CN105933935B - A kind of method for synchronizing time for wireless sensor network - Google Patents
A kind of method for synchronizing time for wireless sensor network Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W28/00—Network traffic management; Network resource management
- H04W28/02—Traffic management, e.g. flow control or congestion control
- H04W28/08—Load balancing or load distribution
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W40/00—Communication routing or communication path finding
- H04W40/02—Communication route or path selection, e.g. power-based or shortest path routing
- H04W40/04—Communication route or path selection, e.g. power-based or shortest path routing based on wireless node resources
- H04W40/10—Communication route or path selection, e.g. power-based or shortest path routing based on wireless node resources based on available power or energy
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W56/00—Synchronisation arrangements
- H04W56/001—Synchronization between nodes
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W84/00—Network topologies
- H04W84/18—Self-organising networks, e.g. ad-hoc networks or sensor networks
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
- Y02D30/00—Reducing energy consumption in communication networks
- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
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Abstract
The present invention relates to communication control fields, a kind of method for synchronizing time for wireless sensor network is provided, when including: topology initialization, a message is broadcasted since root node, all neighbor nodes for receiving message open synchronization request timer, and message is constantly forwarded until making all nodes all start the timer；In earlier synchronous phase, by message exchange, most of node, which is realized, to be synchronized；Node after synchronizing can cancel synchronization request timer, until Network Synchronization stops；In the repetitive requests stage, when the synchronization request timer of a non-synchronization node is to the time, it sends the synchronous message of request and reopens synchro timer if do not replied；And if the message is received by some slave node, the slave node for receiving message starts to execute message exchange synchronized algorithm；This process is performed repeatedly until that all nodes are synchronous.The present invention can be such that all node deadlines in network synchronize, and keep network energy balanced, extend Network morals.
Description
Technical field
The present invention relates to communication control field more particularly to a kind of method for synchronizing time for wireless sensor network.
Background technique
In recent years, in wireless sense network, a critically important problem is exactly to realize time synchronization.It is same in many applications
Step is very crucial, such as wireless sensor network is realized in the fields such as synchronous, secure synchronization and positioning synchronous under water
It is particularly important.Time synchronization, which refers to the process of, provides a common time for distributed system.And a large amount of wireless sensor network
Node of the network application requirement in some region safeguards a time shaft jointly, completes common task to cooperate with.Therefore right
Become particularly significant in the research of time synchronization.
In broadcasted in the method synchronized in pairs using more cluster Sensor Networks, pairs of broadcast coherency protocol is given
(PBS) two kinds of networking modes (GPA, NPA), pairs of broadcast coherency protocol are that a kind of net synchronization capability is preferable, and can effectively drop
The agreement of low synchronizing process power consumption.Especially in dense network, it can greatly reduce the function of entire synchronizing process
It is synchronous to reach the whole network finally under conditions of not losing synchronization accuracy for consumption.But GPA and NPA both networking modes, building
Still many energy are consumed during network.In the low-power consumption method for synchronizing time based on Embedded Network Device, purpose
It is to reduce whole network as far as possible to synchronize required power consumption, it makes full use of RRP model and SRP model, it guarantees that
Sufficiently high synchronization accuracy.Especially in denser network, the power consumption of network becomes very few.But pass through theory analysis
And emulation experiment, in some cases, which can not make all nodes in network range synchronous.Main cause is algorithm
Slave node in design can not send any message, this results in the part neighbours of slave node to have certain probability complete
At synchronization.
Summary of the invention
Present invention mainly solves energy consumption in prior art building network development process is more, and cannot make in network range
It the technical issues of all nodes reach time synchronization proposes a kind of method for synchronizing time for wireless sensor network, can make
All nodes are fully synchronized in network and keep low-power consumption, and the balancing energy of root node selection strategy.
The present invention provides a kind of method for synchronizing time for wireless sensor network, including following procedure:
Step 100, it determines root node, and opens the synchronization request timer of each node；
Step 200, the node in wireless sensor network is synchronized in advance, including following sub-step:
Step 201, the message of one I type of root node broadcast, wherein the message of the I type is that notice initialization is same
The message of step process；
Step 202, for receiving the nodes of all undefined types of I message, synchronization request timer is closed simultaneously
Open synchro timer；After the synchro timer of undefined type node is to the time, the node type of node becomes backbone section
Point, while broadcasting the message of S type, wherein the message of the S type is synchronous message, and destination address is its father node, and
Carry the first local time stamp T 1；
Step 203, for receiving all nodes of S message, if being matched with the destination address of S message and being
Backbone type node then recording the second local time stamp T2, and replys the message of a type-A, and when sending, record is sent
Time stamp T 3, wherein the message of the type-A is the synchronous message of confirmation, comprising the second local time stamp T2 and sends type-A
The sending time of message stabs T3；If the destination address of S message mismatch and synchro timer be in operating status,
Third local time stamp T5 is recorded, and stops synchro timer, marking the type of the node is slave node；
Step 204, for receiving all nodes of the message of type-A, the matched node of destination address with type-A, note
The 4th local time stamp T4 is recorded, formula is utilizedDetermine time offset, wherein △
(α, β) indicates time offset, and using determining time offset, carries out time synchronization to node；With the mesh of type-A message
The unmatched node in address, read type-A message in the second local time stamp, it is true using formula △ (alpha, gamma)=T2-T5
It fixes time offset, wherein △ (alpha, gamma) indicates time offset, and using determining time offset, when carrying out to node
Between it is synchronous；
Step 205, the node after time synchronization makes surrounding undefined section to the message of surroundings nodes broadcast initialization
Point successively executes step 202 to 204, so that entire wireless sensor network be made to carry out earlier time synchronization；Until in network no longer
There are broadcast message, the earlier synchronization of Stop node；
Step 300, using synchronization request timer, the non-synchronization node in wireless sense network is synchronized, including with
Lower sub-step:
Step 301, after the synchronization request timer of undefined type node is to the time, which sends disappearing for R type
Breath；
Step 302, the type of the node is become if it is slave node for receiving all nodes of R message
Backbone node, and broadcast the message of I type, wherein the message of R type is the synchronous message of repetitive requests, and the message of I type is
The message of the synchronous process of notice initialization；
Step 303, for receiving all nodes of I message, step 202 is successively executed to 204 and carries out time synchronizations；
Step 304, step 301 is repeated in 303, is synchronized until the node deadlines all in wireless sensor network.
Further, in step 100, the mode of root node is determined are as follows:
First it is subsynchronous when, root node random selection, the start node as time synchronization process；
When synchronizing again, the node for selecting the energy residual in the last round of neighbours for synchronizing middle root node most is as new one
The root node of wheel.
Further, in step 100, it determines root node, and opens the synchronization request timer of each node, comprising:
Since root node, in the form of flooding, to the message of surroundings nodes broadcast Z type, wherein the Z type
Message is the message of notice setting synchronization request timer；
The node of Z message is received, synchronization request timer is set, and continues to broadcast the Z type to surroundings nodes
Message.
A kind of method for synchronizing time for wireless sensor network provided by the invention is low in a kind of wireless sense network
The method for synchronizing time of power consumption is arranged a synchronization to each node and is asked in the whole network incipient stage with the sequence of spanning tree
It seeks timer, in synchronizing process, the two kinds of method of SRP and RRP is combined, because PN node does not need to send out in RRP method
Any message is sent, so, this method can still keep the characteristic of low-power consumption.And when network node density is bigger, it is this excellent
Gesture becomes apparent from.Synchronizing process does not need to be grouped, not additional energy consumption expense.Invention increases multiple timers to come
Request synchronizes, so that all nodes can be completed to synchronize, when node cannot synchronize, timer can be overtime, thus to neighbours
In slave node initiate request so that all nodes can be completed to synchronize, realize that the whole network is synchronous.In addition, this method provides
A kind of root node selection strategy selects dump energy is most in the adjacent node of root node node as new root node,
Energy can be made more balanced.The present invention uses the form of timer request, it is ensured that all nodes of whole network are realized
It is synchronous, any node is not omitted, and the power consumption of synchronizing process keeps very low, which can also protect in mostly wheel synchronizing process
The node load balance in network is held, to extend Network morals.
Detailed description of the invention
Fig. 1 is implementation flow chart of the present invention for the method for synchronizing time of wireless sensor network；
Fig. 2 is the schematic diagram of the original state of network；
Fig. 3 is the schematic diagram that synchronization request timer is arranged；
Fig. 4 is the schematic diagram of earlier synchronous phase；
Fig. 5 is the schematic diagram in repetitive requests stage；
Fig. 6 is the schematic diagram for completing the repetitive requests stage；
Fig. 7 is the schematic diagram for selecting next round root node；
Fig. 8 is the schematic diagram of SRP method and RRP method.
Specific embodiment
To keep the technical problems solved, the adopted technical scheme and the technical effect achieved by the invention clearer, below
The present invention is described in further detail in conjunction with the accompanying drawings and embodiments.It is understood that specific implementation described herein
Example is used only for explaining the present invention rather than limiting the invention.It also should be noted that for ease of description, attached drawing
In only some but not all of the content related to the present invention is shown.
For some Time synchronization algorithms based on spanning tree, the node in network is divided into 3 seed types: (1) undefined section
Point: being the original state of all nodes, i.e., non-synchronous regime；(2) slave node: being that synchronous node is completed with RRP algorithm, together
Broadcast message is not sent during step.(3) backbone node: it is the node synchronous using SRP algorithm, constitutes the core section of spanning tree
Point.All nodes of original state are all undefined nodes, i.e., are all non-synchronization nodes.Due to algorithm or signal problem,
After the completion of common synchronization algorithm, does not complete and synchronize there are also part of nodes in network.The present invention proposes what a kind of repetitive requests synchronized
Scheme, the method by the way that initialization timer is arranged.
Fig. 1 is implementation flow chart of the present invention for the method for synchronizing time of wireless sensor network.As shown in Figure 1, this hair
The method for synchronizing time for wireless sensor network that bright embodiment provides includes:
Step 100, it determines root node, and opens the synchronization request timer of each node.
The targeted wireless sensor network of the present embodiment is the distributed network as made of multiple sensors combination of nodes, respectively
A node operates on different chips, possesses oneself clock, so the time is nonsynchronous.Fig. 2 is the original state of network.
In the present embodiment, the mode of root node is determined are as follows: randomly choose for the first time, start to save as time synchronization process of the present invention
Point.When building topology again later, the node for selecting the energy residual in the last round of neighbours for synchronizing middle root node most is as new
The root node of one wheel.
After determining root node, whole network is since root node, in the form of flooding, is to surroundings nodes broadcast type
The data packet of Z, the node for receiving data packet is checked if the type of data packet is Z, synchronization request timer is just arranged, and continue
The message is broadcasted, so that all nodes in network are switched on synchronization request timer, at this point, other sections in addition to root node
Point all sets undefined node type for node type.As all nodes in addition to node A in Fig. 3 have been switched on synchronization
Request timer.
Wherein, timer is a tool critically important in the present invention, for assisting completing timer task.In general nothing
In wire module, there is the design of timer.Each timer includes an initial value, for indicate timer timing when
Between, when a timer fires, timing is since 0, when timer timing is equal to the initial value of setting, i.e. timer to time
?.The synchronization request timer in the present embodiment, is switched in the incipient stage, and realization is closed after synchronizing；If formerly
After phase synchronously completes, after synchronization request timer to time, node is not synchronized also, then synchronizes request.Its initial value etc.
In the period (obtaining an average value by experiment) synchronous in advance.
The data usually carried in the data packet (broadcast message) that the present invention uses include: destination address, source address, message
Type, father node, grade and timestamp, wherein destination address is the destination address of broadcast data packet；Source address is to send message
Node address；Type of message indicates the type of the message, used in the different phase of time synchronization process, shares 6 kinds of message classes
Type, specifically, C indicates that the message of synchronization request timer is arranged in message, Z expression notice for selecting root node, I indicates logical
Know that the message of the synchronous process of initialization, S indicate that the message of synchronization, A indicate that the synchronous message of confirmation, R indicate that repetitive requests are same
The message of step；Father node is the parent node address for recording sending node；Grade is the grade (default is -1) of sending node, is used to
Indicate level of the node in spanning tree；Timestamp can be multiple, such as sending time stamp and local time stamp etc..
Step 200, the node in wireless sensor network is synchronized in advance, including following procedure:
Step 201, one initial message of root node broadcast (I type).Referring to Fig. 3, for example, node A is chosen as root section
Point, root node A broadcast the message that a type is I.
Step 202, for receiving the nodes of all undefined types of I message, by the node of transmission types I message
Labeled as the father node of oneself, the grade that the grade of oneself is set as sending information node is added 1, closes synchronization request timing
Device, while opening synchro timer.Later, if after the synchro timer to time of the node of any one undefined type,
The node of synchro timer to time can become the node type of oneself backbone node, while broadcasting a type is disappearing for S
It ceases (synchronization message), wherein type is that the message destination address of S is the father node just recorded, and carries the first local zone time
Stab T1；If synchro timer not timed out of the node of any one undefined type, closing the synchronization request timer.
In practical applications, the state that can check a timer illustrates also to be less than the time if timer is in operating status, such as
Fruit timer is in idle condition, and illustrates that time is up.
The synchro timer in the present embodiment, for selecting backbone node, all undefined nodes receive backbone
When node sends the message of I type (message of initialization procedure), synchro timer is opened, and realizes the node after synchronizing and closes
Synchro timer.If time is up for synchro timer when not synchronous, which is just converted to backbone node for oneself.
In order to avoid multiple node conflicts, the initial value of synchro timer is a random value.
For example, Fig. 3 interior joint E, B, C, G are the sections for receiving the undefined type of message (i.e. initial message) of I type
The node A for sending initial message is labeled as the father node of oneself, the grade of oneself is set as saving by point, node E, B, C, G
The grade of point A adds 1, while opening synchro timer.Later, if node E, C synchro timer are to the time, node E, C can be
The node type of oneself becomes backbone node, while broadcasting a synchronization message (message that type is S), the synchronization message purpose
Address is the father node A just recorded, records local zone time T1 (timestamp is retained in local, does not put in the message) at this time,
If synchronization request timer is in operating status, the synchronization request timer is closed.
Step 203, for receiving all nodes that type is S (i.e. synchronization message), if the purpose with the synchronization message
The node of address matching and the node are backbone type node, then recording the second local time stamp is that T2 (receives S type to disappear
The time of breath), and the message (i.e. confirmation message) of a type-A is replied, when sending, record sending time stabs T3, the A class
Sending time stamp in the message of type comprising the second local time stamp and reply type-A message；If the purpose of the synchronization message
The synchro timer of the unmatched node in address and the node is in operating status, then record third local time stamp is T5
(no need to send go out the timestamp), and stop synchro timer, marking the type of the node is slave node；If discontented
The node of sufficient two above condition ignores this message.
For example, node A, B, G receive the synchronization message of node E or C broadcast, if the type is the mesh of the synchronization message of S
Address be node A and node A be backbone type node, then it is T2 that node A, which records the second local time stamp, reply one
Type is the confirmation message of A, wherein comprising receiving the time T2 of synchronization message and sending the hair of type-A message in confirmation message
Send time stamp T 3；If the synchro timer that the destination address of B, G message is not node B, G and node B, G is in operation shape
State then record third local time stamp is T5, and stops synchro timer, and the type of flag node B, G is slave node.No
The node for meeting two above condition ignores this message.
Step 204, for receiving a type for all nodes of the message (i.e. confirmation message) of A, with confirmation message
The matched node of destination address, the 4th local time stamp of record are T4, and using carrying in T1, T4 and the confirmation message
This 4 timestamps of T2, T3 carry out time offset estimation using SRP method, after determining time offset and father node
Carry out time synchronization；With the unmatched node of destination address of confirmation message, the T2 value in confirmation message is read, according to remembering before
The time stamp T 5 of record and this T2 can carry out time offset estimation using RRP method to oneself and father node, thus with
Father node is synchronous.
Be illustrated referring to Fig. 8 to SRP method and RRP method: Fig. 8 interior joint α is synchronized node, and Node β
It is the pre- node synchronized with γ.What solid line and dotted line indicated in Fig. 8 is all broadcast message, the number for the message that solid line indicates
It is oneself according to destination address in content, dotted line indicates that the destination address is not directed to oneself.
SRP method: Node β is the synchronization completed using SRP, and at a time, it is S that Node β, which broadcasts a type of message,
The message of (synchronization message type) simultaneously records the local time stamp T 1 of transmission first.Receive the node alpha that this type is S message, note
The second local time stamp T2 is recorded, sending time is then recorded and stabs T3, and broadcasts and replys a type disappearing for A (confirmation type)
It ceases, the value of T2 and T3 is carried in the message.It receives the Node β replied message and records the 4th local zone time T4.At this point, Node β
The calculating of time offset is just carried out according to the value of T1, T2, T3, T4, the calculation formula of time offset is as follows:
Wherein, △ (α, β) indicates the time offset of any synchronization node α and any presynchronization Node β, further
The local zone time of oneself is added the time offset by Node β, is considered as Node β and is had been completed time synchronization.
RRP method: the synchronization that node γ utilizes RRP to complete, after the message that the type of message for receiving Node β broadcast is S,
Record third local zone time T5.When node alpha broadcast type is the message of A (confirmation type), node γ also has received the message,
And the second time stamp T 2 is also obtained.Using the calculating of T2 and T5 deadline offset, calculation formula is as follows:
△ (α, γ)=T2-T5
Wherein, △ (alpha, gamma) indicates the time offset of any synchronization node α and any presynchronization node γ, into one
It walks node B and the local zone time of oneself is added into △ (alpha, gamma), be considered as completing with node γ synchronous.
For example, if the destination address of the confirmation message is directed to the (destination of node E, C and confirmation message node E, C
Location matching), then record local time stamp is T4, then the node can be with carrying in T1, T4 and the confirmation message
This 4 timestamps of T2, T3 carry out time deviation estimation with SRP, thus synchronous with father node.If the mesh of the confirmation message
Address be not directed to node B, G (such as node B, G and the destination address of confirmation message mismatch), then reading the T2 in message
Value, according to the time stamp T 5 that records before and this T2 can to oneself and father node using RRP progress time deviation estimation,
To synchronous with father node.The node for being unsatisfactory for two above condition ignores the message.
Step 205, the node after time synchronization makes surrounding undefined section to the message of surroundings nodes broadcast initialization
Point successively executes step 202 to 204, so that entire wireless sensor network be made to carry out earlier time synchronization.
Then step 202- step 204 starts constantly to execute, and time synchronization process is made to continue to extend, until in network not
There is broadcast message again, synchronizing can not continue at this time, and the feature of the slave node defined according to us, such section
Point cannot broadcast the message, so earlier synchronizing process cannot be guaranteed that the node of slave node surrounding neighbours can also synchronize, pass through
Experiment discovery, has quite a few node that cannot synchronize (particular number is related with topology), synchronize stopped at this time.
This step is synchronous with RRP progress message exchange using SRP since root node, completes earlier synchronous phase.It should
Process can make most of node complete to synchronize, and there is backbone node and slave node now in network, due to signal problem or
Starting causes the reason of losing message and algorithm itself more slowly, there is likely to be the node of undefined type in network, fails
Disposably synchronize in step 200.As shown in figure 4, wherein realize that the node in circle is the node that the process is synchronized, and circle
The node (K, R, O in such as Fig. 5) of outside is all not synchronous.Synchronization so in order to synchronize these nodes, in step 100
Request timer just plays a role.
Step 300, using synchronization request timer, the non-synchronization node in wireless sense network is synchronized, including with
Lower process:
Step 301, after the synchronization request timer of the node of undefined type is to the time, which sends out to surroundings nodes
Sending type is the message (i.e. synchronization request message) of R, such as node K and R in Fig. 5.
Step 302, if the node for receiving synchronization request message is slave node (node G, J in such as Fig. 5), then will
The type of the node becomes backbone node, and broadcast type is the initial message of I.
Step 303, for receiving all nodes of I message, step 202 is triggered execution, has started a synchronization
Process successively executes step 202 to 204 progress time synchronizations.Other types node ignores the message.
Step 304, step 301 is repeated in 303, is synchronized until the node deadlines all in wireless sensor network.
For example, the node M in Fig. 5 is the node of undefined type, after the synchronization request timer of node M is to the time,
The message that the node is R to surroundings nodes transmission types, since its surroundings nodes K, N are also the node of undefined type, so
If can not receive any reply (this refers to the message that type is I) in specified time, synchronization request message is sent again,
Until receiving I message, step 301 is further repeated in 303 progress time synchronizations.
Referring to Fig. 5, for example, node M sends synchronization after the synchronization request timer of undefined type node M is to the time
Request message.If can not receive any reply in node M 10s, synchronization request message is sent again.When undefined type section
After the synchronization request timer to time of point K and R, the message (synchronization request message) of R type is sent, synchronization request message is received
Node G, J be slave node, then the node type of oneself is become backbone node by node G, J, and send initialization and disappear
Breath.Then step 202- step 204 is triggered execution；Other types node ignores the message.
In order to keep the energy of each root node of wireless sensor network more balanced, the present invention may be selected different root nodes and carry out
The multiple network optimization (time synchronization).The mode of root node selection in the present embodiment are as follows: randomly choose for the first time, as this hair
The start node of bright time synchronization process.When building topology again later, the energy in the last round of neighbours for synchronizing middle root node is selected
Root node of the remaining most node of amount as a new round.Originally the node type for the root node selected become backbone node, it is specified that
Its grade is 0.Such as the A in Fig. 3 is chosen as root node in the first round.And for the second wheel, as shown in fig. 7, all neighbours of A
It occupies in node, the dump energy of B is most, is chosen as the root node of next round.
After completing the aforementioned steps, all nodes in whole network all realize time synchronization.Synchronous state is such as
Shown in Fig. 6.All nodes are all backbone node or slave node.
Provided by the present invention for the method for synchronizing time of wireless sensor network, (1) in topology initialization, from root node
Start to broadcast a message, all neighbor nodes for receiving message open synchronization request timer, and message is constantly forwarded until making
All nodes all start the timer；(2) in earlier synchronous phase, by message exchange, most of node, which is realized, to be synchronized；It is synchronous
Node afterwards can cancel synchronization request timer, until Network Synchronization stops；(3) the repetitive requests stage, when a non-synchronization node
Synchronization request timer to the time when, it sends the synchronous message of request and reopens synchronization timing if do not replied
Device；And if the message is received by some slave node, the slave node for receiving message starts execution message exchange and synchronizes
Algorithm；This process is performed repeatedly until that all nodes are synchronous.The present invention is a kind of time of the low-power consumption in wireless sense network
Synchronous method, with the sequence of spanning tree, is provided with a synchronization request timing to each node in the whole network incipient stage
Device combines the two kinds of method of SRP and RRP and carries out time synchronization, can make whole nodes in region that can synchronize,
Corresponding adjustment is had also been made to the timing of synchronizing process, ensure that synchronous correctness.Root node selection strategy is increased, can be made
The balancing energy of whole network extends Network morals.Since in RRP method, slave node disappears no need to send any
Breath, so the present invention can keep the characteristic of low-power consumption.And when network node density is bigger, this advantage becomes very bright
It is aobvious.Synchronizing process does not need to be grouped, not additional energy consumption expense.
Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention., rather than its limitations；To the greatest extent
Present invention has been described in detail with reference to the aforementioned embodiments for pipe, those skilled in the art should understand that: its is right
Technical solution documented by foregoing embodiments is modified, or is equally replaced to some or all of the technical features
It changes, the range for technical solution of various embodiments of the present invention that it does not separate the essence of the corresponding technical solution.
Claims (3)
1. a kind of method for synchronizing time for wireless sensor network, which is characterized in that including following procedure:
Step 100, it determines root node, and opens the synchronization request timer of each node；
Step 200, the node in wireless sensor network is synchronized in advance, including following sub-step:
Step 201, the message of one I type of root node broadcast, wherein the message of the I type is that notice initialization synchronized
The message of journey；
Step 202, it for receiving the nodes of all undefined types of I message, closes synchronization request timer and simultaneously opens
Synchro timer；After the synchro timer of undefined type node is to the time, the node type of node becomes backbone node, together
When broadcast S type message, wherein the message of the S type is synchronous message, and destination address is its father node, and is carried
First local time stamp T 1；
Step 203, for receiving all nodes of S message, if being matched with the destination address of S message and being backbone
Type node then recording the second local time stamp T2, and replys the message of a type-A, records sending time when sending
Stab T3, wherein the message of the type-A is the synchronous message of confirmation, comprising the second local time stamp T2 and sends type-A message
Sending time stab T3；If the destination address of S message mismatches and synchro timer is recorded in operating status
Third local time stamp T5, and stop synchro timer, marking the type of the node is slave node；
Step 204, for receiving all nodes of the message of type-A, the matched node of destination address with type-A, record the
Four local time stamp T4, utilize formulaDetermine time offset, wherein △ (α,
It β) indicates time offset, and using determining time offset, time synchronization is carried out to node；With the purpose of type-A message
The unmatched node in address reads the second local time stamp in type-A message, is determined using formula △ (alpha, gamma)=T2-T5
Time offset, wherein △ (alpha, gamma) indicates time offset, and using determining time offset, carries out the time to node
It is synchronous；
Step 205, the node after time synchronization makes surrounding undefined node to the message of surroundings nodes broadcast initialization,
Step 202 is successively executed to 204, so that entire wireless sensor network be made to carry out earlier time synchronization；Until in network there is no
Broadcast message, the earlier synchronization of Stop node；
Step 300, using synchronization request timer, the non-synchronization node in wireless sense network is synchronized, including following son
Step:
Step 301, after the synchronization request timer of undefined type node is to the time, which sends the message of R type；
Step 302, the type of the node is become into backbone if it is slave node for receiving all nodes of R message
Node, and broadcast the message of I type, wherein the message of R type is the synchronous message of repetitive requests, and the message of I type is notice
Initialize the message of synchronous process；
Step 303, for receiving all nodes of I message, step 202 is successively executed to 204 and carries out time synchronizations；
Step 304, step 301 is repeated in 303, is synchronized until the node deadlines all in wireless sensor network.
2. the method for synchronizing time according to claim 1 for wireless sensor network, which is characterized in that in step 100
In, determine the mode of root node are as follows:
First it is subsynchronous when, root node random selection, the start node as time synchronization process；
When synchronizing again, the node for selecting the energy residual in the last round of neighbours for synchronizing middle root node most is as a new round
Root node.
3. the method for synchronizing time according to claim 1 or 2 for wireless sensor network, which is characterized in that in step
In 100, root node is determined, and open the synchronization request timer of each node, comprising:
Since root node, in the form of flooding, to the message of surroundings nodes broadcast Z type, wherein the message of the Z type
For the message of notice setting synchronization request timer；
The node of Z message is received, synchronization request timer is set, and continues to broadcast disappearing for the Z type to surroundings nodes
Breath.
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