Different Approaches of Angle of Arrival Techniques In Wireless Sensor Networks

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1 Differet Approaches of Agle of Arrival Techiques I Wireless Sesor Networks Sharmilla Mohapatra Sambit Kar Sasmita Behera Departmet of CSE Departmet of CSE Departmet of IT VSSUT, Burla , Idia KIIT, BBSR-75104, Idia VSSUT, Burla , Idia Abstract- Despite of the fact that localizatio techiques i Wireless Sesor Networks are studied durig last may years but there is o uaimity o the existece of simple, accurate, decetralized ad eergy efficiet techiques o localizatio i WSN. For static WSNs, localizatio is ot much a problem because oce ode positios have bee determied they are ulikely to chage. Whereas mobile sesors must frequetly estimate their positio, which takes tim ad eergy ad cosumes other resources eeded by the sesig applicatio. 1. Itroductio I Wireless Sesor Networks, localizatio of sesors is a key eablig techology because the sesor odes eed to kow their locatios i order to detect ad record evets so that their data is meaigful. Maual assigmet of ode coordiates is oe possibility but is ofte impractical or impossible due to the umber of odes or the method of deploymet. Equippig each sesor with a GPS receiver is aother solutio, however it is ofte cost prohibitive i terms of both hardware ad power refiemets. Moreover, sice GPS requires lie of sight betwee the receiver ad the satellites, it may ot work well i buildigs or i the presece of obstructios such as dese vegetatios, buildigs or moutais blockig the direct view to the GPS satellites. There are several group of techiques that eables the sesors to detect their positios. Despite of huge research effort, there is still o well accepted techique o how to solve the localizatio issue i outdoor sesor etworks.. ocalizatio i wireless sesor etworks The process of fidig the locatio of the odes is called ocalizatio. I this process we try to fid the approximate locatio of the sesor ode with high accuracy. The process of localizatio ivolves collectig the iformatio about the logitude, latitude ad altitude of the sesor ode. ocalizatio ca be classified ito two types: ocal or Relative ocalizatio i which locatio of a poit is give i referece to a local poit. I this techique local referece poits are used to describe locatio of a object, ad aother is Global or Absolute ocalizatio i which the locatio is give with respect to the world with the help of latitude, logitude ad altitude. ocatio ca be specified i two ways: Geometric: the locatio of a object ca be specified usig distace ad agle. Topological: locatio is give by coectios with the ladmarks. Some localizatio methods examies the received sigal stregth of a message broadcast from a kow locatio. Sice free space sigal stregth model is govered by the iverse square law, accurate localizatio is possible. 1

2 .1 Need of localizatio? Wireless sesor etworks are ofte deployed i uatteded ad hostile eviromets, leavig idividual sesors dagerous to security compromise. Node self localizatio capability is a highly desirable characteristic of sesor etwork because sesor readigs are meaigless without a coordiate tag. Most of the routig protocols use floodig techique for routig of packets. If we kow the locatio of each ad every sesor ode, a selective forward routig techique ca be used to route packets. Selective forwardig reduces the Network load ad icreases the etwork lifetime by savig power of the idividual ode. Sesor data must be registered to its physical locatio to permit deploymet eergy efficiet routig schemes ad source localizatio algorithms.. Troubles i localizatio i wireless sesor etwork Most of the Wireless Sesor Network uses GPS receiver for ocalizatio. But the sesor odes is dese i ature ad usig GPS receiver is ot ecoomically good. GPS based receiver techique caot be used for idoor localizatio. GPS receiver system require satellite commuicatio, so it requires more battery power. Moreover GPS receivers are expesive. Sice GPS requires lie of sight with the receiver ad the satellite, it may ot work well i buildigs or i the presece of obstructios blockig the direct view to the GPS satellites..3 Alteratives to GPS i sesor etwork localizatio I the search for ocalizatio i the Wireless Sesor Networks there could be two types of techiques used for Sesor ocalizatio amely: Cooperative ad No-cooperative. I the first approach few base statios are used for localizatio where every sesor ode receives sigals directly from base statio i which distace betwee ode ad base statio ca be measured o the basis of sigal stregth ad time of arrival (TOA), ad i the secod approach a small o of achor odes are used i etwork, where the achor odes have prior kowledge of locatio. The achor odes receives its locatio iformatio either from GPS or from maual deploymet of the sesor ode. This sesor ode helps the other odes i the etwork to localize themselves usig some algorithms. I this approach there is o eed to get the sigal direct from the base statio to localize a sesor ode..4 Requiremet of algorithms for localizatio Sesor Network requires localizatio algorithm because it is ot possible to provide the sesor odes with locatio iformatio at the time of deploymet. I some sesor etwork the sesor odes are mobile ad whe the sesor odes move they eed localizatio because of some applicatios..4.1 Differet localizatio algorithms Usig Time of arrival estimatio(toa): ocalizatio by Time of Arrival measures the time a sigal takes to arrive at the sesors. This requires to kow the time whe the sigal was trasmitted ad requires tight time sychroizatio betwee the seder ad the receiver. The mai drawback of this approach is that it is difficult to precisely record the arrival time of the radio sigals, sice they travel close to the speed of light. Time of arrival uses the time of arrival at certai base statio rather tha the measured time differece betwee departig from oe ad arrivig at the other statio.

3 Usig Time differece of arrival(tdoa): Time differece of arrival improves upo time of arrival by elimiatig the eed to kow whe the sigal was trasmitted. May time sychroized odes receive the sigal ad estimate the time differece of arrival or the differece i the sigal phase at a specific time istat. As the sigals travel at a costat speed, the source positio ca easily be determied if there are sufficiet umber of participatig odes. Usig Received sigal stregth(rss): Received sigal stregth is aother localizatio algorithm that measures the sigal stregth of a message broadcast from a kow locatio. Sice the free-space sigal stregth is govered by iverse square law accurate localizatio is possible. RSS based ragig is attractive as a meas of distace estimatio because it is essetially free, wireless sesor odes already have radios, ad sigal stregth methods make extesive use of recogizable is ofte beig measured for each radio packet ladmarks. This method is proposed uder the somehow. RSS method uses the kowledge of the trasmitter power, the path loss model ad the power of the received sigal to measure the distace of the receiver from the trasmitter. Usig Agle of arrival(aoa): Agle of arrival method uses array atea to estimate the directio of arrival ad at least two receivers called as sub array are required to locate sources. The agle of arrival method ivolves determiig agular separatio betwee two beacos or a sigle beaco ad a fixed axis. By determiig the agle of arrival at a umber of sesor odes, agulatio ca be used to estimate the positio. 3.Agle of arrival estimatio approaches Agle-Of-Arrival ocalizatio is a well-kow techique ad thoroughly described i the ope literature, there are ot may papers dealig with AoA schemes appropriate for wireless sesor etworks ad their specific objectives, requiremets ad applicatios. 3.1 Ad Hoc positioig system usig AoA Ad hoc etwork are mostly studied i the cotext of high mobility, high power odes ad moderate etwork sizes. The mai features of ad hoc etworks are large umber of uatteded odes, lack of deployig supportig ifrastructure ad high cost of huma supervised maiteace. Here we address the self positioig ad orietatio of the odes i the field. This positioig ad orietatio algorithm is appropriate for idoor locatio aware applicatios, where the problem is ot the upredictable highly mobile topology rather the ad hoc deploymet[3][17][18]. The orietatio ad positioig problems have bee itesively studied i the cotext of mobile robot avigatio[8]. The assumptio that a small fractio of etwork has oly the positio capability. The proposed method is differet from the other methods based o the capability of the odes to sese the directio from which the sigal is received which is kow as the agle of arrival(aoa). AoA sesig requires either a atea array or several ultrasoud receivers but alog with positioig it also provides the orietatio capability. The etwork is a collectio of ad hoc deployed odes where ay ode ca oly commuicate directly oly with its immediate eighborig odes withi radio rage. I the ideal case, whe radio coverage of a ode is circular, these etworks are modeled as a fixed radius radom graphs. Each ode i this etwork is assumed to have oe mai axis agaist which all agles are reported ad the capacity to 3

4 estimate approximately accurate directio from which a eighbor is sedig data. Fig. 1. Node with AoA Capability We assume that after the deploymet, the axis of the ode has a arbitrary, ukow headig. Some of the odes, called ladmarks have additioal kowledge about their positio, from some exteral source, such as a GPS receiver, or maual iput. The term bearig refers to a agle measuremet with respect to aother object [1][]. Radial is a reverse bearig, or the agle uder which a object is see from aother poit. We use the term headig with the meaig of bearig to orth, that is, the absolute orietatio of orietatios. Ufortuately, these methods require a strog cooperatio betwee eighbor odes, ad they are proe to error accumulatios. 3. Agle of arrival estimatio usig Cricket compass By aalogy to a traditioal compass, kowledge of orietatio through cricket compass attached to a mobile device ehaces various applicatios icludig way-fidig ad avigatio, directioal service discovery. Cotext aware applicatios which adapt their behavior to evirometal cotext such as physical locatio are a importat class of applicatios i emergig pervasive computig eviromets[19]. The first motivatig applicatio is the Wayfider. This applicatio is desiged to ru i a hadheld computer ad help people avigate toward a destiatio i a ufamiliar setup. The secod motivatig applicatio is called the the mai axis of each ode. I figure 1, for ode B, Viewfider. The user ca poit it ay directio ad bearig to A is radial from A is ad headig is specify a sweep agle ad maximum distace. Usig [3]. i figure 1, Node A sees its eighbors at agles a active map itegrated with a resource discovery ad ad has the possibility of iferrig oe system, the viewfider the retrieves ad displays a represetatio of the set of devices ad services lyig agle of the triagle, For cosistecy iside a sector of iterest specified by the user ad all agles are assumed to be measured i allows the user to iteract with these devices through trigoometric directio. Node A ca also ifer its headig, if headig of oe of the eighbors, say B, is kow. If ode B kows its headig or agle to the orth to be, the A may ifer its headig to be. If o compass is available i ay ode, but each ode kows its positio, headig ca still be foud because the orietatios for the sides of the triagle ca be foud from positios of its vertices[4]. I Ad Hoc positioig system, the AoA schemes are described where sesor odes are forwardig their bearigs with respect to achors, i.e. odes which are assumed to kow their ow coordiates ad the represetatio o the map. Figure shows a beaco B ad a compass with two ultrasoic receivers R 1 ad R which are located at a distace apart from each other. The agle of rotatio of the compass θ with respect to the beaco B is related to the differetial distace d 1 ad d, where d 1 ad d are the distaces of the receivers R 1 ad R from B. Figure (b) shows the beaco B from figure (a) projected oto the horizotal plae alog which the compass is aliged. I this figure, x 1 ad x are the projectios of distaces d 1 ad d o to the horizotal plae. We assume the compass is held parallel to the horizotal plae. 4

5 R1 Beaco B(o ceilig) d1 d Z R θ X Horizotal Plae Fig.. (a) Determiig the agle of Orietatio θ alog the Horizotal plae. (b) A rotated compass leadig to differece i distace betwee the beaco ad the receivers From Figure (a): x 1 = d 1 z (1) x = d z () θ X1 X X / θ / method is to estimate each of these quatities with high precisio so as to produce a accurate estimate of θ. The solutio to this problem is to track the phase differece betwee the ultrasoic sigals at the two differet receivers ad process the iformatio. The secod quatity, z/d, is estimated by determiig the (x,y,z) coordiates of the compass with respect to the plae formed by the beacos. This is doe by placig multiple beacos i a room ad estimatig the time it takes for the ultrasoic sigal to propagate betwee them ad the compass. The differetial distace ca be measured as illustrated i figure 3. x d z Where d1 d d whe d 1, d From Fig (b), x1 ( cos ) ( x si ) ad x ( cos ) ( x si ) x x1 x si Substitutig for x 1 () we get: ad x from Equatios (1) ad et d 1 ad d be the distaces to receivers R 1 adr from the beaco B. et δd = d 1 - d ad let w 1 ad w be the ultrasoic waveforms at the two receivers, ϕ, depeds upo the differece i distaces traversed from B to the receivers by the ultrasoic sigal ad the wavelegth of λ of the sigal is expressed as: d1 d * π δd = d1 d From Beaco d d d d x 1 si ( 1) This may be rewritte as: si d d1 1 z ( ) d Equatio (4) implies that it suffices to estimate two quatities i order to determie the orietatio of the compass with respect to a beaco: (i) (d d 1 ), the differece i the distaces of the two receivers from the beaco, ad (ii) z/d, the ratio of the height of the beaco from the horizotal plae o which the compass is placed to the distace of the beaco from the ceter of the compass. The mai goal of this Fig.3. Receivers R 1 ad R measures the differetial distace from a far away beaco 3.3 Orietatio forwardig The problem i a ad hoc etwork is that a ode ca oly commuicate with its immediate eighbor, which may ot always be the ladmarks. Ad hoc positioig system is a hybrid betwee DV routig ad beaco based positioig. It is similar to DV routig because the iformatio is forwarded i a hop by hop fashio idepedet of each ladmark. This method aims at forwardig orietatio to the odes which are ot i direct cotact with the ladmarks, but still ca ifer their orietatio with respect to the 5

6 ladmark. This method icludes two algorithms: DV- Bearig, which allows each ode to get a bearig to a ladmark ad DV-Radial, which allows a ode to get a bearig ad a radial to a ladmark as illustrated i Figure 4. Fig. 4. Node A ifers its beaig to usig B s ad C s bearig to A c b, which i tur kows their bearig to a far off ladmark. First ode A should fid its bearig to. If B ad C are eighbors of eachother the A has the possibilty to fid all the agles i the triagles ΔABC ad ΔBC. This would allow A to fid the agle AC + AC. Node A cotiues the process of forwardig its estimated bearig to, to its eighbors which will help the farther odes get their estimates for. Forwardig orietatios is doe i a fashio similar to distace vecor routig algorithm. If the radial method is used, a similar argumet holds with the differece that ow A eeds to kow, besides bearigs of B ad C to, the radials of B ad C from. Agle BN, the radial at B is kow the the agle AN, radial at A ca also be foud sice all agles i both the triagles is kow. 3.5 Agle of arrival estimatio usig array of atea C B A atea array[9] ofte called a 'phased array' is a set of or more ateas. The sigals from the ateas are combied or processed i order to N achieve improved performace over that of a sigle atea. The atea array ca be used to: icrease the overall gai provide diversity receptio cacel out iterferece from a particular set of directios "steer" the array so that it is most sesitive i a particular directio determie the directio of arrival of the icomig sigals to maximize the SINR The followig figure shows a example of atea array: Fig.5. Geometry of a arbitrary N elemet atea array. Weightig ad summig of sigals from the ateas to form the output i a Phased Array X 1 X X N W 1 W W N The geeral form of a atea array ca be illustrated as i Figure 5. A origi ad coordiate system are selected, ad the the N elemets are positioed, each at locatio give by: d = [x y z ] The positios of the elemets i the phased array are illustrated i the followig Figure. et x..., 1, x, xn represet the output from ateas 1 thru N, respectively. The output from these ateas are most ofte multiplied by a set of N weights - w..., 1, w, wn - ad added together as show i the Y 6

7 above Figure The output of a atea array ca be writte as: y N 1 w x To uderstad the beefits of atea arrays, cosider a set of 3-ateas located alog the z-axis, receivig a sigal (plae wave or the desired iformatio) arrivig from a agle relative to the z- axis of, as show i Figure 6. atea i, the received sigal is: i j cos zi X e The received sigals are distict by a complex phase factor, which depeds o the atea separatios ad the agle of arrival( ) o the plae wave. If the sigals are summed together, the result is: j cos z1 j cos z j cos z3 Y e e e i m e 1 e j cos z i jm cos So from the atea theory [16], as the gai of the atea is a fuctio of agle of arrival ( ), ca be measured at a particular receiver if the gai is kow. Ad thus ca be helpful i estimatig the locatio of the source. The ateas i the phased array are spaced oe-half wavelegth apart (cetered at z=0). The E-field of the differet iterfereces to achieve accurate output, use plae wave (assumed to have a costat amplitude of a group of atea ad complex calculatios everywhere) ca be writte as: E( x, y, z) e = e = e j ( kxx ky y kz j k (si cos x si si y cos z) jk. r So from the atea theory [16], as the gai of the atea is a fuctio of agle of arrival ( ), ca be measured at a particular receiver if the gai is kow. Ad thus ca be helpful i estimatig the locatio of the source. Though the agle of arrival measuremet becomes highly accurate, overcomig icreases the cost of the techology with the icrease i coectivity, time ad space complexity as well. I spite of all the above drawbacks, it still does t guaratee of the exact agle of arrival calculatio. The size ad the portability issues restrict the system from the use i sesors. E( x, y, z) e = e = e j ( kxx ky y kz j k (si cos x si si y cos z) jk. r z = / #1 ϴ I the above, k is the wave vector, which specifies the variatio of the phase as a fuctio of positio. The (x,y) coordiates of each atea is (0,0); oly the z-coordiate chages for each atea. Further, assumig that the ateas are isotropic sesors, the sigal received from each atea is proportioal to the E-field at the atea locatio. Hece, for z = 0 # z = - / #3 Fig elemet Atea Array receivig a plae wave So as to overcome the drawbacks the other methodology are still i research domai. 7

8 4.COMPARISON AND CONCUSION: Teller, \The cricket compass for cotext-aware AoA measuremet is a importat techology of great practical iterest i WSN. For log rage mobile applicatios", Proc. of the 7th ACM MOBICOM Cof., Rome, Italy, July 001 trasmissios ad high accuracy Agle of Arrival [5] D. Niculescu ad Badri Nath, \Ad hoc measuremet, the most preferred way is always positioig system (APS)", i Proceedigs of GOBECOM, Sa Atoio, November 001. foud to be usig Array of Atea which is ever [6] acceptable for Wireless Sesor etworks used for a [7] R. C. Eberhart ad J. Keedy, A ew optimizer specific low cost, low space ad low weight applicatio due to its high hardware complexity ad cost. But i a situatio where the oise desity is very less ad the trasmissio rage is very small like iside a closed room or i a closed boudary, if the subcetimeter accuracy has to be achieved the devices [8] usig particle swarm theory, i Proc. 6th Symp. Micro Machie ad Huma Sciece, Nagoya, Japa, pp ,1995. Mighui i ad Yilog u Itelliget Systems Cetre, Nayag Techological Uiversity 50, Nayag Drive, Agle of Arrival Estimatio for localizatio ad commuicatio i wireless etworks, Sigapore 16th Europea Sigal like Cricket Compass plays a major role for Agle of Processig Coferece (EUSIPCO 008), Arrival ad the Positio Estimatio. But i sesor ausae, Switzerlad, August 5-9, 008, etworks, those which are meat for some specific purposes ad placed i ope areas ad distributed i a log rage of trasmissio the sub-cetimeter [9] [10] copyright by EURASIP ez, J., Edelstei, A.S., "Magetic sesors ad accuracy is a very hard task to be achieved ad the effect of the atmospheric oise is also very high which ca affect the calculatio of the agle of arrival ad hece the positio of a specific ode. So it is a very challegig research area to fid a suitable techology to achieve a proper techique for this purpose. REFERENCES: [1] D. Niculescu ad B. Nath, Ad hoc positioig system (APS) usig AOA, i Proc. IEEE INFOCOM 003, Sa Fracisco, pp , Mar [] N.B Priyatha, A. Miu, H. Balakrisha ad S. Teller, \The cricket compass for cotext-aware mobile applicatios", Proc. of the 6th ACM MOBICOM Cof., Rome, Italy, July 001. [3] N.B. Priyatha, A. Chakraborty, H. Balakrisha, \The cricket locatio-support system," Proc. 6 th ACM MOBICOM, Bosto, MA, August 000 [4] N.B Priyatha, A. Miu, H. Balakrisha ad S. their applicatios." IEEE Sesors J. 006, 6, [11] Seamaship Techiques:Shipboard ad Marie Operatios, D. J. House, Butterworth Heiema, 004, p. 341 [1] ez, J., Edelstei, A.S., "Magetic sesors ad their applicatios." IEEE Sesors J. 006, 6, [13] Seamaship Techiques:Shipboard ad Marie operatios Operatios, D. J. House, Butterworth-Heiema, 004, p. 341 [14] Ompass [15] mageticfieldsesor [16] Costatie A.Balais Atea,005 [17] Paramvir Bahl ad Vekata N. Padmaabha, \RADAR: A I-Buildig RF-based User ocatio ad Trackig System," Proceedigs of 8

9 IEEE INFO-COM 000, Tel-Aviv, Israel March 000. [18] Nirupama Bulusu, Joh Heidema, Deborah Estri, \GPS-less ow Cost Outdoor ocalizatio For Very Small Devices", IEEE Persoal Commuicatios Magazie, Special Issue o Smart Spaces ad Eviromets, October 000. [19] Oxyge home page. [0]. Yip, K. Comaor, J. Che, R. Hudso, K. Yao, ad.vadeberghe, Array processig for target DOA, localizatio ad classificatio based o AM ad SVM algorithms i sesor etworks, i Proc. IPSN 03, Califoria, pp , Apr [1] J. Ash ad. Potter, Sesor etwork localizatio via received sigal stregth measuremets with directioal ateas, i Proc. 4d Aual Alleto Coferece o Commuicatio, Cotrol, ad Computig, Champaig- Urbaa, I, pp , Sept [] Z. Gu ad E. Guawa, Radiolocatio i CDMA cellular system based o joit agle ad delay estimatio, Wireless Persoal Commuicatios, vol. 3, pp , Mar