Performace Evaluatio of a Volcao Moitorig System Usig Wireless Sesor Networks Romá Lara-Cueva, Member, IEEE, Diego Beítez, Seior Member, IEEE. Atoio Caamaño, Member, IEEE, Marco Zearo, Member, IEEE, ad José Luis Rojo-Álvarez, Seior Member, IEEE Abstract A volcao moitorig system plays a key role for lauchig emergecy early warig, ad the use of alterative techologies have prove their effectiveess i this settig, which is the case of wireless sesor etworks. For surveillace systems, the real-time requiremet is madatory due to the eed for immediate access to the sigals derived from a atural disaster where the goal is safeguardig lives. Previous works did ot report detailed eough performace evaluatio of this kid of systems, either by meas of usig simulatio tools or i a test-bed related to real-time metrics. Our aim was to idetify the optimum umber of sesors to be deployed i a Volcao Moitorig System based o simulatio results ad corroborated with a i-situ testbed. We used s- as simulatio tool, where Radom ad Tessellatio scearios were evaluated. Our study idetified that the optimal sceario i volcao moitorig is Radom, with maximum eightee odes to satisfy metrics such as throughput, time delay, ad packet loss. We deployed sixtee sesors i a strategic area at Cotopaxi Volcao, where the iformatio was obtaied durig three days of cotiuous moitorig. This iformatio was set to a surveillace laboratory located 5 km away from the statio placed at the volcao, ad WiFi-based log distace techology was used for this purpose. The data obtaied with our system allowed to distiguish log period evets ad volcao tectoic earthquakes. Idex Terms WSN, 8.5., throughput, delay, packet loss, moitorig system, volcao. I. INTRODUCTION TO WSN Wireless Sesor Network (WSN) have become critical i the evolutio of Telecommuicatios, ad their costat evolutio makes possible to implemet devices with low cost ad eergy autoomy, without periodic maiteace for obtaiig evirometal iformatio. For these reasos, Cyber-Physical Systems (CPS), Iteret of Thigs (IoT), ad Smart Cities are ew research topics based o WSN techologies. All of them are based i a similar ifrastructure of every heterogeeous etworks, where data must be trasmitted ad processed, for Mauscript received July 5, ; revised August, ; accepted September,. Date of publicatio November 5, R.A. Lara-Cueva ad D. Beítez are with Wireless Commuicatio Research Group (WiCOM) ad Ad Hoc Networks Research Ceter (CIRAD), Electrical ad Electroic Departmet, Uiversidad de las Fuerzas Armadas ESPE, Sagolquí-Ecuador, 7-5-B e-mail: (see http://wicom.espe.edu.ec/cotactos.html). A. Caamaño is with Iformatio ad Commuicatio Techology Departmet, Rey Jua Carlos Uiversity, Madrid, España M. Zearo is with ICT for Developmet Laboratory, The Abdus Salam Iteratioal Cetre for Theorical Physics, Trieste-Italy J.L. Rojo-Álvarez is with Iformatio ad Commuicatio Techology Departmet, Rey Jua Carlos Uiversity, España, ad Prometeo Program, Electrical ad Electroic Departmet, Uiversidad de las Fuerzas Armadas ESPE, Ecuador. fially eablig people usig ay applicatio to moitor or to cotrol objects [] [6]. Ecuador has a special iterest i the use of WSN for volcao moitorig applicatios, as it is located i the Pacific Rig of Fire a place with high seismic activity. WSN systems are much cheaper ad reliable tha bulky ad eergy-hugry traditioal systems. Curretly, South America lacks of eough permaet moitorig WSN-based systems deployed i active volcaoes, i previous works such systems have bee istalled just for a couple of weeks. Volcao moitorig usig WSN still requires further research i order to preset iformatio i real-time ad to lauch early emergecy warigs. The mai costrait to be cosidered as real-time systems is the time delay i data processig. There are some solutios at Network ad MAC layer referred to data acquisitio i-situ, data gatherig ad data dissemiatio, which sigificatly reduce the time delay. However, it is ot possible yet to give a early warig with this kid of systems, because data are processed off-lie i a far distaced surveillace laboratory. The time delay related to digital sigal processig ad sigal propagatio must be solved usig appropriate processig ad telecommuicatio techiques [7] []. Previous works did ot report detailed eough performace evaluatio of this kid of systems, either by meas of usig simulatio tools, or i a test-bed, related to metrics for cosiderig a system as a real-time oe. Our aim was two-fold: first, we idetified the umber of sesors that maximize the etwork capacity, cosiderig the mai metrics to evaluate a WSN for real-time applicatios; ad secod, we corroborated the simulatio results by a i-situ testbed deployed at Cotopaxi volcao. The rest of the paper is orgaized as follows. Sectio summarizes previous research o the subject. Sectio describes the performace evaluatio of the WSN i detail. Sectios ad 5 describe the simulatio results obtaied ad the experimetal study performed, respectively. Fially, Sectio 6 presets our coclusios ad future work. II. RELATED WORK Our iterest cosists i determiig the etwork behavior, which ca be evaluated by Quality of Service (QoS) metrics, such as: availability, reliability, time respose, time delay, throughput, badwidth capacity, ad packet loss ratio. I order to offer real-time i WSN with guarateed QoS metrics, the etwork must be aalyzed i a differet way tha traditioal real-time systems. 978--799-76-6//$. c IEEE
WSN requires to meet certai severe challeges due to its wireless ature, distributed architecture ad dyamic etwork topology. The state of the art of real-time solutios curretly developed have bee preseted with emphasis at MAC level, routig, data processig, ad cross layer. This deotes a direct relatioship betwee real-time ad QoS metrics, as well as ew geeral cocepts related to real-time WSN systems [] []. Real-time WSN ca be defied as a etwork capable of esurig maximum sustaied traffic rate (throughput), ad miimum latecy ad packet loss (PL) as mai QoS metrics. A ideal developmet process starts from the theoretical aalysis of the protocol to provide bouds ad iformatio about its performace [], [5], the it has to be verified ad refied by simulatios [6] [], ad fially cofirmed i a testbed [], []. We foud several works which preseted a mixed aalysis, sice i real scearios it is possible to obtai measures of mai metrics as: received sigal stregth idicatio, packet error rate, ad ed-to-ed delay (EED), usig tools developed by maufactures [] [6]. However these results of WSN performace evaluatio are isufficiet for our case, sice i this work we are proposig the use of WSN as a ew alterative for volcao moitorig systems. III. PERFORMANCE EVALUATION A. Real-Time WSN Requiremets for Volcao Moitorig For our applicatio we have to cosider the eviromet preseted by a Volcao a wild terrai ad lack of eergy supply to implemet a WSN. A mesh topology presets the best way to commuicate amog sesors i this kid of sceario, while is quite true the positios of the odes have to be defied accordig to the requiremets that a i-situ visit could give us accordig to the variables to be moitored. We wated to cosider also a performace evaluatio by takig ito accout the odes positio. We selected three mai metrics required for a real-time moitorig: ormalized throughput (η), EED, ad PL. As metioed i previous works, there are other metrics that ca also be cosidered, but all of them have a direct relatio to our mai metrics, for example: duty cycle, eergy cosumptio, average jitter, load factor, ad traffic type. After several meetigs with experts i volcaology from Istituto Geofísico de la Escuela Politécica Nacioal (IGEPN), we cocluded that the system must be able to work i a permaet way to moitor several variables i a volcao. For this reaso, it is ieffective to set a WSN i a savig power mode, therefore we did ot cosider the power cosumptio metric. With respect to our metrics, we eed a maximum η, PL must be less tha %, a miimum EED, ad at least 5 statios should be eeded. B. Simulatio Eviromet There is wide rage of simulators that ca be used to test WSN i order to obtai several results to be aalyzed. Followig [7], we have chose s- as simulatio tool. I order to obtai the performace of the etwork usig simulatios, we aalyzed two types of topologies, amely, TABLE I SIMULATION PARAMETERS Geeral Parameters Value Radio Propagatio Model Two-Ray Groud Routig Protocol AODV Raw Bit Rate (kbps) 5 Atea Type Directioal Simulatio Time (s) 6 Trasmissio Time (s) Power Parameters Value Trasmissio Power (dbm) (mw) Sesitivity (dbm) -9 Trasmissio atea gai Gt (db). Receptio atea gai Gr (db). Trajectory loss (db). Nodes Parameters Value Traffic type FTP Traffic directio all to Coordiator Package size 55 bytes Number of Coordiators coordiator Distace betwee odes m Number of odes to 66 odes Eabled Beaco mode Beaco Order: Superframe Order: a regular ad a radom distributio topology. For the first oe we have chose a triagular tessellatio patter etwork {, 6}, whereas for the secod oe we defied a radom positio of sesor odes placed o the plae at a distace of meters each (typical mea value for coectio i practice). The umber of odes i the triagular tessellatio ca be obtaied as a fuctio of umber of layers C, this is, =+C(C +). () I both scearios, we started with 6 odes growig util 66 odes i 6 odes steps. We defied oe coordiator ad full-fuctio devices (FDD), ad all the trasmissios were directed to the coordiator. We assumed a evet occurrig with a duratio equal to secods i a approximated area of m. For our simulatio process, it was ecessary to specify the umber of replicatios to reduce the mea square error. Accordigly, we ru 6 replicatios for Tessellatio sceario, whereas we ru replicatios for each Radom sceario. The mai simulatio parameters that we defied were simulatio time, topology, routig protocol, ad trasmissio rate. We clustered all of them i three mai groups: geeral parameters, power parameters, ad ode parameters. The rest of the parameters used to simulate the etwork model are detailed i Table I. The simulatio scearios for both etwork topologies are show i Figure. For throughput we used the iformatio that allowed us to defie Eq.(), ad we calculated η defied i Eq.() [8], [9], meawhile for EED ad PL we used the iformatio obtaied i the trace file. We used a tool developed by Jaroslaw Malek, amed tracegraph [], to aalyze the trace file, yieldig T hroughput =8 B t tx [ bits s ], () where B is the umber of trasmitted bytes, ad t tx is the time of trasmissio i secods. Also, the parameter η represets
Positio y (m) 5 5 5 Coordiator Nodes TABLE II COMPARISON DEPLOYMENTS, ACOUSTIC, SEISMO-ACOUSTIC, SEISMO WSN Variables/ Number Operatio Frequecy Duratio Deploy. Platform sesors frequecy Samplig (Days) (MHz) (Hz) [7] A /Micaz [8] SA /Tmote 6 9 [9] SA/Imote 5 9 Abidig Proposed S /Micaz 6 6 Work ad Iris Fig.. Positio y (m) 5 5 5 5 5 Positio x (m) 5 5 5 Coordiator Nodes 5 5 5 5 5 Positio x (m) Tessellatio ad Radom scearios evaluated. the ormalized throughput, ad it is calculated by η = T hroughput, () RBR where RBR is the theoretical bite rate = 5 kbps. IV. SIMULATION RESULTS Figures ad show our mai metrics related to the umber of odes obtaied i Tessellatio ad Radom scearios. Figure a shows a irregular decay of η i Tessellatio sceario, where the maximum ad miimum values were.58 ad.8, respectively. Their boxplots correspoded a lie because its stadard deviatio was egligible. Meawhile, Figure a shows a direct relatioship betwee η ad i Radom sceario, its maximum ad miimum values were.57 ad., respectively. Their boxplots showed a sigificat stadard deviatio due to its ow radom ature. Note that i Figure b, Tessellatio sceario preseted more irregularity tha Radom sceario. Related to this metric, both scearios preseted a mea value aroud ms. Fially, data suggest that PL i both scearios preseted a icremet as a expoetial fuctio of. I Figure c we ca observe that Tessellatio sceario had irregular PL i the odes from 6 to 8, whereas i Figure c we observed that Radom sceario icreased its PL directly with. The mai differece betwee both scearios was that the Radom sceario had less PL tha the Tessellatio sceario. Accordigly to the specific requiremets gave from IGEPN with respect to PL, which must be less tha %, we observed that i Tessellatio sceario this value is reached whe =, meawhile i Radom sceario, this value is reached whe = 8. Therefore, a Radom sceario allows us to use more odes with same or better characteristics of η ad EED tha those preseted i Tessellatio sceario. V. RESULTS FROM COTOPAXI VOLCANO DEPLOYING The Wireless Commuicatios Research Group (WiCOM) from Uiversidad de las Fuerzas Armadas ESPE, developed a first attempt for replicatig precedig works by usig Micaz ad Iris platforms. Thus, Cotopaxi, which is curretly the highest active sow-capped volcao i the world, was selected for deployig a WSN. This system was deployed at a altitude of 87 meters, where 6 sesor odes were implemeted. Table. II summarizes the compariso amog previous works ad our deploymet. Our first visit to the Cotopaxi Volcao was for locatig the geographic coordiates for placig the wireless commuicatio systems ( o 9 9 S, 78 o 6 7 W), ad to determie the ecessary requiremets for WSN deploymet at the locatio. I our secod visit, WSN were deployed, at a altitude of 87 meters. Two differet kids of motes were deployed motes MICAz ad 6 motes IRIS with MTS ad MTS sesor cards usig two gateways MIB5 each. Mote Cofig. was the software used to cofigure odes. FTSP was implemeted for time sychroizatio. Figure shows the locatio of the two motes etworks deployed. Data were collected cotiuously for three days. The eergy problem was solved with the use of a geerator. The iformatio was stored i a cetral statio placed i situ. We used a wireless lik to trasmit data to the surveillace laboratory, which is 5 km away from the statio placed o the volcao. I this laboratory, sigal processig was off-lie i order to defie whether or ot the evets are false alarms. A. WiFi-Based Log Distace Lik A wireless lik was used for trasportig data sesed by WSN, ad it was prove to be cost effective for log distace applicatios. The two major limitatios for usig WiFi over log distaces (WiLD) are the requiremet for lie of sight betwee the edpoits ad the vulerability to iterferece i the ulicesed bad. Two further hurdles have to be overcome
.7.7.6.6.5.5.. η η...... 6 8 6 8 5 6 66 6 8 6 8 5 6 66 x x.5.5 EED (s).5 EED (s).5.5.5.5.5 6 8 6 8 5 6 66 6 8 6 8 5 6 66 5 5 PL (%) PL (%) 6 8 6 8 5 6 66 6 8 6 8 5 6 66 Fig.. PL. Metrics of QoS for Tessellatio Sceario. η, EED, ad Fig.. Metrics of QoS for Radom Sceario. η, EED, ad PL. whe applyig WiLD Techology, amely, power budget ad timig limitatios. The first was easily solved by usig high gai directioal ateas, while the timig issue was addressed by modifyig the media access mechaism, as proposed i []. IEEE 8.b was selected for our purposes, maily, because the, GHz ISM bad presets less losses that 5,8 GHz ISM bad. We used ateas with gai of dbi ad the trasmissio power of W. I the MAC sublayer, three types of limitatios ca be extracted, amely, the timer waitig of ACKs, RTS/CTS, ad the slottime. We used Alix boards, i which we embedded a middleware that allows us to modify these parameters i order to lik edpoits. The performace of the lik was determied usig DITG traffic ijector, i which the ijectio time was miute, the mea throughput obtaied was less tha Mbps, ad the PL was less tha
x 6.5 g (m/s ) g (m/s ).5 Fig.. Wireless Sesor Networks deployed o Cotopaxi Volcao. Micaz motes ad Iris motes. 5%. This data rate is eough for trasmittig the iformatio sesed by our WSN, but the packet loss must still be improved. B. Seismic Sigal Aalysis Figures 5a ad 6a show the origial volcaic iformatio obtaied by our system. Figures 5b ad 6b show the processed sigal after we used z-score techique, the ormalized process to ecode the distributio ad remove the depedece o the size of the seismic register, ad a bad-pass FIR filter from to 5 Hz. Figures 5c ad 6c show the represetatio of the autoregressive model order zero, this used a movig average cocept with a overlappig value equal to, this method help us to idetify the evets. Fially, we used power spectral desity (PSD) with Welch method, where the mai parameters of the FFT were a overlappig of 5% i order to have a good resolutio i frequecy ad time, a 5 samples widow (correspodig to 5 s), ad the umber of poits were 8. Figures 5d ad 6d show that spectral compoets preseted i the frequecy rage [ - 8 Hz] correspods to a log period evet, ad the sigal spectral cotet betwee [ - Hz] correspod to a volcao tectoic evet. VI. CONCLUSION AND FUTURE WORKS We determied that the optimal sceario for volcao moitorig system usig WSN is Radom, it presets the best performace related to the metrics cosidered i this work with its cosequet maximizatio of the throughput. Data showed that the maximum throughput is approximately equal to 5 kbps, the PL is less tha %, ad the EED equal to ms. These results were corroborated with a i-situ deploymet, where we obtaied a maximum throughput equal to kbps, PL of 5%, ad mea value of EED of, s. The mai differece betwee simulatio ad testbed was referred to EED, data suggested that the processig data took to much time ad this value is ot cosidered i the simulatio tool. As future work, we will model this system cosiderig the value of EED related to processig data. We are also iterested i feature extractio from volcaic or seismic sigals i order to automatically classify evets. VII. ACKNOWLEDGMENTS The authors gratefully ackowledge the cotributio of Uiversidad de las Fuerzas Armadas ESPE for the ecoomical support i the developmet of this project by Research Normalized Amplitude 5 6.8.6.. 5 6 Amplitude 5 6 8 x 7 6 5 5 5 5 Frequecy (Hz) Fig. 5. Evet - Log Period. Origial Sigal, Processed Sigal, Evet Detectio, ad (d) Power Spectral Desity. g(m/s ) Normalized Amplitude x 6 5 6.8.6.. 5 6 g(m/s ) Amplitude.5.5 (d) 5 6 6 x 5 5 5 5 Frequecy (Hz) Fig. 6. Evet - Volcao Tectoic Earthquake. Origial Sigal, Processed Sigal, Evet Detectio, ad (d) Power Spectral Desity. Project -PIT-. This work has bee partly supported by Research Projects TEC-96 ad TEC-89- C--R (Spaish Govermet), ad by the Prometeo Project of the Secretariat for Higher Educatio, Sciece, Techology ad Iovatio of the Republic of Ecuador. REFERENCES [] T. Saislav ad L. Miclea, Cyber-physical systems-cocept, challeges ad research areas, Joural of Cotrol Egieerig ad Applied Iformatics, vol., o., pp. 8,. (d)
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