阅读说明：本技术 一种基于dbscan的参考点加权三边质心定位方法 (Reference point weighted trilateral centroid positioning method based on DBSCAN ) 是由 夏超 陈静 屈琪 于 2020-11-18 设计创作，主要内容包括：本发明涉及一种基于DBSCAN的参考点加权三边质心定位方法,首先从若干信标节点中选取三个信标节点,其选择条件为信标节点所在位置不接近一条直线上,且接收到目标节点所发射的RSSI信号最大,其次分别对三个信标节点接收的RSSI信号进行M次采样并构成M个RSSI信号三元组,对其进行DBSCAN聚类以获得去噪后的RSSI信号三元组,随后基于去噪后的RSSI信号三元组计算三个信标节点到目标节点的距离,然后以各信标节点为圆心,三个距离为半径形成三个定位圆,基于参考点公式分别计算位于三个定位圆重叠部分弧上的三个参考点,最后基于三个参考点利用加权三边质心定位算法计算目标节点的坐标。本发明在测距和定位两方面有效地做出了改善,大大的提高了测距和定位精度。(The invention relates to a reference point weighted trilateral centroid locating method based on DBSCAN, which comprises the steps of firstly selecting three beacon nodes from a plurality of beacon nodes, the selection conditions are that the position of the beacon node is not close to a straight line, the received RSSI signal transmitted by the target node is the maximum, secondly, respectively carrying out M times of sampling on the RSSI signals received by the three beacon nodes and forming M RSSI signal triples, performing DBSCAN clustering on the three beacon nodes to obtain denoised RSSI signal triples, then calculating the distances from the three beacon nodes to the target node based on the denoised RSSI signal triples, then, each beacon node is used as a circle center, three distances are used as radii to form three positioning circles, three reference points located on arcs of the overlapped parts of the three positioning circles are calculated respectively based on a reference point formula, and finally, the coordinates of the target node are calculated based on the three reference points by using a weighted trilateral centroid positioning algorithm. The invention effectively improves the two aspects of distance measurement and positioning, and greatly improves the precision of distance measurement and positioning.)

1. A reference point weighted trilateral centroid locating method based on DBSCAN is characterized by comprising the following steps:

step S1: selecting three beacon nodes from the plurality of beacon nodes, wherein the selection conditions are that the positions of the beacon nodes are not close to a straight line, and the received RSSI (received signal strength indicator) signals transmitted by the target nodes are the largest;

step S2: sampling RSSI signals received by the three beacon nodes for M times and forming M RSSI signal triples so as to form a sampling matrix of the RSSI signals;

step S3: carrying out DBSCAN clustering on the M RSSI signal triples to eliminate small-probability large interference in the RSSI signals and obtain denoised RSSI signal triples;

step S4: calculating the distances from the three beacon nodes to the target node based on the denoised RSSI signal triple;

step S5: forming three positioning circles by taking each beacon node as a circle center and the distance from the beacon node to the target node as a radius, and respectively calculating three reference points positioned on arcs of the overlapped parts of the three positioning circles based on a reference point formula;

step S6: and calculating the coordinates of the target node by using a weighted trilateral centroid location algorithm based on the three reference points.

2. The reference point weighted trilateral centroid locating method based on DBSCAN according to claim 1, wherein the step S1 specifically includes:

step S1.1: the RSSI signal values received by all the beacon nodes are sorted from large to small and are recorded as { RSSI₁,RSSI₂,…,RSSI_N}，N is the number of all beacon nodes;

step S1.2: selecting the first three RSSI values to find out three corresponding beacon nodes, wherein the coordinates of the three beacon nodes can be recorded as: (x)₁,y₁)、(x₂,y₂)、(x₃,y₃)；

Step S1.3: the slope of the connecting straight line of any two beacons can be calculated according to the coordinates of the three beacons:

step S1.4: setting a threshold value delta, if₁-k₂|<δ, the number of the beacons needs to be increased according to the sequence, the combination between the beacons is performed again, and the steps S1.2 to S1.4 are repeated until three beacons meeting the conditions are selected.

3. The reference point weighted trilateral centroid locating method based on DBSCAN according to claim 1, wherein the sampling matrix of the RSSI signal specifically is:

4. the reference point weighted trilateral centroid locating method based on DBSCAN according to claim 1, wherein the step S3 specifically includes:

step S3.1: establishing a class number set cluster, and aiming at the set R ═ { R ] formed by the M signal triples₁,R₂,…,R_MClustering, storing the number result after clustering in a cluster, assigning MinPts to beta, and specifically setting the radius as follows:

in the formula, beta (0)<β<1) For the designed number factor, gamma represents the gamma distribution, Prod (x) represents the product of the return vectors, R_maxIs the maximum value in the set R, R_minIs the minimum value in the set R;

step S3.2: selecting any one unvisited point P from the set R, if the number of all objects in the field of P is greater than or equal to MinPts, then P is a core point, and the class number of the core point is assigned as cluster;

step S3.3: searching each object which can be reached from the P density, and assigning the class numbers of the objects as cluster;

step S3.4: removing the core point, scanning other data objects in the set, and repeating the steps until the clustering is finished when no core point can be found in the data set R;

step S3.5: comparing the number alpha and MinPts of the data points in all clusters, if alpha is less than MinPts, rejecting the cluster, and selecting one cluster with the most data points in the rest other clusters as a standard cluster;

step S3.6: and calculating the mass center of the standard cluster as a denoised RSSI signal triple.

5. The reference point weighted trilateral centroid locating method based on DBSCAN according to claim 1, wherein the step S5 specifically includes:

step S5.1: forming three positioning circles by taking each beacon node as a circle center and the distance from the beacon node to the target node as a radius;

step S5.2: with one of the reference pointsFor example, it is located in the beacon node M₁(x₁,y₁) As a circle center, a beacon node M₁(x₁,y₁) Distance d to target node₁The positioning circle with radius satisfies that:

step S5.3: reference pointThe reference point formula that needs to be satisfied is:in the formula (I), the compound is shown in the specification,denotes a reference point A₁To the beacon node M₂The distance of (a) to (b),denotes a reference point A₁To the beacon node M₃The distance of (d);

step S5.4: combining the above steps to calculate the reference pointThe other two reference points can be calculated by the same principleAnd

6. the reference point weighted trilateral centroid locating method based on DBSCAN according to claim 1, wherein the coordinates of the target node specifically are:

Technical Field

The invention relates to the field of wireless sensor node positioning, in particular to a reference point weighted trilateral centroid positioning method based on DBSCAN.

Background

With the development of information technology, wireless sensing technology has become an essential technology in the fields of environmental monitoring, military reconnaissance, traffic positioning and the like. In the wireless sensor network, the position information is important for the monitoring activity of the wireless sensor network, and the monitoring message without the position information is usually meaningless. Therefore, the wireless sensor node positioning technology plays a key role in the effectiveness of the wireless sensor network application.

In various wireless sensor node positioning technologies, most wireless communication modules support the RSSI ranging function, so that a positioning algorithm based on RSSI ranging has become a mainstream indoor positioning method, but when the RSSI signal is propagated in an actual environment, the RSSI signal is inevitably interfered by noises such as multipath fading, diffraction, antenna gain, non-line-of-sight and the like, and uncertain propagation loss is generated, so that the ranging is inaccurate, and the positioning result is influenced. Although a common average filtering algorithm can reduce a ranging error caused by environmental factors, the common average filtering algorithm is easily affected by some small-probability and large-interference, and therefore, a new RSSI signal extraction method based on a wireless signal propagation principle is required to be provided for ensuring and improving the ranging accuracy of the algorithm.

Meanwhile, the estimation method of the node position is also extremely important, and the traditional centroid positioning algorithm is simple and easy to implement because the coordination between the beacon node and the target node is not needed, but neglects the influence of the distance between the beacon node and the target node on the positioning result of the target node, so that the positioning error is larger; although the influence of the distance factor between the beacon node and the target node is considered in the common weighted trilateral centroid location algorithm, the location accuracy is still not high, and therefore an improved weighted trilateral centroid location algorithm needs to be provided to improve the location accuracy of the target node.

Disclosure of Invention

In view of the above, the invention provides a reference point weighted trilateral centroid locating method based on DBSCAN, which fully considers the influence of environmental factors on RSSI signal transmission, effectively eliminates noise signals with small probability and large interference, and greatly improves ranging accuracy and anti-interference performance.

In order to achieve the purpose, the invention adopts the following technical scheme:

a reference point weighted trilateral centroid locating method based on DBSCAN includes the following steps:

step S1: selecting three beacon nodes from the plurality of beacon nodes, wherein the selection conditions are that the positions of the beacon nodes are not close to a straight line, and the received RSSI (received signal strength indicator) signals transmitted by the target nodes are the largest;

step S2: sampling RSSI signals received by the three beacon nodes for M times and forming M RSSI signal triples so as to form a sampling matrix of the RSSI signals;

step S3: carrying out DBSCAN clustering on the M RSSI signal triples to eliminate small-probability large interference in the RSSI signals and obtain denoised RSSI signal triples;

step S4: calculating the distances from the three beacon nodes to the target node based on the denoised RSSI signal triple;

step S5: forming three positioning circles by taking each beacon node as a circle center and the distance from the beacon node to the target node as a radius, and respectively calculating three reference points positioned on arcs of the overlapped parts of the three positioning circles based on a reference point formula;

step S6: and calculating the coordinates of the target node by using a weighted trilateral centroid location algorithm based on the three reference points.

Compared with the prior art, the invention has the beneficial effects that:

1. in the aspect of distance measurement: generally, the average value of the RSSI signal characteristics is selected as the positioning RSSI value, however, due to the complexity and dynamics of the environment, the interference of noises such as multipath fading, diffraction, antenna gain, non-line-of-sight and the like often exists in the signal propagation process, the average value of the RSSI signal cannot well approach the true value of the RSSI, and the robustness of the RSSI signal cannot be effectively ensured. Based on the RSSI signal extraction strategy of the DBSCAN, the abnormally attenuated RSSI signal sampling data caused by the environmental noise interference is effectively abandoned. Therefore, theoretically, the invention has higher anti-interference performance and ranging precision;

2. in the aspect of positioning: the traditional weighted trilateral centroid location algorithm needs three location circles with a beacon node as a circle center to intersect in pairs to form 3 inside intersection points. However, in practice, the situation that two positioning circles intersect with each other cannot be formed due to various reasons, and the three reference points can be calculated to accurately position the target node by the reference point weighted centroid positioning algorithm adopted by the invention no matter whether the three positioning circles intersect with each other or not, so that the positioning accuracy of the target node is greatly improved.

Drawings

FIG. 1 is a schematic flow diagram of an embodiment of the present invention;

fig. 2 is a schematic diagram of an RSSI signal extraction flow based on DBSCAN in the embodiment of the present invention;

FIG. 3 is a schematic structural diagram of a reference point weighted trilateral centroid location algorithm according to an embodiment of the present invention.

Detailed Description

In order to facilitate the understanding and implementation of the present invention for those of ordinary skill in the art, the present invention is further described in detail with reference to the accompanying drawings and examples, it is to be understood that the embodiments described herein are merely illustrative and explanatory of the present invention and are not restrictive thereof.

Referring to fig. 1, the reference point weighted trilateral centroid locating method based on DBSCAN provided by the present invention includes the following steps:

step S1: selecting three beacon nodes from the plurality of beacon nodes, wherein the selection conditions are that the positions of the beacon nodes are not close to a straight line, and the received RSSI (received signal strength indicator) signals transmitted by the target nodes are the largest;

the specific implementation comprises the following substeps:

step S1.1: the RSSI signal values received by all the beacon nodes are sorted from large to small and are recorded as { RSSI₁,RSSI₂,…,RSSI_NN is the number of all beacon nodes;

step S1.2: selecting the first three RSSI values to find out three corresponding beacon nodes, wherein the coordinates of the three beacon nodes can be recorded as: (x)₁,y₁)、(x₂,y₂)、(x₃,y₃)；

Step S1.3: the slope of the connecting straight line of any two beacons can be calculated based on the coordinates of the three beacons:

step S1.4: setting a threshold value delta, if₁-k₂|<Delta, then according to the requirementsAnd increasing the number of the beacon nodes in sequence, recombining the beacon nodes, and repeating the step S1.2 to the step S1.4 until three beacon nodes meeting the conditions are selected.

Step S2: sampling the RSSI signals received by the three beacon nodes for M times and forming M RSSI signal triplets so as to form a sampling matrix of the RSSI signals, wherein the sampling matrix is in the specific form of:

step S3: carrying out DBSCAN clustering on the M RSSI signal triples to eliminate small-probability large interference in the RSSI signals and obtain denoised RSSI signal triples;

the RSSI signal extraction flow diagram based on DBSCAN is shown in fig. 2, and the specific implementation includes the following sub-steps:

step S3.1: establishing a class number set cluster, and aiming at the set R ═ { R ] formed by the M signal triples₁,R₂,…,R_MClustering, storing the number result after clustering in a cluster, assigning MinPts to beta, and specifically setting the radius as follows:

in the formula (1), beta (0)<β<1) For the designed number factor, gamma represents the gamma distribution, Prod (x) represents the product of the return vectors, R_maxIs the maximum value in the set R, R_minIs the minimum value in the set R;

step S3.2: selecting any one unvisited point P from the set R, if the number of all objects in the field of P is greater than or equal to MinPts, then P is a core point, and the class number of the core point is assigned as cluster;

step S3.3: searching each object which can be reached from the P density, and assigning the class numbers of the objects as cluster;

step S3.4: removing the core point, scanning other data objects in the set, and repeating the steps until the clustering is finished when no core point can be found in the data set R;

step S3.5: comparing the number alpha and MinPts of the data points in all clusters, if alpha is less than MinPts, rejecting the cluster, and selecting one cluster with the most data points in the rest other clusters as a standard cluster;

since RSSI signal interference is a random, small probability event, the cluster with the most elements is selected as the standard cluster to calculate the accurate value of RSSI. However, sometimes the RSSI signal distribution is more dispersed due to the influence of environment or noise, and it is necessary to further determine whether the selected standard cluster meets the condition for calculating the accurate RSSI value.

Assuming that J is standard clustering and the number of elements contained in J is m, the method is broken under the following conditions:

(1) if M is larger than or equal to 1/2M, the RSSI signals are concentrated, and the RSSI accurate value can be calculated through the standard cluster J;

(2) if M is less than 1/2M, the RSSI signal is greatly influenced by the environment, the signal distribution is relatively divergent, and the RSSI signal needs to be sent to the unknown node again by the anchor node for calculation.

Step S3.6: calculating the center of mass of the standard cluster as a denoised RSSI signal triple, and recording the triple as RSSI ═ RSSI₁,RSSI₂,RSSI₃}。

Step S4: calculating the distances from the three beacon nodes to the target node based on the denoised RSSI signal triples, and recording the distances as d ═ d { (d)₁,d₂,d₃}；

And substituting the RSSI signal strength into a common Shadowing model to calculate the distance between the beacon node and the target node, wherein the form of the Shadowing model is as follows:

in the formula (2), PI (d)_i) For a distance signal transmitting end d_iSignal strength of (d), PI (d)₀) For a distance signal transmitting end d₀Is (d)₀For reference distance, typically 1m), and n is the pathRadial decay index, G_δIs a gaussian random variable with a mean of 0 and a variance of δ.

Step S5: forming three positioning circles by taking each beacon node as a circle center and the distance from the beacon node to the target node as a radius, and respectively calculating three reference points positioned on arcs of the overlapped parts of the three positioning circles based on a reference point formula;

the structural diagram of the reference point weighted trilateral centroid location algorithm is shown in fig. 3, and M is calculated₁(x₁,y₁) As the center of a circle, d₁Reference point on circle for locating radiusDue to A₁At M₁As the center of a circle, d₁On a circle of radius, then:

A₁to two other beacons M₂、M₃The distance of (a) is:

the reference point formula that needs to be satisfied is:

there may be multiple solutions due to the reference point satisfying the reference point condition, but Δ M needs to be screened out₁M₂M₃Internal solution participation weighted centroid algorithmPositioning can be carried out by determining a straight line by the two beacon nodes, and the reference point and the other beacon node are positioned at the same side of the straight line. At the same time, it can be demonstrated at Δ M₁M₂M₃There is only one solution satisfying the reference point condition inside, so that the reference point can be calculated

Similarly, M can be calculated separately₂As the center of a circle d₂Is a radius, M₃As the center of a circle d₃As a reference point on a radiusAnd

step S6: and calculating the coordinates of the target node by using a weighted trilateral centroid location algorithm based on the three reference points.

The coordinates of the target node are noted asThe concrete form is as follows:

it will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.

Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.