CN110312306B - Unmanned aerial vehicle cluster cooperative positioning method and device based on asynchronous information - Google Patents
Unmanned aerial vehicle cluster cooperative positioning method and device based on asynchronous information Download PDFInfo
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Abstract
The invention discloses an unmanned aerial vehicle cluster cooperative positioning method and device based on asynchronous information, wherein the method comprises the following steps: s1, correspondingly configuring a database for storing information required by node positioning for each non-anchor node in an unmanned aerial vehicle cluster; s2, when the target non-anchor node measures or receives the state of the anchor node or receives messages sent by other nodes, updating the database corresponding to the target non-anchor node, and executing the step S3 after the updating is finished; and S3, the target non-anchor node generates broadcast information according to the information in the corresponding database so as to broadcast the broadcast information to the adjacent nodes for updating the state information, and updates the position information of the target non-anchor node, so that the positioning of the unmanned aerial vehicle node is completed. The method is suitable for large-scale unmanned aerial vehicle clusters, and has the advantages of simple implementation method, small communication bandwidth and calculation overhead, high positioning accuracy and the like.
Description
Technical Field
The invention relates to the technical field of unmanned aerial vehicle cluster positioning, in particular to an unmanned aerial vehicle cluster cooperative positioning method and device based on asynchronous information.
Background
The unmanned aerial vehicle cluster receives unprecedented attention in the global scope with unique advantages, and has great application and economic value in the military and civil fields. The cooperative positioning of the unmanned aerial vehicle cluster can enable the cluster to better adapt to complex environments, so that the unmanned aerial vehicle cluster has great application prospect. The drone is a kind of mobile node, and an effective solution is not available at present for cooperative positioning of the mobile node, which has a series of problems such as network synchronization and delay problems.
In the prior art, a positioning method for a mobile node mainly adopts a BP (Belief Propagation) positioning method, which is based on a Factor Graph (Factor Graph) and uses a Sum-Product algorithm to propagate a confidence probability in the whole Factor Graph, when no loop (Cycle) exists in the Factor Graph, the Sum-Product algorithm can accurately obtain an edge probability, but for the positioning algorithm, the Factor Graph extends to two directions of time and space, even if the space dimension does not contain a loop, the time dimension necessarily contains a loop, otherwise, no mutual measurement between nodes exists, cooperative positioning cannot be realized, and when the Factor Graph contains a loop, the Sum-Product method cannot obtain an accurate result, iteration can be performed only by repeatedly transmitting information, and the more the number of iterations is, the more the result is accurate.
At present, the mainstream BP positioning method cannot be effectively exerted in the cooperative positioning of the unmanned aerial vehicle cluster, and has the following defects:
(1) huge communication cost and computational complexity. The BP positioning method requires repeated interaction iterations, each interaction iteration corresponds to the overhead of communication and calculation resources, and the overhead is increased with the increase of the scale of the positioning network. Even if only the delay caused by the communication architecture is considered (i.e. the communication bandwidth constraint and the constraint of the computing resource are ignored), the BP positioning method can hardly support the real-time positioning of more than 10 mobile nodes, which is worse if the limitation of the communication resource of the actual system is considered. However, for a drone cluster, the number of drone nodes will be much greater than 10. Therefore, the existing traditional BP algorithm cannot solve the problem of slightly scaled unmanned aerial vehicle cluster cooperative positioning.
(2) The dependence on clock synchronization. The BP positioning method needs all nodes in a network to have synchronous clocks, and the essential reason is that a moving node discretization model is established based on an information propagation clock. Once the clocks are out of synchronization, ambiguity occurs in time between nodes, and the ambiguity gradually accumulates along with the increase of the network scale, so that the motion information is wrong.
In summary, in the existing unmanned aerial vehicle cluster positioning method, because the adopted filter is based on the discrete time, the clocks of the networks need to be accurately aligned, and the communication in the whole unmanned aerial vehicle cluster needs to be strictly synchronized, so the synchronization of network communication needs to be relied on, and meanwhile, because the adopted filter is based on the discrete time, the synchronization of measurement needs to be performed, the measurement time deviation of different unmanned aerial vehicles causes inaccuracy of the positioning result, so the synchronization still needs to be relied on, while the main stream BP positioning method needs to be iterated repeatedly, and the communication cost is high, so the current cooperative positioning method can only be applied to an extremely small unmanned aerial vehicle cluster, and cannot be adapted to the cooperative positioning of the slightly-scaled unmanned aerial vehicle cluster.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: aiming at the technical problems in the prior art, the invention provides the unmanned aerial vehicle cluster cooperative positioning method and device based on asynchronous information, which can be suitable for large-scale unmanned aerial vehicle clusters, and has the advantages of simple implementation method, low communication bandwidth and calculation cost and high positioning precision.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
an unmanned aerial vehicle cluster cooperative positioning method based on asynchronous information comprises the following steps:
s1, correspondingly configuring a database for storing information required by node positioning for each non-anchor node in an unmanned aerial vehicle cluster, wherein the non-anchor node is an unmanned aerial vehicle node which is unknown in position and needs to be positioned;
s2, when the target non-anchor node measures or receives the state of the anchor node or receives messages sent by other nodes, updating the database corresponding to the target non-anchor node, and executing the step S3 after the updating is finished;
and S3, generating broadcast information by the target non-anchor node according to the corresponding information in the database so as to broadcast the broadcast information to the adjacent nodes for updating state information, updating the position information of the target non-anchor node, and completing the positioning of the unmanned aerial vehicle node.
As a further improvement of the method of the present invention, the data recorded at each time in the database of the non-anchor node includes four parts, namely, a local prior probability, a local posterior probability, a local measurement set, and a local anchor node state set, where the local prior probability includes prior joint probability density information of a node related to positioning and is continuously updated, the local posterior probability includes posterior joint probability density information of a node related to positioning and is continuously updated, the local measurement set includes all anchor node state information related to positioning and is continuously selected or updated, the local anchor node state set includes all anchor node state information related to positioning and is continuously selected or updated, and the broadcast information includes three parts, namely, the local prior probability, the local measurement set, and the local anchor node state set.
As a further improvement of the method of the present invention, the database of the non-anchor node is specifically:
wherein the content of the first and second substances,a database corresponding to the ith non-anchor node,in order to update the database after the update,is a set of update times for the database,updating for the k time of the database;
wherein the content of the first and second substances,for the database inThe recording of the time of day is carried out,for the set of all the recording moments,is the local prior probability that the current probability is,is the local a-posteriori probability,is a local measurement set;a local anchor node state set; t is the current time of day and t is,the recording time of the s-th time in the k-th updating is shown, wherein k and s are positive integers respectively;
the broadcast information is specifically:
wherein the content of the first and second substances,for the broadcast information generated at the kth update of the ith non-anchor node,is that makeSet of established time instants.
As a further improvement of the method of the present invention, in step S2, a local time axis is updated first, and a distributed prior segmentation method is adopted to update a local measurement set, a local anchor node state set, a local prior probability and a local posterior probability in the database based on the updated time axis, and the specific steps include:
s21, judging whether the current time is the database time which is the latest time in the local time axis, if so, executing the step S22, and if not, exiting;
s22, local measurement set and local anchor node state set updating: judging whether the updating time corresponds to the database time, if so, adding a new measurement set in the local measurement set to obtain an updated local measurement set, and adding a new anchor node state set in the local anchor node state set to obtain an updated local anchor node state set, otherwise, adding the measurement set in the interaction information in the local measurement set to obtain an updated local measurement set, and adding the anchor node state set in the interaction information in the local anchor node state set to obtain an updated local anchor node state set;
s23, priori fusion: respectively searching out a neighbor node j with the minimum prior variance for each node l' contained in a database of the node l, and splicing the prior distributions of all the searched nodes to form combined prior distribution;
s24, prior segmentation: subset based on local measurement setLocal prior state setAnd a subset of a local anchor node state setDefining a triple SNCAMST, selecting the triple SNCAMST with the minimum segmentation difference and calculating the edge probability;
s25, posterior updating and prior forecasting: updating the local posterior probability using the calculated marginal probability, and predicting the local prior probability using the updated local posterior probability at the last moment of the database.
As a further improvement of the method of the invention, said updating of the local timeline usesTo limit the maximum number of moments contained in the database, whereinIs a maximum memory constraint (e.g. ofMeaning that the database of node l can contain up to 3 past times of information), i.e., the updated local timelineIs a summary time axisThe aggregate timelineIs an old database timelineUnion with the new incoming message timeline.
As a further improvement of the method of the present invention, the step S23 specifically includes: defining local prior varianceTo reflect the local prior probability of node lUncertainty of whereinIn order to be the state of the node l',selecting the node corresponding to the minimum local prior variance from other nodes l' stored in the database for the s-th recording time in the k-th updating and j is the serial number of the neighbor nodeAsThe sequence number of the smallest local prior variance is specifically as follows:
whereinFor the returned optimal node sequence number corresponding to the l', namely the sequence number of the minimum local prior variance,for inclusion of local prior variance in the databaseA set of all nodes of (a);
and then carrying out prior splicing according to the following formula:
wherein the content of the first and second substances,and (4) forming a set by the optimal node serial numbers corresponding to all l'.
As a further improvement of the method of the present invention, the step S24 specifically includes: defining is based on a set of local measurementsThe local measurement map of (1) is:
whereinFor measuring maps locallyCorresponding vertex set as local measurement mapA corresponding set of edges;
defining the triple SNCAMST asWhereinAndare respectivelyAndis selected from the group consisting of (a) a subset of,is the local prior probability,Is the local posterior probability,In order to measure the set of measurements locally,a local anchor node state set;
the segmentation difference is as follows:
wherein the content of the first and second substances,as a priori probabilities for the location after segmentation,the prior probability which is left after segmentation and is not used for positioning;
order toIs the maximum number of states ofSaid triplet SNCAMST, denoted asAll segmentation differences will constitute a set:
the SNCAMST that yields the smallest segmentation difference is:
calculating the edge probability by adopting the following formula to the SNCAMST with the minimum segmentation difference
Wherein the content of the first and second substances,is a subset of the local prior state set, andhas a probability density function of
As a further improvement of the method of the present invention, the step S25 specifically includes:
s251, judging whether the local prior set and the local anchor node state set are empty, if the local prior set or the local anchor node state set is not empty, executing the step S252, otherwise, executing the step S253;
s252, updating the local posterior probability by using the calculated marginal probability through a Bayesian method, and executing a step S253;
and S253, judging whether the current database time is the last time in the database, if so, predicting the local posterior probability by using the current local posterior probability and adopting a Kolmogorov equation.
As a further improvement of the method of the present invention, the formula for updating the local posterior probability by using the bayesian method is as follows:
wherein the content of the first and second substances,for the set of local a-priori states,in order to be the edge probability,is thatIs selected from the group consisting of (a) a subset of,is a local measurement set;
the formula for predicting the local posterior probability by adopting the Kolmogorov equation is as follows:
wherein the content of the first and second substances,for a set of local prior statesThe corresponding support set (i.e., the set with non-zero probability density).
An unmanned aerial vehicle cluster cooperative positioning apparatus based on asynchronous information comprises a computer device programmed to execute the steps of the unmanned aerial vehicle cluster cooperative positioning method based on asynchronous information.
Compared with the prior art, the invention has the advantages that:
1. the invention configures a database for each unmanned aerial vehicle node needing positioning in the unmanned aerial vehicle cluster, updates the database when a non-anchor node measures or receives the state of the anchor node or receives messages sent by other nodes, broadcasts state information to adjacent nodes according to the updated database, and updates the position of the node, can realize multi-unmanned aerial vehicle cluster cooperative positioning based on asynchronous information, does not need to rely on clock synchronization, can still describe correct node motion information during network asynchronous communication and asynchronous measurement, has communication volume and calculation amount independent of the scale of the network, and can realize large-scale unmanned aerial vehicle cluster cooperative positioning.
2. The method can be suitable for asynchronous communication and asynchronous measurement in a large-scale unmanned aerial vehicle cluster, can accurately position the unmanned aerial vehicle by self on the premise of occupying a small amount of communication bandwidth, solves the problem that the traditional mainstream BP-based positioning method cannot process asynchronous communication and asynchronous measurement information, is not limited by network scale, has small communication and calculation overhead when a large-scale dynamic network is positioned, and effectively solves the problem that huge communication and calculation overhead is needed when the large-scale dynamic network is positioned in the prior art.
3. The invention further realizes the database updating based on a distributed prior segmentation method, can ensure the correct acceptance and rejection of partial local prior states based on the continuity of the prior segmentation difference and the positioning estimation difference, and can effectively reduce the positioning difference and improve the positioning efficiency compared with the traditional method based on global information.
Drawings
Fig. 1 is a schematic flow chart of an implementation process of the unmanned aerial vehicle cluster cooperative positioning method based on asynchronous information according to the present embodiment.
Fig. 2 is a schematic diagram of measurement between an anchor node and a non-anchor node in the present embodiment.
Fig. 3 is a schematic diagram of the communication broadcast time of the non-anchor node in the embodiment.
Fig. 4 is a diagram illustrating the packet reception time in this embodiment.
Fig. 5 is a schematic flow chart of a specific implementation of non-anchor node location in this embodiment.
Fig. 6 is a detailed implementation flow diagram of implementing database update based on a distributed prior segmentation method in this embodiment.
Fig. 7 is a detailed implementation flow diagram of the local posterior update and the prior prediction in this embodiment.
Detailed Description
The invention is further described below with reference to the drawings and specific preferred embodiments of the description, without thereby limiting the scope of protection of the invention.
As shown in fig. 1, the method for cooperatively positioning a cluster of unmanned aerial vehicles based on asynchronous information in this embodiment includes the steps of:
s1, correspondingly configuring a database for storing information required by node positioning for each non-anchor node in an unmanned aerial vehicle cluster, wherein the non-anchor node is an unmanned aerial vehicle node which is unknown in position and needs to be positioned;
s2, when the target non-anchor node measures or receives the state of the anchor node or receives messages sent by other nodes, updating the database corresponding to the target non-anchor node, and executing the step S3 after the updating is finished;
and S3, generating broadcast information by the target non-anchor node according to the corresponding information in the database so as to broadcast the broadcast information to the adjacent nodes for updating state information, updating the position information of the target non-anchor node, and completing the positioning of the unmanned aerial vehicle node.
In this embodiment, a database is configured for each unmanned aerial vehicle node (non-anchor node) that needs to be positioned in an unmanned aerial vehicle cluster, the database is updated whenever the non-anchor node measures or receives the state of the anchor node or receives messages sent by other nodes, state information is broadcast to adjacent nodes according to the updated database, and the position of the unmanned aerial vehicle node is updated at the same time.
Different from a discrete time node motion model used in a traditional BP positioning method, the node motion model in the embodiment is based on continuous time, so that measurement information and communication interaction information are not limited by time slot synchronization any more, and subsequent asynchronous information processing is facilitated. The concrete model is as follows (the system specifically comprises I nodes, and the set is usedTo represent):
dxi(t)=fi(xi(t),t)dt+dβi(t), (1)
yi(t)=gi(xi(t)), (2)
wherein, formula (1) is a system equation, formula (2) is a position equation, and states x of the nodes i are described respectivelyi(t) evolution law and position yi(t) law of change, fiAnd giRespectively a system function and a position function, betai(t) is Brownian motion.
The measurement information used in this embodiment is distance measurement information, which can be obtained by TOA (time of arrival ranging method), TDOA (time difference of arrival ranging method), or RSS (received signal strength ranging method). When node i is at node jWhen measurement is carried out at any moment, the measurement equation is as follows:
In a specific application embodiment, the inter-measurement information between unmanned aerial vehicle nodes is shown in fig. 2, where a1,a2,a3For an anchor node, the state of the anchor node is precisely known,/1,...,l5The states of the non-anchor nodes obey a certain random distribution for the non-anchor nodes, and the hatched portions bounded by the dotted lines in the figure represent regions where the non-anchor nodes may appear with high probability. By way of measurement, the high probability region of non-anchor nodes has an overall decreasing trend.
In this embodiment, communication information is only transferred between non-anchor nodes, and the content includes distance measurement information and location prior information of a node set. The communication information is delivered in the form of broadcast packets, the broadcast time of which is shown in fig. 3, taking node 1 as an example,representing the first packet broadcast by node 1, with a start time ofThe end time isThe time when the data packet is received in this embodiment is shown in fig. 4, where there is a processing delay between the broadcast stop time and the received time. For the anchor node, only the passive response of the anchor node state information sending request sent by the non-anchor node is needed.
This embodiment specifies each non-anchor nodeComprising a databaseThe database stores the information needed by the node l for self positioning; after measurement, receiving the state of the anchor node, or receiving the message sent by other nodes, the non-anchor node l will correspondingly update its own database(ii) a Once the database is updated, the non-anchor node l designs broadcast information according to the existing information in the database to help the neighbor node to update corresponding state information; once the database is updated, the non-anchor node l updates the position information of the non-anchor node l by using the information in the database, and all unmanned planes in the unmanned plane cluster can estimate the real-time position of the non-anchor node l through mutual cooperation.
As shown in fig. 5, the detailed steps of implementing the non-anchor node location by the unmanned aerial vehicle cluster cooperative location algorithm based on asynchronous information in this embodiment are as follows:
Step 2: if measuring other nodes or receiving the state information of the anchor node or receiving the information sent by other nodes, executing the step 3;
And 4, step 4: database with a plurality of databasesAfter updating, the broadcast information is designed and pressedCalculating state distribution;
In this embodiment, positioning of a non-anchor node is specifically realized by configuring an unmanned aerial vehicle cluster cooperative positioning algorithm based on asynchronous information, and a specific flow of the algorithm is shown as the following algorithm 1:
in this embodiment, the data recorded at each time in the database of the non-anchor node includes four parts of data, namely, a local prior probability, a local posterior probability, a local measurement set, and a local anchor node state set, where the local prior probability isThe prior joint probability density information containing nodes related to positioning is continuously updated, and the local posterior probability isThe posterior joint probability density information containing the nodes related to the positioning is continuously updated, and the local measurement set isContaining all measurements related to positioning and continuously accepting or updating, the local anchor node state set isIncluding all anchor node state information related to positioning and continuously accepting or updating, t being the current time,the recording time of the s-th time in the k-th updating is shown, wherein k and s are positive integers respectively; the broadcast information comprises three parts of information of local prior probability, the local measurement set and a local anchor node state set.
In this embodiment, the database of the non-anchor nodeUpdates are only made after making measurements, receiving anchor node status, or receiving messages sent by other nodes, and soThe change is made at discrete moments, namely:
wherein the content of the first and second substances,a database corresponding to the ith non-anchor node,in order to update the database after the update,is a set of update times for the database,for the kth update of the database.
wherein the content of the first and second substances,for the database inThe recording of the time of day is carried out,for the set of all the recording moments,is the local prior probability,Is the local posterior probability,In order to measure the set of measurements locally,is a local anchor node state set, t is the current time,is the s-th recording time in the k-th update (wherein k and s are positive integers respectively). For recordingIt is composed of four parts, namely a local priorLocal posteriorLocal measurement setAnd local anchor node state set
In this embodiment, there is only local priorLocal measurement setAnd local anchor node state setParticipating in information interaction between nodes, local posterioriThe interaction is not participated, that is, the broadcast information only contains the above three kinds of information, and the specific form is:
wherein the content of the first and second substances,is that makeSet of established moments, i.e.Only the different parts of the current database from the previous database are included.
In view of the actual communication conditions, not all parts of the broadcast information can be successfully received by other nodes, and thus the received information may be all or only a portion of the broadcast information. In this embodiment areAt this time, the specific form of receiving information from node j by non-anchor node l is as follows:
whereinConsisting of three parts, i.e. local priorsLocal measurement setLocal anchor node state setThe concrete form is as follows:
in step S2 of this embodiment, a local time axis is updated first, and a distributed prior segmentation method is used to update a local measurement set, a local anchor node state set, a local prior probability, and a local posterior probability in a database based on the updated time axis, and the specific steps include:
s21, judging whether the current time is the database time, wherein the database time is the latest time in the local time axis, if so, executing the step S22, and if not, exiting;
s22, local measurement set and local anchor node state set updating: judging whether the updating time corresponds to the database time, if so, adding a new measurement set in the local measurement set to obtain an updated local measurement set, and adding a new anchor node state set in the local anchor node state set to obtain an updated local anchor node state set, otherwise, adding the measurement set in the interaction information in the local measurement set to obtain an updated local measurement set, and adding the anchor node state set in the interaction information in the local anchor node state set to obtain an updated local anchor node state set;
s23, priori fusion: respectively searching out a neighbor node j with the minimum prior variance for each node l' contained in a database of the node l, and splicing the prior distributions of all the searched nodes to form combined prior distribution;
s24, prior segmentation: subset based on local measurement setLocal prior state setAndsubsets of local anchor node state setsDefining a triple SNCAMST, selecting the triple SNCAMST with the minimum segmentation difference and calculating the edge probability;
s25, posterior updating and prior forecasting: and updating the local posterior probability by using the calculated marginal probability, and predicting the local prior probability by using the updated local posterior probability at the last moment of the database.
In the embodiment, the database is updated by the distributed prior segmentation method, and based on the continuity of the prior segmentation difference and the positioning estimation difference, the correct accepting or rejecting of the local prior partial state can be ensured.
In this embodiment, at each database update timeThe non-anchor node l will have its database fromIs updated toThe update of the database comprises five parts: a local timeline, a local measurement set, a local anchor node state set, a local prior, and a local posterior. The local time axis is updated, and then other parts are updated based on the updated local time axis. Due to the limited computational and memory capabilities of the nodes,it cannot contain data at all past times, especially when k becomes very large over time, and this embodiment usesTo limitThe maximum number of time instants contained in (a),is a maximum memory constraint (e.g. ofMeaning that the database of node l can contain up to 3 past times of information), i.e., the updated local timelineIs a summary time axisWherein the timeline is aggregatedIs an old database timelineUnion with the new incoming message timeline.
In this example, the local measurement setAnd local anchor node state setWhen updating, ifAndcorrespondingly (i.e. the updated data time corresponds to the latest time in the local time axis), the updated local measurement set is added to the new measurement set on the original basisAt the moment, the updated local anchor node state set is added into the new anchor node state set on the original basisIf it is notAndif the local measurement sets are not equal, the updated local measurement set is added with a new measurement set contained in the interactive information on the original basisAt this time, the updated local anchor node state set is added to the new anchor node state set contained in the interactive information on the original basis
Since the prior distribution of each node l 'contained in the database of the node l is multiple, that is, each neighbor j of the node l provides different prior information of the node l', however, due to the limitation of information, the prior information given by the neighbor is good or bad. In the embodiment, prior fusion is to find out the neighbor node j with the smallest prior variance (i.e. the best estimation effect) for each l', and record the neighbor node j asFinally, all the l' prior distributions are spliced together to form a joint prior distribution. During splicing/fusion, coupling between different neighbor information is ignored, that is, assuming that prior information given by different j is independent, joint distribution is equal to the product of distribution given by different j.
In this embodiment, step S23 returns the fused priorThe method comprises the following specific steps: first, a local prior variance is definedTo reflect that node l' is locally a prioriUncertainty of whereinIn order to be the state of the node l',is the s-th recording time in the k-th updating, and j is the serial number of the neighbor node. Local prior varianceThe smaller, theThe smaller the uncertainty there is, the embodiment chooses the one corresponding to the smallest local prior varianceAnd use it asAccording to a probability ofA priori stitching is performed, wherein,for inclusion of local prior variance in the databaseA set of all nodes.
In this embodiment, the specific step of step S24 includes: first, defining a measurement state triplet with a state quantity constraintSNCAMST. SNCAMST relies on local measurement maps, based on local measurement setsThe local measurement map of (a) is defined as:
whereinFor measuring maps locallyCorresponding vertex set as local measurement mapA corresponding set of edges;
on the basis, a state constraint measurement state triple (SNCAMST) is definedWhereinAndare respectivelyAnda subset of (a).
The estimated variance (estimation gap) is a segmentation gapIn whichFor the priors used in the positioning algorithm after segmentation,representing the residual priors after segmentation (i.e. the priors not used by the localization algorithm), the present embodiment can obtain better localization effect by selecting a prior with the minimum segmentation difference.
Order toIs the maximum number of states ofSNCAMST of (D)All segmentation differences will constitute a set:
the SNCAMST that yields the smallest segmentation difference is:
on the basis, the SNCAMST with the minimum segmentation difference is calculated by adopting the following marginal probability formula
Wherein the content of the first and second substances,is a subset of the local prior state set, andhas a probability density function of
In this embodiment, the step S25 includes the following steps:
s251, judging whether the local prior set and the local anchor node state set are empty, if the local prior set or the local anchor node state set is not empty, executing the step S252, otherwise, executing the step S253;
s252, updating the local posterior probability by using the calculated marginal probability and adopting a Bayesian method, and executing a step S253;
and S253, judging whether the current database time is the last time in the database, if so, predicting the local posterior probability by using the current local posterior probability and adopting a Kolmogorov equation.
In this embodiment, specifically, if the local prior set or the local anchor node state set is not empty, the local posterior is updated by using a bayesian method:
if it is notIs not provided withThe updated local a posteriori is used as the computed local a prioriLocal posterior probabilities were predicted using the Kolmogorov equation:
wherein the content of the first and second substances,for a set of local prior statesThe corresponding support set (i.e., the set with non-zero probability density).
In the specific application embodiment, the time axis is updated based onLocal measurement set, local anchor node state set, local prior and local posterior update are realized by configuring a distributed prior segmentation algorithm, and the specific process of the distributed prior segmentation method is shown as algorithm 2.
In the above algorithm 2, the databaseAccording to time setThe time in the database is updated sequentially from element to element in the order from small to large, and the elements in the database are updated sequentially from element to elementThe updating comprises five parts of local measurement set updating, local anchor node state set updating, prior fusion, prior segmentation, posterior updating and prior prediction.
As shown in fig. 6, the detailed flow of the distributed prior segmentation algorithm for implementing the local measurement set, the local anchor node state set, the local prior and the local posterior update is as follows:
step 1: judging whether the current time is the database time, namely whether the current time is satisfiedIf yes, the step 2 is executed, otherwise, the operation is ended;
step 2: judging whether the updating time is the corresponding database time, namely whether the updating time meets the requirementsIf yes, executing step 3, otherwise executing step 4;
and step 3: push buttonAdding a new measurement set in the local database, and pressingAdding a new anchor node state set into a local database, and executing the step 5;
and 4, step 4: push buttonJoining measurement sets in the interaction information at the local database, andadding a new anchor node state set in the interactive information into the local database, and executing the step 5;
and 5: for other nodes l' stored in each database, the minimum local prior variance sequence number is taken
and step 9: the local posteriori is updated and the prior probability is predicted.
The foregoing is considered as illustrative of the preferred embodiments of the invention and is not to be construed as limiting the invention in any way. Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical spirit of the present invention should fall within the protection scope of the technical scheme of the present invention, unless the technical spirit of the present invention departs from the content of the technical scheme of the present invention.
Claims (7)
1. An unmanned aerial vehicle cluster cooperative positioning method based on asynchronous information is characterized by comprising the following steps:
s1, correspondingly configuring a database for storing information required by node positioning for each non-anchor node in an unmanned aerial vehicle cluster, wherein the non-anchor node is an unmanned aerial vehicle node which is unknown in position and needs to be positioned;
s2, when the target non-anchor node measures or receives the state of the anchor node or receives messages sent by other nodes, updating the database corresponding to the target non-anchor node, and executing the step S3 after the updating is finished;
s3, the target non-anchor node generates broadcast information according to the corresponding information in the database to broadcast the broadcast information to adjacent nodes for state information updating and updating the position information of the target non-anchor node, and positioning of the unmanned aerial vehicle node is completed;
the data recorded at each moment in the database of the non-anchor node comprises four parts of data of a local prior probability, a local posterior probability, a local measurement set and a local anchor node state set, wherein the local prior probability comprises prior joint probability density information of a node related to positioning and is continuously updated, the local posterior probability comprises posterior joint probability density information of the node related to positioning and is continuously updated, the local measurement set comprises all anchor node state information related to positioning and is continuously selected or updated, the local anchor node state set comprises all anchor node state information related to positioning and is continuously selected or updated, and the broadcast information comprises three parts of information of the local prior probability, the local measurement set and the local anchor node state set;
in step S2, a local time axis is updated first, and a distributed prior segmentation method is used to update the local measurement set, the local anchor node state set, the local prior probability, and the local posterior probability in the database based on the updated time axis, and the specific steps include:
s21, judging whether the current time is the database time which is the latest time in the local time axis, if so, executing the step S22, and if not, exiting;
s22, local measurement set and local anchor node state set updating: judging whether the updating time corresponds to the database time, if so, adding a new measurement set in the local measurement set to obtain an updated local measurement set, and adding a new anchor node state set in the local anchor node state set to obtain an updated local anchor node state set, otherwise, adding the measurement set in the interaction information in the local measurement set to obtain an updated local measurement set, and adding the anchor node state set in the interaction information in the local anchor node state set to obtain an updated local anchor node state set;
s23, priori fusion: respectively searching out a neighbor node j with the minimum prior variance for each node l' contained in a database of the node l, and splicing the prior distributions of all the searched nodes to form combined prior distribution;
s24, prior segmentation: subset based on local measurement setLocal prior state setAnd a subset of a local anchor node state setDefining a triple SNCAMST, selecting the triple SNCAMST with the minimum segmentation difference and calculating the edge probability;
s25, posterior updating and prior forecasting: updating the local posterior probability using the calculated marginal probability, and predicting the local prior probability using the updated local posterior probability at the last moment of the database.
2. The unmanned aerial vehicle cluster cooperative positioning method based on asynchronous information as claimed in claim 1, wherein the database of the non-anchor node is specifically:
wherein the content of the first and second substances,a database corresponding to the ith non-anchor node,in order to update the database after the update,is a set of update times for the database,updating for the k time of the database;
wherein the content of the first and second substances,for the database inThe recording of the time of day is carried out,the collection of all recording moments;is the local prior probability that the current probability is,is the local a-posteriori probability,in order to measure the set of measurements locally,a local anchor node state set; t is the current time of day and t is,the recording time of the s-th time in the k-th updating is shown, wherein k and s are positive integers respectively;
the broadcast information is specifically:
3. The cooperative positioning method for unmanned aerial vehicle cluster based on asynchronous information as claimed in claim 1, wherein the updating of local time axis usesTo limit the maximum number of moments contained in the database, whereinFor maximum memory constraint, i.e. updated local time axisIs a summary time axisThe aggregate timelineIs an old database timelineUnion with the new incoming message timeline.
4. The unmanned aerial vehicle cluster cooperative positioning method based on asynchronous information as claimed in claim 1, wherein the step S23 specifically comprises: defining local prior varianceTo reflect the local prior probability of node lUncertainty of whereinIn order to be the state of the node l',selecting the node corresponding to the minimum local prior variance from other nodes l' stored in the database for the s-th recording time in the k-th updating and j is the serial number of the neighbor nodeAsThe sequence number of the smallest local prior variance is specifically as follows:
whereinFor the returned optimal node sequence number corresponding to the l', namely the sequence number of the minimum local prior variance,for inclusion of local prior variance in the databaseA set of all nodes of (a);
and then carrying out prior splicing according to the following formula:
5. The unmanned aerial vehicle cluster cooperative positioning method based on asynchronous information as claimed in claim 1, wherein the step S24 specifically comprises: defining is based on a set of local measurementsThe local measurement map of (1) is:
whereinFor measuring maps locallyCorresponding vertex set as local measurement mapA corresponding set of edges;
defining the triple SNCAMST asWhereinAndare respectivelyAndis selected from the group consisting of (a) a subset of,for the set of local a-priori states,is the local prior probability,Is the local posterior probability,In order to measure the set of measurements locally,a local anchor node state set;
the segmentation difference is as follows:
wherein the content of the first and second substances,as a priori probabilities for the location after segmentation,is left after divisionLower prior probability not used for positioning;
order toIs the maximum number of states ofSaid triplet SNCAMST, denoted asAll segmentation differences will constitute a set:
the SNCAMST that yields the smallest segmentation difference is:
calculating the edge probability by adopting the following formula to the SNCAMST with the minimum segmentation difference
6. The unmanned aerial vehicle cluster cooperative positioning method based on asynchronous information as claimed in claim 1, wherein the step S25 comprises the following steps:
s251, judging whether the local prior set and the local anchor node state set are empty, if the local prior set or the local anchor node state set is not empty, executing the step S252, otherwise, executing the step S253;
s252, updating the local posterior probability by using the calculated marginal probability through a Bayesian method, and executing a step S253;
and S253, judging whether the current database time is the last time in the database, if so, predicting the local posterior probability by using the current local posterior probability and adopting a Kolmogorov equation.
7. The cluster cooperative positioning method for unmanned aerial vehicles based on asynchronous information as claimed in claim 6, wherein the formula for updating the local posterior probability by Bayesian method is as follows:
wherein the content of the first and second substances,for the set of local a-priori states,in order to be the edge probability,is thatIs selected from the group consisting of (a) a subset of,is a local measurement set;
the formula for predicting the local posterior probability by adopting the Kolmogorov equation is as follows:
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