KR100889860B1 - Operating method of wireless sensor network system for improving energy efficiency of sensor node using base station, and method therefor - Google Patents

Abstract

The present invention discloses a method of operating a wireless sensor network system that improves energy efficiency of a sensor node using a base station. The present invention includes the steps of (a) a base station communicating with a sensor node forming a wireless sensor network, the location and identification means of the sensor node; (b) a base station performing a coverage operation for determining a sleep node included in a range in which sensing regions of the entire sensing region are added together using the position of the sensor node and identification means; (c) the base station sleeping the sleep node based on the coverage calculation result; (d) sensing the ambient situation by the non-sleeping sensor node; And (e) the base station receiving a sensing value from the sensor node, and (b) step (ba) if at least three sensor nodes are provided in the sensing field to form a group, the base station determines the location and the identification means. Deriving at least two intersection points of a sensing area boundary line between sensor nodes included in the group using the at least two nodes; And (bb) a base station calculating a minimum value of an angle formed by an intersection of a second sensor node located in a sensing area of a first sensor node included in the group and an angle formed by the base station, and performing a coverage operation (bb) In step (a5), the base station extracts a second sensor node that is predicted to be a sleep node, and extracts background nodes that determine whether the base station is at least two including the first sensor node and whether the second sensor node is a sleep node. Doing; (b5) acquiring, by the base station, information on the position or direction of the second sensor node and the background nodes; (c5) classifying, by the base station, the center angle of the second sensor node based on the intersection point of the background nodes, which is one of the background nodes, to the left and right angles with respect to the one background node; (d5) acquiring, by the base station, coordinate values of both intersections forming a minimum value from the left and right angles; And (e5) the base station calculates the central angle of the second sensor node from the coordinate values of both intersections, and performs a coverage operation. According to the present invention, an infinitely energized base station can perform all tasks except for sensing and data communication in place of the sensor node, thereby improving the energy efficiency of the sensor node.

Base Station (BS), Wireless Sensor Network (WSN), Coverage Preservation Method, Clustering, LEACH, CAC, ECAC

Description

Operating method of wireless sensor network system for improving energy efficiency of sensor node using base station, and method therefor}

1 is a conceptual diagram showing the configuration of a wireless sensor network system according to a preferred embodiment of the present invention;

2 is a block diagram for explaining in detail the internal configuration of the base station according to an embodiment of the present invention;

3A to 3G are conceptual views illustrating characteristics of a base station according to a preferred embodiment of the present invention;

4 is a flowchart illustrating a method of operating a wireless sensor network system according to a preferred embodiment of the present invention;

5A to 5J are conceptual views illustrating a method for determining a center angle according to a preferred embodiment of the present invention;

6 is a flowchart illustrating a coverage calculation method according to a preferred embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

100: wireless sensor network system 110: sensor node

112: sensor field 120: base station (BS)

130: wired and wireless communication network 140: sensing data management server

142: sensing data management database 150: administrator terminal

152: user terminal 200: communication unit

210: memory unit 212: coverage calculating unit

214: awakening strategy spoken part 220: cluster component part

230: multiple access schedule generation unit 240: main control unit

242: power supply unit 300: sleep node

310: cluster 320: representative node

322: general node

The present invention relates to a method of operating a wireless sensor network system that improves energy efficiency of a sensor node using a base station. More specifically, the method of preserving coverage to sleep some sensor nodes with overlapping detection areas or to wake up a node to replace a sensor node that has reached the end of life as needed, clustering for optimal cluster formation, and data transmission and reception The present invention relates to a method of operating a wireless sensor network system that improves energy efficiency of a sensor node by using a base station, wherein a base station performs a task of predicting energy consumption such as a schedule generation instead of a sensor node.

Recently, wireless sensor network (WSN) has emerged as a new research field due to the development of wireless communication technology, low power circuit design, and miniaturization of arithmetic unit. In particular, with the advent of the ubiquitous era in which users can easily connect to the network anytime and anywhere without consciousness of terminals such as computers, such wireless sensor networks combine existing computing environments with physical physical environments. It is expected to carry out further attention.

In general, a wireless sensor network refers to an autonomous network formed by arranging a sensor node granted with computing capability and wireless communication capability in a natural environment or an electric field. The wireless sensor network is configured to provide the base station with information obtained while the sensor nodes independently operate in the sensor field. The wireless sensor network can be applied to various fields from military, firefighting, transportation, medical, environmental monitoring, building control, home network, etc. to industrial and everyday life.

For the efficient operation of such a wireless sensor network, the following requirements are required. First, it is necessary to minimize power consumption so that a sensor node having a limited lifetime can maintain its lifetime for a longer period of time. Second, the sensor node needs to be closely arranged in the field so as to satisfy the sensing information is large and accurate. Third, it is necessary to have a self-organizing capability so that the network protocol can adapt to the dynamic situation change according to the arbitrary arrangement of the sensor nodes. Fourth, it is necessary to select an access order so that effective communication between nodes is achieved. Fifth, it is necessary to secure security for data communication to maintain confidentiality and integrity. These can generally be solved by applying an ad hoc network, using TDMA / CDMA scheduling, and encrypting and decrypting using a symmetric-key or public-key.

However, above all, the task to be decided in the wireless sensor network is to secure energy efficiency of the sensor node. In order to realize this, the following methods have been proposed.

① LEACH (Low-Energy Adaptive Clustering Hierarchy) Method: LEACH method, which is a clustering-based routing method, introduces a cluster head (CH) and data aggregation (DA) into a wireless sensor network. This feature is characterized by sharing the residual energy information between the sensor nodes to induce the nodes provided in the cluster to take charge of the cluster head. In this way, the method can reduce the energy consumption of the sensor node as much as possible and achieve process dispersion.

Coverage-Preserving Scheme The coverage preservation method described above is characterized by calculating overlapping detection areas between nodes in order to realize sleep of nodes that do not need detection. This is well represented in Korean Patent Registration Publication No. 667,354 "Wireless Sensor Network System and Wireless Sensor Network Communication Method with High Efficiency in Energy Consumption". According to this patent, before the sensor nodes forming the wireless sensor network form a cluster, neighboring nodes and nodes overlapping the detection area enter a sleep state. They are then woken up by specific nodes as needed. This coverage preservation method ultimately contributes to long-term survival of the wireless sensor network.

③ Clustering: An optimal cluster formation algorithm is required for efficient configuration of clusters that deploy data communication in the network. This was done by Soheil Ghiasi, Ankur Srivastava, Xiaojian Yang and Majid Sarrafzadeh in July 2002 by MDPI Sensors, Vol. 2, No. 7, pp. This is well illustrated in "Optimal energy aware clustering in sensor networks" published in 258-269. The Balanced Cluster Technique (BCT) method proposed in the paper is characterized in that each cluster has almost the same number of members and the distance between the members is minimized.

However, the above-described methods (①, ②, ③) are aimed at improving energy efficiency of sensor nodes in wireless sensor network environment because the sensor node still takes charge of energy consuming tasks (eg, arithmetic functions). Is not the best.

On the other hand, Di Tian and Nicolas D. Georganas of 2002 ACM International workshop on WSNA, pp. The Central Angle Calculation (CAC) method proposed in the “A coverage-preserving node scheduling scheme for large wireless sensor networks” presented at 32-41 and by Azzedine Boukerche, Xin Fei and Regina B. Araujo in October 2005, Proc. of the second ACM International workshop on PE-WASUN '05, pp. The Extended Central Angle Calculation (ECAC) method proposed in "An Energy Aware Coverage-Preserving Scheme for Wireless Sensor Networks" published in 205-213 was mainly used. These methods (i.e., the method of calculating the central angle) are characterized by calculating the detection areas overlapping between the sensor nodes from the central angles of the respective sensor nodes, focusing on the detection area of the sensor nodes forming a circle. In particular, the latter case makes it possible to more accurately find nodes that do not require detection, thereby enabling efficient cluster construction.

However, these conventional methods change the central angle according to the position of the sensor node as a target, and the overlapping detection area is changed. At this time, if only one of them is taken into account without considering all the positional changes of the sensor node, it may result in the occurrence of an undetected node or an area that is not sensed in the sensor field. This mass-produces a problem that degrades the quality of the wireless sensor network. On the other hand, when considering all the change in the position of the sensor node, it is impossible to solve this only by the conventional method of calculating the central angle.

The present invention has been made to solve the above-described problems, the wireless base station using the base station to improve the energy efficiency of the sensor node, characterized in that the base station to perform all the tasks except for sensing and data communication An object of the present invention is to provide a method of operating a sensor network system. Specifically, the service includes a coverage calculation for finding and sleeping a node whose detection area is guaranteed by a neighboring node, and waking up a node in a sleeping state to replace a node that has reached the end of its lifetime while sensing an allocated area. Wake-up strategy, cluster formation using BCT method, choice of their nodes according to LEACH method, generation of spreading codes and schedules for minimizing interference between clusters and minimizing interference between clusters (Creation of spreading code and TDMA schedules).

In addition, the present invention, the energy efficiency of the sensor node using the base station, characterized in that reflecting the central angle determination method considering all the change in the position of the sensor node to the center angle calculation method based on the CAC method or ECAC method An object of the present invention is to provide an improved method of operating a wireless sensor network system.

The present invention is to achieve the above object, (a) a base station communicating with a sensor node forming a wireless sensor network, the step of recognizing the location and identification means of the sensor node; (b) performing, by the base station, a coverage operation for determining a slip node that is included in a range in which the entire sensing area is added to the sensing areas of other sensor nodes by using the position of the sensor node and the identification means; (c) the base station sleeping the sleep node based on the coverage calculation result; (d) sensing an ambient situation by the non-sleeping sensor node; And (e) the base station receiving a sensing value from the sensor node, wherein step (b) includes (ba) at least three sensor nodes provided in a sensing field to form a group. Deriving at least two intersection points of a sensing area boundary line between sensor nodes included in the group by using a position and the identification means; And (bb) calculating, by the base station, a minimum value of an angle formed by the second sensor node located in the sensing area of the first sensor node included in the group with the derived intersection point, and performing the coverage operation. The step (bb) may include (a5) extracting a second sensor node predicted by the base station to be the sleep node, wherein the base station is at least two including the first sensor node, and the second sensor node is the sleep node. Extracting background nodes that determine whether the node is a node; (b5) acquiring, by the base station, information about the position or direction of the second sensor node and the background nodes; (c5) The center angle of the second sensor node based on the intersection point where the base station meets the background nodes and is one of the background nodes is classified into left and right angles around the one background node. Doing; (d5) acquiring, by the base station, coordinate values of both intersections forming a minimum value from the left and right angles; And (e5) the base station calculating the center angle of the second sensor node from the coordinate values of the two intersections and executing the coverage operation. .

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Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. First of all, in adding reference numerals to the components of each drawing, it should be noted that the same reference numerals are used as much as possible even if displayed on different drawings. In addition, in describing the present invention, when it is determined that the detailed description of the related known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted. In addition, the following will describe a preferred embodiment of the present invention, but the technical idea of the present invention is not limited thereto and may be variously modified and modified by those skilled in the art.

1 is a conceptual diagram showing the configuration of a wireless sensor network system according to a preferred embodiment of the present invention. As shown in FIG. 1, the wireless sensor network system 100 according to a preferred embodiment of the present invention includes a sensor node 110, a base station (BS) 120, a wired / wireless communication network 130, and sensing data. The management server 140, the sensing data management database 142, the manager terminal 150, and the user terminal 152 are included.

In the wireless sensor network system 100 according to the present invention, when the sensor node 110 distributed in the sensor field 112 senses specific data, the base station 120 collects the specific data through a predetermined path and passes through the wired / wireless communication network 130. It is delivered to the sensing data management server 140. The sensing data management server 140 determines whether an abnormality occurs using this, and stores related data in the sensing data management database 142. Accordingly, the user (a concept in which the user includes an observer) may be connected to the sensing data management server 140 through the user terminal 152 to confirm this. Or, by receiving the relevant data to the user terminal 152 by the sensing data management server 140, the user can perform an appropriate action based on this.

For example, if the sensor field 112 is a specific forest area, the sensing data may be data on whether or not a fire has occurred, and when the sensing data management server 140 confirms the fire, the user may select the area. It is possible to act to dispatch fire brigade. Meanwhile, the base station 120 may directly transmit sensing data to the user terminal 152 through the wired / wireless communication network 130. In this case, it is preferable that the base station 120 or the user terminal 152 process the sensing data so that the user can easily understand the data displayed on the display device.

The wireless sensor network system 100 according to the present invention has a hierarchical structure in consideration of the energy efficiency of the sensor node 110. This will be described in detail as follows. Wireless sensor networks are generally classified into planar networks and hierarchical networks according to their structure.

In a planar network, all nodes act as routers, so each node must perform direct / indirect communication to the destination via other nodes dynamically selected by the routing algorithm. For this purpose, a table-driven routing algorithm or an on-demand routing algorithm, which is a method in which each node discovers its own path, is mainly used. Since they do not exist separately in the node, the nodes themselves control data transmission through a distributed method through a competition method such as carrier sensing multiple access / collision avoidance (CSMA / CA).

On the other hand, in the hierarchical network, a representative node (CH) that manages a plurality of nodes is elected, and the elected node is responsible for allocating and controlling IDs and radio resources of the nodes it manages. Here, a group formed by aggregating a representative node and general nodes controlled by resource allocation is called a cluster, and a set of representative nodes are selected from all nodes in the wireless sensor network and a series of clusters are formed. The process is called clustering. In a hierarchical network, such clustering must be preceded before data transmission and reception, which has a superior effect than that of a planar network in consideration of the energy efficiency of nodes. Therefore, in consideration of this aspect, the wireless sensor network system 100 according to the present invention is preferably a multi-hop ad hoc network in the form of a hierarchical network.

However, the sensor network of the hierarchical network type has a limitation of mutual interference between nodes. Accordingly, in the present invention, a multiple access schedule is applied to a wireless sensor network as a solution for solving the limitation. Specifically, a time division multiple access (TDMA) schedule using the same code channel is applied to communication between a general node and a representative node occurring in a cluster. Then, different time slots are allocated to each general node, so that the general node can pass the sensing data to the representative node without any communication collision. On the other hand, a code division multiple access (CDMA) schedule using different code channels is applied to communication between representative nodes occurring outside the cluster or between the representative node and the base station. In this case, the set spreading code is known to each representative node before data transmission and reception are performed. Accordingly, each representative node can develop communication without collision by the spreading code. Such a multiple access schedule may be referred to, for example, what is shown in Korean Patent Publication No. 2005-101491 "Method of transmitting data between mobile communication terminals" or Korean Patent Publication No. 200,553 "Direct mobile communication system and method between terminals." On the other hand, in the practice of the present invention, the wireless sensor network system 100 may configure a hierarchical network having only a single channel. In this case, in order to maximize network scalability, resource efficiency, and energy efficiency, for example, Kim Il-hwan, Kim Yong-seok and Kang Choong-gu presented in the 2005 First Telecommunication Standardization Proceedings, "The Dual-Layer Evolutionary Media Access for Wireless Sensor Networks. It is also possible to apply the HiPERMAC (Hierarchically Paired Evolutionary Radio MAC) protocol proposed in "Control and Network Protocol: Cross Layer Design Approach".

The wireless sensor network system 100 according to the present invention is characterized in that it is operated using a clustering-based hierarchical routing protocol. In particular, the wireless sensor network system 100 is characterized by operating using the LEACH protocol as described above. In general, in the wireless sensor network system 100 having a hierarchical structure, data aggregation is required to prevent energy waste due to redundant transmission of similar data between adjacent nodes. In other words, if similar data on an event occurring in an adjacent area is delivered to the representative node, the representative node performs data reduction to enable more energy efficient routing. In addition, delivery by the representative node to the requested query can prevent flooding of the inefficient query. Wireless sensor network system 100 according to the present invention, for example, Wendi Rabiner Heinzelman, Anantha Chandrakasan and Hari Balakrishnan published in 2000 "Proceedings of the 33rd Hawaii International Conference on System Sciences, 1-10" "Energy-Effcient Communication It is also possible to use the LEACH protocol proposed in "Protocol for Wireless Microsensor Networks."

On the other hand, the wireless sensor network system 100 according to the present invention, depending on how the data movement path is set, the proactive routing protocol, the reactive routing protocol, and the hybrid scheme It is also possible to use a routing protocol or the like. Here, the dictionary method refers to a method in which all data movement paths are established at the same time a network is formed. The reactive method refers to a method in which a specific path is established in the network only when a data movement path is needed. In addition, the hybrid method refers to a method in which the two methods are appropriately mixed and set.

On the other hand, the wireless sensor network system 100 according to the present invention more preferably reflects scalability and adaptability to the network to respond quickly and effectively to changes in network size or changes in topology. .

The sensor node 110 is a sensing device provided with computing power, and refers to an intelligent communication device constituting a wireless sensor network. The sensor node 110 is usually provided with a sensor, a local storage module, a communication module, a processor and a battery therein. Such a sensor node 110 is, for example, as shown by Jamal N. Al-Karaki and Ahmed E. Kamal in "Routing Techniques in Wireless Sensor Networks: A Survey," published in IEEE Wireless Communications 11, 6-28, 2004. Can be configured.

The sensor node 110 is a crossbow Mica series, Intel's iMote, Moteive's Telos, Octacom's Nano-24, Macpole's TIP series, Hanbaek Electronics ZigbeX Mote, Huins UStar-2000 And the like. In this case, the sensor node 110 may use a Tiny OS developed by UC Berkeley, Nano-Q-Plus developed by ETRI (Korea Institute of Electronics and Telecommunications Research Institute), etc. in consideration of size and energy efficiency. In addition, in the present invention, the sensor node 110 may be implemented by Certicom Security (http://www.govtech.net/magazine/channel_story.php/99039) made by Certicom, Canada. Certicom Security provides the ability to secure data using elliptic curve passwords.

On the other hand, the sensor node 110 may be provided with a location finding system such as a GPS module so that the sensing information management server 130 can easily recognize the location in the embodiment of the present invention.

In the embodiment of the present invention, the sensor node 110 acts as a general node or a representative node when a cluster is configured. Description of these is as follows. The general node collects physical situation data and transmits real-time situation detection information to the representative node using wireless communication in response to the situation change. Herein, the wireless communication refers to a general RF communication, and Zigbee, Bluetooth, Wi-Fi, etc. may be applied thereto. On the other hand, the representative node is a cluster head that manages IDs of general nodes and reserves time slots for data transmission and reception to them, and is responsible for controlling general nodes to which they belong. The representative node collects the data acquired by the general nodes and provides the representative node to another representative node or the base station 120.

Base station 120 is a mobile or fixed wireless station that acts as a gateway. The base station 120 communicates with the representative nodes using RF (particularly, CDMA), and is connected to the sensing data management server 140 through the wired / wireless communication network 130. The base station 120 receives sensing data collected from representative nodes and delivers the sensing data to the sensing data management server 140. The base station 120 has the following unique features in the embodiment of the present invention.

Ⓐ base station 120 according to the present invention is characterized in that it recognizes the ID of all the sensor nodes (110) provided in the sensor field (112). Alternatively, the base station 120 according to the present invention may store the ID in the sensing data management database 142 and receive it if necessary through the sensing data management server 140. In this case, the ID refers to information for identifying each sensor node 110.

Ⓑ The base station 120 according to the present invention is characterized by operating with an algorithm related to the coverage preservation method. Specifically, the base station 120 first performs a function of performing a coverage operation based on the IDs of all the sensor nodes 110 and the algorithm. Thereafter, the base station 120 functions to instruct the specific sensor node 110 to sleep based on the calculation value derived by the coverage calculation result. In addition, the base station 120 searches for the sensor node 110 that is stopped functioning by consuming all the energy, and serves to wake up the sensor node 110 to cover it among the adjacent sensor nodes 110. In this case, the base station 120 uses a wake-up strategy based on the algorithm. In the present invention, it is preferable that the base station 120 checks the current state (amount of residual energy) of all the sensor nodes 110 in order to realize the above. To this end, the base station 120 may develop communication with the sensor node 110 at any time / periodically. However, when considering the energy efficiency improvement of the sensor node 110 which is an object of the present invention, it is more preferable that the base station 120 is provided with residual energy amount information of all nodes in the cluster when sensing data is received from the representative node.

Ⓒ The base station 120 according to the present invention targets the sensor nodes 110 (ie, the remaining nodes except the sleeping or disabled node) that are set to an active state after performing a coverage operation (and a wake-up strategy). It is characterized by configuring a cluster. In addition, the base station 120 performs a function of selecting a representative node for each cluster after completing the configuration of the cluster.

The base station 120 according to the present invention is characterized by generating the above-described multiple access schedule. The base station 120 delivers the generated multiple access schedules to all nodes constituting the cluster as soon as the representative node is selected. Then, the representative node communicates with the general nodes based on this, and transmits the sensed data collected to the base station 120 without any confusion with other representative nodes.

In addition, the base station 120 may add a function in consideration of the following description. In general, in the wireless sensor network, the sensor node 110 operates independently without the influence of other media. Therefore, the sensor node 110 has no choice but to completely rely on the driving of the energy stored therein. However, the sensor node 110 usually consumes energy while performing functions such as sensing, processing, and communicating. In particular, the sensor node 110 consumes a lot of energy when performing a communication function. Thus, frequent communication of the sensor node 110 significantly shortens its lifespan, resulting in the problem of placing the new sensor node 110 back in the sensor field 112. Thus, the base station 120 according to the present invention is preferably provided to solve this problem. For example, the base station 120 may record a method of delivering next-order sensing data of a specific general node in a TDMA schedule. Then, when the general node fails to deliver the sensing data to the representative node for a predetermined number of times, the sensing data can be delivered through the general node at the most recent distance of the representative node.

The wired / wireless communication network 130 is a communication network that relays the base station 120 and the sensing data management server 140, and is configured as a mobile communication network such as a CDMA network in an embodiment of the present invention. However, the wired / wireless communication network 130 is not limited thereto, and may be implemented as a GPS network, a wireless personal area network (WPAN) network, or a combination with the Internet network.

The sensing data management server 140 is a server that receives the sensing data from the base station 120 and processes the same. The sensing data management server 140 determines whether there is an abnormality in the sensor field 112 based on the sensing data in the embodiment of the present invention, and records the result in the sensing data management database 142 or the user terminal ( 152).

Sensing data management server 140 is a distributed processing for operating one or more applications in a cooperative environment to achieve the desired results desired by the client through the cooperative work between the client requesting the service and the server processing the client's request It processes and provides requests of the manager terminal 150 and the user terminal 152 through various communication networks in a client / server manner. The sensing data management server 140 may include a series of application programs for providing various services according to the present invention, in addition to a server program that is commonly used.

The sensing data management database 142 stores a data generated by the sensing data management server 140 or provides a database containing various information. The sensing data management database 142 stores the sensing data and the result value in the embodiment of the present invention.

The manager terminal 150 is a terminal to which an administrator responsible for operating the sensing data management server 140 is connected. The manager terminal 150 is connected to the sensing data management server 140 from time to time in the embodiment of the present invention performs a function of checking whether it is operating in a normal state.

The user terminal 152 is a terminal to which a person who installs the sensor node 110 in the sensor field 112 or a person who requests a result value of sensing data is connected. The user terminal 152 performs the function of displaying the result or requesting the sensing data management server 140 in the embodiment of the present invention. Meanwhile, in the present invention, when the sensing data management server 140 receives a connection request from the user terminal 152, the user terminal 152 authenticates the user terminal (that is, a user who requests a connection through the user terminal 152 is a legitimate user). To determine whether or not it is). This is to improve the security of the sensing data or the result value.

Next, the characteristics of the base station 120 according to the present invention described above will be described in detail with reference to the drawings. 2 is a block diagram for explaining in detail the internal configuration of the base station according to an embodiment of the present invention. Referring to FIG. 2, the base station 120 according to the preferred embodiment of the present invention includes a communication unit 200, a memory unit 210, a coverage calculating unit 212, an awakening strategy speaking unit 214, and a cluster constructing unit 220. , A multiple access schedule generation unit 230, a main control unit 240, and a power supply unit 242.

The communication unit 200 performs a function of setting and providing a communication path to enable signal exchange with the sensor node 110 and the sensing data management server 140 in the embodiment of the present invention.

The memory unit 210 stores IDs of all sensor nodes provided in the sensor field 112 in the embodiment of the present invention. In addition, the memory unit 210 stores the content processed by the components constituting the base station 120 in cooperation with the main controller 240 in the embodiment of the present invention. The memory unit 210 may not be provided in the embodiment of the present invention.

The coverage calculator 212 performs a coverage operation to determine a sensor node where the detection area overlaps. For coverage calculation, the present invention proposes a coverage calculation method reflecting the center angle determination method in the conventional center angle calculation method. However, embodiments of the present invention are not limited thereto, and the CAC method and the ECAC method described above may also be referred to.

The coverage calculation unit 212 can determine the distribution relationship of the entire sensor node 110 as shown in FIG. 3A through the coverage calculation. Thereafter, the coverage calculating unit 212 extracts nodes (hereinafter, abbreviated to the sleep node 300) in which the values sensed by the overlapping nodes and the detection area overlap with each other as shown in FIG. 3B. . Thereafter, the sleep nodes 300 are set to the sleep state as instructed by the coverage calculator 212.

Meanwhile, the coverage calculation method will be described in detail below with reference to FIG. 5.

The wakeup strategy speech unit 214 wakes up a particular sleep node 300. To this end, the wake-up strategy speaking unit 214 first communicates with all sensor nodes to determine the current state of each node. Subsequently, the wake-up strategy speaking unit 214 detects the position based on the ID when the general node in which the function is stopped is extracted. Thereafter, the wake-up strategy speaking unit 214 extracts a node to replace the general node. At this time, the wake-up strategy speaking unit 214 extracts all of the slip nodes 300 located in the vicinity of the normal node that is disabled so that the undetected area (coverage-hole) does not occur, and simulates their sensing area. It is then desirable to determine the replacement node.

The cluster configuration unit 220 performs a function of configuring a cluster for sensor nodes set to an active state. In this case, the cluster configuration unit 220 configures the cluster 310 as shown in FIG. 3C in consideration of the BCT method. Then, the cluster configuration unit 220 may be able to place the same number of nodes in each cluster 310, it is possible to minimize the distance between the nodes. However, in the embodiment of the present invention, the cluster configuration unit 220 does not use only the BCT method for configuring the cluster 310.

When the cluster 310 is configured, the cluster configuration unit 220 selects a specific sensor node as the representative node 320 in the cluster 310 as shown in FIG. 3D. The remaining nodes then automatically become generic nodes 322. At this time, the cluster configuration unit 220 is preferably in consideration of the energy efficiency of the node so that all the nodes in the cluster 310 can be selected as the representative node 320 in a fair manner. Thereafter, the cluster configuration unit 220 notifies the sensor node of the result so as to perform a function as a representative node. On the other hand, it has already been mentioned that the wireless sensor network system 100 according to the present invention is operated by the LEACH protocol. Therefore, the cluster configuration unit 220 according to the present invention is described in Korean Patent Application No. 2006-115798, "Method for generating a communication encryption key according to data density in a wireless sensor network, a data communication method using the same, and a system for them". The representative node 320 can be determined using the described method.

The multi-access schedule generator 230 performs a function of generating the multi-access schedule described above in the embodiment of the present invention. In detail, the multiple access schedule generator 230 generates a TDMA schedule and a CDMA schedule and notifies all nodes constituting the cluster. In the TDMA schedule, as shown in FIG. 3E, a time slot is input so that the general node can transmit sensing data to the representative node. In the CDMA schedule, as shown in FIG. 3F, a spreading code is input so that the representative node can transmit the sensing data collected to the base station 120. The representative node can transmit the sensing data acquired by the general node to the base station 120 without retransmission based on these (㉠, ㉡). In this case, however, the communication method inside the cluster follows TDMA, and the communication method outside the cluster follows CDMA. This is a Korean Patent Registration Publication No. 646,824 "Method of controlling TDMA data transmission in a wireless network including a plurality of nodes and a sensor network system and a computer-readable recording medium using the same" and Korean Patent Publication No. 2006-124498 " As the media access control method in the wireless sensor network "is widely used technology, this is considered in the present invention. However, the present invention is not limited thereto, and any method may be used as long as the data can be smoothly transmitted without retransmission. For example, all communication schemes can be based on CDMA.

Meanwhile, the multiple access schedule generator 230 may create a TDMA schedule as shown in FIG. 3G, for example. Hereinafter, a method of determining a communication order between a representative node and a general node in a cluster having a spread code of 101 will be described.

Referring to FIG. 3G, timeslots in the first round are allocated in the order of the representative node 10100, the first general node 10101, the second general node 10110, and the third general node 10111. Here, the timeslot is implemented with a certain time. Accordingly, in the first round, data communication proceeds as follows. First, the representative node takes a break during the timeslot. Alternatively, the representative node transfers the sensed data collected so far to the base station using the spreading code. Next, the first general node transmits the sensing data to the representative node during the timeslot, and then the second general node and the third general node sequentially transmit the sensing data.

As described above, when the first round ends, the second round proceeds. The timeslots in the second round are allocated in order of the first general node 10100, the representative node 10101, the second general node 10110, and the third general node 10111. Accordingly, data communication in the second round proceeds as follows. First, the first general node transmits the sensing data to the representative node. Next, the representative node takes a break or transfers the collected sensing data to the base station using a spreading code. Subsequently, the second general node and the third general node sequentially transmit the sensing data to the representative node.

Similarly, data communication in the third and fourth rounds proceeds based on the above.

Next, the operation method of the wireless sensor network system 100 according to the preferred embodiment of the present invention configured as described above is as follows. 4 is a flowchart illustrating a method of operating a wireless sensor network system according to a preferred embodiment of the present invention.

Referring to FIG. 4, the wireless sensor network system 100 according to the present invention proceeds in the order of an initial phase, a setup phase, and a late data gathering phase. Briefly describing each step, in the previous step, the base station 120 performs a coverage calculation task. This electrical step is no longer executed before the sensor node 110 is relocated to the sensor field 112. In the middle stage, the base station 120 performs all the main tasks according to the present invention, such as the cluster 320 configuration, representative node 322 election, multiple access schedule generation. Then, in the later stage, overall data transmission and reception are performed to achieve the purpose of the wireless sensor network.

Each round in the wireless sensor network system 100 is composed of a middle stage and a late stage. The total of these rounds is determined by the duration of the wireless sensor network. Hereinafter, each step will be described in detail.

① Electric phase: S400 ~ S404

The main control unit 240 of the base station 120 first identifies IDs and locations of all sensor nodes forming the sensor field 112 (S400). This may be used in the memory unit 210, but is not limited thereto. For example, when the main controller 240 requests IDs and locations from all sensor nodes, the nodes may notify the base station 120 of their IDs and locations. Alternatively, the main controller 240 may determine the location by communicating with the sensor nodes based on IDs of all the sensor nodes provided. However, considering the energy efficiency of the sensor node, it is more preferable that the node ID and location are stored in the memory unit 210 or the sensing data management database 142.

Thereafter, the coverage calculating unit 212 performs a coverage calculating task to extract the slip node 300 from the sensor field 112 (S402). Thereafter, the main control unit 240 commands the sleep node 300 to enter the sleep state through the communication unit 200 (S404). Then, the sleep node 300 maintains the sleep state until a further command does not proceed with the sensing operation anymore.

② Middle stage: S410 ~ S422

When the electric step is completed, the wake-up strategy speaking unit 214 determines whether there is no node disabled in the sensor field 112 (S410). At this time, when the node is stopped, the wakeup strategy unit 214 determines the most preferred node as a replacement node within the range where coverage-holes are not generated, and wakes up the node through the main control unit 240 ( S412). Steps S410 and S412 are preferably performed after a predetermined time has elapsed after the wireless sensor network is configured in the embodiment of the present invention.

Thereafter, the cluster configuration unit 220 configures the cluster 310 with reference to the BCT method (S414). Thereafter, the cluster configuration unit 220 selects the representative node 320 from each cluster 310 (S416), and informs the corresponding node of the fact through the main control unit 240 (S418). Thereafter, the multi-access schedule generator 230 generates a multi-access schedule (S420). Thereafter, the multiple access schedule generator 230 transmits the multiple access schedule to all nodes forming the cluster 310 through the main controller 240 (S422). Of course, the multiple access schedule generator 230 may transmit the multiple access schedule to the representative node 320 of each cluster 310, and allow the representative node to notify the general node later.

③ late stage: S430 ~ S444

When the intermediate stage is completed, the general nodes in each cluster 310 execute their own sensing tasks. Thereafter, the general nodes transmit the sensing data obtained as a result of the execution to the representative node 320 according to the multiple access schedule (S430). The representative node 320 collects the sensing data through the data compression process (S432). In general, since data detected in neighboring areas has highly correlated spatial locality, it is preferable to collect data of adjacent nodes through data fusion and compression. Then, it is possible to improve the accuracy of the data and to reduce the size of the data so that energy consumption during transmission and reception can be reduced as much as possible. Thereafter, the representative node 320 transmits the collected sensing data to the base station 120 according to the spreading code (S434).

When the collected data is transmitted from all representative nodes, the main control unit 240 collects the collected data and transmits the collected data to the sensing data management server 140 through the wired / wireless communication network 130 (S436). Then, the sensing data management server 140 determines whether an abnormality occurs based on this (S438). Then, the sensing data management server 140 provides the result value to the user terminal 152 (S440).

After the main control unit 240 transmits the collected data to the sensing data management server 140, the main controller 240 determines whether the corresponding round is terminated (S442). If the round is not finished, the main controller 240 requests sensing data from all representative nodes. That is, the process proceeds again from step S430. On the other hand, if the round is ended, the main control unit 240 determines whether all nodes have stopped functioning through the wake-up strategy speaking unit 214 (S444). If all the nodes have not stopped functioning, the wakeup strategy speaking unit 214 proceeds to step S410 again. On the other hand, if all nodes are disabled, the main control unit 240 terminates all work. Alternatively, the main controller 240 requests the user terminal 152 to relocate the sensor node to the sensor field 112.

Next, the coverage calculation method will be described. The coverage calculation method according to the present invention is largely composed of a center angle calculation method and a center angle determination method. First, these are demonstrated. Since the method of calculating the central angle is based on the CAC method and the ECAC method as described above, the two documents described in [the technical field to which the invention belongs and the prior art in that field] are referred to. Hereinafter, only the method of determining the central angle will be described. 5A to 5J are conceptual views illustrating a method for determining a center angle according to a preferred embodiment of the present invention.

First, referring to FIG. 5A, a plurality of sensor nodes that form a wireless sensor network, that is, sensor node m and sensor node n have a dense distribution in the sensor field 112, and thus, overlapping sensing as shown in the drawing. Has an area 500. Thus, when the overlap region 500 is calculated as the center angle 502 at the sensor node m as shown in FIG. 5B, the equation for calculating the center angle may be defined as follows.

는 중첩영역(500)에 대한 센서노드 m에서의 센서노드 n 방향으로의 중앙각도(502)이고, R은 센서노드 m가 형성하는 원의 반지름이다. 그리고, d(m,n)은 센서노드 m과 센서노드 n 간의 거리를 말한다.From here,

Is the central angle 502 in the sensor node n direction from the sensor node m with respect to the overlapping region 500, and R is the radius of the circle formed by the sensor node m. And d (m, n) refers to the distance between sensor node m and sensor node n.

On the other hand, the equation for determining the central angle direction can be defined as follows.

는 센서노드 m에서 센서노드 n으로의 방향성(예컨대, 도 5c의 도면부호 504)을 의미하고, X_m, X_n, Y_m 및 Y_n은 각각 센서노드 m의 x축 좌표와 y축 좌표, 센서노드 n의 x축 좌표와 y축 좌표를 말한다. 한편, 상기 방향성에 따른 중앙각도(502)는 센서노드 n을 기준으로 좌(Left) 성분(506a)과 우(Right) 성분(506b)으로 분류할 수 있다.From here,

Is the direction from sensor node m to sensor node n (e.g., 504 in Figure 5c), where X _m , X _n , Y _m and Y _n are the x and y axis coordinates of sensor node m, Refers to the x-axis and y-axis coordinates of sensor node n. Meanwhile, the central angle 502 according to the direction may be classified into a left component 506a and a right component 506b based on the sensor node n.

Next, a method of calculating the overlapping region 500 implemented in various forms according to various arrangements of the sensor nodes 110 will be derived using the above equations. First, according to the CAC method, when node q, node r, and node s are located in the sensing region of a specific node p, the sensing region 510 of node p sums the sensing region of nodes q to node s 512. (See FIG. 5D). On the other hand, according to the ECAC method, when only the node q is located in the sensing region of the specific node p, but a plurality of nodes (node r to node t) are located around (where R <d ₁ , d ₂ , d ₃ <). Also in 2R), the sensing region 514 of the node p is within the sensing region summation range 516 of the nodes q to t (see FIG. 5E). That is, from the above, when one node q is in the range of 'd ₄ <R' and the other node r is in the range of 'R <d ₅ <2R' for the specific node p, the node p is the node q and the node. It can be seen that there is an overlap region 500 with respect to r (see FIG. 5F).

However, even though the relationship between the node p and the node q and the node r is as described above, as shown in FIGS. 5G to 5J, the central angle 520 and the overlapping area of the node p according to the positions of the node q and the node r ( 500) will be different. As mentioned above, it is impossible to determine any one of the bars shown in FIGS. 5G to 5J as the central angle 520 and the overlapping region 500 at the node p. Suggest. Hereinafter, the method of determining the central angle will be described with reference to FIGS. 5G to 5J as follows. First, assume two things.

In order to avoid the unsensed area in the sensor field 112, the center angle is classified into left and right components with reference to the bar proposed in FIG. 5C.

Ⓑ For accurate derivation of slip node, the central angle should be the minimum value among the comparison targets.

Considering ⓐ and ⓑ, the following equation can be extracted.

Where min (a, b) defines the smaller of a and b. In addition, A and D represent intersection points of two circles when the sensing ranges of the sensor node p and the sensor node r are respectively shown as circles. In addition, B and C indicate intersection points of two circles when the sensing ranges of the sensor node q and the sensor node r are respectively shown as circles. And, B 'and C' refers to the intersection point where the extension line in the sensor node p for the B and the C meets a circle representing its sensing range.

From this, a definition for determining the central angle 520 at the node p is derived as follows.

Computing this definition using Equations 1 and 2 leads to the following conclusions.

Next, a coverage calculation method according to the present invention will be described based on the center angle calculation method and the above-described center angle determination method. 6 is a flowchart illustrating a coverage calculation method according to a preferred embodiment of the present invention.

Referring to FIG. 6, an object node and a background node are extracted from a plurality of sensor nodes distributed in a predetermined region for coverage calculation (S600). Herein, the target node is an object predicted to be a slip node, for example, the sensor node p of FIGS. 5G to 5J corresponds thereto. The background node is one or more nodes for determining whether the target node corresponds to a sleep node, for example, the sensor node q and the sensor node r of FIGS. 5G to 5J correspond to this. Next, information about the position or direction of the destination node and the background node is obtained (S602). Then, as shown in FIGS. 5G to 5J, it is possible to obtain the central angles of various types of destination nodes according to the relative positions of the background nodes.

Thereafter, each central angle at the destination node is classified into an angle of a left component and an angle of a right component (S604). And the minimum value of the angle of a left component and the minimum value of the angle of a right component are acquired, respectively. Then, it is possible to obtain the left and right coordinate values for determining the central angle that is suitable for the purpose of the present invention (S606). In this case, the reason why the minimum value is taken is to prevent the non-sensing area of the sensor field 112. Specifically, it will be described with reference to FIGS. 5G to 5J. Hereinafter, '∠' means that the angle. First, compare ∠Cpr (or ∠C'pr) with ∠Dpr. If ∠Cpr is greater than ∠Dpr, compare ∠rpB and ∠rpA. If ∠rpB is greater than ArpA, ∠CpB is determined as the median angle of the target node according to the present invention in which the angle of the left and right components is a minimum value. Otherwise, ∠CpA is determined as the median angle. Meanwhile, even when ∠Cpr is smaller than 작은 Dpr, ∠rpB and ∠rpA are compared later. At this time, when ∠rpB is larger than ∠rpA, ∠DpB is determined as the central angle. Otherwise, ∠ DpA is determined as the median angle. As described above, when the central angle is determined, its coordinate value is substituted into the equation (5). Then, the left and right coordinate values described above can be obtained.

When both coordinate values are obtained, the actual central angle of the target node for the purpose of the present invention is calculated with reference to the central angle calculation method (S608). Specifically, first, the angle that both coordinate values have for the target node and the target node is calculated. Subsequently, the angle that one coordinate value has for the target node and the target node is subtracted from the angle that the other coordinate value has for the target node and the target node. Then, the central angle according to the present invention can be obtained. However, since this is an angle existing on a plane, the central angle may have a negative value. Therefore, in this case, it is more preferable that the center angle is calculated by adding the other angles other than the remaining large angle from 360 degrees.

The above description is merely illustrative of the technical spirit of the present invention, and those skilled in the art to which the present invention pertains various modifications, changes, and substitutions without departing from the essential characteristics of the present invention. will be. Accordingly, the embodiments disclosed in the present invention and the accompanying drawings are not intended to limit the technical spirit of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by the embodiments and the accompanying drawings. . The scope of protection of the present invention should be interpreted 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.

As described above, according to the present invention, the base station which is infinitely supplied with energy may perform all tasks except for sensing and data communication instead of the sensor node, thereby improving the energy efficiency of the sensor node. In addition, it is possible to further extend the duration of the wireless sensor network. In addition, since the base station performs the coverage operation in a centralized manner, global clock synchronization is guaranteed. This prevents the phenomenon that a plurality of adjacent nodes are determined to sleep at the same time (i.e., an undetectable coverage-hole occurrence) that is caused when each node performs a coverage operation, thereby reducing the quality of the overall coverage. This will solve the conflict problem.

In addition, according to the present invention, it is possible to prevent the sensing of the slip node and the appearance of the unsensed area through the coverage calculation method reflecting the center angle determination method in the center angle calculation method. This has the effect of improving the quality of the wireless sensor network.

Claims (21)

delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete (a) a base station communicating with a sensor node forming a wireless sensor network, recognizing the position and identification means of the sensor node; (b) performing, by the base station, a coverage operation for determining a slip node that is included in a range in which the entire sensing area is added to the sensing areas of other sensor nodes by using the position of the sensor node and the identification means; (c) the base station sleeping the sleep node based on the coverage calculation result; (d) sensing an ambient situation by the non-sleeping sensor node; And (e) the base station receiving a sensing value from the sensor node Including; In step (b), (ba) If at least three sensor nodes are provided in the sensing field to form a group, the base station uses at least two intersection points of sensing area boundary lines between the sensor nodes included in the group by using the position and the identification means. Deriving abnormalities; And (b) the base station calculates a minimum value of an angle formed by the second sensor node located in the sensing area of the first sensor node included in the group and the derived intersection; Including, (Bb) step, (a5) Background in which the base station extracts a second sensor node predicted as the sleep node, wherein the base station determines at least two base stations including the first sensor node and determines whether the second sensor node is the sleep node. Extracting nodes; (b5) acquiring, by the base station, information about the position or direction of the second sensor node and the background nodes; (c5) The center angle of the second sensor node based on the intersection point where the base station meets the background nodes and is one of the background nodes is classified into left and right angles around the one background node. Doing; (d5) acquiring, by the base station, coordinate values of both intersections forming a minimum value from the left and right angles; And (e5) the base station calculating the center angle of the second sensor node from the coordinate values of the two intersections and performing the coverage operation; Operation method of a wireless sensor network system comprising a. The method of claim 19, In the step (e5), when the center angle due to the difference between the two angles has a negative value, a value calculated by adding the remainder obtained by subtracting the greater angle from the two angles from 360 degrees and the smaller angle of the two angles. Operating method of a wireless sensor network system, characterized in that for specifying the central angle. The method of claim 19, In the step (d5), the coordinates of the two intersections obtained by the base station is

(only,

Is the direction from sensor node p to sensor node r,

Is the angle from sensor node p to sensor node r,

Is the angle, Y _r is the Y axis coordinate of sensor node r, Y _p is the Y axis coordinate of sensor node p, X _r is the X axis coordinate of sensor node r, X _p is the X axis coordinate of sensor node p, and R is sensor Operating area of a wireless sensor network system, characterized in that the sensing area formed by the node is a radius.

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