Node Placement and Mobility Control in Mobile Wireless Sensor Networks

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1 Prprns of h 18h IFAC Worl Congrss o Placmn an Mobly Conrol n Mobl Wrlss Snsor works Mnchol Km an Song-Lyun Km School of Elcrcal an Elcronc Engnrng, Yons Unvrsy, 50 Yons-ro, Soamun-gu, Soul , Kora -mal: {mckm, Absrac: In hs papr, w propos a no placmn sragy n lnar nworks an mobly conrol sragy for qually-spac placmns. Our purpos s o maxmz h snsng ara by solvng h problm of unbalanc raffc loa n h snsor nwork. Through smulaons, w vrfy ha hs srags hav sgnfcan bnfs on h oal snsng ara of a gvn sysm. Fnally, w xn our no placmn sragy o a 2-mnsonal nwork an nfy s avanags. Kywors: Mobl robos, Snsor sysms, Locaon, Rlays. 1. ITRODUCTIO As mobl robo chnology has volv, s applcaon has bn xn o varous fls nvolvng xploraon, sarch, an rscu opraons. On h ohr han, wrlss snsor nworks (WSs) hav also rawn much anon, bcaus hy nabl mobl robos o opra ffcnly wh low cos an low powr consumpon. A gnral WS s sngush from ohr nworks bcaus has svral lmaons, such as n bary powr, no nsy, an aa sz (Dav al., 2004). In parcular, powr savng s of gra mporanc mosly o prolongng h lfm of h nwork. In sac WS, on obcv s o xn h lfm by conrollng h acvy of ach snsor no, whras prmary concrn n mobl no sysms s o xn h snsng ara of h nr sysm whl mnmzng nrgy consumpon caus by no movmn an communcaons (Pour an Sukham, 2004). In sac WSs, svral approachs hav bn suggs o prolong h lfm. Ths nclu rucng runan l lsnng m of snsor nos an mnmzng sanby powr consumpon (Sursh an Raghavnra, 1998) va propr proocol sgn an avanc mhos of harwar mplmnaon. In aon, loa balancng s an mporan facor n consrng h lfm of sac WSs. L us assum a many-o-on sysm, whr on snk no collcs aa from many of h ohr nos. os closr o h snk no wll suffr from hgh raffc loa bcaus hy mus rlay aa from h our nos, whras h our nos rlay lss aa; hnc, h nwork lfm bcoms mor pnn on h closr nos. In mobl WSs, mos rsarch s conuc on h assumpon ha nrgy consumpon by movmn conrol s rlavly hgh, compar o h powr consumpon by communcaon proocols. Howvr, as h sysm volvs an h applcaon ara s xn, h powr rqur o mov nos crass whras h ransmsson powr ncrass gvn h ncras volum of mulma raffc (Akylz al., 2007). Thrfor, n mobl WSs ha hanl mulma snsng aa, nrgy consumpon by ransmsson an movmn shoul b consr smulanously. Ths s h man opc of hs papr. Thr ar svral prvous sus on rsolvng of unblanc raffc loa wh no placmn opmzaon (Cao al., 2008; Chng al., 2004; Yu al., 2005). Our suy s ffrn from hs n h sns ha w consr h mobly of h nos. In hs papr, w o no sgn any nrgyffcn communcaon proocols. Insa, w amp o mnmz nrgy consumpon va loa balancng of mobl snsor nos. On h ohr han, by conrollng h poson of h nos, w can balanc h loa so ha h nrgy consumpon among h nos bcoms far. Hr w consr hs nrgy-snsng ara raoff caus by mobl movmn. Th rs of hs papr s organz as follows: Scon 2 scrbs h problm an h sysm mol. In Scon 3, w llusra our no placmn srags n lnar nworks. A movmn sragy bas on qually-spac placmn wll b al wh n Scon 4. In Scon 5, w show smulaon rsuls an compu prformanc bouns. An xnson o planar nworks s consr n Scon 6. Fnally, w conclu h papr wh rmarks on fuur rsarch n Scon SYSTEM MODEL AD PROBLEM DEFIITIO Consr a lnar snsor nwork, whr snsor nos ar plac along a ln wh a snk no a h lf n of h ln. Each snsor no has homognous nal nrgy P an h capacy for mobly. From h no a h rgh n of h ln, h aa collc urng snsng ar ransm o h snk no squnally along h lnar rou. Copyrgh by h Inrnaonal Fraon of Auomac Conrol (IFAC) 13899

2 Prprns of h 18h IFAC Worl Congrss X 1 X 2 X X +1 Fg. 1. Lnar mobl WS. o Placmn In Fgur 1, X nos h h mobl snsor no from h snk no. Th valu 1 s h movng sanc of X 1 from h snk no o h fnal pon of X 1. W assum ha ach no collcs aa procally an h amoun of aa collc n a un sanc pr un m s consan an qual o h aa nsy, D. If X movs along h sanc,, hn h amoun of collc aa s D. W assum ha h nrgy consumpon ra for movmn, ransmsson, an rcpon ar fx a cran valus. 1 Snsng Transmsson,+1 = CR l +1 Fg. 2. o placmn algorhm. 3. ODE PLACEMET ALGORITHM Thr ar hr sps n h sysm; no placmn, snsng, an ransmsson. Th opmum placmn of nos s scrb n Scon 3. Afr placmn, ach no movs o collc aa n h srvc ara whch s fn as a ln n hs papr. Durng movmn, h nos sns aa, such as mpraur, hgh an ohr nformaon n h form of mags, souns, an vo srams. If all nos fnsh gahrng aa, ach no sns h aa o s nghbor no n h rcon o h snk no. For xampl, X only ransms h collc aa o h nghbor no whl X -1 ransms s own aa an rlays h rcv aa from X o X -2. Thrfor, h closr a no s loca o h snk no, h grar h powr rqur o ransm an rlay aa o h nghbor no. I can b asly nfrr ha h xploraon ara of h nos clos o h snk no shoul b lss han ha of h nos far from h snk no. To rsolv h loa mbalanc an maxmz h nr snsng ara of a WS, n h nx scon w propos an algorhm ha nally placs mulpl nos a h opmal pon. Wh snsng nos plac opmally n h no placmn sp, h snsng ara s maxmz an h nrgy consumpon for aa lvry an mobl movmn s mnmz. In Fgur 2, h hr sps of h sysm ar scrb. In h no placmn sp, h opmal nal pon s sl consrng h communcaon rang, maxmum powr consumpon P an h numbr of nos. Th nos ar plac a h nal pon, whr X an X +1 ar spac apar by,+1. In h snsng sp, X movs by n h rcon of X +1, hn snss an collcs h aa. In hs papr, w call h pon a a snsng sanc of from h nal placmn of h no X as a vsng pon. Fnally, n h ransmsson sp, X movs back as l, h sanc bwn h vsng pon an h fnal pon, o guaran h conncvy of h nos, hn h sanc bwn X an X +1 s lss han CR, h communcabl rang. Throughou h papr, our obcv s o fn an ffcv no placmn schm ha maxmzs h snsng ara n lnar snsor nworks (lar xn o planar nworks), whl mnmzng h nrgy consumpon of communcaons (for aa lvry) an mobl movmn (for snsng). 3.1 o placmn wh nfn communcaon rang Th propos algorhm cs h opmal nal placmn of h nos an h sanc. Inal placmn an vsng pons ar calcula wh rspc o h rgarng oal snsng ara an h conncvy. For h purpos, w consr wo cass; n whch h communcaon rang s hr nfn or fn. In h no placmn sp, h propos algorhm cs an opmally placs nos so ha hy can sns an collc as much aa as possbl an say connc wh ach ohr. To calcula, h oal powr consumpon of X, P, s oban by (1), for =1,, -1. P P( l ) G P ( DG ) P P (1) 1 r 1 Th oal powr consumpon consss of powr for snsng an communcaon (rcvng an ransmng) for =1,, -1. P (pr un sanc), P r (pr pack), an P (pr pack) ar h powr valus for snsng, rcvng, an ransmng, rspcvly. Th oal powr consumpon shoul b lss han h maxmum powr consumpon P. Th amoun of aa lvr from X, G can b scrb by (2). G D for =2,, -1 (2) 1 A no X rlays h aa from X +1, X +2,X o X -1. Unr h assumpon of h nfn communcaon rang, h no os no ncssarly mov back o s fnal pon,.., l =0. P DP P For h las no X, h snsng sanc s gvn as (3), whr X only ransms s own snsng aa o h nghbor no X -1. For =1,,-1, h snsng sanc s gvn as (4). P D( P P ) r 1 DP P (3) for =1,, -1 (4) 13900

3 Prprns of h 18h IFAC Worl Congrss START Fgur 3. P DP p =1, =0 =-1 + > CR o =+1 Ys P DP ( P) 1 r DP P =+1 Dc fnal poson of X + an l + wh P + usng (5) o +=? =0 =1? o =-1 Ys Ys Upa rsual powr of X ED Fg. 3. Flow char of no placmn algorhm (Infn communcaon rang). Toal rsual powr=0? Ys o ED Whr X rcvs aa from X +1 an rlays o X -1, hnc, h snsng sanc s calcula n scnng orr, from =-1 o =1. If w know h xac valus of D, P r, P, P, an P, w can compu h snsng ara of ach no from X o X 1. Ths procss s summarz n Fgur o placmn wh fn communcaon rang In praccal sysms, h communcaon rang, CR, s lm bcaus of h cos an powr of h vc an s an mporan facor for sgnng a WS (Ab-Alham al., 2008). Guaranng h conncvy bwn nos bcoms crucal unr conons of lm communcaon rang. In hs scon, h algorhm n Scon 3.1 s labora o guaran conncvy by consrng CR. If X canno communca wh h nghbor nos a h vsng pon, movs o h propr poson o ransm h aa. W call hs propr poson h fnal pon. I can b asly shown ha f X movs from h vsng pon mor owar h fnal pon, h snsng sanc crass bcaus of lm powr consumpon. To fn h snsng sanc an h fnal pon, h algorhm ravly calculas h oal powr consumpon of X as n (5). By ravly calculang h oal powr consumpon, h snsng sanc an h fnal pon can b rv. Fg. 4. Flow char of no placmn algorhm (Fn communcaon rang). P G 1Pr ( DG 1) P P P P( CR 2 l l 1) G 1Pr (( CR l ) DG 1) P P Equaon (5) rprsns h powr consumpon of X whr l s h sanc from h vsng pon o h fnal pon of X. Gvn ha l -1 an G +1 ar nrac, h soluon of l canno b oban n a clos form. Fgur 4 s a flow char of hs procss ha s appn o h ED of Fgur 3. Wh hs rav approach, w can calcula h vsng pon of X, an fnally c h snsng ara of h nos. 4. MOBILITY COTROL OF EQUALLY-SPACED PLACEMET SYSTEM In hs scon, w llusra h mobly conrol of quallyspac placmn (ESP). Wh mobl nos, ESP s mporan bcaus gvs clus abou h mobly conrol of a sysm wh pr-ploy nos. In conras o Scon 3, CR CR (5) 13901

4 Prprns of h 18h IFAC Worl Congrss w o no conrol h nal pon of h nos. Th purpos of hs scon s o maxmz h snsng ara of h sysm by conrollng h vsng an fnal pons of h nos. L p no qual sancs bwn ach aacn par of nos. Whn nos ar ploy, hy communca wh ach ohr o vrfy h sancs, q, bwn hm. Afr hy rmn h sanc, whch s smallr han CR, hy can fn h vsng an fnal pons ha maxmz h oal snsng ara. As sa n Scon 1, h lfm of a WS s pnn on ha of h no closs o h snk no. A gnral WS works unl h no closs o h snk no shus own. Whn h P 1 xcs P, X 1 canno ransm h aa collc by slf an lvr from X 2. Thrfor, h sysm s nval. Howvr, wh mobly conrol, f X 1 suffrs from a lack of powr, hn X 2 can suppor by an ncras snsng sanc. As shown n Fgur 5, f X 1 canno affor o mov by q bcaus of lack of powr, movs along 1 solly o sns aa. X 2 movs o compnsa for h sanc ha X 1 canno xplor. If X 2 also has nsuffcn powr, X 3 suppors X 2. Ths procss s rpa n ascnng orr. In hs cas, X movs h sam sanc as n Scon 3, whn comparng h posons a h nal placmn an a ransmsson. Howvr, h sanc bwn h vsng pon an h fnal pon, l, s ffrn from ha n Scon 3, bcaus h fnal poson of X -1 s s o h nal pon of X. Ths s summarz n (6). CR CR l CR I appars srang ha only X follows an acvy rul ha s ffrn from ha of ohr nos. Howvr, mus b known o calcula h sancs n scnng orr, from -1 o 1. Thr s no ohr way o slc rcly whn w know us nal powr of nos an q. P l P 1 1 (7) DPr DP 1 Th oal powr consumpon of X s gvn as (7), whr l = +l +1 - q for =1,, -2, an l -1 = -1 - q as Fgur 5. 1 (6) As mnon avob, acs as n Scon 3. Thn h fnal pon of X -1 s gvn as (8). 1 P q P D P Pr 2 P DP If w assum ha h oal powr consumpon of ach no s qual o h powr lm P, hn h movng sanc of X s gvn as (9) whr =1,, P ( q l1 ) P DP Pr 1 2 P DP I s also possbl ha X also movs lf o suppor X -1 lk Scon 3. Howvr, n ha cas, canno b calcula n a clos form. Furhrmor, usng anohr smpl smulaon, w fn ha h abov algorhm provs an opmal conrol n h ESP sysm. 5. SIMULATIO RESULTS W llusra h numrcal rsuls an compar h snsng ara an rsual powr of ach no o vrfy h mprovmns of h propos algorhm. W us P = mW, P = 16000mW/m, P r = 36mW/pack, P s = 60mW/pack, D = 30pack/m, CR = 5m, an = 5 n h smulaon as n Rham al.(2003). D s s o a larg valu so as o mol mulma aa. In Fgur 6 an Fgur 7, w compar h oal snsng aras of h propos algorhm wh nfn an fn communcaon rangs, rspcvly. Boh sancs ar normalz by h oal snsng ara n h cas of nfn communcaon rang (26.46m ) Wh a fn communcaon rang, hr s a 5.04% rucon n h snsng ara rlav o nfn communcaon rang nworks. Th op, ml, an boom rows rprsn h no placmn, snsng, an ransmsson sps, rspcvly Fg. 6. Toal snsng ara of opmal placmn Infn communcaon rang. (8) (9) Fg. 5. Mobly conrol n an ESP sysm. 1 You shoul gv an anon ha h fnon of an l s ffrn o Fgur Fg. 7. Toal snsng ara of opmal placmn Fn communcaon rang

5 Prprns of h 18h IFAC Worl Congrss Fg. 8. Toal snsng ara of hr WS sysms. Fgur 8 shows h oal snsng ara for hr cass: h opmal no placmn sragy, h rsul from h mobly conrol algorhm on ESP propos n Scon 4, an h uppr boun of h convnonal sragy on ESP. Wh convnonal sragy, X movs o h nal pon of X +1 whou suppor of X +1, hn h nos clos o h snk no suffr from havy loa as xplan n nroucon. In Fgur 8, h sancs ar normalz by h oal snsng ara of h opmal placmn sragy wh fn communcaon rang. Th normalz oal snsng aras ar 1, 0.965, an for h opmal no placmn algorhm, n mobly conrol algorhm, an convnonal sragy on ESP, rspcvly. Th mobly conrol algorhm on ESP las o a 5.19% xnson of h snsng ara han convnonal sragy. I woul bcom largr whn aa nsy ncrass. Tabl 1 shows h rao of h rsual powr o h nal powr for ach no. By usng h rsual powr of ach no n h convnonal sragy, h oal snsng ara can b xn wh mobly conrol algorhm. W also xamn h oal snsng ara of ach sysm whl varyng h numbr of nos from 3 o 10. Th rsuls ar shown n Fgur 9. Th sancs ar normalz by h oal snsng ara of h opmal no placmn algorhm wh fn communcaon rang. As h numbr of nos ncrass, h snsng aras of h mobly conrol algorhm an convnonal sragy cass cras rlav o h opmal no placmn cas. Fgur 9 shows ha h opmal no placmn clarly mprovs h prformanc of h sysm n rms of h oal snsng ara. Whn nos ar pr-ploy, our mobly conrol algorhm xns ovr h oal snsng ara, vn hough prformanc n hs cas s lowr han ha of h opmal no placmn algorhm. Fg. 9. Comparson of snsng ara for hr sysms. 6. PLAAR ETWORK In hs scon, w xn h opmal no placmn algorhm o 2-mnsonal planar nworks. In h prvous scons, h snsng rang of ach no s gnor bcaus s a lnar WS. Howvr, n hs scon, h snsng rang of nos s consr as an mporan facor. Thrfor, w a a nw varabl r ha rprsns h raus of h snsng rang. Accorng o h rpor by Chng al. (2004), hr ar wo kns of placmn n a 2-mnsonal WS: h lnar approxmaon mo an h sar mo. Chng conclu ha h sar mo s mor ffcn han h lnar approxmaon mo n rms of oal powr consumpon. For hs papr, w xamn a nw mol, whch w call as h r mol. I s a hrarchcally ploy mol, as rprsn n Fgur 10. Each crcl on whch nos ar loca s no as a no lvl. Lvl 1 ncas h smalls crcl, an h lvls ncras as h crcls mov ouwar. Th smulaon s smlar o ha n Scon 5. Th rason for hs s ha, by makng uppr-lvl nos mov for snsng rlavly small aras compar o lowr-lvl nos, h raffc loa of h sysm s balanc whn h uppr-lvl nos rlay h aa from h lowr-lvl nos. Howvr, h problm bcoms much mor complca whn s xn o 2-mnsonal ara. Th roung algorhm Tabl 1 Rsual powr rao of ach no X 1 X 2 X 3 X 4 X 5 Opmal o Placmn & Mobly Conrol algorhm Convnonal Sragy on ESP Fg. 10. Tr mol no placmn srags n a 2-mnsonal WS nwork

6 Prprns of h 18h IFAC Worl Congrss bcoms mor complx han h lnar sysm. In aon, no placmn for h oal snsng ara covrs h nr rgon. Hnc, s xrmly har o fn an opmal placmn sragy. Thrfor, w prov hursc algorhms bas on h nsghs from h lnar nwork. Our hursc no placmn sragy s o c h propr placmn of nos so ha all of nos can sns h assgn aras an collc all aa from h nos aggrgang owars h cnr. Our purpos s o mnmz h numbr of nos gvn a cran crcl shap rgon. umbr of nos Lnar approxmaon Sar mo Tr mol W compar h r mol hursc sragy an h sar mo sragy an h lnar approxmaon mho n Fgur 11, n rms of h oal numbr of nos n o covr h nr rgon. W us sam paramrs as n Scon 5, P = mW, P = 16000mW/m, P r = 36mW/pack, P s = 60mW/pack, D = 30pack/m, an CR = 5m. W a on mor varabl, sng h snsng rang o r = 1m. Th lnar approxmaon mho rqurs mor nos o covr h rgon. Th rason for hs s ha mor nos mus b ploy o rlay h aa a h rmnal s of nworks, whr h raffc loa s much havr. Howvr, as h raus ncrass, h ovrlap n h snsng ara also ncrass. Thrfor, prformanc for h sar mo bcoms wors han ha for h lnar approxmaon mho. Wh h r mol, w can ruc h ovrlap n h snsng ara whl ncrasng h raffc loa. By conrollng h sancs bwn h lvls, h numbr of nos can b ruc. Wh 400 nos, h r mol can covr a crcl ha has ra of 24m, whras ra of 18m an 19m can b covr by h lnar approxmaon mho an sar mo, rspcvly. 7. COCLUSIOS In hs papr, w nvsga h problm of opmal mobl no placmns n lnar WSs. W also llusra an opmal movng sragy on ESP o solv h problm of unbalanc raffc loa. Smulaon rsuls show ha hs sragy has sgnfcan bnfs. Lasly, w consr a planar mol an vrfy ha a r mol has avanags spcally n rms of nr snsng ara. Ths suy has varous applcaons n WS, whch ras mulma aa, spcally on placmn of mobl snsors for xploraon. I s possbl o xplor largr ara wh fwr snsors whn applyng h no placmn algorhm, nrouc n hs papr. I can la o a valuabl conrbuon o mulma WS, whr s nal opology s conrollabl, lk cosysm xploraon, plan xploraon, an ocan xploraon. Th mobly conrol algorhm appl o ESP sysm s also abl o gv an mpac o SO (Slf-Organz work) (Brn, 1994) wh mobl nos whn s xpan o ranomly ploy nos sysms. Challngs for fuur work wll nclu applcaon of powr conrol of ransmsson of aa consrng h sancs bwn nos, al analyss of 2-mnsonal nwork sysms, an xnng h mobly conrol algorhm o sysms wh ranomly ploy nos Raus of Rgon Fg. 11. umbr of nos as a funcon of h raus of rgon. ACKOWLEDGEMET Ths rsarch was suppor by h MKE (Th Mnsry of Knowlg Economy), Kora, unr h ITRC (Informaon Tchnology Rsarch Cnr) suppor program suprvs by h IPA(aonal IT Inusry Promoon Agncy) (IPA C ) 8. REFERECES Ab-Alham, R.A., Horoshnkov, K.V., Hu, Y.F., S, C.H., an Zhou, D. (2008), Masur h rang of snsor nworks, Mcrowavs & RF, unpublsh. Akylz, I.F., Mloa, T., Chowury, K.R. (2007), Wrlss mulma snsor nworks: A survy, IEEE Wrlss Communcaons, volum (16), p Brn, F., (1994) Growng Cll Srucurs A Slf-Organzng work for Unsuprvs an Suprvs Larnng, ural works, volum (7), p , Cao, M., Yang, L.T., Chn, X., an Xon,. (2008), o placmn of lnar wrlss mulma snsor nworks for maxmum nwork lfm, GPC 08, volum (1), p Chng, P., Chuah, C., an Lu, X. (2004), Enrgy-awar no placmn n wrlss snsor nworks, IEEE GLOBECOM 04, volum (5), p Dav, C., Dborah, E., Man, S. (2004), Ovrvw of snsor nworks, Compur, volum (37), p Pour, S., an Sukham, G.S. (2004), Consran covrag for mobl snsor nworks, IEEE ICRA 04, volum (1), p Rahm, M., Shah, H., Sukham, G.S., Hman, J., an Esrn, D. (2003), Suyng h fasbly of nrgy harvsng n a mobl snsor nwork, ICRA 03, volum (1), p Sursh, S., C.S. Raghavnra. (1998), PAMAS - powr awar mul-accss proocol wh sgnallng for a hoc nworks, ACM SIGCOMM Compur Communcaon Rvw, volum (28), Yu, L., Yu-m, Y., an Hu-mn, Z. (2005), Snsors Dploymn n Enrgy Effcn Wrlss Snsor works, Inrnaonal Confrnc on Wrlss Communcaons, workng an Mobl Compung 05, volum (1), p