KR20190059021A - Method for generating of tree and scheduling - Google Patents

Abstract

Disclosed are a method for generating a tree and a scheduling method. The method for generating a tree comprises the steps of: obtaining at least one piece among information on the number of time slots within one operation period, information on a distance between nodes in a network, and information on the number of the nodes in the network; determining a maximum number of child nodes that each node can hold based on at least one piece among the information on the number of time slots within one operation period, the information on the distance between nodes, and the information on the number of the nodes; and generating a tree representing a data collection path of a node in the network such that nodes with the number of child nodes exceeding the maximum number is minimized.

Description

[0001] The present invention relates to a tree creation method and a scheduling method,

The present invention relates to a method of generating a tree and a scheduling method, and more particularly, to a method and a scheduling method for generating a tree which is a collection path of data in a duty-cycle network.

A wireless sensor network (WSN) consists of a number of sensors, each of which is powered by energy harvesting. WSNs are used in a variety of areas such as military surveillance, industrial monitoring, environmental monitoring, and healthcare to collect information and detect specific situations. In WSN, it is very important to collect data from all nodes in the network to sink nodes. In this case, it is very important to reduce the data transmission delay from the leaf node to the sink node since the node between the sink node and the leaf node must transmit the received data to the parent node.

In addition, it is important to reduce energy consumption because many sensors constituting a WSN are supplied with electric power through a battery or an energy harvesting which is generally impossible to charge. For this purpose, a duty-cycle network technology is attracting attention. In the duty-cycle scheme, a working period is divided into a plurality of time slots, and each node is activated only in some time slots and operates in a sleep state in the remaining time slots. This scheme minimizes node power consumption by reducing sensor node activity time. However, in the sleep state, transmission and reception of data can not be performed. Therefore, the transmission delay of data increases, and tree generation and scheduling are important issues to prevent collision between nodes.

To solve the above problem, the maximum number of children that one node can hold is determined based on the number of time slots, the distance between nodes, and the number of nodes. Thereby minimizing the data transmission delay.

The present invention also provides a scheduling method for minimizing a data transmission delay by scheduling a data transmission period of a node so that a collision does not occur considering a time slot of a child node and a time slot of a parent node.

The problems to be solved by the present invention are not limited to the above-mentioned problem (s), and another problem (s) not mentioned can be clearly understood by those skilled in the art from the following description.

According to an aspect of the present invention, there is provided a method for scheduling a data transfer period of a node activated in only some time slots of a plurality of time slots in an operation period, Acquiring first operation period information which is an operation period in which the first operation period information is ready for transmitting data; Obtaining information on a first time slot in which the target node is activated and information on a second time slot in which a parent node receiving data from the target node is activated; And a data transfer period that is an operation period in which the target node transmits data to the parent node based on the information about the first timeslot, the information about the second timeslot, and the first operation period information Step.

Wherein the determining of the data transfer period comprises determining the first operation period as the data transfer period when the second time slot is larger than the first time slot and determining that the second time slot is smaller than the first time slot The second operation period, which is an operation period after the first operation period, may be determined as the data transfer period.

The step of determining the data transfer period may include changing the data transfer period to a next operation period when the determined data transfer period corresponds to a data transfer period of a collision-capable node with respect to the target node .

Wherein the obtaining of the first operation period information includes determining that the first operation period is the fastest operation period when the child node of the target node does not exist and if the child node of the target node exists, The operation period may be determined as an operation period in which data is finally received from the child node.

The scheduling method may further include transmitting information on a data transfer period of the target node to a node within a critical distance from the target node when the data transfer period is determined.

The scheduling method includes: receiving information on a data transfer period of a collision-capable node with respect to the target node; And determining a data transfer period of the collision-capable node as a prohibit operation period during which the target node can not transmit data.

The scheduling method may further include updating information on a second operation period indicating an operation period in which the parent node is ready to transmit data, based on the determined data transfer period.

According to another aspect of the present invention, there is provided a method of generating a tree representing a data collection path of a node activated only in some time slots among a plurality of time slots in an operation period Obtaining at least one of information on the number of time slots in one operation period, information on a distance between nodes in the network, and information on the number of nodes in the network;

Determining a maximum number of child nodes that each node can hold based on at least one of information about the number of timeslots, the inter-node distance information, and the node number information; And generating a tree representing a data collection path of a node in the network such that a node exceeding the maximum number of child nodes is minimized.

Wherein the step of generating the tree comprises the steps of: searching for a singular node having a number of candidate parent nodes capable of transmitting data among a plurality of nodes in the network, And determining one of the candidate parent nodes for the singular node as a parent node for the singular node.

Wherein the step of generating the tree comprises the steps of: selecting a target node constituting the tree; And a transmission delay time which is a time required for transmitting data from a neighbor node to the target node to a sink node which is a final node through which the data is transmitted via the target node, And optionally registering with the node.

Wherein the step of selectively registering the child node with the child node comprises the steps of: if the neighboring node is a singular node whose number of candidate parent nodes to which data can be transmitted is a threshold value or less, Can be registered as a node.

The step of selectively registering with the child node may not register the neighbor node as a child node of the target node when the number of child nodes of the target node is equal to or greater than a limit number of children.

The step of generating the tree may further include a step of controlling a message to notify that the neighbor node is registered as a child node of the target node to a node within a critical distance from the target node.

The generating of the tree may further include controlling the neighboring node for the target node to exclude the target node from the candidate parent list if the number of child nodes of the target node is equal to or greater than the maximum number of child nodes can do.

A maximum number of children that a node can hold is determined based on the number of time slots, the distance between nodes, and the number of nodes, and a tree is generated such that a node exceeding the maximum number of children is minimized, The problem of data transmission delay as the number of exceeding nodes increases is solved.

In addition, when all the child nodes of the target node for searching and registering the child node complete the tree configuration, the search and registration of the child node is continued even if the target node exceeds the maximum number of children, So that the data transmission delay can be minimized.

In addition, scheduling is performed in consideration of the time slot in which the child node is activated, the time slot in which the parent node is activated, and the data transfer period of the collision-capable node, so that the child node and the parent node can transmit data in the same operation period Minimize data transmission delays.

In addition, data transmission delay is minimized by transmitting data in the fastest operation period while avoiding the data transfer period of the collision-capable node.

FIG. 1A is a diagram schematically illustrating a data reception (transmission) schedule of a sensor operating in a duty-cycle manner according to an embodiment of the present invention.
1B is a view for explaining a case where a collision occurs in a data transmission / reception process of a sensor operating in a duty-cycle manner according to an embodiment of the present invention.
FIG. 1C is a view for explaining another case where a collision occurs in a data transmission / reception process of a sensor operating in a duty-cycle manner according to an embodiment of the present invention.
2 shows a block diagram of a tree generating apparatus 200 according to an embodiment of the present invention.
FIG. 3 is a diagram illustrating an algorithm for generating a tree in the tree generating unit 230 according to an embodiment of the present invention. Referring to FIG.
4 is a diagram illustrating another example of an algorithm for explaining a process of generating a tree in the tree generating unit 230 according to an embodiment of the present invention.
FIG. 5 is an example of an algorithm for registering a node V from a node U to a child node according to the line 18 in FIG.
FIG. 6 is an example of an algorithm representing the tree join process of node V according to line 27 of FIG.
FIG. 7 is an example of an algorithm showing an activator search process according to the line 35 of FIG.
8 is a block diagram of a scheduling apparatus 800 according to an embodiment of the present invention.
9 is a diagram illustrating an algorithm for describing a process of scheduling a data transmission period in the scheduling apparatus 800 according to an embodiment of the present invention.
FIG. 10 is a diagram for explaining a process of scheduling a data transfer period of a node in the scheduling apparatus 800 according to an embodiment of the present invention.
11 is a flowchart illustrating a tree generation method according to an embodiment of the present invention.
12 is a flowchart illustrating a tree generation method according to another embodiment of the present invention.
13 is a flowchart illustrating a tree generation method according to an embodiment of the present invention.
FIG. 14 is a flowchart illustrating a scheduling method according to an embodiment of the present invention.
15 is a diagram illustrating the relationship between the number of nodes and the maximum number of child nodes and network performance in a duty-cycle network according to an embodiment of the present invention.
16 is a diagram showing a relationship between a node-to-node distance (network side length, L) and network performance in a duty-cycle network according to an embodiment of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. Like reference numerals are used for like elements in describing each drawing.

The terms first, second, A, B, etc. may be used to describe various elements, but the elements should not be limited by the terms. For example, without departing from the scope of the present invention, a first component may be termed a second component, and similarly, the term " second component " The second component may also be referred to as the first component. The term < RTI ID = 0.0 > and / or < / RTI > includes any combination of a plurality of related listed items or any of the plurality of related listed items.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, . On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

Unless defined otherwise, 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 this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

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

FIG. 1A is a diagram schematically illustrating a data reception (transmission) schedule of a sensor operating in a duty-cycle manner according to an embodiment of the present invention.

In a duty-cycle network, the total activation time of each node is divided into a plurality of working periods having the same length of time. At this time, the time slot constituting the operation period is divided into a length of time sufficient for one node to receive data. Each node is assigned one of T time slots according to a specific rule (or randomly), and does not operate during the remaining T-1 time slots in each operation period. In this case, the duty-cycle of the network is determined as 1 / T%. In the case of FIG. 1A, since there are five time slots in one operation period, the duty-cycle of the corresponding network is 20%. For convenience of description, it is assumed herein that each node can receive data during an activated time-slot, and transmission of data is possible at any time. However, it is assumed that transmission and reception of data at the same node can not be performed simultaneously during one time-slot.

In this specification, a child node is a node for transmitting data, and a parent node is a node for receiving data. One node in the network may be a child node for node A and a parent node for node B, A parent node can contain multiple child nodes, receives data from all child nodes, combines them, and delivers the data to its parent node. If one packet is transmitted through one time slot and the corresponding node has two child nodes A and B, the node receives packets from A and B, processes them into one packet, And transmits the packet to the parent node C. The type and number of packets to be transmitted / received / processed may vary according to the embodiment, and the present invention is not limited thereto.

The sink node is the node corresponding to the final destination to which the data is transferred. The sink node is the parent node for another node, and can not be a child node. That is, the data collection process is terminated at the sink node, and the sink node no longer transmits data to the other node.

In FIG. 1A, a square box represents a time slot, and a number in a box represents a number of the time slot. Referring to FIG. 1A, each time slot is repeated every predetermined period. In the present specification, a time length corresponding to the period is referred to as an operation period.

In one example, the first operating period 110 is comprised of '5' timeslots 111, 122, 123, 124 and 125. In the first time slot 111, the node corresponding to '0' is activated and receives data, and the remaining nodes are not activated. Similarly, in the second time slot 112, the node corresponding to '1' is activated and receives data, and the remaining nodes are not activated.

For convenience of explanation, it is assumed that a node having a node ID of '2' is activated only in a time slot '2'. A node with a node ID of '2' is active in the third slot in each operation period and inactive in the remaining time slots. Therefore, in order to transmit data to a node having a node ID '2', data must be transmitted at a time corresponding to the third slot.

1B is a view for explaining a case where a collision occurs in a data transmission / reception process of a sensor operating in a duty-cycle manner according to an embodiment of the present invention.

1B, a first node 141, a second node 142 and a third node 143 are present in the network, and the first node 141 and the second node 142 are connected to a third node 143 ). ≪ / RTI > In addition, a circle having a radius of 'R' represents a data transmission range of the node, and it is assumed that the first node 141, the second node 142, and the third node 143 all have a transmission range of 'R' do.

Referring to FIG. 1B, if the first node 141 and the second node 142 simultaneously transmit data to the third node 143 in the same operation period, the third node 143 transmits complete data Can not be received. In this specification, a case where data is not successfully received from a node due to interference or collision is referred to as a data collision. In particular, the case where interference occurs due to data transmission from nodes in the data collection path is referred to as direct collision.

FIG. 1C is a view for explaining another case where a collision occurs in a data transmission / reception process of a sensor operating in a duty-cycle manner according to an embodiment of the present invention.

1C, a path for data collection is set between the first node 141 and the third node 143, and a path for data collection is set between the second node 142 and the fourth node 144. In FIG. Since the data transmission range is overlapped, the data transmitted from the second node 142 is not transmitted to the fourth node 144, because the data transmission range is not set between the second node 142 and the third node 143. However, As well as the third node 143. [

Accordingly, when the first node 141 and the second node 142 transmit data to the third node 143 and the fourth node 144, respectively, at the same time, the third node 143 can not successfully As shown in FIG. In this way, the interference caused by the data transmission at the node where the path for data collection is not set is named indirect collision, and in this specification, both direct collision and indirect collision are considered as collision.

In this specification, a set of nodes that are likely to collide during transmission of data is referred to as a collision candidate node. 1B and 1C, the second node 142 is a collision candidate node CS (u) for the first node 141. When data tree and scheduling are performed in the duty-cycle type network quirk, it is important to prevent data collision. Therefore, when data is transmitted from the first node 141, the second node 142 does not transmit data It is important to schedule so that

2 shows a block diagram of a tree generating apparatus 200 according to an embodiment of the present invention. The tree generating apparatus 200 according to an embodiment of the present invention includes a parameter obtaining unit 210, a determining unit 220, and a tree generating unit 230.

The parameter obtaining unit 210 obtains parameters necessary for generating a tree. The parameter acquisition unit 210 acquires time slot number information, inter-node distance information, and node number information.

The number of time slots means the number of time slots constituting the operation period.

The distance between nodes indicates the distance between the nodes in the network. When the space in which the nodes are arranged in the network is defined as one plane, the distance between the nodes is a distance corresponding to one side of the plane Maximum distance between nodes).

In a duty-cycle network, the network latency will be proportional to the time until all data is collected at the sink node, and will depend on how many operating periods are required until the sink node collects all the data. Such network performance can be determined according to the maximum number of child nodes. Hereinafter, with reference to FIG. 15 to FIG. 17, the effect of each parameter acquired by the parameter acquisition unit 210 and the maximum number of child nodes on network performance will be examined.

15 is a diagram illustrating the relationship between the number of nodes and the maximum number of child nodes and network performance in a duty-cycle network according to an embodiment of the present invention.

15, the horizontal axis represents the number of nodes, and the vertical axis represents the number of operation periods required for the sink node to collect all the data. The smaller the number of operation periods required for the sink node to collect all the data, the better the performance of the network. Therefore, under the same conditions, the smaller the value of the y-axis, the better the performance of the network.

15A shows the relationship between the number of nodes and the number of operation periods when the inter-node distance (network side length L in Fig. 13) = 200 m and the number of timeslots T = 10.

Fig. 15B shows the relationship between the number of nodes and the number of operation periods when the inter-node distance (network side length L in Fig. 13) = 200 m and the number of timeslots T = 100.

Fig. 15C shows the relationship between the number of nodes and the number of operation periods when the inter-node distance (network side length L in Fig. 13) = 50 m and the number of timeslots T = 100.

16 is a diagram showing a relationship between a node-to-node distance (network side length, L) and network performance in a duty-cycle network according to an embodiment of the present invention.

In FIG. 16, the horizontal axis represents the distance between nodes, and the vertical axis represents the number of operation periods required for the sink node to collect all the data.

16A shows the relationship between the inter-node distance and the number of operation periods when the number of nodes N = 400 and the number of timeslots T = 2.

16B shows the relationship between the inter-node distance and the number of operation periods when the number of nodes N = 400 and the number of timeslots T = 10.

16C shows the relationship between the distance between nodes and the number of operation periods when the number of nodes N = 400 and the number of timeslots T = 100.

17 is a diagram illustrating a relationship between the number of timeslots and network performance in a duty-cycle network according to an embodiment of the present invention.

17, the horizontal axis represents the number of time slots, and the vertical axis represents the number of operation periods required for the sink node to collect all the data.

Fig. 17A shows the relationship between the number of timeslots and the number of actuators in the operation period when the number of nodes N = 400 and the inter-node distance L = 50m.

17B shows the relationship between the number of timeslots and the number of operation periods when the number of nodes N = 400 and the inter-node distance L = 100 m.

17C shows the relationship between the number of timeslots and the number of operation periods when the number of nodes N = 400 and the inter-node distance L = 200 m.

Referring again to FIG. 2, the determination unit 220 determines the maximum number of child nodes that one node can have, based on at least one of the time slot number information, the inter-node distance information, and the node number information. As described above, since the optimal maximum number of children depends on the number of timeslots, the distance between nodes, and the number of nodes, the determining unit 220 determines the maximum number of child nodes suitable for the network according to the number of timeslots, the distance between nodes, . The maximum number of children may be determined so that each node has a different value, and all nodes may be determined to have the same value.

The tree generating unit 230 generates a tree representing a data transmission flow between the nodes in the network such that the number of nodes exceeding the maximum number of child nodes is minimized. The tree generating unit 230 generates a tree so that there is no node exceeding the maximum number of child nodes if possible, but exceptionally, the node exceeds the maximum number of child nodes only when a specific condition is satisfied. For example, if there is no more candidate parent node for a child node that has not yet determined the parent node, the node exceeding the maximum number of child nodes may exceptionally become the parent node.

First, the tree generating unit 230 searches for a node whose number of candidate parent nodes is less than a threshold value among nodes whose parent nodes have not been determined. In this specification, a node whose number of candidate parent nodes is less than or equal to a threshold value (for example, one node) is designated as an anomaly node, and a node whose candidate parent node exceeds a threshold value is referred to as a general node.

For convenience of explanation, suppose that the singular node is node A, the candidate parent node to node A is node B, and the neighbor node to node B is node C.

First, the tree generating unit 230 searches for a node A, which is a singular node, and registers the node B, which is the only candidate parent node for the node A, as a parent node for the node A. Thereafter, when the number of child nodes of the node B is equal to or greater than the maximum number of nodes, the node B is set so that it is no longer the parent node of another node (for example, the node C). As an example, node B is removed from the candidate parent node of node C.

If a parent node is determined for all the singular nodes, the tree generating unit 230 determines a child node from the sink node.

A target node to which a child node is to be determined transmits a search message requesting participation to a child node to neighboring nodes.

Among neighbor nodes, nodes whose parent nodes are not specified, that is, nodes whose target nodes are included in the candidate parent node list, transmit a response message corresponding to the search message to the target node.

The tree generating unit 230 generates a tree based on the transmission delay time, which is a time required for the node that transmitted the response message to transmit data to the sink node via the target node, as a child node of the destination node And decides whether to register. The transmission delay time can be determined by the following equation (1).

[Equation 1]

t (u, v) = d (u) + sl (u, v) + r and (0,1) + n ch (v) * T

d (u): time from data collection from end node to u

sl (u, v): the time taken to transfer data from node u to node v

r _and (0,1): a random number between 0 and 1

n _ch (v): the number of children of node V

The tree generating unit 230 forms a tree with a more advantageous path when the node that transmitted the response message is requested to join from the plurality of nodes to the child node. However, if the target node is the only node that transmitted the search message, the target node is determined as the parent node.

When the tree generating unit 230 determines that the node that transmitted the response message is a child node for the target node, the tree generating unit 230 notifies the other nodes in the distance within the threshold. In this case, if the number of children of the target node is equal to or greater than the number of children of the target node, the neighboring nodes transmit the facts together so that the target node can not be selected as the parent node.

FIG. 3 is a diagram illustrating an algorithm for generating a tree in the tree generating unit 230 according to an embodiment of the present invention. Referring to FIG.

The algorithm shown in FIG. 3 is the first step performed to construct a tree, which is referred to as a [start-up] process in this specification.

First, for convenience of description, variables used in the start-up algorithm 300 are defined.

n _n (u): the number of neighbor nodes for node u

ChS (u): List of child nodes of node u

n _ch (u): the number of child nodes of node u

n _apc (u): the number of candidate parent nodes of node u

NAS (u): a list of selected activators of u (that is, nodes of u whose nodes have not been created)

state (u): Indicates the state of node u, separated by WAIT, ACTIVATED, LISTEN, COMPLETE.

Singular node: n _apc (u) = 1

General node: n _apc (u)> 1

P (u): parent node of u

The initialization line indicates the initialization process of the variables.

Line 1 indicates that the starter-up process is performed while there is a singular node for which the parent node is not determined.

Line 2 shows a process in which a singular node V transmits a message (JOIN_REQ) requesting registration to a child node to a neighboring node.

In line 3, when the node U receives the request message from the singular node V,

In line 4, n _ch (u) and n _apc (u) are updated. That is, after registering the node V as a child node of the node U, the number of child nodes of the node U is increased by one. Also, since node V can no longer be the parent node of node U, it reduces the number of candidate parent of node U by one.

At line 7, when node V receives an accept message (JOIN_ACCEPT)

On line 8, register node U as the parent node of node V and change the state of node U to " COMPLETE ".

In line 10, if the number of child nodes of node U is equal to or greater than the threshold child number, node U can no longer be the parent node of neighboring nodes (e.g., node X). Thus, the number of candidate parent nodes of neighboring nodes, i.e., n _apc (x), is reduced by one.

4 is a diagram illustrating another example of an algorithm for explaining a process of generating a tree in the tree generating unit 230 according to an embodiment of the present invention.

The algorithm shown in FIG. 4 is performed after the [start-up] process to construct a tree, and is called a [regular] process.

In line 1, it is confirmed whether all neighbor nodes of the sink node S are set as child nodes. If all the neighbor nodes of the sink node S are set as child nodes, the [normal process] is terminated because the tree creation operation is completed.

In lines 4 to 5, the sink node S is selected as the first activator and the state of the sink node S is changed to " ACTIVATED " until the normal process is completed.

In line 6, the state of the activator node (U) is changed to " ACTIVATED ". The activator node (U) is a child node whose tree generation process has not been completed, and becomes a target node for searching for child nodes. For example, when the sink node S is selected as the first activator node, and the child node of the sink node S is found, the child nodes of the searched child nodes that have not completed the tree creation process are added as new activator nodes do.

At line 7, the enabler node U sends a search message FIND_CHILD to the neighboring nodes to retrieve the child node.

In line 8, the neighboring node V for the activator node U in the WATI state transmits a request message JOIN_REQ in response to the search message.

In lines 12-13, if the node (V) that transmitted the request message is a singular node, set the back-off time (t (u, v)) to zero. The singular node is to register as a child node for the activator node U regardless of the transmission delay.

At line 15, if the node V that sent the request message is a generic node, update the back-off time t (u, v) and register the neighbor node V as a child node during the back- .

On line 17, if the node V that transmitted the request message is a generic node and has already received a commit message (JOIN_CONFIRM) from another enabler node Z, the node V may be a child node of the enabler node U, . This is because data transmission to node V ==> node Z ==> node S is more suitable than data transmission to node V ==> node U ==> node S (ie, transmission delay is shorter).

If the node V that transmitted the response message is a general node and does not receive a confirmation message (JOIN_CONFIRM) from another enabler node Z before the back-off time on line 18, the acceptance process according to FIG. 5 is performed do.

FIG. 5 is an example of an algorithm for registering a node V from a node U to a child node according to the line 18 in FIG.

In line 1, the node V is added as a child node of the activator node U, and the number of child nodes of the activator node U is increased by one.

In line 2, the enabler node U sends a message (JOIN_ACCETP) to the neighboring node indicating that node V is accepted as a child node.

In lines 3 to 4, it is determined whether the node V is a singular node. If the node V is an arbitrary node, the node V is added as an activator node to retrieve a child node for the node V. [

On line 5, it is determined whether the number of children of the activator node U is equal to or greater than the threshold number of children. This is to restrict the enabler node (U) from setting another neighbor node as a parent when the number of children of the enabler node (U) is more than the number of children of the enabler node (U).

On line 6, if the number of children of the enabler node U is less than the number of children, the back-off time for another neighbor node is maintained to decide whether to register another neighbor node as a child node.

On line 8), if the number of children of the enabler node U is greater than the number of children, the back-off time for the other neighbor node is canceled.

In line 11, if the enabler node U does not select another enabler node (for example, if all the child nodes of the enabler node U are singular nodes, or if all child nodes have completed the search of the child nodes If the number of children of the enabler node (U) is more than the number of children, it maintains the back-off time for other neighbor nodes. This is to allow the neighbor node to be registered as a child node exceptionally, even if the number of children of the activator node U is equal to or greater than the number of children, because the tree can not be completed unless a new activator node is present.

Returning again to FIG. 4, in lines 23-24, if a new enabler node for the enabler node U is no longer found, a complete message STUCK is sent to the parent node P (U) of the enabler node U, And changes the state of the activator node U to " COMPLETE ".

On the other hand, in the line 27, the node V that has received the accept message JOIN_ACCEPT from the activator node U performs the tree join process according to FIG.

FIG. 6 is an example of an algorithm representing the tree join process of node V according to line 27 of FIG.

In line 1, the node V registers the node U as the parent node P (V) and updates the delay time d (v).

In line 2, the node V sends a message (JOIN_CONFIRM) to the neighbor node confirming that the node V is registered as a child node of the node U.

In lines 3 to 4, if the node V is a singular node, the state of the node V is changed to " COMPLETE ". This is because all the neighbor nodes of the node V participate in the tree when the node V is a singular node.

On line 6, if node V is a generic node, modify the state of node V to " ACTIVATE " and retrieve the child node for node V. [

Referring back to FIG. 4, lines 30-33 are descriptions of the operation of the neighboring node (Y) with respect to the activator node (U).

In line 30, the neighboring node Y in the "WAIT" state receives a message (JOIN_ACCEPT) indicating that the enabler node U has accepted the node V as a child node.

Since in the line 31, it should be, except when less than number of child nodes can limit a child of the activator node (U), is active in the candidate parent node of the neighbor node (Y) the own node (U), candidate can parent node (n _apc (y )).

Line 35 performs an activator search process according to FIG. 7 when a " STUCK " message is received from all the enabler nodes.

FIG. 7 is an example of an algorithm showing an activator search process according to the line 35 of FIG. 4 in the process of generating a tree in the tree generating apparatus 200 according to an embodiment of the present invention.

At line 1, the enabler node U retransmits the search message (FIND_CHILD) to the neighboring node.

In line 2, if the enabler node U does not receive a request message (JOIN_REQ) from the general node, the enabler node U on line 3 sends a "STUCK" message to the parent node P (U) Change the status to "COMPLETE".

On line 5, if the sink node S does not receive a response message (JOIN_REQ) from the general node, it changes the state of the sink node S to " COMPLETE " on line 6 and ends the tree creation process.

8 is a block diagram of a scheduling apparatus 800 according to an embodiment of the present invention.

The scheduling apparatus 800 may include a first information obtaining unit 810, a second information obtaining unit 820, and an operation duration determining unit 830. [

The first information obtaining unit 810 obtains information on a child node to which data is to be transmitted and a type slot on which a parent node to receive data from the child node is activated. For convenience of explanation, FIG. 8 shows a case where a child node to determine a data transmission time is designated as a target node, a time slot in which a target node is activated is referred to as a first time slot, a time slot in which a parent node is activated is referred to as a second time slot do.

The second information obtaining unit 820 obtains information on the first operation period, which is an operation period in which the target node can transmit data.

In the WSN, in order for the target node to transmit data to the parent node, data must be received from all the child nodes of the target node. Therefore, if the target node does not have a child node, the first operation period in which data transmission is started in the network is the first operation period. However, if the target node has more than one child node, Is the first operation period.

The operation period determination unit 830 compares the first time slot with the second time slot and determines a period during which the target node transmits data.

If the first time slot is faster than the second time slot (i.e., the number of the second time slot is larger than the number of the first time slot), the operation period determination unit 830 determines the first operation period As shown in FIG. That is, data is transmitted in the second time slot, which is the time point at which the parent node is activated in the first operation period.

However, if the first time slot is slower than or equal to the second time slot, the operation period determination unit 830 determines the second operation period, which is the earliest operation period after the first operation period, as a period during which the target node transmits data .

However, when the data transmission period determined by comparing the first time slot and the second time slot is included in the forbidden operation period set, the operation period determination unit 830 determines that the target node transmits data in the next operation period do. The prohibited operation period set is an operation period in which a node that is likely to collide with a target node transmits data.

9 is a diagram illustrating an algorithm for describing a process of scheduling a data transmission period in the scheduling apparatus 800 according to an embodiment of the present invention.

First, for convenience of description, terms used in FIG. 9 are defined.

rank (u): Represents the rank of node u. The rank of a node can be determined based on the level at which the node is located on the tree and the identification information of the node. For example, the node with the longest distance from the sink node (i.e., the node with the largest number of hops) has the highest level. The manner of determining the ranking of the nodes may vary according to the embodiment, for example, assigning a high ranking to a node with a high level, and assigning a high ranking to a node preceding the node in the case of the same level .

tsch (u): Indicates the period of operation in which node u transmits data to its parent node. That is, it means the data transfer period of the node u.

tmin (u): represents the minimum operation period in which node u can transmit data to the parent node. That is, the first operation period is an operation period in which the node u is ready to transmit data to the parent node. The node u can transmit data to the parent node after data collection from the child node is completed.

nuch (u): Indicates the number of child nodes of u whose scheduling is not completed.

CS (u) is a node that may collide when transmitting node u.

FS (u) represents an operation period in which node u can not transmit data, and is a prohibited operation period. During the prohibited operation period, the data transmission period of the node belonging to CS (u), that is, the first scheduled node among the possible collision nodes, is included.

Hereinafter, a process of scheduling a data transfer period in the scheduling apparatus 800 will be described with reference to FIG.

Line 0 initializes all variables.

In lines 1 to 4, a target node to be scheduled is determined based on the rank. For example, if there is no child node of the node U and the ranking is the highest among the competing nodes (for example, possible collision nodes), the data transfer period of the target node U is set to " operating node 1 " .

In lines 6 to 9, the time slot in which the node U and the parent node P (U) of the node U are activated is identified. If the time slot of the node U is smaller than the time slot of the parent node P (U), the data transfer period is determined as the first operation period. The fact that the time slot of node U is smaller than the time slot of parent node P (U) means that node U is first activated and ready to transmit data before parent node P (U) is activated within the same operating period it means. On the other hand, if the time slot of the node U is larger than the time slot of the parent node P (U), the data transfer period is determined as the first operation period + 1 (i.e., the second operation period).

In lines 12 to 13, it is determined whether or not the data transfer period of the node U corresponds to the prohibited operation period. If the data transfer period of the node U corresponds to the prohibited operation period, the data transfer period is increased by one.

In line 15, the scheduling information of the node U (that is, the information about the data transfer period of the node U) is transmitted to a neighboring node (for example, a node within two hops).

Lines 16-19 refer to the operation at the neighboring node that received the scheduling information for node U. The node V which has received the scheduling information for the node U adds the data transfer period of the node U to the prohibited operation period FS (V). In addition, since the node U has already completed the scheduling, node U is removed from the collision node set CS (V).

Lines 20-24 relate to operations in the parent node P (U) that received the scheduling information for node U). The parent node P (U) receiving the scheduling information for the child node U) reduces one from the number of unscheduled child nodes (n _uch (v)). Also, when the data transfer period of the node U is after the first operation period of the parent node P (U)), the first operation period of the parent node P (U) is changed to the data transfer period of the node U.

FIG. 10 is a diagram for explaining a process of scheduling a data transfer period of a node in the scheduling apparatus 800 according to an embodiment of the present invention.

10A is a diagram showing time slots in which each node is activated.

Referring to FIG. 10A, there are three time slots in one operation period.

Referring to FIG. 10A, the sink node is activated in time slot '2'.

Further, the node V1 is activated in the time slot '1'

Node V2 is activated in time slot '1'

Node V3 is activated in time slot '0'

Node V4 is activated in time slot '1'

Node V5 is activated in time slot '0'

Node V6 is activated in time slot '0'.

FIG. 10B illustrates a scheduling apparatus 800 according to an embodiment of the present invention in which scheduling for a data transmission period of a node is completed.

For convenience of explanation, it is assumed that nodes V3, V4, V5, and V6 have received all the data in the operation period '0', or that the leaf node having no child node has already prepared to transmit data.

First, the scheduling apparatus 800 selects a node having the highest rank and determines a data transfer period. In Fig. 10, it is assumed that the node V3 has the highest rank.

i) The scheduling apparatus 800 determines the data transfer period of the node V3 as the operation period '1' which is the fastest operation period.

ii) Next, the scheduling apparatus 800 determines a data transfer period of the node V4. Since node V4 is a node that may collide with node V3, data must be transmitted in a different operation period than the data transmission period of node V3. Therefore, the data transfer period of the node V4 is determined to be the operation period '2'.

iii) Next, the scheduling apparatus 800 determines a data transfer period of the node V5. Since the node V5 is a node that may collide with the node V4, the node V5 must transmit data in the fastest operation period, which is different from the data transfer period of the node V5. Since the node V4 transmits data in the operation period '2', the data transfer period of the node V5 is determined as the operation period '1'.

iv) Next, the scheduling apparatus 800 determines the data transfer period of the node V6. Since the node V6 is a node that may collide with the node V4 and the node V5, data can not be transmitted in the operation period '1' and the operation period '2'. Therefore, the data transfer period of the node V6 is determined to be the operation period '3'.

v) Next, the scheduling apparatus 800 determines a data transfer period of the node V1. Since the node V1 is activated in the time slot '1', the time when the node V1 receives all the data from the child node will be in the time slot '1' of the operation period '2'. As a result, the node V1 can transmit data to the sink node S in the operation period '2'. At this time, since the time slot in which the parent node S is activated is the time slot '2', the node V 1 can transmit data to the time slot '2' in the operation period '2'. Therefore, the data transfer period of the node V1 is determined to be '2'.

vi) Finally, the scheduling device 800 determines the data transfer period of the node V3. Since the node V3 is activated in the time slot '0', the time point at which the node V3 receives all the data from the child node will be in the time slot '0' of the operation period '3'. As a result, the node V3 can transmit data to the sink node S in the time slot '2' of the operation period '3'. At this time, although the node V1 is a node in which a collision may occur with the node V3, since the data transfer period of the node V3 is the operation period '2', the node V3 can transmit data to the sink node S in the operation period '3'.

In the past, when there is a collision-capable node, data must be transmitted after a data transfer period of a collision-capable node. Therefore, when there are many collision-capable nodes, the data transfer period becomes long. (For example, The data transfer period of the node V5 = the data transfer period of the node V4 + 1). However, in the scheduling apparatus 800 according to an embodiment of the present invention, Since data is transmitted in the fastest operating period within the range, it is possible to reduce the time for data to reach the sink node.

Also, conventionally, the parent node transmits data after the data transfer period of the child node. (For example, the data transfer period of node V1 = the data transfer period of node V4 + 1) However, in the case of satisfying the specific condition (i.e., the time of the parent node If the slot is larger than the time slot of the child node, the time for the data to reach the sink node can be reduced because the parent node and the child node can transmit data in the same operation period.

11 is a flowchart illustrating a tree generation method according to an embodiment of the present invention. 11 is a flowchart for explaining a start-up process.

In step s1110, the singular node V 1101 transmits a message (JOIN_REQ) requesting the neighbor node to register itself as a child node.

In step s1120, the node U 1102 that has received the request message registers the node V 1101 as a child node and updates the number of child nodes and the number of candidate parent nodes of the node U 1102. [

In step s1130, the node U 1102 sends a message (JOIN_ACCEPT) informing the node V 1101 and the neighboring node X 1103 to register the node U as a child node.

At step s1140, node V 1101 registers node V as its parent node and changes its state to complete.

In step s1150, when the number of the child nodes of the node U 1102 becomes equal to or greater than the number of child nodes, the neighboring node X 1103 decreases the number of candidate parent nodes by 1 (i.e., the node U is excluded from the candidate parent node) .)

12 is a flowchart illustrating a tree generation method according to another embodiment of the present invention. 12 is a flowchart for explaining a regular process of tree generation.

In step s1212, the activator node U1 1201 transmits a message (FIND_CHILD) to the neighboring node V 1202 to search for the child node.

In step s1214, another activator node Z 1203 also transmits a message FIND_CHILD to the neighboring node V 1202 to search for the child node.

In step s1222 and step s1224, the neighboring node V 1202 sends a request message (JOIN_REQ) to the initiator node U 1201 and the initiator node Z 1203.

At step s1230, initiator node U1 1201 updates the back-off time for neighbor node V (1202). If the neighboring node V 1202 is a singular node, the back-off time is set to '0' in order to register as a child node. However, if the neighboring node V 1202 is not a singular node, the back-off time corresponding to the neighboring node V 1202 is set based on the transmission delay time. If, during back-off time, neighbor node V 1202 receives a request from another enabler node (e.g., node Z) to a child node and sends a commit message (JOIN_CONFIRM) message, (1201) excludes the neighboring node V (1202) from the child candidate node. This is because the data delay to the neighbor node V 1202 ==> the activator node Z 1203 ==> the sink node is delayed by the neighbor node V 1202 ==> the activator node U 1201 ==> Lt; / RTI > is shorter than the data delay < RTI ID = 0.0 >

At step s1240, the enabler node U1 1201 sends an accept message JOIN_ACCETP to the neighboring node V1202.

In step s1250, the neighboring node V 1202 registers the enabler node U1201 as a parent node.

In step s1260, the neighboring node V 1202 transmits a confirmation message (JOIN_CONFIRM) to its neighboring node (i.e., the activator node U, Z).

In step s1270, the activator node U 1201 determines whether the number of child nodes is equal to or greater than the threshold child number, and ends the search for the child node if the number is equal to or greater than the threshold child number. However, if the number of registered child nodes is less than the limit number of children, the number of registered child nodes is reduced to the number of child nodes. The search for the child node is continued while maintaining the back-off time for the child node.

In step s1280, neighboring node V 1202 changes its state. If the neighboring node V 1202 is an anonymous node, the status is changed to completed, and if not, the new node becomes a new enabler node to search for its own child node.

13 is a flowchart illustrating a tree generation method according to an embodiment of the present invention. A method of generating a tree according to an embodiment of the present invention is for duty-cycle data transmission.

In step s1310, at least one of information on the number of time slots included in the operation period, information on the distance between nodes in the network, and information on the number of nodes in the network is obtained.

In step s1320, the number of maximum child nodes that each node can hold is determined based on at least one of the information on the number of time slots, the inter-node distance information, and the node number information.

In step s1330, a tree is created on the data collection path between the nodes in the network (i.e., the path from the leaf node to the sink node) so that the number of nodes exceeding the maximum number of child nodes is minimized.

First, the singular node in the network is searched. The singular node is a node whose candidate parent node is below the threshold (for example, one), and determines the parent node of the singular node first.

Next, the child node is searched and registered from the sink node. At this time, if the number of registered child nodes is equal to or greater than the maximum number of child nodes, the search and registration procedure of child nodes is stopped. (Except in exceptional cases)

FIG. 14 is a flowchart illustrating a scheduling method according to an embodiment of the present invention.

In step s1410, the first operation period information for the target node to be scheduled is obtained. The first operation period means the earliest operating period during which the target node can transmit data.

In step s1420, information about the first time slot in which the target node is activated and information about the second time slot in which the parent node is activated are obtained.

In step s1430, based on the information about the first timeslot, the information about the second timeslot, and the first operation period information, the data transfer period during which the target node transmits data is determined. Specifically, if the second time slot is as large as the first time slot (i.e., slower), the first operation period is determined as the data transfer period of the target node. But,

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and / or features of the present invention, and how to accomplish them, will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined by the scope of the appended claims and equivalents thereof.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, Modification is possible. Accordingly, the spirit of the present invention should be understood only in accordance with the following claims, and all equivalents or equivalent variations thereof are included in the scope of the present invention.

200: tree generating device
210: Parameter acquisition unit
220:
230: tree generating unit

Claims (14)

A method for scheduling a node that is active only in some time slots among a plurality of time slots in an operation period,
Acquiring first operation period information which is an operation period in which a target node is ready to transmit data;
Obtaining information on a first time slot in which the target node is activated and information on a second time slot in which a parent node receiving data from the target node is activated; And
Determining a data transfer period that is an operation period in which the target node transmits data to the parent node based on the information about the first timeslot, the information about the second timeslot, and the first operation period information The scheduling method comprising the steps of: 2. The method of claim 1, wherein determining the data transfer period comprises:
And determines the first operation period as the data transmission period when the second time slot is larger than the first time slot, and when the second time slot is smaller than or equal to the first time slot, And the second operation period that is a subsequent operation period is determined as the data transfer period. 2. The method of claim 1, wherein determining the data transfer period comprises:
And changing the data transfer period to a next operation period when the determined data transfer period corresponds to a data transfer period of a collision-capable node with respect to the target node. 2. The method of claim 1, wherein obtaining the first operating period information comprises:
If the child node of the target node does not exist, the first operation period is determined to be the fastest operation period, and if the child node of the target node exists, Wherein the scheduling period is determined as a period of operation. 2. The method of claim 1,
Further comprising the step of transmitting information on the data transfer period to a node within a critical distance from the target node when the data transfer period is determined. 2. The method of claim 1,
Receiving information on a data transfer period of a collision-capable node with respect to the target node; And
Further comprising the step of determining a data transfer period of the collision-capable node as a prohibit operation period in which the target node can not transmit data. 2. The method of claim 1,
Further comprising updating information on a second operation period indicating an operation period in which the parent node is ready to transmit data based on the determined data transmission period. A method of generating a tree representing a data collection path of a node activated only in some time slots among a plurality of time slots in one operation period,
Obtaining at least one of information on the number of time slots in one operation period, information on a distance between nodes in the network, and information on the number of nodes in the network;
Determining a maximum number of child nodes that each node can hold based on at least one of information about the number of timeslots, the inter-node distance information, and the node number information; And
Generating a tree representing a data collection path of a node in the network such that a node exceeding the maximum number of child nodes is minimized. 9. The method of claim 8, wherein generating the tree comprises:
Searching for an odd node whose number of candidate parent nodes capable of transmitting data among the nodes in the network is equal to or less than a threshold value; And
And determining one of the candidate parent nodes for the singular node as a parent node for the singular node. 10. The method of claim 9,
Selecting a target node constituting the tree; And
And a transmission delay time which is a time required for transmitting data from a neighbor node to the target node to a sink node that is a final node through which the data is transmitted via the target node, The method comprising the steps of: 11. The method of claim 10, wherein selectively registering with the child node comprises:
Wherein the neighboring node is registered as a child node for the target node regardless of the transmission delay time if the number of candidate parent nodes to which the neighbor node is able to transmit data is less than or equal to a threshold value. . The method of claim 10, wherein selectively registering with the child node comprises:
Wherein the neighbor node is not registered as a child node of the target node when the number of child nodes of the target node is equal to or greater than the number of children of the target node. 11. The method of claim 10, wherein generating the tree comprises:
Further comprising the step of controlling to transmit a message informing that the neighbor node is registered as a child node of the target node to a node within a critical distance from the target node. 8. The method of claim 8,
Further comprising the step of controlling the neighboring node for the target node to exclude the target node from the candidate parent list if the number of child nodes of the target node is equal to or greater than the maximum number of child nodes .

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