CN111405514A - Cooperative positioning method and system for wireless sensor network under hollow terrain - Google Patents

Cooperative positioning method and system for wireless sensor network under hollow terrain Download PDF

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CN111405514A
CN111405514A CN202010216586.0A CN202010216586A CN111405514A CN 111405514 A CN111405514 A CN 111405514A CN 202010216586 A CN202010216586 A CN 202010216586A CN 111405514 A CN111405514 A CN 111405514A
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CN111405514B (en
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柴森春
王昭洋
张百海
崔灵果
姚分喜
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Beijing Institute of Technology BIT
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W4/00Services specially adapted for wireless communication networks; Facilities therefor
    • H04W4/30Services specially adapted for particular environments, situations or purposes
    • H04W4/38Services specially adapted for particular environments, situations or purposes for collecting sensor information
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W40/00Communication routing or communication path finding
    • H04W40/02Communication route or path selection, e.g. power-based or shortest path routing
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W40/00Communication routing or communication path finding
    • H04W40/24Connectivity information management, e.g. connectivity discovery or connectivity update
    • HELECTRICITY
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    • H04WWIRELESS COMMUNICATION NETWORKS
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Abstract

The invention relates to a method and a system for cooperative positioning of a wireless sensor network under a hollow terrain. The cooperative positioning method and the system for the wireless sensor network under the cavity terrain construct a cooperative positioning model after acquiring application data of the wireless sensor network under the cavity terrain, determine an optimal auxiliary node in the cooperative positioning model according to an optimal selection strategy or a suboptimal selection strategy, determine an iteration parameter in the cooperative positioning model by adopting an update rule transmitted by variation messages according to the optimal auxiliary node, and finally realize accurate positioning on the wireless sensor network under the cavity terrain according to the iteration parameter. Moreover, the construction of the cooperative positioning model provided by the invention can further solve the problem of sparsity in the positioning process.

Description

Cooperative positioning method and system for wireless sensor network under hollow terrain
Technical Field
The invention relates to the technical field of system engineering, in particular to a method and a system for cooperative positioning of a wireless sensor network under a hollow terrain.
Background
Wireless Sensor Networks (WSNs) are composed of a large number of sensor nodes randomly deployed in a monitoring area, and a multi-hop ad hoc network system is formed in a wireless communication manner, wherein the sensor nodes can acquire monitoring information and upload the monitoring information to a central management system, but the monitoring information has practical application value only on the premise of knowing a monitoring position, so that the research on the wireless sensor network positioning technology has very important significance.
At present, wireless sensor network positioning research is focused on homogeneous network positioning technology, homogeneous network positioning methods are mature and widely applied in various fields, but wireless sensor networks often face complex distribution environments, and in actual network deployment and application, due to the deployment mode (random distribution of aircrafts), physical space limitations (natural environmental factors such as buildings, lakes, mountains or basins) and some non-predictable factors (node faults) and the like, positioning accuracy is reduced or even positioning fails under special conditions, and the wireless sensor networks are prevented from executing predetermined functions. The heterogeneous network caused by the complex environment is not suitable for a general positioning method, and the positioning precision can not meet the actual engineering requirement.
In part of researches, a heterogeneous network is taken as a research object, the influence of the heterogeneous network on the ranging precision is considered, the positioning problem of the heterogeneous network is researched from the distance estimation direction, and a selective multi-lateralization (SM) method is provided to realize positioning after the screening of anchor nodes is combined. Partial research also provides a DV-maxHop method, and an interactive extended Pymote simulation framework is adopted for deep statistics and visual analysis. In addition, the influence of network topological structures, particularly cavity networks, on node positioning results under various non-ranging models is explored, the characteristic of cavity terrain is explored, the ranging accuracy of the nodes under the cavity terrain is improved by creating virtual nodes, and positioning achieved by adopting a heuristic multi-dimensional scaling method is also an important direction in heterogeneous network positioning research. However, most of the research on the problem of the holes in the heterogeneous network is focused on the non-cooperative positioning method, when the number of anchor nodes and unknown nodes is small, the positioning failure is easily caused, and the positioning accuracy of the non-cooperative positioning method is still to be improved compared with the actual engineering requirement.
Disclosure of Invention
The cooperative positioning method and system for the wireless sensor network under the hollow terrain can solve the problem of node sparsity in the positioning process of the heterogeneous sensor network, and further improve the positioning accuracy of the wireless sensor network under the hollow terrain.
In order to achieve the purpose, the invention provides the following scheme:
a method for cooperative positioning of a wireless sensor network under a hollow terrain comprises the following steps:
acquiring application data of a wireless sensor network under a hollow terrain; the application data includes: the method comprises the following steps that the distance between an unknown node in a wireless sensor network and other unknown nodes in the communication radius of the unknown node under the hollow terrain, the distance between the unknown node and anchor nodes in the communication radius of the unknown node, the initial position of the unknown node and the actual positions of all anchor nodes in the network are determined;
constructing a co-location model according to the application data;
determining an optimal auxiliary node in the co-location model according to an optimal selection strategy or a suboptimal selection strategy;
determining iteration parameters in the cooperative positioning model by adopting an updating rule transmitted by variation messages according to the optimal auxiliary node;
and finishing the positioning of the wireless sensor network under the hollow terrain according to the iteration parameters.
Optionally, the constructing a co-location model according to the application data specifically includes:
constructing a maximum likelihood probability model of the collaborative position of the unknown node according to the distance between the unknown node and other unknown nodes in the communication radius of the unknown node in the wireless sensor network under the hollow terrain, the distance between the unknown node and anchor nodes in the communication radius of the unknown node, the initial position of the unknown node and the actual positions of all anchor nodes in the network;
determining maximum likelihood probability models of the collaborative positions of all nodes in the wireless sensor network under the hollow terrain according to the maximum likelihood probability models of the collaborative positions of the unknown nodes;
determining a position maximum likelihood probability model of all nodes in the wireless sensor network under the hollow terrain according to the initial position of the unknown node;
and constructing the cooperative positioning model according to the maximum likelihood probability model of the cooperative positions of all the nodes in the wireless sensor network under the hollow terrain.
Optionally, the determining an optimal auxiliary node in the co-location model according to the optimal selection strategy or the sub-optimal selection strategy specifically includes:
determining a node corresponding to the minimum folding angle on the shortest path tree in the co-location model as an optimal auxiliary node;
and if a plurality of nodes corresponding to the minimum folding angles on the shortest path tree in the cooperative positioning model are determined, constructing a selection triangle, and determining the vertex corresponding to the two adjacent sides with the minimum difference in the selection triangle as the optimal auxiliary node.
Optionally, the determining, according to the optimal auxiliary node, an iteration parameter in the co-location model by using an update rule transmitted by a variation message specifically includes:
get factor node gmn
According to the update rule of the variation message transmission, passing through a formula
Figure BDA0002424690600000031
Determining from the factor node gmnMessages to variable node z
Figure BDA0002424690600000032
Wherein,
Figure BDA0002424690600000033
as an initial value of the path tree break angle, θmFor the actual position of the unknown node m, θnThe actual location of unknown node n within communication range of any anchor node or m,
Figure BDA0002424690600000034
is known as
Figure BDA0002424690600000035
Expectation of lower variable node z, p (—) is occurrence probability;
by the formula
Figure BDA0002424690600000036
Determining the position parameter of the unknown node m after l iterations
Figure BDA0002424690600000037
Wherein,
Figure BDA0002424690600000038
for the initial position of the unknown node m,
Figure BDA0002424690600000039
as the initial position of unknown node m
Figure BDA00024246906000000310
N is any anchor node or unknown node within communication range of m,
Figure BDA00024246906000000311
s is a set of anchor nodes, dmnFor unknown measured distances between node m and node n,
Figure BDA00024246906000000313
is dmnThe variance of (a) is determined,
Figure BDA00024246906000000314
for the location parameters of the unknown node after l-1 iterations,
Figure BDA00024246906000000315
for a revised distance between the unknown node m and any anchor node or unknown node n within communication range of m at i-1 iterations,
Figure BDA0002424690600000041
to learn the calculated distance of the estimated location of node m from node n at l-1 iterations,
Figure BDA0002424690600000042
for the location parameter of the unknown node m after l-1 iterations,
Figure BDA0002424690600000043
is a set of other unknown nodes within the communication radius of the unknown node m.
By the formula
Figure BDA0002424690600000044
Determining variance parameter of unknown node m after l iterations
Figure BDA0002424690600000045
By the formula
Figure BDA0002424690600000046
Determining variance of shortest path tree of nodes m and n after l iterations
Figure BDA0002424690600000047
By the formula
Figure BDA0002424690600000048
Determining the break angle of the shortest path tree of the nodes m and n after l iterations
Figure BDA0002424690600000049
Wherein,
Figure BDA00024246906000000410
is node mN, variance of the shortest path tree after l iterations,
Figure BDA00024246906000000411
is the initial value of the shortest path tree break angle,
Figure BDA00024246906000000412
is composed of
Figure BDA00024246906000000413
The initial variance of the measured time period of the time period,
Figure BDA00024246906000000414
and
Figure BDA00024246906000000415
are all intermediate variables of l-1 iterations,
Figure BDA00024246906000000416
is an estimate of the dog-ear after l-1 iterations.
A co-location system of a wireless sensor network under hollow terrain, comprising:
the application data acquisition module is used for acquiring application data of the wireless sensor network under the hollow terrain; the application data includes: the method comprises the following steps that the distance between an unknown node in a wireless sensor network and other unknown nodes in the communication radius of the unknown node under the hollow terrain, the distance between the unknown node and anchor nodes in the communication radius of the unknown node, the initial position of the unknown node and the actual positions of all anchor nodes in the network are determined;
the cooperative positioning model building module is used for building a cooperative positioning model according to the application data;
the optimal auxiliary node determining module is used for determining the optimal auxiliary node in the cooperative positioning model according to the optimal selection strategy or the suboptimal selection strategy;
the iteration parameter determining module is used for determining iteration parameters in the cooperative positioning model by adopting an updating rule transmitted by variation messages according to the optimal auxiliary node;
and the positioning module is used for finishing the positioning of the wireless sensor network under the hollow terrain according to the iteration parameters.
Optionally, the co-location model building module specifically includes:
the first maximum likelihood probability model building unit is used for building a maximum likelihood probability model of the collaborative position of an unknown node according to the distance between the unknown node and other unknown nodes in the communication radius of the unknown node in the wireless sensor network under the hollow terrain, the distance between the unknown node and anchor nodes in the communication radius of the unknown node, the initial position of the unknown node and the actual positions of all anchor nodes in the network;
the second maximum likelihood probability model building unit is used for determining maximum likelihood probability models of the collaborative positions of all the nodes in the wireless sensor network under the hollow terrain according to the maximum likelihood probability models of the collaborative positions of the unknown nodes;
the position maximum likelihood probability model building unit is used for determining position maximum likelihood probability models of all nodes in the wireless sensor network under the hollow terrain according to the initial position of the unknown node;
and the cooperative positioning model building unit is used for building the cooperative positioning model according to the maximum likelihood probability models of the cooperative positions of all the nodes in the wireless sensor network under the hollow terrain and the position maximum likelihood probability model.
Optionally, the optimal auxiliary node determining module specifically includes:
the optimal auxiliary node determining unit is used for determining one node corresponding to the minimum folding angle on the shortest path tree in the cooperative positioning model as an optimal auxiliary node;
and if a plurality of nodes corresponding to the minimum folding angles on the shortest path tree in the cooperative positioning model are determined, constructing a selection triangle, and determining the vertex corresponding to the two adjacent sides with the minimum difference in the selection triangle as the optimal auxiliary node.
Optionally, the iteration parameter determining module specifically includes:
a factor node acquisition unit for acquiring a factor node gmn
A message determining unit for determining the update rule of the variation message transmission according to the formula
Figure BDA0002424690600000061
Determining from the factor node gmnMessages to variable node z
Figure BDA0002424690600000062
Wherein,
Figure BDA0002424690600000063
as an initial value of the path tree break angle, θmFor the actual position of the unknown node m, θnThe actual location of unknown node n within communication range of any anchor node or m,
Figure BDA0002424690600000064
is known as
Figure BDA0002424690600000065
Expectation of lower variable node z, p (—) is occurrence probability;
a position parameter determination unit for determining the position of the object by formula
Figure BDA0002424690600000066
Determining the position parameter of the unknown node m after l iterations
Figure BDA0002424690600000067
Wherein,
Figure BDA0002424690600000068
for the initial position of the unknown node m,
Figure BDA0002424690600000069
as the initial position of unknown node m
Figure BDA00024246906000000610
N is any anchor node or m-channelAn unknown node within the range of the signal,
Figure BDA00024246906000000611
s is a set of anchor nodes, dmnThe distance between node m and node n is unknown,
Figure BDA00024246906000000613
is dmnThe variance of (a) is determined,
Figure BDA00024246906000000614
for the location parameters of the unknown node after l-1 iterations,
Figure BDA00024246906000000615
the corrected distance between the unknown node m and any anchor node or unknown node n in the communication range of the unknown node m,
Figure BDA00024246906000000616
to learn the calculated distance of the estimated location of node m from node n at l-1 iterations,
Figure BDA00024246906000000617
for the location parameter of the unknown node m after l-1 iterations,
Figure BDA00024246906000000618
is a set of other unknown nodes within the communication radius of the unknown node m.
A variance parameter determination unit for determining variance of the received signal by formula
Figure BDA00024246906000000619
Determining variance parameter of unknown node m after l iterations
Figure BDA00024246906000000620
A variance determining unit for determining variance by formula
Figure BDA0002424690600000071
Determining the shortest-path tree of nodes m, n after l iterationsVariance (variance)
Figure BDA0002424690600000072
A break angle determining unit for determining a break angle by a formula
Figure BDA0002424690600000073
Determining the break angle of the shortest path tree of the nodes m and n after l iterations
Figure BDA0002424690600000074
Wherein,
Figure BDA0002424690600000075
is the variance of the shortest path tree of the nodes m and n after l iterations,
Figure BDA0002424690600000076
is the initial value of the shortest path tree break angle,
Figure BDA0002424690600000077
is composed of
Figure BDA0002424690600000078
The initial variance of the measured time period of the time period,
Figure BDA0002424690600000079
and
Figure BDA00024246906000000710
are all intermediate variables of l-1 iterations,
Figure BDA00024246906000000711
is an estimate of the dog-ear after l-1 iterations.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
according to the cooperative positioning method and the system for the wireless sensor network under the hollow terrain, the cooperative positioning model is constructed after application data of the wireless sensor network under the hollow terrain are obtained, the optimal auxiliary node in the cooperative positioning model is determined according to the optimal selection strategy or the suboptimal selection strategy, then the iteration parameter in the cooperative positioning model is determined according to the optimal auxiliary node by adopting the update rule of variation message transmission, and finally the accurate positioning of the wireless sensor network under the hollow terrain is realized according to the iteration parameter. In addition, the construction of the cooperative positioning model provided by the invention can further solve the problem of node sparsity in the positioning process.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
Fig. 1 is a flowchart of a co-location method for a wireless sensor network under a hollow terrain according to an embodiment of the present invention;
FIG. 2 is a diagram illustrating a relationship between node distance measurement and a cavity location according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of an optimal selection strategy according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a sub-optimal selection strategy according to an embodiment of the present invention;
fig. 5 is a schematic structural diagram of a cooperative positioning system of a wireless sensor network under a hollow terrain according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The cooperative positioning method and the system for the wireless sensor network under the hollow terrain can solve the problem of sparsity in the positioning process, so that the wireless sensor network under the hollow terrain can be accurately positioned.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
Fig. 1 is a flowchart of a co-location method for a wireless sensor network under a hollow terrain according to an embodiment of the present invention, and as shown in fig. 1, the co-location method for the wireless sensor network under the hollow terrain includes:
s1, acquiring application data of the wireless sensor network under the hollow terrain; the application data includes: the method comprises the following steps that the distance between an unknown node in a wireless sensor network and other unknown nodes in the communication radius of the unknown node under the hollow terrain, the distance between the unknown node and anchor nodes in the communication radius of the unknown node, the initial position of the unknown node and the actual positions of all anchor nodes in the network are determined;
s2, constructing a co-location model according to the application data;
s3, determining the optimal auxiliary node in the co-location model according to the optimal selection strategy or the suboptimal selection strategy;
s4, determining iteration parameters in the co-location model by adopting an update rule transmitted by variation messages according to the optimal auxiliary node;
and S5, positioning the wireless sensor network under the hollow terrain according to the iteration parameters.
Wherein the step of constructing the co-location model according to the application data in S2 includes:
constructing a maximum likelihood probability model of the collaborative position of an unknown node according to the distance between the unknown node and other unknown nodes in the communication radius of the unknown node, the distance between the unknown node and anchor nodes in the communication radius of the unknown node and the actual positions of all the anchor nodes in the wireless sensor network under the hollow terrain;
determining maximum likelihood probability models of the collaborative positions of all nodes in the wireless sensor network under the hollow terrain according to the maximum likelihood probability models of the collaborative positions of the unknown nodes;
determining a position maximum likelihood probability model of all nodes in the wireless sensor network under the hollow terrain according to the initial position of the unknown node;
and constructing the cooperative positioning model according to the maximum likelihood probability model of the cooperative positions of all the nodes in the wireless sensor network under the hollow terrain.
The specific implementation process for constructing the co-location model comprises the following steps:
suppose there is M-N in a wireless sensor networkA+NaA node, wherein NAIndicating the number of anchor nodes, NaIndicating the number of unknown nodes, the position of the mth node is
Figure BDA0002424690600000091
Wherein
Figure BDA0002424690600000092
A set of unknown nodes is represented as,
Figure BDA0002424690600000093
representing a set of anchor nodes, with an actual distance between nodes m, n of
Figure BDA0002424690600000094
Where | · | | represents the 2 norm of the vector.
The unknown nodes are assumed to be randomly distributed in a certain area, a direct communication mode is adopted for the unknown nodes in the communication radius, the distance between the unknown nodes in the communication radius is calculated through Received Signal Strength (RSS), in the positioning process of the nodes, only the unknown nodes in the communication radius generate a synergistic effect, and the unknown nodes outside the communication radius do not consider positioning synergy temporarily. The distance between the unknown node and the anchor node is estimated by adopting a multi-hop mode, namely the shortest distance between the node m and the node n, which is calculated by the shortest path tree, represents the distance d between the unknown node and the anchor nodemnBut due to the presence of holesAs shown in fig. 2, a rectangle H in the graph represents a void, m represents an unknown node, n represents an unknown node in any anchor node or m communication range, a connecting line between m, o, and n represents a shortest path tree spanning the void between the nodes m and n, wherein a node o represents a node on a boundary of the void, also called an auxiliary node, for a path not passing through the void, no auxiliary node exists, r represents a communication radius, a distance between nodes is represented by a shortest path tree, and a distance d between nodes is represented by a shortest path treeso≈d1,dot≈d2,dgo≈d3,dgs≈d4,dgt≈d5The node g is any node of the communication radius inner points of the node o and is called a virtual node. Therefore, the distance d between the nodes is determined according to the formula (1)mnIs modified into
Figure BDA0002424690600000101
As shown in equation (1).
Figure BDA0002424690600000102
Wherein the node o is the node m, the node located at the void boundary on the shortest path of n, dmo,donThe shortest paths between nodes m, o and between nodes o, n,
Figure BDA0002424690600000103
for the break angle ∠ sot on the shortest path tree of the node m and n, the modified node distance follows normal distribution
Figure BDA0002424690600000104
For the unknown nodes and the unknown nodes within the communication radius, the observation distance does not relate to the hole problem, so that
Figure BDA0002424690600000105
In summary, the maximum likelihood model of cooperative location compliance of a single unknown node is
Figure BDA0002424690600000106
Wherein,
Figure BDA0002424690600000107
represents the distance set of the unknown node m and the unknown node and the anchor node i in all communication radiuses, j represents any node in the wireless sensor network,
Figure BDA0002424690600000108
for other unknown node sets within the communication radius of node m, p (×) represents the probability of an event occurring.
The maximum likelihood model to which all nodes in the network are subjected is
Figure BDA0002424690600000109
Wherein,
Figure BDA00024246906000001010
represents the set of the modified distances between all unknown nodes and the anchor nodes in all communication radiuses,
Figure BDA00024246906000001011
representing the set of all unknown node locations.
Accordingly, the objective function of the co-location model is
Figure BDA0002424690600000111
Wherein,
Figure BDA0002424690600000112
initial positions obtained for all unknown nodes by external measurement or other methods, assuming variance of
Figure BDA0002424690600000113
The location obeys a Gaussian distribution of
Figure BDA0002424690600000114
The probability density function related to the maximum likelihood function comprises Gaussian distribution of node distance and Gaussian distribution of break angle on shortest path, wherein the Gaussian distribution of the node distance is
Figure BDA0002424690600000115
Wherein,
Figure BDA0002424690600000116
representing the variance of the distance estimate between nodes m, n.
The distribution may be expressed as when the inter-node distance degenerates to an unknown inter-node distance within the communication radius
Figure BDA0002424690600000117
Furthermore, the break angle compliance parameter on the shortest path tree is
Figure BDA0002424690600000118
The probability density function of the normal distribution of (1) is as follows:
Figure BDA0002424690600000119
s3, determining the optimal auxiliary node in the co-location model according to the optimal selection policy or the sub-optimal selection policy includes:
determining a node corresponding to the minimum folding angle on the shortest path tree in the co-location model as an optimal auxiliary node;
and if a plurality of nodes corresponding to the minimum folding angles on the shortest path tree in the cooperative positioning model are determined, constructing a selection triangle, and determining the vertex corresponding to the two adjacent sides with the minimum difference in the selection triangle as the optimal auxiliary node.
The specific implementation process of S3 is as follows:
in the process, the connection line between the shortest path and the actual distance is simplified into a triangular model, but the nodes passing through the shortest path tree may pass through the boundary nodes of a plurality of holes, different hole boundary nodes are different as the vertices of the triangle to influence the positioning result, and the hole boundary nodes serving as the vertices of the triangle are selected to be called as auxiliary nodes.
The Cramer-Rao lower bound is the minimum achievable variance of unbiased estimation, so that the optimal achievable estimation performance is established by setting the lower bound of an estimator, and the Cramer-Rao method can depict the robustness of the estimation method, the Cramer-Rao lower bound (CR L B) of position estimation under a special configuration is given, CR L B has progressive compactness and can be regarded as a measurement standard in wireless sensor network positioning, however, the solution of CR L B needs to derive a closed-loop solution of a marginal probability density function, and is difficult to realize in mathematical derivation, and in addition, CR L B cannot give the mean square error of a random variable, namely a hidden variable, in a mixed estimation problem.
Therefore, the invention adopts a Hybrid Cram é -Rao lower bound (HCR L B) to represent the positioning limit of the algorithm, and the HCR L B can be obtained by combining probability densities and can represent the bound of any generalized unbiased estimation.
Compared with the non-cooperative HCR L B, the cooperative HCR L B increases the influence of unknown nodes in the communication radius on the positioning result, and the node ranging in the communication radius is not influenced by the hole terrain, so that the derivation is carried out by the HCR L B in the non-cooperative mode when the hole auxiliary node is selected, the derivation process and the conclusion can be simplified, and the selection result is not influenced.
HCR L B for node positioning under hollow terrain and relation thereof with lower error bound are
Figure BDA0002424690600000121
Wherein,
Figure BDA0002424690600000131
as an estimate of position and angle, phim=[Θmm]The true values of position and angle. ΨmThe true value of the dog-ear on the shortest path tree is represented.
Figure BDA0002424690600000132
For the expectation operator, it means that the variable in parentheses is expected, and if the subscript exists, it means that the variable indicated by the subscript is expected, as
Figure BDA0002424690600000133
Presentation pair
Figure BDA0002424690600000134
In the expectation that the position of the target is not changed,
Figure BDA0002424690600000135
represents a pair dmIn the expectation that the position of the target is not changed,
Figure BDA0002424690600000136
is shown to be known
Figure BDA0002424690600000137
Under the condition of dmThe expectation is that.
Figure BDA0002424690600000138
Is a Hybrid Information Matrix (HIM), defined as:
Figure BDA0002424690600000139
after derivation, HIM is converted to
Figure BDA00024246906000001310
In the derivation of the above formula, there is a non-linear term
Figure BDA00024246906000001311
And processing in a second-order Taylor expansion mode. Meanwhile, in the process of solving the expectation of the equation, the product of adjacent edges is processed by means of a trilateral relation formula of a triangle, wherein the trilateral relation formula is as follows
Figure BDA00024246906000001312
Wherein, a triangle formed by the sensor nodes m, n and the middle point o defines an angle amn=∠onm,bmn=∠omn。
Further derivation can obtain
Figure BDA00024246906000001313
Final positioning model with respect to thetamAnd
Figure BDA00024246906000001314
submatrix of HIM
Figure BDA00024246906000001315
Can be expressed as
Figure BDA0002424690600000141
Figure BDA0002424690600000142
Figure BDA0002424690600000143
Wherein diag (×) represents a diagonal matrix, i represents any anchor node from 1 to n,
Figure BDA0002424690600000144
oirepresenting an auxiliary node in the shortest path tree between nodes m, i, the derivative variable y in the equationi,G'mi,G”mnAre respectively defined as
Figure BDA0002424690600000145
Figure BDA0002424690600000146
Figure BDA0002424690600000147
Wherein,
Figure BDA0002424690600000148
αmnrepresents the angle theta between the connecting line of the nodes m and n and the abscissa axis of the distribution areai=(xiYi) represents the coordinates of any anchor node,
Figure BDA0002424690600000151
is the initial estimation value of the folding angle on the shortest path tree of the node m, i.
In a positioning model with holes, a better positioning effect can be achieved when the estimated CR L B of the determined parameters is equal to HCR L B, and the importance of the CR L0B of the determined parameters is proved to be stronger than that of HCR L1B under the normal condition, the CR L2B related to the position of an unknown node is larger than that of HCR L B, under the premise that the position of the node and the measurement variance are known, the HCR L B of the unknown node is constant, but the CR L B cannot be obtained due to the reason that the integral term closed-loop solution cannot be obtained, therefore, one way of reducing the CR L B of the unknown node is obtained by analyzing the essential condition of the asymptotic importance of the HCR L B, because the HCR L B is known and fixed, when the essential condition is met, the CR L B can approach the HCR L B infinitely, and the essential condition is that
Figure BDA0002424690600000152
Substituting each expression into the sufficient condition to obtain
Figure BDA0002424690600000153
The above conditions indicate the tightness of HCR L B with variable (a)mi-bmi) And
Figure BDA0002424690600000154
in this regard, when the network topology is fixed, the other variables in the equation are constants, but since there is more than one hole boundary node on the shortest path tree between nodes, when selecting different hole boundary nodes to form a triangle (where the node is defined as an auxiliary node), the essential condition of importance is dependent on the variable (a)mi-bmi) And
Figure BDA0002424690600000155
a change is made. However, most of the auxiliary nodes cannot satisfy the essential conditions in the equation, so that the asymptotic tightness cannot be achieved, but the optimal auxiliary node can be found to be more approximate to the conditions in the equation. Therefore, the present invention defines a tightness function according to the above equation, and analyzes the tightness achieved by different auxiliary nodes, as shown below
Figure BDA0002424690600000161
It can be shown that when the variables satisfy the conditions
Figure BDA0002424690600000162
|ami-bmi|∈[0,π/3]Tightness function with respect to break angle
Figure BDA0002424690600000163
Monotonically decreasing. When in use
Figure BDA0002424690600000164
It can be shown that the tightness function is less than 0. Following the angle of the corner
Figure BDA0002424690600000165
Increasing from 1/2 π to π, the tightness function decreases monotonically. The process shows that when the folding angle is satisfied
Figure BDA0002424690600000166
When the condition (2) is satisfied, the tightness function is closer to 0, and when the tightness function is 0, the lower error bound of the estimator can be effectively reduced. Therefore, the smaller the angle of the break angle on the shortest path tree is, the closer the compactness function is to 0, and the better the positioning effect of the node is. In the hole network of the present invention, the break angle of the auxiliary node is usually between 1/2 pi and pi, and the difference between the other two angles of the triangle is usually between 0 and 1/3 pi.
According to the above-mentioned deduction the optimum selection strategy can be obtained, i.e. the break angle correspondent to auxiliary node on the shortest path tree
Figure BDA0002424690600000167
The smaller the lower bound of positioning error. FIG. 3 is a schematic diagram of an optimal selection strategy, in which
Figure BDA0002424690600000168
All unknown nodes, S1Being anchor nodes, all nodes and their dotted lines constitute a shortest path tree between nodes,
Figure BDA0002424690600000169
and the two nodes can form a triangle with the node to be positioned and the anchor node on the inner boundary of the cavity, but the corresponding break angles of the two nodes are different in size. If a node is selected
Figure BDA00024246906000001610
Constructing a triangular model with a smaller corresponding angle,therefore, the influence of the holes on node ranging can be reflected better, and the trilateral estimation of the formed triangle is more accurate by taking the node as an auxiliary node. If a node is selected
Figure BDA00024246906000001611
Then the node
Figure BDA00024246906000001612
Inaccurate estimation of the distance caused by the connection line will seriously affect the positioning result. The above analysis is consistent with the expression of the optimal selection strategy.
In the same manner, the variable cos (a) is analyzedmi-bmi) The effect on the fitness function is seen as the variable cos (a)mi-bmi) Derivative of (a) is by break angle
Figure BDA00024246906000001613
Determine relative angle of break
Figure BDA00024246906000001614
Influence on the tightness function, variable cos (a)mi-bmi) Has a negligible effect, so that the selection of the auxiliary node should first take into account the break angle
Figure BDA00024246906000001615
Only when the shortest path tree has a special condition that the folding angles are equal or close, the cosine values of the analysis angle difference select the auxiliary nodes, although the probability of the special condition is smaller, the invention still provides a corresponding analysis and selection mode.
Can prove when
Figure BDA0002424690600000171
|ami-bmi|∈[0,π/3]When the condition is satisfied, the tightness function is related to the variable cos (a)mi-bmi) Monotonically increasing. The compactness function is close to 0 when the cosine of the angle difference is around 1, and is far from 0 when the cosine of the angle difference is around 0.5. According to the method, a sub-optimal selection strategy can be obtained, namely, the auxiliary node firstly selects the most according to the selection strategyAnd selecting the optimal selection strategy, and when the optimal selection strategy cannot provide enough judgment basis, selecting the auxiliary node with smaller length difference between two adjacent sides of the auxiliary node in the triangle, so that the lower limit of the positioning error is smaller.
The above problem can be explained by geometric means, and fig. 4 shows a schematic diagram of a suboptimal selection strategy, in a shortest path tree between nodes, if the shortest path is more tortuous, the linear distance between nodes depends on the angle of the path bending, otherwise, the linear distance between nodes has a smaller relationship with the degree of the path bending. In this case, the auxiliary node located in the middle of the shortest path tree can obtain better positioning results. As shown in FIG. 4, the two break angles on the shortest path tree are similar in size, i.e.
Figure BDA0002424690600000172
Then the node
Figure BDA0002424690600000173
Figure BDA0002424690600000174
Is greater than the node
Figure BDA0002424690600000175
Of the distance between them, thus
Figure BDA0002424690600000176
The above equation shows that when the auxiliary node is located near the midpoint of the shortest path, a better positioning effect can be obtained.
At S4, according to the optimal auxiliary node, the specific implementation process of determining the iteration parameters in the co-location model by using the update rule of variation message delivery includes:
the cooperative positioning model under the known hole terrain can be abstracted to solve the maximum value of the joint likelihood estimation objective function, in order to solve the maximum value of the target, the invention adopts a cooperative method of message transmission to realize optimized solution, and the following parameters of cooperative positioning are deduced.
Based on a network structure of local factorization in a joint likelihood function, the wireless sensor network containing the holes can carry out derivation under a factor graph framework, and variable nodes and factor nodes realize association inference by a message transfer algorithm. Among various message passing algorithms, the variation message passing updating rule is used for deducing the cooperative positioning parameter in the invention due to the excellent characteristic in distributed calculation.
Definition of
Figure BDA0002424690600000181
The rule slave factor node g is updated based on the VMP messagemnMessages to the relevant variable node z can be represented as
Figure BDA0002424690600000182
Wherein,
Figure BDA0002424690600000183
as an initial value of the path tree break angle, θmFor the actual position of the unknown node m, θnThe actual location of unknown node n within communication range of any anchor node or m,
Figure BDA0002424690600000184
is known as thetam、θn
Figure BDA0002424690600000185
The expectation of the lower variable node Z, p (×) is the probability of occurrence.
The probability distribution of the estimated values in the expectation operator is from the trial distribution of the previous iteration, and correspondingly, the posterior distribution of the variable nodes is
Figure BDA0002424690600000186
The logarithm of the likelihood function for the anchor node and the unknown node in the above equation is known as
Figure BDA0002424690600000187
Figure BDA0002424690600000188
According to the variable node posterior distribution formula, the result is from the factor node gmnMessages to related variable nodes may be represented in the following form
Figure BDA0002424690600000189
Figure BDA0002424690600000191
Slave factor node gmnThe variables to node location can be expressed as anchor nodes and unknown node factor variable distinctions respectively
Figure BDA0002424690600000192
Figure BDA0002424690600000193
Wherein,
Figure BDA0002424690600000194
respectively the coordinates of the nodes m, n and the distance d after the previous iterationmnThe measured distance between the unknown node and the unknown node in the communication radius is the estimated distance after the previous iteration
Figure BDA0002424690600000195
Can be respectively expressed as
Figure BDA0002424690600000196
Figure BDA0002424690600000197
Slave factor node gmnThe calculation of the folding angle variable on the shortest path to the node is due to the non-linear item
Figure BDA0002424690600000198
And
Figure BDA0002424690600000199
therefore, nonlinear terms in the equation are derived in the form of Taylor expansion, and the derived result can be expressed as
Figure BDA00024246906000001910
Wherein the intermediate variable
Figure BDA0002424690600000201
Intermediate variables
Figure BDA0002424690600000202
Intermediate variables
Figure BDA0002424690600000203
Intermediate variables
Figure BDA0002424690600000204
Further derivation of the Slave factor node gmnAngle of tree to shortest path
Figure BDA0002424690600000205
Is expressed as
Figure BDA0002424690600000206
In order to ensure that the message transmission information is in a closed loop form, the node position and the back of the shortest path break angle are assumedIf the probability of experience is still Gaussian distribution, the position variable and the shortest path break angle variable of the unknown node m, any anchor node or unknown node n in the communication range of m are transmitted to the factor node g after each message updatemnRespectively is
Figure BDA0002424690600000207
Figure BDA0002424690600000208
Figure BDA0002424690600000209
In the derivation, the position parameter of the unknown node m after l iterations
Figure BDA00024246906000002010
And variance parameter
Figure BDA00024246906000002011
Are respectively as
Figure BDA0002424690600000211
Figure BDA0002424690600000212
Wherein,
Figure BDA0002424690600000213
is the initial position of the unknown node m, follows the prior distribution of the positions of the unknown node m,
Figure BDA0002424690600000214
for unknown node m initial position
Figure BDA0002424690600000215
N is any anchor node or unknown node within m communication rangeThe point(s) is (are) such that,
Figure BDA0002424690600000216
s is a set of anchor nodes, dmnThe distance between node m and node n is unknown,
Figure BDA0002424690600000217
is dmnThe variance of (a) is determined,
Figure BDA0002424690600000218
for the location parameters of the unknown node after l-1 iterations,
Figure BDA0002424690600000219
the corrected distance between node m and node n is unknown,
Figure BDA00024246906000002110
to learn the calculated distance of the estimated location of node m from node n at l-1 iterations,
Figure BDA00024246906000002111
for the location parameter of the unknown node m after l-1 iterations,
Figure BDA00024246906000002112
is a set of other unknown nodes within the communication radius of the unknown node m.
Break angle of shortest path tree of node m, n after l iterations
Figure BDA00024246906000002113
And its variance
Figure BDA00024246906000002114
Are respectively as
Figure BDA00024246906000002115
Figure BDA00024246906000002116
Wherein,
Figure BDA0002424690600000221
is the variance of the shortest path tree of the nodes m and n after l iterations,
Figure BDA0002424690600000222
is the initial value of the shortest path tree break angle,
Figure BDA0002424690600000223
is composed of
Figure BDA0002424690600000224
The initial variance of the measured time period of the time period,
Figure BDA0002424690600000225
is an intermediate variable of l-1 iterations and
Figure BDA0002424690600000226
Figure BDA0002424690600000227
is an intermediate variable of l-1 iterations and
Figure BDA0002424690600000228
Figure BDA0002424690600000229
is an intermediate variable of l-1 iterations
Figure BDA00024246906000002210
Figure BDA00024246906000002211
Is an intermediate variable of l-1 iterations and
Figure BDA00024246906000002212
Figure BDA00024246906000002213
is an estimate of the dog-ear after l-1 iterations.
Compared with the prior art, the cooperative positioning method of the wireless sensor network under the hollow terrain has the following advantages that:
1. the invention solves the positioning problem of the heterogeneous network, particularly the situation that the distribution terrain of the wireless sensor network contains holes, provides a positioning method and improves the positioning precision;
2. aiming at the situations of low node density and limited communication radius in the cavity network, a cooperative positioning model is established, and the problem of sparse network in the positioning process is solved;
3. the method adjusts the estimated position of the unknown node by means of the information of other unknown nodes in the communication range, provides iterative parameters and a process of the cooperative positioning method, and effectively improves the positioning accuracy of the sparse network.
4. The invention further provides a method for selecting the auxiliary node in the cavity boundary node by means of the tightness analysis of the Clarmero boundary, further improves the positioning process and improves the positioning precision.
In addition, aiming at the provided method for the cooperative positioning system of the wireless sensor network under the hollow terrain, the invention also correspondingly provides a cooperative positioning system of the wireless sensor network under the hollow terrain. As shown in fig. 5, the system includes: the system comprises an application data acquisition module 1, a cooperative positioning model construction module 2, an optimal auxiliary node determination module 3, an iteration parameter determination module 4 and a positioning module 5.
The application data acquisition module 1 is used for acquiring application data of the wireless sensor network under the hollow terrain; the application data includes: the method comprises the following steps that the distance between an unknown node in a wireless sensor network and other unknown nodes in the communication radius of the unknown node under the hollow terrain, the distance between the unknown node and anchor nodes in the communication radius of the unknown node, the initial position of the unknown node and the actual positions of all anchor nodes in the network are determined; the cooperative positioning model building module 2 is used for building a cooperative positioning model according to the application data; the optimal auxiliary node determining module 3 is used for determining an optimal auxiliary node in the co-location model according to an optimal selection strategy or a suboptimal selection strategy; the iteration parameter determining module 4 is configured to determine an iteration parameter in the co-location model by using an update rule transmitted by a variation message according to the optimal auxiliary node; and the positioning module 5 is used for positioning the wireless sensor network under the hollow terrain according to the iteration parameters.
The cooperative localization model building module 2 specifically includes: the device comprises a first maximum likelihood probability model building unit, a second maximum likelihood probability model building unit, a position maximum likelihood probability model building unit and a co-location model building unit.
The first maximum likelihood probability model building unit is used for building a maximum likelihood probability model of the collaborative position of an unknown node according to the distance between the unknown node and other unknown nodes in the communication radius of the unknown node in the wireless sensor network under the hollow terrain, the distance between the unknown node and anchor nodes in the communication radius of the unknown node and the actual positions of all anchor nodes in the network; the second maximum likelihood probability model building unit is used for determining maximum likelihood probability models of the collaborative positions of all the nodes in the wireless sensor network under the hollow terrain according to the maximum likelihood probability models of the collaborative positions of the unknown nodes; the position maximum likelihood probability model building unit is used for determining position maximum likelihood probability models of all nodes in the wireless sensor network under the hollow terrain according to the initial position of the unknown node; and the cooperative positioning model building unit is used for building the cooperative positioning model according to the maximum likelihood probability models of the cooperative positions of all the nodes in the wireless sensor network under the hollow terrain and the position maximum likelihood probability model.
The optimal auxiliary node determining module 3 specifically includes: and an optimal auxiliary node determining unit.
The optimal auxiliary node determining unit is used for determining one node corresponding to the minimum folding angle on the shortest path tree in the cooperative positioning model as an optimal auxiliary node; and if a plurality of nodes corresponding to the minimum folding angles on the shortest path tree in the cooperative positioning model are determined, constructing a selection triangle, and determining the vertexes corresponding to the two adjacent sides with the minimum difference in the selection triangle as the optimal auxiliary nodes.
The iteration parameter determining module 4 specifically includes: the device comprises a factor node acquisition unit, a message determination unit, a position parameter determination unit, a variance determination unit and a folding angle determination unit.
Wherein, the factor node obtaining unit is used for obtaining a factor node gmn
The message determining unit is used for passing a formula according to the update rule of the variation message transmission
Figure BDA0002424690600000241
Determining from the factor node gmnMessages to variable node Z
Figure BDA0002424690600000242
Wherein,
Figure BDA0002424690600000243
as an initial value of the path tree break angle, θmFor the actual position of the unknown node m, θnThe actual location of unknown node n within communication range of any anchor node or m,
Figure BDA0002424690600000244
is known as thetam、θn
Figure BDA0002424690600000245
Expectation of lower variable node Z, p (—) is occurrence probability;
the position parameter determining unit is used for passing the formula
Figure BDA0002424690600000246
Determining the position parameter of the unknown node m after l iterations
Figure BDA0002424690600000247
Wherein,
Figure BDA0002424690600000248
for the initial position of the unknown node m,
Figure BDA0002424690600000249
as the initial position of unknown node m
Figure BDA00024246906000002410
N is any anchor node or unknown node within communication range of m,
Figure BDA00024246906000002411
s is a set of anchor nodes, dmnThe distance between the unknown node m and any anchor node or unknown node n in the communication range of the unknown node m,
Figure BDA00024246906000002412
is dmnThe variance of (a) is determined,
Figure BDA00024246906000002413
for the location parameters of the unknown node after l-1 iterations,
Figure BDA0002424690600000251
to do so for the revised distance between the unknown node m and the anchor node n at l-1 iterations,
Figure BDA0002424690600000252
to iterate over l-1 times the computed distance of the estimated location of unknown node m from any anchor node or unknown node n within communication range of m,
Figure BDA0002424690600000253
for the location parameter of the unknown node m after l-1 iterations,
Figure BDA0002424690600000254
is a set of other unknown nodes within the communication radius of the unknown node m.
The variance parameter determination unit is used for passing the formula
Figure BDA0002424690600000255
Determining variance parameter of unknown node m after l iterations
Figure BDA0002424690600000256
The variance determining unit is used for passing the formula
Figure BDA0002424690600000257
Determining variance of shortest path tree of nodes m and n after l iterations
Figure BDA0002424690600000258
The bevel angle determining unit is used for passing the formula
Figure BDA0002424690600000259
Determining the break angle of the shortest path tree of the nodes m and n after l iterations
Figure BDA00024246906000002510
Wherein,
Figure BDA00024246906000002511
is the variance of the shortest path tree of the nodes m and n after l iterations,
Figure BDA00024246906000002512
is the initial value of the shortest path tree break angle,
Figure BDA0002424690600000261
is composed of
Figure BDA0002424690600000262
The initial variance of the measured time period of the time period,
Figure BDA0002424690600000263
is an intermediate variable of l-1 iterations and
Figure BDA0002424690600000264
Figure BDA0002424690600000265
is an intermediate variable of l-1 iterations and
Figure BDA0002424690600000266
Figure BDA0002424690600000267
is an intermediate variable of l-1 iterations
Figure BDA0002424690600000268
Figure BDA0002424690600000269
Is an intermediate variable of l-1 iterations and
Figure BDA00024246906000002610
Figure BDA00024246906000002611
is an estimate of the dog-ear after l-1 iterations.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. For the system disclosed by the embodiment, the description is relatively simple because the system corresponds to the method disclosed by the embodiment, and the relevant points can be referred to the method part for description.
The principles and embodiments of the present invention have been described herein using specific examples, which are provided only to help understand the method and the core concept of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.

Claims (8)

1. A method for cooperative positioning of a wireless sensor network under a hollow terrain is characterized by comprising the following steps:
acquiring application data of a wireless sensor network under a hollow terrain; the application data includes: the method comprises the following steps that the distance between an unknown node in a wireless sensor network and other unknown nodes in the communication radius of the unknown node under the hollow terrain, the distance between the unknown node and anchor nodes in the communication radius of the unknown node, the initial position of the unknown node and the actual positions of all anchor nodes in the network are determined;
constructing a co-location model according to the application data;
determining an optimal auxiliary node in the co-location model according to an optimal selection strategy or a suboptimal selection strategy;
determining iteration parameters in the cooperative positioning model by adopting an updating rule transmitted by variation messages according to the optimal auxiliary node;
and finishing the positioning of the wireless sensor network under the hollow terrain according to the iteration parameters.
2. The method according to claim 1, wherein the constructing a co-location model according to the application data specifically includes:
constructing a maximum likelihood probability model of the collaborative position of an unknown node according to the distance between the unknown node and other unknown nodes in the communication radius of the unknown node, the distance between the unknown node and anchor nodes in the communication radius of the unknown node and the actual positions of all the anchor nodes in the wireless sensor network under the hollow terrain;
determining maximum likelihood probability models of the collaborative positions of all nodes in the wireless sensor network under the hollow terrain according to the maximum likelihood probability models of the collaborative positions of the unknown nodes;
determining a position maximum likelihood probability model of all nodes in the wireless sensor network under the hollow terrain according to the initial position of the unknown node and the actual position of the unknown node;
and constructing the cooperative positioning model according to the maximum likelihood probability model of the cooperative positions of all the nodes in the wireless sensor network under the hollow terrain.
3. The method according to claim 1, wherein the determining an optimal auxiliary node in the co-location model according to an optimal selection strategy or a sub-optimal selection strategy specifically comprises:
determining a node corresponding to the minimum folding angle on the shortest path tree in the co-location model as an optimal auxiliary node;
and if a plurality of nodes corresponding to the minimum folding angles on the shortest path tree in the cooperative positioning model are determined, constructing a selection triangle, and determining the vertexes corresponding to the two adjacent sides with the minimum difference in the selection triangle as the optimal auxiliary nodes.
4. The method according to claim 1, wherein the determining, according to the optimal auxiliary node, the iteration parameter in the co-location model by using an update rule of variational message transfer specifically comprises:
get factor node gmn
According to the update rule of the variation message transmission, passing through a formula
Figure FDA0002424690590000021
Determining from the factor node gmnTo variable node
Figure FDA00024246905900000212
Of a message
Figure FDA0002424690590000022
Wherein,
Figure FDA0002424690590000023
as an initial value of the path tree break angle, θmFor the actual position of the unknown node m, θnThe actual location of unknown node n within communication range of any anchor node or m,
Figure FDA0002424690590000024
is known as thetam、θn
Figure FDA0002424690590000025
Lower variable node
Figure FDA00024246905900000213
P () is the probability of occurrence;
by the formula
Figure FDA0002424690590000026
Determining the position parameter of the unknown node m after l iterations
Figure FDA0002424690590000027
Wherein,
Figure FDA00024246905900000214
for the initial position of the unknown node m,
Figure FDA0002424690590000028
as the initial position of unknown node m
Figure FDA00024246905900000215
N is any anchor node or unknown node within communication range of m,
Figure FDA0002424690590000029
Figure FDA00024246905900000210
is a set of anchor nodes, dmnThe distance between the unknown node m and the anchor node n,
Figure FDA00024246905900000211
is dmnThe variance of (a) is determined,
Figure FDA0002424690590000031
the position parameter of the unknown node after l-1 iterations is l-1Iterating the corrected distance between the unknown node m and the node n,
Figure FDA0002424690590000032
to learn the calculated distance of the estimated location of node m from node n at l-1 iterations,
Figure FDA0002424690590000033
for the location parameter of the unknown node m after l-1 iterations,
Figure FDA0002424690590000034
is a set of other unknown nodes within the communication radius of the unknown node m.
By the formula
Figure FDA0002424690590000035
Determining variance parameter of unknown node m after l iterations
Figure FDA0002424690590000036
By the formula
Figure FDA0002424690590000037
Determining variance of shortest path tree of nodes m and n after l iterations
Figure FDA0002424690590000038
By the formula
Figure FDA0002424690590000039
Determining the break angle of the shortest path tree of the nodes m and n after l iterations
Figure FDA00024246905900000310
Wherein,
Figure FDA00024246905900000311
is the most node m, nThe variance of the short-path tree after l iterations,
Figure FDA00024246905900000312
is the initial value of the shortest path tree break angle,
Figure FDA00024246905900000313
is composed of
Figure FDA00024246905900000314
The initial variance of the measured time period of the time period,
Figure FDA00024246905900000315
and
Figure FDA00024246905900000316
are all intermediate variables of l-1 iterations,
Figure FDA0002424690590000041
is an estimate of the dog-ear after l-1 iterations.
5. A cooperative positioning system of a wireless sensor network under a hollow terrain comprises:
the application data acquisition module is used for acquiring application data of the wireless sensor network under the hollow terrain; the application data includes: the method comprises the following steps that the distance between an unknown node in a wireless sensor network and other unknown nodes in the communication radius of the unknown node under the hollow terrain, the distance between the unknown node and anchor nodes in the communication radius of the unknown node, the initial position of the unknown node and the actual positions of all anchor nodes in the network are determined;
the cooperative positioning model building module is used for building a cooperative positioning model according to the application data;
the optimal auxiliary node determining module is used for determining the optimal auxiliary node in the cooperative positioning model according to the optimal selection strategy or the suboptimal selection strategy;
the iteration parameter determining module is used for determining iteration parameters in the cooperative positioning model by adopting an updating rule transmitted by variation messages according to the optimal auxiliary node;
and the positioning module is used for finishing the positioning of the wireless sensor network under the hollow terrain according to the iteration parameters.
6. The system of claim 5, wherein the co-location model building module specifically comprises:
the first maximum likelihood probability model building unit is used for building a maximum likelihood probability model of the collaborative position of the unknown node according to the distance between the unknown node and other unknown nodes in the communication radius of the unknown node in the wireless sensor network under the hollow terrain, the distance between the unknown node and anchor nodes in the communication radius of the unknown node and the actual positions of all anchor nodes in the network;
the second maximum likelihood probability model building unit is used for determining maximum likelihood probability models of the collaborative positions of all the nodes in the wireless sensor network under the hollow terrain according to the maximum likelihood probability models of the collaborative positions of the unknown nodes;
the position maximum likelihood probability model building unit is used for determining position maximum likelihood probability models of all nodes in the wireless sensor network under the hollow terrain according to the initial position of the unknown node;
and the cooperative positioning model building unit is used for building the cooperative positioning model according to the maximum likelihood probability models of the cooperative positions of all the nodes in the wireless sensor network under the hollow terrain and the position maximum likelihood probability model.
7. The system of claim 5, wherein the optimal auxiliary node determination module specifically comprises:
the optimal auxiliary node determining unit is used for determining one node corresponding to the minimum folding angle on the shortest path tree in the cooperative positioning model as an optimal auxiliary node;
and if a plurality of nodes corresponding to the minimum folding angles on the shortest path tree in the cooperative positioning model are determined, constructing a selection triangle, and determining the vertexes corresponding to the two adjacent sides with the minimum difference in the selection triangle as the optimal auxiliary nodes.
8. The system of claim 5, wherein the iterative parameter determination module specifically comprises:
a factor node acquisition unit for acquiring a factor node gmn
A message determining unit for determining the update rule of the variation message transmission according to the formula
Figure FDA0002424690590000051
Determining from the factor node gmnTo variable node
Figure FDA0002424690590000057
Of a message
Figure FDA0002424690590000052
Wherein,
Figure FDA0002424690590000053
as an initial value of the path tree break angle, θmFor the actual position of the unknown node m, θnThe actual location of unknown node n within communication range of any anchor node or m,
Figure FDA0002424690590000054
is known as thetam、θn
Figure FDA0002424690590000055
Lower variable node
Figure FDA0002424690590000058
Expectation of (1), p (.)) Is the probability of occurrence;
a position parameter determination unit for determining the position of the object by formula
Figure FDA0002424690590000056
Determining the position parameter of the unknown node m after l iterations
Figure FDA0002424690590000061
Wherein,
Figure FDA00024246905900000615
for the initial position of the unknown node m,
Figure FDA0002424690590000062
as the initial position of unknown node m
Figure FDA00024246905900000616
N is any anchor node or unknown node within communication range of m,
Figure FDA0002424690590000063
Figure FDA0002424690590000064
is a set of anchor nodes, dmnThe distance between the unknown node m and the anchor node n,
Figure FDA0002424690590000065
is dmnThe variance of (a) is determined,
Figure FDA0002424690590000066
for the location parameters of the unknown node after l-1 iterations,
Figure FDA0002424690590000067
to do so for the revised distance between the unknown node m and the anchor node n at l-1 iterations,
Figure FDA0002424690590000068
to learn the calculated distance of the estimated location of node m from node n at l-1 iterations,
Figure FDA0002424690590000069
for the location parameter of the unknown node m after l-1 iterations,
Figure FDA00024246905900000610
is a set of other unknown nodes within the communication radius of the unknown node m.
A variance parameter determination unit for determining variance of the received signal by formula
Figure FDA00024246905900000611
Determining variance parameter of unknown node m after l iterations
Figure FDA00024246905900000612
A variance determining unit for determining variance by formula
Figure FDA00024246905900000613
Determining variance of shortest path tree of nodes m and n after l iterations
Figure FDA00024246905900000614
A break angle determining unit for determining a break angle by a formula
Figure FDA0002424690590000071
Determining the break angle of the shortest path tree of the nodes m and n after l iterations
Figure FDA0002424690590000072
Wherein,
Figure FDA0002424690590000073
is the variance of the shortest path tree of the nodes m and n after l iterations,
Figure FDA0002424690590000074
is the initial value of the shortest path tree break angle,
Figure FDA0002424690590000075
is composed of
Figure FDA0002424690590000076
The initial variance of the measured time period of the time period,
Figure FDA0002424690590000077
and
Figure FDA0002424690590000078
are all intermediate variables of l-1 iterations,
Figure FDA0002424690590000079
is an estimate of the dog-ear after l-1 iterations.
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