Ultrasonic Sensor System for Ecology Observation and Timing Synchronization of ZigBee Network

Transcription

1 Ulrasonic Sysem for Ecology Observaion and Timing of ZigBee Nework Asushi MORIKAWA, Hiroshi YAMAMOTO, Maki YAMAMOTO, Kasuyuki YAMAZAKI Nagaoka Universiy of Technology, Kamiomioka, Nagaoka, Niigaa Japan Absrac Timing synchronizaion is essenial in case where muliple sensor nodes wih ulrasonic sensors are deployed on he same place. This is because he ulrasonic sensors should be powered a an appropriae iming so as o preven ulrasonic inerference. In his paper, we propose a harmful bird aack sysem and a new iming synchronizaion mehod for ZigBee sensor nework. In his iming synchronizing mehod, by concenraing he processing load o he server, he amoun of calculaion on each node can be minimized and is unaffeced by he increase in he number of nodes. Evaluaion of he proposed mehod has shown ha i sufficienly fulfills he iming requiremen for he proposed harmful birds aack sysem. Keywords Nework, ZigBee, Ulrasonic Disance, Timing, Reference Broadcas I. INTRODUCTION Environmenal and ecology observaion have been performed by human beings (ecologiss) wih a limied se of equipmen. However, a field of he observaion is very severe for he ecologiss o walk around freely, hence he real-ime observaion have no been performed. A sensor nework is an emerging echnology for he real-ime observaions, which makes i possible o auomaically collec daa from a large number of sensors dispersed over a vas field. On he oher hand, iming synchronizaion is needed in case where muliple sensor nodes such as ulrasonic sensors are deployed on he same place. This is because he ulrasonic sensors should be powered a an appropriae iming so as o preven ulrasonic inerference. However, exising iming synchronizaion mehods [1] [4] have hose problems as hey require a processing power o sensor nodes, and hence do no scale well when many and low-cos sensor nodes are o be deployed. Therefore, in his paper, we propose a new iming synchronizaion mehod on ZigBee sensor nework. In he proposed sysem, he amoun of processing on each node is unaffeced by he increase in he number of nodes, hence i can be used widely for low-cos sensor nodes. An ecology observaion is an example use of he proposed mehod, which is also presened in his paper. II. RELATED WORKS AND OBJECTIVES OF THIS STUDY A. Issues of Harmful Birds In recen years, he number of predaion damages by harmful birds such as herons and grea cormorans has been increasing. These birds have a high level of submerging, flying and breeding abiliies, and ea wide variey of fishes. I was repored ha esimaed damage in 2007 was abou 7.3 billion yen [5]. A fishway is a srucure consruced for fishes o he upper sream over barriers (such as dams) as shown in Figure 1 [6]. However, many fishes are eaen here by birds because fishes should pass he narrow way, and hence become easy arges. Ascending of salmon has a criical role o keep ecosysem in a river, hence he predaion issue has no only a risk of fishery damages bu also a risk of ecosysem desrucion. Figure 1. Fishway Figure 2 shows a fishing weir, which is one of he raps for river fishes. The fishing weir enables o capure a lo of fishes (e.g., sweefishes) effecively. Those capured sweefishes are subjec o culivaion for appropriaely mainaining ecological environmen in a river. In hese fishing weirs, here are also predaion problems of he fish by harmful birds. ISBN February 16~19, 2014 ICACT2014

2 Camera Flashing Ligh Daa Acquisiion Acuaor Conrol Timing Speaker ZigBee Bird Figure 2. Fishing weir B. Use of Nework Unil now, a fishway and a fishing weir have been defended by a sound of a radio or a scarecrow. However, he birds are very clever, and become accusomed o he monoonous simulaion. Therefore, a variey of simulaions is needed in order o scare hem off effecively in he long run. In his sudy, we propose o solve he problem by inroducing a wireless sensor nework ha deecs birds using muliple sensors (e.g., ulrasonic sensors) and scares hem away by acuaing various aacking devices dynamically. C. ZigBee Nework A ZigBee sensor nework is appropriae for ecology observaion. A use of ZigBee echnology was uilized for observaion of birds ha build a nes on a seep hill [7], [8]. In addiion, cos reducions and miniaurizaions of boh sensors and communicaion modules are ensured in recen years. As a resul, hey enable us o deploy many sensor nodes. However, cooperaion among muliple sensor nodes ha have acuaors or ulrasonic sensors needs a iming synchronizaion. Furhermore, a sensor nodes used for ZigBee sensor nework is no inended for a lo of communicaion and calculaion. Considering hese siuaions, we propose a new iming synchronizaion mehod ha is suiable for ZigBee sensor neworks. III. OVERVIEW OF THE PROPOSED SYSTEM A. Overview of he Sysem Figure 3 shows an overview of a proposed harmful bird aack sysem, and he devices uilized for he sysem are summarized in Table 1. The sensor nework is consruced by sensor nodes [9], sensor arrays o deec birds, several bird aack devices and a server. The sensor array consiss of ulrasonic disance sensors ha are arranged in an arc shape so as o measure a wide area. The sensor node obains sensor daa from he sensor arrays, and ransmis ha o he server hrough ZigBee nework. The proposed sysem uses hree differen kind of aacking devices (speakers, flashing lighs and guns) so as o give various simuli. If birds are deeced by he sensors, he aacking devices drive off hem. Server ZigBee Timing Gun Array Node Figure 3. Overview of he harmful birds aack sysem Prevening Inerference of Ulrasonic Waves TABLE 1. DEVICES CONSTRUCTING THE PROPOSED SYSTEM Role Device Noe server Soring sensed daa ZigBee Conrolling he sensors and he communicaion node aacking devices Bird deecion array Consruced by ulrasonic sensors Flashing ligh Bird aacking Gun Conrolled by he sensor nodes Speaker Conrolled by he sensor server Acquiring Insalled for an experimenal Camera reference daa evaluaion B. Proposed Ulrasonic Array There are many sudies of bird deecion mehod using camera images [10], [11]. However, accuracy of he deecion is affeced by changes of brighness around he camera, and i canno be used a nigh. Therefore, a sensor array ha consiss of several ulrasonic disance sensors is proposed as illusraed in Figure 4. Coverage of one ulrasonic sensor array node Ulrasonic disance sensor Bird daa Bird deecion noificaion Figure 4. Bird deecion mehod using a sensor array Server ISBN February 16~19, 2014 ICACT2014

3 Here, when muliple ulrasonic sensors are used a he same ime, hey canno ge he correc resuls due o inerference of heir ulrasonic waves shown in Figure 3. Therefore, he sensor node mus accuraely conrol ON/OFF of each sensor so as o preven he inerference. IV. PROPOSED TIME SYNCHRONIZATION METHOD FOR ZIGBEE SENSOR NETWORK A. Timing Requiremen of Nodes When muliple sensor arrays are uilized, he inerference beween ulrasonic sensors mus be avoided. Therefore, i is necessary o synchronize he iming beween he sensor nodes and conrol he ulrasonic sensors so as o avoid he inerference among he sensor arrays conneced o differen sensor nodes as illusraed in Figure 5. The ulrasonic disance sensor used in he sysem is XL- MaxSonar-EZL0 [12]. I generaes ulrasonic waves, and a disance from an objec is calculaed from a ime inerval beween generaing waves and receiving he echo. The maximum range of he sensor is 1067 [cm] and he sound velociy a sea level is 340 [m/s], hence he maximum ime inerval for ransmiing he ulrasonic is 61.9 [ms]. On he oher hand, in he previous sudy [13], we have performed a people observaion by using he sensor array. From his sudy, i has been found ha he sensor array can accuraely deec a pedesrian by operaing each sensor a every 100 [ms]. Therefore, we assume ha he sensor can deec a bird by he same sampling rae as he previous research. In order o operae he sensors a every 100 [ms], he synchronizaion error should be decreased lower han 38.1 ( ) [ms], which becomes he requiremen for he iming synchronizaion beween sensor nodes. Node Conrol Signal 1 100[ms] [ms] Ulrasonic s 1 2 Synchronizing he Timing 3 4 Conrol Signal 3 4 B. Issues of s in ZigBee Nework NTP (Nework Time Proocol) [1], [2] is ofen used as a iming synchronizaion mehod on he Inerne, and synchronizes a clock of a node o he NTP server. However, he sensor nework in our sudy does no need an absolue ime, bu requires synchronized iming among nodes. In addiion, he NTP can no be used wihou connecing o he Inerne, and he sensor nework may be deployed in rural areas where an Inerne access canno be provided. On he oher hand, PTP (Precision Time Proocol) [14], [15] is a proocol ha enables erminals o accuraely synchronize wih ohers. However, he PTP should be implemened a a hardware-level, and hence canno be easily adaped o he sensor nework. Furhermore, GPS (Global Posiioning Sysem) [16] is also used as a iming synchronizaion mehod. The ime synchronizaion mehod using he GPS akes high cos and consumes oo much power because a lo of compuaion is needed. In addiion, i canno be used in a place where he radio wave from he saellie is blocked by he special errain or plans. Thus, he mehod is no suiable for he sensor nework. In he sensor neworks, RBS (Reference Broadcas ) [3], [4] is a candidae for he iming synchronizaion mehod. The procedures of he RBS are summarized as follows. 1. A server broadcass a packe for synchronizaion called a reference packe. 2. Nodes receiving he packe record an arrival ime of he reference packe. 3. The recorded ime informaion is exchanged among nodes. 4. Each node calculaes he ime difference beween he own node and a reference node (e.g., he node wih he earlies clock) based on he ime informaion, and ses he ime so ha he difference becomes zero. In RBS, each node calculaes correcion ime, hence he amoun of calculaion in each node increases wih he increase in he number of nodes. However, many wireless sensor nodes do no have high processing power because a power saving performance ofen has he highes prioriy for an ecology observaion. Thus, RBS is no appropriae for he objecive. Considering hese siuaions, we propose a scalable iming synchronizaion mehod for ZigBee sensor nework as an expansion of RBS. C. Procedure of Proposed Timing Mehod The sensor nodes used in his sudy do no need a real ime clock. Therefore, a value of a couner based on he CPU clock is a arge of he synchronizaion. Figure 5. Timing synchronizaion ISBN February 16~19, 2014 ICACT2014

4 V. EVALUATION OF THE PROPOSED TIMING SYNCHRONIZATION METHOD Server Node 1 Node 2 Node 3 Reference Packe + Informaion Couner Value Find he Earlies Couner Value Reference Packe + Informaion Couner Drif Wai a Random Time Couner Value Couner Drif Wai a Random Time Couner Value Figure 6. Sequence of he proposed synchronizaion mehod Couner Drif Wai a Random Time We propose a new iming synchronizaion mehod ha can reduce he compuaional load on each sensor node. Figure 4 represens he sequence of he proposed synchronizaion mehod. In he mehod, all nodes should be insalled in a locaion where hey are able o communicae direcly wih he server. Timing synchronizaion is performed as he following seps. 1. Iniializaion Process A server broadcass a packe for synchronizaion called a reference packe. Each node obains a couner value when receiving he reference packe. 2. Couner Process Afer a random inerval is passed, he node sends he value of he couner o he server. The server finds he earlies couner value and sends he nex reference packe including he value. Each node obains he couner value a he arrival ime of he packe, and adjuss is couner o ha of he earlies node. In addiion, a node ha has a slow speed CPU clock should correc is drif. Thus, if a node correced is couner hree imes coninuously, i performs he drif correcion process below. 3. Drif Process The node calculaes differences beween is couner and he earlies node s couner per uni ime as a correcion value. The median value of he las hree correcion values is added o is icking. By concenraing he processing load o he server, he amoun of calculaion on a node can be reduced, and unaffeced by he increase in he number of nodes. A. Condiions of he Experimen To evaluae he proposed iming synchronizaion mehod, we have implemened he proposed mehod o wo sensor nodes and a server. Firs, a synchronizaion inerval is se. When he wo nodes are no synchronized, heir clocks drif 1.0 [ms] per a second. Before he drif correcion, a maximum synchronizaion inerval is deermined by he following equaion. (1) 2 is a arge value of iming synchronizaion accuracy, and is a drif rae of clocks. In he environmen, he drif rae of he sensor nodes is 0.1 [%]. In addiion, he synchronizaion accuracy should be reduced lower han 38.1 [ms] as menioned in Secion IV. Accordingly, he synchronizaion should be execued a inervals of derived by Eq. (2) or shorer ime inerval [ ms] 19.1[ s] (2) In our evaluaion, he synchronizaion inerval is se o 15.0 [s] in order o adequaely mee he iming requiremen. B. Resuls and Discussions Figure 7 shows he difference of he couner values beween he wo nodes when hey are no synchronized and when hey are synchronized by he proposed mehod. Under he condiion of he nodes wihou iming synchronizaion, he difference of he couner values is linearly increased by he error of clock. On he oher hand, he difference is suppressed by synchronizing he iming. Difference of couner values beween nodes[msec] Wihou iming synchronizaion Wih iming synchronizaion Timing requiremen Elapsed ime[sec] Figure 7. Difference of couner values The iming synchronizaion process is clearly shown in Figure 7. Firs, each node receives a reference packe wihou a synchronizaion informaion when elapsed ime is 0 [s]. Then, afer 15 [s] passed, he nodes receive he nex reference packe, and he delayed node correcs is couner o ha of he ISBN February 16~19, 2014 ICACT2014

5 earlier node. Similarly, he couner correcion is performed a 30 [s] and 45 [s]. Afer he process is performed hree imes coninuously by he same node, he drif correcion is processed, and hence he difference of he couner value remains saic. Afer he fourh couner correcion, i remains almos he same. The iming synchronizaion is compleed afer he fourh couner correcion a he earlies. Saisics of he difference of he couner values from ha ime are summarized in Table 2. TABLE 2. STATISTICS OF THE DIFFERENCE OF THE COUNTER VALUES AFTER THE FOURTH COUNTER CORRECTION Afer he fourh couner correcion Maximum error [ms] Average [ms] Sandard deviaion [ms] The sandard deviaion is 0.6 [ms], and here is a sligh variaion in he difference of couner values beween he synchronized nodes. I is caused mainly by a buffer of a ZigBee module XBee Series 2 [17] ha is mouned on he node. We have measured a ime from when he module receives radio wave of a packe ill when i ransmis he packe as serial daa. Is sandard deviaion is 0.84 [ms], and hence i is clear from he resul ha he variabiliy is a major cause. However, in his resul, he maximum error is 2 [ms], and i is sufficienly lower han 38.1 [ms] ha is he iming requiremen of he proposed harmful birds aack sysem. Therefore, he proposed iming synchronizaion mehod has sufficien accuracy of iming synchronizaion for he sysem. VI. AN EXPERIMENT AT A FISHING WEIR The harmful birds aack sysem is being insalled a a fishing weir in Nagaoka Ciy [18] as shown in Figure 8. Server and Node Infrared Ligh Camera Solar Panel Flashing Ligh The purpose of he experimen is o confirm ha he sensor daa shows he differen endency from he usual when he bird appears in he weir. Furhermore, he sysem has an infrared camera in order o ge reference daa. Moreover, a flashing ligh is uilized as an aacking device, and power is supplied from a baery and a solar panel o he sysem because he sysem is se up on he river. From he experimen, a heron was capured by he camera images as shown in Figure 9. Thus, we will analyze he sensed daa in order o esablish a bird deecion algorihm. Heron Figure 9. An example of he camera image VII. CONCLUSIONS AND FUTURE WORKS This paper has proposed a harmful birds aack sysem. Specific feaures of his sysem are ha 1) i can deec birds in wide area by using he ulrasonic sensor arrays and 2) i has a wide variey of aacking devices in order o scare clever harmful birds off. In addiion, a new iming synchronizaion mehod for ZigBee sensor nework o avoid ulrasonic inerference has been proposed. This mehod has a feaure ha he amoun of calculaion on a sensor node is small and unaffeced by he increase in he nodes. Evaluaion of he proposed iming synchronizaion mehod has shown ha he maximum iming error is 2 [ms] and i sufficienly fulfills he iming requiremen for he proposed sysem. In he fuure sudy, we ll focus on deecing and driving away harmful birds. Paricularly, we will implemen a conrol funcion of an ice gun [19], which is one of he aacking devices as shown in Figure 10. This sudy was parly suppored by MEXT/JSPS KAKENHI Gran Number Baery Figure 8. Insalled equipmen Array ISBN February 16~19, 2014 ICACT2014

6 Insiue of Elecronics, Informaion and Communicaion Engineers Tech. Rep., vol.109, IA , February, [16] D. E. Comer, Compuer Neworks and Inernes, Prenice Hall, pp , [17] Digi Inernaional, hp:// [18] Echigo Kawaguchi Yanaba, hp://kawaguchiyanaba.s1.bindsie.jp/ [19] T. Yamane, and S. Kamimura, Developmen of Ani-Vermin Ice Gun -Par 2 ballisic of Ice bulle and poin of impac-, Proc. of he Japanese Sociey of Snow and Ice and Japan Sociey for Snow Engineering Join Conference, p. 119, Sepember, Asushi Morikawa received B.E. degree from Nagaoka Universiy of Technology in '12. He is currenly a graduae school suden in Nagaoka Universiy of Technology. His research ineress include compuer neworks and sensor neworks. Figure 10. An ice gun REFERENCES [1] RFC1129, Inerne Time : he Nework Time Proocol [2] RFC2030, Simple Nework Time Proocol (SNTP) Version 4 for IPv4, IPv6 and OSI [3] J. Elson, L. Girod and D Esrin, Fine-grained Nework Time using Reference Broadcass, Proc. of Operaional Sysems and Design Implemenaion, vol. 36, pp , Dec [4] J. Elson and K. Romer, "Wireless Neworks: A New Regime for Time ", Proc. of he Firs Workshop on Ho Topics in Neworks (HoNes-I), Ocober [5] Naional Federaion of Inlandwaer Fisheries Cooperaives, Heisei 18 Nendo Kawau Syokugai Chousa, hp:// [6] Hokuriku Regional Developmen Bureau Minisry of Land, Infrasrucure and Transpor Shinanogawa River Office Ayu No Sojo, hp:// Accessed December 9, [7] S. Uchiyama, M. Yamamoo, K. Nakamura, and K. Yamazaki, Nework for Observaion of Seabirds in Awashima Island, Proc. of IEEE Informaion Neworking (ICOIN), 2011 Inernaional Conference on, pp.64-67, January 2011 [8] H. Kurazono, H. Yamamoo, M. Yamamoo, K. Nakamura, and K. Yamazaki, RFID and ZigBee Nework for Ecology Observaion of Seabirds, Advanced Communicaion Technology (ICACT), h Inernaional Conference on, pp , January 2013 [9] S. Minomi, H. Yamamoo, K. Nakamura, and K. Yamazaki, A Sudy of Digial Signage Aenion Esimaion Sysem wih Ulrasonic Disance, The Insiue of Elecronics, Informaion and Communicaion Engineers Trans., Vol.J95-D, No.5, pp , May [10] Y. Kuboyama, N. Mia, and T. Yoshioka, Bird Deecion in Images wih Opical Flow, Forum on Informaion Technology vol. 6(3), pp , Augus [11] W. W. Versraeen, B. Vermeulen, J. Suckens, S. Lhermie, D. Van der Zande, and e al., Webcams for bird deecion and monioring: A demonsraion sudy, s 2010, 10, [12] MaxBoix, hp:// [13] A. Morikawa, H. Yamamoo, K. Nakamura, and K. Yamazaki, Evaluaion of Ulrasonic Array for Crowd Observaion Sysem, Proc. of he Insiue of Elecronics, Informaion and Communicaion Engineers Shin-esu Session, P2-1, p. 192, Ocober [14] IEEE Sandard 1588, IEEE Sandard for a Precision Clock Proocol for Neworked Measuremen and Conrol Sysems, November [15] M. Hiyama, M. Kaneko, and K.Yamazaki, Implemenaion of Precision Clock Proocol o IEEE802.11, The Hiroshi Yamamoo received M.E. and D.E. degrees from Kyushu Insiue of Technology, Iizuka, Japan in '03 and '06, respecively. From April '06 o March '10, he worked a FUJITSU LABORATORIES LTD., Kawasaki, Japan. Since April '10, he has been an Assisan Professor in he Deparmen of Elecrical Engineering, Nagaoka Universiy of Technology. His research ineress include compuer neworks, disribued applicaions, and neworked services. He is a member of he IEEE. Kasuyuki Yamazaki received B.E. and D.E degrees from he Universiy of Elecro-communicaions and Kyushu Insiue of Technology in '80 and '01, respecively. A KDD Co. Ld., he had been engaged in R&D and inernaional sandardizaion of ISDN, S.S. No.7, ATM neworks, L2 neworks, IP neworks, mobile and ubiquious neworks, ec., and was responsible for R&D sraegy of KDDI R&D Labs. He is currenly a Professor of Nagaoka Universiy of Technology. ISBN February 16~19, 2014 ICACT2014