A method and system for compact allocation of conflict-free time slots in shallow water underwater acoustic networks

Abstract

The present invention belongs to the technical field of underwater acoustic communication and underwater acoustic network data processing, and specifically relates to a method for compactly allocating conflict-free time slots for shallow water underwater acoustic networks. The method comprises: utilizing a pre-established shallow water underwater acoustic network to obtain all nodes, performing clock synchronization on each node, and enabling each node to obtain the geographical location and depth of each other node; calculating propagation delays between different nodes and establishing a time-space conflict matrix for all nodes; judging the conflict situations between any two nodes in the established time-space conflict matrix based on conflict-free transmission conditions; and allocating conflict-free time slots to each node that meets the conflict-free transmission conditions based on the judgment results, thereby completing compact allocation of conflict-free time slots and improving the throughput of the underwater acoustic network using the TDMA protocol.

Description

Technical Field

[0001] The present invention belongs to the technical field of underwater acoustic communication and underwater acoustic network data processing, and in particular relates to a method and system for compactly allocating conflict-free time slots for shallow water underwater acoustic networks. Background Art

[0002] Generally speaking, a shallow water underwater acoustic network refers to a network composed of nodes deployed in shallow water areas, and uses underwater acoustic communication as the physical layer for information exchange. The existing methods belong to the medium access control (MAC) layer protocol of shallow water underwater acoustic networks. At present, MAC layer protocols can be divided into three categories: contention access, allocation access, and hybrid access. Among them, contention access means that different nodes access the channel through an agreed method to send their own signals, allocation access means that different nodes access the channel only in the time slots, frequency bands or other resources allocated to them to send their own signals, and hybrid access means the mixed use of contention access and allocation access. The above three types of MAC layer protocols are applicable to different scenarios, which will not be introduced in detail here, and they are all existing technologies.

[0003] Considering that sound waves propagate at only approximately 1500 m / s in water, competitive access requires frequent handshakes between nodes to avoid signal collisions. At a propagation speed of 1500 m / s, handshakes take a long time, which can easily lead to a decrease in network throughput. Time Division Multiple Access (TDMA), a common access method in shallow water underwater acoustic networks, requires allocating a longer time slot to each node to avoid signal collisions, which can also lead to a decrease in network throughput. Frequency Division Multiple Access (FDMA), which is limited by the narrow frequency band of underwater acoustic communications, and Code Division Multiple Access (CDMA), which is limited by the significant near-far effect in underwater acoustic communications, are both impractical. Hybrid access also struggles to avoid the above issues.

[0004] Specifically, in shallow-water underwater acoustic networks composed of submerged buoy nodes, underwater acoustic communication is generally used as the physical layer. However, underwater acoustic communication uses sound waves as the information carrier, which is subject to various unfavorable factors and is generally limited to half-duplex communication. Half-duplex communication is prone to signal conflicts, resulting in incorrect signal reception. Specific conflicts include:

[0005] 1. Transmission and reception conflict: A node cannot receive signals while transmitting them; a node cannot receive signals while transmitting them.

[0006] 2. Reception conflict: When a node receives signals from two or more other nodes at the same time, the signals from the two or more other nodes will interfere with each other, resulting in the inability to receive any of them.

[0007] Since buoy nodes rarely move after deployment, time division multiple access (TDMA) remains the mainstream access method. Each node is assigned a dedicated time slot to avoid signal conflicts with other nodes. Furthermore, considering that sound waves propagate as spherical waves in an infinitely large body of water and gradually attenuate due to water absorption, underwater acoustic communication signals transmitted by a node can only be received by other nodes within a certain time and space range. By constructing a spatiotemporal conflict matrix to describe the conflicts between nodes, the transmission time of priority nodes is then delayed based on the conflict-free conditions, achieving the goal of compact access allocation in conflict-free time slots. Summary of the Invention

[0008] To address the above-mentioned defects in the prior art, the present invention proposes a method for compactly allocating conflict-free time slots for shallow water underwater acoustic networks, which solves the problem of low throughput of underwater acoustic networks caused by the use of the TDMA protocol. The method comprises:

[0009] Using a pre-established shallow water hydroacoustic network, all nodes are acquired and their clocks are synchronized, so that each node can obtain the geographic location and depth of each other node.

[0010] By calculating the propagation delay between different nodes, a spatiotemporal conflict matrix for all nodes is established;

[0011] According to the conflict-free transmission condition, the conflict situation between two nodes in the established time-space conflict matrix is ​​judged; according to the judgment result, a conflict-free time slot is allocated to each node that meets the conflict-free transmission condition, thereby completing the compact allocation of conflict-free time slots.

[0012] As one of the improvements to the above technical solution, the spatiotemporal conflict matrix for all nodes is established based on the calculation of the propagation delay between different nodes. The specific process is as follows:

[0013] Assume that T nodes are used to establish a shallow water acoustic network, and T nodes are obtained from the shallow water acoustic network to establish a T×T spatiotemporal conflict matrix M and initialize it to all 0s;

[0014] Among them, the element in the i-th row and j-th column is the propagation delay between node i and node j, denoted as m ij , m ij is a real number with unit of s; i=0,1,…,T–1; j=0,1,…,T-1; when i=j, m ijIndicates the moment when node i starts to transmit the signal; when i≠j, m ij represents the time when node j starts to receive the signal transmitted by node i;

[0015] Calculate the propagation delay between any two nodes in a shallow water acoustic network based on the geographic location and depth of each node;

[0016] Assume that nodes i and j are any two nodes, so the propagation delay τ between nodes i and j is ij :

[0017] τ ij =sqrt[(lat i –lat j ) 2 ×LON1 2 + (alt i –alt j ) 2 + (lon i –lon j ) 2 ×LAT1 2 ×cos((lat i +lat j )×π / 360.0) 2 ] / c (1)

[0018] Among them, lat i ,lon i 、alt i are the latitude, longitude and depth of node i respectively; lat j ,lon j 、alt j are the latitude, longitude and depth of node j respectively; LON1 is the distance in longitude corresponding to a 1-degree difference in latitude, which is a known value; LAT1 is the distance in latitude corresponding to a 1-degree difference in longitude at the equator, which is a known value; π is the pi;

[0019] Repeat the above calculation process to obtain multiple propagation delays, and put them into the time-space conflict matrix M, denoted as m ij =τ ij ;

[0020] According to the underwater acoustic propagation model, the propagation loss l between node i and node j is calculated. ij , i≠j; further improve the space-time conflict matrix;

[0021] When the propagation loss l ijWhen h, it is considered that the signal transmitted by node i will interfere with the signal received by node j from other nodes, and there is a conflict situation between node i and node j. At this time, keep τ ij unchanged; where h is a preset node interference threshold;

[0022] When the propagation loss l ij ≥h, it is considered that the signal transmitted by node i will not interfere with the signal received by node j from other nodes, and there is no conflict situation between node i and node j. At this time, assign m ij a negative value;

[0023] Based on the above process, complete the establishment of the spatio-temporal conflict matrix M;

[0024]

[0025] As one of the improvements of the above technical solution, the conflict-free transmission condition is that the minimum conflict interval in the spatio-temporal conflict matrix is greater than the longest signal reception time of all nodes' transmissions; or ∪ k＝0,1,…,T-1 {abs(m xk –m yk )>p|y∈Set v ,m xk ≥0,m yk ≥0};

[0026] where m xk is the element in the spatio-temporal conflict matrix corresponding to node x; m yk is the element in the spatio-temporal conflict matrix corresponding to node y; p is the longest signal reception time of each node.

[0027] As one of the improvements of the above technical solution, according to the conflict-free transmission condition, judge the conflict situation between pairwise nodes in the established spatio-temporal conflict matrix; according to the judgment result, allocate conflict-free time slots to each node that meets the conflict-free transmission condition to complete the compact allocation of conflict-free time slots; the specific process is as follows:

[0028] Step 1-1) Denote all the nodes in the established spatio-temporal conflict matrix as T nodes, sort all T nodes and assign priorities;

[0029] Sum each spatio-temporal conflict matrix corresponding to the T nodes by column to obtain T delay sums sm i , arrange the T nodes in ascending order of the delay sum sm[[ID=B]] i and number them accordingly;

[0030] Step 1-2) Calculate the minimum conflict interval in the spatio-temporal conflict matrix;

[0031] Calculate the absolute value of the difference between any two non - negative elements m in each column of the space - time conflict matrix in sequence. ik and m jk From the absolute values of the multiple differences calculated for all columns, record the minimum value among the results obtained for all columns, denoted as the minimum conflict interval mc, and the corresponding nodes i and j of mc; where, i = 0, 1, …, T–1; j = 0, 1, …, T–1; k = 0, 1, …, T–1; i≠j;

[0032] Judge the conflict situation between pairwise nodes in the established space - time conflict matrix;

[0033] Assume that the longest signal reception time for each node is p;

[0034] If mc < p, it is considered that there is still a signal conflict situation between nodes i and j at this time, and go to step 1 - 3);

[0035] If mc≥p, it is considered that there is no signal conflict situation between nodes i and j, and go to step 1 - 4);

[0036] Step 1 - 3) Delay the transmission time of the node with lower priority;

[0037] Assume that the priority of node i is lower and the priority of node j is higher

[0038] If the element m corresponding to node i in the space - time conflict matrix ik > the element m corresponding to node j in the space - time conflict matrix jk , then shift the transmission time slot of the node i with lower priority backward, and set the delay time delay1 = p - mc. Add this delay time delay1 to all elements m ik in the i - th row of the space - time conflict matrix;

[0039] If the element m corresponding to node i in the space - time conflict matrix ik ≤ the element m corresponding to node j in the space - time conflict matrix jk , then shift the transmission time slot of the node i with lower priority backward, set the delay time delay2 = p + mc; add this delay time delay2 to all elements m ik in the i - th row of the space - time conflict matrix, and return to step 1 - 2); where, k = 0, 1, …, T–1;

[0040] Step 1 - 4) Allocate conflict - free time slots;

[0041] For any node k’, the diagonal element m of the established space - time conflict matrix k’kTake out as the start time of its transmission time slot, and assign p as the transmission time slot length to the node k', denoted as p' = p; where k' = 0, 1, ..., T–1; p' is the transmission time slot length; k' = k;

[0042] Repeat the above process to assign a transmission slot start time and a transmission slot length p' to each node, completing the conflict-free time slot compact allocation.

[0043] As one of the improvements to the above technical solution, the conflict situation between each node in the established time-space conflict matrix is ​​determined based on the conflict-free transmission condition; based on the determination result, a conflict-free time slot is allocated to each node that meets the conflict-free transmission condition, thereby completing the compact allocation of conflict-free time slots. The specific process is as follows:

[0044] Step 2-1) Assign all T nodes to corresponding sets and assign priorities;

[0045] Create an empty set, denoted as Set0'; assign node 0 to Set0' to obtain a non-empty set Set0. At this time, the number of non-empty sets N = 1;

[0046] Calculate the conflict between node 1 and all nodes in the non-empty set Set0 in turn. If the conflict-free emission condition is met,

[0047] ∪ k＝0,1,…,T-1 {abs(m 1k –m yk )>p|y∈Set0,m 1k ≥0,m yk ≥0} (3)

[0048] This indicates that there is no conflict between node 1 and all nodes in the non-empty set Set0, node 1 and all nodes in the non-empty set Set0 transmit signals at the same time, and node 1 is assigned to the non-empty set Set0;

[0049] If node 1 does not meet the conflict-free transmission condition shown in the above formula (3) for the non-empty set Set0, then the number of non-empty sets N is increased by 1, and another empty set is established, recorded as Set1', and node 1 is then assigned to the empty set Set1' to obtain the non-empty set Set1;

[0050] Step 2-2) Calculate the remaining nodes 2 to node T-1 and the existing non-empty sets Set0, Set1, ..., Set N-1 The conflict of all nodes in Set v Satisfy the following formula

[0051] ∪ k＝0,1,…,T-1 {abs(m xk –myk )>p|y∈Set v ,m xk ≥0,m yk ≥0} (4)

[0052] This indicates that the node x is associated with a non-empty set Set v There is no conflict among all nodes in Set , and node x is not an empty set. v All nodes in the set emit signals simultaneously and assign node x to the non-empty set Set v In which x=2,3,…,T-1,v=0,1,…,N-1;

[0053] If node x does not meet the conflict-free transmission condition shown in formula (4) for the existing N non-empty sets, then the number of non-empty sets N is increased by 1, and an empty set is created, which is recorded as Set N-1 ', then assign node x to the empty set Set N-1 ', set Set N-1 'Become a non-empty set Set N-1 ;

[0054] Repeat step 2-2) until each node is assigned to a corresponding non-empty set, and until there are no nodes that have not been assigned to a non-empty set, then proceed to step 2-3);

[0055] Step 2-3) Sort the N non-empty sets in descending order of the number of nodes in the set. The set with more nodes has a higher priority.

[0056] If there are two or more sets with the same number of nodes, the non-empty set with the smaller number has a higher priority;

[0057] Step 2-4) Calculate the minimum conflict interval mc between any two non-empty sets;

[0058] Assume that any two non-empty sets are sets u and Set v , Set u The priority is higher than the set Set v ;u=0,1,…,N-1; v=0,1,…,N-1, u≠v;

[0059] Iterate over a Set u Any node x and set Set v For any node y, calculate the set Set in turn according to formula (5) u and Set v The minimum conflict interval mc:

[0060] mc = min{abs(m xk -m yk ), x ∈ Set u , y ∈ Set v , k = 0, 1, …, T - 1 (5)

[0061] where m xk ≥ 0, m yk ≥ 0; where k = 0, 1, …, T - 1;

[0062] Until traversing the set Set u and the set Set v for any pair of nodes x, y, record the minimum conflict interval mc, and record the elements m xk and the element m yk corresponding to the time delay values mx and my at this time;

[0063] If mc < p, it is considered that there is a signal conflict situation between the set Set u and the set Set v , and go to step 2 - 5);

[0064] If mc ≥ p, it is considered that there is no signal conflict situation between the set Set u and the set Set v , and go to step 2 - 6);

[0065] Step 2 - 5) Delay the transmission time of the set Set v with lower priority;

[0066] If mx > my, set the delay time delay1 = p + mc; for all nodes y in the set Set v , add all elements m yk in the y - th row of the spatio - temporal conflict matrix by delay1; return to step 2 - 2);

[0067] If mx ≤ my, set the delay time delay2 = p - mc; for all nodes y in the set Set v , add all elements m yk in the y - th row of the spatio - temporal conflict matrix by delay2; return to step 2 - 2);

[0068] Step 2 - 6) Allocate non - conflicting time slots;

[0069] For any node k', for the diagonal elements m k’kTake out as the start time of its transmission time slot, and assign p as the transmission time slot length to the node k', denoted as p' = p; where k' = 0, 1, ..., T–1; p' is the transmission time slot length; k' = k;

[0070] Repeat the above process to assign a transmission slot start time and a transmission slot length p' to each node, completing the conflict-free time slot compact allocation.

[0071] The present invention also provides a conflict-free time slot compact allocation system for shallow water underwater acoustic networks, the system comprising:

[0072] The underwater acoustic network establishment module is used to use the pre-established shallow water acoustic network to obtain all nodes, synchronize the clocks of each node, and each node can obtain the geographic location and depth of each other node;

[0073] The matrix building module is used to build a spatiotemporal conflict matrix for all nodes based on the propagation delays between different nodes.

[0074] The allocation module is used to judge the conflict situation between two nodes in the established time-space conflict matrix according to the conflict-free transmission condition; according to the judgment result, the conflict-free time slot is allocated to each node that meets the conflict-free transmission condition, thereby completing the compact allocation of conflict-free time slots.

[0075] As one of the improvements to the above technical solution, the specific implementation process of the matrix establishment module is as follows:

[0076] Assume that T nodes are used to establish a shallow water acoustic network, and T nodes are obtained from the shallow water acoustic network to establish a T×T spatiotemporal conflict matrix M and initialize it to all 0s;

[0077] Among them, the element in the i-th row and j-th column is the propagation delay between node i and node j, denoted as m ij , m ij is a real number with unit of s; i=0,1,…,T–1; j=0,1,…,T-1; when i=j, m ij Indicates the moment when node i starts to transmit the signal; when i≠j, m ij represents the time when node j starts to receive the signal transmitted by node i;

[0078] Calculate the propagation delay between any two nodes in a shallow water acoustic network based on the geographic location and depth of each node;

[0079] Assume that nodes i and j are any two nodes, so the propagation delay τ between nodes i and j is ij :

[0080] τ ij =sqrt[(lati – lat j ) 2 × LON1 2 + (alt i – alt j ) 2 + (lon i – lon j ) 2 × LAT1 2 × cos((lat i + lat j ) × π / 360.0) 2 / c (1)

[0081] Where lat i , lon i , alt i are the latitude, longitude and depth of node i respectively; lat j , lon j , alt j are the latitude, longitude and depth of node j respectively; LON1 is the distance difference in longitude corresponding to a 1-degree difference in latitude, which is a known value; LAT1 is the distance difference in latitude corresponding to a 1-degree difference in longitude at the equator, which is a known value; π is the pi;

[0082] Repeat the above calculation process to obtain multiple propagation delays and put them into the spatio-temporal conflict matrix M, denoted as m ij = τ ij ;

[0083] According to the underwater acoustic propagation model, calculate the propagation loss l ij between node i and node j, i ≠ j; further improve the spatio-temporal conflict matrix;

[0084] When the propagation loss l ij < h, it is considered that the signal transmitted by node i will interfere with the signal received by node j from other nodes, and there is a conflict situation between node i and node j. At this time, keep τ ij unchanged; where h is a preset node interference threshold;

[0085] When the propagation loss l ij ≥ h, it is considered that the signal transmitted by node i will not interfere with the signal received by node j from other nodes, and there is no conflict situation between node i and node j. At this time, assign m ij a negative value;

[0086] Based on the above process, complete the establishment of the spatio-temporal conflict matrix M;

[0087]

[0088] The beneficial effects of the present invention compared with the prior art are:

[0089] The method of the present invention establishes a time-space conflict matrix suitable for shallow water underwater acoustic networks, clarifies the conflict-free transmission conditions of shallow water underwater acoustic networks using the TDMA protocol, and provides an optimal allocation method for the NP problem of allocating transmission time slots of each node according to the time-space conflict matrix. The method allocates a corresponding transmission time slot to each node, so that multiple nodes can transmit simultaneously, thereby making the transmission time slot allocation of different nodes as compact as possible and non-conflicting, thereby greatly improving the network throughput to a certain extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0090] Figure 1 It is a flow chart of a method for compactly allocating conflict-free time slots for shallow water underwater acoustic networks according to the present invention;

[0091] Figure 2(a) is a schematic diagram of 8-node simulation scenario 1;

[0092] Figure 2(b) is a schematic diagram of 8-node simulation scenario 2;

[0093] Figure 2(c) is a schematic diagram of 8-node simulation scenario 3;

[0094] Figure 2(d) is a schematic diagram of 8-node simulation scenario 4;

[0095] Figure 2(e) is a schematic diagram of 8-node simulation scenario 5;

[0096] Figure 2(f) is a schematic diagram of 8-node simulation scenario 6;

[0097] Figure 2(g) is a schematic diagram of 8-node simulation scenario 7;

[0098] Figure 2(h) is a schematic diagram of the 8-node simulation scenario 8;

[0099] Figure 2(i) is a schematic diagram of an 8-node simulation scenario 9;

[0100] FIG2( j ) is a schematic diagram of an 8-node simulation scenario 10 ;

[0101] Figure 3(a) is a schematic diagram of 10-node simulation scenario 1;

[0102] Figure 3(b) is a schematic diagram of 10-node simulation scenario 2;

[0103] Figure 3(c) is a schematic diagram of 10-node simulation scenario 3;

[0104] Figure 3(d) is a schematic diagram of 10-node simulation scenario 4;

[0105] Figure 3(e) is a schematic diagram of the 10-node simulation scenario 5;

[0106] Figure 3(f) is a schematic diagram of 10-node simulation scenario 6;

[0107] Figure 3(g) is a schematic diagram of the 10-node simulation scenario 7;

[0108] Figure 3(h) is a schematic diagram of the 10-node simulation scenario 8;

[0109] Figure 3(i) is a schematic diagram of a 10-node simulation scenario 9;

[0110] FIG3( j ) is a schematic diagram of a 10-node simulation scenario 10 . DETAILED DESCRIPTION

[0111] The present invention will now be further described with reference to the accompanying drawings and examples.

[0112] like Figure 1 As shown, the present invention provides a method for compact allocation of conflict-free time slots for shallow water underwater acoustic networks. In a shallow water underwater acoustic sensor network with clock synchronization and geographical location information of each node, the method estimates the propagation delay and propagation loss between any two nodes based on information such as the geographical location of each node, establishes a time-space conflict matrix, and allocates corresponding transmission time slots to each node based on the established time-space conflict matrix to avoid signal conflicts. In addition, the method of the present invention utilizes the slow propagation speed of underwater acoustic signals. Under the premise of avoiding signal conflicts, the transmission time slots of different nodes are allocated as compactly as possible, thereby achieving the purpose of improving network throughput. Among them, the method of the present invention belongs to the medium access control (MAC) layer protocol of shallow water underwater acoustic networks.

[0113] like Figure 1 As shown, the method includes:

[0114] Using a pre-established shallow water hydroacoustic network, all nodes are acquired, the clocks of each node are synchronized, and each node can obtain the geographic location and depth of each other node;

[0115] Specifically, the specific process of establishing the shallow water acoustic network is as follows:

[0116] Step 1) Set basic parameters;

[0117] Set the total number of nodes T included in the network and each node identifier t with a unique identification symbol for the node; wherein T is a positive integer, T≥2; t=0,1,…,T-1, and it should be ensured that the node identifier t of different nodes is unique in the network; record the longest signal reception time (including the channel multipath expansion time) as p, in units of s; measure the underwater acoustic environment parameters of the water area where the nodes are deployed, and calculate the node mutual interference threshold according to the underwater acoustic propagation model, recorded as h, in units of dB; and calculate the average sound speed in the water, recorded as c, in units of m / s; wherein, the specific underwater acoustic environment measurement method, underwater acoustic propagation model and calculation method, and the calculation of the average sound speed in the water are all calculated using existing methods, and are not the innovation of the method of the present invention; wherein, the underwater acoustic propagation model includes: bellhop model, marsh-schulkin model, parabolic approximation model and simple normal wave model, etc.; and the underwater acoustic environment parameters adopted by different models are also different, and different models and different underwater acoustic environment parameters all belong to the existing technology.

[0118] Step 2) Calibrate the GPS absolute coordinate position and depth for each node

[0119] Assuming that a buoy with a GPS antenna is used as a node, the drift range of the buoy should be minimized as much as possible to obtain the geographical location and depth of the node; in other specific embodiments, a submerged buoy can also be used as a node. In this case, it is necessary to use existing underwater positioning methods to accurately calibrate the geographical location of the submerged buoy to obtain the geographical location and depth of the node;

[0120] Step 3) Establishing a shallow water acoustic network

[0121] T nodes are deployed in water to establish a shallow water underwater acoustic network to ensure that all nodes can communicate with each other. When deploying, attention should be paid to the spacing between nodes to avoid isolated nodes that cannot communicate with any other nodes. A shallow water underwater acoustic network is established for all deployed nodes through a self-organizing method. After the self-organization is completed, the clocks of each node are synchronized. The geographic location information and depth information of each node are interacted through the underwater acoustic network, so that any node can obtain the geographic location information and depth information of all other remaining nodes. The specific self-organizing method and clock synchronization method are both existing technologies.

[0122] Step 4) Based on the calculated propagation delays between different nodes, a spatiotemporal conflict matrix for all nodes is established;

[0123] Specifically, a space-time conflict matrix is ​​established; the specific process is as follows:

[0124] Assume that T nodes are used to establish a shallow water acoustic network, and T nodes are obtained from the submersible acoustic network. A T×T spatiotemporal conflict matrix M is established and initialized to all 0s.

[0125] Among them, the element in the i-th row and j-th column is the propagation delay between node i and node j, denoted as m ij , m ij is a real number with unit of s; i=0,1,…,T–1; j=0,1,…,T-1; when i=j, m ij Indicates the moment when node i starts to transmit the signal, that is, the diagonal element; when i≠j, m ij represents the moment when node j starts to receive the signal transmitted by node i; the parameters in italics are variables whose values ​​change during the execution of the steps;

[0126] Since it is assumed that all nodes transmit signals at time 0, each diagonal element m of the spatiotemporal conflict matrix M corresponding to each node ij (i.e., i=j) are all 0; and the remaining elements τ in the spatiotemporal conflict matrix ij (i.e., i≠j) are the propagation delays from node i to each of the remaining nodes;

[0127] Calculate the propagation delay between any two nodes in a shallow water acoustic network based on the geographic location and depth of each node;

[0128] Assume that nodes i and j are any two nodes, so the propagation delay τ between nodes i and j is ij :

[0129] τ ij =sqrt[(lat i –lat j ) 2 ×LON1 2 + (alt i –alt j ) 2 + (lon i –lon j ) 2 ×LAT1 2 ×cos((lat i +lat j )×π / 360.0) 2 ] / c (1)

[0130] Among them, lat i ,lon i 、alt i are the latitude, longitude and depth of node i respectively; lat j ,lon j 、alt jThey are the latitude, longitude and depth of node j respectively; LON1 is the distance difference in longitude corresponding to a 1-degree difference in latitude, which can generally be taken as 110945.8 meters; LAT1 is the distance difference in latitude corresponding to a 1-degree difference in longitude at the equator, which can generally be taken as 111319.5 meters; π is the pi.

[0131] Repeat the above calculation process to obtain multiple propagation delays and put them into the spatio-temporal conflict matrix M, denoted as m ij = τ ij ;

[0132] According to the underwater acoustic propagation model, calculate the propagation loss l between node i and node j ij , i≠j; further improve the spatio-temporal conflict matrix; in this embodiment, the underwater acoustic propagation model is the classical Marsh-Schulkin model, which is an existing model well-known in the art. The involved underwater acoustic environment parameters are node spacing, sea area depth, mixed layer depth, absorption coefficient, shallow sea effective attenuation coefficient, near-field correction, where the absorption coefficient is related to salinity in thousandths, relaxation frequency, signal frequency, atmospheric pressure, and water temperature;

[0133] When the propagation loss l ij <h, it is considered that the signal emitted by node i will interfere with the signal received by node j from other nodes, and there is a conflict situation between node i and node j. At this time, keep τ ij unchanged; where h is a preset node interference threshold;

[0134] When the propagation loss l ij ≥h, it is considered that the signal emitted by node i will not interfere with the signal received by node j from other nodes, and there is no conflict situation between node i and node j. At this time, assign τ ij a negative value, for example, τ ij =-1;

[0135] Based on the above process, complete the establishment of the spatio-temporal conflict matrix M;

[0136]

[0137] Step 5) According to the conflict-free transmission condition, judge the conflict situation between each node in the established spatio-temporal conflict matrix; according to the judgment result, allocate conflict-free time slots to each node that meets the conflict-free transmission condition to complete the compact allocation of conflict-free time slots.

[0138] The conflict-free transmission condition is that the minimum conflict interval in the time-space conflict matrix is ​​greater than the longest signal reception time of all nodes (including the channel multipath spread time), that is, when a node transmits a signal, it will not interfere with the signals transmitted by the remaining nodes; and there is no conflict between the signals transmitted by the remaining nodes received by the node; or k＝0,1,…,T-1 {abs(m xk –m yk )>p|y∈Set v ,m xk ≥0,m yk ≥0}; where m xk is the element in the spatiotemporal conflict matrix corresponding to node x; m yk is the element in the space-time conflict matrix corresponding to node y; p is the longest signal reception time of each node (including channel multipath expansion time).

[0139] Specifically, under the premise that all nodes take turns transmitting the longest signal, the maximum network throughput r is calculated:

[0140] r=b×T / O

[0141] Where b is the number of bits carried by the longest signal; O is the time required for all T nodes to complete a transmission in turn, in seconds; the larger r is, the more compact the node transmission time slot allocation is, and the smaller the O value will be; in this case, traditional TDMA needs to allocate a length of at least max(m ij )+p time slots, where max(m ij ) represents the maximum value in the spatiotemporal conflict matrix M; O is at least T×(max(m ij )+p);

[0142] The conflict-free transmission condition takes advantage of the slow propagation speed of sound waves in water. By allowing as many nodes as possible to transmit simultaneously, the value of O can be minimized on the one hand, and the number of erroneous retransmissions can be reduced on the other hand by avoiding conflicts.

[0143] Take a shallow water acoustic network with two nodes (T=2) established in a shallow water area as an example:

[0144] When node 0 and node 1 can communicate with each other, there are no negative numbers in the space-time conflict matrix, and the node distance d>p×c, the two nodes can transmit signals to each other at the same time without causing interference; at this time, m 00 =m 11 =0,m 01 With m 10 are equal to d / c, O>d / c+p=max(m ij)+p; while the O of traditional TDMA is at least 2×(d / c+p); the conflict-free transmission condition when T=2 is: {m 10 -m 00 >p}∪{m 01 -m 11 >p}; that is, when node 0 receives the signal transmitted by node 1, node 0 itself is not transmitting the signal, and vice versa, that is, when node 1 receives the signal transmitted by node 0, node 1 itself is not transmitting the signal;

[0145] Take a shallow water acoustic network with three nodes (T=3) established in a shallow water area as an example:

[0146] Assuming that any two nodes can communicate with each other and there is no negative number in the space-time conflict matrix, the conflict-free transmission condition is that any node k (k = 0, 1, ..., T-1) must not only meet the requirement that when receiving a signal transmitted by any other node i, node k itself is not transmitting a signal, that is, {abs(m ik -m kk )>p|i≠k}; and it is also necessary to satisfy that the two signals transmitted by nodes i and j do not conflict at node k, that is, {abs(m ik -m jk )>p|i≠j}; further observe that when j=k, the above two conditions can be combined, that is: {abs(m ik -m jk )>p|i≠j}; where m ik is the time when the signal transmitted by node i reaches node k; m kk is the start time of signal transmission by node k; m jk is the time when the signal transmitted by node j reaches node k;

[0147] When T is taken as other values, this idea is still applicable, and the conflict-free transmission conditions of any number of underwater acoustic network nodes deployed in the same shallow water area can be obtained as shown in the following formula:

[0148] ∪ i,j,k＝0,1,…,T-1 {abs(m ik -m jk )>p|i≠j,m ik ≥0,m jk ≥0}

[0149] Among them, ∪ means taking the union, that is, the conditions in {} should be satisfied at the same time; m ik ≥0,m jk ≥0 means that negative numbers in the spatiotemporal conflict matrix do not participate in the determination of conflict-free emission conditions;

[0150] Specifically, based on the conflict-free transmission condition, sorting all nodes and finding the minimum value of O is a non-deterministic polynomial (NP) problem of polynomial complexity. When the number of nodes is small (for example, T ≤ 8), the computational time for obtaining the global optimal solution (i.e., the minimum value of O) using the full permutation method is still within an acceptable range. When the number of nodes is large (for example, T > 8), the method of the present invention can be used to obtain a feasible suboptimal solution within an acceptable computational time.

[0151] Method 1 is used to assign conflict-free time slots to each node that meets the conflict-free transmission conditions, completing the compact allocation of conflict-free time slots. The nodes in the shallow water underwater acoustic network are randomly deployed, and there is no guarantee that there will be no conflicts between nodes if all nodes transmit simultaneously. For nodes in conflict, conflicts are avoided by delaying the transmission time of low-priority nodes. Once the transmission time of a node is delayed, the spatiotemporal conflict matrix M will change, and the elements in the matrix need to be added with the corresponding delay time. When the transmission time of node x is delayed, the time when other nodes receive the signal transmitted by node x will also be delayed accordingly.

[0152] Specifically, step 1-1) records all nodes in the established spatiotemporal conflict matrix as T nodes, sorts all T nodes and assigns priorities;

[0153] Sum each spatiotemporal conflict matrix corresponding to T nodes by column to obtain T delays and sm i , divide T nodes into two groups according to delay and sm i Arrange in ascending order and number them accordingly. The smaller the number, the higher the priority of the corresponding node. Among them, the delay and sm of the i-th node i The smaller it is, the smaller the number of the corresponding node i is, and the higher the corresponding priority is;

[0154] If there are two or more nodes with delay and sm i If they are equal, the nodes are sorted according to the size of the numbers. The nodes with smaller numbers have higher priorities.

[0155] Step 1-2) Calculate the minimum conflict interval in the spatiotemporal conflict matrix;

[0156] Calculate any two non-negative elements m in each column of the spatiotemporal conflict matrix in sequence ik and m jk The absolute value of the difference between the two columns is calculated. The minimum value among the results obtained in all columns is recorded as the minimum conflict interval mc, and the node i and node j corresponding to mc; where i = 0, 1, ..., T–1; j = 0, 1, ..., T–1; i ≠ j;

[0157] Judge the conflict situation between pairwise nodes in the established spatio-temporal conflict matrix; assume that the longest signal reception time (including the channel multipath extension time) of each node is p;

[0158] If mc < p, it is considered that there is still a signal conflict situation between node i and node j at this time, and go to step 1-3);

[0159] If mc ≥ p, it is considered that there is no signal conflict situation between node i and node j, and go to step 1-4);

[0160] Step 1-3) Delay the transmission time of the node with lower priority;

[0161] Assume that the priority of node i is lower and the priority of node j is higher

[0162] If the element m corresponding to node i in the spatio-temporal conflict matrix ik > the element m corresponding to node j in the spatio-temporal conflict matrix jk , then move the transmission time slot of the node i with lower priority backward, and set the delay time delay1 = p - mc, and add all elements m ik in the i-th row of the spatio-temporal conflict matrix by this delay time delay1;

[0163] If the element m corresponding to node i in the spatio-temporal conflict matrix ik ≤ the element m corresponding to node j in the spatio-temporal conflict matrix jk , then move the transmission time slot of the node i with lower priority backward, set the delay time delay2 = p + mc; add all elements m ik in the i-th row of the spatio-temporal conflict matrix by this delay time delay2, and return to step 1-2); where, k = 0, 1, …, T–1;

[0164] Step 1-4) Allocate conflict-free time slots;

[0165] For any node k', take out the diagonal element m k’k of the established spatio-temporal conflict matrix as the start time of its transmission time slot, and assign p as the length of the transmission time slot to this node k', denoted as p' = p; where, k' = 0, 1, …, T–1; p' is the length of the transmission time slot; where, the diagonal element is m in the spatio-temporal conflict matrix when k' = k k’k ;

[0166] Repeat the above process, assign the start time of the transmission time slot and the length p' of the transmission time slot to each node, and complete the compact allocation of conflict-free time slots.

[0167] Using method 2, a conflict-free time slot is allocated to each node that meets the conflict-free transmission condition, thereby completing the compact allocation of conflict-free time slots.

[0168] Specifically,

[0169] Step 2-1) Assign all T nodes to corresponding sets and assign priorities;

[0170] Create an empty set, denoted as Set0'; assign node 0 to Set0' to obtain a non-empty set Set0. At this time, the number of non-empty sets N = 1;

[0171] Calculate the conflict between node 1 and all nodes in the non-empty set Set0 in turn. If the conflict-free emission condition is met,

[0172] ∪ k＝0,1,…,T-1 {abs(m 1k –m yk )>p|y∈Set0,m 1k ≥0,m yk ≥0} (3)

[0173] This indicates that there is no conflict between node 1 and all nodes in the non-empty set Set0, node 1 and all nodes in the non-empty set Set0 transmit signals at the same time, and node 1 is assigned to the non-empty set Set0;

[0174] If node 1 does not meet the conflict-free transmission condition shown in the above formula (3) for the non-empty set Set0, then the number of non-empty sets N is increased by 1, and another empty set is established, recorded as Set1', and node 1 is then assigned to the empty set Set1' to obtain the non-empty set Set1;

[0175] Step 2-2) Calculate the remaining nodes 2 to node T-1 and the existing non-empty sets Set0, Set1, ..., Set N-1 The conflict of all nodes in Set v Satisfy the following formula

[0176] ∪ k＝0,1,…,T-1 {abs(m xk –m yk )>p|y∈Set v ,m xk ≥0,m yk ≥0} (4)

[0177] This indicates that the node x is associated with a non-empty set Set v There is no conflict among all nodes in Set , and node x is not an empty set. v All nodes in the set emit signals simultaneously and assign node x to the non-empty set Setv In which x=2,3,…,T-1,v=0,1,…,N-1;

[0178] If node x does not meet the conflict-free transmission condition shown in formula (4) for the existing N non-empty sets, then the number of non-empty sets N is increased by 1, and an empty set is created, which is recorded as Set N-1 ', then assign node x to the empty set Set N-1 ', set Set N-1 'Become a non-empty set Set N-1 ;

[0179] Repeat step 2-2) until each node is assigned to a corresponding non-empty set, and until there are no nodes that have not been assigned to a non-empty set, then proceed to step 2-3);

[0180] Step 2-3) Sort the N non-empty sets in descending order of the number of nodes in the set. The set with more nodes has a higher priority.

[0181] If there are two or more sets with the same number of nodes, the non-empty set with the smaller number has a higher priority;

[0182] Step 2-4) Calculate the minimum conflict interval mc between any two non-empty sets;

[0183] Assume that any two non-empty sets are sets u and Set v , Set u The priority is higher than the set Set v ;u=0,1,…,N-1; v=0,1,…,N-1, u≠v;

[0184] Iterate over a Set u Any node x and set Set v For any node y, calculate the set Set in turn according to formula (5) u and Set v The minimum conflict interval mc:

[0185] mc=min{abs(m xk -m yk )},x∈Set u ,y∈Set v ,k=0,1,…,T-1 (5)

[0186] Among them, m xk ≥0, m yk ≥0; where k = 0, 1, …, T-1;

[0187] until the set Set is traversed completely u with the set Set v For any pair of nodes x and y, record the minimum conflict interval mc, and record the element m corresponding to mc at this time xk and the element m yk as the corresponding time delay values mx and my;

[0188] If mc < p, it is considered that there is a signal conflict situation between the set Set u and the set Set v and enter step 2-5);

[0189] If mc ≥ p, it is considered that there is no signal conflict situation between the set Set u and the set Set v and enter step 2-6);

[0190] Step 2-5) Delay the transmission time of the set Set with lower priority v of;

[0191] If mx > my, set the delay time delay1 = p + mc; for all nodes y in the set Set, add all elements m in the y-th row of the spatio-temporal conflict matrix v by delay1; return to step 2-2); yk

[0192] If mx ≤ my, set the delay time delay2 = p - mc; for all nodes y in the set Set, add all elements m in the y-th row of the spatio-temporal conflict matrix v by delay2; return to step 2-2); yk

[0193] Step 2-6) Allocate non-conflicting time slots;

[0194] For any node k', take out the diagonal element m of the established spatio-temporal conflict matrix k’k as the start time of its transmission time slot, and allocate p as the length of the transmission time slot to this node k', denoted as p' = p; where, k' = 0, 1,..., T–1; p' is the length of the transmission time slot; k' = k;

[0195] Repeat the above process to allocate the start time of the transmission time slot and the length p' of the transmission time slot for each node, and complete the compact allocation of non-conflicting time slots.

[0196] The present invention also provides a system for compact allocation of non-conflicting time slots for a shallow water underwater acoustic network, and the system includes:

[0197] ​​The underwater acoustic network establishment module is used to use the pre-established shallow water acoustic network to obtain all nodes, synchronize the clocks of each node, and each node can obtain the geographic location and depth of each other node;

[0198] The matrix building module is used to build a spatiotemporal conflict matrix for all nodes based on the propagation delays between different nodes.

[0199] The allocation module is used to judge the conflict situation between two nodes in the established time-space conflict matrix according to the conflict-free transmission condition; according to the judgment result, the conflict-free time slot is allocated to each node that meets the conflict-free transmission condition, thereby completing the compact allocation of conflict-free time slots.

[0200] As one of the improvements to the above technical solution, the specific implementation process of the matrix establishment module is as follows:

[0201] Assume that T nodes are used to establish a shallow water acoustic network, and T nodes are obtained from the shallow water acoustic network to establish a T×T spatiotemporal conflict matrix M and initialize it to all 0s;

[0202] Among them, the element in the i-th row and j-th column is the propagation delay between node i and node j, denoted as m ij , m ij is a real number with unit of s; i=0,1,…,T–1; j=0,1,…,T-1; when i=j, m ij Indicates the moment when node i starts to transmit the signal; when i≠j, m ij represents the time when node j starts to receive the signal transmitted by node i;

[0203] Calculate the propagation delay between any two nodes in a shallow water acoustic network based on the geographic location and depth of each node;

[0204] Assume that nodes i and j are any two nodes, so the propagation delay τ between nodes i and j is ij :

[0205] τ ij =sqrt[(lat i –lat j ) 2 ×LON1 2 + (alt i –alt j ) 2 + (lon i –lon j ) 2 ×LAT1 2 ×cos((lat i +latj )×π / 360.0) 2 / c (1)

[0206] where lat i , lon i , alt i are the latitude, longitude and depth of node i respectively; lat j , lon j , alt j are the latitude, longitude and depth of node j respectively; LON1 is the distance difference in longitude corresponding to a 1-degree difference in latitude, which is a known value; LAT1 is the distance difference in latitude corresponding to a 1-degree difference in longitude at the equator, which is a known value; π is the pi;

[0207] Repeat the above calculation process to obtain multiple propagation delays and put them into the spatio-temporal conflict matrix M, denoted as m ij = τ ij ;

[0208] According to the underwater acoustic propagation model, calculate the propagation loss l ij between node i and node j, i≠j; further improve the spatio-temporal conflict matrix;<q

[0209] When the propagation loss l ij <h, it is considered that the signal transmitted by node i will interfere with the signal received by node j from other nodes, and there is a conflict situation between node i and node j. At this time, keep τ ij unchanged; where h is a preset node interference threshold;

[0210] When the propagation loss l ij ≥h, it is considered that the signal transmitted by node i will not interfere with the signal received by node j from other nodes, and there is no conflict situation between node i and node j. At this time, assign m ij a negative value;

[0211] Based on the above process, complete the establishment of the spatio-temporal conflict matrix M;

[0212]

[0213] Example 1.

[0214] The method of the present invention uses MATLAB software to simulate an underwater acoustic network randomly deployed within a certain range in a shallow water area.

[0215] I. Simulation parameter setting

[0216] Based on a shallow-water test, the simulation parameters were set as follows: signal center frequency 12 kHz, bandwidth 4 kHz, maximum signal reception time p = 2.2 s, sea depth 300 m, average sound speed in water c = 1496.6 m / s, and node mutual interference threshold h = 81.82 dB. Simulations were conducted for ten scenarios with eight nodes and ten scenarios with ten nodes.

[0217] 2. Simulation Settings and Process

[0218] Take the 8-node case 1 shown in Figure 2(a) as an example. Its initial space-time conflict matrix is ​​shown in Table 1. This table is the initial space-time conflict matrix formed after all nodes complete the network self-organization. Among them, the 8 0 elements on the diagonal represent that all 8 nodes transmit signals at time 0; the other elements m ij (i≠j), if a positive real number, indicates the propagation delay from node i to node j. If -1, it indicates that the signal transmitted by node i does not interfere with node j's reception. For a maximum signal length of 2.2 seconds, the table shows that the arrival time of signals transmitted by nodes 2 and 3 at node 0 is 5.4714 and 5.4351 seconds, respectively. This will cause a collision at node 0, preventing it from receiving the signal.

[0219] Table 1 Initial spatiotemporal conflict matrix for 8-node scenario 1 shown in Figure 2(a)

[0220] node 0 1 2 3 4 5 6 7 0 0 4.4184 5.4714 5.4351 6.4522 3.6752 4.0675 4.6246 1 4.4184 0 -1 1.0428 -1 2.5798 1.1641 2.1733 2 5.4714 -1 0 -1 1.3206 4.6901 -1 5.5291 3 5.4351 1.0428 -1 0 -1 3.0888 1.9936 2.3163 4 6.4522 -1 1.3206 -1 0 4.9177 -1 5.5464 5 3.6752 2.5798 4.6901 3.0888 4.9177 0 3.3279 1.1122 6 4.0675 1.1641 -1 1.9936 -1 3.3279 0 3.1965 7 4.6246 2.1733 5.5291 2.3163 5.5464 1.1122 3.1965 0

[0221] 3. Simulation Results Analysis

[0222] for Figures 2(a)-2(j) Table 3 shows a total of 10 random placements of 8 nodes, and a comparison of the most compact periods obtained by the traditional TDMA method and the global search method.

[0223] Table 3 Figures 2(a)-2(j) Comparison of results for 10 8-node scenarios shown

[0224]

[0225]

[0226] for Figures 3(a)-3(j) Table 4 shows a comparison of 10 random placements of 10 nodes with the most compact periods obtained by the traditional TDMA method and the global search method.

[0227] Table 4 Comparison of results for the 10 cases with 10 nodes shown in Figure 3

[0228] Deployment situation Traditional TDMA cycle This method 1 cycle This method has 2 cycles The most compact cycle 10 nodes_1 100s 58.2s 49.7s 37.0s 10 nodes_2 100s 59.3s 54.9s 41.9s 10 nodes_3 100s 46.1s 38.7s 30.8s 10 nodes_4 100s 61.0s 61.0s 42.7s 10 nodes_5 100s 72.9s 67.7s 43.0s 10 nodes_6 100s 55.6s 54.2s 37.2s 10 nodes_7 100s 62.9s 52.9s 42.9s 10 nodes_8 100s 58.1s 50.2s 39.5s 10 nodes_9 100s 54.6s 46.9s 39.4s 10 nodes_10 100s 63.8s 44.7s 33.2s average 100s 59.3s 52.1s 38.8s

[0229] As shown in Tables 3 and 4, compared to traditional TDMA methods, this method can reduce the time required for all nodes to transmit by at least 52% for 8 nodes and by at least 40% for 10 nodes. However, this method still lags behind the global search method. Considering the factorial increase in global search computation time, the global search computation time for 8 nodes is approximately 1.5 seconds, and for 10 nodes is approximately 300 seconds, while the computation time for this algorithm remains on the order of 10 milliseconds. Therefore, it is recommended to use this method to obtain a feasible solution with better performance when the number of nodes exceeds 8.

[0230] Finally, it should be noted that the above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention and are intended to be encompassed by the claims of the present invention.

Claims

1. A conflict - free time - slot compact allocation method for shallow - water underwater acoustic networks, the method comprising: Utilize a pre - established shallow - water underwater acoustic network to obtain all nodes, synchronize the clocks of each node, and each node can obtain the geographical locations and depths of other nodes. Establish a spatio - temporal conflict matrix for all nodes according to the calculated propagation delays between different nodes. Judge the conflict situation between pairwise nodes in the established spatio - temporal conflict matrix according to the conflict - free transmission condition; according to the judgment result, allocate conflict - free time - slots to each node that meets the conflict - free transmission condition, and complete the conflict - free time - slot compact allocation. The conflict-free transmission condition is that the minimum conflict interval in the time-space conflict matrix is ​​greater than the longest signal reception time of all nodes; or k＝0,1,…,T-1 {abs(m xk –m yk )>p|y∈Set v ,m xk ≥0,m yk ≥0}; Among them, m xk is the element in the spatiotemporal conflict matrix corresponding to node x; m yk is the element in the spatiotemporal conflict matrix corresponding to node y; p is the longest signal receiving time of each node; Set v is a non-empty set, and Set v All nodes in the can transmit signals simultaneously; It is characterized in that, according to the conflict - free transmission condition, judge the conflict situation between pairwise nodes in the established spatio - temporal conflict matrix; according to the judgment result, allocate conflict - free time - slots to each node that meets the conflict - free transmission condition, and complete the conflict - free time - slot compact allocation; the specific process is as follows: Step 1 - 1): Denote all nodes in the established spatio - temporal conflict matrix as T nodes, sort all T nodes and allocate priorities. Sum each spatiotemporal conflict matrix corresponding to T nodes by column to obtain T delays and sm i , divide T nodes into two groups according to delay and sm i Arrange them in order from small to large and number them accordingly; Step 1 - 2): Calculate the minimum conflict interval in the spatio - temporal conflict matrix. Calculate any two non-negative elements m in each column of the spatiotemporal conflict matrix in sequence ik and m jk The absolute value of the difference between the two columns is calculated. From the absolute values ​​of the differences of all columns, the minimum value obtained in all columns is recorded as the minimum conflict interval mc, and the node i and node j corresponding to mc; where i = 0, 1, ..., T–1; j = 0, 1, ..., T–1; k = 0, 1, ..., T–1; i ≠ j; Judge the conflict situation between pairwise nodes in the established spatio - temporal conflict matrix. Assume that the longest signal reception time of each node is p. If mc < p, it is considered that there is still a signal conflict situation between node i and node j at this time, and go to Step 1 - 3). If mc≥p, it is considered that there is no signal conflict situation between node i and node j, and go to Step 1 - 4). Step 1 - 3): Delay the transmission time of the node with a lower priority. Assume that the priority of node i is lower and the priority of node j is higher. If the element m corresponding to node i in the spatiotemporal conflict matrix ik >Element m corresponding to node j in the spatiotemporal conflict matrix jk , then the transmission time slot of the node i with lower priority is shifted back, and the delay time is set to delay1 = p-mc, and all elements m in the i-th row of the time-space conflict matrix are ik Add the delay time delay1 to all of them; If the element m corresponding to node i in the spatiotemporal conflict matrix ik ≤ element m corresponding to node j in the spatiotemporal conflict matrix jk , then the transmission time slot of the node i with lower priority is shifted back, and the delay time is set to delay2=p+mc; all elements m in the i-th row of the time-space conflict matrix are ik Add the delay time delay2 to each of them and return to step 1-2); where k = 0, 1, ..., T–1; Step 1 - 4): Allocate conflict - free time - slots. For any node k', the diagonal element m of the established spatiotemporal conflict matrix is k’k Take out as the start time of its transmission time slot, and assign p as the transmission time slot length to the node k', denoted as p' = p; where k' = 0, 1, ..., T–1; p' is the transmission time slot length; k' = k; Repeat the above process to allocate the start time of the transmission time - slot and the length p' of the transmission time - slot for each node, and complete the conflict - free time - slot compact allocation.

2. The method for compact allocation of conflict-free time slots for shallow water underwater acoustic networks according to claim 1, characterized in that: The process of establishing a spatio - temporal conflict matrix for all nodes according to the calculated propagation delays between different nodes is as follows: Assume that a shallow - water underwater acoustic network is established with T nodes, obtain T nodes from the shallow - water underwater acoustic network, establish a T×T spatio - temporal conflict matrix M, and initialize it to all 0s. Among them, the element in the i-th row and j-th column is the propagation delay between node i and node j, denoted as m ij , m ij is a real number with unit of s; i=0,1,…,T–1; j=0,1,…,T-1; when i=j, m ij Indicates the moment when node i starts to transmit the signal; when i≠j, m ij represents the time when node j starts to receive the signal transmitted by node i; Calculate the propagation delays between any two nodes in the shallow - water underwater acoustic network according to the geographical locations and depths of each node. Assume that nodes i and j are any two nodes, so the propagation delay τ between nodes i and j is ij : τ ij =sqrt[(lat i -years j ) 2 ×LON1 2 + (alt i –alt j ) 2 + (lon i –lon j ) 2 ×LAT1 2 ×cos((lat i +years j )×π / 360.0) 2 ] / c(1) Among them, lat i ,lon i 、alt i are the latitude, longitude and depth of node i respectively; lat j ,lon j 、alt j are the latitude, longitude and depth of node j respectively; LON1 is the distance in longitude corresponding to a 1-degree difference in latitude, which is a known value; LAT1 is the distance in latitude corresponding to a 1-degree difference in longitude at the equator, which is a known value; π is the pi; Repeat the above calculation process to obtain multiple propagation delays, and put them into the time-space conflict matrix M, denoted as m ij =τ ij ; According to the underwater acoustic propagation model, the propagation loss l between node i and node j is calculated. ij , i≠j; further improve the space-time conflict matrix; When the propagation loss l ij <is less than h, it is considered that the signal transmitted by node i will interfere with the signal received by node j from other nodes, and there is a conflict situation between node i and node j. At this time, keep τ ij unchanged; where h is a preset node interference threshold; When the propagation loss l ij When ≥h, it is considered that the signal transmitted by node i will not interfere with the signal transmitted by other nodes received by node j, and there is no conflict between node i and node j. At this time, m ij Assign a negative value; Based on the above process, complete the establishment of the spatio - temporal conflict matrix M.

3. The method for compact allocation of conflict-free time slots for shallow water underwater acoustic networks according to claim 1, characterized in that: The process of judging the conflict situation between each node in the established spatio - temporal conflict matrix according to the conflict - free transmission condition; according to the judgment result, allocate conflict - free time - slots to each node that meets the conflict - free transmission condition, and complete the conflict - free time - slot compact allocation is as follows: Step 2 - 1): Allocate all T nodes to the corresponding sets and allocate priorities. Establish 1 empty set, denoted as Set0'; allocate node 0 to Set0' to obtain a non - empty set Set0. At this time, the number N of non - empty sets is 1. Successively calculate the conflict situations between node 1 and all nodes in the non - empty set Set0. If the conflict - free transmission condition is met. ∪ k＝0,1,…,T -1{abs(m 1k – m yk ) > p | y ∈ Set0, m 1k ≥ 0, m yk ≥ 0} (3) This indicates that there is no conflict between node 1 and all nodes in the non-empty set Set0, node 1 and all nodes in the non-empty set Set0 transmit signals at the same time, and node 1 is assigned to the non-empty set Set0; If node 1 does not meet the conflict-free transmission condition shown in the above formula (3) for the non-empty set Set0, then the number of non-empty sets N is increased by 1, and another empty set is established, recorded as Set1', and node 1 is then assigned to the empty set Set1' to obtain the non-empty set Set1; Step 2-2) Calculate the remaining nodes 2 to node T-1 and the existing non-empty sets Set0, Set 1,…, Set N-1 The conflict of all nodes in Set v Satisfy the following formula ∪ k＝0,1,…,T -1{abs(m xk – m yk ) > p | y ∈ Set v , m xk ≥ 0, m yk ≥ 0} (4) This indicates that the node x is associated with a non-empty set Set v There is no conflict among all nodes in Set , and node x is not an empty set. v All nodes in the set emit signals simultaneously and assign node x to the non-empty set Set v In which x=2,3,…,T-1,v=0,1,…,N-1; If node x does not meet the conflict-free transmission condition shown in formula (4) for the existing N non-empty sets, then the number of non-empty sets N is increased by 1, and an empty set is created, which is recorded as Set N-1 ', then assign node x to the empty set Set N-1 ', set Set N-1 'Become a non-empty set Set N-1 ; Repeat step 2-2) until each node is assigned to a corresponding non-empty set, and until there are no nodes that have not been assigned to a non-empty set, then proceed to step 2-3); Step 2-3) Sort the N non-empty sets in descending order of the number of nodes in the set. The set with more nodes has a higher priority. If there are two or more sets with the same number of nodes, the non-empty set with the smaller number has a higher priority; Step 2-4) Calculate the minimum conflict interval mc between any two non-empty sets; Assume that any two non-empty sets are sets u and Set v , Set u The priority is higher than the set Set v ;u=0,1,…,N-1; v=0,1,…,N-1, u≠v; Iterate over a Set u Any node x and set Set v For any node y, calculate the set Set in turn according to formula (5) u and Set v The minimum conflict interval mc: mc=min{abs(m xk -m yk )},x∈Set u ,y∈Set v ,k=0,1,…,T-1 (5) Among them, m xk ≥0, m yk ≥0; where k = 0, 1, …, T-1; Until the set is traversed u and Set v For any pair of nodes x and y, record the minimum conflict interval mc and the element m corresponding to mc at this time. xk and element m yk are the corresponding delay values ​​mx and my; If mc < p, then the set Set is considered u to have a signal conflict with the set Set v and proceed to step 2-5); If mc≥p, then the set Set u and Set v There is no signal conflict between them, and proceed to step 2-6); Step 2-5) Defer the set with low priority v The launch time; If mx>my, then set the delay time delay1=p+mc; for the set Set v All nodes y in the spatiotemporal conflict matrix will be all elements m in the yth row yk Add delay1 to each; return to step 2-2); If mx≤my, then set the delay time delay2=p-mc; for the set Set v All nodes y in the spatiotemporal conflict matrix will be all elements m in the yth row yk Add delay2 to both; return to step 2-2); Step 2-6) Allocate conflict-free time slots; For any node k', the diagonal element m of the established spatiotemporal conflict matrix is k’k Take out as the start time of its transmission time slot, and assign p as the transmission time slot length to the node k', denoted as p' = p; where k' = 0, 1, ..., T–1; p' is the transmission time slot length; k' = k; Repeat the above process to assign a transmission slot start time and a transmission slot length p' to each node, completing the conflict-free time slot compact allocation.

4. A conflict-free time slot compact allocation system for shallow water underwater acoustic networks, characterized in that: For implementing the method according to any one of claims 1 to 3, the system comprises: The underwater acoustic network establishment module is used to use the pre-established shallow water acoustic network to obtain all nodes, synchronize the clocks of each node, and each node can obtain the geographic location and depth of each other node; The matrix building module is used to build a spatiotemporal conflict matrix for all nodes based on the propagation delays between different nodes. The allocation module is used to judge the conflict situation between two nodes in the established time-space conflict matrix according to the conflict-free transmission condition; according to the judgment result, the conflict-free time slot is allocated to each node that meets the conflict-free transmission condition, thereby completing the compact allocation of conflict-free time slots.

5. The conflict-free time slot compact allocation system for shallow water underwater acoustic network according to claim 4, characterized in that: The specific implementation process of the matrix establishment module is as follows: Assume that T nodes are used to establish a shallow water acoustic network, and T nodes are obtained from the shallow water acoustic network to establish a T×T spatiotemporal conflict matrix M and initialize it to all 0s; Among them, the element in the i-th row and j-th column is the propagation delay between node i and node j, denoted as m ij , m ij is a real number with unit of s; i=0,1,…,T–1; j=0,1,…,T-1; when i=j, m ij Indicates the moment when node i starts to transmit the signal; when i≠j, m ij represents the time when node j starts to receive the signal transmitted by node i; Calculate the propagation delay between any two nodes in a shallow water acoustic network based on the geographic location and depth of each node; Assume that nodes i and j are any two nodes, so the propagation delay τ between nodes i and j is ij : τ ij =sqrt[(lat i -years j ) 2 ×LON1 2 + (alt i –alt j ) 2 + (lon i –lon j ) 2 ×LAT1 2 ×cos((lat i +years j )×π / 360.0) 2 ] / c(1) Among them, lat i ,lon i 、alt i are the latitude, longitude and depth of node i respectively; lat j ,lon j 、alt j are the latitude, longitude and depth of node j respectively; LON1 is the distance in longitude corresponding to a 1-degree difference in latitude, which is a known value; LAT1 is the distance in latitude corresponding to a 1-degree difference in longitude at the equator, which is a known value; π is the pi; Repeat the above calculation process to obtain multiple propagation delays, and put them into the time-space conflict matrix M, denoted as m ij =τ ij ; According to the underwater acoustic propagation model, the propagation loss l between node i and node j is calculated. ij , i≠j; further improve the space-time conflict matrix; When the propagation loss l ij <is less than h, it is considered that the signal transmitted by node i will interfere with the signal received by node j from other nodes, and there is a conflict situation between node i and node j. At this time, keep τ ij unchanged; where h is a preset node interference threshold; When the propagation loss l ij When ≥h, it is considered that the signal transmitted by node i will not interfere with the signal transmitted by other nodes received by node j, and there is no conflict between node i and node j. At this time, m ij Assign a negative value; Based on the above process, the spatiotemporal conflict matrix M is established;

Images