Analysis of Energy Consumption Performance towards Optimal Radioplanning of Wireless Sensor Networks in Heterogeneous Indoor Environments

Transcription

1 852 P. L. ITURRI, L. AZPILICUETA, J. A. NAZABAL, C. FERNÁNDEZ-VALDIVIELSO, J. SORET, F. FALCONE, ANALYSIS OF ENERGY.. Analyss of Energy Consumpton Performance towards Optmal Radoplannng of Wreless Sensor Networks n Heterogeneous Indoor Envronments Peo LÓPEZ ITURRI 1, Lere AZPILICUETA 1, Juan Antono NAZABAL 1, Carlos FERNÁNDEZ-VALDIVIELSO 1, Jesús SORET 2, Francsco FALCONE 1 1 Dept. of Electrcal and Electronc Engneerng, Publc Unv. of Navarre, Campus de Arrosadía, 31006, Pamplona, Span 2 Dept. of Electrcal and Electronc Engneerng, Unversty of Valenca, Burjassot, Valenca, Span {peo.lopez, leyre.azplcueta, juanantono.nazabal, carlos.fernandez, jesus.soret@uv.es Abstract. In ths paper the mpact of complex ndoor envronment n the deployment and energy consumpton of a wreless sensor network nfrastructure s analyzed. The varable nature of the rado channel s analyzed by means of determnstc n-house 3D ray launchng smulaton of an ndoor scenaro, n whch wreless sensors, based on an n-house CyF mplementaton, typcally used for envronmental montorng, are located. Receved sgnal power and current consumpton measurement results of the nhouse desgned wreless motes have been obtaned, statng that adequate consderaton of the network topology and morphology lead to optmal performance and power consumpton reducton. The use of radoplannng technques therefore ad n the deployment of more energy effcent elements, optmzng the overall performance of the varety of deployed wreless systems wthn the ndoor scenaro. Keywords Radoplannng, wreless sensor networks, energy consumpton, ray launchng, CyF. 1. Introducton The use of wreless sensor networks s growng rapdly nto a large number of felds of applcaton, such as ndustral montorng, farmng and agrculture, structural montorng, health assstance, locaton and gudng or securty and defense, among others [1-8]. The use of these wreless sensor networks wthn domestc envronments s leadng towards the fast paced development of the so called smart homes, lnked wth the more global concept of Internet of Thngs. One of the key ssues s to reduce energy consumpton of the ndvdual elements of these wreless sensor networks, due to the fact that n the near future, a great deal of these devces wll be operatng wthn a conventonal ndoor envronment. Ths s n lne wth ambtous energy reducton strateges, such as those stated n Europe 20/20 strategy. Typcally, the deployment of wreless systems s performed by ntal coverage estmatons (usually by emprcal based models) whch can later on be valdated by feld measurements. These feld measurements, n the case of WLAN/WPAN systems are performed by usng snffers or protocol analyzers n order to obtan estmatons of RSSI values and ntal metrcs of lnk level qualty, such as Packet Error Rato levels. In the case of moble networks, performance analyss s conducted typcally by means of test drves and Key Performance Indcator valdaton, based on moble termnal tracng as well as by correlaton to network statstcs managed by the rado subsystem. Even though these approaches gve an ntal pont to valdate network operaton, ssues such as ntra-system or ntersystem nterference are not consdered, as well as the large varablty n sgnal strength and qualty due to the strong multpath characterstcs nherent to ndoor scenaros. Furthermore, not only coverage should be consdered but also dynamc varaton due to changes n traffc demands (and hence, n overall nterference values) should be taken nto account, leadng to coverage-capacty relatons. Ths s a relevant ssue that s ganng mportance as a larger amount of wreless networks are coexstng, leadng to a heterogeneous wreless envronment. Moreover, mnmzng energy consumpton has become one of the man goals, drven by nternatonal Green polces. In ths context, rado channel features of ndoor envronments pose a challenge to energy consumpton, due to the fact that the complexty of the scenaro ncreases losses due to strong multpath propagaton and mult-screen dffracton, as well as absorpton due to lossy dspersve meda, as t s shown n prevous works [9]. The exstence of nterference sources n these complex envronments also affects the deployment strateges and overall power consumpton [10]. In ths paper, the topologcal nfluence of a layout of n-house developed CyF based wreless sensors wll be analyzed n terms of power consumpton and rado coverage. For that purpose, the characterstcs of the CyF motes are presented n Secton 2. Then, n Secton 3, the analyss of the consdered scenaro by means of an n-house devel-

2 RADIOENGINEERING, VOL. 23, NO. 3, SEPTEMBER oped 3D ray tracng smulaton tool s presented, showng radoplannng results as receved power planes, power delay profles or current consumpton planes. Fnally, n Secton 4, receved power and consumpton measurements are presented for dfferent test cases, showng the dependence between network topology and power consumpton. In concluson, the applcaton of determnstc radoplannng approaches, lke the method presented n ths work, lead to an optmal network confguraton, mnmzng energy consumpton and achevng desred qualty of servce. 2. CyF Wreless Devces For the purpose of ths work, a system based on a set of wreless motes has been desgned n house by the Unversty of Valenca. Each mote ncludes sensor/actuator elements, a PSoC processor core, expanson ports and power, and a CyF transcever. Dependng on the role that the nodes play n the protocol, the motes can be confgured as a master or as a slave. The basc network topology s a star confguraton, n whch a master node manages a certan number of perpheral slave nodes. Followng a herarchcal scheme, dfferent master nodes can be connected at slave-type stages to form a second layer around a master node that s responsble for montorng the platform. Each mote has two parts: a man card whch contans the mcrocontroller, and an addtonal one that contans the rado frequency part. The man board conssts of dfferent blocks, as shown schematcally n Fg. 1. The real mplementaton can be seen n Fg. 2. The mcrocontroller s the Cypress CY8C24894 PSoC. It ncorporates an 8-bt mcrocontroller M8C and up to 4 MIPS. As reconfgurable elements, t contans 4 dgtal blocks and 6 analog blocks, n addton to 1KB of SRAM and 16KB of Flash. Also, the devce has the possblty to communcate va USB wthout requrng any addtonal tems. The humdty and temperature sensor used s an SHT75 model. Ths s calbrated at the factory, controlled dgtally, has hgh resoluton and accuracy, wth an operatng range of 0-100% relatve humdty and a temperature range between -40ºC and 123ºC. The used CyF technology s a cost effectve lowpower wreless soluton developed by Cypress Semconductor that operates n the unlcensed 2.4 GHz ISM band, wth actve lnk and power management features. The network topology conssts n a smple star network controlled by a central hub. Due to the lghtweght network protocol stack of CyF nodes, a bdrectonal communcaton to up to 250 nodes s provded. CyF output maxmum power s 4 dbm and the recever senstvty -97 dbm, wth a typcal range n a lne of sght, nterference-free envronment between 50 m and 70 m. The mentoned actve lnk and power management provde nterestng dynamc functonaltes. For more robustness, the transmtter changes the modulaton and data rates dynamcally between 1 Mbps and 250 Kbps dependng on the envronment s nterference. If the nterference ncreases, then the power output level s dynamcally ncreased to overcome that nterference. Besdes, f a node detects that ts power output s excessve, t wll dynamcally reduce t, reducng power consumpton. Also, to ensure that the central hub of the network receves packets correctly, an nterference free channel s selected whenever possble. If the hub detects a nosy channel, a CyF network wll look for a clean channel and settle there. The dynamc power handlng capablty, n terms of coverage/capacty estmaton, wll lead to smaller coverage radus as overall transmsson speed ncreases, as wll be shown n the followng sectons. Fg. 1. Block dagram for the mplemented mote devce. Fg. 2. Image of the man board (left) and the rado frequency module (rght) of the mote devce. 3. Indoor Scenaro Analyss In order to perform estmatons of the nfluence of the ndoor envronment n a wreless sensor network, radoplannng smulaton results have been obtaned. For that purpose, radopropagaton analyss can be performed by means of emprcal methods (such as COST-231, Walfsh- Berton, Okumura Hata, etc.) [11-13], based on statstcal approaches and non-lnear regresson technques. They gve rapd results but requre calbraton based on measurements to gve an adequate ft of the results. On the other hand, determnstc methods [14-20] are based on numercal approaches to the resoluton of Maxwell s equatons, such as ray launchng and ray tracng (based on geometrcal approxmatons) or full-wave smulaton technques (method of moment (MoM), fnte dfference tme doman (FDTD) [21], FITD, etc.). These methods are precse but are tme-consumng to nherent computatonal complexty.

3 854 P. L. ITURRI, L. AZPILICUETA, J. A. NAZABAL, C. FERNÁNDEZ-VALDIVIELSO, J. SORET, F. FALCONE, ANALYSIS OF ENERGY.. As a mdpont, methods based on geometrcal optcs, for radoplannng calculatons wth strong dffractve elements, offer a reasonable trade-off between precson and requred calculaton tme [22]. The Ray Tracng method combned wth unform theory of dffracton (UTD) [23] s most frequently appled to rado coverage predcton [24-27]. The Ray Tracng models, ncludng modfcatons as recepton sphere technque [28], potentally represent the most accurate and versatle methods for urban and ndoor multpath propagaton characterzaton or predcton [29-33]. 3.1 Smulaton Technque Ths work presents an n-house developed 3D Ray Launchng algorthm to analyze the nfluence of the ndoor envronment n the propagaton of electromagnetc sgnals, valdated n prevous works [34-38]. The novelty of the proposed method s that t takes nto account all the obstacles wthn the scenaro, wth ther dfferent shapes and materal propertes. It s mportant to emphasze that a grd s defned n the space to save the parameters of each ray. Accordngly, the envronment s dvded nto a number of cubods of a fxed sze. When a ray enters a specfc hexahedron, ts parameters are saved n a matrx. Electromagnetc phenomena such as reflecton, refracton and dffracton are taken nto account, based on Geometrcal Optcs and Geometrcal Theory of Dffracton. Frstly, an ndoor scenaro has been created, takng nto account the materal parameters of all of the elements wthn t (e.g., furnture, walls, wndows, etc.), n terms of conductvty and delectrc permttvty. Electromagnetc phenomena such as reflecton, refracton and dffracton have been taken nto consderaton. T t E E 2 2 cos cos (4) cos 1 where 1 120, r and r 2,, r t are the ncdent, reflected and transmtted angles respectvely. The dffracton coeffcents are consdered by the Unform Theory of Dffracton (UTD) [39-40] as follows 2 1 cotg F kla 2 1 2n 2 1 j / 4 cotg F kla 2 1 e 2n D 2n 2k 2 1 R 0 cotg F kla 2 1 2n 2 1 Rn cotg F kla 2 1 2n (5) where nπ s the wedge angle, Ф 2 and Ф 1 angles, F, L and a are defned n [39], R 0,n are the reflecton coeffcents for the approprate polarzaton for the 0 face or n face, respectvely. The commtment between accuracy and computatonal tme s acqured wth the number of launchng rays and the cubods sze of the consdered scenaro. Several transmtters can be placed wthn an ndoor scenaro. Parameters such as frequency of operaton, radaton patterns of the antennas, number of multpath reflectons, separaton angle between rays and cubods dmenson are ntroduced. Fg. 4 depcts ray launchng method wthn a defned ndoor scenaro. 2 t Fg. 3. Prncple of Ray Launchng method. Fg. 3 shows the prncple of ray launchng method. The equvalent transmtter antenna located n the smulaton scenaro launches rays n dfferent drectons followng the radaton pattern of the antenna. The reflecton and refracton coeffcents are calculated usng the well-known Fresnel s equatons by Et 2 2 cos( ) T E cos( ) cos( ), (1) R E E r r 2 1 2cos( ) 1cos( t) cos( ) cos( ), (2) cost cos E 1 cos R, (3) E 1 cos 2 t t t Fg. 4. Schematc of 3D ray launchng wthn an ndoor scenaro. The scenaro that has been analyzed n ths paper s the Radocommuncaton Laboratory, placed n the Electrc and Electronc Engneerng Department of the Publc Unversty of Navarra. The scenaro has the nherent complexty of an ndoor scenaro, as t has nteror columns, many furnture elements, dfferent types of nstruments and walls made of dfferent materals (wood, concrete, brcks, metal and glass). The scenaro can be seen n Fg. 5a and ts schematc representaton for the ray launchng software can be seen n Fg. 5b. Red ponts n Fg. 5b represent the dfferent ponts where the wreless motes have been placed. These postons have been chosen n order to smulate a possble morphology of a real wreless network. For that

4 RADIOENGINEERING, VOL. 23, NO. 3, SEPTEMBER reason, the motes have been placed at dfferent heghts. The exact coordnates for the motes are shown n Tab. 1. wth a sngle transmtter (Fg. 6a) and fnshng wth a wreless network composed by fve transmtters (Fg. 6e). (a) (a) (b) (b) Fg. 5. (a) Indoor scenaro under analyss, correspondng to Radocommuncaton Laboratory, UPNA. (b) Schematc descrpton of the scenaro n the 3D ray launchng software. (c) (d) Transmtter TX1 TX2 TX3 TX4 TX5 Coordnates (2, 2, 0.81) m (6.5, 21, 2.7) m (11, 4, 1.5) m (0.3, 12.5, 2.1) m (7, 12.5, 2.1) m Tab. 1. Coordnates where the wreless motes are placed n the ndoor scenaro. 3.2 Smulaton Results 3D ray launchng smulaton results have been obtaned for the whole volume of the smulaton scenaro. The parameters used n the smulaton are the followng: unform cubods resoluton of 20 cm, vertcal plane angle resoluton θ = π/180, horzontal plane angle resoluton Φ = π/180, maxmum number of tolerated reflectons N = 5, frequency of operaton 2.4 GHz and power transmsson of 4 dbm. The consdered parameters are equvalent to those of a conventonal ZgBee system. Fg. 6 shows the obtaned receved power levels for the same bdmensonal plane at heght 0.81 m (the same heght as the tables wthn the laboratory) for dfferent number of transmtters. For each of the represented planes (from Fg. 6a to Fg. 6e), a new transmtter has been added consecutvely, startng (e) Fg. 6. RSSI 3D ray launchng smulaton results obtaned at a bdmensonal plane at a heght of 0.81 m for dfferent number of transmtters: (a) TX 1, (b) TX1 and TX2, (c) TX1, TX2 and TX 3, (d) TX1, TX2, TX3 and TX4, (e) TX1, TX2, TX3, TX4 and TX5. As t can be seen from the prevous fgures, receved power level s strongly dependent on the poston of the potental recever element and the morphology of the wreless network. Varatons can be n order of 10 db wthn 1 meter when the number of transmtters s low,

5 856 P. L. ITURRI, L. AZPILICUETA, J. A. NAZABAL, C. FERNÁNDEZ-VALDIVIELSO, J. SORET, F. FALCONE, ANALYSIS OF ENERGY.. whch has a strong mpact on the performance of the sensors, not only n terms of recever senstvty lmts but also on overall system capacty, whch s dependent on sgnal level as well as on sgnal to nose rato. As t s shown n Fg. 6, ths receved power varatons can be strongly mtgated changng the morphology (e.g. addng wreless motes) of the wreless network, thus obtanng a reasonable receved power level for every poston of the complete ndoor scenaro. The multpath propagaton s the strongest phenomenon n ths type of complex ndoor envronments, hence, to apprecate the varablty of estmated receved power level more precsely, Fg. 7 shows ths varablty wthn a gven lne path for a fxed value of X for two dfferent heghts n the ndoor scenaro. The X value has been set to 3.5 m randomly, snce ths phenomenon happens all alke wthn the whole scenaro. As stated above, the sgnal varaton s drven by strong multpath components, as can be seen from the short term varaton component wthn the receved power level. For a more thorough analyss of the mpact of the multpath propagaton n the scenaro, tme doman results are shown n Fg. 8 and Fg. 9. Specfcally, power delay profles are presented for the locatons of TX2 and TX3 respectvely, when TX1 transmts. A red lne has been depcted n both graphcs to delmt the senstvty level of the CyF motes. As expected, a lot of components reached the TX2 and TX3 ponts due to the multpath propagaton, but n Fg. 8, whch corresponds to the farthest mode of the network (from TX1), there are a lot of components under the senstvty level, due manly the dstance. On the other hand, n Fg. 9 most of the components are above the senstvty level, as t corresponds to the nearest node of the network. In order to complete the tme doman results, the delay spread for a plane of 0.81 m heght (the heght of the tables and TX1) s presented n Fg. 10. Fg. 8. Power Delay Profle at locaton of TX2 (the farthest node), whle TX1 s transmttng. Fg. 9. Power Delay Profle at locaton of TX3 (the nearest node), whle TX1 s transmttng. ea d (n s) Del ay Spr Delay Spread for a plane at 0.81m heght X - D s Fg. 7. Smulaton results for heght 0.81 m and heght 2.3 m, for X = 3.5 m, along the Y-axs of the ndoor scenaro under analyss. The obtaned smulaton results and manly the estmated values of receved power can lead to the analyss of the performance of the wreless system. As an example, Fg. 12 represents the sgnal to nose rato (SNR) for two dfferent heghts n the same scenaro, whch could be used to consder the most adequate deployment strategy of a set 6 ta n c e 4 n m e 5 2 Y -D s ta nc e e nm s te r te rs Fg. 10. Delay Spread values for a plane at 0.81 meters heght (.e. the heght of TX1 wthn the scenaro). of wreless sensor networks wthn the ndoor scenaro. Specfcally, SNR planes depcted n Fg. 12 have been calculated takng nto account that the whole CyF network s deployed (see Fg. 6e) and as nose sources, an nterferng WF network (an access pont and 3 laptops) operatng at the same frequency band of the CyF motes has been smulated. The smulaton parameters have been the same

6 RADIOENGINEERING, VOL. 23, NO. 3, SEPTEMBER than those used for the smulaton of the CyF motes, but the transmtted power of WF nodes has been set to 20 dbm, whch corresponds to a typcal maxmum transmtted power of a commercal devce. In Fg. 11 the schematc confguraton of the wreless networks wthn the scenaro s shown. Tab. 2 shows the poston wthn the scenaro of the WF nodes. Devce WF access pont Laptop1 Laptop2 Laptop3 Coordnates (3, 3, 2.5) m (4.5, 6.9, 0.9) m (2, 13.5, 0.9) m (8.5, 17.7, 0.9) m Tab. 2. Coordnates where WF devces have been placed wthn the scenaro. terms of SNR, n Fg. 13, the SNR at each recever CyF mote s depcted, when a sngle mote s transmttng. In Tab. 3 the preset transmsson power levels for the CyF motes are shown, whch have been used for the calculaton of the SNR, n order to show how t affects the SNR at the recever motes. As the CyF motes can change dynamcally the transmsson rate between 1 Mbps and 250 Kbps, the mnmum SNR needed has been calculated for both data rates, and these lmts have been depcted by red dashed lnes (0 db for 1 Mbps, and db for 250 Kbps). Fg. 13a shows the results for the worst nose case,.e. when the WF devces transmt 20 dbm, whlst Fg. 13b shows the results for WF devces transmttng 0 dbm. These results show that the presented method can ad n an adequate deployment strategy wthn a harsh ndoor scenaro, whch has a drect mpact on the network effcency. Defned nternal level Transmtted power (dbm) Fg. 11. Schematc representaton of the scenaro used to calculate the SNR planes of Fg. 12. Tab. 3. CyF motes preset levels and ther correspondent transmsson power level. (a) (a) (b) Fg. 12. Spatal dstrbuton of sgnal to nose rato n the ndoor scenaro of Fg. 5 for two dfferent heghts: (a) 0.81 meters, (b) 2.3 meters. Thus, the SNR value s obtaned for each pont wthn the room, gvng valuable nformaton about the zones and ponts where the placement of a mote wll be better n terms of receved sgnal qualty, whlst mantanng the optmal wreless power transmsson (and hence energy consumpton) of the system. As can be clearly seen n Fg. 12, the zones where nterferng devces have been placed are the zones wth lower SNR, as expected. For a more n-depth analyss of the proposed CyF network n (b) Fg. 13. SNR values at each CyF mote poston for a sngle transmttng mote, whle WF-nterference sources are transmttng (a) 20 dbm and (b) 0 dbm.

7 858 P. L. ITURRI, L. AZPILICUETA, J. A. NAZABAL, C. FERNÁNDEZ-VALDIVIELSO, J. SORET, F. FALCONE, ANALYSIS OF ENERGY.. Consderng the overall power consumpton of the deployed motes s also a hghly mportant ssue n rado plannng strateges. As t has been shown prevously, the locaton of the transcever has a sgnfcant role n terms of the varatons of the expected value of receved power wthn the scenaro, whch has a great mpact on the power consumpton of transmttng motes. Ths s gven by the fact that as the receved power vares, the lnk balance wthn the senstvty threshold lmt also vares, modfyng the requred current for the transcever to operate. Therefore, t s possble to estmate energy consumpton of the transmtter as a functon of the recever locaton. In order to gan nsght on the effect of topology and morphology on energy consumpton n the prevous scenaro, Fg. 14 shows the consumpton ncrease maps for two cases: frst when only two motes are operatng (TX1 and TX2) and afterwards when the whole wreless network s operatng (5 transmtters), whch corresponds to the optmal confguraton of the network for the presented ndoor scenaro. These maps represent the overall ncrease of current consumpton of the transmttng motes placed at the scenaro for each possble recever locaton. From the real measurements explaned n the next secton, t s shown that the lowest measured consumpton of a mote when transmttng s 40.5 ma (dstance between transmtter and recever of 5 cm). So, as t can be seen n the consumpton maps for the frst case (Fg. 14a), a maxmum current consumpton ncrease of 6.03 ma s reached for a specfc locaton (ths maxmum peak seems not to reach that value, but t s due to the perspectve of the graph). Ths corresponds to the worst locaton for a recever to be placed n terms of current consumpton. Ths means that for that recever locaton, the overall current consumpton for the transmtters wll ncrease n 6.03 ma due to the power level receved at that locaton, whch s equal to 14.8% more consumpton. On the other hand, for the optmal case of 5 transmtters deployed (Fg. 14b), the worst recever locaton mples an ncrease of 3.11% of the total consumpton of the fve transmttng motes of the network. Ths lower ncrease of consumpton s expected as the receved power level for the whole scenaro s hgher due to the hgher amount of deployed transmttng nodes. These results can be really useful n order to plan the desgn of the optmal network, takng nto account the number of employed nodes, the requred transmsson bandwdth and the senstvty level. Moreover, as t s shown n Fg. 14, the densty of the nodes wthn the network has a clear mpact on energy consumpton, due to the fact that lnk balance lmtatons are lower when the whole network s operatng. Nevertheless, t s mportant to acheve a commtment between the densty of nodes and nterference levels, because a larger number of nodes could lead to ncreased nterference levels, whch could degrade system performance. (a) (b) Fg. 14. Estmaton of energy consumpton n terms of current values n ma for dfferent locatons of the scenaro depcted n Fg Measurement Results of Deployed Wreless Sensors In order to valdate the prevously obtaned smulaton estmatons, n whch the morphologcal dependence of the network performance n terms of receved sgnal s observed, wreless CyF motes have been confgured and measured. For that purpose, power dstrbuton and current consumpton measurement results are presented. In Fg. 15, a layout of the tested setup s shown. The laboratory has two zones, separated by several metallc shelves. For the purpose of the study, the left hand zone has been measured, due to the fact that ths s a zone of nteracton wth students and collaborators, leadng to a realstc stuaton for the deployment and use of a wreless sensor network. The measurements have been performed by programmng a test setup among the motes, gven by a coordnator element and a wreless sensor. Fg. 15. Schematc of the ndoor scenaro (Publc Unversty of Navarre).

8 RADIOENGINEERING, VOL. 23, NO. 3, SEPTEMBER Intally, the RSSI values n dfferent ponts of the scenaro (Fg. 15) have been measured: The transmtter s located n coordnates (2, 2) and t s represented by a red pont. The recever has been placed n dfferent ponts, whch are represented by blue X marks n the fgure. Both the transmtter and recever have been placed at the same heght of 81 cm, whch s the heght of the tables located n the scenaro. The same antenna orentaton n all the measurements has been carefully mantaned n order to mnmze varatons due to the radaton pattern of the recevng antenna. The motes have been programmed to transmt at low data rate of 1 packet every 20 seconds, emulatng a possble wreless sensor network applcaton lnked to Ambent Intellgence or Smart Homes. The RSSI values have been read drectly from the data provded by the motes, by means of protocol analyss of the ar nterface. The obtaned values for dfferent postons n the laboratory are shown n Fg. 16. The scale has been set up to -100 dbm n order to account for the senstvty value of the motes (-97 dbm). As expected, due to the CyF s actve lnk and power management, sgnal level does not clearly decrease wth the dstance as t happens n a common radowave transmsson (wth a transmtter transmttng a fxed power level). The sgnal level s mantaned qute well wthn the scenaro, although varatons on receved power can be seen due to the multpath radopropagaton effects (manly dffracton and reflecton), very sgnfcant n an ndoor complex scenaro lke ths. Y-Dstance n meters Receved power measurements 2 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0 X-Dstance n meters [dbm] Fg. 16. Measured power levels n dbm for a par of mote coordnator/sensor n the ndoor scenaro. To gan more nsght n the operaton of the sensor motes and the nfluence of the topology and morphology of the scenaro, current consumpton has been measured for several postons. For that purpose, the motes have been programmed to transmt at ther hghest packet transmsson rate (1 packet per 15 ms) and the hghest transmsson power level (4 dbm) n order to ncrease the current demand of the motes. As n the prevous case, both the transmtter and recever have been placed at the same heght of 81 cm. Wth ths new approach, unlke the prevous case, at certan dstance from the coordnator no packets are receved. The RSSI values shown n Fg. 17 are the mean values of the RSSI data of the packets receved n a 2-second duraton tme slot, whch correspond approxmately to 130 packets as long as the communcaton has been correctly done. Y-Dstance n meters Receved power measurements 2 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0 X-Dstance n meters [dbm] Fg. 17. Measured power levels n dbm for a par of mote coordnator/sensor n the ndoor scenaro at hghest transmsson data rate. When the dstance s hgher, the communcaton has problems and the number of receved packets decreases up to 10 packets n 2 seconds due to the approach of the receved power to the senstvty level of the motes. Fg. 17 shows how the receved power level near the transmtter s qute constant as well as the senstvty level zone, n whch no packets are receved. Ths s due, once agan, to the automatc regulaton of transmt power that s embedded n the motes. But, despte of that, varatons on receved power level could be measured (on a smaller extent than n a case wthout transmtter power regulaton), once agan, due to the partculartes of radopropagaton wthn a heterogeneous scenaro wth a complex morphology lke ths (a lot of furnture composed of dfferent materals). As an example, although coordnates (6,6) are located further from the transmtter than coordnates (2,6), and the transmtter tres to mantan the receved power level throughout the scenaro, the zone correspondng to coordnates (2,6) has lower receved power level. It s worth notng that due to the ncrease n the overall transmsson rate, the senstvty of the motes s decreased, leadng to lower coverage zones, as clearly observable from Fg. 17. Ths agan s gven by the auto regulaton power functon embedded wthn the motes, reducng the avalable transmsson power n order to handle a decreased senstvty value gven by a hgher transmsson speed. As an example, a PER (Packet Error Rate) measurement has been made between a transmtter n (2,2) and a recever n (2,6). As mentoned prevously, a low receved power zone s detected surroundng the coordnate (2,6). Ths zone has the same characterstcs as the zone near the senstvty level, n whch the number of receved packets decreases abruptly. Ths s clearly shown n the PER value obtaned for the transmsson of 100,000 packets: only 1,363 packets arrved (PER = %).

9 860 P. L. ITURRI, L. AZPILICUETA, J. A. NAZABAL, C. FERNÁNDEZ-VALDIVIELSO, J. SORET, F. FALCONE, ANALYSIS OF ENERGY.. In order to see the evoluton of the current consumpton of the transmtter n ths scenaro, the recever has been placed at dfferent dstances from the transmtter. A Tektronx DPO 3014 osclloscope has been used to obtan the current consumpton measurements. For ths purpose, a 1 ohm resstor has been ntroduced n seres n the feedng crcut of the mote. In ths way, by measurement of the voltage dfference n the resstor, an estmaton of the current value s obtaned. The obtaned results are shown n Fg. 18 and Fg. 19. As t can be seen n Fg. 18, a clear dfference exsts between the standby (orange curve) and the transmt mode (the rest of the curves), whch s expected due to the normal operatonal procedure n the wreless transcever. In Fg. 19, a detal of the dfferent transmt mode current values can be seen, gven for dfferent postons of the sensor wthn the scenaro. These dstances have been 0.05 m, 2 m and 4.2 m, respectvely. The last dstance corresponds to the pont n whch the senstvty level has been almost reached, n whch few packets are receved. Ths senstvty pont vares between 4 and 6 m dependng on the envronment and the objects surroundng the motes. From the measured values of the current consumpton from the motes n operatng mode at dfferent dstances, an ncrease n current consumpton n the order of 4.2% n the case of 2 m and 5.4% n the case of 4.2 m s observed. Therefore, by consderng the pre-exstent levels of nterference as well as the expected fadng losses of the scenaro, the optmal locaton of the motes can be planned pror to real network deployment. As the dstance ncreases, the power consumpton level also ncreases, whch s n accordance to the operaton of the power management of CyF motes: By ncreasng the dstance between motes, the recever power decreases. But due to the power management features of the motes, the transmtted power level ncreases n order to mantan the receved power level n each poston, leadng to hgher power demands of the transmtter. Fg. 18. Power consumpton varaton as a functon of tme for dfferent postons. The bottom curve (13.2 ma) s for standby, whereas as the rest of the curves span from the closest to the farthest mote wthn the measurement scenaro. 5. Conclusons In ths work, the topologcal and morphologcal nfluence n the operaton of a wreless sensor network s descrbed. An ndoor scenaro has been analyzed by means of determnstc 3D ray launchng n-house algorthm as well as by measurements wth an n-house developed wreless sensor platform. The results show that the radopropagaton characterstc of ndoor scenaros s complex, leadng to strong topologcal dependences n the overall receved sgnal power, whch affects other parameters such as capacty of the wreless sensor network. The results show that by consderng radoplannng ssues n the deployment of the wreless sensor networks, power consumpton as well overall system performance can be strongly optmzed, due to drect mpact on energy consumpton of the wreless transcevers. In the future, these results can ad deployment and plannng of complex ndoor sensor networks, optmzng the overall power consumpton wthout degradng system performance. Wth the advent of LTE and Internet of Thngs, the use of precse radoplannng technques to ad n wreless transcever deployment can be a determnng factor for successful adopton of these emergng technologes. Fg. 19. Detal on the power consumpton for the desgned mote devce wthn the ndoor scenaro. The mean values for dfferent currents are proportonal to the separaton between motes. Acknowledgements Ths work has been supported by projects TEC C2-1-R, funded by the Mnstry of Economy and Competveness, Government of Span.. References [1] BOSE, R. Sensor networks-motes, smart spaces and beyond. IEEE Pervasve Computng, 2009, vol. 8, no. 3, p [2] GROSSE, C.U., GLASER, S.D., KNUGER, M. Intal development of wreless acoustc emsson sensor motes for cvl nfrastructure state montorng. Smart Structures and Systems, 2010, vol. 6, no. 3, p [3] BUCKNER, B.D., MARKOV, V., LAI, L.C., EARTHMAN, J.C. Laser-scannng structural health montorng wth wreless sensor motes. Optcal Engneerng, 2008, vol. 47, no. 5, Art. No

10 RADIOENGINEERING, VOL. 23, NO. 3, SEPTEMBER [4] BERISHA, V., KWON, H., SPANIAS, A. Real-tme acoustc montorng usng wreless sensor motes. In Proceedngs of the IEEE Internatonal Symposum on Crcuts and Systems. Island of Kos (Greece), 2006, p [5] TRUBILOWICZ, J., CAI, K., WEILER, M. Vablty of motes for hydrologcal measurements. Water Resources Research, 2009, vol. 45, Art. No. W00D22. [6] KUANG, K.S.C., QUEK, S.T., MAALEJ, M. Remote flood montorng system based on plastc optcal fbers and wreless motes. Sensors and Actuators A Physcal, 2008, vol. 147, no. 2, p [7] YUNSEOP, K., EVANS, R.G., IVERSEN, W.M., Remote sensng and control of an rrgaton system usng a dstrbuted wreless sensor network. IEEE Transactons on Instrumentaton and Measurement, 2008, vol. 57, no. 7, p [8] RUIZ-GARCÍA, L., BARREIRO, P., ROBLA, J.I., LUNADEI, L. Testng ZgBee motes for montorng refrgerated vegetable transportaton under real condtons. Sensors, 2010, vol. 10, no. 5, p [9] NAZABAL, J.A., LOPEZ ITURRI, P., AZPILICUETA, L., FAL- CONE, F., FERNÁNDEZ-VALDIVIELSO, C. Performance analyss of IEEE complant wreless devces for heterogeneous ndoor home automaton envronments. Internatonal Journal of Antennas and Propagaton, 2012, artcle number [10] LOPEZ ITURRI, P., NAZABAL, J.A., AZPILICUETA, L., ROD- RIGUEZ, P., BERUETE, M., FERNÁNDEZ-VALDIVIELSO, C., FALCONE, F. Impact of hgh power nterference sources n plannng and deployment of wreless sensor networks and devces n the 2.4 GHz frequency band n heterogeneous envronments. Sensors, 2012, vol. 12, no. 11, p [11] HATA, M. Emprcal formula for propagaton loss n land moble rado servces. IEEE Transactons on Antennas and Propagaton, 1980, vol. 29, no. 3, p [12] IKEGAMI, F., YOSHIDA, S., TAKEUCHI, T., UMEHIRA, M. Propagaton factors controllng mean feld strength on urban streets. IEEE Transactons on Antennas and Propagaton, 1984, vol. 32, no. 8, p [13] PHAIBOON, S., PHOKHARATKUL, P. Path loss predcton for low-rse buldngs wth mage classfcaton on 2-D aeral photographs. Progress n Electromagnetcs Research, 2009, vol. 95, p [14] LEE, S. H. A photon modelng method for the characterzaton of ndoor optcal wreless communcaton. Progress n Electromagnetcs Research, 2009, vol. 92, p [15] LEE, D. J. Y., LEE, W. C. Y. Propagaton predcton n and through buldngs. IEEE Transactons on Vehcular Technology, 2000, vol. 49, no. 5, p [16] TAN, S. Y., TAN, H. S. A mcrocellular communcatons propagaton model based on the unform theory of dffracton and multple mage theory. IEEE Transactons on Antennas and Propagaton, 1996, vol. 44, no. 10, p [17] KANATAS, A. G., KOUNTOURIS, I. D., KOSTARAS, G. B., CONSTANTINOU, P. A UTD propagaton model n urban mcrocellular envronments. IEEE Transactons on Vehcular Technology, 1997, vol. 46, no. 1, p [18] DIMITRIOU, A. G., SERGIADIS, G. D. Archtectural features and urban propagaton. IEEE Transactons on Antennas and Propagaton, 2006, vol. 54, no. 3, p [19] FRANCESCHETTI, M., BRUCK, J., SCHULMAN, L. J. A random walk model of wave propagaton. IEEE Transactons on Antennas and Propagaton, 2004, vol. 52, no. 5, p [20] BLAS PRIETO, J.,LORENZO TOLEDO, R. M., FERNÁNDEZ REGUERO, P., ABRIL, E. J., BAHILLO MARTÍNEZ, A., MAZUELAS FRANCO, S., BULLIDO, D. A new metrc to analyze propagaton models. Progress In Electromagnetcs Research, 2009, vol. 91, p [21] SCHUSTER, J. W., LUEBBERS, R. J. Comparson of GTD and FDTD predctons for UHF rado wave propagaton n a smple outdoor urban envronment. In IEEE Antennas and Propagaton Socety Internatonal Symposum. 1997, vol. 3, p [22] ISKANDER, M. F., YUN, Z. Propagaton predcton models for wreless communcatons systems. IEEE Transactons on Mcrowave Theory and Technques, 2002, vol. 50, p [23] KOUYOUMJIAN, R. G., PATHAK, P. H. A unform theory of dffracton for an edge n a perfectly conductng surface. Proc. IEEE, 1974, vol. 62, no. 4, p [24] GENNARELLI, G., RICCIO, G. A UAPO-based model for propagaton predcton n mcrocellular envronments. Progress n Electromagnetcs Research, 2009, vol. 17, p [25] SON, H. W., MYUNG, N. H. A determnstc ray tube method for mcrocellular wave propagaton predcton model. IEEE Transact. on Antennas and Propagaton, 1999, vol. 47, no. 8, p [26] TAYEBI, A., GÓMEZ J., DE ADANA, F. S., GUTIERREZ, O. The applcaton of arrval and receved sgnal strength n multpath ndoor envronments. Progress In Electromagnetcs Research, 2009, vol. 91, p [27] SONG, H. B., WANG, H. G., HONG, K., WANG, L. A novel source localzaton scheme based on untary esprt and cty electronc maps n urban envronments. Progress In Electromagnetcs Research, 2009, vol. 94, p [28] LU, W., CHAN, K. T. Advanced 3D ray tracng method for ndoor propagaton predcton. Electroncs Letters, 1998, vol. 54, no. 12, p [29] SEIDEL, S. Y., RAPPAPORT, T. S. Ste-specfc propagaton predcton for wreless n-buldng personal communcaton system desgn. IEEE Transactons on Vehcular Technology, 1994, vol. 43,no. 4, p [30] DURGIN, G., PATWARI, N., RAPPAPORT, T. S. An advanced 3D ray launchng method for wreless propagaton predcton. In IEEE 47 th Vehcular Technology Conference. Phoenx (AZ, USA), 4-7 May [31] CHANG-FA YANG, BOAU-CHENG WU, CHUEN-JYI KO. A ray-tracng method for modelng ndoor wave propagaton and penetraton. IEEE Transactons on Antennas and Propagaton, 1998, vol. 46, no. 6, p [32] LOTT, M. On the performance of an advanced 3D ray tracng method. In Proc. of European Wreless & ITG Moble Communcaton. Munch (Germany), 6-8 Oct [33] ROSSI, J.-P., GABILLET, Y. A mxed ray launchng/tracng method for full 3-D UHF propagaton modelng and comparson wth wde-band measurements. IEEE Transactons on Antennas and Propagaton, 2002, vol. 50, no. 4, p [34] AZPILICUETA, L., FALCONE, F., ASTRÁIN, J. J., VILLA- DANGOS, J., GARCÍA ZUAZOLA, I. J., LANDALUCE, H., ANGULO, I., PERALLOS, A. Measurement and modelng of a UHF-RFID system n a metallc closed vehcle. Mcrowave and Optcal Technology Letters, 2012, vol. 54, no. 9, p [35] AGUIRRE, E., ARPÓN, J., DE MIGUEL, S., RAMOS, V., FAL- CONE, F. Evaluaton of electromagnetc dosmetry of wreless systems n complex ndoor scenaros wth human body nteracton. Progress In Electromagnetc Research B, 2012, vol. 43, p. 189 to 209. [36] LED, S., AZPILICUETA, L., AGUIRRE, E., MARTÍNEZ DE ESPRONCEDA, M., SERRANO, L., FALCONE, F. Analyss and descrpton of HOLTIN servce provson for AECG montorng n complex ndoor envronments. Sensors, 2013, vol. 13, no. 4, p

11 862 P. L. ITURRI, L. AZPILICUETA, J. A. NAZABAL, C. FERNÁNDEZ-VALDIVIELSO, J. SORET, F. FALCONE, ANALYSIS OF ENERGY.. [37] AGUIRRE, E., ARPON, J., AZPILICUETA, L., LOPEZ, P., DE MIGUEL, S., RAMOS, V., FALCONE, F. Estmaton of electromagnetc dosmetrc values from non-onzng radofrequency felds n an ndoor commercal arplane envronment. Electromagnetc Bology and Medcne, publshed onlne n Aug [38] AGUIRRE, E., LOPEZ ITURRI, P., AZPILICUETA, L., DE MIGUEL-BILBAO, S., RAMOS, V., GARATE, U., FALCONE, F. Analyss of estmaton of electromagnetc dosmetrc values from non-onzng radofrequency felds n conventonal road vehcle envronments. Electromagnetc Bology and Medcne, publshed onlne n Jan [39] LUEBBERS, J. R. A heurstc UTD slope dffracton coeffcent for rough lossy wedges. IEEE Transactons on Antennas and Propagaton, 1989, vol. 37, no. 2, p [40] LUEBBERS, J. R. Comparson of lossy wedge dffracton coeffcents wth applcaton to mxed path propagaton loss predcton. IEEE Transactons on Antennas and Propagaton, 1988, vol. 36, no. 7, p About Authors Peo LÓPEZ ITURRI receved hs Telecommuncatons Engneerng Degree from the Publc Unversty of Navarre (UPNA), Pamplona, Navarre, n Snce then he has been workng n the FASTER research project at UPNA. He obtaned a Master of Communcatons n 2012, held by the UPNA and he s currently pursung the Ph.D degree n Telecommuncaton Engneerng. Hs research nterests nclude rado propagaton, modelng of rado nterference sources and moble rado systems. Lere AZPILICUETA receved her Telecommuncatons Engneerng Degree from the Publc Unversty of Navarre (UPNa), Pamplona, Span, n In 2010 she worked n the R&D department of RFID Osés as rado engneer. In 2011, she obtaned a Master of Communcatons held by the Publc Unversty of Navarre. She s currently pursung the Ph.D. degree n telecommuncaton engneerng. Her research nterests are on rado propagaton, moble rado systems, ray tracng and channel modelng. Juan Antono NAZABAL was born n Pamplona, Span, n He receved hs B.S. degree n Telecommuncatons Engneerng from the Publc Unversty of Navarre (UPNA), Pamplona, Span, n In 2010, he obtaned a Master of Communcatons held by the Publc Unversty of Navarre. He s currently pursung the Ph.D. degree n Telecommuncaton Engneerng. Hs research nterests are system ntegraton, buldng automaton and moble rado systems. Carlos FERNÁNDEZ-VALDIVIELSO receved hs Telecommuncatons Engneerng Degree n 1998 and n 2003 hs PhD n Communcatons, both from the Unversdad Públca de Navarra, Navarra, Span. In 1998 he cofounded Ingenería Domótca, a company devoted to smart buldngs and home automaton systems. In 2005 he became an Assocate Professor at UPNA. Snce 2012 he s Drector of SODENA, a venture captal company. Jesús SORET receved hs Telecommuncatons Engneerng Degree n 1998 and n 2003 hs PhD n Communcatons, both from the Unversdad de Valenca (UV), Span. Snce 2005 he s an Assocate Professor at UV, workng on wreless sensor systems. Francsco FALCONE receved hs Telecommuncatons Engneerng Degree n 1999 and hs PhD n Communcatons n 2005, both from the Unversdad Públca de Navarra, Navarra, Span. From 1999 to 2000 he worked n Semens-Italtel as a Mcrowave Engneer. From 2000 to 2008 he was a Rado Network Engneer n Telefónca Móvles. In 2009 he co-founded Tafco Metawreless, a spn-off company devoted to complex EM meda. In parallel, he was an Assstant Professor at UPNA and snce 2009, an Assocate Professor at UPNA.