CN109951248B - Time synchronization method for underwater sensor network - Google Patents

Time synchronization method for underwater sensor network Download PDF

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CN109951248B
CN109951248B CN201910119974.4A CN201910119974A CN109951248B CN 109951248 B CN109951248 B CN 109951248B CN 201910119974 A CN201910119974 A CN 201910119974A CN 109951248 B CN109951248 B CN 109951248B
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陈凌宇
郑韵思
施海彬
连国景
吴泽石
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Xiamen University
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Abstract

The invention discloses a time synchronization method of an underwater sensor network, which is realized on the basis of the underwater sensor network with a plurality of nodes, wherein the nodes are underwater sensors, and the underwater sensor network comprises a processor, an underwater sound transceiver, a transducer and a hydrophone; the processor is electrically connected with the underwater acoustic transceiver; the processor is electrically connected with the current position and time information providing module, in the underwater sensor network, the sensor nodes to be synchronized can fit the linear regression expression of the clock time of each neighbor node and the clock time of the sensor nodes to be synchronized through exchanging the clock time of the sending/receiving clock of the data packet with the neighbor nodes, and the clock time parameters of the sensor nodes are continuously updated in an iterative manner, so that the clock synchronization among the sensor nodes is realized; the time synchronization of the network node allowed by the invention does not depend on a special node (time reference node), and has the characteristics of high convergence rate, strong survivability and the like.

Description

Time synchronization method for underwater sensor network
Technical Field
The invention relates to the technical field of underwater acoustic communication, in particular to a time synchronization method for an underwater sensor network.
Background
With the continuous development of human society, the ocean is more important in the field of human living activities, but people need to arrange an underwater acoustic sensor network in the ocean to research the underwater acoustic sensor network. With the increasing emphasis on ocean strategy, the underwater sensor network has gained wide attention. The underwater sensor network plays a key role in submarine detection, ocean development and national security. Time synchronization among network nodes is the basis of cooperative operation among sensor nodes, but the underwater sensor network adopts an underwater acoustic communication mode and has different characteristics from a land sensor network, so that a new challenge is brought to the research of a time synchronization algorithm.
In the sensor network, the local clocks of the nodes are not uniform due to the inherent crystal frequency of the nodes. In the time synchronization process of the underwater acoustic sensor network, two parameters of clock drift rate and clock deviation need to be estimated. The existing underwater sensor network node mainly realizes time synchronization by means of bidirectional data packet exchange between a node to be synchronized and a time reference node, realizes time synchronization of two nodes by utilizing timestamps carried in data packets at the time of sending and receiving the data packets, and then achieves time synchronization of the whole network through synchronization of every two nodes.
Different from a land wireless environment, the underwater sound signal propagation speed is low, underwater node resource energy is limited, and synchronous operation cannot be performed frequently as on land. The existing method for solving the problem of time synchronization of two underwater nodes comprises TSHL, MU-Sync, E MU-Sync, Mobi-Sync, D-Sync, DA-Sync and the like. However, most of the existing synchronization methods do not fully utilize the natural broadcast characteristics of the underwater acoustic channel, have low synchronization efficiency and depend on the reference node. The method provided by the patent can allow the time synchronization of the network nodes not to depend on a special node, and has the characteristics of high convergence rate, strong survivability and the like.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a time synchronization method for an underwater sensor network, which solves some technical problems in the prior art.
In order to achieve the purpose, the invention is realized by the following technical scheme: a time synchronization method of an underwater sensor network is realized on the basis of the underwater sensor network with a plurality of nodes, wherein the nodes are underwater sensors, and the underwater sensor network comprises a processor, an underwater acoustic transceiver, a transducer and a hydrophone; the processor is electrically connected with the underwater acoustic transceiver; the processor is electrically connected with the current position and the time information providing module, the underwater sound transceiver is electrically connected with the transducer and the hydrophone, and the transducer and the hydrophone are electrically connected with the underwater sound channel;
the processor is used for operating the CO-Sync protocol, receiving the acquired current position and time information, writing the information of the log and the transceiving data packet operated by the CO-Sync protocol in real time, and performing a series of calculation analysis processing;
the underwater sound transceiver is used for sending the electric signal to the transducer for conversion, and receiving the converted electric signal from the hydrophone.
The transducer converts electric energy into sound energy, and the electronic oscillator generates an electric signal to excite the transducer to generate mechanical vibration so as to push the aqueous medium to emit sound waves into water.
The hydrophone is responsible for converting a hydroacoustic signal into an electrical signal, i.e. acoustic energy into electrical energy, which is excited by acoustic waves to vibrate, thereby converting the acoustic signal into an electrical signal.
The synchronization method comprises the following steps: in the underwater sensor network, the sensor nodes to be synchronized can fit the linear regression expression of the clock time of each neighbor node and the clock time of the sensor nodes by exchanging the clock time of the sending/receiving of the data packet with the neighbor nodes, and continuously update the clock time parameters of the sensor nodes in an iterative manner, so that the clock synchronization among the sensor nodes is realized; the method specifically comprises the following steps:
step 1, initializing clock face time correction coefficients α of all nodes in sensor networkiAnd βi，
Figure RE-GDA0002049527850000021
While setting the iteration counter value to 0;
step 2, each node communicates with the neighboring nodes around to obtain the receiving and sending time of all data packets of the two parties, and the linear regression expression of the clock time of all the neighboring nodes around and the clock time of the node is fitted to carry out parameter estimation by comparing the clock time of the other party, so as to obtain the coefficient of the relation between the clock time of the local node and the clock time of the neighboring nodes;
step 3, each node in the underwater sensor network updates parameters of the clock face time correction coefficient according to the relation coefficient (estimation value) with the clock face time of the neighbor node obtained in the step 2, and updates the clock face time;
and 4, adding 1 to the iteration counter value m, namely m is m +1, and jumping to the step 2.
Furthermore, the nodes of the sensor to be synchronized interact with each other through a series of data packets carrying the sending/receiving clock face time.
Furthermore, under the condition of establishing clock face time of the underwater sensor network nodes and network topology models in different forms, each node carries out multiple times of synchronous time information interaction to obtain observed quantity of the system, and the observed quantity of the system obtained by a series of interactions is utilized to carry out fitting to obtain updated clock face time parameters, so that estimated values of clock drift and deviation of the sensor nodes to be synchronized are realized.
Further, the clock face time correction coefficients in step 1 are clock drift rates α of the node to the local time of the nodeiCorrection amount β of sum clock deviationiClock face time correction factor αiAnd βiAdjustments and updates are required to be made continuously during the synchronization of the underwater sensor network.
Further, the clock face time correction factor is typically a time-varying quantity. The purpose of the synchronization of the underwater sensor network is to adjust the clock face time correction coefficient of each node, so that the clock deviation of any two nodes approaches to 0.
Further, the data packets communicated by the node in step 2 all carry the clock time that the node has recently received the data packet and the clock time that the data packet has been sent. Therefore, clock face time for transmitting and receiving all data packets of the two nodes can be obtained between the two nodes in communication. And solving the coefficient of the relation between the clock face time of the local node and the clock face time of the neighbor node by utilizing linear regression.
Further, the calculation method of the linear regression is as follows:
setting two communication parties as a node i and a node j, and setting local clock face time of the node i and the node j as T when the mth iteration is carried outi (m)(t) and
Figure RE-GDA0002049527850000041
the node i estimates the relation between the clock time of the node j and the local clock time thereof as
Figure RE-GDA0002049527850000042
When the node i obtains the time of the receiving and sending clock faces of more than two data packets, the linear regression is utilized to obtain the time
Figure RE-GDA0002049527850000043
Relative to Ti (m)Slope of (t)
Figure RE-GDA0002049527850000044
And
Figure RE-GDA0002049527850000045
relative to Ti (m)(t) longitudinal intercept
Figure RE-GDA0002049527850000046
The same node j can also calculate the coefficient of the corresponding relational expression
Figure RE-GDA0002049527850000047
And
Figure RE-GDA0002049527850000048
further, in each iteration, each node i and all the surrounding neighbor nodes
Figure RE-GDA0002049527850000049
All the above-mentioned methods are implemented by fitting linear regression expression to obtain all
Figure RE-GDA00020495278500000410
And
Figure RE-GDA00020495278500000411
further, each node in step 3 updates the clock face time parameter according to the relationship between the clock face time parameter of the node and the coefficient of the relational expression obtained in step 2, where the specific relationship includes:
Figure RE-GDA00020495278500000412
wherein | NiAnd | represents the number of neighbor nodes of the node i.
Furthermore, the clock of the nodes can be kept consistent through the algorithm steps.
Advantageous effects
The invention provides a time synchronization method for an underwater sensor network. The method has the following beneficial effects: the time synchronization of the network node allowed by the invention does not depend on a special node (time reference node), and has the characteristics of high convergence rate, strong survivability and the like.
Drawings
FIG. 1 is an example of a network topology for an underwater sensor network of the present invention;
FIG. 2 is a flow chart of the method of the present invention;
FIG. 3 is a general configuration of the underwater sensor of the present invention;
fig. 4 is a schematic diagram of a communication process between two nodes according to the present invention.
In the figure: a processor (101), an underwater acoustic transceiver (102), a transducer (103), and a hydrophone (104).
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1 to 4, the present invention provides a time synchronization method for an underwater sensor network, where the synchronization method is implemented based on an underwater sensor network with multiple nodes, where the nodes are underwater sensors, and the underwater sensor network includes a processor 101, an underwater acoustic transceiver 102, a transducer 103, and a hydrophone 104; the processor 101 is electrically connected to the photoacoustic transceiver 102; the processor 101 is electrically connected with the current position and the time information providing module, and the underwater sound transceiver 102 is electrically connected with the transducer 103, the hydrophone 104, the transducer 103 and the hydrophone 104 are electrically connected with the underwater sound channel;
the processor 101 is used for operating the CO-Sync protocol, receiving the acquired current position and time information, writing the information of the log and the transceiving data packet operated by the CO-Sync protocol in real time, and performing a series of calculation analysis processing;
the underwater acoustic transceiver 102 is used for sending an electric signal to the transducer 103 for conversion, and receiving a converted electric signal from the hydrophone 104;
the transducer 103 converts electric energy into sound energy, and the electronic oscillator generates an electric signal to excite the transducer 103 to generate mechanical vibration to push the aqueous medium to emit sound waves into water;
the hydrophone 104 is responsible for converting the underwater acoustic signals into electrical signals, that is, converting acoustic energy into electrical energy, which generates vibration under the excitation of acoustic waves, thereby converting the acoustic signals into electrical signals;
the synchronization method comprises the following steps: in the underwater sensor network, the sensor nodes to be synchronized can fit the linear regression expression of the clock time of each neighbor node and the clock time of the sensor nodes by exchanging the clock time of the sending/receiving of the data packet with the neighbor nodes, and continuously update the clock time parameters of the sensor nodes in an iterative manner, so that the clock synchronization among the sensor nodes is realized; the method specifically comprises the following steps:
step 1, initializing clock surface time correction coefficients of all nodes in the sensor network, and simultaneously setting the value of an iteration counter to be 0, namely setting the clock drift rate α of the node to the local time of the nodeiCorrection amount β of sum clock deviationiAre all set to be 0 and are,
Figure RE-GDA0002049527850000061
while setting the iteration counter value m to 0, the clock face time correction factor αi、βiIt needs to be adjusted and updated continuously during the synchronization process of the network, which is usually a time-varying quantity, and the purpose of the network time synchronization is to adjust the clock face time correction factor α of each nodeiAnd βiSo that the clock skew for any two nodes approaches 0, i.e. | Ti(t)-Tj(t)|→0；
Step 2, each node communicates with the neighboring nodes around to obtain the receiving and sending time of all data packets of the two parties, and the linear regression expression of the clock time of all neighboring nodes around and the clock time of the node is fitted to carry out parameter estimation by comparing the clock time of the other party, so as to obtain the relation system between the clock time of the local node and the clock time of the neighboring nodesCounting; and further, the clock face time correction coefficient of the local node is obtained, and the clock face time of the local node is adjusted to approach the clock face time of the opposite side. Setting two communication parties as a node i and a node j, and setting local clock face time of the nodes i and j as T when the mth iteration is carried outi (m)(t) and
Figure RE-GDA0002049527850000062
the node i estimates the relation between the clock time of the node j and the local clock time thereof as
Figure RE-GDA0002049527850000063
For the equation, after the node i obtains the receiving and sending clock face time of more than two data packets, the linear regression can be used to obtain the time
Figure RE-GDA0002049527850000064
Relative to Ti (m)Slope of (t)
Figure RE-GDA0002049527850000065
And
Figure RE-GDA0002049527850000066
relative to Ti (m)(t) longitudinal intercept
Figure RE-GDA0002049527850000067
The same node j can also calculate the coefficient of the corresponding relational expression
Figure RE-GDA0002049527850000068
And
Figure RE-GDA0002049527850000069
communication from two nodes is further expanded to a local node i and all surrounding neighbor nodes
Figure RE-GDA00020495278500000610
Communication is carried out, and in each iteration, each node i and all the surrounding neighbor nodes
Figure RE-GDA00020495278500000611
All the above-mentioned methods are implemented by fitting linear regression expression to obtain all
Figure RE-GDA00020495278500000612
And
Figure RE-GDA00020495278500000613
obtaining the relation coefficient between the clock face time of the local node and the clock face time of all the neighbor nodes;
step 3, each node in the underwater sensor network updates parameters of the clock face time correction coefficient according to the relation coefficient (estimation value) with the clock face time of the neighbor node obtained in the step 2, and updates the clock face time; the relationship between the clock face time parameter and the relational coefficients is:
Figure RE-GDA00020495278500000614
wherein | NiL represents the number of neighbor nodes of the node i;
and 4, adding 1 to the iteration counter value m, namely m is m +1, and jumping to the step 2.
As shown in fig. 4, the iterative process adopted in this embodiment is that two nodes continuously send and receive data packets to obtain the transceiving time of all data packets of the two nodes
Figure RE-GDA0002049527850000071
Figure RE-GDA0002049527850000072
When enough calculation data is obtained, the coefficients of the relational expression of the clock time of the two parties can be calculated, the adjustment quantity of the clock time correction coefficient of the local node is obtained, and the local clock time correction coefficient α is updatediAnd βiAnd finally, the time synchronization among the nodes to be synchronized of the underwater sensor network is realized.
As can be seen from the CO-Sync step, it is a purely distributed algorithm. After observing the clock face time deviation of the opposite side, the nodes adjust the clock face time of the nodes to approach the clock face time of the opposite side, so that the positions of the nodes are equal in the algorithm, time reference nodes are not needed, and the established underwater sensor network has certain survivability.
Communication system of underwater sensor: the distributed time synchronization method is applied to the nodes of the underwater sensor network. An underwater sensor network is generally composed of a large number of underwater sensor nodes distributed at different positions underwater. An example of an underwater sensor network is given in figure 1. Circles in the graph represent nodes to be synchronized, and line segments in the graph represent nodes that are connected and between which communication can be performed. For example, node 1 and node 2 may receive data transmitted by each other.
The structure of the underwater sensor is shown in fig. 3, and the underwater sensor mainly comprises modules such as a processor, an underwater acoustic transceiver, a transducer, a hydrophone and the like. The CO-Sync protocol of the distributed time synchronization method provided by the patent runs in the processor, and can effectively realize the time synchronization of the underwater sensor network.
As shown in fig. 1, let a set of nodes of the underwater acoustic sensor network be V { (i ═ 1, 2.. times, N }, where an edge connecting two nodes i and j is denoted as (i, j), it means that i and j can communicate with each other, and a set of all edges is denoted as E { (i, j) | i, j ∈ V }, and a set of adjacent nodes of the node i is denoted as NiIt should be noted that nodes on both sides of one edge can perform bidirectional communication, that is, G is an undirected graph, and the corresponding adjacency matrix is a real symmetric matrix.
It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims (3)

1. An underwater sensor network time synchronization method is realized based on an underwater sensor network of a plurality of nodes, wherein the nodes are underwater sensors, and the underwater sensor network comprises a processor (101), an underwater acoustic transceiver (102), a transducer (103) and a hydrophone (104); the processor (101) is electrically connected with the underwater acoustic transceiver (102); the processor (101) is electrically connected with the current position and the time information providing module, the underwater sound transceiver (102) is electrically connected with the transducer (103) and the hydrophone (104), and the transducer (103) and the hydrophone (104) are electrically connected with the underwater sound channel;
the processor (101) is used for running a protocol, receiving the acquired current position and time information, writing the information of a protocol running log and a receiving and sending data packet in real time, and performing a series of calculation analysis processing;
the underwater acoustic transceiver (102) is used for sending an electric signal to the transducer (103) for conversion, and receiving a converted electric signal from the hydrophone (104);
the transducer (103) converts electric energy into sound energy, and the electronic oscillator generates an electric signal to excite the transducer (103) to generate mechanical vibration to push the aqueous medium to emit sound waves into water;
the hydrophone (104) is responsible for converting the underwater acoustic signals into electric signals, namely converting acoustic energy into electric energy, and generating vibration under the excitation of acoustic waves so as to convert the acoustic signals into the electric signals;
the synchronization method comprises the following steps: in the underwater sensor network, the sensor nodes to be synchronized can fit the linear regression expression of the clock time of each neighbor node and the clock time of the sensor nodes by exchanging the clock time of the sending/receiving of the data packet with the neighbor nodes, and continuously update the clock time parameters of the sensor nodes in an iterative manner, so that the clock synchronization among the sensor nodes is realized; the method specifically comprises the following steps:
step 1, initializing clock face time correction coefficients of all nodes in a sensor network, and simultaneously setting the value of an iteration counter to be 0;
step 2, each node communicates with neighboring nodes around to obtain the receiving and sending time of all data packets of the two parties, and the linear regression expression of the clock time of all neighboring nodes around and the clock time of the node is fitted to carry out parameter estimation by comparing the clock time of the other party, so as to obtain the coefficient of the relation between the clock time of the local node and the clock time of the neighboring nodes;
step 3, each node in the underwater sensor network updates parameters of the clock face time correction coefficient according to the relation coefficient with the clock face time of the neighbor node obtained in the step 2, and updates the clock face time;
step 4, adding 1 to the value m of the iteration counter, namely m is m +1, and jumping to the step 2;
the linear regression calculation method is as follows:
setting two communication parties as a node i and a node j, and setting local clock face time of the node i and the node j as T when the mth iteration is carried outi (m)(t) and
Figure FDA0002546175060000021
the node i estimates the relation between the clock time of the node j and the local clock time thereof as
Figure FDA0002546175060000022
When the node i obtains the time of the receiving and sending clock faces of more than two data packets, the linear regression is utilized to obtain the time
Figure FDA0002546175060000023
Relative to Ti (m)Slope of (t)
Figure FDA0002546175060000024
And
Figure FDA0002546175060000025
relative to Ti (m)(t) longitudinal intercept
Figure FDA0002546175060000026
The same node j can also calculate the coefficient of the corresponding relational expression
Figure FDA0002546175060000027
And
Figure FDA0002546175060000028
in each iteration, each node i and all surrounding neighbor nodes
Figure FDA0002546175060000029
All the above-mentioned methods are implemented by fitting linear regression expression to obtain all
Figure FDA00025461750600000210
And
Figure FDA00025461750600000211
and in the step 3, each node updates the clock face time parameter according to the relationship between the clock face time parameter and the relational expression coefficient obtained in the step 2, wherein the specific relationship comprises:
Figure FDA00025461750600000212
Figure FDA00025461750600000213
wherein | NiAnd | represents the number of neighbor nodes of the node i.
2. The underwater sensor network time synchronization method of claim 1, wherein: the sensor nodes to be synchronized interact with each other through a series of data packets carrying the sending/receiving clock time.
3. The underwater sensor network time synchronization method of claim 1, wherein: under the condition of establishing clock face time of the nodes of the underwater sensor network and network topology models in different forms, each node carries out multiple times of synchronous time information interaction to obtain observed quantity of the system, and the observed quantity of the system obtained by a series of interactions is utilized to carry out fitting to obtain updated clock face time parameters, so that estimated values of clock drift and deviation of the nodes of the sensor to be synchronized are realized.
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CN103889046A (en) * 2014-04-09 2014-06-25 青岛科技大学 Network time synchronization method for underwater sensor
CN108668356A (en) * 2018-04-19 2018-10-16 厦门大学 A kind of underwater sensor method for synchronizing time

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US7778226B2 (en) * 2006-03-30 2010-08-17 Intel Corporation Device, system and method of coordination among multiple transceivers
CN105554872B (en) * 2016-02-03 2019-05-14 广东顺德中山大学卡内基梅隆大学国际联合研究院 The method for synchronizing time and system of underwater sensor network

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CN103889046A (en) * 2014-04-09 2014-06-25 青岛科技大学 Network time synchronization method for underwater sensor
CN108668356A (en) * 2018-04-19 2018-10-16 厦门大学 A kind of underwater sensor method for synchronizing time

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