CN117651325A - Mobile ad hoc network time-frequency self-synchronization method - Google Patents
Mobile ad hoc network time-frequency self-synchronization method Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
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- H04W56/00—Synchronisation arrangements
- H04W56/001—Synchronization between nodes
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- H04W56/0035—Synchronisation arrangements detecting errors in frequency or phase
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- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W56/00—Synchronisation arrangements
- H04W56/0055—Synchronisation arrangements determining timing error of reception due to propagation delay
- H04W56/006—Synchronisation arrangements determining timing error of reception due to propagation delay using known positions of transmitter and receiver
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- H—ELECTRICITY
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Abstract
The invention provides a time-frequency self-synchronizing method of a mobile ad hoc network, which mainly solves the problems of larger influence of measurement errors and larger clock drift during time synchronization. The invention is based on the time-frequency self-synchronizing algorithm of spread spectrum communication, realize the unidirectional ranging among the nodes of the mobile ad hoc network through the means of signal processing, combine the accurate position of the node, can calculate the clock error parameter of each node relative to source node in the mobile ad hoc network, utilize clock error parameter of each node to compensate its clock error and frequency difference, realize the time-frequency synchronization of each node and source node.
Description
Technical Field
The invention belongs to the technical field of mobile ad hoc networks, and relates to a time-frequency self-synchronizing method of a mobile ad hoc network.
Background
The Mobile self-organizing network (Mobile AdhocNetwork, MANET) is a self-organizing network without centers, hops and autonomy, which is formed by a series of Mobile nodes through wireless links, and a communication infrastructure is not required to be established in advance, so that the network structure is flexible and various, networking can be performed at any time according to the change of the demands of tasks, and the network is flexible. Compared with a single communication node, the communication mode of multi-hop forwarding adopted by the MANET effectively expands the communication distance and the perception range, and meanwhile, the network has stronger anti-destruction capability and self-healing capability.
The premise of the nodes in the MANET network to cooperate is to establish a unified time-frequency reference. In the Link16 data Link, a master-slave synchronization mode is adopted to perform time synchronization, each terminal is required to work on the same relative time reference, and a designated unit serving as a network time reference establishes system time. The time synchronization of Link16 data Link terminals is divided into two steps: the first step: coarse synchronization is realized by obtaining network access information; and a second step of: the fine synchronization includes active fine synchronization and passive fine synchronization. The method and the device are used for correcting clock errors of the user and the network time reference unit by exchanging round trip timing information with the network time reference unit, so that clock synchronization, namely active fine synchronization, is realized. The manner of achieving fine synchronization without sending a round trip timing message becomes passive fine synchronization.
However, in the Link16 data chain, the time synchronization method only uses one time of measurement data to calculate the time deviation, although the time deviation results calculated by multiple times are averaged, the influence of the measurement error is still larger, in addition, the clock of the node has frequency difference, drift can occur along with time, and the time deviation is larger and larger.
Disclosure of Invention
The invention provides a time-frequency self-synchronizing method of a mobile ad hoc network, which mainly solves the problems of larger influence of measurement errors and larger clock drift during time synchronization.
The invention is realized by the following technical scheme:
a time-frequency self-synchronizing method of mobile self-organizing network includes the following steps:
step one, taking a cluster head node as a time base node, and synchronizing own time frequency with the time base node by other nodes in the mobile ad hoc network; the networking starting stage, the time base node periodically broadcasts a synchronous control frame;
step two, the 1-hop node of the time base node receives the time base node signal and then carries out ranging, obtains a ranging value, marks the ranging moment, analyzes from the synchronous control frame to obtain node category, signal transmitting moment and position information, and records the ranging value and the ranging moment of the time base node and the position information of the time base node;
step three, the 1-hop node m of the time base node obtains own position information through a central computer, and the distances between N ranging time nodes m and the time base node o are calculated through interpolation;
step four, establishing an observation equation according to the distance measurement values of the N distance measurement moment nodes m to the time base nodes in the step three;
calculating a clock difference model of the observation time node m relative to the time base node according to the observation equation;
step six, solving the clock error model by using a least square method to obtain clock error parameters;
step seven, according to the calculated clock error parameter, correcting the local time frequency of the node m to realize the synchronization of the node m and the time base node;
step eight, after time-frequency synchronization is completed by the 1-hop node of the time base node, periodically collecting a ranging value, repeatedly calculating clock error parameters, calibrating a time-frequency quality factor, and broadcasting a synchronization control frame;
and step nine, after receiving signals, the other nodes m perform ranging to obtain ranging values, marking ranging time, analyzing from the synchronous control frame to obtain node types, local time-frequency synchronous identifications, time-frequency reference node ids, time-frequency quality identifications, signal transmitting time and position information, and if the time-frequency quality of the nodes m is lower than 1-hop node, recording the ranging values, the ranging time and the position information of the 1-hop node for the 1-hop node, and synchronizing the local time-frequency with the 1-hop node.
The invention has the beneficial effects that:
1. the invention does not need an external time-frequency reference source, and can realize time-frequency self-synchronization in a network;
2. the method adopts the least square method to estimate the clock error parameter, the frequency error parameter and the Zhong Piao parameter, is the optimal estimation of the clock error parameter, has small influence of measurement errors, and improves the calculation precision of the local clock error parameter;
3. according to engineering practice, calculating the clock error correction quantity a 0 Correction amount a of frequency difference 1 And Zhong Piao a 2 The local time frequency is corrected, so that the local clock is smaller than Zhong Piao of the system clock, and the frequency of time frequency maintenance is reduced.
Drawings
FIG. 1 is a schematic diagram of the pseudo-range computation between nodes according to the present invention.
Detailed Description
Exemplary embodiments of the present invention are described in detail below with reference to the accompanying drawings. It is to be understood that the embodiments shown and described in the drawings are merely illustrative of the principles and spirit of the invention and are not intended to limit the scope of the invention.
The realization idea of the invention is as follows: the invention is based on the time-frequency self-synchronizing algorithm of spread spectrum communication, realize the distance measurement among the nodes of the mobile ad hoc network through the means of signal processing, combine the accurate position of the node, can calculate the clock error parameter of each node relative to source node in the mobile ad hoc network, utilize the clock error parameter of each node to compensate its clock error and frequency error, realize the time-frequency synchronization of each node and source node.
As shown in fig. 1, the time-frequency self-synchronizing method of the mobile ad hoc network specifically includes the following steps:
step one, using a cluster head node as a time-frequency reference node, namely a time-base node for short, and synchronizing own time frequency with the time-base node by other nodes in the mobile ad hoc network; the networking starting stage, the time base node periodically broadcasts a synchronous control frame;
in this embodiment, the format of the synchronization control frame is defined as shown in table 1 below:
TABLE 1 synchronous control frame Structure Specification
Step two, the 1-hop node of the time base node receives the time base node signal and then carries out ranging, obtains a ranging value, marks the ranging moment, analyzes from the synchronous control frame to obtain node category, signal transmitting moment and position information, and records the ranging value and the ranging moment of the time base node and the position information of the time base node;
step three, the 1-hop node m of the time base node obtains the position information of the node m through a central computer, and N distance measuring moments (t) are calculated through interpolation 1 ，t 2 ，…，t N ) Distance(s) of node m from time-frequency reference node o (time base node) 1 ，s 2 ，…，s N )；
Step four, according to the N distance measuring moments (t 1 ，t 2 ，…，t N ) The ranging value of node m to the time-frequency reference node o is (ρ 1 ，ρ 2 ，…，ρ N ) An observation equation is established, and the following formula is established:
ρ i ＝r i +δt mi +τ mr_i +τ ot_i +τ m_ant +τ o_ant +τ rel +ε i (1)
in the formula, i=1, 2, …, N, the number N of ranging values involved in the calculation is set according to engineering practice, and the setting strategy is as follows: the more the number of the ranging values involved in the calculation, the higher the clock error parameter calculation accuracy, the larger the calculated amount; r is (r) i The geometric distance between the node m and the time-frequency reference node o; δt mi The clock difference of the node m relative to the time-frequency reference node o; τ mr_i 、τ ot_ i is the receiving channel delay of the node m and the transmitting channel delay of the node o respectively; τ mr_ant 、τ ot_ant Antenna phase center correction parameters of the node m and the node o respectively; τ rel For relativistic effect delay, the delay is negligible in the application scene of the mobile ad hoc network; epsilon i To measure noise.
In the specific implementation, the receiving channel delay, the transmitting channel delay and the antenna phase center correction parameters of all nodes of the whole network are fixed values, and each node stores the receiving channel delay, the transmitting channel delay and the antenna phase center correction parameters of all nodes of the whole network, and the parameters can be set through instructions. Interpolation is carried out by utilizing a Chebyshev fitting algorithm to calculate the position of the node m at the observation time, and the distance r between the node m and the time-frequency reference node o is calculated by combining the position information of the time-frequency reference node at the signal transmitting time i The method comprises the steps of carrying out a first treatment on the surface of the The time delay of the transmitting channel and the time delay of the receiving channel of each node can be calibrated before the equipment leaves the factory, the time delay is generally of nanosecond magnitude, the correction parameter of the antenna phase center is the position deviation of the antenna phase center of the node relative to the center of mass of the node, the position information of the node represents the center of mass of the node, and the correction parameter of the antenna phase center is used for correcting the signal propagation time delay deviation and can be obtained through calculation.
Calculating a clock difference model of the observation time node m relative to the time-frequency reference node o according to the observation equation; the specific formula is as follows:
δ tmi =ρ i -r i -τ mr_i -τ ot_i -τ m_ant -τ o_ant (2)
according to the clock characteristics of the nodes, a linear clock difference model is constructed as follows:
in the above, Δt i =t i -t 0 For the distance measurement value ρ i Corresponding distance measuring time t i The difference between the first distance measurement value and the distance measurement time of the first distance measurement value selected by the current calculation, and the clock difference correction quantity a 0 Correction amount a of frequency difference 1 And Zhong Piao a 2 For the parameters to be estimated, the clock difference model conforms to the following form:
Ax=b (4)
step six, solving the clock error model by using a least square method to obtain a clock error parameter a 0 、a 1 、a 2 The method is characterized by comprising the following steps:
if the frequency difference correction quantity a is calculated 1 And Zhong Piao a 2 Then in formula (4)
Wherein the clock correction amount a 0 To solve for the parameter, the frequency difference correction amount a 1 And Zhong Piao a 2 Whether to solve according to instruction setting: then the least square method is used to obtain the clock error parameter a 0 、a 1 、a 2 Least squares estimation of (2) is
If the frequency difference correction quantity a is calculated 1 Not resolving Zhong Piao a 2 Then in formula (4)
Then the least square method is used to obtain the clock error parameter a 0 、a 1 Least squares estimation of (2) is
Zhong Piao a 2 The correction is not performed, and the correction amount is 0.
Step seven, according to the calculated clock error parameter a 0 、a 1 、a 2 Correcting the local time frequency of the node m, and realizing the synchronization of the node m and a time frequency reference node o;
in specific implementation, after local time-frequency synchronization of the node m, the local time-frequency synchronization identifier is set to 0xFF, the time-frequency reference node id is set to the id of the time-frequency reference node o, and the current time-frequency synchronization time is set to the local time after the latest time-frequency synchronization adjustment.
Step eight, after time-frequency synchronization is completed by the 1-hop node of the time base node, periodically collecting a ranging value, repeatedly calculating clock error parameters, calibrating a time-frequency quality factor, and broadcasting a synchronization control frame;
and step nine, after receiving signals, the other nodes m perform ranging to obtain ranging values, marking ranging time, analyzing from the synchronous control frame to obtain node types, local time-frequency synchronous identifications, time-frequency reference node ids, time-frequency quality identifications, signal transmitting time and position information, and if the time-frequency quality of the nodes m is lower than 1-hop node, recording the ranging values, the ranging time and the position information of the 1-hop node for the 1-hop node, and synchronizing the local time-frequency with the 1-hop node.
And in the specific implementation, repeating the step one to the step nine, and finishing the time-frequency synchronous nodes until all the nodes in the network finish the time-frequency synchronous.
In this embodiment, all nodes in the network complete time-frequency synchronization, and the time reference node is selected according to the following priority order:
time base node > nodes synchronized to time base nodes (higher time frequency quality, higher priority) synchronized to nodes of completed time frequency synchronization of non-time base nodes (higher time frequency quality, higher priority); and each node in the mobile ad hoc network selects the node with the highest visible priority as a time-frequency reference node, and performs time-frequency synchronization.
It can be seen that each node in the mobile ad hoc network directly or indirectly synchronizes the local time frequency with the time base node by adopting the method, so that the time frequency synchronization of the whole network is realized. Because of the characteristic of the node clock, clock drift phenomenon can occur along with time, when the clock difference between the node and the time-frequency reference node exceeds a threshold value, the local time-frequency is synchronized with the time-frequency reference node again, and the time-frequency synchronization clock difference threshold value of the node can be set according to the actual passing instruction of engineering.
Those of ordinary skill in the art will recognize that the embodiments described herein are for the purpose of aiding the reader in understanding the principles of the present invention and should be understood that the scope of the invention is not limited to such specific statements and embodiments. Those of ordinary skill in the art can make various other specific modifications and combinations from the teachings of the present disclosure without departing from the spirit thereof, and such modifications and combinations remain within the scope of the present disclosure.
Claims (5)
1. The time-frequency self-synchronizing method for the mobile self-organizing network is characterized by comprising the following steps:
step one, taking a cluster head node as a time base node, and synchronizing own time frequency with the time base node by other nodes in the mobile ad hoc network; the networking starting stage, the time base node periodically broadcasts a synchronous control frame;
step two, the 1-hop node of the time base node receives the time base node signal and then carries out ranging, obtains a ranging value, marks the ranging moment, analyzes from the synchronous control frame to obtain node category, signal transmitting moment and position information, and records the ranging value and the ranging moment of the time base node and the position information of the time base node;
step three, the 1-hop node m of the time base node obtains own position information through a central computer, and the distances between N ranging time nodes m and the time base node o are calculated through interpolation;
step four, establishing an observation equation according to the distance measurement values of the N distance measurement moment nodes m to the time base nodes in the step three;
calculating a clock difference model of the observation time node m relative to the time base node according to the observation equation;
step six, solving the clock error model by using a least square method to obtain clock error parameters;
and step seven, according to the calculated clock error parameter, correcting the local time frequency of the node m, and realizing the synchronization of the node m and the time base node.
2. The method of time-frequency self-synchronization of mobile ad hoc network according to claim 1, further comprising, after the step seven:
step eight, after time-frequency synchronization is completed by the 1-hop node of the time base node, periodically collecting a ranging value, repeatedly calculating clock error parameters, calibrating a time-frequency quality factor, and broadcasting a synchronization control frame;
and step nine, after receiving signals, the other nodes m perform ranging to obtain ranging values, marking ranging time, analyzing from the synchronous control frame to obtain node types, local time-frequency synchronous identifications, time-frequency reference node ids, time-frequency quality identifications, signal transmitting time and position information, and if the time-frequency quality of the nodes m is lower than 1-hop node, recording the ranging values, the ranging time and the position information of the 1-hop node for the 1-hop node, and synchronizing the local time-frequency with the 1-hop node.
3. The mobile ad hoc network time-frequency self-synchronizing method according to claim 2, wherein said clock difference model has the following specific formula:
δt mi ＝ρ i -r i -τ mr_i -τ ot_i -τ m_ant -τ o_ant (2)
according to the clock characteristics of the nodes, a linear clock difference model is constructed as follows:
in the above, Δt i ＝t i -t 0 For the distance measurement value ρ i Corresponding distance measuring time t i The difference between the first distance measurement value and the distance measurement time of the first distance measurement value selected by the current calculation, and the clock difference correction quantity a 0 Correction amount a of frequency difference 1 And Zhong Piao a 2 For the parameters to be estimated, the clock difference model conforms to the following form:
Ax＝b (4)。
4. a mobile ad hoc network time-frequency self-synchronizing method as defined in claim 3, wherein said least square method is used to calculate said clock error model to obtain clock error parameter a 0 、a 1 、a 2 (II), (III), (V), (; the method comprises the following steps:
if the frequency difference correction quantity a is calculated 1 And Zhong Piao a 2 Then in formula (4)
Wherein the clock correction amount a 0 To solve for the parameter, the frequency difference correction amount a 1 And Zhong Piao a 2 Whether to solve according to instruction setting: then the least square method is used to obtain the clock error parameter a 0 、a 1 、a 2 Least squares estimation of (2) is
If the frequency difference correction quantity a is calculated 1 Not resolving Zhong Piao a 2 Then in formula (4)
Then the least square method is used to obtain the clock error parameter a 0 、a 1 Least squares estimation of (2) is
Zhong Piao a 2 The correction is not performed, and the correction amount is 0.
5. A mobile ad hoc network time-frequency self-synchronizing method as claimed in claim 3, wherein all nodes in said network complete time-frequency synchronization, and the time reference nodes are selected according to the following priority order:
the time base node > the node synchronous with the time frequency synchronization completed by the non-time base node, each node in the mobile ad hoc network selects the node with the highest visible priority as the time frequency reference node, and performs time frequency synchronization.
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