KR101144486B1 - Distance estimation method based on sequential rearrangement of received signal strength in wireless sensor networks - Google Patents

Abstract

Disclosed is a distance measuring method in a wireless sensor network using a sequentially ordered RSS. In the distance measuring method of a wireless sensor network, a distance measuring method of a wireless sensor network system measuring a distance of a sensor node using a path loss exponent (PLE), the method comprising: transmitting a beacon message from an anchor node serving as a reference point; ; Receiving a beacon message at the sensor node and transmitting RSS (received signal strength) information and hop information to the anchor node with respect to the beacon message; Registering the sensor node transmitting the RSS information in the anchor node as a member node within its propagation range and calculating a propagation radius using the RSS information and the hop information transmitted by the member node; Calculating a unit area and a mapping distance for the member node using the propagation radius and the number of member nodes at the anchor node; Calculating the PLE using the RSS information and the mapping distance for each member node in the anchor node, and then setting the average value of the PLE to the common PLE and transmitting the PLE to the member node; And measuring a distance from the anchor node through the common PLE and RSS information in the member node.

Description

DISTANCE ESTIMATION METHOD BASED ON SEQUENTIAL REARRANGEMENT OF RECEIVED SIGNAL STRENGTH IN WIRELESS SENSOR NETWORKS}

Embodiments of the present invention relate to a distance measuring method for measuring a distance of a sensor node using received signal strength (RSS) in a wireless sensor network.

A wireless sensor network is one of systems for monitoring a specific area or object using multiple sensor nodes or detecting events occurring in the network. The wireless sensor network system is composed of a few anchor nodes capable of independently obtaining their own location information and a plurality of sensor nodes capable of determining their own location using location information of the anchor nodes.

When an event occurs, the sensor node detects that an event has occurred in its sensing area and sends a message to the user. If there is no location information, the user cannot know where the event occurred and cannot respond to it. We need a positioning algorithm to find out.

In order to find the position of the sensor node in the positioning algorithm, it is necessary to know the distance from at least three anchors. The more accurate the distance measured from the anchor is, the more accurate the position of the sensor node can be obtained.

The method of using RSS in the distance measuring method has the advantage that it is suitable for wireless sensor networks because it is generally used because it is easy to implement and does not require an additional device in existing radio frequency (RF) terminals, but it is necessary to detect accurate RSS. Prerequisites are required.

In general, RF systems follow a path loss model, which quantifies that the strength of a transmitted signal decreases with distance. That is, the relationship between the strength of the transmitted signal and the strength of the received signal is represented by distance and a specific parameter. In this case, the parameter may be variable according to an environment, which is called PLE (path loss exponent).

Conventional distance measurement algorithms using RSS were based on the assumption that the PLE is the ideal value, or the PLE for the environment is fixed by measuring the RSS repeatedly and fixing the distance in the environment where the system will be constructed.

However, even in the same space, the PLE may be variable in time due to various factors such as weather or obstacles, and in some cases, the PLE may not be acquired by artificial measurement in advance.

Accordingly, the wireless sensor network needs a method of actively acquiring PLE and measuring distance and position through the PLE.

In order to obtain the distance information that each sensor node needs to determine its position in the wireless sensor network, RSS is reported to the anchor node, and the anchor node predicts the PLE of each sensor node based on the collected RSS. Disclosed is a distance measuring method capable of calculating a PLE applicable in common.

A method of designating a probabilistic predicted position of each node to find a common PLE that can be applied in common, Anchor node calculates its propagation radius based on RSS and hop information of a plurality of sensor nodes in an unknown environment, A method is disclosed in which an anchor node obtains a PLE that can be commonly used by member nodes within its propagation range.

A distance measuring method of a wireless sensor network system for measuring a distance of a sensor node using a path loss exponent (PLE), the method comprising: transmitting a beacon message at an anchor node serving as a reference point; Receiving a beacon message at the sensor node and transmitting RSS (received signal strength) information and hop information to the anchor node with respect to the beacon message; Registering the sensor node transmitting the RSS information in the anchor node as a member node within its propagation range and calculating a propagation radius using the RSS information and the hop information transmitted by the member node; Calculating a unit area and a mapping distance for the member node using the propagation radius and the number of member nodes at the anchor node; Calculating the PLE using the RSS information and the mapping distance for each member node in the anchor node, and then setting the average value of the PLE to the common PLE and transmitting the PLE to the member node; And measuring a distance from the anchor node through the common PLE and RSS information in the member node.

According to one side, the propagation radius of the anchor node is set to be larger than the propagation radius of the sensor node, the anchor node transmits the beacon message in a broadcast (broadcasting) method that transmits a message to the sensor node without targeting a specific node In addition, the sensor node transmits the RSS information and the hop information in a multi hop flooding manner, in which a sensor node relays and transmits another sensor node existing between the anchor nodes.

According to another aspect, the step of calculating the propagation radius, the maximum propagation radius of the anchor node using the RSS information of the boundary node that is the sensor node with the smallest RSS value and the hop information of the sensor node with the largest hop number Can be calculated.

According to another aspect, the calculating of the unit area and the mapping distance of the member node, after setting the area divided by the propagation radius by the number of member nodes to the unit area of the member node, according to the hop information using the unit area You can assign a mapping distance, which is an expected distance where each member node will be located.

When sensor nodes receive beacon messages from anchor nodes, they report their RSS and register as member nodes, and anchor nodes actively estimate the PLE, which is variable according to the environment, based on collected RSS, so that each sensor node has its own location. Can contribute to judging.

Since the propagation radius of the anchor node is larger than the propagation radius of the sensor node, it is possible to reduce the number of anchor nodes required for the system, which is effective in cost reduction, and it is possible to spontaneously predict the propagation radius of the variable anchor node according to the environment. The network can be freely configured by using an anchor node or by adjusting the propagation radius of the anchor node.

Therefore, the PLE, which can change over time, can be obtained more actively to reduce the distance error for the sensor node and to further improve the accuracy of the distance and position measurement.

1 is a flowchart illustrating a distance measuring method in a wireless sensor network according to sequential RSS alignment according to an embodiment of the present invention.
2 is a view for explaining the operation of the anchor node and the sensor node in the wireless sensor network, according to an embodiment of the present invention.
3 is a view for explaining a mapping distance according to a unit area according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In this specification, the terms defined are as follows.

Anchor Node: Node that is the base of the distance

Sensor Node: Node to get distance from anchor node

Member Node: Node within range of anchor node

Boundary node: outermost node

Broadcasting: Transmission method that informs one-sided without targeting a specific node

Multi-hop flooding: how to relay and forward other nodes in the middle to deliver messages to target nodes

Beacon message: Messages sent by anchor nodes periodically

Unit area: The area divided by the number of member nodes divided by the propagation of the anchor node.

Mapping distance: Estimated distance of member nodes found using unit area

One embodiment of the present invention relates to a distance measurement algorithm applied to a wireless system such as a wireless sensor network. According to an exemplary embodiment of the present invention, an anchor node receiving RSS from each node sequentially arranges these values in an area where the distribution of sensor nodes is even and has a high distribution density, and then obtains PLE at each node and averages each PLE. The common PLE can be obtained by And, according to an embodiment of the present invention, nodes within a propagation range of an anchor node may measure their distance by applying a common PLE.

Particularly, in an embodiment of the present invention, in a network in which a node has a small propagation radius and a plurality of nodes, such as a wireless sensor network, the sink node is based on the collected data in a system in which packet flow is concentrated to a specific sink node. It is possible to determine the PLE that can be commonly applied within the range of, and to estimate its propagation range through RSS and hop number collected from sensor nodes by anchor nodes whose propagation range is unknown in unknown environment. Can be.

1 is a flowchart illustrating a distance measuring method in a wireless sensor network according to sequential RSS alignment according to an embodiment of the present invention.

In step 101, the wireless system periodically broadcasts a beacon message using a larger radio radius than the sensor node at the anchor node.

In step 102, the wireless system reports the RSS received in response to the sensor node receiving the beacon message to the anchor node sending the beacon message as multi-hop flooding.

In step 103, the wireless system regards and registers a sensor node, which is within its propagation radius at the anchor node, receives its periodic beacon message and reports RSS, the strength of the received signal, as its member node. If any sensor node receives a beacon message from several anchor nodes, the sensor node reports the RSS of the message received from each anchor node to each anchor node. The distance measuring method according to an embodiment includes a method in which one anchor node communicates with member nodes to obtain a distance between each sensor node, and a sensor node obtains its own location information by obtaining distance information from various anchor nodes. Does not include However, the method for obtaining location information of the sensor node may be derived through an existing positioning algorithm when distance information is obtained. Since the sensor node has a smaller propagation radius than the anchor node, the sensor node unicasts the multihop to report the RSS to the anchor node. In this process, the hop information is also transmitted to the anchor node.

In step 104, the wireless system can obtain the ID, RSS, and hop information of the member node from the anchor node, and arranges the member nodes in a table in which the RSS values have the greatest order.

In step 105, the wireless system calculates its propagation radius R _max using the RSS and the hop number of the member node at the anchor node.

In steps 106 to 109, the wireless system _{obtains a} mapping distance from the unit area S _unit using the propagation radius R _max at the anchor node, and finally calculates a common PLE within its range and transmits it to the member nodes. .

In step 110, the wireless system estimates the distance from the anchor node using common PLEs and RSS at the member nodes.

The process of steps 106 to 110 will be described in detail with reference to Equations 1 to 11.

In general, the size of a transmission signal generated at a transmitting node decreases as the transmission distance becomes longer, so that the RSS of the signal received at the receiving node can be represented by a log-normal model.

Where P _r ( d ) is the strength of the received signal at distance d and is expressed in decibels. P _r (d ₀₎ is the received reference value by the signal strength at the distance d ₀ d ₀ In general, = 1 β is PLE and its value varies depending on the environment and generally ranges from 2 to 6.

In one embodiment of the present invention, the anchor node includes a method for obtaining its propagation radius R _max based on information obtained from member nodes. Also, the unit area occupied by one member node using the propagation radius R _max and the number of member nodes. It includes how to get S _unit . In addition, the method includes acquiring the PLE at each node through the expected distance of each member node derived from the unit area S _unit at the anchor node and the RSS reported by the member node. The average of the PLEs acquired from each node in the anchor node is unified to one PLE, and this value is informed to each member node. It includes a method.

2 is a view for explaining the operation of the anchor node and the sensor node in the wireless sensor network, according to an embodiment of the present invention. As shown in Figure 2, the anchor node delivers the beacon message to the broadcast (210), the sensor node reports the RSS to the anchor node in the multi-hop flooding 220, the hop count is reported in the process. In FIG. 2, the circle of solid line represents the propagation radius R _max 230 of the anchor node and the circle of dotted line represents the propagation radius 240 of the sensor node. In FIG. 2, it is assumed that member node m 250 is located 10 hops away from the anchor node.

The process of the anchor node obtaining its propagation radius R _max includes using the RSS and the hop count of all its member nodes. If the largest hop number from the number of hops reported by the member node is called H _max , the i- th hop distance d ⁱ from the anchor node can be calculated using Equation 2 using R _max .

In one embodiment of the present invention, using the RSS of the boundary node having the smallest RSS of each hop, the PLE of each boundary node, and the propagation radius using Equation 2 It includes how to find R _max .

RSS ratios of the i- th hop and the j- th hop, C _{i , j} can be obtained as Equation 3 if RSS ⁱ of the boundary node of the i- th hop is RSS ⁱ .

Since the same PLE is used within the range of the anchor node, if the PLE is the same in each boundary node, it can be expressed as Equation 4.

β ⁱ , β ^j are the PLE at the i , j th hops, respectively, and RSS ⁱ , RSS ^j is the RSS at each i , j th hop, d ⁱ , d ^j is the i , j th hop distance, respectively. To sum up Equation 4, it can be expressed in the form of the right side of Equation 3 and using Equation 2, C _{i , j} is determined by Equation 5 which is a relationship between the hop number, H _max , R _max .

If Equation 5 is summarized for R _max , it becomes the propagation radius of the anchor node obtained using the RSS ratio C _{i , j} . Therefore, in particular _, R _{max ( i, j )} obtained using C _{i , j} and can be obtained by Equation 6.

Finally, the propagation radius R _max of the anchor node is determined using Equation 7, which _is an average of R _{max ( i, j )} for all C _{i , j} .

The anchor node can find the unit area S _unit occupied by one member node using its propagation radius and the number of member nodes. This unit area is probabilistically the range that there will be at least one node and is determined by Equation (8).

Where N is the number of member nodes.

과

의 차이(310)는 클 확률이 높지만

와

의 차이(320)는 k가 증가함에 따라 감소함을 보여준다. k가 N에 가까워질수록

(330)로 간주할 수 있다. k번째 멤버 노드의 맵핑거리

는 수학식 9에 의해 결정된다.3 is a view for explaining a mapping distance according to a unit area according to an embodiment of the present invention. In FIG. 3, the size of the ring shape A _k is the same as S _unit . Nearest to the anchor node

and

Although the difference 310 is likely to be large,

Wow

The difference 320 shows that it decreases as k increases. As k approaches N

Can be regarded as (330). Mapping distance of k th member node

Is determined by equation (9).

를 이용해 k번째 멤버 노드에 해당하는 PLE β_k를 구하고 이것의 평균을 취하여 공통 PLE

를 계산하며 수학식 10에 의해 결정된다.The anchor node has a mapping distance from the RSS value RSS _k of the kth member node.

Find the PLE β _k corresponding to the k th member node using, and take the average of these to find the common PLE

It is calculated by the equation (10).

를 구하며 수학식 11에 의해 결정된다. The member node that acquired the common PLE from the anchor node is finally the distance from the anchor node.

Is determined by Equation (11).

As described above, according to embodiments of the present invention, when sensor nodes receive a beacon message from an anchor node, they report their RSS and register as a member node, and the anchor node actively performs a PLE variable according to the environment based on the collected RSS. By estimating, each sensor node can measure its position more accurately.

As described above, the present invention has been described by way of limited embodiments and drawings, but the present invention is not limited to the above embodiments, and those skilled in the art to which the present invention pertains various modifications and variations from such descriptions. This is possible.

Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the claims below but also by the equivalents of the claims.

Claims (5)

In the distance measuring method of a wireless sensor network system for measuring the distance of the sensor node using the path loss exponent (PLE),
Transmitting a beacon message at an anchor node which is a node serving as a reference point;
Receiving the beacon message at the sensor node and transmitting RSS (received signal strength) information and hop information to the anchor node with respect to the beacon message;
Registering the sensor node having transmitted the RSS information in the anchor node as a member node within its propagation range and calculating a propagation radius using the RSS information and the hop information transmitted by the member node;
Calculating a unit area and a mapping distance for the member node using the propagation radius and the number of member nodes at the anchor node;
Calculating, by the anchor node, the PLE using the RSS information and the mapping distance for each member node, and setting the average value of the PLE as a common PLE to transmit the PLE to the member node; And
Measuring a distance between the anchor node through the common PLE and the RSS information in the member node;
Distance measuring method of a wireless sensor network system comprising a. The method of claim 1,
The propagation radius of the anchor node is set to be larger than the propagation radius of the sensor node,
The anchor node transmits the beacon message in a broadcasting manner, which is a method of transmitting the beacon message without targeting a specific node with respect to the sensor node.
The sensor node transmits the RSS information and the hop information in a multi hop flooding manner, in which the sensor node relays and transmits another sensor node existing between the anchor node.
Distance measuring method of a wireless sensor network system, characterized in that. The method of claim 1,
Calculating the propagation radius,
Calculating the maximum propagation radius of the anchor node using the RSS information of the boundary node, the sensor node having the smallest RSS value, and the hop information of the sensor node having the largest hop number.
Distance measuring method of a wireless sensor network system, characterized in that. The method of claim 3,
The distance measuring method,
And sorting the member nodes in the order in which the RSS values are high in the anchor node and managing the members in a table.
Calculating the propagation radius,
Calculating an RSS ratio for the boundary node using RSS information of the member nodes arranged in the table
Distance measuring method of a wireless sensor network system, characterized in that. The method of claim 1,
Computing the unit area and the mapping distance of the member node,
Setting an area obtained by dividing the propagation radius by the number of member nodes as the unit area of the member node, and then allocating a mapping distance that is an expected distance at which each member node is to be located according to the hop information using the unit area;
Distance measuring method of a wireless sensor network system, characterized in that.

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