Wireless Sensor Network (WSN) Conﬁguration Method to Increase Node Energy Efﬁciency Through Clustering and Location Information

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Article Wireless Sensor Network (WSN) Conﬁguration Method to Increase Node Energy Efﬁciency through Clustering and Location Information

Jinsoo Kim 1, Donghwan Lee 2, Jaejoon Hwang 3 , Sunghoon Hong 1, Dongil Shin 2 and Dongkyoo Shin 2,*

1 NetCom Systems Co., Ltd., #1903, Daesung D-Polis Knowledge Industry Center A, Seobusaet-Gil 606, Geumcheon-Gu, Seoul 08504, Korea; [email protected] (J.K.); [email protected] (S.H.) 2 Department of Computer Engineering, Sejong University, Seoul 05006, Korea; [email protected] (D.L.); [email protected] (D.S.) 3 Hanwha Systems, Seongnam 13524, Korea; [email protected] * Correspondence: [email protected]

Abstract: Wireless Sensor Network (WSN) technology, for services that are difficult to access or which need to be continuously monitored regardless of location, needs further research and development due to an expansion of fields where it can be applied and due to increases in efficiency. In particular, in the field of defense, research on the latest IT technologies including sensor networks is being actively conducted as an alternative to the risky use of personnel in areas such as surveillance and surveillance reconnaissance. This paper experimented with analyzing the conditions necessary for increasing the energy efficiency of the nodes constituting a sensor network using a clustering routing technique and a location-based routing technique. The derived factors include a method for selecting Citation: Kim, J.; Lee, D.; Hwang, J.; a cluster head (CH), a method for establishing a path from each channel to a base station (BS), and a Hong, S.; Shin, D.; Shin, D. Wireless method for transmitting collected data. We experimented with the derived factors and proposed a Sensor Network (WSN) WSN configuration method that increases the energy efficiency of each node by applying optimal Configuration Method to Increase results and methods that were verified experimentally. Node Energy Efficiency through Clustering and Location Keywords: Wireless Sensor Network (WSN); cluster head (CH); base station (BS); cluster-based Information. Symmetry 2021, 13, 390. routing protocol; location-based routing protocol https://doi.org/10.3390/sym13030390

Academic Editors: Simona Halunga, Octavian Fratu and Michel Planat 1. Introduction

Received: 14 January 2021 Wireless Sensor Network (WSN) technology is suitable for applications that are diffi- Accepted: 22 February 2021 cult to access or require continuous monitoring due to geographical and physical factors. Published: 27 February 2021 Recently, the importance of this technology has been highlighted due to the development of related technologies, an expansion of fields where it can be applied, and increases in Publisher’s Note: MDPI stays neutral efficiency. In particular, various sensor-related technologies based on low power are ex- with regard to jurisdictional claims in panding WSN applications to private sectors, including large-scale manufacturing, defense published maps and institutional affil- areas aimed at monitoring, natural disaster response, and social safety nets [1–3]. An iations. example of a sensor network use case in the defense field is an unmanned boundary system using Ubiquitous Sensor Network (USN) technology. In this regard, research is being conducted on the Surveillance and Reconnaissance Sensor Network (SRSN) to build an unmanned boundary system [1]. SRSN is a system that applies sensor network technology Copyright: © 2021 by the authors. to transmit sensing information in real-time according to the function of a sensor in the Licensee MDPI, Basel, Switzerland. field of surveillance reconnaissance. This article is an open access article The general physical configuration of the sensor network system applied to SRSN distributed under the terms and consists of a sensor node, base station (BS) or sinkhole, and a database/web server that conditions of the Creative Commons collects necessary data, as shown in Figure1. The sensor node performs the function of Attribution (CC BY) license (https:// transmitting data to the BS after obtaining information such as magnetic, acoustic, vibration, creativecommons.org/licenses/by/ and temperature readings [2,3]. 4.0/).

Symmetry 2021, 13, 390. https://doi.org/10.3390/sym13030390 https://www.mdpi.com/journal/symmetry Symmetry 2021, 13, x FOR PEER REVIEW 2 of 11

Symmetry 2021, 13, 390 2 of 11 transmitting data to the BS after obtaining information such as magnetic, acoustic, vibration, and temperature readings [2,3].

FigureFigure 1. 1.Wireless Wireless Sensor Sensor Network Network (WSN) (WSN) physical physical structure. structure.

TheThe physical physical configuration configuration of of a a typical typical WSN WSN system system is is as as follows: follows: Sensor Sensor nodes nodes that that transmittransmit data data directly directly to to the the BS BS are are classified classified as as routers routers or or gateways, gateways, and and sensor sensor nodes nodes thatthat transmit transmit data data to to the the routers routers or or gateways gateways are are classified classified as as end end nodes. nodes. Sensor Sensor nodes nodes correspondingcorresponding to to routers routers or or gateways gateways can can reduce reduce transmission transmission and and reception reception of meaningless of meaning- dataless bydata applying by applying a function a function of integrating of integrating the the data data of endof end nodes nodes when when designing designing and and implementingimplementing a a routing routing protocol. protocol Additionally,. Additionally, the the BS BS performs performs the the function function of of receiving receiving datadata from from the the sensor sensor node node and and transmits transmits it it to to the the database database server. server. Unlike Unlike normal normal sensor sensor nodes,nodes, the the BSBS usesuses constant power, power, thus thus it it operates operates without without being being affected affected by byenergy energy con- consumptionsumption during during data data transmission transmission and and recept reception.ion. The The database/web database/web server server analyzes analyzes the thedata data received received from from the theBS and BS andderives derives the des theired desired results results from the from corresponding the corresponding service, service,such as such boundary as boundary and surveillance and surveillance reconnaissance reconnaissance information, information, and performs and performs the function the functionof providing of providing it to the it administrator to the administrator through through the web the server. web server. InIn this this study, study, we we propose propose a a method method to to reduce reduce energy energy consumption consumption when when transmittransmit- ting/receivingting/receiving data data between between sensor sensor nodes nodes and and BSs BSs by by reflecting reflecting the the physical physical structure structure of of thethe WSN, WSN, thereby thereby increasing increasing the the lifespan lifespan of of the the nodes nodes and and the the service service life life of of the the entire entire sensorsensor network. network. TheThe composition composition of of this this paper paper is is as as follows. follows. Section Section2 reviews2 reviews related related research research that that examinesexamines routing routing methods methods to to reduce reduce the the energy energy consumption consumption of of sensor sensor nodes. nodes. Section Section3 3 proposes routing methods to reduce the energy consumption of sensor nodes. In Section4, proposes routing methods to reduce the energy consumption of sensor nodes. In Section the performance of the proposed method is verified through simulation. Section5 provides 4, the performance of the proposed method is verified through simulation. Section 5 pro- conclusions and future tasks. vides conclusions and future tasks. 2. Related Work 2. Related Work WSN studies can be divided into methods for improving the performance of the WSN systemWSN studies through can performance be divided improvementinto methods offor the improving sensor node, the performance which is a major of the component,WSN system and through methods performance for improving improvement performance of bythe reducing sensor node, energy which consumption is a major duringcomponent, data transmission/reception, and methods for improving such as throughperformance improvements by reducing in routing. energy Inconsumption this paper, weduring proposed data atransmission/reception, method to improve the such lifetime as th ofrough a WSN improvements through improvements in routing. in In routing. this pa- Accordingly,per, we proposed we compare a method and analyzeto improve various the li proposedfetime of routing a WSN protocols through forimprovements a WSN. in routing.WSN Accordingly, routing protocols we compare can be and divided analyze into various flat-based proposed protocols, routing hierarchy-based protocols for a protocols,WSN. and location-based protocols. The features of each configuration method have variousWSN advantages routing andprotocols disadvantages. can be divided into flat-based protocols, hierarchy-based protocols, and location-based protocols. The features of each configuration method have var- 2.1.ious Flat-Based advantages Protocol and disadvantages. In a flat-based protocol, each sensor node performs the same role and function and also includes the ability to collaborate with neighboring nodes to collect data. Data transmission to the BS exchanges control information with neighboring nodes to establish a transmission path and transmits the data through the established path. Typical protocols using a flat-

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2.1. Flat-Based Protocol In a flat-based protocol, each sensor node performs the same role and function and Symmetry 2021, 13, 390 also includes the ability to collaborate with neighboring nodes to collect data. Data 3trans- of 11 mission to the BS exchanges control information with neighboring nodes to establish a transmission path and transmits the data through the established path. Typical protocols basedusing protocola flat-based include protocol Sensor in Protocolsclude Sensor for Information Protocols for via NegotiationInformation (SPIN)via Negotiation [3,4] and Direct(SPIN) Diffusion [3,4] and [Direct4–6]. Diffusion [4–6]. SPINSPIN adoptsadopts thethe conceptconcept ofof metadatametadata andand usesuses aa negotiationnegotiation techniquetechnique thatthat ensuresensures thatthat onlyonly usefuluseful datadata isistransmitted transmitted whenwhen exchangingexchanging datadata betweenbetween neighboringneighboring sensorsensor nodes.nodes. This This minimizes minimizes implosion implosion and and overlapping overlapping problems problems that that occur occur in a in flat-based a ﬂat-based pro- protocoltocol when when flooding. ﬂooding. SPIN SPIN has has a adrawback drawback in in that that an an individual individual sensor node needsneeds onlyonly informationinformation about about its its immediate immediate neighbor neighbor node, node, and and if aif very a very simple simple protocol protocol or destination or destina- existstion exists far away far away and aand sensor a sensor node node in the in middlethe middle does does not not request reques datat data transmission, transmission, it mayit may fail fail to transmitto transmit data data to itsto destination.its destination. Figure Figure2 shows 2 shows the the process process of transmitting of transmitting to neighboringto neighboring nodes nodes using using the the above above three three types types of messages of messages when when sensor sensor node node A collects A col- newlectsdata new indata SPIN. in SPIN.

FigureFigure 2.2. SensorSensor ProtocolsProtocols forfor InformationInformation viavia NegotiationNegotiation (SPIN)(SPIN) datadata transmissiontransmission process.process. NodeNode A starts by advertising its data to node B (a). Node B responds by sending a request to node A (b). A starts by advertising its data to node B (a). Node B responds by sending a request to node A (b). After receiving the requested data (c), node B then sends out advertisements to its neighbors (d), After receiving the requested data (c), node B then sends out advertisements to its neighbors (d), who who in turn send requests back to B (e, f). in turn send requests back to B (e,f). Direct Diffusion is a data-centric routing protocol that propagates requests using in- Direct Diffusion is a data-centric routing protocol that propagates requests using terest inquiries from the BS and sends data through reports from sensor nodes with events interest inquiries from the BS and sends data through reports from sensor nodes with events matching the interest. In this method, the path from the sensor node to the BS is estab- matching the interest. In this method, the path from the sensor node to the BS is established lished by applying an enhancement function of the path generated in the opposite direc- by applying an enhancement function of the path generated in the opposite direction to thetion gradient, to the gradient, which is which the propagation is the propagation path of interest.path of interest. Therefore, Therefore, if the requested if the requested content ofcontent the BS of is the continuous, BS is continuous, it can be it used can be properly used properly because because data is data transmitted is transmitted to the routeto the setroute through set through route reinforcement. route reinforcement. However, However, if the request if the isrequest a one-time is a one-time event, it isevent, difﬁcult it is todifficult properly to properly apply because apply it because requires it continuous requires continuous interest inquiry interest and inquiry route and reinforcement. route rein- Symmetry 2021, 13, x FOR PEER REVIEWFigureforcement. 3 shows Figure the interest3 shows propagation the interest processpropagation in the process BS and in the the process BS and of the reporting process4 anof of11

eventreporting to the an BS event from to a the sensor BS from node a thatsensor detects node anthat event detects matching an event the matching interest. the interest.

Figure 3. Direct Diffusion data transmission process. (a) Interest propagation. (b) Gradient estab- Figure 3. Direct Diffusion data transmission process. (a) Interest propagation. (b) Gradient establish- lishment. (c) Send probe data. (d) Reinforce path. ment. (c) Send probe data. (d) Reinforce path. 2.2. Hierarchy-Based Protocol In a hierarchy-based protocol, after dividing the entire network into several groups called clusters, a cluster head (CH) representing an individual cluster is selected, and then the CH transmits data on behalf of the cluster. The CH collects data and receives data collected by general sensor nodes in the cluster, and then performs data aggregation and transmits the data to the BS. Therefore, CH may have problems in terms of energy consumption compared to normal sensor nodes, and resolution requires the ability to change the CH by taking into account the selection of CH, the duration of the CH role, etc., as well as the derivation of the required number of clusters across the entire network and the scope of clusters. Typical examples of hierarchy-based protocols are Low-Energy Adap- tive Clustering Hierarchy (LEACH) [7] and Energy-Efficient Uneven Clustering (EEUC) [8]. LEACH is the beginning of a hierarchy-based protocol for WSN, and clusters the entire network to create groups and then selects the CH for each cluster. At this time, the CH manages all sensor nodes in the cluster, and the data transmitted by the sensor nodes are integrated and transmitted to the BS. Therefore, CH consumes more energy than a general sensor node. To address this, a separate CH is selected for each round. When selecting a CH in LEACH, all sensor nodes in the cluster are eligible to be equally selected as CH, which causes all sensor nodes to consume energy evenly. However, a limitation of LEACH is that it does not reflect energy consumption according to the physical location of the sensor node when selecting CH. Based on the distance between the BS and the sensor nodes, EEUC configures a cluster with a smaller range of clusters located closer to the BS than other clusters. This is because the CH in the cluster close to the BS performs a relay function of data transmitted from the other CH to the BS, so energy consumption is large. However, as shown in Figure 4, EEUC operates smoothly when sensor nodes close to the BS are evenly distributed. There is a disadvantage in this approach in that the energy of the sensor nodes adjacent to the BS is rapidly consumed.

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2.2. Hierarchy-Based Protocol In a hierarchy-based protocol, after dividing the entire network into several groups called clusters, a cluster head (CH) representing an individual cluster is selected, and then the CH transmits data on behalf of the cluster. The CH collects data and receives data collected by general sensor nodes in the cluster, and then performs data aggregation and transmits the data to the BS. Therefore, CH may have problems in terms of energy consumption compared to normal sensor nodes, and resolution requires the ability to change the CH by taking into account the selection of CH, the duration of the CH role, etc., as well as the derivation of the required number of clusters across the entire network and the scope of clusters. Typical examples of hierarchy-based protocols are Low-Energy Adaptive Clustering Hierarchy (LEACH) [7] and Energy-Efficient Uneven Clustering (EEUC) [8]. LEACH is the beginning of a hierarchy-based protocol for WSN, and clusters the entire network to create groups and then selects the CH for each cluster. At this time, the CH manages all sensor nodes in the cluster, and the data transmitted by the sensor nodes are integrated and transmitted to the BS. Therefore, CH consumes more energy than a general sensor node. To address this, a separate CH is selected for each round. When selecting a CH in LEACH, all sensor nodes in the cluster are eligible to be equally selected as CH, which causes all sensor nodes to consume energy evenly. However, a limitation of LEACH is that it does not reflect energy consumption according to the physical location of the sensor node when selecting CH. Based on the distance between the BS and the sensor nodes, EEUC configures a cluster with a smaller range of clusters located closer to the BS than other clusters. This is because the CH in the cluster close to the BS performs a relay function of data transmitted from the other CH to the BS, so energy consumption is large. However, as shown in Figure4, EEUC operates smoothly when sensor nodes close to the BS are evenly distributed. There Symmetry 2021, 13, x FOR PEER REVIEWis a disadvantage in this approach in that the energy of the sensor nodes adjacent to the5 of BS 11

is rapidly consumed.

Figure 4. Energy-Efficient Uneven Clustering (EEUC) operation process. Figure 4. Energy-Efﬁcient Uneven Clustering (EEUC) operation process. 2.3.2.3. Location-Based Location-Based Protocol Protocol AA location-based location-based protocol protocol uses uses the the location location information information of of the the sensor sensor node node and and BS BS to to setset the the transmission transmission path path of of the the collected collected data. data. Therefore, Therefore, a a location-based location-based protocol protocol does does notnot require require separateseparate energy consumption consumption for for pa pathth setting setting or or maintenance. maintenance. Geographic Geographic and andEnergy-Aware Energy-Aware Routing Routing (GEAR) (GEAR) [9] is [9 a] repres is a representativeentative example example that can that minimize can minimize band- bandwidthwidth consumption. consumption. GEARGEAR is is divided divided into into a a step step that that transmits transmits a a packet packet from from a a BS BS to to a a target target region region and and anotheranother stepstep toto propagate a a packet packet within within a atarget target region. region. When When transmitting transmitting packets packets from fromthe BS the to BS the to target the target area, area, gradual gradual routing routing is used is used so that so that neighboring neighboring sensor sensor nodes nodes use useenergy energy evenly evenly by applying by applying the concept the concept of learning of learning cost and cost prediction and prediction cost. In cost. the Inpacket the propagation stage within the region, a recursive transmission method using location information is applied instead of flooding, which consumes much energy. The recursive transmission technique is a method of dividing a target region into sub-regions and then copying and propagating packets to each sub-region. However, when the density of the sensor node in the target area is low and the communication range of the sensor node does not reach the entire sub-area, packet propagation is performed inside the area using limited flooding, which limits the hop count of packets to 1 or 2.

3. Suggested Techniques 3.1. WSN Operating Process The proposed WSN routing method simultaneously applies a cluster-based protocol and location-based protocol. Figure 5 shows the detailed configuration and operation process of the WSN. Cluster selection can be preset in a grid pattern due to the introduction of a location-based protocol, and each node collects the cluster information based on the acquired location information and then sets the CH to transmit the collected information to the CH of the cluster. CH integrates this and transmits it to BS, and when transmitting data from CH to BS, a Shortest Path First (SPF) algorithm is applied to minimize energy consumption during long-distance transmission.

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packet propagation stage within the region, a recursive transmission method using location information is applied instead of ﬂooding, which consumes much energy. The recursive transmission technique is a method of dividing a target region into sub-regions and then copying and propagating packets to each sub-region. However, when the density of the sensor node in the target area is low and the communication range of the sensor node does not reach the entire sub-area, packet propagation is performed inside the area using limited ﬂooding, which limits the hop count of packets to 1 or 2.

3. Suggested Techniques 3.1. WSN Operating Process The proposed WSN routing method simultaneously applies a cluster-based protocol and location-based protocol. Figure5 shows the detailed conﬁguration and operation process of the WSN. Cluster selection can be preset in a grid pattern due to the introduction of a location-based protocol, and each node collects the cluster information based on the acquired location information and then sets the CH to transmit the collected information to the CH of the cluster. CH integrates this and transmits it to BS, and when transmitting Symmetry 2021, 13, x FOR PEER REVIEW 6 of 11 data from CH to BS, a Shortest Path First (SPF) algorithm is applied to minimize energy consumption during long-distance transmission.

FigureFigure 5.5. WSNWSN operatingoperating process.process.

3.2.3.2. PerformancePerformance ImprovementImprovement ConsiderationsConsiderations forfor WSNWSN ConﬁgurationConfiguration InIn thisthis study,study, wewe pre-setuppre-setup clustersclusters basedbased onon locationlocation informationinformation andand obtainobtain clustercluster informationinformation toto whichwhich thethe nodesnodes belongbelong toto derivederive factorsfactors thatthat affectaffect thethe performanceperformance ofof WSN,WSN, suchsuch asas shownshown inin TableTable1 ,1, which which include include the the following following considerations. considerations.

TableTable 1. 1.WSN WSN performanceperformance improvementimprovement considerations. considerations.

SortationSortation Considerations Considerations

- Residual- Residualenergy of energy sensor of sensornode node CH Selection - Position of sensor node (distance from the center of CH Selection - Position of sensor node (distance from the center cluster) of cluster) Choosing a route be- - Energy consumption during direct communication tween CH and BS between- CHEnergy and consumption BS by way duringof CH direct communication Choosing a route between CH and BS between CH and BS by way of CH 3.3. Suggested Routing Protocol 3.3. SuggestedThe proposed Routing routing Protocol protocol suggests the way to minimize energy consumption in an environmentThe proposed where routing each protocol node acquires suggests ph theysical way location to minimize and cluster energy information consumption in inadvance. an environment In addition, where through each nodethis method, acquires energy physical consumption location and is cluster evenly information distributed inamong advance. nodes In to addition, improve through network this life method, and ensu energyre smooth consumption operation. is The evenly proposed distributed protocol is divided into a CH selection step, a channel selection step between CH and BS, and a collection data transmission step.

3.3.1. CH Selection The proposed protocol works for each round like LEACH. CH selection for each cluster is selected in consideration of the residual energy of each sensor node and the position of the sensor node derived from the WSN performance improvement considerations of Table 1. Each cluster selects a CH that transmits data to BS every round, and a score function is introduced for CH selection. The conditions of the node to be selected as CH are as follows: 1. Nodes with high residual energy. 2. Nodes close to the center of the cluster. It is possible to calculate the center of the cluster and the distance of the sensor nodes by using the Global Positioning System (GPS) installed by each sensor node. The reason for introducing the weight is to determine which of the above conditions should be weighted. The following score function is introduced for this purpose:

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among nodes to improve network life and ensure smooth operation. The proposed protocol is divided into a CH selection step, a channel selection step between CH and BS, and a collection data transmission step.

3.3.1. CH Selection The proposed protocol works for each round like LEACH. CH selection for each cluster is selected in consideration of the residual energy of each sensor node and the position of the sensor node derived from the WSN performance improvement considerations of Table1 . Each cluster selects a CH that transmits data to BS every round, and a score function is introduced for CH selection. The conditions of the node to be selected as CH are as follows: 1. Nodes with high residual energy. 2. Nodes close to the center of the cluster. It is possible to calculate the center of the cluster and the distance of the sensor nodes by using the Global Positioning System (GPS) installed by each sensor node. Symmetry 2021, 13, x FOR PEER REVIEW 7 of 11 The reason for introducing the weight is to determine which of the above conditions should be weighted. The following score function is introduced for this purpose:

1 Score(CH ) = αE + (1 − α)1 (1) Score i 1i 2 D i (1) In Equation (1), E is the amount of remaining energy of sensor node i in a cluster, In Equation (1), i is the amount of remaining energy of sensor node i in a cluster, D is the distance between sensor node i and the center of the cluster, and α(0 ≤ α ≤ 1) i is the distance between sensor node i and the center of the cluster, and α0 α 1 isis the the weight. weight. ByBy applyingapplying Equation (1), the the node node with with the the highest highest score score in in each each cluster cluster is isselected selected as as CH. CH. When When selecting selecting the the CH CH node, node, the the selection selection of ofthe the weight weight (α) ( αcan) can affect affect the theperformance performance of the of theproposed proposed routing routing protocol, protocol, so the so theoptimal optimal weight weight was was selected selected by per- by performingforming the the following following simulation. simulation. α FigureFigure6 6shows shows that that the the results results in in a a round round with with 100 100 nodes nodes are are down down when when weight weight ( (α)) isis 0.8. 0.8. If If 100 100 nodes nodes go go down down in in the the 522nd 522nd round, round, it it provides provides optimal optimal results. results. Based Based on on this this α result,result, this this study study applied applied 0.8 0.8 to to weight weight ( (α).).

FigureFigure 6. 6.Round Round when when 100 100 nodes nodes by by weight weight are are down. down.

3.3.2.3.3.2. Route Route Selection Selection between between CH CH and and BS BS AfterAfter thethe CHCH isis selected,selected, aa pathpath settingsetting stepstep isis requiredrequired toto transmittransmit datadata toto thethe BS.BS. TransmittingTransmitting data data directly directly from from CH CH to to BS BS consumes consumes a considerable a considerable amount amount of energyof energy due due to theto the relatively relatively large large transmission transmission distance. distance. To solve To solve this this problem, problem, the shortestthe shortest transmission transmis- pathsion betweenpath between CH and CH BS and is selected BS is selected by applying by applying a Dijkstra a algorithmDijkstra algorithm [10]. To this [10]. end, To thethis operationend, the operation process is process as follows: is as follows: 1. Nodes selected as CH transmit node location information to BS. 2. BS calculates the shortest transmission path between BSs in individual CHs by using the location information of the aggregated CH nodes. 3. BS transmits the calculated shortest path (next hop of individual CH) to the corresponding CH.

3.3.3. Collection Data Transmission The nodes belonging to the cluster transmit the collected data to the CH of the corresponding cluster, and the CH performs the process of collecting and integrating the received data. According to Reference [11], more than 50% of the total energy consumed by WSN occurs during data transmission. Therefore, the process of integrating aggregated data to reduce the amount of data transmitted from CH to BS is recognized as an important function. The CH transmits the integrated data to the BS, and the BS collects the data received from each CH and sends it to the database/web server to perform the service.

4. Performance Evaluation

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1. Nodes selected as CH transmit node location information to BS. 2. BS calculates the shortest transmission path between BSs in individual CHs by using the location information of the aggregated CH nodes. 3. BS transmits the calculated shortest path (next hop of individual CH) to the corresponding CH.

3.3.3. Collection Data Transmission The nodes belonging to the cluster transmit the collected data to the CH of the corresponding cluster, and the CH performs the process of collecting and integrating the received data. According to Reference [11], more than 50% of the total energy consumed by WSN occurs during data transmission. Therefore, the process of integrating aggregated data to reduce the amount of data transmitted from CH to BS is recognized as an important function. The CH transmits the integrated data to the BS, and the BS collects the data received from each CH and sends it to the database/web server to perform the service.

4. Performance Evaluation To evaluate the performance of the proposed routing protocol, we utilized LEACH, a representative routing protocol, and did performance analysis. The performance evaluation criteria considered the number of surviving nodes and the amount of energy consumed by the surviving nodes after each round of transmission.

4.1. Performance Evaluation Environment The simulation was conducted using C language, and the WSN range was set to 200 × 200, and 16 clusters with a range of 50 × 50 were applied. The sensor node randomly placed 200 nodes, and the BS determined a ﬁxed location to perform performance evaluation. In addition, to reduce the variation in data values caused by random node positioning, the performance evaluation results averaged the values performed in 100 topologies. Table2 shows the values of the main variables used in the performance evaluation.

Table 2. Performance evaluation environment variables.

Environment Variable Value BS (Base Station) (210, 210) Number of Nodes 200 Initial energy/node 20 J

Eelec 50 nJ/bit 2 Ef s 7 nJ/bit/m 2 Eamp 100 pJ/bit/m 2 Emp 0.0013 pJ/bit/m Control Data Size 10 Byte (80 bit) Packet Size 250 Byte (2000 bit)

4.2. Protocol Performance Evaluation Result and Analysis To evaluate the performance of the proposed protocol, the number of surviving nodes per round was compared and analyzed for direct communication, LEACH protocol, and proposed technique. As shown in Figure7, after performing 200 rounds, 39 nodes, 20% of all nodes, survive. In contrast, in the proposed protocol and LEACH, more than 95% of all nodes survive after 200 rounds. After 400 rounds, the proposed protocol shows that more than 90% of the 181 nodes survived, while for LEACH, 47% of the 94 nodes survived, indicating that the proposed protocol survived by 43% or more compared to LEACH. This is because the proposed protocol up to 400 rounds uses energy more evenly and efﬁciently at the sensor node compared to LEACH. Surviving nodes are the same number in the Symmetry 2021, 13, 390 8 of 11

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Symmetry 2021, 13, x FOR PEER REVIEW 9 of 11 proposed protocol and LEACH at 700 rounds, where both measures cannot be signiﬁcant because only 3% of the nodes survive and cannot perform the services of WSN.

FigureFigure 7. 7.Survival SurvivalSurvival nodes nodes nodes per per per round. round. round.

TheThe singularity singularitysingularity is is is that that that after after after 700 700 700 rounds, rounds, rounds, the the the direct direct direct communication communication communication method method method survives survives survives withwith more more nodes nodesnodes than thanthan LEACH LEACH LEACH or or or the the the proposed proposed proposed method. method. method. The The The reason reason reason is is that that is asthat as shown shown as shown in in in FigureFigure8 ,8, a a fewa fewfew sensor sensorsensor nodes nodes nodes located located located close close close to to the tothe BSthe BS do BS do not do not consumenot consume consume much much much energy energy energy due due to dueto to thethe relatively relatively small smallsmall distance distance distance when when when transmitting transmitting transmitting data data data to to the tothe the BS. BS. However,BS. However, However, these these these are are only onlyare only 4.5%4.5% (9) (9) of ofof the thethe surviving survivingsurviving sensor sensor sensor nodes, nodes, nodes, and and and in in this inthis this situation, situation, situation, the the WSNthe WSN WSN service service service cannot cannot cannot be be be smoothlysmoothly performed. performed.performed.

Figure 8. Distribution of surviving nodes among direct communication nodes after 700 rounds. FigureFigure 8. 8.Distribution Distribution of of surviving surviving nodes nodes among among direct direct communication communication nodes nodes after after 700 rounds. 700 rounds. Figure 9 shows the average energy consumption of each node per round. After 50 rounds,FigureFigure the9 showsproposed9 shows the theprotocol average average consumes energy energy consumption 30–40%consumption less ofenergy eachof each nodethan node the per averageper round. round. LEACH After After 50 50rounds,per rounds, node, the and the proposed proposedthe trend protocolcontinues, consumesconsumes and after 30–40% 30030–40% rounds, less less energy the energy average than than theconsumes averagethe average more LEACH thanLEACH perper30% node, node, less energy and and the the per trend trend node continues, continues, than LEACH. and and after This after 300 means 300 rounds, rounds, that the the averagethe sensor average nodes consumes consumes in the more proposed more than than 30%30%protocol less less energy useenergy energy per per node morenode than uniformlythan LEACH. LEACH. and This Thiseffi meansciently means that than that the LEACH. sensorthe sensor nodes After nodes in 700 the inrounds, proposed the proposed the protocolprotocolaverage useenergy use energy energy consumption more more uniformly uniformly per node and andshows efﬁciently effi necientlyar-similar than than LEACH. energyLEACH. After consumption After 700 rounds,700 rounds,in both the the average energy consumption per node shows near-similar energy consumption in both the averagethe proposed energy protocol consumption and LEACH. per Atnode this shows point, bothnear-similar protocols energy are alive consumption with only sensor in both proposed protocol and LEACH. At this point, both protocols are alive with only sensor thenodes proposed of less thanprotocol 5% and and therefore LEACH. WSN’s At this servicespoint, both cannot protocols be performed are alive and with cannot only sensorbe nodesconsidered. of less In than addition, 5% and the therefore proposed WSN’s protocol services consumes cannot 70% be to performed 80% less energy and cannot than be direct communication per node up to 200 rounds, and the difference gradually becomes considered. In addition, the proposed protocol consumes 70% to 80% less energy than direct communication per node up to 200 rounds, and the difference gradually becomes

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Symmetry 2021, 13, x FOR PEER REVIEW 10 of 11 nodes of less than 5% and therefore WSN’s services cannot be performed and cannot be considered. In addition, the proposed protocol consumes 70% to 80% less energy than directsmaller. communication This is because per in node direct up tocommunication, 200 rounds, and most the difference nodes consume gradually energy becomes in the first smaller.200smaller. rounds, This This isand is because because more in than in direct direct 80% communication, communication,of the nodes afterwards most most nodes nodes consumedo not consume work energy properly.energy in the in ﬁrst the first 200200 rounds, rounds, and and more more than than 80% 80% of theof the nodes nodes afterwards afterwards do not do worknot work properly. properly.

Figure 9. Average energy consumption per node per round. FigureFigure 9. 9.Average Average energy energy consumption consumption per per node node per round.per round. Figure 10 shows the residual energy distribution of all sensor nodes after 400 rounds FigureFigure 10 10 shows shows the the residual residual energy energy distribution distribution of all of sensor all sensor nodes no afterdes after 400 rounds 400 rounds of communication by applying the proposed protocol. When a cluster is located closer to ofof communication communication by by applying applying the the proposed proposed protocol. protocol. When When a clustera cluster is locatedis located closer closer to the BS, the residual energy of the sensor nodes existing in the cluster decreases. In the tothe the BS, BS, the the residual residual energyenergy ofof the the sensor sensor nodes nodes existing existing in thein the cluster cluster decreases. decreases. In the In the proposed protocol, CHs located at a distance from the BS transmit data via a CH adjacent proposedproposed protocol, protocol, CHs CHs located located at aat distance a distance from from the BSthe transmit BS transmit data data via a via CH a adjacent CH adjacent tototo the thethe BS BS without without transmitting transmittingtransmitting data datadata directly directly directly to the to to BS the the to BS reduce BS to to reduce reduce energy energy consumptionenergy consumption consumption due to due due long-distancetoto long-distancelong-distance data datadata transmission. transmission.transmission. That is,That That nodes is, is, no no indes thedes in cluster in the the cluster adjacentcluster adjacent adjacent to the BSto to the consume the BS BS consume consume a largeaa largelarge amount amount of energy of energyenergy for relay forfor relayrelay transmission transmissi transmissi ofon dataon of of transmitted data data transmitted transmitted from the from from other the the different other other differ- differ- CHs to the BS. entent CHs to the BS.

FigureFigure 10. Residual energyenergy distributiondistribution of of sensor sensor nodes nodes after after 400 400 rounds rounds (proposed (proposed protocol). protocol). Figure 10. Residual energy distribution of sensor nodes after 400 rounds (proposed protocol).

5.5.5. Conclusions Conclusions InIn this this paper, paper, we wewe proposed proposedproposed a method a a method method to extend to to extend extend the servicethe the service service life oflife life WSN of of WSN byWSN improving by by improving improving thethethe uniform uniformuniform energy energy use useuse in inin sensorsensor sensor nodesnodes nodes byby by simultaneouslysi simultaneouslymultaneously applyingapplying applying thethe the cluster-basedcluster-based cluster-based pro- pro- tocoltocol and the location-based protocol. protocol. The The perf performanceormance of of the the proposed proposed protocol protocol was was eval- eval- uateduated and analyzed throughthrough simulation,simulation, an andd the the proposed proposed protocol protocol showed showed improved improved resultsresults in terms ofof thethe numbernumber of of survivin survivingg nodes nodes per per round round and and the the average average energy energy con- con- sumptionsumption per node perper roundround compared compared to to the the comparative comparative protocol, protocol, LEACH. LEACH. Compared Compared toto LEACH,LEACH, which sequentiallysequentially selects selects CH, CH, the the proposed proposed protocol protocol selects selects CH CH based based on on the the sensorsensor node’s location informationinformation and and residual residual energy, energy, so so that that the the energy energy of of each each sensor sensor

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protocol and the location-based protocol. The performance of the proposed protocol was evaluated and analyzed through simulation, and the proposed protocol showed improved results in terms of the number of surviving nodes per round and the average energy consumption per node per round compared to the comparative protocol, LEACH. Compared to LEACH, which sequentially selects CH, the proposed protocol selects CH based on the sensor node’s location information and residual energy, so that the energy of each sensor node can be used more evenly and efﬁciently. In addition, the simulation shows that LEACH sends data directly from all CH to BS, while the proposed protocol reduces energy consumption by allowing CH to pass if there is a CH in the middle of the path to reduce energy consumption when transmitting data from CH to BS. However, looking at the energy consumption distribution of each node in the proposed protocol, as the distance from the base station increases, the energy consumption of the sensor node adjacent to the base station increases and the energy consumption decreases. This is a phenomenon that occurs when a channel of a clusters adjacent to the base station continuously relays data transmitted by another channel to the base station. To solve this problem, it is necessary to study how to set the optimal number of clusters and cluster range by using the total number of sensor nodes of the WSN and the location information of each sensor node. In addition, the BS’s location-based approach [12] can overcome the limitations revealed by the Restriction Protocol. In future research, we will continue to study two methods, how to determine the number of clusters to be set and how to transmit access depending on the location of the base station.

Author Contributions: J.K. and D.S. (Dongkyoo Shin) proposed the WSN configuration method detection and identified papers for the review; S.H., D.S. (Dongil Shin) and J.H. reviewed the papers, gathering information; J.K. and D.L. wrote the main manuscript text; D.S. (Dongkyoo Shin) reviewed the manuscript. All authors have read and agreed to the published version of the manuscript. Funding: This work was supported by the Defense Acquisition Program Administration and Agency for Defense Development under the contract UD190016ED. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Not applicable. Conflicts of Interest: The authors declare no conflict of interest.

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