KR20190069965A - Method for estimating location of target node in wireless network consisting of multiple nodes and Apparatuses thereof - Google Patents

Abstract

Embodiments of the present invention relate to a method for increasing the precision in estimating the position of a target node, whose position is desired to be estimated, in a wireless network configured by a plurality of nodes and an apparatus thereof. According to an embodiment of the present invention, the method for estimating a position of the target node in the wireless network configured by the plurality of nodes comprises: a step of calculating the number of hops between each anchor node and target node from among three anchor nodes whose positions are informed; a step of, if the number of the hops with the target node from among the anchor nodes is two or lower for the number of one-person anchor node, calculating a position candidate area based on the position of each anchor node and the calculated number of hops; and a step of calculating a current probability density of the target node based on the previous probability density of the target node and the position candidate area.

Description

Field of the Invention The present invention relates to a method and apparatus for estimating the location of a target node in a wireless network composed of a plurality of nodes,

In the present exemplary embodiments, the target node that estimates the position in a wireless network including a plurality of nodes calculates connection information between the target node and another node, and calculates the accuracy of the position estimation of the target node based on the calculated connection information And to a method and apparatus for increasing the height.

Various methods are being studied to estimate the position of a node in a wireless network composed of a plurality of nodes. In this case, the node means a device capable of transmitting / receiving a wireless signal, and may be a mobile terminal (e.g., a smart phone) or a sensor or device fixed in position.

The node has an anchor node that knows the current location, and a mobile node that is a node whose location changes. A node to estimate the location of the mobile node can be referred to as a target node.

There is a method of using the probability density as a general method of estimating the position of the target node. The probabilistic density of the target node indicates the probability of existence of the target node according to the position (the position can be expressed by x and y coordinate values) in the two-dimensional environment represented by the x and y coordinates, and the probability density value The function to be calculated is called a probability density function.

If the probability density is distributed in a narrow region, that is, if the distribution of the probability density is small, it can be determined that the accuracy of the position estimation value with respect to the target node is high. Conversely, when the probability density distribution is large, It can be determined that the accuracy of the position estimation value for the target node is low.

In this case, since the target node changes its position while moving as a mobile node, the current probability density of the target node is obtained based on the radio signal received from the neighboring node different from the previous probability density, which is the value of the most recently obtained probability density, The current position of the target node can be estimated based on the current position of the target node.

Specifically, a plurality of anchor nodes, which are nodes that know a position among a plurality of nodes, are obtained, and the information about the radio signal strength received from each anchor node by the target node is reflected in the previous probability density value to obtain the current probability density I ask.

At this time, in order to use the same method as the triangulation method generally used for position measurement, the number of anchor nodes receiving the radio signal by the target node must be at least three. However, if at least one of the three anchor nodes is far from the target node, the radio signal received from the anchor node far from the target node has a large uncertainty, so that the accuracy of the estimated position of the target node is reduced .

It is an object of the present embodiments to provide a method and apparatus for increasing the accuracy of position estimation of a target node in a wireless network composed of a plurality of nodes. A method for calculating the connection information between the target node and the anchor node, that is, the number of hops between the target node and each anchor node, and reducing the variance of the current probability density of the target node based on the information, The device will be described.

According to an embodiment of the present invention, there is provided a method for estimating a location of a target node in a wireless network including a plurality of nodes, the method comprising: calculating a number of hops based on the position of each anchor node and the calculated number of hops when the number of anchor nodes having a hop count of 1 from the target node is two or less among the anchor nodes, Calculating a current probability density of the target node based on the previous probability density of the target node and the position candidate region, and calculating the current probability density of the target node based on the previous probability density of the target node and the current probability density of the target node, When the intensity of the radio signal of the second node received at the first node is equal to or greater than a predetermined threshold signal intensity, the number of hopes between the first node and the second node becomes 1 , The strength of the radio signal of the second node received by the first node is equal to or greater than the threshold signal strength and the strength of the radio signal of the third node received by the first node is less than the threshold signal strength and the hop between the second node and the third node And when the number is N, the number of hops between the first node and the third node is (N + 1).

In an exemplary embodiment of the present invention, an apparatus for estimating a location of a target node in a wireless network including a plurality of nodes, the apparatus comprising: a calculation unit configured to calculate a number of hops between each anchor node and a target node for three anchor nodes, A position calculation unit for calculating a position candidate region based on the position of each anchor node and the calculated number of hops when the number of anchor nodes having a hop count of 1 from an anchor node is two or less; And a probability density calculation unit for calculating a current probability density of the target node based on the previous probability density of the target node and the position candidate region, and for the first node, the second node and the third node as arbitrary nodes, The number of hops between the first node and the second node becomes 1 when the strength of the radio signal of the second node received by the first node is equal to or greater than a predetermined threshold signal intensity, When the intensity of the radio signal of the node is equal to or greater than the threshold signal intensity and the intensity of the radio signal of the third node received by the first node is less than the threshold signal intensity and the number of hops between the second node and the third node is N, And the number of hops between the third node is (N + 1).

The accuracy of the location estimation of the target node in the wireless network including a plurality of nodes can be improved and the connection information can be obtained using the next generation communication technology such as 5G and location awareness communication D2D (Device-to-Device), and V2X (Vehicle-to-X).

1 is a diagram showing a configuration of an apparatus for estimating the position of a target node in the present embodiment.
2 is a flowchart illustrating a method of estimating a position of a target node in the present embodiment.
3 is a diagram illustrating a method for obtaining the number of hops between nodes.
4 is a diagram illustrating a connection between a target node and another node when there are two anchor nodes located within one hop in the present embodiment.
FIG. 5 is a diagram illustrating a probability density of a target node received from an anchor node when there are two anchor nodes located within one hop in the present embodiment.
FIG. 6 is a diagram showing a current probability density of a target node when two anchor nodes located within one hop in the present embodiment are two.
FIG. 7 is a diagram illustrating a location candidate region when there are two anchor nodes located within one hop in the present embodiment.
FIG. 8 is a diagram illustrating a current probability density of a target node based on information on a location candidate region when two anchor nodes located within one hop in the present embodiment are two.
FIG. 9 is a diagram illustrating a connection between a target node and another node when there is one anchor node located within one hop in the present embodiment.
10 is a diagram showing the probability density of a target node received from an anchor node when there is one anchor node located within one hop in the present embodiment.
11 is a diagram showing a current probability density of a target node when there is one anchor node located within one hop in the present embodiment.
FIG. 12 is a diagram illustrating a location candidate region when there is one anchor node located within one hop in the present embodiment.
13 is a diagram showing a current probability density of a target node based on information on a position candidate region when there is one anchor node located within one hop in the present embodiment.

Hereinafter, the embodiments will be described in detail with reference to exemplary drawings. It should be noted that, in adding reference numerals to the constituent elements of the drawings, the same constituent elements are denoted by the same reference symbols as possible even if they are shown in different drawings. In the following description of the present invention, detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present disclosure rather unclear.

1 is a diagram showing a configuration of an apparatus for estimating the position of a target node in the present embodiment.

Referring to FIG. 1, a target node position estimation apparatus 100 includes a hop calculation unit 110, a position candidate region calculation unit 120, and a probability density calculation unit 130.

The hop calculation unit 110 calculates the number of hops between the anchor node and the target node for the three anchor nodes that know the location.

In this case, the number of hops between each node can be calculated as follows.

First, a first node, a second node and a third node, which are arbitrary nodes, are defined. The first node, the second node and the third node may each be an anchor node, a target node or another mobile node existing in the wireless network.

The number of hops between a node and another neighboring node can be determined based on the strength of the radio signal of another neighboring node received at the node, since wireless signals can be transmitted and received between the nodes. At this time, since the intensity of the radio signal received from the neighboring node decreases as the distance between the nodes increases, the distance between the nodes can be judged to be less than the specific distance value if the strength of the radio signal is greater than the specific threshold signal strength. Accordingly, when the strength of the radio signal is equal to or greater than a preset threshold signal strength, the number of hops between the node and the neighboring node can be determined to be one. In this case, the above-described specific distance value can be defined as the maximum communication radius.

For example, suppose that the maximum communication radius corresponding to one hop of the number of hops between nodes is 20m, and the intensity of a wireless signal received from another node is 30dB when the distance between nodes is 20m. In this case, if the intensity of the radio signal received from the neighboring node is greater than 30 dB, the number of hops with the neighboring node becomes 1. If the intensity of the radio signal received from the neighboring node is less than 30 dB, It can be a large value.

The actual distance between each node can be measured only when the number of hops between nodes is one. If the number of hops between nodes is greater than 1, the value of the radio signal received from the counterpart node is likely to be inaccurate, and the error of the position of the node calculated based on the strength of the radio signal becomes large. If the number of hops between nodes is 1, the distance between the nodes can be measured through UWB (Ultra-wideband) sensor module.

That is, when the intensity of the radio signal of the second node received at the first node is equal to or greater than a predetermined threshold signal strength, the number of hops between the first node and the second node becomes one.

If it is incorrect to calculate the number of hops by directly calculating the strength of a radio signal received from the counterpart due to a long distance between nodes (when the strength of the radio signal is less than the threshold signal strength described above) A method of obtaining the number of hops with the counterpart node based on the hop count information between the neighboring node and the counterpart node can be used.

For example, assume that the number of hops between node A and node B is 1, and the number of hops between node B and node C is 1. In this case, instead of determining the number of hops with the radio signal received from the node C, the number of hops between the node A and the node B is 1 and the number of hops between the node B and the node C is 1, 1 + 1 = 2 hops.

As another example, assuming that the number of hops between node A and node B is 1 and the number of hops between node B and node C is 3, the number of hops between node A and node C can be determined as 1 + 3 = 4.

That is, when the intensity of the radio signal of the second node received by the first node is equal to or greater than the threshold signal strength and the intensity of the radio signal of the third node received by the first node is less than the threshold signal strength, When the number of hops between nodes is N, the number of hops between the first node and the third node is (N + 1).

In order for a node to know the number of hops between other nodes, each node broadcasts its connection information, that is, the number of hops for itself and other nodes it knows, Lt; / RTI > This process will be described in more detail in FIG.

When the number of anchor nodes having a hop count of 1 from the target node is two or less among the anchor nodes, the position candidate region calculating unit 120 calculates the position candidate region based on the position of each anchor node and the number of hops calculated by the hop calculating unit 110 The position candidate region is calculated.

The location candidate region means a region where there is a probability that a target node exists. That is, it can be defined that the target node exists only within the determined position candidate region, and it can be determined that the probability that the target node exists outside the position candidate region is zero. Therefore, the current probability density for the target node can also be limited to within the position candidate region.

If there are three or more anchor nodes that can find the correct position within the neighbor of the target node, that is, within one hop, the distance between the target node and each anchor is measured, Method can be used to calculate the exact position. Therefore, it is not necessary to calculate the position candidate region separately.

However, if the distance between the target node and each anchor node is measured, if the number of hops to the target node is one or less than two (one or two), an accurate position is calculated by the method used in the conventional position estimation technique Can not. Therefore, it is necessary to increase the accuracy of the current probability density for the target node based on the calculation of the position candidate region.

In this case, the position candidate region is divided into three anchor nodes (the number of hops between two or less anchor nodes and the target node is one, and the number of hops between the other anchor nodes and the target node is greater than one) The three circles having the radius of the maximum estimated distance for each anchor node among the three anchor nodes may overlap.

The maximum estimated distance for each anchor node means the maximum value of the distance for each anchor node that the target node can have. For example, if the maximum estimated distance is 40m for any anchor node, it means that the target node exists within a circle with a radius of 40m around at least any of the anchor nodes described above.

The maximum estimated distance for each anchor node can be determined by the number of hops between the target node and each anchor node. For example, a distance value corresponding to the above-described critical signal strength, that is, a value obtained by multiplying the maximum communication radius by the target node and the number of hops between each anchor node.

For example, suppose that the maximum communication radius corresponding to one hop is set to 20m when the number of hops between nodes is one hop. In this case, for the three anchor nodes A, B, and C for the target node, if the number of hops between the target node and the anchor node A is 1, a circle with a radius of 1 * 20 = 20 m is obtained from the position of the anchor node A, If the number of hops between the node B and the target node A is 2, then a circle with a radius of 2 * 20 = 40m is obtained from the position of the anchor node B, and if the number of hops between the target node and the anchor node C is 3, I draw. Then, the region where the three circles overlap can be determined as the position candidate region.

The probability density calculation unit 130 calculates the current probability density of the target node based on the previous probability density of the target node and the above-described position candidate region.

The previous probability density of the target node means the probability density of the most recently determined target node from the current point of view. Since the target node can move its position after the time when the probability density has been previously determined, the information about the probability density is received from the anchor node for the target node and is multiplied by the previous probability density to update the current probability density of the target node.

The probability density from the anchor node means the probability density of the target node determined based on the radio signal strength of the target node received by the anchor node. In this case, since the accuracy of inter-node distance can be guaranteed only when the number of hops between nodes is 1 as described above, the probability density information is received only from an anchor node having a hop count of one hop from the target node.

Then, the probability density value received from the anchor node having the previous probability density of the target node and the hop count of one hop from the target node is multiplied by a mask corresponding to the position, and a value obtained by multiplying the probability density value by the position is set as the current probability density of the target node. In this case, the mask value may be a value between 0 and 1. If the target node is less likely to exist, the mask value may be set to a value close to 0 or 0 to increase the accuracy of the current probability density of the target node have.

In this case, for example, the above-described position candidate region may be used to set a mask value. That is, the mask is set to 1 for the position inside the position candidate region, and the mask is set to be 0 for the position outside the position candidate region. If all the connection information between the target node and the three anchor nodes, that is, the number of hops, is trusted, the target node may exist only within the position candidate region. Therefore, by setting the mask to 0 for the position outside the position candidate region, the current probability density of the target node with respect to the position outside the position candidate region can be made zero.

Hereinafter, the content of obtaining the current probability density of the above-described target node will be described in detail using an equation.

(인덱스 값은 서로 다른 노드를 구별하기 위한 값으로서 양의 정수가 될 수 있다)에 대해 전술한 위치 후보 영역을

라고 하면

에 대한 마스크 값

은 수학식 1과 같이 표현될 수 있다.The location of the node with index i

(The index value is a value for distinguishing different nodes from each other and can be a positive integer)

When you say

The mask value for

Can be expressed as Equation (1).

And a relative distance measurement between nodes j at node i, where the index is i, j, respectively

는 아래 수학식 2와 같이 표현될 수 있다.

Can be expressed by Equation (2) below.

는 노드 i와 노드 j 간의 거리(이 때, 거리값은 노드 i와 노드 j간에 송수신된 무선 신호의 세기를 이용해 결정할 수 있다)를 의미하며

는 d에 대한 분산인

에 대한 제로-평균 가우시안 노이즈(zero mean Gaussian noise)를 의미한다. 전술한

에 대한 가능도(likelihood)는 다음의 수학식 3에 의해 표현될 수 있다. 이 때, 가능도는 노드 i와 노드 j의 위치인

,

에 의한 함수로 표현될 수 있다.At this time,

Is the distance between node i and node j (where the distance value can be determined using the strength of the wireless signal transmitted between node i and node j)

Is the variance of d

Mean zero-mean Gaussian noise for the < / RTI > Described above

The likelihood for the input signal can be expressed by the following equation (3). In this case, the likelihood is the position of node i and node j

,

As shown in FIG.

가 최대가 되는 위치로 추정할 수 있다. 노드 i에 대한 신뢰도(belief)는 다음의 수학식 4에 의해 표현될 수 있다.The location for node i represents the belief for node i.

Can be estimated as a position where the maximum value is obtained. The belief for node i can be expressed by the following equation (4).

는 노드 i로부터의 홉 수가 1인 노드인 이웃 노드 j로부터 수신한 확률 밀도에 대한 메시지를 나타낸다. 그리고 J는 노드 i로부터의 홉 수가 1인 노드인 이웃 노드의 개수를 나타낸다. 이 때,

는 다음의 수학식 5에 의해 표현될 수 있다.At this time,

Represents a message about the probability density received from a neighbor node j, which is a node with a hop count of 1 from node i. And J represents the number of neighbor nodes, which are nodes having a hop count of 1 from node i. At this time,

Can be expressed by the following equation (5).

는 노드 i의 이전 확률 밀도를 나타내는 함수로서 수학식 1의 마스크를 반영하여 다음의 수학식 6과 같이 표현될 수 있다.At this time,

Is a function representing the previous probability density of the node i, and can be expressed as the following Equation (6) by reflecting the mask of Equation (1).

2 is a flowchart illustrating a method of estimating a position of a target node in the present embodiment.

Hereinafter, a description will be given of an example in which the present method is implemented by the position estimation apparatus 100 of the target node described with reference to FIG.

Referring to FIG. 2, the hop calculation unit 110 may calculate the number of hops between the anchor nodes and the target nodes for the three anchor nodes that know the location (S210).

In this case, in order to calculate the number of hops between the anchor node and the target node, the first node, the second node, and the third node, which are arbitrary nodes, The number of hops between the first node and the second node is 1 when the intensity is equal to or greater than a predetermined threshold signal strength and the intensity of the radio signal of the second node received by the first node is equal to or greater than the threshold signal intensity, The number of hops between the first node and the third node is (N + 1) when the intensity of the radio signal of the third node received by the second node is less than the threshold signal strength and the number of hops between the second node and the third node is N .

If the number of anchor nodes having a hop count of 1 from the target node is two or less among the anchor nodes based on the calculation result from the hop calculation unit 110, the position candidate region calculation unit 120 calculates the position of each anchor node The location candidate region can be calculated based on the calculated number of hops (S220).

In this case, the position candidate region is an area in which three circles overlap each other with the radius of the maximum estimated distance for each anchor node being the center of the position of each anchor node. The maximum estimated distance for each anchor node is the above- The distance value corresponding to the strength, and the number of hops between each anchor node and the target node.

Then, the probability density calculation unit 130 may calculate the current probability density of the target node based on the previous probability density of the target node and the position candidate region calculated by the position candidate region calculation unit 120 (S230).

At this time, the current probability density is calculated as the product of the previous probability density of the target node, the probability density received from the anchor node with one hop from the target node and the mask according to the position, 1 for the internal position, and 0 for the position outside the position candidate region.

3 is a diagram illustrating a method for obtaining the number of hops between nodes.

It is assumed that the first node 300, the second node 310, the third node 320, and the fourth node 330 exist on the wireless network. A circle 301 having a maximum communication radius centering on the first node 300, a circle 311 having a maximum communication radius centered on the second node 310, and a third node 320 A circle 321 having a maximum communication radius and a circle 331 having a maximum communication radius centered on the fourth node 330 may exist.

The first node 300, the second node 310, the third node 320, and the fourth node 330 may all broadcast information about the number of hops between itself and another node.

The first node 300 broadcasts a radio signal and the second node 310 receives the radio signal. The second node 310 may determine that the number of hops with the first node 300 is one based on the received radio signal. In contrast, the first node 300 may also receive a radio signal from the second node 310 and may determine that the number of hops with the second node 310 is one.

When the second node 310 broadcasts a radio signal, the second node 310 also includes information indicating that the number of hops between the first node 300 and the second node 310 is one hop, Can be performed. Accordingly, the third node 320 receiving the corresponding signal from the second node 310 can determine that the hop count with respect to the second node 310 is one hop, The number of hops between itself and the first node 300 is 2 hops because the number of hops between the first node 300 and the first node 300 is one hops. That is, the third node 320 can know the number of hops with the first node 300 without receiving the signal broadcasted from the first node 300 directly.

When the third node 320 broadcasts a radio signal, the third node 320 transmits information indicating that the number of hops between the third node 320 and the second node 310 is one hop and the third node 320 And the number of hops between the first node 300 and the first node 300 is also included, thereby performing broadcasting. Accordingly, the fourth node 330 can know that the number of hops between itself and the first node 300 is three hops and that the number of hops between itself and the second node 310 is two hops.

In this way, when each node repeatedly broadcasts, connection information between all the nodes, that is, information on the number of hops between nodes can be grasped for all nodes on the wireless network.

In the following embodiments, a method for estimating the position of the target node through the above-described target node position estimating apparatus will be described in detail. The number of anchor nodes having a hop count of 1 with respect to the target node is two or less, that is, one or two.

The embodiments described below may be applied individually or in any combination.

Since the position of the node can be expressed by a two-dimensional coordinate (x, y), FIGS. 4 to 13 will be described with reference to a two-dimensional plane defined by the x-axis and the y-axis.

FIGS. 4 to 8 are diagrams for explaining a method of obtaining a probability density for a target node when there are two anchor nodes located within one hop in the present embodiment.

4 is a diagram illustrating a connection between a target node and another node when there are two anchor nodes located within one hop in the present embodiment.

Referring to FIG. 4, a first anchor node 430, a second anchor node 440, and a third anchor node 450, which are anchor nodes, can be set for the target node 400 to estimate the position. The number of hops between the target node 400 and the first anchor node 430 and the second anchor node 440 is one. Accordingly, the distance between the target node 400 and the first anchor node 430 and the second anchor node 440 can be measured based on the intensity of the radio signal.

The first node 410 and the second node 420 exist between the target node 400 and the third anchor node 450. The target node 400 receives information via the first node 410 and the second node 420 by the method described with reference to FIG. 3, and can recognize that the number of hops with the third anchor node 450 is three.

In order to obtain the position candidate region, a first circle 431 and a second anchor node 440 having a maximum estimated distance as a radius around the first anchor node 430 are centered, A third circle 451 having the radius of the maximum estimated distance about the circle 441 and the third anchor node 450 may be set. At this time, since the number of hops between the target node 400 and the third anchor node 450 is 3, the size of the third circle 451 is larger than that of the first circle 431 and the second circle 441.

FIG. 5 is a diagram illustrating a probability density of a target node received from an anchor node when there are two anchor nodes located within one hop in the present embodiment.

Each anchor node can obtain the probability density for the target node 400 based on the wireless signal transmitted and received between the target node 400 and the target node 400 and transmit the probability density to the target node 400.

In this case, overlapping portions may occur between the probability density 501 received from the first anchor node 430 and the probability density 502 received from the second anchor node 440. In the case of trusting information from two anchor nodes, it is possible to determine that there is a possibility that the target node 400 exists at the position corresponding to the overlapping part described above, and there is no possibility that the target node 400 exists at other positions have.

FIG. 6 is a diagram showing a current probability density of a target node when two anchor nodes located within one hop in the present embodiment are two.

When the previous probability density is multiplied by the probability density received from the two anchor nodes as described above with reference to FIG. 5, the value of the current probability density exists in the overlapping portion described in FIG. Therefore, the current probability density can be distributed around two points 600 and 601 in FIG. In this case, it is unclear where the target node actually exists among the two points of 600 and 601, so additional work is required to increase the accuracy of the probability density.

FIG. 7 is a diagram illustrating a location candidate region when there are two anchor nodes located within one hop in the present embodiment.

A first circle 431 whose radius is the maximum estimated distance around the first anchor node 430, a second circle 441 whose radius is the maximum estimated distance about the second anchor node 440, The area 700 where the third circle 451 having the maximum estimated distance as the radius is superimposed on the anchor node 450 becomes the position candidate area.

The number of hops between the first anchor node 430 and the target node, the number of hops between the second anchor node 440 and the target node, the number of hops between the second anchor node 440 and the third anchor node 450, It can be determined that the target node is located within the area of 700 because there is a contradiction with at least one of the number of hops between the target nodes.

FIG. 8 is a diagram illustrating a current probability density of a target node based on information on a location candidate region when two anchor nodes located within one hop in the present embodiment are two.

If the mask is set to 1 for the position inside the position candidate region and the mask is set to 0 for the position outside the position candidate region and then the mask value is multiplied by the probability density obtained in FIG. 6, the current probability density is calculated as 800 do. In other words, in FIG. 6, the distribution is centered on only one point of 800 in FIG. 8, and is limited to the inside of the position candidate region 700 derived in FIG. Thus, the variance of the current probability density of the target node decreases and the accuracy increases.

9 to 13 are diagrams for explaining a method of obtaining a probability density for a target node when there is one anchor node located within one hop in the present embodiment. The nodes described below are assumed to be nodes separate from the nodes described in FIGS.

FIG. 9 is a diagram illustrating a connection between a target node and another node when there is one anchor node located within one hop in the present embodiment.

Referring to FIG. 9, a first anchor node 930, a second anchor node 940, and a third anchor node 950, which are anchor nodes, can be set for a target node 900 to estimate a position. The number of hops between the target node 900 and the first anchor node 930 is one. Therefore, the distance between the target node 900 and the first anchor node 930 can be measured based on the intensity of the radio signal.

A first node 910 exists between the target node 900 and the second anchor node 940. The target node 900 can receive information via the first node 910 and know that the number of hops with the second anchor node 940 is two.

A second node 920 exists between the target node 900 and the third anchor node 950. The target node 900 can receive information via the second node 920 and know that the number of hops with the third anchor node 950 is two.

In order to obtain the position candidate region, a first circle 931 and a second anchor node 940 having a maximum estimated distance as a radius around the first anchor node 930 are centered, A third circle 951 having a radius that is the maximum estimated distance around the circle 941 and the third anchor node 950 may be set. Since the number of hops between the target node 900, the second anchor node 940 and the third anchor node 950 is 2, the size of the second circle 941 and the third circle 951 is 1 (931).

10 is a diagram showing the probability density of a target node received from an anchor node when there is one anchor node located within one hop in the present embodiment.

The first anchor node 930 having a hop count of 1 with respect to the target node 900 can obtain a probability density of 1010 for the target node 900 based on the radio signal transmitted and received between the target node 900 and itself, To the target node 900.

11 is a diagram showing a current probability density of a target node when there is one anchor node located within one hop in the present embodiment.

When the probability density received from the first anchor node is multiplied by the previous probability density of the target node, the current probability density of the target node may be distributed around the region 1110 in FIG. In this case, since the region 1110 is widely distributed around the region where the probability density of 1010 is overlapped with the previous probability density value, the accuracy of the calculated probability density of the target node is lowered. Therefore, additional work is needed to increase the accuracy of the probability density.

FIG. 12 is a diagram illustrating a location candidate region when there is one anchor node located within one hop in the present embodiment.

A second circle 941 having a maximum estimated distance as a radius centered on a first circle 931 and a second anchor node 940 having a maximum estimated distance as a radius around the first anchor node 930, A region 1200 in which a third circle 951 having a maximum estimated distance as a radius is superposed on the anchor node 950 is a position candidate region.

The number of hops between the first anchor node 930 and the target node, the number of hops between the second anchor node 940 and the target node, the number of hops between the third anchor node 950 and the target node, It can be determined that the target node is located within the area of 1200 because there is a contradiction with at least one of the number of hops between the target nodes.

13 is a diagram showing a current probability density of a target node based on information on a position candidate region when there is one anchor node located within one hop in the present embodiment.

If the mask is 1 for the position within the position candidate region and the mask is 0 for the position outside the position candidate region, then multiplying the mask value by the probability density obtained in FIG. 11, the current probability density of the target node is 1300 Respectively. That is, compared with the probability density of 1110 in FIG. 11, since the probability density is distributed only in the position candidate region obtained in FIG. 12 in FIG. 13, the accuracy of the probability density increases.

The current probability density of the target node described above represents the distribution of the position where the target node may exist, and further work may be required to determine the position of the correct target node. At this time, the current position can be estimated using the MAP (maximum a posterior) method for the current probability density. The MAP method is a method for correcting the problem that the probability varies sensitively according to the measured value which is a disadvantage of the maximum likelihood estimation (MLE), and is a method of finding a value having a maximum probability with respect to given data.

The above description is merely illustrative of the technical idea of the present embodiment, and various changes and modifications may be made by those skilled in the art without departing from the essential characteristics of the embodiments. Therefore, the content disclosed in this embodiment is not intended to limit the technical idea of the present embodiment, but is intended to be illustrative, and the scope of the technical idea of the present embodiment is not limited by these embodiments. The scope of protection of the present embodiment should be construed according to the following claims, and all technical ideas within the scope of equivalents thereof should be construed as being included in the scope of the present invention.

Claims (8)

A method for estimating a location of a target node in a wireless network comprising a plurality of nodes,
Calculating the number of hops between the anchor node and the target node for the three anchor nodes that know the location;
Calculating a position candidate region based on the position of each anchor node and the calculated number of hops when the number of anchor nodes having a hop count of 1 from the target node is 2 or less among the anchor nodes; And
Calculating a current probability density of the target node based on the previous probability density of the target node and the position candidate region,
For the first node, the second node and the third node, which are arbitrary nodes,
When the intensity of the radio signal of the second node received by the first node is equal to or greater than a predetermined threshold signal strength, the number of hops between the first node and the second node is 1,
When the strength of the radio signal of the second node received by the first node is equal to or greater than the threshold signal strength and the strength of the radio signal of the third node received by the first node is less than the threshold signal strength, And if the number of hops is N, the number of hops between the first node and the third node is (N + 1).
The method according to claim 1,
Wherein the position candidate region comprises:
Wherein the anchor node is an area in which three circles, each of which has a radius as a maximum estimated distance for each of the anchor nodes,
The maximum estimated distance for each of the anchor nodes is calculated as:
Wherein the maximum communication radius is determined by multiplying the maximum communication radius determined by the critical signal strength by the number of hops between each anchor node and the target node.
The method according to claim 1,
Wherein the current probability density
A previous probability density of the target node, a probability density from an anchor node with one hop to the target node, and a mask according to the location.
The method of claim 3,
Wherein,
The position within the position candidate region is 1, and the position outside the position candidate region is 0.
An apparatus for estimating a location of a target node in a wireless network comprising a plurality of nodes,
A hop calculation unit for calculating the number of hops between the anchor node and the target node for three anchor nodes that know the location;
A position candidate region calculation unit for calculating a position candidate region based on the position of each of the anchor nodes and the calculated number of hops when the number of anchor nodes having a hop count of 1 from the target node is 2 or less among the anchor nodes; And
And a probability density calculation unit for calculating a current probability density of the target node based on the previous probability density of the target node and the position candidate region,
For the first node, the second node and the third node, which are arbitrary nodes,
When the intensity of the radio signal of the second node received by the first node is equal to or greater than a predetermined threshold signal strength, the number of hops between the first node and the second node is 1,
When the strength of the radio signal of the second node received by the first node is equal to or greater than the threshold signal strength and the strength of the radio signal of the third node received by the first node is less than the threshold signal strength, And when the number of hops is N, the number of hops between the first node and the third node is (N + 1).
6. The method of claim 5,
Wherein the position candidate region comprises:
Wherein the anchor node is an area in which three circles, each of which has a radius as a maximum estimated distance for each of the anchor nodes,
The maximum estimated distance for each of the anchor nodes is calculated as:
Wherein the maximum communication radius is determined by multiplying the maximum communication radius determined by the critical signal strength by the number of hops between each anchor node and the target node.
6. The method of claim 5,
Wherein the current probability density
A previous probability density of the target node, a probability density from an anchor node with a hop count of one hop to the target node, and a mask according to the position.
6. The method of claim 5,
Wherein,
The position of the position candidate region is 1, and the position of the position candidate region is 0 for the position outside the position candidate region.

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