KR102239797B1 - Method and apparatus for determining aggregation node in wireless sensor network - Google Patents

Abstract

According to one embodiment of the present invention, a merging node decision method in a sink node collecting data through a merging node of an energy collection type wireless sensor network and a mobile sink may comprise the steps of: adaptively determining, by the sink node, the number of merging nodes in consideration of the number of sensor nodes belonging to the wireless sensor network and the amount of data sensed by the sensor nodes; and selecting, by the sink node, as many merging nodes as the number of merging nodes among nodes on a moving path of the sink node for the mobile sink. When the merging node decision method in the wireless sensor network according to the present invention is used, the connectivity and data collection amount of the wireless sensor network can be increased.

Description

A method and apparatus for determining a merge node in a wireless sensor network.

The present invention relates to a method and apparatus for determining a merge node in a wireless sensor network. In more detail, it relates to a method and apparatus for determining a merge node in consideration of wireless power transmission in an energy-collecting wireless sensor network.

A wireless sensor network (WSN) has recently been in the spotlight as a technique for monitoring the environment in an area that is difficult to access or in a wide area. The wireless sensor network is composed of a number of sensor nodes distributed and distributed to measure physical and environmental conditions such as temperature and air pressure, and a sink node that collects information from the sensor nodes through wireless.

As described above, the wireless sensor network collects environmental data with a large number of small sensor nodes, but generally operates with a battery, so there is a problem that the lifespan is short. In other words, the sensor nodes must collect data of the surrounding environment and transmit the collected environmental data to the sink node. However, the battery is consumed during the data collection and transmission process, so it may be difficult to operate for a long time.

To increase the availability of such a wireless sensor network, the battery of each node must be periodically replaced or replaced with a new node. In order to overcome this, recently, a method of using an energy collection type sensor node that collects environmental energy and charges a battery has appeared. For example, it uses sunlight to increase its availability by charging the battery of the sensor node.

However, the energy-collecting sensor node has a disadvantage in that it is difficult to stably supply energy because it is highly affected by changes in the environment. In addition, since recent sensors have to transmit large amounts of data such as photos and images, the consumption of transmission energy increases rapidly, and it is often difficult to satisfy the energy requirements of the sensor node only with environmental energy.

Another way to solve this energy shortage problem is wireless power transmission that transmits energy over a long distance. In order to wirelessly supply energy to sensor nodes, a method of charging energy while moving by attaching a charger to a car or UAV (Unmanned Aerial Vehicle) is used.

If you use a car, you can install a high-end charger, but because you can only move where there is a road, there are many restrictions on the operating environment. So, in order to ensure availability, research on energy transmission methods using UAVs such as drones instead of cars are gradually increasing.

The advantage of using a drone is that it is highly available compared to a car because it moves in the air. However, due to the limitation of the transport weight, there is a disadvantage in that the weight of the transport equipment is limited, and the flight time is limited because the drone also uses a battery. So, in the case of using a drone, an efficient path setting and battery management technique are required.

In addition, in the wireless sensor network, there is a problem in that the energy consumption of the node is large in a hot spot where data is concentrated. To solve this problem, there is a method of using a mobile sink in which a sink node directly visits a sensor node and collects data. The energy consumed in data transmission is affected by the amount and distance of data to be transmitted. This is a method of reducing energy consumption by reducing the transmission distance.

However, since the sink node cannot visit all the sensor nodes individually, an aggregation node is selected from among several sensor nodes, and the data of the neighboring sensor nodes is collected from the merge node, and then the sink node visits only the merge node for data. You can use a method of collecting.

Nevertheless, a hotspot problem may occur in the vicinity of the merge node. If the operation is stopped because the battery of the merge node runs out, all data passing through the merge node is lost, so data loss may increase. In the absence of an alternate node, normal network operation may be difficult.

In order to solve this problem, there is a need for research on efficient movement path setting and battery management using a drone capable of wireless power transmission in an energy-collecting wireless sensor network. In addition, there is a need for research on how to efficiently select and manage merge nodes.

Korean Patent Publication No. 10-1825993 “Data transmission system and method of solar energy-based wireless sensor network” (2018.01.31)

In order to solve the above problem, in the present invention, when collecting mobile synchro data using a drone capable of wireless power transmission, in order to solve the hotspot problem and improve network connectivity, a merge node that temporarily collects data is selected and managed. Then, a method of transmitting energy to the merge node through wireless power transmission is proposed.

That is, in the present invention, a drone, which is a sink node, traverses a fixed path, selects a certain number of nodes as a merge node in this path, and the drone visits the merge node to collect data, and at the same time, the remaining energy of the drone is combined with the merge node. It is intended to alleviate the problem that the merge node goes into a power outage state due to lack of energy by supplying it.

A method for determining a merge node according to an embodiment of the present invention for achieving the above object is a sink node that collects data through a merge node of an energy-collecting wireless sensor network and a mobile sink, the sink Adaptively determining, by a node, the number of merge nodes in consideration of the number of sensor nodes belonging to the wireless sensor network and the amount of data sensed by the sensor node; And selecting, by the sink node, a merge node as many as the number of the merge nodes from among nodes on a movement path of the sink node for the mobile sink.

Preferably, the step of adaptively determining the number of merge nodes comprises: energy consumed by the sink node for moving the movement path from energy consumed for data collection in one round and the energy consumed by the merge node Calculating a first value obtained by subtracting the sum of the minimum amount of energy to be supplied by charging and the energy consumed in the idle state of the sink node; Calculating, by the sink node, a second value that is a sum of energy consumed by the merge node for take-off/landing, energy consumed to collect data from the merge node, and energy consumed to select a merge node for the next round ; And determining a largest natural number as the number of merge nodes among values smaller than a value obtained by dividing the first value by the second value.

Preferably, the step of calculating the first value comprises calculating a minimum amount of energy to be supplied by the wireless charging in a value proportional to a value obtained by multiplying the number of sensor nodes and the amount of data sensed by the sensor nodes. It may include steps.

Preferably, selecting the merge nodes as many as the number of merge nodes may include distributing the merge nodes to have a value obtained by dividing the movement path by the number of merge nodes at intervals.

Preferably, the sink node transmitting a first message notifying that a merge node has been selected as the selected merge node; Receiving, by the selected merging node, the first message and transmitting a second routing message including a node ID of the merging node; And setting, by the first sensor node, the second routing message, and setting the node ID included in the second routing message as a merge node to which the first sensor node should transmit data. have.

Preferably, the first sensor node includes the node ID as a merge node ID, the ID of the first sensor node is a source node ID, and a third routing including the number of hops to the merge node. Sending a message; When the second sensor node receives the third routing message and the number of hops included in the third routing message is smaller than the number of hops up to a previously set merge node, the second sensor node sets the merge node ID to the second sensor node. It may further include updating to a merge node to which data is to be transmitted.

A sink node, which is an apparatus for determining a merge node according to an embodiment of the present invention for achieving the above object, is a sink node that collects data through a merge node of an energy-collecting wireless sensor network and a mobile sink. , The sink node adaptively determines the number of the merge nodes in consideration of the number of sensor nodes belonging to the wireless sensor network and the amount of data sensed by the sensor node, and the sink node determines the mobile sink. A merge node is selected as many as the number of the merge nodes among nodes on the movement path of the sink node for, and the sink node collects data from the merge node while visiting the merge node. It is characterized in that it supplies energy.

Preferably, energy is wirelessly supplied to the merge node at a value proportional to a product of the number of sensor nodes and the amount of data sensed by the sensor node.

When the method of determining the merge node in the wireless sensor network according to the present invention is used, the connectivity of the wireless sensor network and the amount of data collection can be increased.

Specifically, by selecting the merge node at a predetermined interval, the number of data transmission hops is reduced to reduce the number of data transmission hops of the sensor nodes, and as a result, the availability of the sensor node can be secured by reducing energy consumption.

In addition, it is possible to prevent discharging of the merged node and improve network connectivity by selecting a node that has energy capable of transmitting data from among several nodes as the merge node, and the drone directly visits them to charge the energy.

1 is a diagram illustrating a wireless sensor network according to an embodiment of the present invention.
2 is a diagram illustrating a process of determining a moving path of a drone, which is a sink node, according to an embodiment of the present invention.
3 is a diagram illustrating an energy model of a sensor node and a merge node according to an embodiment of the present invention.
4 is a diagram illustrating an energy model of a sink node according to an embodiment of the present invention.
5 to 6 are diagrams for explaining a data collection process in a wireless sensor network according to an embodiment of the present invention.
7 is a pseudo code for explaining a process of selecting a merge node according to an embodiment of the present invention.
8 to 19 are diagrams for explaining the effect of a method for determining a merge node according to an embodiment of the present invention.
20 is a diagram illustrating an apparatus for determining a merge node according to an embodiment of the present invention.

In the present invention, various modifications may be made and various embodiments may be provided, and specific embodiments will be described in detail with reference to the drawings. However, this is not intended to limit the present invention to a specific embodiment, it should be understood to include all changes, equivalents, or substitutes included in the spirit and scope of the present invention. In describing each drawing, similar reference numerals have been used for similar elements.

Terms such as first, second, A, and B may be used to describe various elements, but the elements should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another component. For example, without departing from the scope of the present invention, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element. The term and/or includes a combination of a plurality of related items or any of a plurality of related items.

When a component is referred to as being "connected" or "connected" to another component, it should be understood that it is directly connected to or may be connected to the other component, but other components may exist in the middle. something to do. On the other hand, when a component is referred to as being "directly connected" or "directly connected" to another component, it should be understood that there is no other component in the middle.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present application, terms such as "comprise" or "have" are intended to designate the presence of features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, but one or more other features. It is to be understood that the presence or addition of elements or numbers, steps, actions, components, parts, or combinations thereof does not preclude in advance.

Unless otherwise defined, all terms used herein including technical or scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms as defined in a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related technology, and should not be interpreted as an ideal or excessively formal meaning unless explicitly defined in the present application. Does not.

Throughout the specification and claims, when a certain part includes a certain component, it means that other components may be further included rather than excluding other components unless otherwise stated.

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

1 is a diagram illustrating a wireless sensor network according to an embodiment of the present invention.

Referring to FIG. 1, it can be seen that a plurality of sensor nodes are distributed in a wireless sensor network. Sensor nodes are marked with white circles in FIG. 1. It is assumed that each sensor node can charge the battery through energy collection.

Referring to FIG. 1, since there are four merge nodes, it can be seen that the wireless sensor network is divided into four zones: a green zone, a yellow zone, an orange zone, and a blue zone. The wireless sensor network is divided into zones by the number of merge nodes. A method of determining the number of merge nodes will be described in more detail later.

Then, the drone 100 collects data as it moves through each area. In FIG. 1, a mobile sink travel area of the drone 100 is indicated as a gray area with a dotted line boundary. It is assumed that the drone 100 can transmit power wirelessly. That is, while collecting data, energy can be delivered to the aggregation node at the same time.

Since the drone 100 is also operated through a limited battery, instead of visiting all sensor nodes, the present invention selects a merge node from among sensor nodes on the movement path of the drone 100 in consideration of efficiency. That is, sensor nodes on the movement path of the drone 100 may be candidates for the merge node. The merge node is also referred to as an anchor node in other words. Hereinafter, the merge node and the anchor node have the same meaning.

In FIG. 1, anchor node candidates are marked with an X in a white circle. Among them, a total of four merge nodes, namely anchor nodes 110a, 110b, 110c, and 110d, are selected for each area, and the drone 100 visits each anchor node, and each anchor node collects from other sensor nodes in the area. Collect data.

At the same time, the drone 100 wirelessly supplies energy to each of the anchor nodes 110a, 110b, 110c, and 110d. In FIG. 1, data collection of the drone 100 and each of the anchor nodes 110a, 110b, 110c, and 110d is indicated by a red arrow, and energy supply is indicated by a green arrow.

Each sensor node in FIG. 1 periodically transmits sensing data to the merge node. The drone 100 travels a fixed path and visits the merge node to receive data collected during one round. At this time, the merge node is not fixed to a specific sensor node, but collects data by selecting the next merge node while one round is in progress and notifying the sensor node in the corresponding area.

Through this process, the merge node prevents a power outage and increases the availability of the wireless sensor network. In the present invention, since the drone 100 serves as a sink node and energy supply, it is possible to stably collect data even in an area that is difficult to access by automobiles or people.

2 is a diagram illustrating a process of determining a moving path of a drone, which is a sink node, according to an embodiment of the present invention.

Since the drone 100 used as a sink node in the present invention also flies with a limited battery, there is a limitation on a movement path. That is, a distance that is shorter than the distance that the drone 100 can fly with a single charge must be set as a moving path in the wireless sensor network. In this case, the travel path should be close to the central part of the wireless sensor network. This enables efficient data collection with fewer travel routes.

In addition, since the merge node is selected from among the sensor nodes in the moving path, the number of transmission hops in the process of transmitting data to the merge node in the sensor node distant from the moving path may increase. If the number of transmission hops is too large, it can cause performance degradation of the wireless sensor network. Therefore, if necessary, it is necessary to reduce the number of hops by using multiple drones 100 and dividing the wireless sensor network into small areas.

At this time, when selecting a merge node (or anchor node) among sensor nodes near the moving path, the shape of the network can be considered. For example, when the network field is a square, it is advantageous in terms of data collection that the positions of the anchor nodes are also the vertices of the square.

Referring to FIG. 2, a process of setting a path of a mobile sink to collect data while the drone 100 flies in a rectangular wireless sensor network can be seen. First, the distance between the sensor node that is far from the center of the wireless sensor network and the center of the wireless sensor network is calculated, the position corresponding to the midpoint of the distance calculated in the next step is calculated, and the total length of the moving path connecting the midpoints Is calculated to determine whether the distance that the drone 100 can fly. Where possible, the route is determined as the flight route.

3 is a diagram illustrating an energy model of a sensor node and a merge node according to an embodiment of the present invention.

은 현재 라운드에서의 남은 에너지

에서 소비 에너지

를 빼고, 수집 에너지

를 더한 값이다. 이를 수학식으로 표현하면 다음의 수학식 1과 같다.3, the remaining energy in the next round of the sensor node

Is the remaining energy in the current round

Energy consumption in

Minus, collect energy

Is the sum of This can be expressed as Equation 1 below.

[Equation 1]

는 기상 환경 등을 고려하면 정량적으로 예측이 가능하다. 그리고 소비 에너지

는 데이터를 전송하는데 소모되는 에너지

와 데이터를 수신하는데 소모되는 에너지

및 기타 아이들(Idle)상태에서 센서 노드의 작동에 소모되는 에너지

가 포함된다. 이를 수학식으로 표현하면 다음의 수학식 2와 같다.Energy collected here

Can be predicted quantitatively by taking into account the weather environment, etc. And energy consumption

Is the energy consumed to transmit data

And energy consumed to receive data

And other energy consumed in the operation of the sensor node in the idle state

Is included. This can be expressed as Equation 2 below.

[Equation 2]

와 센서 노드의 작동에 소모되는 에너지

는 센서 노드의 설정을 통해서 예상할 수 있다. 왜냐하면 해당 에너지들은 센서 노드의 트랜시버(Transceiver)가 켜진 시간 및 센서 노드의 작동 시간에 의존하기 때문이다. 그리고 데이터 송신에 소모되는 에너지

는 데이터의 양과 전송 거리에 따라서 다양한 값을 가진다. 이에 대한 에너지 소비 모델을 적용하면 다음의 수학식 3과 같이 표현할 수 있다.Energy consumed to receive data here

And energy consumed in the operation of the sensor node

Can be expected through the configuration of the sensor node. This is because the energies depend on the turn-on time of the sensor node's transceiver and the operating time of the sensor node. And the energy consumed in data transmission

Has various values depending on the amount of data and the transmission distance. When the energy consumption model is applied to this, it can be expressed as Equation 3 below.

[Equation 3]

는 전송해야 할 패킷의 길이(byte)이며,

는 에너지 소비 상수로 거리당 바이트당 소비되는 에너지로

단위를 가진다. 그리고

은 노드의 전송 거리이며,

는 경로 손실로 2부터 5사이의 값을 가진다(2 <=

<= 5). 수학식 2와 수학식 3을 수학식 1에 대입하면 다음의 수학식 4와 같이 표현할 수 있다.here

Is the length (byte) of the packet to be transmitted,

Is the energy consumption constant, which is the energy consumed per byte per distance.

Have a unit. And

Is the transmission distance of the node,

Is the path loss and has a value between 2 and 5 (2 <=

<= 5). Substituting Equation 2 and Equation 3 into Equation 1 can be expressed as Equation 4 below.

[Equation 4]

은 현재 라운드에서의 남은 에너지

에서 데이터 수신에 소비되는 에너지

와 센서 노드의 작동에 소모되는 에너지

를 빼고, 수집 에너지

를 더한 값이다.The energy model of the sensor node has been examined above, and next, the energy model of the merge node will be examined. 3, the remaining energy of the next round of the anchor node

Is the remaining energy in the current round

Energy consumed to receive data from

And energy consumed in the operation of the sensor node

Minus, collect energy

Is the sum of

는 생략하고 다음의 수학식 5와 같이 표현될 수 있다.Since the merge node also transmits data to the sink node, energy is consumed in the data transmission process as well. However, since the merge node transmits data only when the sink node visits and receives data until then, it consumes less energy than other nodes adjacent to the merge node until the sink node visits. Therefore, unlike Equation 4, which shows the energy model of the sensor node, the energy model of the merge node shows energy consumed for data transmission.

May be omitted and expressed as in Equation 5 below.

[Equation 5]

보다 커야 한다. 이를 수학식으로 표현하면 다음의 수학식 6과 같다.When a merge node (=anchor node) is blacked out, using that merge node stops data collection from all sensor nodes in the zone, so this value is the minimum energy value required to operate the anchor node.

Should be greater than This can be expressed as Equation 6 below.

[Equation 6]

The merge node consumes energy and also charges energy through energy collection and receives energy from the drone 100, which is a sink node. Therefore, it is preferable that the remaining energy amount of the anchor node is not larger than the energy storage capacity of the anchor node. This is because overcharging the battery wastes energy in the wireless sensor network, where the energy itself is limited. This can be expressed as Equation 7 below.

[Equation 7]

보다 크고 앵커 노드의 에너지 저장 용량

보다 작은 값을 가진 노드를 병합 노드 후보군 중에서 병합 노드로 선택한다. 도 3을 통해서 센서 노드와 병합 노드의 에너지 모델을 살펴보았으므로 다음에는 싱크 노드인 드론(100)의 에너지 모델을 살펴보기로 한다.In the present invention, in consideration of Equations 6 and 7, the minimum energy value required for the operation of the anchor node

Larger and the energy storage capacity of the anchor node

A node with a smaller value is selected as a merge node from among the merge node candidates. Since the energy model of the sensor node and the merge node has been examined through FIG. 3, the energy model of the drone 100, which is a sink node, will be described next.

4 is a diagram illustrating an energy model of a sink node according to an embodiment of the present invention.

, 병합 노드로부터 데이터를 수집하는데 소비되는 에너지, 병합 노드에 공급하는 에너지

, 다음 라운드의 병합 노드를 선정하는데 소모되는 에너지, 아이들(Idle) 상태에서 드론의 작동에 소모되는 에너지

를 고려해서 에너지 모델을 설계할 수 있다.The energy model of the drone 100 may consider the following items. Energy consumed by the drone's movement

, Energy consumed to collect data from the merge node, energy supplied to the merge node

, Energy consumed to select the merge node for the next round, and energy consumed to operate the drone in the idle state.

The energy model can be designed by taking into account.

In addition, the drone 100 must wirelessly transmit energy to the merge node while visiting the merge node selected in the previous round and receiving data of neighboring sensor nodes aggregated by each merge node. In this process, the drone 100 must stay at the location of the merge node for a certain period of time for data reception and energy transmission. Landing and take-off energy may be consumed during this process, and energy may also be consumed in data transmission/reception. This can be expressed as Equation 8 below.

[Equation 8]

는 병합 노드에 집계된 데이터의 패킷의 길이(byte)이며,

는 아까 수학식 3에서 살펴본 에너지 소비 상수이며,

는 드론(100)의 데이터 전송 범위이며,

는 데이터를 수신하는 동안 소모되는 에너지이다.In Equation 8

Is the length (byte) of the packet of data aggregated in the merge node,

Is the energy consumption constant examined in Equation 3,

Is the data transmission range of the drone 100,

Is the energy consumed while receiving data.

라고 하면 한 라운드 동안 병합 노드로부터 병합 노드의 데이터를 수집하는데 소비되는 에너지의 총량은 다음의 수식

와 같이 표현할 수 있다.The energy in Equation 8 is the energy consumed for data collection in one merge node, and the total energy consumed for data collection is as much as the number of merge nodes for which the drone 100 needs to collect data, so the number of merge nodes is reduced.

The total amount of energy consumed to collect data of the merge node from the merge node during one round is the following formula:

It can be expressed as

라고 하면 다음 라운드의 병합 노드를 선정하는데 소모되는 에너지는

와 같이 표현할 수 있다.In addition, as one round progresses, the drone 100 must select a merge node to collect data in the next round and guide it to the corresponding node. Energy consumption is also incurred in this process, and the number of merge nodes in the next round is determined.

If so, the energy consumed to select the merge node for the next round is

It can be expressed as

는 무선 센서 네트워크의 크기에 따라 고정된다. 드론의 이동에 소모되는 에너지

와 데이터의 송수신에 소모되는 에너지와 다음 라운드의 병합 노드를 선정하는데 소모되는 에너지와 병합 노드에 충전해주는 에너지 및 아이들(Idle) 상태에서 드론(100)의 운영에 소모되는 에너지를 고려하면 드론(100)의 에너지 모델은 다음의 수학식 9와 같이 표현할 수 있다.Finally, since the drone 100 moves a fixed path in a wireless sensor network, energy consumed for movement

Is fixed according to the size of the wireless sensor network. Energy consumed by the drone's movement

Considering the energy consumed to transmit and receive data and the energy consumed to select a merge node for the next round, the energy to charge the merge node, and the energy consumed to operate the drone 100 in an idle state, the drone 100 The energy model of) can be expressed as Equation 9 below.

[Equation 9]

와 드론의 이착륙에 소모되는 에너지

, 데이터의 송수신에 소모되는 에너지

는 거의 고정된 값이다.Energy consumed to move the drone in Equation 9

And the energy consumed for takeoff and landing of drones

, Energy consumed in sending and receiving data

Is almost a fixed value.

는 고정된 값이므로, 병합 노드의 수와 각 병합 노드에 공급되는 에너지는 트레이드 오프 관계이다. 즉 드론(100)이 공급할 수 있는 에너지의 총량은 제한적이므로, 병합 노드의 수가 많아지면 각 병합 노드에 공급할 수 있는 에너지의 양도 적어지게 된다.Energy that the drone 100 can supply to the merge node in Equation 9

Since is a fixed value, the number of merge nodes and the energy supplied to each merge node are in a trade-off relationship. That is, since the total amount of energy that the drone 100 can supply is limited, as the number of merge nodes increases, the amount of energy that can be supplied to each merge node decreases.

와 다음 라운드의 앵커의 수

에 따라 현재 라운드에서 드론이 소모하는 총 에너지양

가 결정된다. 특히 데이터를 수집하는 과정의 에너지(Data Communication Energy)는 현재 라운드의 앵커의 수

에 영향을 받고 다음 라운드의 병합 노드를 선정하는 과정의 에너지(Anchor Selection Energy)는 다음 라운드의 앵커의 수

에 영향을 받는다.Referring to FIG. 4 showing Equation 9 as a drawing, the number of anchors in the current round

And the number of anchors in the next round

Depending on the total amount of energy the drone consumes in the current round

Is determined. In particular, the energy of the process of collecting data (Data Communication Energy) is the number of anchors in the current round.

The energy of the process of selecting the merge node for the next round is affected by the number of anchors in the next round.

Is affected by

5 to 6 are diagrams for explaining a data collection process in a wireless sensor network according to an embodiment of the present invention.

3 to 4, the energy model of the drone 100, which is a sensor node, a merge node, and a sink node, was modeled together with an equation. In FIG. 5, energy models for each node will be compared in order to comprehensively examine this.

The drone 100, which is a sink node, performs two tasks during one round. One is to visit the merge node and collect data. The sink node periodically moves a fixed path and collects aggregated data in the merge node (Data Communication Energy). At this time, the sink node prevents the merge node from falling into a power outage by supplying the remaining energy to each merge node.

Another task is to select the next round of merge nodes (Anchor Selection Energy). In this process, state information of nodes corresponding to the merge node candidate group is collected, and a merge node of the next round is selected from among the state information. When setting the merge node for the next round, it is checked whether the merge node to be selected is a node capable of surviving until the next round in consideration of Equations 5 to 6.

A node that satisfies Equation 6 with respect to the state information request of the sink node transmits its next round expected residual energy to the sink node. In this case, the sink node selects a sensor node having the least estimated residual energy of the next round from among the merge node candidate groups in each region as the merge node.

은 다음의 수학식 10과 같이 표현할 수 있다.The reason why the node with the lowest residual energy expected in the next round is selected as the merge node is because the drone 100 supplies energy while visiting the node and collecting data, power failure of the merge node through energy supply. This is to prevent. The sink node receives status information of each node, selects a merge node from among them, and informs that it has been selected as a merge node. Energy consumed in this process

Can be expressed as in Equation 10 below.

[Equation 10]

와 각 노드로부터 상태 정보를 수신하는데 소모되는 에너지

와 병합 노드로 선정된 노드를 무선 센서 네트워크에 브로드 캐스트 하는데 소모되는 에너지

를 합한 값과 같다.In other words, the energy consumed to request state information of each node

And energy consumed to receive state information from each node

Energy consumed to broadcast the node selected as the merge node with the wireless sensor network

It is equal to the sum of

When all data is collected during one round, the drone 100 needs to be charged for the next round flight. However, since charging of the drone 100 may take a lot of time, 1) set the time between flight rounds of the drone 100 to be larger than the time required for charging, 2) use multiple drones, or 3) Consider using multiple batteries.

Referring to FIG. 5, neighboring nodes 120a, 120b, and 120c of one hop in the merge node 110a collect data from other sensor nodes around the merge node 110a and transmit the data back to the merge node 110a. Therefore, when a specific node is selected as the merge node, the nodes around it consume more energy due to hot spots.

Therefore, the node with the lowest estimated residual energy of the next round among the merge node candidate groups is selected as the merge node. Then, the node selected as the merge node can receive energy from the sink node, and the nodes with relatively high energy around it can serve as a hot spot for delivering messages to the merge node.

Referring to FIG. 5, among nodes (Outside Sensor Node) located farther than one hop from the merge node 110a, the first node 130a is a total of 3 cells for transmitting and receiving data from a total of 8 remaining batteries. You can see that is consumed.

In contrast, it can be seen that among the 1-hop neighbor nodes, the second node 120c consumes a total of 7 cells for transmitting and receiving data from a total of 8 remaining batteries. This is due to the hot spot phenomenon.

Lastly, it can be seen that the third node 110a among the merge nodes consumes three batteries for data transmission and reception in a total of eight remaining batteries. The reason that the energy consumption of the merge node is the lowest is that energy is wirelessly supplied from the drone 100, which is a sink node.

Referring to FIG. 6, a process of selecting a merge node for the next round can be seen. First, the area of the wireless sensor network is divided by the number of merge nodes selected as merge nodes in the current round. In FIG. 6, it can be seen that it is divided into a green area, a yellow area, an orange area, and a blue area. Next, the data collected by the sensor nodes in each area is transmitted to the merge node.

The drone 100 requests status information from a sensor node belonging to the merge node candidate group while moving along a predetermined movement path, receives the status information, and then has energy among sensor nodes satisfying Equations 5 to 6 among the merge node candidate group. The lowest node is selected as the merge node and a notification is broadcast.

Then, the sensor nodes around the merge node transmit data to the merge node, and the merge node transmits the data back to the drone 100 to collect data of the wireless sensor network.

At this time, the drone 100 may wirelessly provide energy to each merge node. Since the merge node consumes a lot of energy in transmitting and receiving data, it needs to supply energy. Since energy supply from the drone 100 is considered, a node having the lowest energy among sensor nodes satisfying Equations 5 to 6 is selected as the merge node in the preceding process.

In this case, the number of hops of the sensor node is determined according to the location of the merge node to which data is to be transmitted. As the number of hops increases, the transmission of data consumes a lot of energy. Therefore, efficient selection of the number and location of merge nodes is a way to increase the overall availability of the wireless sensor network.

In order to minimize the number of hops of sensor nodes, a merge node should be selected so that the number of merge nodes is as much as possible and the distribution is as uniform as possible during one round. At this time, since the drone 100, which is a sink node, moves along a predetermined path, if the number of merge nodes is fixed, the merge node is selected to have a value obtained by dividing the distance of the moving path of the drone 100 by the number of merge nodes. do. When selecting a merge node in this way, each sensor node can minimize the number of hops since it only needs to transmit data to the nearest merge node.

Since the merge node is charged with the energy provided by the sink node, it is very important to select an appropriate number of merge nodes that collect data from all sensor nodes and transmit it to the sink node to maximize the availability of the wireless sensor network. .

At this time, assuming that the total amount of data to be transmitted by one sensor node during one round is assumed to be s, and the number of sensor nodes is assumed to be n, the total amount of energy required for data transmission is from Equation 3 to Equation 11 below. Is derived as

[Equation 11]

Since the sink node must be able to supply at least this amount of energy to each merge node, the minimum amount of energy that the sink node must supply to all the merge nodes is derived as in Equation 12 below.

[Equation 12]

는 에너지 전송 효율이다. 본 발명에서는 무선 센서 네트워크의 크기가 고정되어 있고, 센서 노드는 주기적으로 동일한 양의 데이터를 수집하기 때문에 병합 노드의 수는 크게 변하지 않는다. 따라서 현재 라운드의 병합 노드의 수

와 다음 라운드의 병합 노드의 수

는 동일하다고 가정할 수 있으므로 수학식 9로부터 다음의 수학식 13을 유도할 수 있다.here

Is the energy transfer efficiency. In the present invention, the size of the wireless sensor network is fixed, and since the sensor nodes periodically collect the same amount of data, the number of merge nodes does not change significantly. So the number of merge nodes in the current round

And the number of merge nodes in the next round

Since can be assumed to be the same, the following Equation 13 can be derived from Equation 9.

[Equation 13]

에 관해서 정리하면 다음의 수학식 14를 얻을 수 있다.Equation 13

In summary, the following Equation 14 can be obtained.

[Equation 14]

In order to reduce the number of hops of sensor nodes, it is desirable to select as many merge nodes as possible, so from Equation 14 we can determine the number of merge nodes as follows.

[Equation 15]

이며, 만약 센서 노드의 배터리 에너지 저장 용량을 초과하는 경우에는 더 이상 충전할 필요는 없이 다음 병합 노드에 남은 에너지를 더 공급하면 된다.Therefore, the amount of energy the sink node must supply to each merge node is

If the battery energy storage capacity of the sensor node is exceeded, there is no need to charge any more, and the remaining energy can be supplied to the next merge node.

7 is a pseudo code for explaining a process of selecting a merge node according to an embodiment of the present invention.

Previously, a method of determining the number of merge nodes to be selected during one round was described through Equation 15. Next, a method of dividing a set of sensor nodes that transmits data through the corresponding merge node, that is, a zone will be described. Earlier, I briefly mentioned that the zone is divided by the number of merge nodes. Let's take a closer look at this.

When a specific node is selected as a merge node, the node broadcasts a routing message indicating that it has been selected as a merge node. The information included in the message may include the ID of the merge node and the number of hops to the merge node (a value of 0).

Then, each sensor node that has received the routing message sets the ID of the corresponding merge node as the ID of the merge node to which it needs to transmit data. At this time, after recording the ID of the merge node included in the routing message, the number of hops to the merge node, and the ID of the node that transmitted the message to itself, the routing message can be transmitted again by updating the information of this message.

When updating a routing message, the maximum number of hops of the message is subtracted, and the ID of the node that transmitted the routing message is changed to its own ID. This is written in pseudo code in lines 17 and 19 in FIG. 7. The reason for subtracting the maximum number of hops of a message is to prevent a message from being transmitted to too many nodes at this time. Therefore, routing messages are transmitted only when this value is greater than 0. This is written in pseudo code on line 18 in FIG. 7.

If the sensor node has already set the ID of the merge node to which it needs to transmit data through another routing message, the number of hops to the new merge node included in the newly delivered routing message and the hops to the existing merge node that have already been saved. By comparing the number, data can be transmitted to a merge node with a smaller number of hops. Even if a new merge node is set while data is already being transmitted, sensing data can be transmitted by changing the merge node. This is written in pseudo code in lines 14 to 16 in FIG. 7.

As described above, a method for determining a merge node proposed in the present invention has been described. Using the method proposed in the present invention, when collecting data through a mobile sink in a wireless sensor network, it is possible to optimize the number of merge nodes, and provide a criterion for selecting which node as a merge node. If selected, the area of the sensor node to transmit data to the corresponding merge node can be determined.

In addition, since the sink node supplies energy to the merge node during the data collection process, power failure of the merge node can be prevented and the availability of the wireless sensor network can be increased. This has the effect of increasing the efficiency of data collection. We will check this together with the specific experimental results.

8 to 19 are diagrams for explaining the effect of using the method of determining a merge node according to an embodiment of the present invention.

For the test, the following control will be used. 1) A wireless sensor network in which the location of the merge node is fixed while supplying energy through wireless charging (hereinafter, Fixed), 2) A wireless sensor network in which the location of the merge node is random while supplying energy through wireless charging (hereinafter, referred to as Random), 3) There is no energy supply due to wireless charging, and the simulation is conducted with a wireless sensor network (hereinafter, Random-No charge) in which the location of the merge node is random.

In this case, it is assumed that the number of merge nodes in all wireless sensor networks is fixed. Methods 1 and 2 with wireless charging assume that the drone will charge all of the batteries of the merge node when it arrives at the merge node. The characteristics of each control group are summarized as follows.

In the fixed method No. 1, a certain number of merge nodes is pre-selected. The drone visits a pre-selected merge node and collects data. The drone supplies the total energy to be charged wirelessly to each merge node divided by the number of merge nodes. If the energy supplied wirelessly exceeds the amount that the merge node can store, charging is no longer performed, and the remaining energy is supplied to other merge nodes that the drone has not yet visited.

In the second random method, the drone randomly selects a certain number of merge nodes for each round. The location of the merge node is randomly selected within the drone's movement path every round to alleviate the energy imbalance problem. Like the 1st fixed method, the drone supplies the total energy to be charged wirelessly by the number of merge nodes to each merge node. If the energy supplied wirelessly exceeds the amount that the merge node can store, charging is no longer performed, and the remaining energy is supplied to other merge nodes that the drone has not yet visited.

No. 3 Random-No Charge method is the same as No. 2 Random method except that the drone does not transmit energy.

For the simulation, the change in the number of black out nodes according to the change in the amount of data collected by the mobile sink, the amount of data detected by the sensor node, the number of sensor nodes and merge nodes, and density was measured. Each test was performed 30 times for 60 days to obtain an average value, and Table 1 shows the main parameters used in the simulation.

[Table 1]

8 to 10, the number of blackout nodes that occurred during about 1000 to 1200 rounds for 8 days in a wireless sensor network with a node density of 0.04, the amount of data sensed by the sensor node, and the drone collected. You can check the amount of data.

Since the sensor node recharges energy using solar energy, there are few blackout nodes during the day, but the energy is not recharged at night, so that a number of nodes become blackouts as shown in FIG. 8.

In particular, referring to FIG. 8, it can be seen that a larger number of nodes become blackout nodes than the No. 1 fixed method (green line) and the No. 2 random method (yellow line). This is because even if energy is supplied by wireless charging, fixed merge nodes consume a lot of energy for data transmission. Of course, in the case of the No. 3 Random-No Charge method (purple line) without energy supply, the number of blackout nodes is overwhelmingly larger than the No. 1 and No. 2 methods. On the other hand, if the scheme (red line) proposed in the present invention is used, the number of blackout nodes can be very reduced.

Referring to FIG. 9, it can be seen that the amount of data sensed by the sensor node decreases significantly at night. This is because a large number of sensor nodes become blackout nodes because energy supply through solar energy decreases at night, as described in FIG. 8. In FIG. 9, as in FIG. 8, method 3 has the worst availability, method 1 has the next poorest availability, method 2 has the next poorest availability, and the method proposed in the present invention provides the most stable data. You can check the sensing.

Referring to FIG. 10, it can be seen that the amount of data collected by the sink node decreases significantly at night. This is because a large number of sensor nodes become blackout nodes because energy supply through solar energy decreases at night, as described in FIG. 8. In FIG. 10, as in FIG. 8, method 3 has the worst availability, method 1 has the next poorest availability, method 2 has the next poor availability, and the method proposed in the present invention provides the most stable data. You can check what you collect.

Next, in FIGS. 11 to 13, simulation results for availability when the number of nodes increases can be confirmed. When the number of nodes is increased from 50 to 500 in increments of 50 while the node density is fixed at 0.04, it is possible to check how much blackout nodes occur.

Referring to FIG. 11, as the number of nodes increases, the merge node needs to collect more data, so it can be seen that the number of blackout nodes increases due to a hot spot problem. Nevertheless, it can be seen that the scheme proposed in the present invention has the smallest number of blackout nodes.

Referring to FIG. 11, in the case of method 3, since there is no energy supply due to wireless charging, if the merge node is down, all sensor nodes using the merge node are also blocked, so that the blackout node rapidly increases. In the case of method 1, since the merge node is fixed, there is no energy consumption in selecting a new merge node for the next round. Nevertheless, it can be seen that the number of blackout nodes is large even though energy is supplied by wireless charging because the energy consumption of the fixed merge node is large. On the other hand, it can be seen that using the scheme proposed in the present invention, even if the number of nodes increases, the number of blackout nodes does not increase rapidly.

Referring to FIG. 12, as the number of nodes increases, the amount of data sensed by the sensor node can be checked, and referring to FIG. 13, the amount of data collected by the sink node can be checked as the number of nodes increases. As can be seen in FIGS. 12 and 13, it can be seen that the scheme proposed in the present invention has the highest availability.

Next, in FIGS. 14 to 16, simulation results for availability when the density of nodes is changed can be confirmed. Referring to FIG. 14, when the number of nodes is fixed and the density of nodes is changed from 0.02 to 0.07, it can be seen how much blackout nodes occur.

If the node density is low, the number of hops between the sensor node and the merge node increases, so the relay node consumes more energy. So, as the density decreases, a greater number of blackout nodes occur. Conversely, if the density of nodes is high, since many sensor nodes are connected to one merge node, the hot spot problem is reduced and the number of occurrences of blackout nodes is reduced. Also, since the merge node transmits data only when the mobile sink arrives, the number of blackouts is reduced.

14 to 16, as previously described in other simulations, it can be seen that even though the density of nodes decreases, the scheme proposed in the present invention is the most highly available. Since the number of blackout nodes is small, it can be seen that the scheme proposed by the present invention senses more data and collects more data.

Next, in FIGS. 17 to 19, simulation results for availability when the number of merge nodes is changed can be confirmed. Referring to FIG. 17, when the number of anchor nodes is changed from 6 to 26, it is possible to check how much blackout nodes occur.

As the number of merge nodes increases, the number of blackout nodes decreases. This is because the range of choices that each sensor node can select as a merge node is widened, reducing the influence of hot spots. However, when the number of merge nodes starts to exceed 18, it can be seen that the number of blackout nodes increases.

This is because the energy that can be supplied by the sink node decreases due to frequent take-off and landing, and the energy must be shared with other merge nodes to be supplied. As a result, the efficiency of wireless charging of energy using drones decreases, and the number of blackout nodes of the first method is sharply increased rather than the third method without wireless charging.

On the other hand, since the method proposed by the present invention adaptively selects the number of merge nodes in consideration of the amount of energy of the drone, such a problem can be prevented in advance. From the simulation results, the present invention was operated by selecting the number of merge nodes as 18. So it can be seen that it has high availability compared to other methods.

As described above, through FIGS. 8 to 19, it was confirmed that the method proposed in the present invention can stably collect data despite a change in the number of merge nodes, a change in node density, and a change in the number of nodes. This is because in the present invention, the number of merge nodes is determined in consideration of the size of the network, the number of nodes, the amount of sensing data, and the amount of energy consumed, and the merge node is dynamically selected for each round.

20 is a diagram illustrating an apparatus for determining a merge node according to an embodiment of the present invention.

As described above, the apparatus 14000 for determining a merge node according to an embodiment of the present invention may be a drone 100 serving as a sink node in a wireless sensor network. However, in addition to that, a specific node of the wireless sensor network may perform the corresponding role. That is, it may correspond to any fixed/mobile electronic device including the configuration of FIG. 20.

Referring to FIG. 20, the apparatus 14000 for determining a merge node includes a communication unit 14010, a processor 14020, and a storage unit 14040.

The communication unit 14010 may be connected to the processor 14020 to transmit/receive wireless/wired signals. The communication unit 14010 may transmit data transmitted from the processor 14020 or may transmit received data to the communication unit.

In the present invention, the communication unit 14010 may receive state information from each sensor node, determine a merge node, and transmit data guiding it back to each node of the wireless sensor network. In addition, the communication unit 14010 may transmit data for executing the method of the present invention to each node. In addition, the communication unit 14010 may receive environmental data collected by the sensor node and transmit it to the processor 14020.

The storage unit 14030 is connected to the processor 14020 and stores various information for driving the processor 14020. The storage unit 1430 may store various data, information, instances, and commands such as location information of the merge node, energy state information, and sensed environmental data. The storage unit 1430 may be connected to an external database to the merge node determining apparatus 14000 to provide the collected data again.

The processor 14020 may be connected to the communication unit 14010 and the storage unit 14030 to perform operations according to various embodiments of the present disclosure according to the drawings and descriptions described above. At least one of a module, data, program, or software implementing the method for determining a merge node according to various embodiments of the present disclosure may be stored in the storage unit 1430 and executed by the processor 14020.

The above description is merely illustrative of the technical idea of the present invention, and those of ordinary skill in the art to which the present invention pertains will be able to make various modifications and variations without departing from the essential characteristics of the present invention. Accordingly, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention, but to explain the technical idea, and the scope of the technical idea of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

100: sink node (drone)
110a, 110b, 110c, 110d: merge node (= anchor node)
120a, 120b, 120c: 1-hop neighbor node of the merge node
130a: A node outside the merge node farther than 1 hop
14000: merge node determination device

Claims (8)

In the method of determining a merge node in a wireless sensor network of a merge node of an energy collecting wireless sensor network and a sink node that collects data as a mobile sink,
Adaptively determining, by the sink node, the number of merge nodes in consideration of the number of sensor nodes belonging to the wireless sensor network and the amount of data sensed by the sensor node; And
And selecting, by the sink node, a merge node as many as the number of merge nodes from among nodes on a moving path of the sink node,
The step of adaptively determining the number of merge nodes,
The sink node, from the energy consumed for data collection in one round, the energy consumed to move the movement path, the minimum amount of energy to be supplied to the merge node by wireless charging, and consumed in the standby state of the sink node. Calculating a first value obtained by subtracting the sum of the energy;
Calculating, by the sink node, a second value that is a sum of energy consumed by the merge node for take-off/landing, energy consumed to collect data from the merge node, and energy consumed to select a merge node for the next round ; And
Including the step of determining a largest natural number as the number of merge nodes among values smaller than a value obtained by dividing the first value by the second value,
How to determine the merge node in the wireless sensor network.
delete The method of claim 1,
The step of calculating the first value,
Comprising the step of calculating a minimum amount of energy to be supplied by the wireless charging in a value proportional to a value obtained by multiplying the number of sensor nodes and the amount of data sensed by the sensor nodes,
How to determine the merge node in the wireless sensor network.
The method of claim 1,
The step of selecting the merge nodes as many as the number of merge nodes,
Distributing the merge nodes to have a value obtained by dividing the movement path by the number of merge nodes at intervals,
How to determine the merge node in the wireless sensor network.
The method of claim 1,
Transmitting, by the sink node, a first message informing that the selected merge node has been selected as a merge node;
Receiving, by the selected merging node, the first message and transmitting a second routing message including a node ID of the merging node; And
The first sensor node, further comprising the step of receiving the second routing message, and setting the node ID included in the second routing message as a merge node to which the first sensor node should transmit data,
How to determine the merge node in the wireless sensor network.
The method of claim 5,
The first sensor node transmits a third routing message including the node ID as the merge node ID, the ID of the first sensor node as the originating node ID, and the number of hops to the merge node. step;
When the second sensor node receives the third routing message and the number of hops included in the third routing message is smaller than the number of hops up to a previously set merge node, the second sensor node sets the merge node ID to the second sensor node. Further comprising the step of updating to the merge node to which the data is to be transmitted,
How to determine the merge node in the wireless sensor network.
In the merge node of the energy-collecting wireless sensor network and a sink node that collects data as a mobile sink,
The sink node adaptively determines the number of the merge nodes in consideration of the number of sensor nodes belonging to the wireless sensor network and the amount of data sensed by the sensor node,
The sink node selects as many merge nodes as the number of merge nodes among nodes on a moving path of the sink node,
The sink node wirelessly supplies energy to the merge node while collecting data from the merge node when visiting the merge node,
In order to adaptively determine the number of the merge nodes, the sink node must supply energy consumed for moving the movement path from energy consumed for data collection in one round and the energy consumed to move the moving path through wireless charging. Calculate a first value obtained by subtracting the sum of the minimum amount of energy and the energy consumed in the standby state of the sink node, energy consumed for takeoff/landing at the merge node, energy consumed for collecting data from the merge node, and the following A second value, which is a sum of energy consumed to select a round merge node, is calculated, and a largest natural number among values smaller than a value obtained by dividing the first value by the second value is determined as the number of merge nodes. doing,
Sink node.
The method of claim 7,
In a value proportional to a product of the number of sensor nodes and the amount of data sensed by the sensor node, energy is wirelessly supplied to the merge node.
Sink node.

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