CN101977433B - Method for average clock synchronization of wireless sensor network - Google Patents
Method for average clock synchronization of wireless sensor network Download PDFInfo
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Abstract
The invention discloses a method for the average clock synchronization of a wireless sensor network, which is mainly used for solving the problems that the exiting method is not suitable for low-density networks and has restrictions on the expansibility for networks. The method comprises the following steps: (1) abstracting a topological structure of a wireless sensor network into a graphical model G, and taking a clock value of a network node at an initial moment as the initial value of the node; (2) simultaneously transferring data packets to carry out communication by edges eij controlled by a switching signal s (k), and sending and receiving three packets by nodes i and j connected with the edges eij so as to realize the average time operations of the nodes and complete the updating of respective local clock; and (3) repeating the step 2 until the maximum difference between network nodes gradually tends to an error within an allowable range, thereby realizing the average clock synchronization of the network and the continuous operation of network nodes, and keeping the synchronized state of the clocks stably. The invention can be applied to any high-density or low-density networks so as to synchronize the network with the average value of the nodes, and can stably keep the synchronized state of the clocks, thereby improving the expansibility for network.
Description
Technical field
The invention belongs to the wireless sensor network technology field, relate to a kind of method for average clock synchronization, the method can be used for solving in network communication of wireless sensor, how to make the distributed time synchronized that reaches fast of network node, improve the extensibility of network, effectively reduce the problem in energy loss and prolonging wireless sensor network life-span.
Background technology
In the epoch of current information technology develop rapidly, the progress of microelectric technique, computing technique and wireless communication technology etc., promoted the fast development of low-power consumption Multifunction Sensor, make its can the integrated information collection in micro volume, data are processed and the several functions such as radio communication.Wireless sensor network (wireless sensor network, WSN) be exactly to form by being deployed in cheap microsensor nodes a large amount of in surveyed area, the network system of the multi-hop ad hoc formed by communication, its objective is the information of perceptive object in perception collaboratively, acquisition and processing network's coverage area, and send to the observer.People can pass through the direct perception of sensing network objective world, thereby greatly expand the function of existing network and the ability in the human knowledge world.The application prospect of WSN is boundless, can be widely used in military affairs, environment measuring and forecast, health care, between Smart Home, building condition monitoring, complicated machinery monitoring, urban transportation, space exploration, large car and storehouse management, and the fields such as safety detection of airport, large scale industry garden.Along with further investigation and the extensive use of sensor network, sensor network will be deep into human lives's every field gradually.
Sensor node is comprised of some low power consuming devices, so, unlike legacy network, WSN has its resource constraint, comprises the limited energy, little communication range, low bandwidth and limited processing and the storage capacity of each node; Simultaneously WSN also has design constraint, i.e. the environment based on monitoring and for application dependency.In sensor network, most nodes are unattended, and each node battery pack is only carried a small amount of limited energy, is the main energy sources of sensor node, also can lot of energy even intercepted communication.Due to those above-mentioned limitation, make the consumption of energy become problem, can not change easily battery or sensor node in complex environment, when electric weight exhausts, sensor node just can't be worked, and can affect the life-span of network, so the preservation of energy plays a very important role.
In wireless sensor network, nodal clock is synchronously a disclosed research topic, and this sends for route and be energy-conservation is very important.Energy can be saved when signal conflict with while repeating to transmit all seldom, when node is intermittent work, also energy can be saved.The data that transducer obtains must have correct time and positional information, otherwise the information gathered is also incomplete.In addition, the synchronous etc. of the timing of the data fusion of sensor node, time division multiple access TDMA, dormancy period all requires sensor node to have the unified time.Length of a game synchronously allows internode collaboration and sequentially transmits on schedule data.On the basis of time synchronized between node, with the seasonal effect in time series target location detect can estimating target the speed of service and direction, can determine that by the propagation time of measuring sound node arrives the distance of sound source or the position of sound source.
NTP (Network Time Protocol) agreement is the upper widely used NTP (Network Time Protocol) of Internet, but is only applicable to the wired network system that structure is relatively stable, link is seldom failed; Gps system can keep synchronizeing with universal time UTC (Universal TimeCoordinated) with the nanosecond precision, but need the fixing expensive receiver of configuration, can't use gps system in indoor, forest or in waiting the environment of blindage under water simultaneously.Therefore, consider the characteristics of sensor network, and the constraint of the aspects such as energy, price and volume, they all are not suitable for being applied in sensor network.Jeremy Elson and Kay Romer propose first and have set forth the research topic of the Time Synchronization Mechanism in the sensor network in the Hot Nets-I in August, 2002 international conference, in the sensor network research field, have caused concern.University and scientific research institution start this field is furtherd investigate one after another, proposed multiple Time Synchronization Mechanism, wherein RBS (Reference BroadcastSynchronization), TINY/MINI-SYNC and TPSN (Timing-sync Protocol forSensor Networks) are considered to three kinds of basic synchronization mechanisms.RBS mechanism is based on recipient-recipient's clock synchronous: a node broadcasts clock reference grouping, two times of advent that node adopts respectively local clock to record reference packet in broadcast domain, by exchanging, realize the clock synchronous between them writing time.All nodes in broadcast domain have to share the temporal information that receives beacon, need a large amount of data of exchange.TINY/MINI-SYNC is the synchronization mechanism of simple lightweight: linear change is followed in the clock drift of supposing node, and the skew between two nodes is also linear so, can divide into groups to estimate two internodal Optimum Matching side-play amounts by the exchange markers.The uncertain timing parameter of accurate estimation.TPSN adopts hierarchical structure to realize the time synchronized of whole network node: all nodes carry out the logic classification according to hierarchical structure, by the node based on sender-recipient to mode, each node can be synchronizeed with certain node of upper level, thus realize all nodes all with the time synchronized of root node.Some other synchronization mechanism also has delay measurements time synchronized (delay measurement time synchronization, DMTS) mechanism, lightweighttree-based synchronization (LTS) synchronized algorithm, Flooding Time SynchronizationProtocol (FTSP), Pairwise broadcast synchronization (PBS) etc.In traditional simultaneous operation, two nodes carry out information exchange and will transmit packet twice, local zone time when including node in packet and receiving information and the time value in information, be received the enough information of Shi Caiyou at packet for the second time and calculate packet delay and internodal time difference, concrete communication process as shown in Figure 2.It can only be step structure that such working mechanism makes the communication of network node, and namely the network node time value all can only be synchronized with the clock of a root node.In general, the working mechanism of these synchronous protocols is used the network-external node as reference basic point (carrying hardware time synchronized device or the UTC coordinated universal time of GPS), or the node of use network internal is as root node, in network, other nodes are by communicating with these reference nodes, the swap data package informatin, finally be synchronized with these reference nodes, form hierarchic structure.
In sum, existing clock synchronization protocol is owing to adopting above-mentioned this level layer structure successively to carry out synchronously, thereby for large-scale network, increase along with the number of plies, make inter-node communication time delay error cumulative rises, not only affect synchronization accuracy and convergence rate, and limited the extensibility of network; Simultaneously because this structure also requires can both mutually communicate between all neighbor nodes of each network node, make this structure to be only applicable to the larger high density network of synchronous limit density, limited the synchronous realization of the low-density network that opposite side density is less.
Summary of the invention
The object of the invention is to overcome the deficiency of above-mentioned existing protocol, a kind of method for average clock synchronization that is applicable to the wireless sensor network of high density arbitrarily or low-density network has been proposed, to reduce the accumulation of inter-node communication time delay error, improve synchronization accuracy and convergence rate, strengthen the extensibility of network.
For achieving the above object, technical scheme of the present invention comprises the steps:
(1) topological structure of wireless sensor network is abstracted into to graph model, draws out this graph model G;
(2) to graph model G={N, V, the node in E} carries out random number 1,2 ..., N, wherein, N means sensor node sum in network, and V means the sensor node collection, and E means the set of all nonoriented edges;
(3) using the clock value of initial time network node as the node initial value, be labeled as T
1(0), T
2(0) ..., T
n(0);
(4) in the operating process to graph model G, the limit set { e controlled by switching signal s (k)
ijcorresponding node communicates as follows simultaneously, and guarantee can not cause communication contention aware, wherein k generates limit set { e
ijiterations, the different corresponding limits set of the value of k { e
ijalso different, in network, all communicated by letter time a time in all limits, k put to 1, again iteration:
(4a) limit set { e
ijin limit e
ijcorresponding node i and j communicate, and node i is by its local zone time T
i1send to node j, node j is at T
j1constantly receive this packet;
(4b) after node j receives the packet from node i, the local zone time T now by oneself
j1reply to node i, node i is at T
i2after constantly receiving this packet, calculate and upgrade local zone time and be: T '
i2=(T
j1+ T
i2+ tau (1))/2, wherein tau (1) is the passing time of node j while sending to the node i packet;
(4c) node i is when upgrading local zone time, the local zone time T now by oneself
i2reply to node j, as node j at T
i2after constantly receiving this packet, calculate and upgrade local zone time and be: T '
j2=(T
i2+ T
j2+ tau (2))/2, wherein tau (2) is the passing time of node i while sending to node j packet;
(5) repeated execution of steps (4), until the progressive error be tending towards in an allowed band of the maximum residual quantity between network node, it is synchronous that network reaches average clock, network node continuous firing, the stable clock synchronous state that keeps.
In above-mentioned method, the described graph model of step (1), in order to mean the topological structure of wireless sensor network, be provided with N node in figure, each node i represents a transducer, records local clock, i=1 wherein, 2, ..., N, internodal fillet e
ijcan transmit packet between representation node and communicate, j=1 wherein, 2 ..., N, i ≠ j.
In above-mentioned method, the described switching signal s of step (4) (k), be used for controlling limit collection { e
ijat synchronization, communicate respectively, guaranteed the distributed operation that average clock is synchronous.
The present invention is not owing to relying on any reference node, and any one node of network internal all can be used as start node and opens distributed average clock simultaneous operation, so be applicable to high density or low-density network arbitrarily; The method that simultaneously due to the present invention, adopts compromise to be averaging, by upgrading the formula of local zone time, make the node time Convergence in intermediate mean values, so maintenance synchronous regime that can be more stable, reduce the accumulation of inter-node communication time delay error, improved the extensibility of network.
The accompanying drawing explanation
Fig. 1 is FB(flow block) of the present invention;
Fig. 2 is existing methodical clock synchronous schematic diagram;
Fig. 3 is the synchronous schematic diagram of average clock of the present invention;
Fig. 4 is the graph model of wireless sensor network in the embodiment of the present invention;
Fig. 5 is change curve when in the embodiment of the present invention, the local clock of network node reaches synchronous;
Fig. 6 is the network diagram of the different edge density of 20 nodes that adopt of emulation experiment of the present invention;
Fig. 7 is the simulation experiment result figure that Fig. 6 is corresponding;
Fig. 8 is the network diagram of different edge density of 50 nodes of the random generation that adopts of emulation experiment of the present invention;
Fig. 9 is the simulation experiment result figure that Fig. 8 is corresponding.
Embodiment
The present invention mainly comprises two parts: the initialization node, distributed average clock is synchronous.Concrete step is described below with reference to Fig. 1:
The present embodiment realizes that mainly for a concrete wireless sensor network average clock is synchronous, the graph model of this network as shown in Figure 4, in order to mean the topological structure of wireless sensor network, 10 nodes are arranged in Fig. 4, each node i represents a transducer, record local clock, i=1 wherein, 2 ..., limit e in 10, Fig. 4
ijcan transmit packet between representation node and communicate, j=1 wherein, 2 ..., 10, i ≠ j; 10 nodes in this Fig. 4 are carried out to random number 1,2..., 10, and generating at random one group, to obey average be 0.5, the value of the Gaussian Profile that variance is 1 is as node initial value ,-0.9676,0.4115,1.0992,0.3438,0.3712,1.5497,0.3698 ,-0.7042,1.7921,0.0491.
The distributed average clock of step 2. is synchronous.
Switching signal s (k) is used for controlling limit collection { e
ijcommunicate respectively i.e. s (k)={ e at synchronization
ij, to guarantee can not cause communication contention aware, realize the distributed operation that average clock is synchronous, wherein k generates limit set { e
ijiterations, value is 1,2,3,4,5.
2.1) when k=1, s (1)={ e
12, e
34, e
57, e
8,10, i.e. node 1 and node 2, node 3 and node 4, node 5 and node 7, node 8 transmits as follows packet with node 10 and communicates, and for convenience of narration, with i, means 1,3,5,8 simultaneously, and the value of corresponding j is respectively 2,4, and 7,10:
2.1a) as shown in Figure 3, node i is by its local zone time T
i1send to node j, node j is T at local zone time
j1the time receive data T
i1;
2.1b) after node j receives the data from node i, by the local zone time T of oneself
j1reply to node i, node i is at T
i2after constantly receiving this packet, calculate and upgrade local zone time and be: T '
i2=(T
j1+ T
i2+ tau (1))/2, wherein tau (1) is the passing time of node j while sending to the node i packet;
2.1c) node i is when upgrading local zone time, by the local zone time T of oneself
i2reply to node j, node j is at T
j2after constantly receiving this packet, calculate and upgrade local zone time and be: T '
j2=(T
i2+ T
j2+ tau (2))/2, wherein tau (2) is the passing time of node i while sending to node j packet;
2.2) when k=2, s (2)={ e
23, e
48, e
9,10, i.e. node 2 and node 3, node 4 and node 8, node 9 with node 10 simultaneously by step 2.1b)～2.1d) the transmission packet communicates, for convenience of narration, mean 2,4 with i, 9, the value of corresponding j is respectively 3,8,10, completes the renewal of node local zone time;
2.3) when k=3, s (3)={ e
26, e
7,10, i.e. node 2 and node 6, node 7 with node 10 simultaneously by step 2.1b)～2.1d) transmit packet and communicate, for convenience of narrating, with i, mean 2,7, the value of corresponding j is respectively 6,10, completes the renewal of node local zone time;
2.4) when k=4, s (4)={ e
58, node 5 with node 8 by step 2.1b)～2.1d) transmit packet and communicate, for convenience of narrating, with i, mean 5, the value of corresponding j is respectively 8 renewals that complete the node local zone time;
2.5) when k=5, s (5)={ e
67, node 6 with node 7 by step 2.1b)～2.1d) transmit packet and communicate, for convenience of narrating, with i, mean 6, the value of corresponding j is respectively 7, completes the renewal of node local zone time;
2.6) after all limits have all been communicated by letter once in network, k is put to 1, repeated execution of steps 2.1)～2.5), until the progressive error be tending towards in an allowed band of network node, it is synchronous that network reaches average clock, and the network node continuous firing keeps the clock synchronous state.
Step 2.6) after carrying out end, obtain synchronized result as shown in Figure 5, wherein Fig. 5 (a) is the change curve of the local zone time of network node with iterations, Fig. 5 (b) is the change curve of the residual quantity of the local zone time of network node and average with iterations, and in Fig. 5, iterations refers in network that all limits network time a time of all communicating by letter reaches the algebraically synchronously experienced.Because the local clock of sensor node is time dependent, so the synchronous curve shown in Fig. 5 (a) is the linear phenomenon that increases; Each node goes to zero at the local zone time in the same moment and the residual quantity of average, has reached average clock synchronous, i.e. curve shown in Fig. 5 (b).
Effect of the present invention can further illustrate by following emulation experiment:
1. simulated conditions:
At CPU, be on core22.4GHZ, internal memory 2G, WINDOWS XP system, to use MATLAB to carry out emulation.
2. emulation content:
Emulation experiment is divided into two groups and carries out:
First group of experiment adopts the network of 20 node different edge density as experimental subjects, network diagram as shown in Figure 6, wherein Fig. 6 (a) is 20 nodes, the network diagram that limit density is 0.1632, Fig. 6 (b) is 20 nodes, the network diagram that limit density is 0.5105, Fig. 6 (c) is 20 nodes, the network diagram that limit density is 0.6579;
Second group of experiment adopts the random network generated as experimental subjects, respectively to 20,50 of random generation, 100,150 and 200 nodes, the network of different edge density is tested, and wherein the network diagram of 50 nodes is as shown in Figure 8, wherein Fig. 8 (a) is random 50 nodes that generate, the network diagram that limit density is 0.3, Fig. 8 (b) is random 50 nodes that generate, the network diagram that limit density is 0.5, Fig. 8 (c) is random 50 nodes that generate, the network diagram that limit density is 0.8.
In experiment, the random node initial time value obedience average generated is 0.5, the Gaussian Profile that variance is 1; The time delay tau of communication is random the generation each time, and the obedience average is 1.0000e-003, the Gaussian Profile that standard deviation is 1.0000e-006; The precision threshold of setting is 1.0000e-006.
3. simulation result
The simulation experiment result of first group of experiment as shown in Figure 7, wherein Fig. 7 (a) is the change curve of the residual quantity of network node local zone time that Fig. 6 (a) is corresponding and average with iterations, Fig. 7 (b) is the change curve of the local zone time of the network node that Fig. 6 (a) is corresponding with iterations, Fig. 7 (c) is the change curve of the residual quantity of network node local zone time that Fig. 6 (b) is corresponding and average with iterations, Fig. 7 (d) is the change curve of the local zone time of the network node that Fig. 6 (b) is corresponding with iterations, Fig. 7 (e) is the change curve of the residual quantity of network node local zone time that Fig. 6 (c) is corresponding and average with iterations, Fig. 7 (f) is the change curve of the local zone time of the network node that Fig. 6 (c) is corresponding with iterations.
Second group the experiment in 50 nodes network diagram the simulation experiment result as shown in Figure 9, wherein Fig. 9 (a) is the change curve of the residual quantity of network node local zone time that Fig. 8 (a) is corresponding and average with iterations, Fig. 9 (b) is the change curve of the local zone time of the network node that Fig. 8 (a) is corresponding with iterations, Fig. 9 (c) is the change curve of the residual quantity of network node local zone time that Fig. 8 (b) is corresponding and average with iterations, Fig. 9 (d) is the change curve of the local zone time of the network node that Fig. 8 (b) is corresponding with iterations, Fig. 9 (e) is the change curve of the residual quantity of network node local zone time that Fig. 8 (c) is corresponding and average with iterations, Fig. 9 (f) is the change curve of the local zone time of the network node that Fig. 8 (c) is corresponding with iterations.
Test concrete experimental data as shown in table 1, table 2 for two groups, wherein in table 1, data are first group of experiment to be carried out to the experimental result of test statistics, the note 1 representative is averaging for 10 times identical time initial value test, and 10 groups of time initial value tests of the random generation of note 2 representative are averaging for 10 times.
In table 2, data are second group of experiment to be carried out to the experimental result of test statistics.
The experimental result that this experimental technique of table 1 is first group
The experimental result that this experimental technique of table 2 is second group
From the simulation experiment result figure and table 1, table 2, can find out, the present invention, for high density or low-density network arbitrarily, can both reach average clock synchronous, and not rely on any outside basic point or certain root node; Network node converges on the time average of node, and maintenance synchronous regime that can be more stable makes the present invention have more robustness and reasonability; Reduce the accumulation of inter-node communication time delay error, applicable to large scale network, improved the extensibility of network.
Claims (2)
1. the method for average clock synchronization of a wireless sensor network, comprise the steps:
(1) topological structure of wireless sensor network is abstracted into to graph model, draws out this graph model G;
(2) to graph model G={N, V, the node in E} carries out random number 1,2 ..., N, wherein, N means sensor node sum in network, and V means the sensor node collection, and E means the set of all nonoriented edges;
(3) using the clock value of initial time network node as the node initial value, be labeled as T
1(0), T
2(0) ..., T
n(0);
(4), in the operating process to graph model G, by switching signal s (k), control limit set { e
ij}
?synchronization communicates respectively as follows, guarantees the synchronous distributed operation of average clock, and wherein k generates limit set { e
ijiterations, the different corresponding limits set of the value of k { e
ijalso different, in network, all communicated by letter time a time in all limits, k put to 1, again iteration:
(4a) limit set { e
ijin limit e
ijcorresponding node i and j communicate, and node i is by its local zone time T
i1send to node j, node j is at T
j1constantly receive this packet;
(4b) after node j receives the packet from node i, the local zone time T now by oneself
j1reply to node i, node i is at T
i2after constantly receiving this packet, calculate and upgrade local zone time and be: T
i2'=(T
j1+ T
i2+ tau (1))/2, wherein tau (1) is the passing time of node j while sending to the node i packet;
(4c) node i is when upgrading local zone time, the local zone time T now by oneself
i2reply to node j, as node j at T
j2after constantly receiving this packet, calculate and upgrade local zone time and be: T
j2'=(T
i2+ T
j2+ tau (2))/2, wherein tau (2) is the passing time of node i while sending to node j packet;
(5) repeated execution of steps (4), until the progressive error be tending towards in an allowed band of the maximum residual quantity between network node, it is synchronous that network reaches average clock, network node continuous firing, the stable clock synchronous state that keeps.
2. the synchronous method of the average clock of wireless sensor network according to claim 1, the described graph model of step (1) wherein, in order to mean the topological structure of wireless sensor network, be provided with N node in figure, each node i represents a transducer, record local clock, i=1 wherein, 2 ..., N, internodal fillet e
ijcan transmit packet between representation node and communicate, j=1 wherein, 2 ..., N, i ≠ j.
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| CN103178917B (en) * | 2011-12-26 | 2015-11-11 | 中国移动通信集团公司 | A kind of clock synchronizing method of collaboration communication, system and information taken node |
| CN102833853B (en) * | 2012-08-31 | 2015-08-12 | 北京联合大学 | Based on the node of the wireless sensor network that Embedded GPS module clock corrects |
| CN103945524B (en) * | 2014-04-30 | 2017-11-10 | 中国科学院上海微系统与信息技术研究所 | Distributed wireless Sensor Network method for synchronizing time |
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