Localization Techniques in Wireless Sensor Networks using Measurement of Received Signal Strength Indicator

Transcription

1 ELERONIS, VOL. 5, NO., JUNE 0 67 Localizaio echiqes i Wireless Sesor Neworks sig Measreme o Receive Sigal Sregh Iicaor M. Srbiovska, V. Dimcev,. Gavrovski a Z. Kokolaski Absrac he presee paper escribes iere localizaio echiqes i wireless sesor eworks (WSN) a correspoig localizaio algorihms. orrec locaio is reqire or ma WSN applicaios, b i is oe oo expesive o icle GS aapers i each sesor oe. Isea o reqirig ever oe o have GS isalle, all localizaio mehos assme ol a ew oes eqippe wih GS harware which kow heir posiios wiho commicaig wih oher oes. he sesors wih kow locaio iormaio a heir cooriaes will be esimae b he sesor ework localizaio algorihms. he mai goal o localizaio proceres is o ece, as accrael as possible, he locaio o a oe rom he parial iormaio obaie rom a se o oes, which alrea kow heir locaio. Measreme o he receive sigal sregh iicaor (RSSI) parameer is se or isace eermiaio bewee sesor oes. he evelope algorihm is implemee i a real sesor ework. Iex erms Wireless sesor eworks, Localizaio, Sesor oes W I. INRODUION ireless eworkig has become a ver poplar research opic, over he las ecae. Rece avaces i wireless commicaios a elecroics have eable he evelopme o low-cos, low-power a mli-cioal sesors ha are small i size a commicae i shor isaces. heap, smar sesors, eworke hrogh wireless liks a eploe i large mbers, provie eormos opporiies or eviromeal moiorig, meical reame, agriclre, miliar aairs b also i hosehols a raic pollio areas []. esie hese, WSN are also se i some ageros workig evirome like mies a clear power saios i orer o moior heir sae sas. he progress o boh sesig a iormaio echolog is makig he phsical worl measreme aa more available M.Srbiovska is wih he Facl o Elecrical Egieerig a Iormaio echologies, Skopje, Maceoia ( [email protected]) V.Dimcev is wih he Facl o Elecrical Egieerig a Iormaio echologies, Skopje, Maceoia ( [email protected]).gavrovski is wih he Facl o Elecrical Egieerig a Iormaio echologies, Skopje, Maceoia ( [email protected]) Z. Kokolaski is wih he Facl o Elecrical Egieerig a Iormaio echologies, Skopje, Maceoia ( [email protected]) a cheap i erms o acqisiio, processig, sorage a rerieval. Iellige sesors, which are possibl arrage i wire or wireless eworks, ca acqire raw aa rom he evirome or log perios o ime a hose aa ca be sael sore [,3]. I sesor eworks, oes are eploe io a plae irasrcre where here is o a priori kowlege o locaio. he problem o esimaig spaial cooriaes o he oe is reerre as localizaio. he mai pracical objecive is o locae each oe as accrael as possible wih a cerai amo o error abo he isaces bewee a sbse o oes i wireless sesor eworks. o iei he cooriaes o sesor oes (also calle kow oes) reqires measrig a isace e.g., measrig ime o arrival (oa) or ime ierece o arrival (oa) [4]. Diiclies cocerig ime measreme resl rom schroizaio o ivolve evices as well as he high mahemaical eor o calclae he posiio. he measreme o he receive sigal sregh (RSS) oers a possibili o eermie isace wih miimal eor. erhaps he simples meho o proviig localizaio is o eqip ever sesor oe wih a GS receiver. However, a GS receiver is expesive i erms o moe, size a eerg. Aoher aleraive is ha-placig each sesor a maall recorig is posiio. his is pracical a error proe approach siable or large sesor eworks a ma o he propose WSN applicaios [5]. Mos o he exisig works ocs o icreasig he accrac i posiio esimaio b sig iere mahemaical echiqes sch as riaglaio, mlilaeraio, mliimesioal scalig, ec. he res o he paper is orgaize as ollows. I secio II measreme echiqes i WSN localizaio are iscsse; hese icle isace relae measremes. I secio III raio sigal measremes are explaie, receive sigal sregh (RSS) base isace measremes, ime o arrival (oa) a ime ierece o arrival (DoA). Secio IV iscsses iere raio sigal propagaio moels or wireless commicaios ha preic sigal sregh loss wih isace pah loss; icle ree space propagaio moel, wo-ra gro moel a log isace moel. Experimeal a measreme resls are give i Secio V. Fiall a smmar is provie i Secio VI.

2 68 ELERONIS, VOL. 5, NO., JUNE 0 II. LOALIZAION EHNIQUES he goal o he locaio esimaio mehos is o calclae he posiio (cooriaes) o sesor oes i wireless sesor eworks. Localizaio i WSN is a complex problem ha ca be solve i iere was [6]. Some localizaio echiqes allow o esimae oes posiio sig iormaio rasmie b a se o oes ha are aware o heir ow locaios (GS or example). I ca be isigishe wo classes o mehos epeig rom he oes harware capabiliies: oecivi base mehos ha se ol coecivi iormaio o locae he eire sesor ework; Disace base mehos ha se ier-sesor isace or agle measremes o eermie locaio o he oes. Disace base mehos reqire aiioal eqipme b wih his meho i ca be reache mch beer resolio ha i case o coecivi base oes. he proximi iormaio bewee oes oe helps o eermie heir geomeric relaioship. he isace bewee hem or agle o a siglar riagle ca be easil esimae. Whe he isaces bewee a objec a a mber o oes are measre, i is also reqire o i he acal posiio o oes b combiig he isace measremes. he mos se mehos or he isace measremes rom hree or more oes are: riaglaio, simple rilaeraio a mlilaeraio. riaglaio is a meho or iig he posiio o a oe, whe he agles are measre b Agle o Arrival echiqe. A example o sch a procere is show i Figre.a. he objec X measres is agles wih respec o he beacos A, A a A3. he measre agles orm hree sraigh lies alog he irecios XA, XA a XA3. he iersecio bewee he hree lies eies he locaio o he oe X. he accrac o his echiqe is heavil epee po he accrac o he emploe agle measreme echiqe Simple rilaeraio is se whe we have a accrae esimae o isaces bewee a oe a a leas hree beaco oes. his simple meho is he iersecio o hree circles ceere a beacos as he posiio o he oe. he sceario is show i Figre.b. Mlilaeraio is accepe as he mos appropriae wa o eermie he locaio o a sesor oe base o locaios o beacos. A example is show i Figre.c, where he oes A, A, A3, a A4 are beacos, wih kow esimaes o heir locaios, while he oe X esimaes is locaio sig a mlilaeraio procere. he procere aemps o esimae he posiio o a oe b miimizig he error a iscrepacies bewee he measre vales. he characerisics o wireless commicaio are pariall eermie b he isace bewee seer a receiver, a i hese characerisics ca be measre a he receiver he ca serve as a esimaor o isace. he mos impora characerisics are ime o Arrival (oa), ime Dierece o Arrival (oa), a Receive Sigal Sregh Iicaor (RSSI). b A a c A 3 A = A + + A cos(c) = A + cos(b) A = + cos(a) a) A A 5 A 4 A Fig.. Localizaio asics a) riaglaio b) rilaeraio c) Mlilaeraio. a A 3 c) A c b) b III. RADIO SIGNAL MEASUREMENS ime o Arrival (oa) ses he relaioship bewee isace a rasmissio ime whe he propagaio spee is kow. I he seer a he receiver kow he ime whe he rasmissio sars he ime o sigal propagaio ca be se o esimae he isace. o provie accepable accrac a ver high accrael schroize clocks are reqire or seer a receiver. o overcome he ee or explici schroizaio, he rorip ime is oe ilize. Rorip propagaio ime measremes measre he ierece bewee he ime whe a sigal is se b a sesor a he ime whe he sigal rere b a seco sesor is receive a he origial sesor., his meho is aece b he ieral ela reqire or halig he sigal i a seco sesor [7]. Aoher echiqe ha is se o overcome he ee o explici schroizaio is ime ierece o arrival (DoA) meho, which ilizes implici schroizaio b irecl proviig he sar o rasmissio iormaio o he receiver. I is possible i wo rasmissio meims o iere propagaio spees are se. For example he seer ca se a lraso a raio sigal simlaeosl. Whe he receiver ges he raio sigal i ca sar measrig he ime il arrival o he lraso rasmissio, sael igorig he propagaio ime o he raio commicaio [7]. he mai isavaage o his echiqe is he ee o wo pes o seers a receivers o each oe.

3 ELERONIS, VOL. 5, NO., JUNE 0 69 echiqe which esimaes he isaces bewee eighborig oes is he meho base o a saar eare o i mos wireless evices, a receive sigal sregh iicaor (RSSI). ase o he kow rasmi power, he eecive propagaio loss ca be calclae. heoreical a empirical moels are se o raslae his loss io a isace esimae. his meho has bee se mail or RF sigals. I pracical scearios, he ieal isribio o RSSI is o applicable, becase he propagaio o he raio sigal is ierere wih a lo o ilecig eecs e.g: Relecio o objecs; Diracio a eges; Reracio b meia wih iere propagaio veloci. he low complexi a he as calclaio recomme his localizaio algorihm as ver poplar a oe se i wireless sesor eworks. coeicie shows he ampig o he sigal. oh parameers ms be eermie empiricall [9]. measrig he RSSI a iere isaces he vales o a A ca be eermie (4). A liear leas sqare approximaio o solve a A shol be implemee. RSSI (m) RSSI as a cio o isace IV. HE RADIO SIGNAL OAGAION MODELING here are ma raio propagaio moels [8] kow or wireless commicaios ha preic sigal-sregh loss wih isace pah loss. here are hree moels wiel se or wireless sesor eworks. Free space propagaio moel is bil o he assmpio ha he rasmier a receiver are i he lie o sigh, a here are o obsacles bewee hem. he receiver sigal power, R is relae o isace,, b he iverse sqare law: -0 isace (m) = = =.5 =3 =4 measre Fig. Measre vs calclae RSSI wih iere. o eermie, RSSI vales wihi 30m are measre a compare wih heoreical crves accorig o eqaio 4 whereb is varie rom o 4 (igre ). 4 = () wo-ra gro moel as relecio o he previos moel. A wo-ra gro moel receiver receives wo ras, irec commicaio ra a relece ra: = () m 6 4 I he real worl he sigal oe ecas a a aser or slower rae, kow as log-isace moel (3) Where: is he loss expoe, is a cosa ha epes rom he rasceiver characerisics, is he power o rasmier sigal. A excepe orm o he relaio bewee isace a receive power simpliie or he case o a oe meer reerece isace is: RSSI [ m ] = 0 log ( ) + A (4) 0 where: eoes he rasmier-o-receiver isace, A represes he RSS vale measre b a receiver ha is locae m awa rom a rasmier, a RSS is he acal measre vale a isace. he sigal propagaio Fig. 3 Roo mea sqare error bewee heoreical a measre RSSI wih iere. he majori o he RSSI vales are i he area bewee heoreical crves = a =3, hs more vales i ierval [.0, 3.0] are researche. he roo mea sqare error bewee heoreical a measre RSSI vales is calclae a compare wih each oher. De o he miimal roo mea sqare error =.5 is chose as he appropriae ampig coeicie. Figre 3 shows he pical errors o isace measremes wih RSSI.

4 70 ELERONIS, VOL. 5, NO., JUNE 0 V. EXERIMENAL RESULS I orer o creae a experimeal sep or a Zigee ework,.4ghz evelopme ki belogig o he Silico Laboraories is se. he boar is show i Fig. 4. Fig. 4. Sesor oe. Each boar eares a silico laboraories 805F microcoroller a a hipco 40 [0].4 GHz rasceiver. Sppor compoes icle a US ierace, JAG programmig ierace, a varie o pshbos a a volage reglaor. I is coce a experime o ivesigae he relaioship bewee he measre RSSI a he isace bewee oes. he locaios o hree mai oes are kow (i he igre ame wih D, E a F), he receive sigal sregh o his oes are kow, he locaio o he hree oes ame wih A, a shol be eermie (Fig.5) e measremes or each posiio a ook he average vale are perorme. he relaioship bewee he receive sigal sregh a he isace is show i ig.6. RSSI base ragig mehos reqire he kowlege o he RSS-o-isace crve as ollows: RSSI A 0 (m) oe Fig.5 osiios o he oes i ree space. E = 0 (5) where eoes he rasmier-o-receiver isace, is he propagaio pah-loss expoe. De o he miimal roo mea sqare error =.5 is chose as he appropriae ampig acor. F А D Fig. 6. Relaioship bewee RSSI a isace he RSS-o-isace reerece crve i (5) is obaie via a leas-sqare liear iig rom several RSS measre vales. he obaie resl is show i Fig.6 alog wih real measremes. I Fig. 6 i) he RSS vales are represee i m as provie b he receiver oes, ii) he isace i x- axis is ormalize o he reerece isace o m, a iii) he iig parameers are A=50.6 a =.5. Obaie resl or he pah-loss expoe compare o he heoreical vale (=) is e o he ac ha receiver oes are locae ver close o hge biligs, which provies cosrcive relece propagaio pah i aiio o he irec oe. I geeral, he resl o a measreme is ol esimae o he vale o he measra a is complee ol whe accompaie b a saeme o he cerai o ha esimae []. hs he ieal meho or evalaig a expressig measreme cerai shol be capable o reail proviig a ierval, i pariclar, oe wih a coverage probabili or level o coiece ha correspos i a realisic wa o ha reqire. he measreme cerai (x) [] is eie as saar eviaio o arihmeic mea x : i= ( ) i ( x) = x x (6) For he cerai o x x is vali: x = x ± s (7) he eqaio (7) is eie as ierval i which he accrae vale will appear wih some probabili, kow as coiece ierval. he measreme cerai eie wih: = x o he kow parameer is ( xi ) (8) i= i where x are he ceraiies o he kow parameers;

5 ELERONIS, VOL. 5, NO., JUNE 0 7 I his case, or he isace ceraiies bewee oes, parameer epes rom he ceraiies o rasmie a receive power : R = (9) R Disace cerai is calclae wih he relaio: = p + (0) he isace ceraiies o he sesor oes are presee i Figre 7. he localizaio error (ig. 7) is icreasig, whe he receivig oes epar rom he rasmier []. he posiios o he oes are show i igre 5. he larges isace bewee oes is 30 meers, or his isace he cerai is m. Localizaio error (m) Fig. 7 Localizaio error Disace (m) For he larges isace o 30 meers he localizaio error is 3%. his iaccrac is e o he ac ha receiver oes are locae ver close o hge biligs, which provies cosrcive relece propagaio pah i aiio o he irec oe. Mlipah arises whe more ha oe pah is available or raio sigal propagaio. Meallic maerials as well as ielecrics (or elecrical islaors) case relecios. Whe mliple sigal propagaio pahs exis, he acal sigal level receive is he vecor sm o all he sigals icie rom a irecio or agle o arrival. A mai challege wih RSS ragig is ha he eec o relecig a aeaig objecs i he evirome ca have larger eecs o RSS ha isace. he presee algorihm i combiaio wih Zigbee oers los o avaages. he mos impora avaage is he simpliie implemeaio process e o alrea eie ameal cios wihi he provie proocol sie o Zigbee. VI. ONLUSIONS Wireless sesor ework localizaio is aracig sigiica research ieres. WSN are wiel applicable o ma pracical applicaios iclig eviromeal moiorig, miliar applicaios, ec. i which sesors ma ee o kow heir geographical locaios. Accrae a low-cos localizaio is a criical reqireme or he eplome o wireless sesor eworks i a wie varie o applicaios. he simplici o RSS is especiall appealig or he localizaio i WSN becase o heir cos, size a power cosmpio. his paper has provie a review o he measreme echiqes i WSN localizaio a he correspoig localizaio algorihms. I his experimeal work a RSSbase localizaio approach or ooor wireless sesor eworks is presee. he RSSI was se o eermie he isaces bewee he sesor oes. his experime has smmarize heoreical a pracical ivesigaios cocerig he aalsis o RSSI measremes. Localizaio ssem ha ses RSSI i a sesor ework base o he Zigbee saar is implemee. he isace measreme accrac o he se echiqe hrogh acal experimeal resls is evalae. I he re research, i is plae o appl measreme o RSSI sig iere aea polarizaio. Roaio o he receive aea rom verical o horizoal will aec he receive eerg rom mliple sigals. I is impora o ivesigae he posiio o a aea i orer o ecrease he scaerig o he receive sigal. REFERENES [] Aa Hac, Wireless Sesor Neworks Desigs, Uiversi o Hawaii a Maoa, Hooll, USA, 003 [] E. allawa,. Gora, L. Heser, J. A. Gierrez, M. Naeve,. Heile, a V. ahl, Home Neworkig wih IEEE : A Developig Saar or Low-Rae Wireless ersoal Area Neworks, IEEE ommicaios Magazie, vol. 40, o. 8, pp , Ags 00 [3] Vlao Haziski, Areas Köpke, Holger Karl, Aam Wolisz, A commo wireless sesor eworks archiecre, echical Repor KN- 03-0, elecommicaio Neworks Grop, echische Uiversiä erli, 003 [4] aolo Sai, opolog orol i Wireless A hoc a Sesor Neworks, Isio i Iormaica e elemaica el NR- Ial, Joh Wile, 005 [5] Kazem Sohrab, Daiel Mioli, aieb Zai, Wireless Sesor Neworks: echolog, roocols a Applicaios, 007 [6] Jaso Leser Hill, Ssem Archiecre or Wireless Sesor Neworks, hd hesis, Uiversi o alioria, erkele, 003 [7] W. ri. Digial rasmissio Ssems erormace Aalsis a Moelig. McGraw-Hill elecommicaios. McGraw-Hill, New York, 998 [8] Holger Karl a Areas Willig, roocols a Archiecres or Wireless Sesor Neworks, Joh Wile & Sos, 005 [9] erhar H. Walke, Sea Magol, Lars erlema, IEEE 80 Wireless Ssems: roocols, Mli-hop Mesh/Relaig, erormace a Specrm oexisece, 006 [0] Daashee or chipco 40.4 GHz IEEE /Zigee RF rasceiver [] Gie o he expressio o cerai i measreme, Eropea commiee or saarizaio, rssels, 999 [] S. Slijepcevic, S. Megeria, a M. okojak. Locaio Errors i Wireless Embee Sesor Neworks: Sorces, Moels, a Eec o Applicaios. AM Mobile ompig a ommicaios Review, 6(3): 67 78, 00