it with the time slot start time recorded at node 0. The time when the moment measurement frame broadcast of all nodes reaches node 0 The conditions and sequence of triggering the ranging frame broadcast listed in the first to fourth steps above, and the mathematical relationship between the ranging frame broadcast and the channel propagation process are listed at node 0:

[0068]

[0069] Transformed into the form of 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] In the underwater node, the matrix equation is solved or other methods are used to solve the problem according to the computing power supported by the actual hardware. Finally, 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. The node distance matrix d is obtained, and the distance measurement results between all nodes in the network are obtained. The node distance data can be used in the node self-positioning process.

[0079] The broadcast ranging process involved in the present invention is as follows Figure 3 As shown in FIG. 1 , the number of times required for the distance measurement method proposed in the present invention and the point-to-point distance measurement method is compared. Figure 4 Compared with the existing method, the present invention obtains the distance between nodes by using the propagation distance difference contained in the broadcast arrival time difference of different nodes. The number of broadcasts required to complete the distance measurement between n nodes is n, which is less than the number of communications required for the point-to-point distance measurement between nodes. Significantly reduces the time and energy consumption required for network node self-positioning. Figure 4 A comparison chart of the required number of ranging measurements is given.

Claims

1. A rapid collaborative ranging method for self-positioning of underwater acoustic sensor network nodes is characterized by The steps include: Step 1: Topology discovery and time slot allocation; After the network nodes are deployed, topology discovery and time slot allocation are performed to determine the total number of nodes participating in the self-positioning 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 of 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 sends out a ranging frame broadcast and records the time when this node sends out the ranging frame. time It also serves as the start of the 0th time slot in the network. After that, the time slots are numbered in sequence from 1, 2, ..., n-1. The time when the ranging frame broadcast sent by node 0 arrives locally is used as the starting time of the ranging time slot of this node. And record, It indicates the time when the ranging frame broadcast sent by node j arrives at node i as observed at node i; if j=i, it indicates the time when ordinary node i sends the ranging frame broadcast as observed at the i-th ordinary node. The time is the local clock value at the observation node and is given by the hardware clock system; Step 3: All nodes record the time when the ranging frame broadcast arrives locally; The i-th common node keeps recording the time when other ranging frames are broadcast and arrive at the local time before the time slot sequence allocated in the first step. Node 0 keeps recording the time when other ranging frames are broadcast and arrive at the local time before the end of the last time slot. Step 4: Ordinary nodes broadcast ranging frames; When the ith ordinary node receives the ranging frame broadcast of the i-1th ordinary node, the ith time slot starts after the delay protection interval Δt. The ith ordinary node calculates the relative time difference of all the moments recorded in the third step, and loads the obtained relative time difference information as the data part in the ranging frame, and sends out the ranging frame broadcast; considering energy saving and the minimum number of valid data required for calculation, the data part of the ranging frame broadcast sent by the ith ordinary node consists of i-1 relative time difference values, and the relative time difference is expressed as represents, k = 1,…,i-1; where, It represents the time difference between the arrival time of the ranging frame broadcast sent by the kth ordinary node and the arrival time of the ranging frame broadcast sent by the jth ordinary node observed at the ith ordinary node, and is represented by Calculated; Step 5: Node 0 performs calculations based on the broadcast of the ranging frame; After the end of the nth time slot, node 0 receives the time when the n-1 ranging frames broadcast from all n-1 common nodes reach node 0, the time difference information carried in the data part of the ranging frames broadcast by n-1 common nodes, and the time when node 0 sends the first ranging frame broadcast. The relative time difference information is converted into the one-way propagation delay between nodes, and then the distance between nodes is calculated based on the one-way propagation delay of the nodes. The distance data between nodes is used in the node self-positioning process.

2. The rapid collaborative ranging method for self-positioning of underwater acoustic sensor network nodes according to claim 1 is characterized by: 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 the time required for one-way communication of all nodes; 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, and ordinary nodes except node 0 wait for the ranging frame broadcast of node 0 after receiving the time slot allocation frame.

3. The rapid collaborative ranging method for self-positioning of underwater acoustic sensor network nodes according to claim 1 is characterized by: In the fifth step, the steps for calculating the distance between nodes are specifically as follows: Assume that the one-way propagation delay between two common nodes a and b is t ab ,According to the conditions and order of triggering the ranging frame broadcast of each node listed in the first to fourth steps, there is a mathematical relationship between the ranging frame broadcasts sent by each node in the propagation process in the underwater acoustic channel. Then, the number of nodes listed at node 0 is The relations: It is transformed into the form of Ax=b, where: Vector x is the point-to-point communication delay: The vector b is composed of the known relative time differences: Based on the total number of nodes n involved in the self-positioning and ranging process determined in the first step, node 0 determines and initializes the size and elements of matrix A and vector x, determines the size of vector b, and extracts and sorts the time when the n-1 ranging frames broadcast from a total of n-1 common nodes reach node 0 and the time difference information carried in the data part, and assigns them to vector b to verify the rank of matrix A. The equation has a solution; In the underwater node, the point-to-point communication delay vector x is solved by solving matrix equations or other methods according to 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, thereby obtaining the distance matrix d between nodes and obtaining the distance measurement results between all nodes in the network.

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, and the one or more programs are configured to execute the method according to any one of claims 1 to 3.

5. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores program codes, and the program codes can be called by a processor to execute the method according to any one of claims 1 to 3.

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