An Improved DV-Hop Localization Algorithm Based on the Node Deployment in Wireless Sensor Networks

Transcription

1 Iteratoal Joural of Smart Home Vol. 9, No. 0, (05), pp A Improved DV-Hop Localzato Algorthm Based o the Node Deploymet Wreless Sesor Networks Jam Zhag, Ng Guo ad Ja L College of Computer, Hea Isttute of Egeerg Zhegzhou 459, Cha Hea Educato Iformato Ceter Zhegzhou 45008, Cha zjm996@63.com, g@haedu.gov.c, lj006@63.com Abstract Localzato algorthm s a mportat ad challegg topc Wreless Sesor Networks (WSNs), especally for the applcatos requrg the accurate posto of the sesed formato. I ths paper, a mproved DV-Hop algorthm based o the ode deploymet was proposed. The proposed algorthm mproves the localzato accuracy by takg the advatage of the ode deploymet whe computg the dstace betwee the ukow ode ad the achor. Smulato results prove that the mproved DV-Hop algorthm offers the better performace compared to the orgal DV-Hop algorthm localzato accuracy wthout requrg addtoal hardware. Keywords: wreless sesor etworks, localzato, DV-Hop. Itroducto I wreless sesor etworks (WSNs), localzato has receved world wld research ad dustral terest, such as border securty, asset maagemet, habtat motorg, buldg automato as well as evromet observato []. WSNs have bee cosdered as a promsg tool for may locato-depedet applcatos, such as battlefeld survellace, evromets motorg, door user trackg. I addto, locato formato s cosdered to be a fudametal requremet for broadcastg ad routg [] WSNs. Although sesor ode localzato plays a mportat role these applcatos, as the costrat sze, power, ad cost of sesor odes, the vestgato of effcet locato algorthm whch satsfy the basc accuracy requremet for WSN meet ew challeges. Sesor odes could be equpped wth a global postog system(gps) to provde them wth ther absolute posto[3], ad ths s curretly a costly soluto or mpossble soluto to some door cases[4]. Therefore, t s ofte the case wth a geeral assumpto that the postos of some odes (called achors),are kow, so that t s possble to fd the absolute postos of the remag odes (called ukow odes) the WSNs. There s a large body of lterature o the localzato problem WSNs ad the sesor odes localzato algorthms fall to the ragedbased schemes rage-free schemes. Rage-based localzato schemes rely o absolute dstace from trasmttg to recevg sesor odes. These algorthms ca be mplemeted by usg the Receved sgal Stregth Idcator (RSSI)[5], Tme of Arrvg[6], Tme Dfferece of Arrval (TDOA)[7], ad Agle of Arrvg sgal[8]. The rage-based schemes geeral provde more accurate locato estmates that the rage-free scheme: however the ragg operato leads to a crease the stallato cost ad reducto the etwork lfetme due to the eed of addtoal hardware of procedure. For these problems that are crtcal to WSNs wth lmted resources, the rage-based schemes are cosdered mproper solutos ISSN: IJSH Copyrght c 05 SERSC

2 Iteratoal Joural of Smart Home Vol. 9, No. 0, (05) to the localzato problem WNS. I cotrast, rage-free algorthms do ot eed absolute rage formato or agle betwee sesor odes, oly eed etwork coectvty ad other formato, so the rage-free algorthms are more ecoomcal, cost-effectve, ad feasble for the large-scale wreless sesor etworks. The accuracy s less tha the rage-based but satsfes may applcatos requremets. Therefore the rage-free algorthms have bee draw much atteto. The typcal rag-free algorthms clude Cerod [9], CPE (Covex Posto Estmato) [0], ad DV-hop (Dstace Vector-hop) [-]. Amog may of rage-free localzato algorthms, DV-Hop algorthm s a eat scheme whch worth further vestgato. The advatages of the DV-Hop scheme are ts smplcty ad easy to mplemet. However, ts average localzato error s the order of 30% of the commucato radus. Oe reaso leads to the low accuracy of DV-Hop s the hop-dstace ambguty problem: Those odes wth the same hop cout to a achor wll the have the same estmated dstace, although they do have dfferet dstaces to the achor. To mprove the localzato accuracy, may algorthms based o DV-hop have bee proposed recetly [3-7]. I [3],the author summed up the ma causes of error based o the aalyss o the process of the DV-Hop algorthm ad amed at the mpact to the locato error whch s brought by the achor odes of dfferet posto ad dfferet quatty. Based o these, the author proposed a ovel localzato algorthm called NDV-Hop_Bo (New DV-Hop based o optmal odes).i [4], the author proposed a mproved algorthm o mprove the poor locatg performace of the DV-Hop algorthm, whch the average oe-hop dstace betwee achor odes s modfed, ad the average oe-hop dstace used by each ukow ode for estmatg ts locato s modfed through weghtg the receved average oe-hop dstaces from achor odes. I [5], the authors proposed a mproved DV-hop algorthm whch troduces threshold M, t uses the weghted average hop dstaces of achor odes wth M hops to calculate the average hop dstace of ukow odes. I [6], the author prmarly vestgated a kd of target localzato techology based o the mproved DV-Hop algorthm wreless sesor etworks. They frstly compute the dstaces measured by RSSI ad the mea value of oe-hop dstace. The they ca use the dffereces betwee the mea ad the actual dstace to get the error correcto betwee the total dstace ad average oe-hop dstace. I [7], the authors preseted two mproved algorthms: Checkout DV-hop ad Selectve 3- Achor DV-hop. Checkout DV-hop algorthm estmates the moble ode posto by usg the earest achor, whle Selectve 3-Achor DV-hop algorthm chooses the best 3 achors to mprove localzato accuracy. I ths paper, we propose a mproved DV-Hop algorthm to crease the locato accuracy. The rest of the paper s orgazed as follows. I the ext secto, we gve the overvew of the DV-Hop algorthm. The proposed works are descrbed Secto 3. I Secto 4, smulato results are show ad localzato performace s dscussed. Fally, the coclusos are gve secto 5.. Overvew of the DV-Hop Algorthm I ths secto we descrbe the DV-Hop algorthm [9, 0] bref. DV-Hop algorthm s a classcal localzato method for WSNs. The basc dea of the ths algorthms s that the ode tself oly exchage formato wth ts adjacet odes, the dstace betwee the ukow odes ad the achor s computed by the product of the etwork average Hop dstace ad the shortest path betwee two odes, ad the uses trlateral measuremet to obta the ode locato formato. The algorthm mplemetato cossts of three steps. 98 Copyrght c 05 SERSC

3 Iteratoal Joural of Smart Home Vol. 9, No. 0, (05) I the frst step, each achor ode broadcasts achor ode packets wth ts locato formato ad hop-cout value talzed to 0. Each sesor ode the etwork, whch receves achor ode packets, matas a table (x, y, HopCout ) for every achor ode, where (x, y ) s the coordate of achor ode ad HopCout s the mmum umber of hops from achor ode. If a receved packet cotas less hop-cout value to a partcular achor ode, the correspodg hopcout HopCout wll be replaced wth the hop cout value of the receved packet. Ad ths packet s forwarded the etworks wth creasg hop-cout value by oe. Otherwse ths packet s dscarded. Through ths mechasm, all odes the etwork have the mmal hop-cout from every achor ode. I the secod steps, the achor ode calculate the average sze for oe hop from other achor odes as follow: HopSze j ( x x ) j j ( y HopCout y ) Where (x,y ), (x j,y j ) are coordates of achor ode ad achor, h j s the mmum umber of hops betwee achor ode ad achor ode j. After calculatg the average hop-sze, each achor ode broadcasts ts hop-sze to etwork by usg cotrolled floodg. Whe the ukow ode receves the average hop-sze, t oly records the frst receved average, ad forwards the receved hop-sze to ts eghbor odes. After obtag hop-sze, usg the followg the equato ukow ode computes the dstace to the achor ode j. j j () d HopCout HopSze () j where HopCout j s the mmal hops betwee achor ode ad ukow ode j. Based o ths method, each achor ode ca covert the dstace to physcal dstace. HopSze s the frst receved average hop-sze. I the thrd step, each ukow ode estmates ts locato coordate by polygo method. Let (x, y) be the ukow ode P locato ad (x, y ) the kow locato of the th achor ode recever. Let d be the th achor ode dstace to ukow odes P, the we have d j ( x x ) ( y y ) (3) If the ode P gets ts dstace to three or more achor odes, the posto of ode P ca be computed by usg the followg equato. where, x x x x A x x y y y y y y AX=B (4) d d d d B d d x x x x y y x y y x y y Copyrght c 05 SERSC 99

4 Iteratoal Joural of Smart Home Vol. 9, No. 0, (05) d d d d b d d x x x x y y x y y x y y x X y Now the least square soluto s estmate for P that mmzes AX b, the the posto of P ca be computed by the followg formula: 3. The Improved CPE Algorthm T T X ( A A) A b (5) I the DV-Hop algorthm, the dstace betwee ukow odes ad the achor odes s estmated by the product of the umber of hop ad the average dstace wth per hop. Ths algorthm has a better result oly the stuato whe the true dstace betwee odes WSN s approxmately close. Whe the odes are dstrbuted uevely, t leads to the low accuracy of DV-Hop. Oe reaso of ths problem s that a ode has the same dstace estmato to all of ts oe -hop eghbors. Those odes wth the same hop couts to a achor wll have the same estmated dstace, although they do have dfferet dstaces the achor. As show Fg, the hop couts betwee the ukow ode ad the achor ode A ad the hop couts betwee the ukow ode U ad the achor A are both 4. I the DV- Hop algorthm the dstace, the dstace betwee the ukow ode U ad the achor ode A s equate to the dstace betwee the ukow ode U ad the achor A, but they are obvously dfferet. To mprove the accuracy the dstace calculatg betwee the achor odes ad the ukow odes, we eed to cosder the odes dstrbuto whle computg the dstace betwee the ukow odes ad the achors. Fgure. Example of Nodes Deploymet After a thorough study of the prcple of orgal DV-Hop localzato algorthms, we proposed a ehaced algorthm to mprove the localzato accuracy by cosderg the odes dstrbuto WSN. Geerally, the hop dstace betwee odes area wth low ode destes s shorter tha that area wth hgh ode destes. As t s dffculty to get the desty of sesor odes WSNs, here we use the eghbors of odes to replace the ode desty. The basc dea of the proposed scheme s that more average eghbors of odes o a gve path, the shorter dstace betwee odes o ths path. The chages mproved algorthm are maly the frst two steps. Ad the detals of chages are descrbed below. I the frst step each termedate ode ot oly get mmal hop-cout from every achor ode but also get have the total umbers of eghbors of odes o the shortest hop path to achor odes. To do ths, the broadcast packet s chaged to (x, y, HopCout, ), where s the total umbers of eghbors of odes o the shortest hop path betwee the ode to achor ode. 00 Copyrght c 05 SERSC

5 Iteratoal Joural of Smart Home Vol. 9, No. 0, (05) I the secod step, we use the weghted hop-sze to replace the smple frst receved hop-sze whe computg the dstace of betwee the ukow ode ad the achor ode. Suppose (x,y ), (x j,y j ) are coordates of achor ode ad achor, HopCut j s the mmum umber of hops betwee achor ode ad achor ode j, j s the total umbers of eghbors of odes of whch are o the way wth mmal HopCout betwee achor. The weght of the hop-sze s computed as followg: w j HopSze k achorodes j / j HopSze Ad the dstace betwee the ukow ode j ad achor ode s computed as followg 4. Smulato ad Aalyss d j j k / k w HopSze HopCout (7) To verfy the performace of the mproved algorthm, ths secto we use Matlab to smulate ad aalyze the tradtoal DV-Hop algorthm ad the mproved algorthm dfferet scearos. The smulatos of all the algorthms ru o 00 tmes radomly geerated sesor ode deploymet scearos, ad the average values are use for comparso. For our smulato expermets, we offer smulato results uder the followg smulato crcumstace: The achor odes ad ukow are all radom deployed two dmesoal area of 00m 00m ad the two algorthms are valdated by chagg the umber of achor odes, the umber of sesor odes ad the commucato rage respectvely. I the smulato, the localzato error s defed as the average error fucto as follows [8, 9]: j (6) e N N ' ( x e x ) r ( y R e y ) r (8) r r e e Where ( x, y ) s the real coordate of the ukow ode s, ( x, y ) s the evaluated coordate, R s the commucato rage of sesor odes, ad N s the total umber of ukow sesor odes, N s the umber of achor odes. The localzato error reflects the accuracy of localzato algorthm. Lower localzato error the algorthm shows better performace. The performace comparso s show Fgure. Fgure (a) gves the mpact of total umber odes o postog error ad Fgure (b) gves the fluece of rato of achor ode o the postog error. I Fg, (a), we suppose that the umber of all odes s 00. Gradually, we creased the rato of achor ode, ad get dfferet results dfferet stuatos. I Fgure (b), we suppose that the rato achor odes are 5%. From the fgure, we ca clearly see that that the proposed scheme s much superor to DV-Hop scheme. As show Fgure (b), wth the rato of achor odes crease, the average postog error two algorthms show a decreasg tred. But uder the same codtos, the average locato error the mproved algorthm s smaller tha tradtoal DV-Hop algorthm. For example, whe the beaco odes rato s 5%the average localzato error s about 44.5% DV-Hop scheme ad 36.50% the proposed scheme. Copyrght c 05 SERSC 0

6 Iteratoal Joural of Smart Home Vol. 9, No. 0, (05) 0.7 Localzato Erro DV-Hop scheme the proposed algorthm Number of Nodes 0.6 (a) Localzato Error DV-Hop scheme the proposed scheme Coclusos Rato of Achor Nodes(%) (b) Fgure. Comparso wth Localzato Error for Two Algorthms I ths paper, we preset a mproved DV-Hop algorthm that reduced the localzato error wthout requrg addtoal hardware cost. The proposed algorthm cosders the odes deploymet whe computg the dstace betwee ukow odes ad achor odes. The smulato studes are carred out to compare the performace the mproved DV-Hop algorthm wth the tradtoal DV-Hop algorthm. The effects of achor ode rato ad etwork desty o the performace o the mproved are vestgated. The smulato results dcate that the mproved DV-Hop algorthm outperform the DV-Hop algorthm all smulato cases. 0 Copyrght c 05 SERSC

7 Iteratoal Joural of Smart Home Vol. 9, No. 0, (05) Refereces [] G. Ha, H. Xu, T. Q. Duog, J. Jag ad T. Hara, Localzato algorthms of wreless sesor etworks: a survey, Telecommucato Systems, vol. 5, o. 4, (03), pp [] A. M. Popescu, G. I. Tudorache, B. Peg ad A. H. Kemp, Surveyg posto based routg protocols for wreless sesor ad ad-hoc etworks, Iteratoal Joural of Commucato Networks ad Iformato Securty (IJCNIS), vol. 4, o., (0), pp.-6. [3] N. B. Pryatha, H. Balakrsha ad E. Demae, Achor-free dstrbuted localzato sesor etworks, Proceedgs of the st teratoal coferece o Embedded etworked sesor systems. (003) November 5. [4] L. Cheg, C. D. Wu ad Y. Z. Zhag, Idoor robot localzato based o wreless sesor etworks, IEEE Trasactos o Cosumer Electrocs, vol. 57, o. 3, (0), pp [5] P. Kumar, L. Reddy ad S. Varma, Dstace measuremet ad error estmato scheme for RSSI based localzato Wreless Sesor Networks, Proceedgs of the Ffth IEEE Coferece o Wreless Commucato ad Sesor Networks (WCSN), (009), pp. -4. [6] P. J. Voltz ad D. Heradez, Maxmum lkelhood tme of arrval estmato for real-tme physcal locato trackg of 80. a/g moble statos door evromets, Proceedgs of Posto Locato ad Navgato Symposum, (004) December 5-9, Allahabad, Ida. [7] Y.She ad M.Z.W, O the accuracy of localzato systems usg wdebad atea arrays, IEEE Trasactos o Commucatos, vol. 58, o., (00), pp [8] L. Kovavsaruch ad K. C. Ho, Alterate source ad recever locato estmato usg TDOA wth recever posto ucertates, Proceedgs of IEEE Iteratoal Coferece o Acoustcs, Speech, ad Sgal Processg, (005) March 8-3, Pesylvaa, USA. [9] P. K. Patro, Localzato wreless sesor etwork wth moble beacos, Proceedgs of the 3rd IEEE Coveto of Electrcal ad Electrocs Egeers, (004) September 6-7, Tel-Avv, Israel. [0] L. Doherty ad L. Ghaou, Covex posto estmato wreless sesor etworks, Proceedgs of the 0th Aual Jot Coferece of the IEEE Computer ad Commucatos Socetes, (00) Aprl -6, Achorage, AK, USA. [] D. Nculescu ad B. Nath, Ad-hoc postog system (APS), Proceedgs of the IEEE GLOGECOM, Sa Atoo,(00) November -9, Sa Atoo, TX, USA. [] D. Nculescu ad B. Nath, DV based postog ad hoc etworks, Joural of Telecommucato Systems, vol., o., (003), pp [3] Q. Qa, X. She ad H. Che, A mproved ode localzato algorthm based o DV-Hop for wreless sesor etworks, Computer Scece ad Iformato Systems, vol. 8, o. 4, (0), pp [4] X. Che ad B. Zhag, Improved DV-Hop ode localzato algorthm wreless sesor etworks, Iteratoal Joural of Dstrbuted Sesor Networks, vol. 0, (0), pp. -7. [5] Y. Hu ad X. L, A mprovemet of DV-Hop localzato algorthm for wreless sesor etworks, Telecommucato Systems, vol. 53, o., (03), pp.3-8. [6] X. Huag, Target Localzato Based o Improved DV-Hop Algorthm Wreless Sesor Networks, Joural of Networks, vol. 9, o., (04), pp [7] L. Gu, T. Val, A. We ad R. Dalceb, Improvemet of rage-free localzato techology by a ovel DV-hop protocol wreless sesor etworks, Ad Hoc Networks, vol. 4, (05), pp Copyrght c 05 SERSC 03

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