C. nip kw trin cdc Ichn vise plan cip
Hinh 2.6 Cdy tzi phdn
Phucmg tien di lqi du& dung tip hqp mkt mirc thitp nhit (dm la, cic to brio trong mpg luoi cay tit phan nhe What) bang each them s6 luqng dja diem au xe mien phi duqc hitt den trong khu Arc. D6 la, lieu mOt chitc xe da nhOn duqc thong tin nguyen ttl mOt s6 nai dOu xe trong cong mOt to bao quadtree, ne c6 the to ra mOt tang hqp cap dial) nhAt. Nheng t6ng hqp nay lui duqc su clung lin nu& 6 khoang each 16n han trong cac muc dO cao han cilia he thong phan cAp quadtree. Chung &Km tqo ra tfr tap hqp cfra cic cap dO dip theo han, bing cfich them clic con s6 tuang Ong cfra nai
dui xe mien phi tfr bon thank phin tang hqp nhe hon. VI vey, tap hap 16n hon la phan cap duqc tqo ra tfr tap hap nhe han.
MOt qua trinh t6ng hqp ca ban bao g6m chc ID vi mite dO he th6ng di) hoc cilia cic to brio quadtree tuang Ong, mOt nhiin thbi gian, vri t6ng s6 dja diem xe mien
phi. Nhu vuy, tang hqp diu ce cling kich thuOc, bit ke kich thuac cart khu vuc, n6 bao g6m vi s6 luqng cic xe tong khu Arc do. Do do, d6i van met mime de tap hap ngay cang tang vi do da gia tang khoang each dja ly tfr khu vuc duqc ma ti s6 Wong de lieu ten mOt earn diet' tich.
So sanh vi hqp nhit tap hqp cac t6ng hqp khu Arc. Trong phin then da de cop den biing cach s>Sr dung cac When th6i gian, ngubi to c6 the dl ding gift lig gia Ili man nhit duqc quan sit thiy d6i vai mOt so tham s6, loui b6 cfic phip do cil. Dieu nay 11 c6 the bei vi vier cup nil& the duqc so sank thin tren clic nhin th2ri gian. ThSit Ich8ng may, (lieu nay Itheng the duqc chuyin mOt citch don gian de gip hqp m8 tit nhieu hem mOt tham s6. do la mOt may phat dien tang hqp - mOt chiec xe hod trong mpg thtrang Ithang ce thong tin "hoar hao" (hoan chinh va duqc cep nhot day du) c6 san cho citc lin tong hqp. Nhu mOt vi du cu the, hay xem x& mOt ling dung ph6 bien thong tin ye tinh hinh nai dui xe. Gia sil rang ba ctic trang web au xe A, B, C niim trong met khu
Lriu oiNiti 2. truyen tnong tm trong mang V anet
Arc duqc tang hqp. Xe x biat rang tai A c6 10 (ha diim d#u xe mien phi tai then gian tl, vi tai theri gian t2 c6 15 dia diem d#u xe mien phi tai B. x kh8ng c6 thong tin vi C.
Ting hqp duqc to ra beri chiic xe x se tat trong khu Arc c45 tang sa 25 dja diim biii d#u xe mien phi. Xe y cer nhiiu thong tin cfp nhig 6 B han x, vi biit duqc 19 dia diem xe mien phi tai mOt si diem trong thii gian dram nhat la t2. y cling biet khoing 13 dja diem d(tu xe mien phi tai C 6 then gian t3, nhung kheng biit bat cir diiu gi vi tang hqp curt A, vi c6 32 dirt diem d#u xe mien phi trong khu Arc. Gia sir bay gi6 ma met chiic xe thir ba z (tryc dip ho#c gian flip) nh(in duqc cac uan Mang ling t>7r ci hai x vi y. 1/#y mOt thong tin co lqi han nen gift lei? Re rang, cau trit lei cho caw hii nay icheng phai la dam grain, niu cer met cau tri 16i xac dinh 6 tat ci. Cac thong tin trong ark pan tang hqp lcha ching cheo, va Itheng xe nio trong sa d6 re rang chiim uu the khac.
TAY vt dy tren to they rang sy tang hap se khong tidal dien "hoin hio" cria tinh hinh hien tai trong khu Arc bao phi, nhung chi gin ding tat 'that li due tren nheng th8ng tin hien tai curt nut no ra. Neu ck nut khac nhau tao ra tong hqp cho cling mOt Ulu Arc, nheng tang hop nay thutmg se duqc dya tren cac thong tin 'chic nhau , vi mOt phlin th8ng tin bj ching cheo. Ck van di ca bin nay sinh la mOt nhan th6i gian duy flat Wrong thi the hien day di, OA da th6i gian cfia tang. met du tic dtt lieu m8 ti t#p hqp cac th8ng tin va citc nhan theri gian twang ling re rang ding khong phii la
mOt lya chon, bed vi ni se can nhic nham myc dich tang hqp nhi, kich thuic se Ming niu dung luqng chin de lieu kheng tang.
ve van di tang hqp vi tap hqp cac ca chi gild guy& khac nhau nhung thong drying ca hai cii nay diu s* dyng cach ping down flan thii gian. Vi du, SOTIS s* dyng thbi gian cia thi he tang hqp nhu la mOt than then gian cho tang hqp,tuy nhien n6 Ong c6 the li met nut yeti thong tin ca vi kheng day di no ra mOt tong hqp, vi tang hqp nay sau di duqc xem nhu c#p nh$t nhiiu hen vi chic chin hen. Cac di an, tang hqp nhAn then gian cho cic TrafficView (ncri ma cac nhin thiti gian quan sat al
What duqc sir dyng) va Caliskan he thing hying din a xe (tinh tofu' cac nhan then gian trung binh) cue cac thinh phan duqc sir dyng cho t#p hqp. Nhang tinh hang c6 the de ding xay dyng tang hqp yen pham vi bao phi Icha taint dien vi cap nhet duqc cap mOt nhan th6i gian lon han t#p hqp via met ca so thong tin yin.
Da c6 de xutit su dyng nheng dit lieu el* dien di khic phyc van de nay: bang cach km try cac quan sat trong caw tric xac suit tring 1#p de lieu nhay aim duqc goi li "soft-state sketches". Nan bin v8 tinh ci nghTa li thong tin da ci mtit 6 ca hai t#p hqp nguan se khan tic dOng tin kit qui Tr61ai vi dy tren, soft-state sketches khang can phai tra 16i cac caw hii "tong hai pan toting hop thi cai nio tat han", bed vi ni co the hop nil& t#p hqp cart x vi y thanh mOt va loai bi tring Tit hai t#p hqp nguen, c6 the tao ra met gip hop z, trong di ce thong tin ve A, B, va C. T6ng hqp sip
Ltiu uevu L. 1 ruyen tnong un trong mung v anet
niy sau d6 s8 ket hqp tit ci cic th8ng tin vi se dui din cho t6ng s6 10 + 19 + 13 = 42 nui xe mien phi.
Bing cich s(r dung ca the de, kheng cin so sitnh cic tap hqp lien quan: khong cin phi i loai b6 mOt trong nheng tap hqp, Uri vi nhung thong tin co trong ci hai tap hqp deu co the duqc luu gift, th8ng qua sip nhep bit cu nui nio NIA bit khi nio "thich hqp" trong mpg. 1Cheng cin mOt chiec xe c6 khi ruing thu thep diy du thong tin cho lin thu tilt) diu tier, me sau d6 phii tinh toin t6ng hqp, vi c6 the chi duqc cep nhet th8ng qua tinh toin hoin chinh. Thay vio de, tip hop c6 the kit hop thong tin mai cic th8ng s6 ben duei bit cir khi nio, trong khi cic xe dang di chuyin xung quanh mung•
Soft-state sketches dip tren ciu trfic dft lieu duqc de xuit boi Flajolet vi Martin , FM-sketches ban diu duqc thiet ke de uoc tinh s6 luqng cdc yeti t6 rieng biet trong mOt thiet lap theo thiii gian tuyen tinh. Vi chung duqc thiet ke phu hqp vhi cic ting dung VANET, do d6 c6 the duqc stl dung de thu th#p vi phan ph6i cic s6 do. Ngotli ra con cho phep mOt phin mtr rung c6 the to dOng log' be (soft-state) cic quan sit cU, neu ne khOng duqc hg trq cac pile') do men. Hun the ctla sketch dip tan nheng dtt lieu xic suit - drc la, no kheng luu trft gii tri chinh xic c6a cic thong s6, nhtmg n6 li xic suit xip xi. DO chinh xic curt soft state sketches c6 the duqc dieu chinh, stir trao ddi giim dO chinh xic d6i v6i kich thuoc t6ng hqp. Nei chung, met dui dien gin ding cfia cic phi!) do c6 ve hqp ly tong cic img dung VANET dien hinh. Phin mem soft- state titer rung cho vies loci be cic dft lieu ci ding c6 the cho kit qui trong kilt:411g thtri gian nhit dinh gifta mOt gii tri thay d6i vi thay d6i duqc phin inh trong cic tong hqp. Trong khoing thtri gian nay, tuy cOng met mire dO nhu ch#m trg gay ra boi trg do yen chuyin dft lieu qua mpg VANET, trong thuc to dieu nay kh6 c6 the trinh lch6i. Met vi du mo rung li lam the nio y Wong nay c6 the duqc sir dung de phan ph6i s6 diem a xe mien phi, n6 sa duqc de cep trong chuang ye cic Ong dung tier lqi VANET. 1Chii quit cic khii niem ve cic khu Arc tap hqp &Cr b#c trong Lochert. Cich tiep can dlra tren cay tir phan duqc dung tong Caliskan cho phip met each clg ding de giii guy& cic khu vuc vi he th6ng phan cip. Tuy nhien, n6 c6 nheng bun the khong xem xet topo colt thinh ph6 nim ben duoi: cling mOt trutmg tren cay ttr phan bao g6m cac khu vuc hiu nhu Icheng kit n6i trong mpg throng be, vi cic thuOc tinh chi yeti trong de c6 the khic nhau vi du, khu vuc hai ben cUa mOt con song hoar duong sit. Cic khu Arc Alp hqp nen thuc hien theo ciu trim lien kit ming duong be cc, ban, vi dua ra mOt ding thfrc chung cua mOt he th6ng philn cip tap hqp, cOng voi mOt s6 gqi y ye lam the nio de ne c6 the duqc that ke de cho phep ket hqp c6 hieu qtui dua ten sketch.
1,11.UUNU Z. truyen thong un trong mong V anet