CN111682919A - Time synchronization method for underground sensing equipment based on time sensitive network - Google Patents
Time synchronization method for underground sensing equipment based on time sensitive network Download PDFInfo
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- CN111682919A CN111682919A CN202010595266.0A CN202010595266A CN111682919A CN 111682919 A CN111682919 A CN 111682919A CN 202010595266 A CN202010595266 A CN 202010595266A CN 111682919 A CN111682919 A CN 111682919A
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- H04—ELECTRIC COMMUNICATION TECHNIQUE
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- H04J3/00—Time-division multiplex systems
- H04J3/02—Details
- H04J3/06—Synchronising arrangements
- H04J3/0635—Clock or time synchronisation in a network
- H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
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- H—ELECTRICITY
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- H04J3/00—Time-division multiplex systems
- H04J3/02—Details
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- H04J3/0635—Clock or time synchronisation in a network
- H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
- H04J3/0658—Clock or time synchronisation among packet nodes
- H04J3/0661—Clock or time synchronisation among packet nodes using timestamps
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Abstract
The invention discloses a time synchronization method of underground sensing equipment based on a time sensitive network. According to the method, a frequency drift factor is introduced on the basis of an original PTP algorithm, a Kalman filtering algorithm is applied to optimize the frequency drift factor, the most accurate clock in a sensor network is selected through an optimal master clock algorithm to serve as a clock basis for global time synchronization, a network topology structure is established, global hierarchical traversal is achieved, and accurate clock synchronization between nodes in an industrial wireless sensor network is achieved through an accurate time synchronization algorithm based on Kalman filtering and a period balancing mechanism. The method effectively solves the problem of global time synchronization of the underground sensing equipment and improves the accuracy and stability of network synchronization.
Description
Technical Field
The invention relates to the field of time synchronization of sensor networks, in particular to a time synchronization method of underground sensing equipment based on a time sensitive network.
Background
With the rapid development of ethernet, real-time ethernet is required to satisfy data transmission real-time and high-precision synchronization in the field of coal mine information interaction. With the development trend of the whole Network IP, a Packet Transport Network (PTN) based on a packet service has gradually replaced a traditional Time-division multiplexing (TDM) Network, and improving the Time synchronization of Time-sensitive data in the Network is a key of coordination work of underground sensing equipment and a coal mine Network, and is also a precondition of technologies such as positioning, data fusion, and the like. At present, the most widely applied Time synchronization technology in a packet network is IEEE 1588v2 Precision Time Protocol (PTP), and the Time delay generated in the process of transmitting a data frame carrying a timestamp and the clock drift difference of different devices can affect the Precision of clock synchronization; especially in the linear distribution environment of underground sensors, the traversing of spanning trees and a point-to-point synchronization mode in the traditional method lead the efficiency of time synchronization of the whole network to be lower; the progressive synchronization approach also results in lower accuracy of node synchronization the farther from the master clock.
Disclosure of Invention
In view of the above problems, the present invention aims to provide an optimization method for precise global clock synchronization in a mine sensing equipment system. Selecting the most accurate Clock in the sensing network as a Clock basis of global Clock synchronization through an optimal Master Clock (BMC); and realizing accurate clock synchronization among all nodes in the industrial wireless sensor network by utilizing global hierarchical traversal, an enhanced accurate time algorithm based on Kalman filtering and a periodic balancing mechanism. The method effectively solves the problem of global time synchronization of the underground sensing equipment, and improves the synchronization precision and stability of the underground sensing equipment on the premise of ensuring the effective utilization of network resources.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
1. a time synchronization method of underground sensing equipment based on a time sensitive network is characterized by comprising the following steps:
step 1: initializing a global network, setting a self clock role as a common clock, a boundary clock or a core clock by each network communication node under a mine according to a network structure, establishing a self clock information vector table and storing the self clock information vector table in a register;
step 2: each node in the network periodically sends an Announce data frame containing a clock information vector table to a neighbor node, compares each clock vector in the table according to an optimal master clock algorithm, selects more optimal clock information to be updated to a port for storage and waiting for next received information to be compared or forwarded, and continuously exchanges information until the optimal clock information is selected as a master clock through global comparison;
and step 3: the method comprises the steps that an optimal master clock selected from a network periodically sends synchronization messages to each node and waits for feedback messages, the slave nodes receive the synchronization messages and then reply the feedback messages, and in each information interaction, each node records timestamp information of information sending or receiving time;
and 4, step 4: the slave node calculates a relative clock drift factor and a clock offset according to an accurate time synchronization algorithm through a timestamp of data interaction, stores the synchronous calculated value at this time and updates the drift factor and the clock offset according to a Kalman filtering algorithm;
and 5: the slave node compensates the local clock according to the clock offset calculated in the step 4, completes one round of master-slave clock synchronization and waits for the next synchronization;
step 6: the slave node records the calculated compensation deviant after the time synchronization process, if the calculated compensation deviant is greater than or equal to the expected highest threshold value, the compensation deviant is fed back to a superior clock in the next synchronous interaction process, so that the preset time synchronization period value is reduced by one time unit, and if the calculated compensation deviant is less than the expected minimum threshold value, the time unit is increased;
and 7: and (3) repeating the steps 3-7 periodically to realize the accurate time synchronization of the underground network sensor equipment.
2. The time synchronization method for the downhole sensing equipment based on the time sensitive network according to claim 1, wherein the interaction process according to the periodic master-slave time synchronization information specifically comprises the following steps:
the boundary clock only has one communication port, and is generally a clock of underground sensor equipment and terminal node equipment in a network; a common clock has a plurality of ports, and a boundary clock is generally used at a network node with low certainty, such as a clock of a switch or a router; the core clock is a converged core switch, and the optimal node clock information of each area is compared so as to obtain the optimal master clock information according to the optimal master clock algorithm.
3. The time synchronization method for the downhole sensing equipment based on the time sensitive network according to claim 1, wherein the setting of the clock role of the downhole sensing equipment according to the network structure specifically comprises:
in order to perform clock synchronization, i.e. point-to-point clock synchronization adjustment, between the master node and the slave nodes in the entire clock network, the master node starts a clock synchronization cycle and sends a timestamp message. Upon receiving these timestamp messages, the slave estimates the offset of its clock relative to the master clock and then adjusts its time accordingly. To further synchronize the clocks, the slave nodes synchronize the traces after receiving the message sequence. The timestamps T1, T3, and T6 transmitted by the master node are plotted according to the master node delay response and delay tracking. At the same time, the slave also records timestamps T2, T4, T5, and T8.
The invention has the beneficial effects that:
the method is improved on the basis of a time synchronization protocol of a time sensitive network and is combined with a Kalman filtering algorithm, so that accurate clock synchronization among nodes in an underground sensing equipment network is realized, and the clock offset estimation precision of the traditional time synchronization protocol is obviously improved. According to the invention, the timestamp is locally recorded and carried in the next transmission, so that the time delay of embedding the timestamp into a data frame is reduced, and the clock synchronization precision is improved; clock drift factors are introduced, and clock frequency drift errors of a master node and a slave node in the underground special environment are reduced; by combining with a Kalman filtering algorithm, the uncertainty error of the noise interference in the well is reduced, the precision is improved, and the synchronization stability is enhanced; the utilization efficiency of network resources can be improved by setting a period balancing mechanism; the clock distribution of the packet nodes is adopted, the clock synchronization transmission efficiency is improved, when an emergency situation such as the breakdown of a master clock occurs, the network can rapidly enter an alternative stage, the safety and the recovery capability of the network are improved, and the network clock synchronization efficiency is greatly improved.
Drawings
FIG. 1 is a block diagram of the overall process of the method of the present invention.
Fig. 2 is a process diagram of the master-slave time information interaction of the method of the present invention.
FIG. 3 is a flow chart of the precise clock synchronization of the method of the present invention.
Detailed Description
As shown in fig. 1, the process of the time synchronization method for the downhole sensing device based on the time sensitive network is as follows:
step 1: initializing a global network, setting a self clock role by each network communication node under a mine according to a network structure, and using a boundary clock as terminal sensor equipment for communication; the boundary clock is used as forwarding routing equipment; the core clock plays a role in forwarding and converging the clock information of the area connected with the switch for the core switch;
step 2: each node periodically sends an Announce data frame containing a clock information vector table to a neighbor node, an optimal master clock of the whole network is obtained through calculation and comparison according to an optimal master clock algorithm, core clock equipment records and sequences the clock performance in a region at a port, and a new master clock is called to reduce the information transmission times of the election master clock under special conditions;
and step 3: each node judges whether the local clock is the optimal master clock, the optimal master clock periodically performs information interaction with the slave clock, the slave clock waits for and feeds back, and the timestamp is recorded according to the graph shown in FIG. 2;
and 4, step 4: calculating a relative clock drift factor and a clock offset from the obtained timestamp according to a precise time synchronization algorithm and a Kalman filtering algorithm, and calculating a final correction offset value according to the probability of an observed value and a prediction model, wherein the detailed steps are shown in FIG. 3;
and 5: the slave node records the calculated compensation deviant after the time synchronization process, if the calculated compensation deviant is greater than or equal to the expected highest threshold value, the compensation deviant is fed back to a superior clock in the next synchronous interaction process, so that the preset time synchronization period value is reduced by one time unit, and if the calculated compensation deviant is less than the expected minimum threshold value, the time unit is increased;
step 6: and continuously carrying out multiple times of synchronization according to the adjusted period value so as to realize accurate time synchronization among the sensor network devices.
As shown in fig. 2, the process of the master-slave time information interaction process of the method of the present invention is:
step 1: the master node sends a SyncRequest message at the time of T1, records the time T1, sends a FollowUp message of time information T1 at the time of T3, and records the time T3 locally;
step 2: receiving a SyncRequest message from the node at the time T2, and recording the receiving time T2 and the receiving time T4 to receive a FollowUp message with SyncRequest message sending time information T1 from the node;
and step 3: then the slave node sends a DelayReq message to the master node at the time of T5, and locally records the sending time T5;
and 4, step 4: after receiving the DelayReq message at the time of T6, the master node locally records the time of T6 and transmits a DelayResp message with time information T3 and T6;
and 5: the slave node waits for receiving the feedback message DelayResp of the master node, and records the sending time T3 and T6 of the FollowUp message.
As shown in fig. 3, the master-slave time precise time synchronization algorithm of the method of the present invention is:
step 1: the information interaction process of a master clock initiating a slave clock feedback is shown in fig. 2, a clock model is established, through periodic error adjustment and periodic sampling discretization, the master-slave time deviation in the (n + 1) th period can be expressed as a formula (1), the clock drift change condition is a formula (2), wherein uθ(n) is a time deviation adjustment value of n, wθ(n)，wα(n) are respectively the noise error (generally set as white Gaussian noise) generated in the synchronization process, and the corresponding variance of the noise is
θ(n+1)＝θ(n)―uθ(n)+α(n)·T(n)+wθ(n) (1)
α(n+1)＝α(n)+wα(n) (2)
Step 2: six time stamps T1 through T6 obtained from a clock. Setting the time offset between master and slave nodesAnd the transmission delay on the path is T respectivelyOffsetAnd TDelayAnd the clock drift correction coefficient a is calculated according to the formula (3), the formula (4) and the formula (5) to obtain TOffsetAnd adjusting the local clock information, and correcting the current time clock according to the clock drift correction coefficient a and the time offset value of T2 to realize clock synchronization. And the accurate clock synchronization between the master device and the slave device is realized.
And step 3: after the above steps are completed, we can obtain the state transition equation such as equation (6) simultaneously according to the clock model equations (1), (2), wherein
In order to be a state transition matrix,
in order to control the matrix of the control,
at the nth time two values of the calculated variable,
in order to correct the value of the data,
for noise errors, an observation equation such as equation (7) can be obtained by the deviation calculation, wherein
For measuring the parameter matrix of the system, PpreThe measurement equation is shown as formula (8), the Kalman gain is shown as formula (9), and the P update equation is shown as formula (10), wherein
R is the measurement noise covariance.
X(n+1|n)＝A·X(n)+B·U(n)+W(n) (6)
Z(n)＝H·X(n)+V(n) (7)
P(n+1|n)＝A·P(n)·AT+Q, (8)
K(n+1)＝P(n+1|n)·HT·(H·P(n+1|n)·HT+R)―1, (9)
P(n+1)＝(I―K(n+1)·H)·P(n+1|n), (10)
The calculation (observation) value assignment is carried out in the nth synchronization period according to the results obtained by the formulas (3) and (5), and theta (n) is made to be TOffset；
And updating the offset value theta of the current period by combining the formulas (6) to (10) and correcting the offset value theta. And finally obtaining an accurately predicted deviation value.
Claims (3)
1. A time synchronization method of underground sensing equipment based on a time sensitive network is characterized by comprising the following steps:
step 1: initializing a global network, setting a self clock role as a common clock, a boundary clock or a core clock by each network communication node under a mine according to a network structure, establishing a self clock information vector table and storing the self clock information vector table in a register;
step 2: each node in the network periodically sends an Announce data frame containing a clock information vector table to a neighbor node, compares each clock vector in the table according to an optimal master clock algorithm, selects more optimal clock information to be updated to a port for storage and waiting for next received information to be compared or forwarded, and continuously exchanges information until the optimal clock information is selected as a master clock through global comparison;
and step 3: the method comprises the steps that an optimal master clock selected from a network periodically sends synchronization messages to each node and waits for feedback messages, the slave nodes receive the synchronization messages and then reply the feedback messages, and in each information interaction, each node records timestamp information of information sending or receiving time;
and 4, step 4: the slave node calculates a relative clock drift factor and a clock offset according to an accurate time synchronization algorithm through a timestamp of data interaction, stores the synchronous calculated value at this time and updates the drift factor and the clock offset according to a Kalman filtering algorithm;
and 5: the slave node compensates the local clock according to the clock offset calculated in the step 4, completes one round of master-slave clock synchronization and waits for the next synchronization;
step 6: the slave node records the calculated compensation deviant after the time synchronization process, if the calculated compensation deviant is greater than or equal to the expected highest threshold value, the compensation deviant is fed back to a superior clock in the next synchronous interaction process, so that the preset time synchronization period value is reduced by one time unit, and if the calculated compensation deviant is less than the expected minimum threshold value, the time unit is increased;
and 7: and (3) repeating the steps 3-7 periodically to realize the accurate time synchronization of the underground network sensor equipment.
2. The time synchronization method for the downhole sensing equipment based on the time sensitive network according to claim 1, wherein the interaction process according to the periodic master-slave time synchronization information specifically comprises the following steps:
the common clock only has one communication port, and is generally a clock of underground sensor equipment and terminal node equipment in a network; a boundary clock has a plurality of ports, and is generally used at a network node with low certainty, such as a clock of a switch or a router; the core clock is a converged core switch, and the optimal node clock information of each area is compared so as to obtain the optimal master clock information according to the optimal master clock algorithm.
3. The time synchronization method for the downhole sensing equipment based on the time sensitive network according to claim 1, wherein the setting of the clock role of the downhole sensing equipment according to the network structure specifically comprises:
in order to perform clock synchronization, i.e. point-to-point clock synchronization adjustment, between the master node and the slave nodes in the entire clock network, the master node starts a clock synchronization cycle and sends a timestamp message. Upon receiving these timestamp messages, the slave estimates the offset of its clock relative to the master clock and then adjusts its time accordingly. To further synchronize the clocks, the slave nodes synchronize the traces after receiving the message sequence. The timestamps T1, T3, and T6 transmitted by the master node are plotted according to the master node delay response and delay tracking. At the same time, the slave also records timestamps T2, T4, T5, and T8.
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Cited By (3)
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| CN114338831A (en) * | 2021-12-02 | 2022-04-12 | 中国科学院空间应用工程与技术中心 | Gateway communication method, communication equipment and storage medium |
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