CN111385825B - Consistency time synchronization method for rapid convergence of wireless sensor network - Google Patents

Consistency time synchronization method for rapid convergence of wireless sensor network Download PDF

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CN111385825B
CN111385825B CN202010118658.8A CN202010118658A CN111385825B CN 111385825 B CN111385825 B CN 111385825B CN 202010118658 A CN202010118658 A CN 202010118658A CN 111385825 B CN111385825 B CN 111385825B
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陈维兴
刘清涛
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Civil Aviation University of China
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
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Abstract

The invention provides a consistency time synchronization method for rapid convergence of a wireless sensor network. The method comprises the steps of constructing a virtual link between two-hop neighbor nodes to enlarge a node reference range and considering consistency iteration updating under a delay condition on the basis. On the basis that only a single-hop node is considered by a reference node in the existing method, the convergence performance of the consistency time synchronization method is optimized by adding two-hop neighbor nodes based on the virtual link construction between the two-hop neighbor nodes of the wireless sensor network, and the relative clock skew is updated and improved under the delay condition, so that the convergence speed is improved well. Compared with other methods such as an average consistency time synchronization method ATS, the method effectively improves the convergence speed.

Description

Consistency time synchronization method for rapid convergence of wireless sensor network
Technical Field
The invention belongs to the technical field of wireless sensor networks, and particularly relates to a consistency time synchronization method for rapid convergence of a wireless sensor network.
Background
Wireless Sensor Networks (WSNs) are Networks that sense, collect, and process monitored environmental information in a distributed manner, and are currently widely used, and time synchronization is a basic support technology for Wireless Sensor Networks. The time synchronization is the basis and the precondition for the wireless sensor network to realize the applications of data fusion, cooperative monitoring, node positioning, intelligent dormancy, communication conflict avoidance and the like. The convergence speed is very important for the time synchronization algorithm, and in the application of the WSNs, particularly large-scale WSNs, the fast convergence time synchronization algorithm is very necessary for the smooth execution of the application. A faster consistency algorithm requires fewer synchronization cycles to achieve time synchronization and, at the same time, can quickly adapt to changes in network topology and time skew. Compared with other algorithms, the average consistency time synchronization algorithm is more robust, but because the distributed synchronization protocol is mainly based on the global node to perform time diffusion and continuous synchronization iteration, and the convergence speed of the distributed time synchronization protocol is slower than that of the classical time synchronization algorithm, a new consistency time synchronization method needs to be found to realize rapid convergence.
Disclosure of Invention
In order to solve the above problems, an object of the present invention is to provide a consistent time synchronization method for fast convergence of a wireless sensor network.
In order to achieve the above object, the consistent time synchronization method for fast convergence of a wireless sensor network provided by the present invention comprises the following steps performed in sequence:
step 1: logic clock skew for initializing initial time of any node i in wireless sensor network
Figure BDA0002392286530000011
To 1, logic clock offset>
Figure BDA0002392286530000012
0, relative clock skew α between nodes ij 1, setting the broadcast period of the node as T;
step 2: node i at time τ i (t)＝lT,l∈N + I.e. in the ith broadcast period T, the broadcast includes its local clock τ i (t l ) Logic clock skew
Figure BDA0002392286530000021
And a logical clock offset>
Figure BDA0002392286530000022
Clock information inside, and records the relative clock skew alpha between the current nodes ij (t l )；
And 3, step 3: when the neighbor node j, j belongs to N i Receiving the clock information<τ i (t l ),
Figure BDA0002392286530000023
>Then, clock information of itself is generated<τ j (t l ),/>
Figure BDA0002392286530000024
>And recording the relative clock skew alpha between the current nodes ji (t l ) Then neighbor nodes j andcombining the clock information of the node i into new combined clock information<τ i (t l ),τ j (t l )；/>
Figure BDA0002392286530000025
>And broadcast to its neighbor nodes;
and 4, step 4: when the node i receives the clock information of the neighbor node<τ j (t l ),τ k (t l )；
Figure BDA0002392286530000026
>Then, the information at this time includes clock information of the neighbor node j of the node i<τ j (t l ),/>
Figure BDA0002392286530000027
>And two-hop neighbor node k, k being N j Clock information of<τ k (t l ),/>
Figure BDA0002392286530000028
>(ii) a At this time, the clock information of the node i is<τ i (t l ),/>
Figure BDA0002392286530000029
>With a relative clock skew of a between the current nodes of alpha ij (t l ) The clock information of the last moment is<τ i (t l-1 ),/>
Figure BDA00023922865300000210
>With relative clock skew between nodes of alpha ij (t l-1 ) (ii) a Then according to the clock information of the neighbor node received by the node i<τ j (t l ),τ k (t l )；/>
Figure BDA00023922865300000211
>For relative clock skew alpha between node i, neighbor node j and two-hop neighbor node k ij Logic clock skew->
Figure BDA00023922865300000212
And a logic clock offset->
Figure BDA00023922865300000213
Carrying out estimation;
and 5: according to the relative clock skew alpha ij Logic clock skew
Figure BDA00023922865300000214
And a logic clock offset->
Figure BDA00023922865300000215
Node i deletes and updates the clock information at the previous time<τ i (t l-1 ),/>
Figure BDA00023922865300000216
>Importing the updated clock information to be called in the next step;
step 6: and jumping to step 2 to circularly execute consistency synchronization.
In step 5, the relative clock skew α between the pair node i, the neighbor node j and the two-hop neighbor node k ij Logic clock skew
Figure BDA00023922865300000217
And a logic clock offset->
Figure BDA00023922865300000218
The method for estimating comprises the following steps:
s1: relative clock skew estimation:
without delay, relative clock skew α between nodes i, j ij The update formula of (2) is:
Figure BDA0002392286530000031
with bounded delay taken into account, as shown in FIG. 2, for a single hop neighborThe residence node delay is
Figure BDA0002392286530000032
For a two-hop neighbor node, since an intermediate node relay is required, two steps are required to complete the transmission of the synchronized clock information, where the processing time Td of the intermediate node is ignored, so its delay ≧>
Figure BDA0002392286530000033
Comprises the following steps:
Figure BDA0002392286530000034
the inter-node delay mainly affects the relative clock skew and thus the logic clock skew estimation. Therefore, in order to avoid the divergence of the synchronization process by applying equation (1), the relative clock skew thereof needs to be compensated, and a weighted average is taken for all the relative clock skews, and the update formula is:
Figure BDA0002392286530000035
s2: logic clock skew estimation:
Figure BDA0002392286530000036
wherein ρ α To converge the gradient coefficient, α ij Is relative clock skew.
S3: logic clock offset estimation:
Figure BDA0002392286530000037
where ρ is b Is the convergence gradient coefficient. The clock skew does not amplify in the case of delays, and the synchronization results are bounded.
Compared with the prior art, the consistency time synchronization method for the rapid convergence of the wireless sensor network provided by the invention has the following advantages and beneficial effects:
the invention optimizes and improves the convergence speed of the consistency time synchronization of the wireless sensor network based on adding the virtual link to the two-hop neighbor node, and the convergence speed is well improved by adding the virtual link to the two-hop neighbor node under the condition of not changing the network topology information. Compared with other methods in the prior art, the method can effectively improve the convergence rate and has superior performance.
Drawings
Fig. 1 is a schematic reference node diagram of a node i in the consistent time synchronization method for fast convergence of a wireless sensor network according to the present invention;
FIG. 2 is a schematic diagram of packet delivery with delay;
FIG. 3 is a diagram of the maximum logical clock error of a wireless sensor network;
FIG. 4 is a diagram showing a relationship between a network topology radius and an algebraic connectivity;
fig. 5 is a graph of the convergence rate of different topologies.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings.
The consistency time synchronization method for the rapid convergence of the wireless sensor network provided by the invention comprises the following steps in sequence:
step 1: logic clock skew for initializing initial time of any node i in wireless sensor network
Figure BDA0002392286530000041
Is 1, the logic clock offset->
Figure BDA0002392286530000042
Is 0, relative clock skew alpha between nodes ij 1, making the broadcast period of the node as T;
the hardware clock of any node i in the wireless sensor network is tau i (t)＝α i t+β i In which α is i For clock skew, which is equivalent to clock speed, ideally it should beIs 1; beta is a beta i Is the clock offset. For nodes in a wireless sensor network, only the local real hardware clock tau can be directly acquired i (t), clock skew α i And clock offset beta i Is not available, so the hardware clock τ i (t) cannot be easily adjusted. Therefore, a logic clock is defined
Figure BDA0002392286530000043
I.e. a synchronized clock, wherein>
Figure BDA0002392286530000044
Is the logic clock skew; />
Figure BDA0002392286530000045
Is the logic clock offset. The aim of the inventive method is to have a global uniform skew for node i>
Figure BDA0002392286530000046
And a global coherency offset>
Figure BDA0002392286530000047
I.e. is>
Figure BDA0002392286530000048
So that the logic clock L of all nodes i (t) achieving consensus.
As shown in fig. 1, in the wireless sensor network of the present invention, the communication relationship between nodes may be represented by a graph G = (V, E) to represent the topological relationship of the information exchange network, where V = {1,2, \8230;, N } represents a node set, N represents the number of nodes in the wireless sensor network, and an edge set
Figure BDA0002392286530000051
Representing the communication relationship among the N nodes.
Step 2: node i at time τ i (t)＝lT,l∈N + I.e. in the ith broadcast period T, the broadcast includes its local clock τ i (t l ) Logic clock skew
Figure BDA0002392286530000052
And logic clock offset->
Figure BDA0002392286530000053
Clock information inside, and records the relative clock skew alpha between the current nodes ij (t l )；
And 3, step 3: when the neighbor node j, j belongs to N i Receiving the clock information<τ i (t l ),
Figure BDA0002392286530000054
>Then, clock information of its own is generated<τ j (t l ),/>
Figure BDA0002392286530000055
>And recording the relative clock skew alpha between the current nodes ji (t l ) Then the clock information of the neighbor node j and the node i are combined into new combined clock information<τ i (t l ),τ j (t l )；/>
Figure BDA0002392286530000056
>And broadcast to its neighbor nodes; />
And 4, step 4: when the node i receives the clock information of the neighbor node<τ j (t l ),τ k (t l )；
Figure BDA0002392286530000057
>Then, the information at this time includes clock information of the neighbor node j of the node i<τ j (t l ),/>
Figure BDA0002392286530000058
>And two-hop neighbor node k, k being N j Clock information of<τ k (t l ),/>
Figure BDA0002392286530000059
>(ii) a At this time, the clock information of the node i is<τ i (t l ),/>
Figure BDA00023922865300000510
>With relative clock skew α between current nodes ij (t l ) The clock information of the previous moment is<τ i (t l-1 ),/>
Figure BDA00023922865300000511
>With relative clock skew between nodes of alpha ij (t l-1 ) (ii) a Then according to the clock information of the neighbor node received by the node i<τ j (t l ),τ k (t l )；/>
Figure BDA00023922865300000512
>For relative clock skew alpha between node i, neighbor node j and two-hop neighbor node k ij Logic clock skew->
Figure BDA00023922865300000513
And a logical clock offset>
Figure BDA00023922865300000514
The following estimates were made:
s1: relative clock skew estimation:
without delay, the relative clock skew α between nodes i, j ij The update formula of (2) is:
Figure BDA00023922865300000515
considering bounded delay, as shown in FIG. 2, for a single-hop neighbor node delay is
Figure BDA00023922865300000516
For two-hop neighbor nodes, because intermediate node relay is needed, two steps are needed to complete transmission of synchronous clock information, and the intermediate node is ignoredIs delayed, so that it is delayed->
Figure BDA00023922865300000517
Comprises the following steps:
Figure BDA0002392286530000061
the inter-node delay mainly affects the relative clock skew and thus the logic clock skew estimation. Therefore, in order to avoid the divergence of the synchronization process by applying equation (1), the relative clock skew thereof needs to be compensated, and a weighted average is taken for all the relative clock skews, and the update formula is:
Figure BDA0002392286530000062
s2: logic clock skew estimation:
Figure BDA0002392286530000063
where ρ is α To converge the gradient coefficient, α ij Is relative clock skew.
S3: logic clock offset estimation:
Figure BDA0002392286530000064
where ρ is b Is the convergence gradient coefficient. The clock skew does not amplify in the case of delays, and the synchronization results are bounded.
And 5: according to the relative clock skew alpha ij Logic clock skew
Figure BDA0002392286530000065
And a logic clock offset->
Figure BDA0002392286530000066
Node i deletes and updates the clock information at the previous time<τ i (t l-1 ),/>
Figure BDA0002392286530000067
>Importing the updated clock information to be called in the next step;
and 6: and jumping to step 2 to circularly execute consistency synchronization.
The invention optimizes the synchronous convergence speed of the wireless sensor network consistent clock through the following ideas. Under the condition of considering transmission delay, the time synchronization of the wireless sensor network is realized by improving the interaction between the intelligent agents of the existing consistency algorithm and the rule of information transmission. Firstly, with reference to fig. 1, a node i transmits its clock information to a neighboring node j, and on this basis, the information of the node i is additionally transmitted to a two-hop neighboring node k through the relay of the neighboring node j, that is, the information of the node i is transmitted to the neighboring node of the neighbor. Therefore, on the premise of not modifying the topological information of the wireless sensor network, the reference range of each node is increased. Then, the node i updates relative clock skew, logic clock skew and logic clock skew according to the received neighbor node information, wherein the neighbor node information is added with information of two-hop neighbor nodes.
In order to verify the effectiveness of the method, the maximum logic clock error is defined as the maximum value of the logic clock error of each node. In consideration of communication delay, fig. 3 shows an error convergence diagram of the method (making it FCATS) and ATS algorithm of the present invention after 300 iterations, and it can be seen from the diagram that after several iterations, the synchronization error is stabilized at 10 -2 And within s, the requirements of most applications can be met. It can also be seen that the logic clock skew error convergence of the ATS algorithm lags the method of the present invention by 20 iteration cycles at the convergence speed, which shows that the convergence of the logic clock skew is improved in speed by adding a virtual link between two-hop nodes of the wireless sensor network in the presence of bounded delay. Linear topologies with different diameters are selected for research, as can be seen from fig. 4Compared with an ATS algorithm, the method has the advantages that the generation number communication rate is relatively increased under the corresponding network diameter by adding the virtual link between the two-hop nodes, and the generation number communication rate is in direct proportion to the convergence speed. The inventor analyzes the convergence condition in different topologies, and respectively selects linear, annular, grid and random network topologies. It can be seen from fig. 5 that the method of the present invention has a shorter convergence time than the ATS algorithm in any of the above types of topologies, and the overall convergence speed is improved by about 50%. In conclusion, compared with the traditional consistency algorithm, the consistency time synchronization method for the rapid convergence of the wireless sensor network provided by the invention is greatly improved in convergence speed.

Claims (1)

1. A consistency time synchronization method for fast convergence of a wireless sensor network is characterized in that: the consistency time synchronization method for the rapid convergence of the wireless sensor network comprises the following steps in sequence:
step 1: logic clock skew for initializing initial time of any node i in wireless sensor network
Figure FDA0004076169170000011
Is 1, the logic clock offset->
Figure FDA0004076169170000012
Is 0, relative clock skew alpha between nodes ij 1, making the broadcast period of the node as T;
step 2: node i at time τ i (t)＝lT,l∈N + I.e. in the ith broadcast period T, the broadcast includes its local clock τ i (t l ) Logic clock skew
Figure FDA0004076169170000013
And a logical clock offset>
Figure FDA0004076169170000014
Clock information inside, and records the phase between the current nodesSkew to clock alpha ij (t l )；
And step 3: when the neighbor node j, j belongs to N i Receiving the clock information
Figure FDA0004076169170000015
Then generates its own clock information &>
Figure FDA0004076169170000016
And records the relative clock skew alpha between the current nodes ji (t l ) And then combines the clock information of the neighbor node j and the node i into new combined clock information->
Figure FDA0004076169170000017
And broadcast to its neighbor nodes;
and 4, step 4: when the node i receives the clock information of the neighbor node
Figure FDA0004076169170000018
Then, the information at this time comprises the clock information ^ of the neighbor node j of the node i>
Figure FDA0004076169170000019
And two-hop neighbor node k, k being N j Clock information of->
Figure FDA00040761691700000110
Figure FDA00040761691700000111
At this time, the clock information of the node i is ^ er>
Figure FDA00040761691700000112
With relative clock skew α between current nodes ij (t l ) The clock information of the last moment is &>
Figure FDA00040761691700000113
Relative clock skew between nodes is alpha ij (t l-1 ) (ii) a Then according to the clock information of the neighbor node received by the node i
Figure FDA00040761691700000114
For relative clock skew alpha among node i, neighbor node j and two-hop neighbor node k ij Logic clock skew>
Figure FDA00040761691700000115
And a logic clock offset->
Figure FDA00040761691700000116
Estimating;
and 5: according to the relative clock skew alpha ij Logic clock skew
Figure FDA0004076169170000021
And a logic clock offset->
Figure FDA0004076169170000022
Based on the evaluation result of (4), the node i deletes and updates the clock information ≥ at the previous time>
Figure FDA0004076169170000023
Importing the updated clock information to be called in the next step;
and 6: skipping to the step 2 to circularly execute consistency synchronization;
in step 4, the relative clock skew α between the pair node i, the neighbor node j and the two-hop neighbor node k ij Logic clock skew
Figure FDA0004076169170000024
And a logical clock offset>
Figure FDA0004076169170000025
The method for estimating comprises the following steps:
s1: relative clock skew estimation:
without delay, the relative clock skew α between nodes i, j ij The update formula of (2) is:
Figure FDA0004076169170000026
with bounded delay taken into account, for a single-hop neighbor node delay of
Figure FDA0004076169170000027
For a two-hop neighbor node, since an intermediate node relay is required, two steps are required to complete the transmission of the synchronized clock information, where the processing time Td of the intermediate node is ignored, so its delay ≧>
Figure FDA0004076169170000028
Comprises the following steps: />
Figure FDA0004076169170000029
The delay between nodes mainly affects the relative clock skew, and thus the logic clock skew estimation, so in order to avoid the divergence of the synchronization process by applying equation (1), the relative clock skew needs to be compensated, a weighted average mode is adopted to take a weighted average of all the relative clock skews, and the update equation is as follows:
Figure FDA00040761691700000210
s2: logic clock skew estimation:
Figure FDA00040761691700000211
where ρ is α To converge the gradient systemNumber, alpha ij Relative clock skew;
s3: logic clock offset estimation:
Figure FDA00040761691700000212
where ρ is b Is the convergence gradient coefficient.
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