I HC QUC GIA H NI TRNG I HC KHOA HC T NHIN

NGUYN GIA NH

MT S THUT TON TIN HA GII BI TON TI U TRONG MNG MY TNH

Chuyn ngnh : C s ton hc cho Tin hc M s : 62.46.01.10

TM TT LUN N TIN S TON HC

H Ni, 2014

Cng trnh c hon thnh ti Trng i hc Khoa hc T nhin,

HQG H Ni

Ngi hng dn khoa hc:

1. PGS.TS L Trng Vnh

2. PGS.TSKH Nguyn Xun Huy

Phn bin 1:

Phn bin 2:

Phn bin 3:

Lun n s c bo v trc Hi ng nh gi lun n cp Trng

hp ti Trng i hc KHTN- i hc Quc gia H Ni

Vo hi.. gi ngy . thng . nm .

C th tm hiu lun n ti: Th vin Quc gia

Th vin Trng i hc Khoa hc T nhin

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M u Ngy nay, mng my tnh tr thnh mt c s h tng quan trng trong nn kinh t

ton cu v s ra i ca Internet lm thay i mnh m ca cuc sng con ngi. Trong cuc cch mng ny, bn cnh s tin b v mt cng ngh th vai tr ca vic nghin cu v xut cc thut ton mi cng c ngha ht sc quan trng. a ra c gii php hu hiu cho mt vn thc t cn s hiu bit c l thuyt thut ton v cc phng tin k thut. Mt trong nhng vn ng quan tm nht ca mng my tnh l hiu nng mng, hiu nng mng tt nht l mc tiu hng n ca nhng nh nghin cu, pht trin v qun tr mng. c hiu nng mng tt cn thit phi c nhng gii php v mt thut ton nhm ti u ha mng. Ti u ha mng my tnh c xem l qu trnh cn bng tt nht gia hiu nng mng my tnh v chi ph mng trong mi tng quan vi cht lng dch v mng.

Trong thc t cc bi ton ti u mng thng gp l cc bi ton ti u t hp (TTH), trong phi tm cc gi tr cho cc bin ri rc lm cc tr hm mc tiu no ([31,60]). a s cc bi ton ny thuc lp NP-kh. Tr cc bi ton c nh c th tm li gii bng cch tm kim vt cn, cn li th thng khng th tm c li gii ti u. i vi cc bi ton c ln khng c phng php gii ng, n nay ngi ta vn dng cc cch tip cn sau:

1) Tm kim heuristic, trong da trn phn tch ton hc, ngi ta a ra cc quy tc nh hng tm kim mt li gii tt.

2) S dng cc k thut tm kim cc b tm li gii ti u a phng.

3) Tm li gii gn ng nh cc thut ton m phng t nhin (xem [31,57,60]) nh m phng luyn kim, gii thut di truyn, ti u by n

Hai cch tip cn u thng cho li gii nhanh nhng khng th ci thin thm li gii tm c, nn cch tip cn th ba ang c s dng rng ri cho cc bi ton c ln. Trong cc phng php m phng t nhin, ti u n kin (Ant Colony Optimization ACO) l cch tip cn metaheuristic tng i mi, c gii thiu bi Dorigo nm 1991 (xem [28,29,31]) ang c nghin cu v ng dng rng ri cho cc bi ton TTH kh (xem [7,9,10,31,36,37,55,59,63]). Ti u ha theo nhm by l mt k thut ti u ha ngu nhin da trn mt qun th c pht trin bi Eberhart v Kennedy, phng theo hnh vi ca cc by chim hay cc n c. PSO tm kim gii php ti u bng vic cp nht cc th h [28]. Cc vn nghin cu lin quan n ti u mng my tnh trn c s tip cn thut ton ti u by n kh phong ph v a dng, c th k n cc vn sau:

i) Bi ton cy truyn thng ti u: Bi ton cy khung truyn thng ti u l bi ton thuc lp NP-kh, c nhiu ng dng trong thc t c bit trong vic thit k cc m hnh mng.

ii) t gateway ti u trong mng Wireless Mesh Network ( WMN): Thng lng l mt trong nhng yu t quan trng nht m bo cc dch v ca WMN p ng cc yu cu ca ngi s dng. pht trin mt thut ton t gateway hng thng lng, mt o hiu nng hiu nng c s dng gi l Multi-hop Traffic-flow weight (MTW) [15] tnh ton nhng nhn t chnh nh hng n thng lng ca WMNs. Nhng nhn t bao gm s router, s client, v s gateway cng nh nhu cu bng thng t cc client, v tr ca

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cc gateway v nh hng gia chng. Da trn MTW, mt thut ton tng tc c xut xc nh v tr tt nht ca mt gateway. Mi ln mt gateway c chn t ti mt router s c MTW cao nht.

iii) nh v cc basestation trong mng Wireless Mesh Network: Xc nh cc Basestation trong mng WMN l mt trong nhng khu quan trng ca qu trnh thit k mng WMN. Vic nh v cc basestation trong mng WMN lin quan n nhiu yu t khc nhau nh lu lng mng , knh truyn, kch bn can thip, s lng base stations v cc thng s quy hoch mng khc.

Nhim v tc gi lun n t ra l: Lun n tp trung gi quyt mt lp vn v ti u trn mng my tnh vi cch tip cn thut ton tin ha PSO

i) Cy khung truyn thng ti u: xut mt hng tip cn mi v cy khung truyn thng ti u ( optimal communication spanning tree). Hng tip cn ny da trn thut ton ti u ha by n PSO. Gii php ny c th t kt qu tt hn so vi thut ton heuristic c bit.

ii) t gateway trong mng WMN: xc nh v tr gateway nhm t thng lng cc i, mt o hiu nng c s dng gi l Multihop Traffic flow weight (MTW) nhm tnh ton nhng nhn t nh hng n thng lng ca mng WMNs.

iii)nh v cc BTS trong mng Mobile Network: Xc nh cc base station trong mng Mobile Network l mt trong nhng khu quan trng ca qu trnh thit k mng. Vic nh v cc BTS lin quan n nhiu yu t khc nhau nh lu lng mng , knh truyn, kch bn can thip, s lng BTS v cc thng s quy hoch mng khc.

iv) Ti u truy cp tp trung trong mng Mobile Network: Mng truy cp trong kin trc h thng di ng t bo gm 4 tng tng tc: tng tc gia cc trm di ng (mobile station-MS) hay tp cc ngi dng n cc trm thu pht sng c s (base transceiver stations-BTS), tng tc gia cc trm thu pht sng c s vi cc trung tm chuyn mch di ng (mobile switching centers-MSC), v tng tc gia cc trung tm chuyn mch di ng vi tng i truy cp tp trung (local exchanges-LE) trong mng PSTN. Ti u truy cp trong mng khng dy. y l cc bi ton quan trng trong thit k v ti u mng.

Cc kt qu ca lun n c cng b trong 5 bo co hi ngh quc t 2, 3 bi bo trn cc tp ch quc t, 1 bi bo tp ch trong nc v 3 bi trn hi tho ton quc Cc ch chn lc ca cng ngh thng tin, 1 bi trn hi tho FAIR.

Ngoi phn m u v kt lun, lun n c t chc nh sau: Chng 1 gii thiu mt s kin thc c bn v mng khng dy cng nh nhng nt chnh ca phng php ti u tm kim by n. Cc vn m lin quan n ti u trong mng khng dy cng c trnh by trong chng 1. Chng 2, lun n xut gii php t gateway trong mng WMN s dng thut ton PSO nhm xc nh v tr gateway nhm t thng lng cc i. Bi ton nh v cc basestation trong mng Mobile Network c trnh by trong Chng 3. Chng 4, lun n xut thut ton PSO p dng ti u truy cp trong mng khng dy.

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Chng 1. Tng quan v ti u mng

1.1 Mng khng dy

1.1.1 Khi nim 1.1.2 S pht trin ca mng thng tin di ng 1.1.3 Kin trc mng thng tin di ng

1.2 Cc vn ca ti u mng

1.2.1 Mc tiu ca ti u mng

Ti u dung lng: Dung lng l mt vn nhiu mt v ph thuc vo nhiu yu t tng tc vi nhau.

Ti u vng ph sng: Vng ph sng cho php ngi dng c th di chuyn thoi mi t mng khng dy hin ti vo cc mng khng dy khc. c bit l trong mng khng dy di ng. Theo ngi dng s chuyn t mt mi trng mng di ng ny sang mi trng mng di ng khc.

Ti u qun l ti nguyn: Qun l ngun ti nguyn c th chia thnh: iu khin cng sut, chuyn giao, iu khin ti.

Ti u quy hoch mng: Trong qu trnh pht trin, xy dng mng cc doanh nghip lun quan tm n vn quy hoch mng nhm dt c nhng mc tiu sau: m bo ti u ha vng ph sng; m bo dung lng cung cp cho cc dch v a phng tin cht lng cao cho khch hng; Ti u ha vic lp t, xy dng mng; Thun tin cho vic bo hnh, bo dng mng; nng cp, sa cha mng.

1.2.2 Cc vn m trong mng khng dy

Truyn thng khng dy chng t tm quan trng ca n trong thi gian qua nh l nn tng iu khin ca s pht trin kinh t, u tin l theo hnh thc mng di ng v gn y l cho cc mng my tnh (WiFi, WiMAX). Trong thp k ti c th n s mang li s pht trin mt cch t ph. Mc pht trin y ca chng khng th d on nhng chc chn s bao gm: Cc dch v bng thng rng: cc dch v triple-play (ging ni, d liu, video) tc ln ti 1Gbit/s cho ngi dng trong mt mi trng ty . Kh nng tnh ton mi ni: Tnh thng minh c phn phi trong mt tp hp cc thit b hot ng mt cch t ch. Cc mng cm bin khng dy cho vic gim st v cm nhn mi trng. lm c nhng iu trn, chng ta cn phi gii quyt trong tng lai cc vn chnh sau y: Qun l ti nguyn v ph thng minh; Cc mng di ng khng ng nht; Vn an ninh cho mng khng dy.

1.2.3 Bi ton ti u

1.3 Cc thut ton tin ha

1.3.1 Thut ton di truyn (GA)

Gii thut di truyn (GA-Genetic Algorithm) [27] l mt k thut ca khoa hc my tnh nhm tm kim gii php thch hp cho cc bi ton ti u t hp (combinatorial optimization).

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Gii thut di truyn l mt phn ngnh ca gii thut tin ha vn dng cc nguyn l ca tin ha nh di truyn, t bin, chn lc t nhin, v trao i cho.

1.3.2 Thut ton ti u ha n kin (ACO)

Cc thut ton kin ln u tin c gii thiu bi Dorigo v cc cng s nh l cch tip cn a tc t ti cc vn v ti u t hp kh, nh bi ton ngi du lch (TSP), bi ton ngi a th. Hin nay s lng cc ng dng cng ngy cng tng v cc nh khoa hc ng dng n vo rt nhiu cc vn ti u ri rc. Cc ng dng gn y c th k n nh cc bi ton lp lch, t mu th, nh hng trong mng truyn thng, v.v

1.3.3 Thut ton ti u ha nhm by (PSO)

Ti u ha theo nhm by l mt k thut ti u ha ngu nhin da trn mt qun th c pht trin bi Eberhart v Kennedy, phng theo hnh vi ca cc by chim hay cc n c. Cng ging nh GA, PSO tm kim gii php ti u bng vic cp nht cc th h. Tuy nhin, khng ging nh GA, PSO khng c cc thao tc tin ha nh l lai ghp hay t bin. Nm 1987, quan st qu trnh chuyn ng ca cc theo by n (by chim, n c), Reynolds [6] a ra nhn ra ba quy lut: Tch bit; Sp hng v Lin kt. T nghin cu ca Renolds, Eberhart v Kennedy [7] a thm gi thuyt v qu trnh tm v t ca by n theo cc quy lut:

(1) Tt c cc phn t trong by n u c xu hng chuyn ng v t

(2) Mi phn t u ghi nh v tr gn t nht n t ti

Tng t nh vy, hai ng a gi thuyt v qu trnh tm mi ca by n trong mt vng khng gian m cc phn t trong by n u bit thng tin v thc n cch bao xa v lu gi v tr gn thc n nht m chng t ti. Khi , cch tt nht tm thc n l theo sau nhng con phn t u n nhng con trong by gn ch thc n nht. T , hai ng xut thut ton PSO phng theo kch bn ny v s dng n gii cc bi ton ti u. Trong PSO, mi gii php n l mt phn t (particle) trong kch bn trn. Mi phn t c c trng bi hai tham s l v tr hin ti ca phn t present[ ] v vn tc v[ ]. y l hai vect trn trng s Rn (n l tham s c xc nh t bi ton c th). ng thi mi phn t c mt gi tr thch nghi (fitness value), c nh gi bng hm o thch nghi (fitness function). Ti thi im xut pht, by n, hay chnh xc l v tr ca mi phn t c khi to mt cch ngu nhin (hoc theo mt cch thc no d da vo tri thc bit trc v bi ton). Trong qu trnh chuyn ng, mi phn t chu nh hng bi hai thng tin: thng tin th nht, gi l pBest, l v tr tt nht m phn t t c trong qu kh; thng tin th hai, gi l gBest, l v tr tt nht m c by n t c trong qu kh. Trong nguyn bn do Eberhart v Kennedy a ra, cc phn t trong PSO s duyt khng gian bi ton bng cch theo sau cc phn t c iu kin tt nht hin thi ( thch nghi ln nht). C th l sau mi khong thi gian ri rc, vn tc v v tr ca mi phn t c cp nht theo cc cng thc:

v[ ] = v[ ] + c1.rand() . (pbest[ ] - present[ ]) ++ c2.rand() * (gbest[ ] -present[ ]) (1.2)

present[ ] = persent[ ] + v[ ] (1.3)

Trong : rand( ) l mt s ngu nhin trong khong (0,1); c1, c2 l cc h s hc, chng thng c chn l c1 = c2 = 2. [10]. M gi ca thut ton PSO c cho di y:

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Thut ton PSO

1 ForEach particle

2 Khi to particle;

3 EndFor

4 Do

5 ForEach particle

6 Tnh fitness value;

7 If (fitness value < pBest) then

8 pBest = the fitness value;

9 EndIf

10 If (pBest < gBest) then

11 gBest =pBest

12 EndIf

13 EndFor

14 ForEach particle

15 Tnh vn tc theo cng thc (1.2);

16 Cp nht v tr theo cng thc (1.3);

17 EndFor

18 While (cha tha mn iu kin dng);

Trong , mt s iu kin dng ph bin l: s ln cp nht, s ln cp nht by n m khng a li kt qu tt hn, s ln cp nht m lng thay i gia hai ln cp nht lin tip nh hn mt ngng no Ngoi ra iu kin dng c th c xc nh t bi ton c th. Phin bn ban u ca PSO c trnh by trn c gi l phin bn tt nht ton cc (global best), trong vn tc ca mi phn t u ch b nh hng bi hai yu t l: yu t ni ti v tr tt nht n tng t c v yu t ton cc v tr tt nht c by t c. Cc ci tin ca PSO a vo yu t cc b, tc l vn tc ca mi phn t trong qu trnh chuyn ng cn b tc ng bi v tr tt nht t c trong s nhng hng xm ca n lbest[ ]. Khi , cng thc cp nht vn tc l:

v[ ] = v[ ] + c1.rand() . (pbest[ ] - present[ ]) + c2.rand() * (gbest[ ] - present[ ])

+ c3.rand() * (lbest[ ] - present[ ]) (1.4)

Theo nghin cu ca M. Clerc [8], vic ch s dng yu t cc b (c gi l phin bn tt nht cc b (local best) ca PSO) thng em li hiu qu tt hn so vi vic s dng yu t ton cc hoc s dng c hai yu t (cc b v ton cc). thng nht trong vic s dng PSO, cc nh nghin cu thng nht a ra phin bn PSO chun v bn chun mi nht hin nay l Standard PSO 2007 (SPSO-07). Thng tin v cc phin bn chun, cc bin th v nhng ng dng ca PSO c th tm thy ti [9].

1.4 Mc tiu v b cc ca lun n

Lun n tp trung gii quyt mt lp vn v ti u trn mng my tnh vi cch tip cn thut ton tin ha PSO

i) Ti u thng lng trong mng li: Phn mng li (Core network-CN) ng vai tr quan trng trong vic quyt nh nng lc phc v cng nh kh nng nng cp mng. Tt c

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cc nhu cu xut pht t phn mng truy nhp u phi thng qua x l ca phn mng li, v bt c nhng s thay i no cng u da trn kh nng phc v ca phn CN. V vy vic nghin cu tnh ton v ti u dung lng mng li CN l ht sc quan trng.

ii) Ti u thng lng trong mng li khng dy: xc nh v tr gateway nhm t thng lng cc i, mt o hiu nng c s dng gi l Multihop Traffic flow weight nhm tnh ton nhng nhn t nh hng n thng lng ca mng WMNs.

iii) Ti u truy cp trong mng khng dy: Xc nh cc base station trong mng khng dy l mt trong nhng khu quan trng ca qu trnh thit k mng khng dy. Vic nh v cc base station trong mng khng dy lin quan n nhiu yu t khc nhau nh lu lng mng , knh truyn, kch bn can thip, s lng basestations v cc thng s quy hoch mng khc. Sau khi ti u c v tr cc trm basestations, cng vic tip theo ti tip cn l ti u truy cp tp trung trong mng khng dy vi s kt hp gia cc BTS, MSC v LE.

Ngoi phn m u v kt lun, lun n c t chc nh sau: Chng 1 gii thiu mt s kin thc c bn v nhng vn m trong ti u mng khng dy. Lun n cng phn tch v gii thiu cc cch tip cn tin ha gii cc bi ton ti u nh thut ton GA, ACO, PSO. Chng 2, lun n xut gii php t gateway trong mng WMN s dng thut ton PSO nhm xc nh v tr gateway nhm t thng lng cc i. Bi ton nh v cc basestation v ti u truy cp tp trung trong mng khng dy c trnh by trong Chng 3.

Cc kt qu ca lun n c cng b trong 5 bo co hi ngh quc t, 4 bi bo trn cc tp ch quc t, 1 bi bo tp ch trong nc, 3 bi trn hi tho quc gia Cc ch chn lc ca cng ngh thng tin, 1 bi trn hi tho FAIR. C th nh sau:

1.5 Kt chng

Chng ny, lun n gii thiu mt s kin thc c bn v nhng vn m trong ti u mng khng dy. Lun n cng phn tch v gii thiu cc cch tip cn tin ha gii cc bi ton ti u nh thut ton GA, ACO, PSO.

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Chng 2. Ti u thng lng trong mng

2.1. Ti u thng lng trong mng li

2.1.1 Pht biu bi ton

Bi ton Cy khung truyn thng ti u (OCST, Optimal Communication Spanning Tree Optimization) c Hu [8] a ra vo nm 1974. Vn cy khung ti thiu c th c nh ngha nh sau: i, j, k =1, 2, ..., n, l ch s ca nt; l=1L l ch s ca loi dch v.

Tham s: n=|V| l s nt , m=|E| l s cnh, stq Q l yu cu ca loi ngun l nt s cha

nt t. iju U l dung lng ca cnh (i, j) , lw W l trng s (u tin) ca dch v thng tin

lin lc l, ijd D l tr ca cnh (i, j) (hoc c cc nh l mt phng php thc hin

cho QoS ca NGN), trong llij l ij ijd wG q u (2.5)

l

ij ijG q u l hm s xc nh tr ca loi dch v l

Cc bin quyt nh: yij: Dung lng yu cu ca lung (i, j) , xij: 0-1 bin quyt nh. Bi ton c m hnh nh sau:

, 1min min 0,

L

l ij iji j E l

f x w y u

(2.6)

Tha mn

1 1

1n n

iji j

x n (2.7)

1 1

1n n

iji j

x S

cho bt k b S ca cc nt (2.8)

1 1

,

0, ,

,

l

ijn n

ij kij k

l

ij

q if i s

y y if i V s t

q if i t

(2.9)

nt ngun v nt cha ca l

ijq , l L (2.10)

0,1 , , 1..ijx i j n (2.11)

2.1.2 Cc nghin cu lin quan

Bi ton OCST c chng minh l bi ton NP-kh [9], iu ny c ngha l khng tn ti thut ton gii chnh xc bi ton vi thi gian a thc, tr khi P = NP. Trn thc t, nhng thut ton chnh xc c xut cng khng th gii quyt nhng bi ton c kch

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thc nh vi thi gian chp nhn c [5]. Do hin nay vic pht trin thut ton tm kim hiu qu a ra nhng li gii cht lng cao cho bi ton OCST l hng nghin cu ang c quan tm.

gii bi ton OCST, mt s thut ton chnh xc c xut in hnh l thut ton nhnh cn ca Ahuja v Murty [21], tuy nhin chng khng tht s hiu qu khi gii quyt bi ton k c vi nhng bi ton kch thc nh [12]. Rt nhiu nhng gii thut xp x c pht trin tuy nhin cht lng li gii kh gii hn. Gii thut heuristic u tin c Palmer v Kershenbaum [2] xut. Trong [8], Chou v cng s da trn m ha ca ngi tin nhim to ra mt s nhim sc th bt hp php (ngha l khng phi cy bao trm). Kt hp khi to ngu nhin n gin, hu ht cc nhim sc th s l bt hp php bi ba l do: thiu nt I, t vng lp, hoc c chu k. Quy trnh sa cha phc tp s c s dng mi th h (chi ph in ton), v sau khi sa cha, con ci ca cc xuyn cho v t bin kh m biu trng cho cc gii php m kt hp cu trc bn di ca b m chng (v tr v kh nng di truyn xu nht). Lin Lin v Misuo Gen trong [15] xut mt cch m ha da trn PrimPred, m ha da trn ngi tin nhim c ci to. Vic khi to ph thuc vo mt thut ton cy bao trm ngu nhin c bn. Quy trnh c th ca cch m ha v gii m ny c gii thiu trong [10].

2.1.3 Ti u cy khung truyn thng s dng thut ton PSO

Trong phn ny, chng ti trnh by ng dng ca phng php PSO cho vn cMST. Xt cu hnh trong thut ton l cc b gm n nt vi lc biu din NBE nh trnh by

trn. Mi c th c m ha bng mt ma trn ij n nx x trong 0,1 , , 1..ijx i j n . khng mt tnh tng qut chng ta c th gi nh rng G l th y v hng. M ha cc node theo NBE (Node Biased Encoding) [8]

M ha: Mi cy khung T ca th G=(V,E) c th hin bng mt vect c n thnh phn thc b=(b1,b2,,bn). (b c gi l vect trng s)

Gii m

- Bc 1: Xy dng th trung gian G=(V,E) vi vic thay i ma t rn khong cch D=(dij)nxn c tnh ton nh sau:

dij=dij+P2+(bi+bj)*dmax

trong dmax=MAX{dij} v P2 l node tham s.

Bc 2: Tnh T l cy khung truyn thng ti u trn th G dng thut ton Prim

Sau khi thc hin thut ton Prim, cc node i vi trn s bi thp s tr thnh cc node interior v cc node khc j vi trn s bj cao s tr thnh cc node l. Hn na, vect trng s cao nht bi, s li tr thnh node l.

Chng ti s dng khi to ngu nhin hon ton khi to qun th tha mn cc rng

buc (2.9) v (2.10). Chng ti to ra th hin mt phn t ca ma trn ij n ny y trong

0, , 1..ijy i j n v c tnh ton bi cng thc (2.5). Hm chi ph cho c th x c tnh

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ton bi cng thc (2.6). iu kin dng c dng trong bi vit ny c xc nh l s tng tc ti a Ngen (Ngen cng l mt tham s c tnh ton).

2.1.4 Kt qu m phng v nh gi

2.1.4.1 Tham s thc nghim

Trong cc th nghim, ti gii quyt mt s trng hp cMST vi mc kh khc nhau c quy nh nh sau:

Ti dng 3 cu trc mng li hon chnh c 20 nt (n=20) vi 3 loi dch v: Loi 1: Truyn hnh cp, Loi 2: in thoi IP, Loi 3: D liu. Trng s (u tin) ca 3 loi ny ln lt l: w1=0.60, w2=0.30. w3=0.10. Dung lng ca mi cnh (i, j) c biu din l cc bin ngu nhin ph thuc vo s phn b ng u: runif (m, 100, 1000). Cc yu cu chu trnh 20 ln ca cc loi dch v khc nhau t nt s n nt t c biu din bi cc bin ngu nhin ph thuc vo cc hm phn b: Loi 1 phn b hm m: r*exp(|Q|, 0.03), Loi 2 phn b loga chun:0.1*r*lnorm(|Q|, 0.1, 0.1), Loi 3 phn b bnh thngr*norm(|Q|,0.01, 0.001)), trong : |Q|=100.

Trong cc th nghim ca mnh, chng ti xc nh sn cc tham s cho thut ton PSO c trnh by Bng 2.1.

Bng 2. 1 C IM CA THUT TON PSO Kch c dn s P = 1000

S tng tc ti a Ngen = 500

Tham s nhn thc c1 = 1

Tham s x hi c2 = 1

Cp nht dn s theo Cng thc (2.6) v (2.7)

S lng ging K = 3

2.1.4.2 Kt qu

Trong cc th nghim, PSO do chng ti xut c so snh vi EA da trn PrimPred [5], EA da trn Cnh cc thut ton tin ha khc nhau, GA da trn s Prufer [7] v thut ton truyn thng ca Prim (m khng xt n hn ch dung lng) [6], Hm mc tiu l tng thi gian tr trung bnh ca thut ton ca chng ti t c hiu sut tt hn nhiu so vi cc thut ton khc.

Hnh 2.1 So snh tng thi gian tr trung bnh ca PSO, EA da trn PrimPred, EA da trn cnh, GA da trn s Prufer v Cc thut ton ca Prim

10

nh gi hiu sut ca thut ton, chng ti s dng tp cc m hnh mng chun sau: Mng Palmer : 6 nt (Palmer6), 12 nt (Palmer12), 24 nt (Palmer24) ; Mng Raidl : 10 nt (Raidl10), 20nt (Raidl20), 50 nt (Raidl50, Raidl50gen); Mng Berrry: 6 nt (Berry6). Chng ti thc hin ci t thut ton ACO cho cc m hnh trn v so snh kt qu thc nghim vi cc thut ton c xut trc nh: GA Palmer, Li and Bouchebabas GA v thut ton PSO.

Trong cc trng hp khc (Raidl50 and Raidl50gen) thut ton ACO cho gii php tt hn so vi Palmers and Li & Bouchebabas. Cc trng hp cui cng (Berry6), tt c cc thut ton u c chung mt gii php ti u. Tuy nhin nhng thut ton ca chng ti vn l nhanh nht. So snh thi gian x l ca cc phng php ti u ha c trnh by trong hnh 2.3.

Hnh 2.2 So snh thi gian x l ca cc thut ton vi lp bi ton Palmer v Raidl

Hnh 2.3 Kt qu so snh hm chi ph ca bn thut ton vi cc trng hp chun

Bng 2.2 So snh kt qu ca cc trng hp chun

2.2. Ti u thng lng trong mng li khng dy

2.2.1 Pht biu bi ton

Instance Palmer' GA

Li & Bouchebaba's

GA PSO ACO

Cost Time Cost Time Cost Time Cost Time

Palmer6 709770 6.88 708090 5 693180 4.1 693162* 3.92

Palmer12 3876488 35.53 3457952 24.7 3428509* 22 3428509* 23

Palmer24 1959790 229.67 1086656* 162 1138360 143 1138364 152

Raidl10 58352 22.21 53674* 15.93 53674* 14 53674* 14.71

Raidl20 165788 138.50 157570* 97.3 157570* 87.3 157570* 86.9

Raidl50 191987 1883.09 134931 1350 107746* 1178 107746* 1176

Raidl50gen 1230130 1883.86 964140 1351 826499* 1177 826499* 1179

Berry6 534* 6.80 534* 5.74 534* 4.6 534* 4.5

11

2.2.1.1 Topology mng

Mt m hnh WMN in hnh cho vic truy cp Internet c xut nh di y v c minh ha trong hnh 2.5. Trong : Nc client c gi nh c phn phi trong mt

hnh vung 2

0,R l . R c phn tch thnh 2

S

ll

t bo nh 2

20, ( 1.. )jS S

S

lR l jl

, Mt router c t ti trung tm ca mi t bo.

Router c chc nng gateway

Router khng c chc nng gateway

Client

Hnh 2.4 Topo ca mt mng WMN c cc gateway

t Nr l s router, th 2

rS

lNl

. Di y chng ta s gii hn trong trng hp

1 r cN N , c nhiu hn 1 router v s router t hn s client. Cc router to thnh mt mng li khng dy cung cp mt c s h tng khng dy cho cc client. Trong mi t bo, cc client c kt ni n router theo m hnh hnh sao, khng c kt ni trc tip gia cc client, v router lm vic nh mt hub cho cc client. Chng hn WMN c cp nh l mt c s h tng WMN trong [2], c mong i s tr nn ph bin trong cc ng dng WMN tng lai.

Gia tt c cc router, c Ng router c ni dy vi Internet, lm vic nh l gateway. Hin nhin l .., s gateway khng th vt qu s router. Vic chn cc topo l li vung v nhng nghin cu hin ti trong s trin khai cc vn [3] ch ra rng cc topo li vung thit thc hn trong vic xy dng hiu nng mng mong mun. Di y l nhng nh ngha v truyn thng s thng xuyn c s dng: Truyn thng cc b (Local communications) ; Truyn thng li (Backbone communications) ; Truyn thng ng xung (Downlink communications) ; Truyn thng ng ln (Uplink communications)

2.2.1.2 M hnh truyn

chi tit thm k hoch t gateway mi v tnh ton thng lng ca n, mt m hnh truyn c ch nh nh di y: Mi router c trang b 2 giao din radio: Mt truyn vi tc W1 bits/s cho truyn thng li; Mt truyn vi tc W2 bits/s trong truyn thng cc b; Mi client truyn vi tc W2 bits/s trong truyn thng cc b. Chng ta gi thit rng W1 v W2 l trc giao truyn thng cc b khng b nhiu bi truyn thng li.

2.2.1.3 Thng lng

12

Bi ton 1: Ti u vic t gateway cc i tng thng lng ca WMNs. Trong m hnh WMN trn, cho Nc, Nr, Ng, W1, W2 v s phn phi ca router, s phn phi ca client, s truyn, vic lp lch v cc giao thc nh tuyn, Ng gateway c chn trong s Nr router :

1

, maxcN

giTH i N

(2.17)

t cc i, trong , gTH i N l thng lng cho mi client ca client th i khi Ng gateway c trin khai.

Bi ton 2: Ti u vic t gateway cc i thng lng ca mi client trong trng hp xu nht trong WMN. Trong m hnh WMN trn, cho Nc, Nr, Ng, W1, W2 v s phn phi ca router, s phn phi ca client, s truyn, vic lp lch v cc giao thc nh tuyn, Ng gateway c chn trong s Nr router

1

min , maxcN

giTH i N

(2.18)

2.2.2 t gateway hiu qu s dng thut ton PSO

p dng c thut ton PSO cho bi ton th vic u tin chng ta phi tm c cch biu din ca cc phn t sao cho mi phn t l mt gii php ca bi ton. Thng thng, c ba phng php m ha: m ha s thc, m ha s nguyn, m ha bt nh phn. Ti s dng phng php m ha s nguyn m ha cc c th. Mi phn t l mt vect K chiu (K l s gateway cn t vo) m mi thnh phn l mt s nguyn tng ng vi v tr ca n s c t trong WMN. C th, k hiu cc gateway l {g1, , gk}, mt phn t j trong thut ton PSO l {aj1, , ajk} th aji s tng ng gateway gi v nhn mt gi tr nguyn c sinh ngu nhin. Gi s m hnh mng WMN, trnh by trong mc 2.2.1, c chia thnh N c nh s t tri sang phi, v t trn xung di. Khi cc aji s nhn gi tr trong khong [0..(N-1)].

{Thut ton gii m i vi mt phn t}

(1) Xc nh v tr t gateways

(2) Tnh thng lng cho trng hp 1 mc 2.2.1.3.

Qun th ban u c khi to vi P phn t (P l tham s thit k). Mi phn t l mt vectK chiu (K l s gateway cn t vo) m mi thnh phn l mt s nguyn tng ng trong khong [0,N-1] c sinh ngu nhin.

Gi s qu trnh thit lp c phn t th j l {aj1, , ajk}. Khi gi tr thch nghi Fj ca phn t j c tnh theo cng thc sau:

Fj = 1 - 1

(,)=1 (2.24)

Cc phn t trong mi mt th h c cp nht theo ng cng thc (3.7) v (3.8) trn. Trong present[j] v v[j] ln lt l c th th j trong qun th thuc th h ang xt v vn tc tm kim ca c th ny. Trong ng cnh ca bi ton ang xt, present[j] v v[j] u l cc vect thc K chiu. V PSO l mt qu trnh ngu nhin, nn chng ta phi nh ngha iu

13

kin dng cho thut ton. Thut ton s dng khi gi tr ca gBest v pBest khng thay i hoc sau G th h (G l mt tham s thit k).

2.2.3 Kt qu m phng v nh gi

2.2.3.1 Tham s m phng

Ti khai bo v ci t cc thut ton trn ngn ng lp trnh C vi cu hnh my thc nghim l chip Intel CPU Duo Core 3.0 GHz, b nh RAM 2G. Cc tham s thit lp khi thc thi thut ton c m t trong Bng 2.4.

Bng 2.3 Cc tham s thit lp khi chy thut ton

Thut ton PSO Gi tr tham s

Kch thc nhm by P = 100

S lng vng lp ti a Ngen = 500

H s hc c1 = c2=1

S ln cn c xem xt K=3

2.2.3.2 Kch bn v kt qu m phng

Vn dng thut ton PSO vo vic xy dng mt k hoch t cc Gateway trong mng WMN nhm ti u thng lng mng, ti t c nhng kt qu nghin cu tt hn nhng phng php trc y, m trc quan nht l phng php phng php t Gateway da trn tham s MTW [15]. Gi thit c 5000 client c phn b ngu nhin trong mt li vung 25x25 , mi c mt router.

Kch bn 1: Chng ti nghin cu mi quan h gia s Gateway t trong mng v thng lng m mng t c. Gi thit bng thng cc b l 10Mbps, (c2W2 = 10) bng thng li l 20 Mbps (c1W1 = 20). Sau ti cho s Gateway tng dn t 10 n 100, mi bc tng 10 Gateway. Kt qu m phng c th hin trong Bng 2.5. Theo kt qu m phng ny chng ta thy khng phi lc no tng s Gateway th thng lng trong mng cng tng ln. V khi s Gateway tng ln, bn cnh vic gim s hop trong truyn thng li, th nhiu nh hng gia cc Gateway cng gia tng, v i khi n lm gim ng k thng lng ca mng.

Bng 2.4 Tng quan so snh thng lng t c khi t Gateway theo thut ton PSO, ACO v theo phng php s dng tham s MTW

Thut ton

S Gateway

10 20 30 40 50 60 70 80 90 100

MTW 681.7 628.6 922.6 804.9 715.7 687.0 1295 1257 1218 1184

PSO 1142 1097 1184 1103 976.3 935.2 1452 1352 1241 1278

ACO 1165 1073 1152 1096 985.1 967.3 1489 1315 1253 1291

Kch bn 2: Ti so snh thng lng thp nht t c ca mi client gia hai phng php trn. Vn gi thit cc tham s nh trong kch bn 1. Theo kt qu m phng nhn c trong Bng 2.6, chng ta li mt ln na d dng nhn ra s u vit ca phng php t Gateway da trn thut ton PSO, ACO so vi phng php dng tham s MTW.

14

Bng 2.5 Tng quan so snh thng lng thp nht ca mi client khi t Gateway theo thut ton PSO, ACO v theo phng php s dng tham s MTW

Thut ton

S Gateway

10 20 30 40 50 60 70 80 90 100

MTW 0.020 0.030 0.058 0.058 0.041 0.040 0.07 0.07 0.071 0.072

PSO 0.035 0.046 0.073 0.058 0.057 0.064 0.18 0.096 0.085 0.093

ACO 0.037 0.041 0.069 0.058 0.061 0.059 0.18 0.092 0.089 0.095

Kch bn 3: nh gi r hn s lng Gateway cn t khi thit k mng, ti xem xt thm trng gi tr thng lng trung bnh t c ca mi Gateway khi s lng Gateway tng dn t 10 n 100, mi bc tng 10 Gateway, theo c 4 phng php: phng php s dng tham s MTW v phng php s dng thut ton GA, PSO v ACO. Gi s bng thng li v bng thng cc b ln lt l 20Mbps v 10Mbps. Kt qu m phng c th hin nh Bng 2.7.

Bng 2.6 Gi tr thng lng trung bnh ca cc Gateway Thut ton

S Gateway

10 20 30 40 50 60 70 80 90 100

MTW 68.17 31.43 30.07 20.12 14.31 11.45 18.50 15.71 13.54 11.84

GA 111.0 52.03 37.29 25.28 18.43 14.51 18.78 15.98 13.76 12.09

PSO 114.6 57.12 38.57 25.28 20.57 14.51 18.93 15.98 13.85 12.24

ACO 116.5 56.41 37.84 26.15 19.44 15.16 18.93 15.98 3.79 12.31

nh gi hiu qu ca v tr cc Gateway, ti s dng 2 tham s: Tng thng lng ca tt c cc Client ca cc thut ton ln lt l PSO_Sum, ACO_Sum. Thng lng ti thiu ca mi Client gi l PSO_Min, ACO_Min.

Kch bn 4: Gi s Nc=200, Nr=36, l=1000m, ta xt 1000 client c phn b trn li hnh vung kch thc 1000m x 1000m. Ta chia thnh 36 hnh vung nh v mi mt router c t ti trung tm hnh vung. Cc tham s c s dng l CRF = 4, SRD=3, IntD=2, bng thng mng li l 20 Mbps v bng thng mng cc b l 10 Mbps.

Trong kch bn 4, ti so snh thng lng ca cc phng n ti u gia cc thut ton trung bnh trong trng hp xu nht v trong trng hp trung bnh. Kt qu so snh c th hin trong Hnh 2.16 v Hnh 2.17.

Hnh 2.5 So snh thng lng trung bnh v xu nhy ca Client trong kch bn 4

Kch bn 5: Tng t nh kch bn 4 nhng ti thay th cc gi tr Nc=400, Nr=64 v lu lng cc b yu cu trn mi router c sinh ngu nhin. Kt qu ca kch bn 5 c th hin trong Hnh 2.6.

15

Hnh 2.6 So snh thng lng trung bnh v xu nht ca Client trong kch bn 5

2.2.3.3 nh gi

Kt qu m phng cho chng ta mt ci nhn tng quan chn s lng gateway cn t khi thit k mng. Khi s lng gateway cng ln, thng lng trung bnh t c bi cc gateway cng nh, iu ny s gy ra s lng ph ti nguyn mng. V vy chng ta cn chn s gateway ph hp m bo thng lng tt nht cho mng, v khng gy lng ph. Kt qu m phng trong Bng 3.4 cn cho chng ta thy vi cng s gateway, phng php s dng thut ton PSO v ACO lun cho gi tr thng lng trung bnh ca cc gateway tt hn. Nh vy d trong bt c trng hp no, phng php t gateway s dng thut ton PSO cho ta kt qu tt hn kt qu t c bi phng php s dng tham s MTW.

2.3 Kt lun chng 2

Trong chng ny, lun n xut mt thut ton PSO gii quyt bi ton ti u thng lng trong mng li. M hnh bi ton c chuyn v cy bao trm ti thiu c kh nng (cMST) m xem xt n cc kh nng ca mng li, s u tin khc nhau cho cc loi hnh dch v v mi trng nng ng khc nhau. Trong thut ton ca ti, cc hm mc tiu c xc nh bi tng s thi gian tr trung bnh da trn ma trn pheromone ca kin tha mn cc hn ch dung lng tm cc gii php thch hp tt. Cc th nghim s vi cc vn mng li thng tin lin lc c quy m khc nhau cho thy tnh hiu qu v hiu qu ca thut ton ca chng ti, iu ny cho thy rng thut ny ny tt hn nhiu so vi nhng nghin cu gn y.

Bi ton t Gateway trong mng WMN nhm ti u thng lng mng - mt vn c ngha thc tin cao s dng thut ton ti u by n (PSO) da trn o tham s MTW nh gi i vi tng Gateway. Cc kt qu m phng c phn tch cho thy r s u vit ca cc phng php ny v c hiu sut ln hi t ca phng n ti u. Hiu sut tt nht t c vi thut ton PSO l mc thp nht v nng lng v thi gian truyn thng. Vi vai tr l mt bi ton c ngha thc tin cao, bi ton t Gateway trong mng WMN nhm ti u thng lng mng hn s cn c nghin cu tip v s cn nhng gii php ti u hn.

16

Chng 3. Ti u truy cp mng

3.1 t trm c s trong mng thng tin di ng

3.1.1 M hnh bi ton

Chng ta c th nh ngha hnh thc m hnh truyn thng trong mng di ng nh sau: C M trm BTS, chng ta cn thit lp N trm BTS thnh cc trm iu khin qun l lu

lng mng ( y N

17

3.1.2 Cc nghin cu lin quan

Ti u thit k mng khng dy c m hnh ha bng 2 bi ton. Bi ton th nht l xc nh cc thit b u cui (Terminal Assignment-TA) [1] vi mc tiu xc nh cc kt ni c chi ph thp nht trong mng thng qua thit lp cc kt ni t mt tp cc thit b u cui n mt tp cc trm thu pht sng di ng vi hai rng buc l mi thit b u cui phi kt ni c ti t nht mt v ch mt trm thu pht sng v dung lng yu cu ca thit b u cui c kt ni phi nh hn hoc bng dung lng cn li ca trm thu pht sng c kt ni. Bi ton th hai l cho trc mt tp cc trm BTS c v tr xc nh, hy thit lp mt s BTS tr thnh cc trm iu khin sao cho tha mn cc rng buc v dung lng v kt ni (Optimal Location of Controller Problem-OCLP) [2]. Hm mc tiu ca bi ton hng n l tng khong cch kt ni t cc trm BTS ti cc trm c thit lp thnh trm iu khin phi l nh nht. C hai bi ton TA v OCLP u thuc lp bi ton kh (NP-Hard) v th hu ht cc hng tip cn gii quyt u da trn Heuristic. Cc thut ton c nghin cu v xut trc l: Nm 2002, F.Houeto v S.Pierre s dng thut ton tm kim Tabu (Tabu Search) gii bi ton TA [3]. Nm 2003, B.Krishnamachari v S.Wicker s dng thut ton luyn thp (Simulated Annealing-SA) [4-5], A.Quintero v S.Pierre s dng thut ton di truyn (GA) [6] gii bi ton xc nh cc cell trong mng di ng. Nm 2007, S.Salcedo-Sanz cng cc cng s gii thiu hng kt hp da trn Heuristic gia SA vi thut ton tham lam gi l SA-Greedy gii bi ton OCLP [7]. Nhng tt c cc thut ton trn u tm phng n ti u bng cch chn cc thit b u cui gn nht vi trm thu pht cn trng c dung lng. iu ny cha thc s gii quyt c ti u bi ton mt cch ton cc. gii quyt bi ton OCLP, c nhiu cch tip cn, lun n ny xut cc thut ton mi da trn tip ti u theo nhm by (Particle Swarm Optimization-PSO) gii quyt bi ton OCLP.

3.1.3 Thut ton PSO cho bi ton OCLP

Mi c th trong thut ton PSO c m ha bng xu nh phn 1 2, ,..., Mx x x x c di M. y, xi=1 c ngha l trm BTS i c la chn thnh trm iu khin v ngc li. khi to nhm by, ti s sinh ngu nhin v tr cc phn t. Sau tin hnh hiu chnh li cc c th sao cho mi c th x s c p bit 1. m bo mi c th c chnh xc N bit 1 ng vi N trm iu khin cn thit lp ti xut hm PSO_Repair hiu chnh cc c th. Vi mi cc th c ng N bit 1 biu din cho N trm iu khin. Ti s xy dng th 2 pha

, ,G I J E da trn mi c th x. Vi 1,2,...,I N l tp hp cc trm iu khin,

1,2,...,J M N l tp cc BTS v E l tp cc cnh kt ni gia trm iu khin ri v BTS lj. tm lung cc i ca th G, thm vo 2 nh ngun S (Source) v nh ch l D (Destination) vi trng s c xc nh nh hnh 3.1.

c(ri,tj)=wj

lj(j=1..M-

N)

c(li,D)=wi

ri(i=1..N)

c(S,ri)=pi

18

Hnh 3.1 th 2 pha ng vi c th x

Trong : Cc cnh t nh S n cc ri c trng s bng dung lng ca ri : c(S,ri)=pi,

(i=1..N). Cc cnh t BTS lj n nh D c trng s bng dung lng yu cu ca BTS lj c(lj,D)=wj, (j=1..M-N). Cc nh t ri n cc trm BTS lj bng bng dung lng yu cu ca

BTS lj: c(ri,lj)=wi. ( ,i j E ). tm lung cc i, chng ti thm vo th G hai nh ngun

S (Source) v nh ch l D (Destination) vi trng s c xc nh nh hnh 3.2. Nh vy, th G tr thnh mt mng vn ti. Ta s tm lung cc i tha mn cc rng buc trong (3.2) da trn thut ton Ford-Fulkerson [9]. Hm mc tiu c xc nh da trn lung cc i l tng khong cch kt ni nh sau:

(3.8)

Hm mc tiu ca bi ton cng c xc nh da trn xy dng th hai pha. iu kin dng ca thut ton c nh ngha bng tham s Ngen- l s vng lp ti a.

3.1.4 Cc kt qu thc nghim v phn tch

3.1.4.1 M hnh thc nghim v thit lp tham s cho cc thut ton

tin hnh thc nghim v phn tch cc thut ton, ti s dng cc bi ton OCLP vi mc kh khc nhau c xc nh da trn cc gi tr ca N, M v kch thc li. M t chi tit 10 bi ton OCLP c cho trong Bng 3.1.

Bng 3.1 So snh kt qu thc nghim gia cc thut ton xut v thut ton trc

Bi ton # S trm BTS (M) S trm iu khin (N) Kich thc li

1 10 2 100x100

2 15 3 100x100

3 20 4 100x100

4 40 6 200x200

5 60 8 200x200

6 80 10 400x400

7 100 15 600x600

8 120 20 800x800

9 150 25 1000x1000

10 200 50 1500x1500

Cc thut ton c khai bo v ci t vi cc tham s c cho trong bng 3.2:

Bng 3.2 Thit lp tham s cho thut ton

Tham s Gi tr

Kch thc qun th P = 100

S vng lp Ngen = 500

H s hc c1 = c2=1

S ln cn c xem xt K=3

3.1.4.2 Phn tch, nh gi cc thut ton

2 21 1 2 21 1

( ) ( )N M N

i j i j

i j

F x r l r l

19

nh gi tnh hiu qu ca cc thut ton ca mnh, ti so snh kt qu thc nghim vi cc thut ton SA, SA-Greedy, LB-Greedy c xut trc . Cc kt qu cho thy cc thut ton mi c xut cho kt qu xp x v tt hn cc thut ton c vi cc s liu c cho trong bng 3.3.

Bng 3.3 So snh hm mc tiu ca cc thut ton xut v thut ton trc

Bi ton # SA SA-Greedy LB-Greedy GA PSO ACO

1 187.4 187.4 187.4 187.4 187.4 187.4

2 315.0 315.0 315.0 315.0 315.0 315.0

3 428.3 427.2 419.6 415.4 412.7 418.7

4 1784.7 1798.5 1658.2 1615.3 1615.3 1615.3

5 2135.9 2215.1 1976.3 1910.6 1911.9 1916.6

6 4863.2 4863.2 4627.5 4507.8 4503.4 4518.1

7 7955.6 8027.2 7371.9 7144.1 7137.1 7136.5

8 12863.7 13753.8 10863.7 9584.3 9563.6 9578.4

9 23638.6 26624.3 19569.2 16896.7 16861.3 16874.7

10 157894.2 168253.7 143665.4 141276.9 141235.8 141257.2

Khi kch thc li v s lng cc trm BTS nh nh cc bi ton #1, #2 v #3 th tt c cc thut ton u cho cc kt qu tt xp x nhau. Tuy nhin, khi kch thc li ln v s lng trm tng ln th cc kt qu c nhng s khc bit r v hm mc tiu nh trong bi ton #6, #7, #8, #9 v #10. nh gi v hiu sut thc thi, chng ti so snh thi gian thc hin cc thut ton trn trong hnh 3.3

.

Hnh 3.2 So snh thi gian thc hin ca cc thut ton xut v thut ton trc

3.2 Ti u truy cp tp trung trong mng khng dy

Mng truy cp trong kin trc h thng di ng t bo gm 4 tng tng tc: tng tc gia cc trm di ng (mobile station-MS) hay tp cc ngi dng n cc trm thu pht sng c s (base transceiver stations-BTS), tng tc gia cc trm thu pht sng c s vi cc trung tm chuyn mch di ng (mobile switching centers-MSC), v tng tc gia cc trung tm chuyn mch di ng vi tng i truy cp tp trung (local exchanges-LE) trong mng PSTN. Kin trc mng truy cp c m t trong Hnh 3.5.

20

BSMS

BSMS

BSMS

BSMS

BSMS

BSMS

MSC

MSC

LE

PSTN

Hnh 3.3 Kin trc mng truy cp khng dy

3.2.1 M hnh bi ton

M hnh bi ton truy cp tp trung [5] c m t nh sau: Gi N l s trm BTS (

1 2, ,..., NT T T ), gi s v tr cc trm bit trc. Gi M l s v tr tim nng ( 1 2, ,..., MS S S ) ni c th thit lp cc trm MSC kt ni cc BTS, cc BTS c th kt ni trc tip n trung tm LE, S0 nh Hnh 3.6.

Hnh 3.4 M hnh mng truy cp khng dy

Hnh 3.6 biu din kin trc kin trc truy cp mng gm 1 LE, 2 MSC, 4 BTS v 18 MSs. Gi s rng MSC ti v tr Sj c th p ng ti a c Pj BTS ( 1.. )j M theo rng

buc v gii hn phn cng v dung lng kt ni ca MSC n LE v trm LE trung tm khng chu rng buc v gii hn v dung lng p ng.

Gi cij l chi ph kt ni t BTS Ti n MSC Sj hoc n v tr trung tm S0, ch rng nu BTS kt ni trc tip n LE th cij=0. Ma trn chi ph C={cij}NxM+1 c biu din nh sau:

10 11 1

20 21 2

1

0 1

M

M

ij N M

N N NM

c c c

c c cC c

c c c

Nu MSC Sj c s dng th chi ph kt ni s l tng chi ph kt ni ca cc BTS Ti kt ni n. Gi fj l vect chi ph kt ni ca MSC Sj n trm trung tm LE S0, v bj l chi ph duy tr hot ng. Hai vect chi ph c m t nh sau:

21

0 1

0 1

, ,...,

, ,...,

M

M

F f f f

B b b b

Trong , b0=0 v f0=0 vi gi thit rng chi ph kt ni v duy tr ca trm trung tm LE l khng b gii hn. Tng t, chng ta c th c t cc rng buc v s lng gii hn ti a cc BTS c p ng bi MSC thng qua vect:

0 1, ,..., MP p p p

Trong , pj l s lng ti a BTS c p ng bi MSC Sj ( 1.. )j M , p0=N (v LE

c th p ng c tt c cc yu cu ca N BTS nu cc BTS ny kt ni trc tip n n).

Ma trn bin th hin cc kt ni c biu din nh sau:

10 11 1

20 21 2

1

0 1

M

M

ij N M

N N NM

x x x

x x xX x

x x x

Trong ,

1

0

i j

ij

i j

if T is connected toSx

if T is not connected toS

Ch rng, mi BTS phi kt ni n t nht mt MSC hoc trc tip n trm trung tm LE. iu c ngha l c mt v ch mt gi tr trn mi dng i trong ma trn X c gi tr 1. Mi ct j trong ma trn X th hin s kt ni ca BTS n MSC Sj ( 0.. )j M , nu tt c cc

gi tr ca ct j u bng 0 th hin rng MSC khng c s dng. T , ta c th biu din cc trm MSC c s dng t ma trn X bng vect sau:

0 1, ,..., MY y y y

Trong , thnh phn yj ( 0.. )j M c nh ngha nh sau:

1

1

1 , 0

1 , 0

N

i iji

j N

i iji

if S used if x

y

if S not used if x

Khi , tng chi ph kt ni trong mng c biu din thng qua ma trn X v vecto Y nh sau:

1 0 0 0

( )

N M M M

ij ij j j j ji j j j

T T T

Z c x f y b y

Z sumdiag C X F Y B Y

Trong XT v YT l ma trn v vecto chuyn v, sumdiag(A) l tng cc thnh phn trong php nhn ma trn.

22

Bi ton ti u truy cp tp trung trong mng c pht biu nh sau: Tm ma trn X v vecto Y sao cho ti thiu chi ph kt ni Z

( ) minT T TZ sumdiag C X F Y B Y

Tha mn rng buc:

X E E TE X P

Rng buc (3.18) th hin tng cc thnh phn trn dng i ca ma trn X phi bng 1 (i=1,2,,N) vi E l vect ct vi cc thnh phn bng 1. Rng buc (3.19) th hin rng tng cc thnh phn trong ct j ca ma trn X phi nh hn hoc bng pj ( 0.. )j M tc l s lng

BTS ti a c th p ng bi MSC Sj

3.2.2 Cc nghin cu lin quan

Cc tc gi trong [5] a ra m hnh kin trc truy cp tp trung trong mng di ng th hin s tng tc gia cc BTS n MSC v gia cc MSC n LE. y l kin trc c trng tiu biu trong cc mng di ng t bo. Trong trng hp hp n gin, kin trc mng c th biu din theo m hnh truy cp tp trung hnh cy. Tc mt trm LE s c s dng iu khin tp cc MSC, mi mt MSC s iu khin truy cpmt tp cc BTS. Cui cng, mi BTS s cung cp cc kt ni n mt nhm cc trm di ng MS thng qua cc kt ni khng dy. y l kin trc rt quan trng, hin ang thu ht c rt nhiu nghin cu vi cc cng b trong [5-9]. Tuy nhin, y l mt bi ton kh v phc tp nn cc nghin cu u tp trung theo hng s dng cac thut ton heuristic gii quyt. Thut ton Exhaustive search sinh ra tt c cc ma trn kt ni c th v kim tra tm ra ma trn kt ni vi chi ph ti thiu c xut trong [6]. Thut ton Heuristic s dng t tng greedy tm kt ni ti u sau mi vng lp vi vic s dng cc MSC gn nht cn dung lng p ng cc yu cu ca BTS c xut trong [7].

3.2.3 Thut ton PSO cho bi ton ti u truy cp tp trung

Mi c th trong thut ton PSO c m ha bng ma trn 1( )ij N Mx x

( 1.. , 0.. )i N j M . vi qui c xij = 1 c ngha l BTS Ti tng ng c kt ni vi MSC

Sj, v ngc li. khi to nhm by, chng ti s sinh ngu nhin v tr cc phn t. Sau tin hnh hiu chnh li cc c th sao cho mi c th x tha mn rng buc (3.18-3.19). m bo mi c th c chnh xc N bit 1 ng vi N trm iu khin cn thit lp ti xut hm PSO_Repair hiu chnh cc c th. Sau khi chun ha, mi c th kin s c tng cc phn t trong dng i ca ma trn bng 1 (i = 1,2, ..., N) v tng cc phn t trong ct j ca ma trn k phi nh hn hoc bng Pj. Hm mc tiu c tnh theo (3.17).

3.2.4 Kt qu thc nghim v nh gi

Thc nghim c tin hnh trn 8 bi ton vi mc kh khc nhau th hin thng qua s lng cc trm N v M. Thng tin v cc d liu, v ma trn chi ph BS-kt ni hin th trong Bng 3.4.

23

Bng 3.4 Thng tin cc bi ton thc nghim

Bi ton # S trm MSCs S trm BTSs

#1 4 10

#2 5 20

#3 8 40

#4 10 80

#5 20 100

#6 40 150

#7 50 200

#8 60 250

Tham s thc nghim chi tit ca cc thut ton PSO c cho trong Bng 3.5

Bng 3.5 Tham s thc nghim ca thut ton PSO Kich thc qun th 100

Tham s hc c1=1, c2=1

S ln cn xem xt K=3

S vng lp ti a Ngen = 500

Thc nghim c tin hnh nhm so snh hiu qu thc thi gia cc thut ton xut vi thut ton Exhaustive Search [5] v Heuristic [8]. Hnh 3.5 th hin kt qu so snh hm mc tiu gia cc thut ton.

Hnh 3.5 So snh hm mc tiu v thi gian gia cc thut ton

Kt qu cho thy cc gi tr hm mc tiu ca thut ton ca chng ti t c mt tt hn nhiu so vi mt thut ton Heuristic v cc gii php tt gn ng ca y Tm kim thut ton. Tuy nhin, hiu sut ca thut ton xut ca chng ti l tt hn so vi thut ton khc. Vic so snh thi gian x l cho thy trong hnh 3.5.

3.3 Kt chng

Trong chng ny, lun n xut thut ton PSO v ACO gii quyt 2 bi ton t cc trm c s trong mng khng dy v ti u truy cp trong mng khng dy. y l cc bi ton quan trng trong thit k v ti u mng. Cc th nghim s vi cc vn mng li thng tin lin lc c quy m khc nhau cho thy tnh hiu qu v hiu qu ca thut ton xut, iu ny cho thy rng thut ton ny tt hn nhiu so vi nhng nghin cu gn y.

24

Kt lun v hng pht trin

1. ng gp ca lun n

Trong lun n ny, ng gp u tin ca lun n l trnh by h thng cc thut ton

phng sinh hc hin nay ang c cng ng nghin cu trong v ngoi nc s dng

nhiu nht gii cc bi ton ti u ha t hp nh GA, PSO, v ACO. T vic phn

tch l thuyt chng ti hng lun n n vic s dng thut ton PSO gii cc

bi ton qui hoch trong mng khng dy. Vic phn tch cc bi ton quan trng trong

qui hoch mng khng dy cng c trnh by trong chi tit.

Cc ng gp tip theo ca lun n l p dng thnh cng PSO gii cc bi ton qui

hoch mng khng dy, c th:

- i vi bi ton t gateway ti u thng lng ca mng li khng dy. Lun

n trnh by trong chi tit cch tnh thng lng ca cc truyn thng li, truyn

thng cc b, thng lng kh thi cho cc mng li khng dy. Sau , chng ti thit

k vic t cc gateway ng thi da trn thut ton PSO khc phc nhc im

ca cc phng php khc khi t ln lt cc gateway do gateway t sau ph thuc

vo gateway t trc. Vi cch lm nh vy, phng php t gateway ca chng ti

xut t c hiu qu cao hp so vi cc phng php tip cn trc .

- i vi bi ton cy truyn thng ti u, lun n ch ra ng dng trong vic nh

tuyn broadcast trong mng khng dy. Vic m ha s thc ca cc c th trong thut

ton PSO kt hp vi NBE cho php thut ton c th tm c li gii gn vi ti u

ton cc khi khng gian tm kim rng hn. Cc kt qu thc nghim ch ra PSO l hiu

qu hn mt s thut ton trc trn nhiu tp d liu mu khc nhau.

- i vi vn ti u ha truy cp, bi ton t cc trm c s v ti u ha truy cp,

lun n trnh by phng php m ha mi chuyn vic gii m cc c th thnh

vic tm cc cc cp ghp ln nht trn th hai pha da vo thut ton tm lung cc

i trong thi gian a thc. Do vic biu din v gii m nh vy, nn thut ton xut

PSO cho hai bi ton ny c hiu qu tt hn cc cch tip cn trc .

25

- Mt vic lm khc ca lun n cng c th xem nh l cc ng gp l so snh

hiu qu ca PSO , lun n cng m phng nh gi so snh PSO vi cc thut ton

phng sinh hc khc nh GA v ACO.

2. nh hng pht trin:

Lun n cha phn tch c s nh hng ca cc tham s trong cc thut ton

phng sinh hc n hiu nng ca thut ton. Mt khc, cc bi ton ti u c xem

xt gim bt cc yu t thc t nh a hnh, nhiu,... bi ton d gii hn hay

vic phn tch v so snh kt qu vi cc thut ton xp x theo l thuyt cng cha

c thc hin. y l cc thiu st ca lun n v l hng pht trin ca lun n trong

thi gian ti.

Cc kt qu ca lun n c cng b trong 3 bi bo ng trong k yu hi ngh quc t, 3 bi bo ng trn cc tp ch quc t, 1 bi ng trn tp ch trong nc v 4 bi trong k yu hi quc gia chuyn ngnh.

DANH MC CC CNG TRNH KHOA HC CA TC GI LIN QUAN N LUN N

1. Gia Nhu Nguyen, Dac Nhuong Le, Vinh Trong Le (2012), Particle Swarm Optimization and Ant

Colony Optimization Algorithms Applied to the Optimal Communication Spanning Tree problem,

K yu hi tho Quc gia Mt s vn chn lc ca Cng ngh thng tin v truyn thng, H

Ni, Vit Nam, trang 334-340.

2. Vinh Trong Le, Anh Tuan Hoang, Gia Nhu Nguyen (2010), A Novel Practicle Swarm

Optimization- based Algorithm for the Optimal Communication Spanning Tree problem, In

Proceeding of IEEE 2010 Conference on Communication Software and Network ( ICCSN 2010),

Singapore, pp. 232-236.

3. Nguyn Gia Nh, L c Nhng, L Trng Vnh ( 2013 ) Ti u qui hoch v tr cc trm BTS

da trn thut ton ti u ha nhm by, K yu Hi tho Quc gia Mt s vn chn lc ca

Cng ngh thng tin v Truyn thng, Nng, trang 23-28.

4. Vinh Trong Le, Dinh Huu Nghia, Gia Nhu Nguyen (2011), A Novel PSO-Based Algorithm for

Gateway Placement in Wireless Mesh Networks, Proceedings 2011 IEEE 3rd International

Conference on Communication Software and Networks ( ICCSN2011 ), May 27-29, 2011, China,

pp 37-42.

5. L c Nhng, Nguyn Gia Nh, L ng Nguyn, L Trng Vnh (2013), So snh nh gi

cc cch tip cn phng sinh hc gii bi ton t trm c s trong mng khng dy, Tr494-501,

2013.

6. Gia Nhu Nguyen, Dac Nhuong Le, Vinh Trong Le (2013), A Novel PSO based Algorithm

Approach for the cMTS to Improve QoS in Next Generation Networks, Journal of Future

Computer and Communication ( IJFCC), Singapore, Vol.2(5), pp 413-417.

7. Dac Nhuong Le , Gia Nhu Nguyen, Vinh Trong Le (2012), A Novel PSO-Based Algorithm for

the Optimal Location of Controllers in Wireless Networks, International Journal of Computer

Science and Network Security, VOL.12(8), August 2012, pp.23-27.

8. Nguyn Gia Nh, L c Nhng ( 2013), Optimal location of Controllers in Wireless network

using Genetic algorithm, Tp ch Khoa hc Cng ngh- i hc Nng, S 6(67).2013, Trang

122-127.

9. L c Nhng, Nguyn Gia Nh (2013), A Novel Particle Swarm Optimization-based

Algorithm for the Optimal Centralized Wireless Access Network, International Journal of

Computer Science Issues, Vol.10, Issue 1, No 1, January 2013, pp 721-727.

10. Dac-Nhuong Le, Gia Nhu Nguyen, Nguyen Dang Le, Nghia Huu Dinh and Vinh Trong Le (2012),

ACO and PSO Algorithms Applied to Gateway Placement Optimization in Wireless Mesh

Networks, Proceeding of 2012 International Conference on Networks and Information (ICNI

2012) pp 8-15.

11. Nguyn Gia Nh, L c Nhng, L Trng Vnh, Nguyn Xun Huy (2014), Ant Colony Optimization and Particle Swarm Optimization Algorithms Applied to Optimizing Access

Centralized in Wireless Network, K yu Hi tho Quc gia Mt s vn chn lc ca Cng ngh thng tin v Truyn thng, Dak Lak.