Location Estimation in Ad-Hoc Networks with Directional Antennas

Transcription

1 Locaion Esimaion in A-Hoc Newoks wih Diecional Anennas N. Malhoa, M. Kasniewski, C. Yang, S. Bagchi, an W. Chappell School of Elecical & Compue Engineeing, Puue Univesiy 65 Nohwesen Avenue, Wes Lafayee, IN 7907 USA. {nmalho, mkasnie, cyang, sbagchi, Absac Wih he evelopmen of locaion awae senso applicaions, locaion eeminaion has become an inceasingly impoan milewae echnology. Numeous cuen echnologies fo locaion eeminaion of senso noes use he eceive signal sengh fom senso noes using omni-iecional anennas. Howeve, an inceasing numbe of senso sysems ae now eploying iecional anennas ue o hei avanages like enegy consevaion an bee banwih uilizaion. In his pape, we pesen echniques fo locaion eeminaion in a senso newok wih iecional anennas une iffeen kins of eploymen of he noes. We show how he locaion esimaion poblem can be solve by measuing he eceive signal sengh fom jus one o wo anchos in a D plane wih iecional anennas. We implemen ou echnique using Bekeley MICA senso moes an show ha i is up o hee imes moe accuae han iangulaion using omni-iecional anennas. We also pefom Malab simulaions ha show he accuacy of locaion eeminaion wih inceasing noe ensiy. Keywos: locaion esimaion, iecional anenna, iangulaion, eceive signal sengh, eceive signal angle. 1 Inoucion Senso newoks povie a pomising infasucue fo gaheing infomaion abou paamees of he physical wol. Tiny wieless noes equippe wih iffeen kins of sensos can be isibue ove a fiel an can collec an ansmi he aa o a aa aggegaion poin, such as a cluse hea o a base saion. In oe o inepe he sense aa, i is ofen necessay o know he locaion of he noe which is he souce of he aa. In aiion, posiion infomaion is valuable fo opimizing he ouing pocess, as shown in many posiion awae ouing poocols [1][]. In geneal, hese saegies seek o avoi wasing valuable banwih by minimizing he conol affic fo oue eeminaion. Mos posiion-base ouing schemes also emove he nee o mainain ouing ables a he noes. Also, he noe s locaion may change. Mobile senso newoks ae becoming an impoan class in which he noes may move in a conolle manne o hough passive mobiliy. I is possible fo a noe o have up-o-ae infomaion of is locaion if i conains locaion eeminaion hawae, such as a GPS eceive, moune on i. Thee ae iffeen easons why i may no be feasible o equip each senso noe wih such hawae. A key esign pinciple fo many senso newok poocols is ha hey shoul be scalable o vey lage numbes, wih up o hunes of housans of noes. Fom an economic sanpoin, he eploymens shoul be cos-effecive. The economic consieaions have been iving he cos of he iniviual senso noes own o he poin whee sub-$1 noes ae beginning o look achievable []. GPS hawae woul incease he pice of senso newoks subsanially. Commecially available GPS eceives come in a wie pice ange of $10-$10,000. The eceives a he lowes en give poo accuacy, wih inaccuacies of ens of mees possible [5]. Receives ha give sub-mee accuacy, which may be neee fo many senso applicaions, ae moe han $5,000 in pice. The hawae also as o he weigh of he uni wih ypical eceives anging upwas of 5 oz. Finally, he baey lives of he eceives ae much shoe han ha of he senso noes hemselves, e.g., ens of hous fo he ypical GPS eceives compae o muliple monhs fo a epesenaive senso noe, he Bekeley moe. Thus, he combine uni of he senso noe an he GPS eceive will have o be eplace fa oo fequenly fo i o be pacicable fo a lage class of eploymens. Moe geneally, he eceive signal sengh fo a GPS can be as low as -130 Bm, oes of magniues less han he sengh of aiionally eceive signals in eesial applicaions an lowe han he sensiiviy of eceives on ypical senso noes (-100 Bm fo Bekeley moes). Theefoe, expensive eceives woul be neee. Also, since elaively unobsuce views ae equie fo GPS localizaion, in many senso newok eploymens, he GPS measuemens woul nee o be supplemene wih anging aa fom he local newok. Though i may no be feasible fo all he noes o be equippe wih special pupose locaion eeminaion hawae, i may be possible o equip a small facion of he 1

2 noes in he newok wih such hawae. Such noes, calle ancho noes, can ac as efeence poins fo locaion infomaion an ohe senso noes, calle age noes, can use infomaion fom ancho noes o esimae hei locaion. In he mos commonly use echnique calle laeaion he isance measuemens ae equie fom (k+1) neighbos in a k imensional plane. The example of laeaion in a -imensional plane is calle iangulaion in which he senso noe nees o know he isances fom hee neighboing noes. Seveal appoaches exis fo esimaing isance fom a neighbo, e.g., signal aenuaion an ime of fligh. In signal aenuaion, he powe of eceive signal is measue by he senso noe an knowing he signal sengh emie by he souce noe an he aenuaion elaionship wih isance (such as, 1/ whee is he sepaaion isance), he elaive isance can be calculae. Typically fo inoo envionmens o lage isances, he aenuaion elaionship becomes complex an ifficul o epesen concisely ue o muli-pah effecs an eflecion of he aio waves. Ohe echniques fo measuing elaive isances, such as ime of fligh ([1],[6]), ae less useful in ou envionmen since he aio signal avels a he spee of ligh an he isances avele fo signals by he senso noes ae elaively sho. Diecional anennas povie impoan benefis in senso newoks. Diecionaliy can be use as a fom of ivesiy buil ino he senso noe, which helps in coping wih he vaiabiliy in he communicaion channel an euce he link eo ae. The iecionaliy povies incease ansmission anges compae o omni-iecional anennas by focusing he ansmission enegy in he esie iecion. They can also incease he secuiy of communicaion by esicing he se of neighbos ha can ovehea a communicaion [15]. Diecionaliy in expensive communicaion sysems is commonly achieve hough he ceaion of a phase aay. Howeve, his is exemely expensive an is use peominanly only in high cos miliay applicaions. In aiion, i is equie ha he elemens of he phase aay be an appeciable facion of a wavelengh apa. This woul no be possible in elecically small fom faco senso noes. This peclues he use of a aiional aay o povie he esie beam scanning. Howeve limie iecionaliy can be cheaply inegae ino a small fom faco senso noe. In his invesigaion, euce size pach anennas have been evelope using sana pach aangemens wih high ielecic consan anennas. Muliple iecional anennas ae uilize an a simple swiching newok enables us o swich beween polaizaion saes ([7],[8]) an he iecion of aiaion. The soluion o locaion eeminaion wih omni iecional anennas is no applicable o iecional anennas since he aiaion paens ae iffeen an he eceive powe is epenan on angle as well as isance. In his pape, we use a moel fo senso noes equippe wih fou iecional anennas. We show ha even if he noes have sizes much smalle han he wave lengh of he RF wave, hen a senso noe can esimae is locaion using infomaion fom a single ancho. The iangulaion meho, in conas, uses hee ancho noes in he ieal case of no eos fo a wo imensional plane. The Eo Resilien Tiangulaion (ERT) echnique o cope wih eos woks as follows. Given a eunan numbe of anchos, a eunan se of linea equaions is se up an solve o minimize he leas squae eo of he posiion esimae. In ou appoach, he muliple isance measuemens, one fom each ancho noe, ae aveage o eemine he age noe s locaion. We pesen he algoihms fo posiion eeminaion fo iffeen kins of eploymen aligne an unaligne, single an muliple anchos. The algoihms ae implemene on Bekeley senso moes commecially available hough Cossbow Inc. of ype Mica an expeimens caie ou wih hem in an ouoo envionmen in a eal senso newok esbe. The expeimenal aa unelines he fac ha simple ipoles o no have a uly omni-iecional aiaion paen an he paen flucuaes wih ime. This opens o quesion esuls fo poocols evelope using ieal aiaion paens. The expeimenal esuls show ha aial isance esimaes ae 11% bee when one of he moes (ancho o age) have iecional anennas compae o a compleely ipole aangemen (i.e. all moes having a uniiecional aiao). The aggegae posiion eo is minimize by employing wo iecional anchos an swiching beween he anennas of he anchos fom which he ansmie signal is gahee. The aveage eo ove muliple ancho an age posiions in his case is 11.6% while ha fo he omniiecional sysem wih 3 anchos he eo is 7.5%. The measuemens wih each noe having iecional anennas lea o he insigh ha even if aiional iangulaion wee o be use, i is useful o employ iecional anennas o gahe he aial isance aa. Even by iscaing he angle of ansmission an ecepion aa, he iangulaion pocess is moe accuae wih iecional anennas. We also buil a simulaion moel whee he geneal case of ancho an age noes being unaligne wih espec o each ohe is simulae. Such oienaions may esul fom some api eploymen of he noes. The simulaion shows esuls fo vaying numbe of ancho noe neighbos. We show hough simulaion ha he aggegae eo is euce hough he use of ou echnique compae o he ERT meho by o 3.5 imes. The es of he pape is oganize as follows. Secion pesens backgoun maeial on locaion eeminaion in a-hoc wieless newoks. Secion 3 ses up he mahemaical moel fo ou soluion appoach wih iecional anennas. Secion pesens he simulaion expeimens an esuls. Secion 5 conclues he pape wih menion of fuue wok. Backgoun Tiangulaion is a common meho fo locaing objecs using ohe objecs which o know hei posiion. This is an applicable moel fo ou envionmen whee he posiions of some senso noes, possibly equippe wih GPS

3 eceives, ae known. A nice oveview of iangulaion base locaion eeminaion echniques is o be foun in [10] an [11]. The iangulaion echniques can be subivie ino wo caegoies laeaion, which uses isance measuemens, an angulaion, which uses angle measuemens along wih isance. If iniviual isance measuemens ae compleely accuae, laeaion equies (n+1) neighbos wih knowlege of locaion o pinpoin he age noe in an n imensional plane. An example of laeaion in wo imensional space is shown in Figue 1(a) an is calle iangulaion. Example use is in he Acive Ba Locaion Sysem [1]. Diffeen appoaches exis fo esimaing he isance fom a neighbo, fo example ime of fligh, aenuaion of signal sengh, an iecionaliy ([11],[13]). Measuing signal sengh elies on he popey ha aio waves aenuae in hei signal sengh wih inceasing isance beween he ansmie an he eceive. The eceive can calculae he isance if i knows he ansmission powe an he aenuaion moel [1]. 1 3 (a) θ 1 1 (b) Ancho noe Tage noe Figue 1. Locaion eeminaion wih neighboing ancho noes. Laeaion is in (a) an angulaion in (b) The aenuaion is ofen moele as 1/, whee is a elaively sho isance ouoos. Inoos, eflecion, an muli-pah faing make he moel an hence, he locaion esimae, inaccuae. The hi way of esimaing locaion is o compue he angle of each efeence poin wih espec o he sensing noe in some efeence fame. The posiion of he mobile noe can hen be compue using angulaion. In pacice, he iniviual isance measuemens ae inaccuae because he exac elaion beween he measuemen of physical popeies, such as signal sengh, an he ine-noe isance is no known. Hence, infomaion fom geae han (n+1) noes is neee fo pinpoining a age noe in an n imensional plane. The wok in [16] pesens an appoach fo minimizing he aggegae eo by consieing measuemens fom a eunan numbe of ancho noes. A eunan se of equaions is lineaize an solve o minimize he leas squae eo. In [17], Savaese e al. popose an ieaive poocol ha iffuses he locaion infomaion gahee fom neaby ancho noes hough he newok. The poocol uns in wo θ phases he Hop-Teain phase whee iniial esimaes ae gahee fom he ancho noes an he Refinemen phase whee he esimaes ae efine wih he noes ha have ecenly acquie ough locaion esimaes hemselves acing as ancho noes. Using his echnique, Bagchi e al. [18] show he elaionship beween he numbe of ancho noes an he eos in he locaion eeminaion, given a ceain eo in one hop neighbo isance esimaion. Fo example, wih 1/5h of he noes having GPS an 5% eo in isance measuemen, 1 samples ae equie fo a locaion esimaion of 10% accuacy. Angulaion is an alenae meho o laeaion fo compuing locaion base on neighbo infomaion, whee angles ae use in aiion o isance. A schemaic of he use of angulaion is shown in Figue 1(b). Diecional anennas ae neee fo he angle measuemens. Pevious wok has use phase anenna aays o use he angulaion echnique [10]. Muliple anennas wih known sepaaion measue he ime of aival of a signal. Given he iffeences in aival imes an he geomey of he eceiving aay, i is hen possible o compue he angle fom which he emission oiginae. If hee ae enough elemens in he aay an lage enough sepaaions, he angulaion calculaion can be pefome. Thee is a class of locaion eeminaion echniques ha o no ely on any popey of he eceive signal. Insea, hey ely on he conneciviy measue, i.e., if a noe α is able o hea fom anohe noe β, hen α is connece o β an is locaion is consaine o be wihin he ansmission ange of β ([13],[19],[0]). This class of echniques base on conneciviy measue povies locaion esimaes which ae quie coase-gaine. The ganulaiy becomes coase wih lage ansmission anges of he efeence noes. An ovehea of beacon o hello messages is also incue an he convegence imes of he algoihms ae ofen sensiive o he fequency of hese messages [0]. Also, some of he poocols ([19],[0]) equie cenalize pocessing which limis hei scalabiliy. Röme poposes a echnique geae o us-size senso noes which only have passive opical communicaion capabiliy an o no have acive RF communicaion capabiliy. I elies on a poweful base saion ha sens a phoo beam an oaes. Each senso noe has a phoo beam eeco an a clock an maks how long i sees he beam an he peio of oaion an eemines is locaion base on his. The meho is only applicable if single hop communicaion is possible beween all noes an he base saion. Also, as has been emonsae in [16] an appeas well accepe, isance measuemens ove lage isances ae vey inaccuae. 3 Soluion fo Diecional Anennas 3.1 Diecional Anenna Moel One of he simples semi-iecional anennas is he pach anenna. This anenna is use as a epesenaive example of an anenna ha may be use fo localizaion an which will 3

4 sill fi on a mobile fom faco. The ieal pach aiaion moel is a hemispheical aiao which allows fo semiiecional aiaion. The ypical gain of a pach anenna is on he oe of 3.5 o 6 Bi, epening on he ielecic subsae use in he esign. A epesenaive angula vaiaion of he gain fo a ypical micosip anenna will be in he ange of βl βl θ G ( θ) θ < < cos sin( ) cos sin( ) whee β is he fee-space consan an l is he longes lengh of pach, assuming he lowes oe moe of opeaion []. The gain is efine as he aio of he inensiy, in a given iecion, o he aiaion inensiy ha woul be obaine if he powe accepe by he anenna wee aiae isoopically. In he E-plane cu, he anenna s aiae e-fiel fom a βl sana pach aiao is ieally E cos sin( θ ). This paen epenence is in elaion o a cooinae sysem wih he z-axis pepenicula o he micosip pach aiao. This is he ieal soluion fo a pach anenna wih an infinie goun plane an is only slighly alee using a finie size goun plane. The goun plane is use o shiel he aiaing fiel fom he es of he cicuiy an he ohe aiaos. Unshiele aiaos, such as hose ha ae sana wih he moes, ae suscepible o paasiic aiaing cuens which esul in asymmeic paens. The eceive powe a an anenna is given by PG( Θ) H ( Θ) λ P, whee an ae he π ansmiing an he eceiving angles, especively, an is he isance beween he ansmie an he eceive. λ is he RF wavelengh of he caie fequency. Since (λ/π) is a consan, we will exclue i fom fuue expessions. I was howeve inclue in calculaing he esuls. A ealisic anenna aiaion paen obaine fom he esign of pach anennas in he HFSS simulaion package is use o moel he gain fo he expeimens. The simulaions wee valiae hough acual expeimens in an anechoic chambe. Fo he senso newok simulaions in his pape we use an anenna moel given by β L G( Θ ) H( Θ ) cos( sin( Θ )). This is he uppe boun of he possible anenna gain given in Secion 3 an is chosen in ou analysis an simulaion so ha an ancho has a lage numbe of age noes wihin is ansmission ange. Howeve, he popose echniques ae equally vali fo any ohe anenna moel. Howeve, he moel fo he eceive powe has implicaions fo he uniqueness of he soluion eemine by ou appoach. Figue (a) shows he consan powe conous fom wo anchos following he cos(ksin(θ)) iecional gain moel an (b) shows he cos(kθ) moel. While he powe conous of he fome moel inesec a jus one poin, ha of he lae inesec a wo poins. Theefoe he posiion of he age noe canno be uniquely eemine fom he eceive powe fom wo ansmies. Ancho 1 (a) Ancho Ancho 1 (b) Ancho Figue. Uniqueness of esimae locaion wih wo iffeen powe conous (a) cos(ksin(θ)) an (b) cos(kθ) 3. Aligne anennas In a numbe of pacical applicaions i is easonable o expec ha he sensos will be manually eploye. Sensos se up o monio a bige s healh have o be place by consucion wokes on he bige fo example. In such scenaios even hough i may no be possible o know he pecise locaion of he senso, i is possible o place hese sensos in a pe-eemine oienaion. Senso B Receive C D Θ Θ 1 Θ c Θ Ancho Receive 1 Θ 1 Figue 3. Locaion eeminaion wih aligne noes If he anennas of a age senso noe ae aligne, hen we can use he powe eceive a muliple eceiving anennas of he age fom a single ansmiing anenna on an ancho fo posiion esimaion. Wihou loss of genealiy consie ha an ancho noe is place o he souh-eas of he age noe as shown in Figue 3. Typically he size of he senso woul be much smalle han he ansmission isance. So /Θ c. Then eceive powe a he wo eceiving anennas of he age noe is given by A

5 P P π P G( Θ ) H( Θ ) G( Θ ) H( Θ ) (1) P P P G( Θ ) H( Θ ) G( Θ ) H( Θ ) P π π G( + Θ ) H( + Θ ) () 1 1 Thus, we have wo equaions (1) an () in wo vaiables 1 an. Since, hese ae nonlinea equaions i is ifficul o ge a close fom soluion fo 1 an in ems of he inpu vaiables P 1 an P. Howeve, hese equaions can be numeically solve by sana mehos o obain 1 an. A baseline expeimen fo his is wih he ancho noe having omni-iecional ipole anennas. In his case he gain of he ansmie, G( ), is consan ove all an enoe G omni. Figue shows his configuaion. Now, since we know he isance as well as he elaive iecion of he age wih espec o he ancho, we can esimae is posiion. This esimae is base on measuemens fom jus one neighboing ancho noe wheeas iangulaion equies measuemens fom a leas hee anchos. The esimaes fom muliple anchos can be aveage o obain a bee esimae of he posiion. Alenaively, he infomaion abou 1 coul be iscae an he ange measuemens () can be use o iangulae he posiion of he senso in a leas squaes manne. Boh, hese saegies have been evaluae in ou simulaions an he aveaging saegy is foun o yiel bee esuls. Senso B Receive θ C D Receive 1 θ 1 θ c θ y θ x A Ancho Figue. Locaion eeminaion wih an omniiecional ansmie an iecional eceive 3.3 Genealizaion o Unaligne Anennas In cases whee i is no possible o ensue a global oienaion of all noes of a newok, aiional measuemens can be use o esimae posiion. Receive powe a wo iffeen anennas of he age noe fom wo ansmiing anennas of he ancho noe is measue. Such an aangemen is shown in Figue 5. Geomeic elaions beween he vaious ansmission an eceiving angles can be eive fom he figue. Θ 6 Θ Θ1 3 π 8 Θ 3 5 Θ 1 7 π + Le P ij enoe he powe eceive by anenna i on he age noe when anenna j is ansmiing on he ancho noe. We can use hese equaions o simplify he eceive powe equaions as follows. P G( π Θ Θ3 Θ ) * H( Θ) P (3) 11 ' π π P G( + Θ3 )* H ( + Θ ) P 1 ' () π π P G( 3 ) * H ( + Θ ) P 1 ' (5) P G( Θ3) * H ( Θ ) P ' (6) Equaions (3) hough (6) in he fou vaiables, 3,, an can again be numeically solve o esimae he locaion of he age noe. Senso Θ N Θ 1 Θ 3 Θ Θ N π-θ N Ancho Θ 1 1 Senso Figue 5. Locaion eeminaion fo unaligne anennas This scheme equies ha wo age anennas be able o simulaneously eceive ansmissions fom wo ancho anennas. This woul equie a ansmie beam wih of 180. This is non-opimal fo fou anennas coveing a 360 plane bu is a aeoff fo incease egees of feeom in he oienaion of he noes. Besies, he incease beamwih will len geae faul oleance o he sysem by poviing geae eunancy in he aeas eache by muliple ansmiing anennas. I will also make he anenna esign easie since high iecionaliy, i.e. naow beam wih is no neee. 3. Aligne Anennas wih Two Anchos The wo locaion eeminaion mehos escibe ealie ely on he iffeence in powe eceive a wo anennas of a senso fom he anennas on he same ancho noe. The eo in he powe eceive can become coelae ue o he poximiy of he wo anennas, even if Θ 6 Θ 8 Θ 7 Ancho Θ 5 5

6 hey ae poine in sepaae iecions. In a eal life scenaio he coelaion can significanly euce he accuacy of he locaion esimae, especially fo a vey small senso noe. To invesigae he pefomance of he locaion eeminaion wih inceasingly uncoelae channels, wo ansmie signals wee sen fom wo moes subsanially emove fom each ohe. This scheme is also useful in siuaions in which moe han one iecional anenna woul no fi on a single moe. The aangemen is shown in Figue 6. Θ 1 Θ Θ 3 Θ Θ 1 1 Ancho 1 Senso 3 Θ 3 Θ Θ 5 Ancho Figue 6. Locaion eeminaion using measuemens fom wo anchos Since he locaion of he wo anchos is known, he paamees 3 an 3 can be eemine. Using geomeic popeies of he sysem we ge he following elaions beween he vaious angles π π Θ 5 Θ Θ1 3 The equaions fo he eceive powe ae given by P P P 1 G( 1) H( 1) (7) P G( ) H( ) (8) Θ Θ Θ Θ Using he law of sines along wih elaions beween he angles eive ealie we ge wo moe equaions 3 (9) cos( Θ +Θ ) sin( Θ +Θ ) Θ Θ Θ +Θ 3 1 cos( ) sin( ) (10) This gives us fou equaions in fou unknowns 1,, 1, an, which can be numeically solve. Thus, he isance an he angle wih espec o each of he wo anchos ae eemine. The senso noe s locaion can be esimae using eihe isance, angle pai an he final locaion esimae using aveaging of each esimae. In his secion, we have povie he mahemaical soluion o he poblem of locaion esimaion wih iecional anennas in hee iffeen scenaios. The noe specificaions an he eploymen coniions will eemine which scenaio is applicable. Expeimens & Resuls.1 Expeimenal Seup Cossbow MICA moes MPR00CB opeaing a 900 MHz an unning TinyOS as he pogamming envionmen ae employe as he senso noes fo ou esbe. Two kins of omni-iecional anennas ae use - quae wave whip anennas (MMA00CA) (on he ansmiing ancho noe, comes off-he-shelf wih he moes) an quae wavelengh monopole anennas wih an expane goun plane (on he eceiving age noes, fabicae fo easy inefacing an co-exisence wih he pach anennas). Diecional anennas ae fabicae an use on boh he age senso noe, whose locaion is o be eemine, an he ancho senso noes, whose locaion is assume o be known. Pach anennas fabicae on uio subsaes, Roges RO3010 whose ielecic consan is 10., ae chosen as he semi-iecional anennas in his esbe ue o hei simple fabicaion, small size, an low-cos. The ohe caniae esigns such as Yagi anennas, hon anennas, an anenna aays, woul have moe iecionaliy bu ae lage an moe expensive an heefoe no applicable. Senso moes wih fou iecional anennas conolle by a swiching newok accoing o he eceive signal sengh inicao (RSSI) a he anennas ae employe o be he age moes (funcioning as eceives). The swiching newok is implemene by a GaAs MMIC SPT swich. Sofwae execuing on he age moes monios he eceive signal powe on he fou anennas an selecs he equisie ones (he bes, o he wo bes) fo is locaion compuaion. The moes ae ese in an ouoo envionmen o obseve he pefomance of he locaion eeminaion sysem wih iffeen kins of wieless faing. The goal of he expeimens is o eemine he esimaion eo of he locaion eeminaion sysem. Thee expeimens ae se up wih ansmiing ancho moes ha iniially have omni-iecional (ipole) anennas (see Figue 7(a)). If necessay, aligne pach anennas ae moune on he ancho moes (see Figue 7(b) an (c)) o have a complee iecional ansmiing an eceiving sysem. The age moes, funcioning as eceives, ae equippe wih he swiche iecional anennas an collec he aa which is fowae o a lapop hough a Univesal Asynchonous Receive/Tansmie (UART) Ineface. Malab pogams ae wien o solve he equaions given in Secion 3 numeically. The sofwae uilizes a gain paen eive fom he pach anenna fom Ansof s High Fequency Simulaion Sofwae (HFSS) package. HFSS, a full wave elecomagneic simulaion commecial sofwae, is he efaul inusy sana RF esign simulaion ool [][5]. The aiaion paen is simulae an compae wih he measuemen of he fabicae pach (Figue 7). I is obseve ha he wo ae in close ageemen an hence he HFSS moel is use fo fuhe analysis. The expeimens in Secion. have 150 samples fo each posiion, aken in hee sepaae ime inevals. These ae aveage fo he epoe numbe. Malab simulaion is 6

7 use o ieaively solve he equaions o minimize he eo in he aial isance an he angle of ecepion HFSS si mul a i on Measu emen 180 Figue 7. Raiaion paen of he pach anenna fom HFSS an he measuemen in anechoic chambe oom If he ieaive Malab simulaion is consiee oo expensive o execue on he moes, a saic lookup able of signal sengh vesus aial isance an angle of ecepion can be ceae an uploae ino he moes. This cus own on he laency of he locaion esimaion as well as he compuaional expense on he simple pocessos of he senso noes, a he expense of he accuacy of he soluion. This appoach will be fuhe invesigae in he fuue. The locaion eo is efine by he eo isance fom he esimae age posiion o he acual age ˆage posiion age,0 ivie by he known acual isance beween he ancho moe an he age moe R ) whee is a wo-imensional posiion veco. Locaion eo R eo ˆ ˆ age age,0 age age,0 R ( ancho,0 age,0 ancho,0 age,0 ( xˆ x ) + ( yˆ y ) age age,0 age age,0 ˆ ancho age,0 + ancho age,0 ( xˆ x ) ( y y ). Expeimenal Resuls (11) Expeimen 1: Aligne case: Single omni-iecional anenna ancho, ual pach anenna age In Expeimen 1, an ancho noe is use wih an omniiecional o ipole ansmi anenna. The age noe has a ipole anenna an wo iecional pach anennas. Tes 1 is he case wih a ipole anenna on he age noe. Tes has he iecional anennas on he age noe. The age noe is place in he cene of a cicle of aius 8 fee. Receive powe measuemens ae mae wih he ancho noe a iffeen poins on he peiphey of he cicle. Tx moe Rx moe Θ1 (a) Θ Rx moe Tx moe Θ1 Θ Tx moe ( c) Pach_W Pach_N Pach_S Rx moe Θ1 Pach_E Θ (b) Tx moe Figue 8. Anenna configuaions fo (a) Expeimen 1 (b) Expeimen (c) Expeimen 3 The elaive isance eo is shown in Figue 9 fo boh ess. The x-axis is he angle of he ancho noe wih espec o he noh-souh axis awn fom he age noe, wih he ancho noe being move on he cicumfeence of a cicle wih he age noe a he cene. When using he iecional anennas, he age noe selecs he wo songes signals on is eceiving anennas o execue he locaion esimaion algoihm. When using he omniiecional anenna,, he posiion canno be eemine since a leas hee ancho noes woul be neee an hence, he isance esimae is use as he basis fo compaison. In his case he Fiis fomula is use wih an expeimenally eemine paamee fo he exponen in he powe loss, R N, N1.89 in he measuemen envionmen. This is classifie as a line-of-sigh an elaively mulipah fee envionmen an is applie o R ˆ ˆTX RX esimae,0,0. The isance eo in he eniely omni-iecional anenna sysem is in he ange of 0-105% wih a mean of 3%, while his eo is euce o 0-90% wih a mean of 3% in he case of he iecional anennas. This esul can be explaine by he fac ha in omniiecional anennas, hee ae moe muli-pah effecs leaing o moe inefeence an moe flucuaion in eceive signal sengh. Thus, even if iangulaion is use base on he isance esimaes wih he pach anennas, iecionaliy of he anennas is useful since i leas o moe accuae esimaes of iniviual isances. Howeve, by using he angula infomaion ha is gaine fom muliple eceiving anennas, he locaion of he age noe can be eemine wih a single moe wihou 7

8 he use of iangulaion (see Secion 3.). The locaion eo R eo of es in Expeimen 1 is shown in Figue 10. The eo is lage han he aius eo because he angle esimaion eo also conibues o he locaion eo. On aveage, he locaion eo is 3.15%. This eo can be fuhe miigae by using ohe esimaion anchos, as Expeimen 3 shows. Figue 11.Disance an angle esimaion eo fo Expeimen. [The soli line is he esimaion an he ashe line is acual measuemen.] Figue 9. Relaive eo in isance esimaion fo Expeimen 1 Figue 10. Locaion esimaion eo fo Expeimen 1, Tes Expeimen : Single pach anenna ancho wih ual pach anenna age In his expeimen iecional pach anennas ae employe in he ansmission moes (see Figue 8(b)). The eceiving anennas ae all iecional. The analyical moel is as shown in Secion 3.. The eos in measue isance an angle ae shown in Figue 11 an he maximum eos in he wo meics ae seen o occu a iffeen posiions. The locaion esimaion eo calculae fom acual measuemens is shown in Figue 1. The locaion eo gows lage as he angle Θ 1 inceases because he ansmission anenna is no oiene owas he age noe. Compae o he expeimen wih omni-iecional ansmiing anenna, he locaion eo is euce when he angle is smalle han 5 egees because he aiaion paen of iecional ansmission anenna ovelaps wih he eceiving anennas. Afe his coss-ove poin, he pach #W on he ancho noe which is oiene o he wes can be use as he ansmission anenna. Hence, he locaion eo can be conolle o be less han 0% in a single ancho. The aveage eo is 9.18%. Figue 1. Locaion esimaion eo fo Expeimen Expeimen 3: Two single pach anenna anchos an single pach anenna age Two anchos can be use o povie aiional aa fo locaion esimaion, as shown in he analysis of Secion 3.. The configuaion of Expeimen 3 is shown in Figue 8(c). The ouoo measuemen esul is shown in Figue 13. Fo his expeimen, measuemens ae aken iniviually fom each iecional ancho noe an no a he same ime. This oes no affec he valiiy of he esuls since he sochasic moel fo he channel is ime invaian. When an aiional ancho povies anohe powe measuemen, he esimaion eo euces fom 9.18% in Expeimen o an aveage of 17.78% in Expeimen 3. The fis cause of his impovemen is he incease in he sepaaion of he wo ansmission pach anennas in Expeimen 3 compae o he elaively small isance of he wo paches in Expeimen. This means ha he eo in he aial isance R an he ecepion angle Θ ae now uncoelae. Secon, he faing channels ae moe uncoelae in Expeimen 3 because he isance beween he wo anchos is much geae han he wavelengh of he RF wave. Thus, we conclue ha significan locaion esimaion impovemen can be obaine by using muliple anchos wih iecional anennas. 8

9 Figue 13. Locaion esimaion eo fo wo ancho noes wih iecional pach anennas We pefom saisical analysis on he aw measuemens o quanify he eos using infomaion fom hee ancho noes. Fo es 1 of expeimen 1 (pue omni-iecional), he eo is 7.5%, fo expeimen 0%, an fo expeimen %. The impovemen is moe siking as he numbe of neighbo anchos inceases as he simulaion esuls show..3 Simulaion Resuls We ae ineese in evaluaing he accuacy of he locaion eeminaion poocols wih vaying numbe of ancho noes. The accuacy is measue fo beween an 30 anchos of iffeen kins: omni-iecional, iecional, unaligne, an he wo ancho case. This ange of expeimen woul be beyon he hawae esouces of ou esbe an hence a simulaion mehoology is use. The isoion in eceive powe is simulae using a Rician faing channel. Each aa poin is base on he aveage of 50 iffeen samples. Fo each sample, he ancho noes ae place anomly wihin a 10x10 mee gi. The ansmie powe is -10 B, equivalen o ha use in hawae, an he size of he enie senso noe is se a 10 cm. Figue 1 is shown wih espec o he inceasing numbe of neighbos. Fom op, he iffeen cuves coespon o: single ancho unaligne, hee omniiecional anchos an omni-iecional age noe, single ancho aligne anenna wih leas squae eo aggegaion, single ancho aligne anenna wih aveaging fo aggegaion, wo anchos wih aligne anenna. Excep fo he omni-iecional case, all he ohes have pach anennas on he age noe. The fis hee fom one goup an he las wo fom anohe. The eos in he fis goup ae noiceably highe han hose in he secon goup. The esimaes in boh goups show a hoizonal en beyon 1 ancho neighbos inicaing ha highe ensiy is no equie fo locaion esimaion puposes. The genealize oienaion, howeve, equies up o 0 neighboing ancho befoe sabilizing. The highes eo is obseve fo he genealize oienaion, inicaing he impoance of appoximae alignmen a he leas. The nex highes eo is fo he omni-iecional ancho anenna, followe by he single ancho wih leas squae eo aggegaion. This inicaes he value of iecional anennas an aveaging as he meho fo aggegaion. The wo ancho case wih aligne anenna an using aveaging as he aggegaion echnique oupefoms he single ancho case a lowe ensiies bu is saisically equivalen a highe noe ensiies. The eo bas coesponing o 95% confience ineval ae shown. We obseve ha aveaging as he meho fo aggegaing gives much bee esuls han leas squae esimaion. One of he pimay easons fo his phenomenon is ha aveaging cancels he eos in esimaes in iniviual measuemens while he effec of eo in leas squaes esimaion is aiive. The esuls shown in Figue 1 have slighly lowe eo aes han hose foun in hawae. This is mos likely ue o a limie abiliy o accoun fo all mulipah popagaion, faing, an ohe envionmenal affecs. Moeove, he aligne cases wee always pefecly aligne in he simulaion, while he expeimens ha elaively aligne anennas, bu wihin some magin of eo ha is vey ifficul o eemine. Pecenage Eo Posiion Esimaion Eo Two Anchos One Ancho LSE One Ancho Unaligne Numbe of Neighbos One Ancho Aveaging OmniDiecional Anenna Figue 1. Evaluaion of esimaion eo fo vaying numbe of neighboing anchos 5. Conclusions In his pape we have pesene vaious echniques fo locaion eeminaion in a-hoc newoks using iecional anennas. The combinaion of he schemes is esigne o mee he vaiey of equiemens an egees of feeom fo eal life applicaions. The vaious aeoffs beween hese schemes, such as feeom of oienaion vesus beam wih an noe size vesus numbe of ancho noes, have also been evaluae. The soluion appoach can fom he founaion fo locaion eeminaion poocols fo he inceasingly popula iecional anennas. Ou esuls, shown hough expeimens on acual senso moes an simulaions, bing ou he fac ha locaion esimaion wih omni-iecional anennas equies a leas hee anchos an is less accuae han wih iecional anennas. Also, using uncoelae communicaion channels hough wo geogaphically sepaae ancho noes pouces bee 9

10 esuls han muliple anennas on he same ancho noe. The eo is euce fom 7.5% in an omni-iecional sysem o 11.6% wih wo iecional ancho noes. In fuue, we inen o expeimenally eemine he exen of coelaion in channel noise a he iffeen anennas of a senso. This will be applie o a sensiiviy analysis of ou schemes. We also popose o analyze locaion esimaes eive fom measuemens fom muliple ansmiing anennas o muliple eceiving anennas. Finally, we will seek o solve he genealize anenna case wih muliple ancho noes. 6. Refeences [1] Y.-B. Ko an N. H. Vaiya, Locaion-Aie Rouing (LAR) in Mobile A Hoc Newoks, ACM/BalzeWieless Newoks (WINET) J., vol. 6, no., 000, pp [] Jög Wime, Main Mauve, Hannes Haensein, Holge Füßle, Posiion-Base Rouing in A-Hoc Wieless Newoks, In Mohamma Ilyas (e.): The Hanbook of A Hoc Wieless Newoks, CRC Pess, Boca Raon, FL, U.S.A., 00. [3] Philo Juang, Hiekazu Oki, Yong Wang, Magae Maonosi, Li-Shiuan Peh, an Daniel Rubensein, Enegyefficien compuing fo willife acking: esign aeoffs an ealy expeiences wih ZebaNe, ASPLOS 00, pages [] J. M. Kahn, R. H. Kaz an K. S. J. Pise, Mobile Newoking fo Sma Dus, ACM/IEEE Inl. Conf. on Mobile Compuing an Newoking (MobiCom 99), Seale, WA, Augus 17-19, [5] Gamin s etex, a hp:// [6] N. B. Piyanha, A. Chakaboy, an H. Balakishnan, The cicke locaion-suppo sysem, In Mobile Compuing an Newoking, pages 3-3, 000. [7] L.-C. Kuo, 3-D FDTD Design Analysis of A. GHz Polaizaion-Divesiy Pine Dipole-Anenna wih Inegae Balun an Polaizaion-Swiching Cicui fo WLAN an Wieless Communicaion Applicaion, IEEE Tans. Micowave Theoy an Techniques, vol.51, no., pp ,feb 003. [8] J. Peiss e al., Polaizaion ivese anenna fo poable communicaion evices, U.S. Paen , 000. [9] M. A. Jensen, an Y. Rahma-Samii, Pefomance Analysis of Anennas fo Hanhel Tansceives Using FDTD, IEEE Tans. Anennas an Popagaion,, 199, pp [10] Jeffey Highowe an Gaeano Boiello, Locaion sensing echniques, Technical Repo of he Univesiy of Washingon CS Depamen, UW-CSE , July 001. [11] J. Highowe an G. Boiello, Locaion sysems fo ubiquious compuing, IEEE Compue, pages 57-66, Augus 001. [1] Any Hae, Any Hoppe, Pee Seggles, Any Wa, an Paul Webse, The anaomy of a conex-awae applicaion, In Mobicom 1999, pages 59-68, Seale, WA, Augus [13] N. Bulusu, J. Heiemann, an D. Esin, GPS-less low cos ouoo localizaion fo vey small evices, IEEE Pesonal Communicaions Magazine, pages 8-3, Ocobe 000. [1] J. Highowe, R. Towe, an G. Boiello, SpoON: An inoo 3 locaion sensing echnology base on RF signal sengh, Technical Repo of he Univesiy of Washingon, CS Depamen, Febuay 000. [15] A. D. Woo an J. A. Sankovic, Denial of sevice in senso newoks, In IEEE Compue, 35(10):5 6, Ocobe 00. [16] Jan Beuel, Geolocaion in a PicoRaio Envionmen, M.S. Thesis, ETH Zuich, Decembe, [17] Chis Savaese, Jan Rabaey, Koen Langenoen, Robus Posiioning Algoihms fo Disibue A-Hoc Wieless Senso Newoks, USENIX Technical Annual Confeence, Moneey, CA, June 00. [18] S. Cabuk, N. Malhoa, L. Lin, S. Bagchi, an N. Shoff, Analysis an evaluaion of opological an applicaion chaaceisics of uneliable mobile wieless a-hoc newok, In Poceeings of he 10h Pacific Rim Depenable Compuing Confeence, (PRDC 0), Mach 00. [19] N. Sunaam an P. Ramanahan, "Conneciviy base locaion esimaion scheme fo wieless a hoc newoks," Poceeings of Globecom vol. 1, pp.13-17, Nov. 00. [0] L. Dohey, L. El Ghaoui, K. S. J. Pise, Convex Posiion Esimaion in Wieless Senso Newoks, Infocom 001, Anchoage, AK, Apil 001. [1] Kay Röme, The Lighhouse Locaion Sysem fo Sma Dus, In MobiSys 003. [] P.J.B. Claicoas, Y. Rahma-Samii, J.R. Wai, Hanbook of Micosip Anenna, Volume 1, IEEE Elecomagneic Waves Seies 8, [3] M. Vossiek, L. Wiebking, P. Gulen, J. Wiegha, C. Hoffmann, P. Heie, Wieless local posiioning, IEEE Micowave Magazine, pages 77-86, Volume:, Issue:, Dec [] HFSS simulaion ool. Available a: hp:// [5] L. Boccia, G. Amenola, G. Massa, Pope moeling using an FEM elecomagneic simulao leas o he esign of a low-cos, lighweigh GPS pach anenna capable of excellen mulipah ejecion, Micowave an RF, Jan See also: hp:// [6] Cossbow Technology Inc., MICA Moe: hp:// pf/ _a_mica.pf. [7] TinyOS Communiy Foum: hp:// 10