Vô tuyến thông minh

8/14/2019 V tuyn thng minh

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V tuyn thng minh: gii php cng ngh s dng hiu qu tn s v tuyn - Phn 1

Vi cng ngh v tuyn thng minh, cc thit b v tuyn thng minh c s dng cmng, nhn din v s dng ph tn v tuyn hiu qu hn na theo thi gian, khng gianv tn s.

Theo Ed Thomas Nu xt ton b gii tn s v tuyn t 0 n 100 GHz v quan trc mtthi gian v khng gian c th, th ch c t 5% n 10% lng ph tn c s dng. Nh vy,c hn 90% ti nguyn ph tn v tuyn b lng ph [1]. Cng ngh v tuyn thng minh hinc xem nh l mt gii php ti u cho vn ny. Bi vit s trnh by tng quan cc khinim, c ch truy cp ph tn ng, m hnh h thngin hnh cng nh tnh kh thi ca cngngh v tuyn thng minh trong cc h thng khng dy th h sau.

I. Khi nim v v tuyn thng minh

H thng v tuyn thng minh l h thng m cc phn t ca n c kh nng thay i cc tham

s (cng sut, tn s) trn c s tng tc vi mi trng hot ng [2]. Theo , thit b vtuyn nh ngha bng phn mm SDR (Software Defined Radio) s l mt phn t quan trngtrong h thng v tuyn thng minh. V cc tham s ca thit b SDR c thay i mt cchlinh ng bng phn mm m khng cn phi thay i cu trc phn cng. Mc ch ca vtuyn thng minh l cho php cc thit b v tuyn khc hot ng trn cc di tn cn trng tmthi m khng gy nhiu n cc h thng v tuyn c quyn u tin cao hn hot ng trn ditn . cho php tn dng ti a ti nguyn ph tn nh trn, v tuyn thng minh phi cnhng tnh nng c bn nh sau:- iu chnh tn s hot ng ca h thng mt cch tc th t mt bng tn ny n mt bngtn khc (cn trng) trn di tn cho php (Hnh 1). - Thit lp mng thng tin v hot ng trn mt phn hoc ton b bng tn c cp pht

- Chia s knh tn s v iu khin cng sut thch ng theo iu kin c th ca mi trng vtuyn, m tn ti nhiu loi hnh dch v v tuyn cng chim dng.

- Thc hin thch ng rng bng tn, tc truyn v cc s m ho sa li cho phpt c thng lng tt nht c th.

- To bp sng v iu khin bp sng thch ng theo i tng truyn thng nhm gim thiunhiu ng knh v ti a cng tn hiu thu.


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Hnh 1: Khi nim h ph ri hnh thnh ln tng v v tuyn thng minh

II. M hnh v tuyn thng minh da trn SDR

M hnh v tuyn thng minh in hnh trn c s SDR nh Hnh 2. Theo , cc chc nng vcc c tnh c bn nh sau :

Khi anten di rng (Wideband antenna) c c im l hot ng trn ton b bng tn v

tuyn thng minh (di tn ny rt rng). tn dng trit ti nguyn ph tn v tuyn cntrng mt cch tc th, anten di rng phi c kh nng qut tn s rt rng sao cho c th phthin c hu ht nhng thay i ca mi trng (thi gian khng s dng ca cc di tn s cp php). Ton b ph tn kh qut c chia thnh N bng nh, v mi thit b v tuyn nhngha bng phn mm (SDR) s hot ng trn mt bng tn nh . Ngoi ra, h thng a antenc xut to bp sng v li phn tp nhm tng cng phn gii khng gian v cithin hiu qu tch sng.

Khi duplexerc dng nh hng (phn b) tn hiu cho cc anten, hay ni cch khc nphn cch tn hiu thu v tn hiu pht.

Hnh 2: M hnh v tuyn thng minh in hnh trn c s SDR

Khi la chn tn s ng (Dynamic Frequency Selection - DFS)l mt qu trnh la chn tns t ng c dng trong vtuyn thng minh trnh gy nhiu n cc h thng v tuynkhc c quyn u tin cao hn khi hot ng cng bng tn. Khi hot ng, ph tn s chc la chn s dng khi n khng b chim dng bi thit b khc, v s dng chim dng ph


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tn ny ngay khi cc thit b v tuyn c quyn u tin cao hn c nhu cu s dng.

Khi v tuyn c nh ngha bng phn mm (Software Defined Radio - SDR)hot ng ngthi trong module thu. Mi khi SDR c iu khin hot ng trong mt di tn nht nhthng qua phn mm m khng phi thay i cu trc phn cng. L do ca vic s dng nhiu

module SDR song song thay v ch mt module SDR duy nht l gim phc tp ca thit bSDR. S liu u ra ca cc khi SDR c a vo cng mt khi chc nng, khi ny thchin quyt nh ti u (thng minh) da trn nhng thng tin t cc SDR thnh phn, trong thc hin la chn v kt hp gia cc lung thng tin sau tch sng ti to lung thng tincng nh cc tn hiu iu khin cc tham s phn pht. Khi cm bin mi trng (Incumbent Profile Detection IPD)pht hin s hin hu ca thitb v tuyn c quyn u tin cao hn da trn cc thng tin v: s phn b ph tn, thi imchim dng ph tn ca cc thit b v tuyn c cp php, v tp tham s cng sut pht. Khi tng hp tn s thch ng pha pht c nhim v to ra tn s sng mang tham khochun mt cch chnh xc phc v cho qu trnh iu ch cao tn v chuyn i bng tn. Munvy, cn phi khai thc thng tin t khi cm bin mi trng (IPD) nh: s phn b ph tn,

thi im chim dng ph tn ca cc thit b v tuyn c cp php, v tp tham s cng sutpht. Cc thng s ny cho php xc nh chnh xc mc cng sut pht nhm m bo v tuynthng minh khng gy nhiu n cc thit b v tuyn khc.Khi iu khin cng sut pht (Transmit Power Control- TPC)cho php thch ng mc cngsut pht theo s thay i tn s lm vic ca thit b v tuyn thng minh.Khi cng nh thi (Timing Gate) cho php m bo rng v tuyn thng minh ch pht tn hiu nhng tn s hin khng b chim dng.III. M hnh mng v tuyn thng minh

Cc khng dy ang tn ti s dng hn hp nhiu chnh sch ph v cng ngh truyn thngkhc nhau. Hn na, mt s phn ph v tuyn c cp php cho cc mc ch khc nhautrong khi mt s bng vn cha c cp php.

Hnh 3 Kin trc mng V tuyn thng minh

Cc thnh phn kin trc ca mng V tuyn thng minh, nh Hnh 3, c th phn thnh hai


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nhm l mngchnh (primary network) v mng V tuyn thng minh. Cc thnh phn c bnca hai nhm mng ny c xc nh nh sau:

- Mng chnh (Primary network): Mng chnh c quyn truy nhp ti mt vi bng ph nhtnh, chng hn nh mng TV qung b, hay mng t ong ni chung. Cc thnh phn ca mng

chnh bao gm:

+ Ngi dng chnh (Primary user): Ngi dng chnh (hay ngi dng c cp php) c giyphp hot ng trong mt bng ph nht nh. Truy nhp ny ch c gim st bi trm gcchnh v khng b nh hng bi nhng hot ng ca bt k ngi dng khng c cp phpkhc. cng tn ti vi cc trm gc V tuyn thng minh v ngi dng V tuyn thngminh, nhng ngi dng chnh ny khng cn bt c s iu chnh hoc chc nng cng thmno.

+ Trm gc chnh (Primary base-station): Trm gc chnh (hay trm gc c cp php) lthnh phn c s h tng mng c c nh, c giy php ph, nh BTS trong mng t ong. V

nguyn tc, trm gc chnh khng c kh nng chia s ph vi nhng ngi dng V tuynthng minh. Tuy nhin, trm gc chnh ny c th yu cu c c kh nng ny.

- Mng V tuyn thng minh: Mng V tuyn thng minh (hay mng xG, mng Truy nhp phtn ng, mng th cp, mng khng c cp php) khng c giy php hot ng trong mtbng mong mun. Do , n ch c php truy nhp ph khi c c hi. Mng V tuyn thngminh c th gm c mng c c s h tng v mng ad hoc, cc thnh phn ca mng V tuynthng minh nh sau:

+ Ngi dng V tuyn thng minh: Ngi dng V tuyn thng minh (hay ngi dng xG,ngi dng khng c cp php, ngi dng th cp) khng c giy php s dng ph. Do ,cn c cc chc nng cng thm chia s bng ph cp php.

+ Trm gc V tuyn thng minh: Trm gc V tuyn thng minh (hay trm gc xG, trm gckhng cp php, trm gc th cp) l thnh phn c s h tng c nh vi cc kh nng ca Vtuyn thng minh. Trm gc V tuyn thng minh cung cp kt ni n chng ti nhng ngidng V tuyn thng minh m khng cn giy php truy nhp ph. Thng qua kt ni ny, ngidng V tuyn thng minh c th truy nhp n cc mng khc.

+ B phn chia ph (Spectrum broker): B phn chia ph (hay server lp lch) l mt thc thmng trung tm ng vai tr trong vic chia s cc ti nguyn ph tn gia cc mng V tuynthng minh khc nhau. B phn chia ph c th kt ni vi tng mng v c th phc v vi tcch l ngi qun l thng tin ph, nhm cho php cc mng V tuyn thng minh cng tn ti.

Mng V tuynthng minh bao gm nhiu loi mng khc nhau: mng chnh, mng V tuynthng minh da trn c s h tng, v mng V tuyn thng minh ad hoc. Mng V tuyn thngminh hot ng di mi trng ph hn hp, bao gm c cc bng cp php v khng cp php.Do , trong mng V tuyn thng minh, c ba loi truy nhp khc nhau, l:

Truy nhp mng V tuyn thng minh (xG network access): Ngi dng V tuyn thng


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minh c th truy nhp ti chnh trm gc V tuyn thng minh c bng cp php v khng cpphp.

Truy nhp mng V tuyn thng minh ad hoc (xG ad hoc access): Ngi dng V tuynthng minh c th truyn thng vi nhng ngi dng V tuyn thng minh khc thng qua kt

ni ad hoc c bng cp php v khng cp php.

Truy nhp mng chnh (Primary network access): Ngi dng V tuyn thng minh cng cth truy nhp ti trm gc chnh thng qua bng cp php.

IV. Hot ng ca mng V tuyn thng minh

Mng V tuyn thng minh c th hot ng trong c bng cp php v khng cp php, do ,cc chc nng yu cu cho mng V tuyn thng minh khc nhau ty theo ph l cp phphay khng.

Trn bng cp php

Nh ch ra trn Hnh 1, ta thy c nhng h ph khng s dng trong bng ph c cpphp. Do , cc mng V tuyn thng minh c th c s dng khai thc cc h ph nythng qua cc cng ngh thng minh. Kin trc ny c miu t trong Hnh 4 trong ccmng V tuyn thng minh cng tn ti vi cc mng chnh ti cng mt v tr v trn cng mtbng ph.

Hnh 4. Mng V tuyn thng minh hot ng trn bng cp php

C nhiu thch thc khc nhau thc hin cc mng V tuyn thng minh trn bng cp phpv s tn ti ca nhng ngi dng chnh. Mc d, mc ch chnh ca mng V tuyn thng

minh l xc nh ph tn c sn tt nht, nhng cc chc nng ca V tuyn thng minh trongbng cp php li bao gm pht hin s c mt ca cc ngi dng chnh. Dung lng knh cacc h ph ph thuc vo nhiu xung quanh nhng ngi dng chnh. Do , vic trnh nhiucho nhng ngi dng chnh l vn quan trng nht trong kin trc ny. Hn na, nu ngidng chnh xut hin trong bng ph b nhng ngi dng V tuyn thng minh chim, thngi dng V tuyn thng minh ngay lp tc phi b li phhin thi v chuyn ti ph misn c khc, gi l chuyn giao ph.


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Trn bng khng cp php

Cc mng V tuyn thng minh c th c thit k hot ng trn cc bng khng cp php ci thin hiu qu ph trong phn ph ny. Mng V tuyn thng minh hot ng trn bngkhng cp php c minh ha trn Hnh 5. Tt c thc th trong mng c quyn nh nhau khi

truy nhp ti cc bng ph. Nhiu mng V tuyn thng minh cng tn ti trong mt vng gingnhau v truyn thng s dng cng mt phn ph nh nhau. Cc thut ton chia s ph thngminh c th ci thin hiu qu s dng ph v h tr QoS cao.

Hnh 5. Mng V tuyn thng minh hot ng trn bng khng cp php

Trong kin trc ny, nhng ngi dng V tuyn thng minh tp trung vo pht hin vic truynca nhng ngi dng V tuyn thng minh khc.Khc vi hot ng trn bng cp php, vicchuyn giao ph khng b kch thch bi s c mt ca nhng ngi dng chnh khc. Tuy nhin,v tt c nhng ngi dng V tuyn thng minh c quyn truy nhp ph nh nhau, nn h phi

cnh tranh vi nhau trongcng bng khng cp php. Do , kin trc ny i hi cc phngphp chia s ph phc tp gia nhng ngi dng V tuyn thng minh. Nu nhiu mng Vtuyn thng minh nm trong cng mt bng khng cp php th phi c phng php chia s phph hp gia cc mng ny.

IV. Truy cp ph tn ng trong mng v tuyn thng minh

>> V tuyn thng minh: Gii php cng ngh s dng hiu qu tn s v tuyn (Phn 1)

c th tn dng c nhng h ph ri nh hnh 1, mt phng php quan trng c pdng trong mng v tuyn thng minh, l phng php truy cp ph tn ng. Phng php

ny cho php cc thit b v tuyn thng minh thc hin thng tin mt cch thng minh theo kh dng ca ph tn.

Truy cp ph tn ng, c th hin khi la chn tn s ng DFS nh trn hnh 2. S kthp ca truy cp ph tn ng vi khi IPD cho php thit b v tuyn khng c cp php truycp vo bng tn c cp php trong mt khong thi gian ngn m khng nh hng nquyn truy cp mng ca thit b c quyn u tin cao hn.
http://khonggianit.vn/VienThong/View.php?idTin=2670http://khonggianit.vn/VienThong/View.php?idTin=2670http://khonggianit.vn/VienThong/View.php?idTin=2670


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Vic chia s ph tn gia cc h thng v tuyn khc nhau thc cht l vic chia s vic s dngcc di tn s gia cc mng truy nhp v tuyn khc nhau m thi. V trong cc h thng, tinguyn v tuyn ch yu c cc mng truy nhp s dng truyn dn tn hiu t mng nkhch hng. C ch hot ng ca phn b tn s ng gia cc mng truy nhp nh sau: Sdng cc khong tn s lin k cp pht cho cc mng truy nhp v tuyn khc nhau. Cc

khong tn s n nh cho mi h thng c phn cch bng mt bng tn bo v, vic lm nycng ging vi c ch phn b tn s c nh hin nay. Tuy nhin, c ch phn b ti nguynny b rng ph gn cho mi mt mng truy nhp v tuyn c thay i ty theo thay i cayu cu ph tn ca tng mng theo thi gian v khng gian nh Hnh 6.

Hnh 6

C ch phn b ph tn lin k ng ny c u im l vic qun l v phn b ti nguyn phtn n gin; trong khi vn c c nhng u im nh i vi phng php phn b tn cnh, nh kim sot c nhiu t cc mng truy nhp v tuyn khc ch cn dng mt bng tn

bo v. Hn th na, c ch ny ti thiu ha vic hp tc qun l gia hai mng truy nhp biv chng ta ch cn xc nh c v tr ca di tn bo v gia hai bng tn n nh lin k. Tuynhin, do s n gin trong vic qun l ph tn ca c ch nn cng c nhng nhc im nh:Nu mun tng bng tn cho mt mng truy nhp v tuyn th bng tn ca mng truy nhp vtuyn ln cn s b ct gim. Do , nu mt mng truy nhp v tuyn c nhu cu tng lngbng tn cp php s khng c p ng nu nh mng truy nhp v tuyn bn cnh khng thct gim bngtn ca mnh c. Mc d cn tn ti nhc im nh vy nhng phng phpphn b ti nguyn ny vn c ngha trong vic tn dng cc bng tn trng ca cc h thngmng truy nhp khch da trn quy lut dch v m khng phi s dng cc thut ton iukhin qu phc tp.

Hin nay, phng php phn b ti nguyn v tuyn ng ang c tp trung nghin cu trongcc mng truy nhp v tuyn l mng di ng 3G (UMTS) v h thng truyn hnh qung b smt t DVB-T. La chn hai loi mng truy nhp ny a vo nghin cu v hai mng truynhp ny c c ch cung cp dch v hon ton khc nhau. Mt bn l cung cp dch v theo yucu ca khch hng (mng di ng) trong khi mng truyn hnh qung b s mt t th phtqung b tn hiu n cc khu vc khc nhau. i vi mng di ng th nhu cu v bng tn chyu tp trung vo gi lm vic trong khi cc dch v truyn hnh li ch yu tp trung vongoi gi lm vic. c im khc bit v quy lut dch v ny lm cho vai tr ca vic phn b


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ph tn ng trn tr nn cp thit v quan trng hn. Hn th na, mng 3G-UMTS v mngtruyn hnh qung b v tuyn s mt t DVB-T c chung b rng sng mang (Vi 3G-UMTSl 5 MHz trong khi DVB-T l 8 MHz). Mt phn tch v qui lut s dng dchv ca hai hthng trn, c trnh by Hnh 7.

Hnh 7. Dng phn b lu lng thay i theo thi gian ca dch v DVB-T v UMTS

Phn b ph tn ng theo thi gian

Thut ton phn b tn s ng lin k theo thi gian s hot ng theo cc chu k nh trccho tng ngy. Nhng tnh ton v ph tn yu cu bi mi mng truy nhp v tuyn da trnnhng d on v ti h thng. Do , vic d on ti ca tng mng truy nhp s l phn tquan trng trong thut ton phn b ph tn ng theo thi gian. Qu trnh d on ti gm hai

vn : Lch s ti, l mt c s d liu v ti trng ca mng trong thi gian trc , vthut ton d on theo chui thi gian. Nu nh cc s kin v ti bt thng sy ra, yu t lchs ti trng s khng th cung cp y thng tin thch ng, do s dn n vic phn bph tn khng hiu qu v chnh xc. Khi , d on chui thi gian s c s dng ctnh ti trng. Da trn d on ti trng, cc mng truy nhp v tuyn s c tnh c s sngmang s phi p ng cho mng truy nhp trong thi gian sp ti. Cc mng truy nhp v tuyns thng bo cho phn h phn b ti nguyn v tuyn ng nhng tn s sng mang hin ti nkhng dng. V cc tn s sng mang trng ny s c gn li cho cc mng truy nhp vtuyn khc nu chng c nhu cu. Lu rng, mt sng mang v tuyn no s c gn chomng truy nhp v tuyn khc nu nh khng c cuc gi no ang c mang i trn n. Thutton phn b ti nguyn s quyt nh cch thc m cc tn s sng mang cn trng c phn

b cho cc mng truy nhp v tuyn. nhiu sng mang trng i vi mt h thng phn b tinguyn v tuyn ng no , cc cuc gi mi trong mng truy nhp thng c truyn titrn cc sng mang cch xa bng tn bo v nht gia hai mng truy nhp v tuyn hoc chuyngiao cc cuc gi hin hnh sang cc tn s nu c th. Do , cc tn s sng mang gn vikhong bo v s c s dng n nh li cho mt mng truy nhp v tuyn khi cn. Chcnng c bn ca phn b ti nguyn v tuyn ng theo thi gian c th hin Hnh.8.


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gim.

Hnh 10 nh hng ca tng quan mu lu lng

Hnh 10 cho thy tng ch ca thut ton phn b ti nguyn ng thay i theo h s tng quanv c tnh lu lng ca cc mng truy nhp v tuyn. li ca thut ton phn b ti nguynng cao hn thut ton phn b ti nguyn c nh khong 40% i vi h s tng quan m.Khi h s tng quan tng dn th li ca thut ton phn b ti nguyn ng s gim. Khi hs tng quan lu lng dch v ca cc mng v tuyn ln hn 0.5 lc ny li ca thut tonphn b ti nguyn c nh s gim i v thp hn so vi thut ton phn b ti nguyn c nh.

Phn b ti nguyn ng trong trng hp d on ti khnghon hoPhn trn xem xt kt qu ca thut ton phn b ti nguyn ng trong trng hp d onti mng truy nhp v tuyn l hon ho. Tuy nhin trn thc t, c nhng trng hp lu lng

ti ca mng truy nhp khc bit hon ton vi lu lng ti ca n trc . V d, do mt skin c bit no m lu lng cuc gi trong mng UMTS tng t bin hoc nhu cu truynhp dch v video s tng vt khi c s kin nng din ra. Trong trng hp nh vy, ba thutton d on khc nhau c s dng th nghim. Thut ton n gin u tin l datrn gi tr ca ti trong khong thi gian trc. Hai thut ton cn li s s dng ti ngay trongchu k trc v nu n nh hn 5% so vi ti lch s th thut ton s s dng ti lch s c tnh ti trng. Ngc li, thut ton s dng chui thi gian s c s dng c tnh titrng trong tng lai. Kt qu cho thy, thut ton s dng chui thi gian s cho kt qu tt hnnh minh ha trn Hnh 11.


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Hnh 11 nh hng ca khongDSA n thut ton d on ti khng hon ho

Nhng yu cu i vi thut ton phn b ti nguyn theo thi gian

Nhng yu cu t ra i vi phn b ti nguyn v tuyn m bo vic n nh ti nguynkhng gy nhiu ln cc mng truy nhp v tuyn khc, khi chng cng chia s ph tn. Sau y

l nhng yu cu c bn

Lu lng ti thay i theo thi gian: thut ton phn b ti nguyn v tuyn theo thigian thc s c hiu qu v mt ph tn, th thut ton ny phi c thc hin trong trng hpti ca cc mng truy nhp v tuyn khc nhau s khc nhau theo thi gian. Nhng lu lng tiny c th m hnh ha v s dng nh gi hot ng ca thut ton phn b ti nguynng.

D on ti:Phn b ti nguyn ng theo thi gian phi c chc nng phn b ph tn theo tic d on cho mt thi im trong tng lai. iu ny thc s cn thit khi thut ton phnb ti nguyn ng khng hot ng trong khong thi gian ngn. Nu nh vic phn b ti

nguyn v tuyn m hot ng vi chu k ngn th khng cn phi d on ti v ti khng ththay i qu nhanh trong mt thi gian ngn gia cc ln n nh li ti nguyn. Tuy vy, tnhhung ny c th khng thc t. Do , ti ca cc mng truy nhp v tuyn phi c d ont nht theo hot ng ca chng ch khng phi hon ton ngu nhin.

Chu k d on gia cc ln n nh li ph: c th hot ng hiu qu, phng phpphn b ti nguyn theothi gian cn phi thc hin n nh li ph tn nhanh c th btkp vi nhng yu cu ph tn ca mng truy nhp v tuyn. Tuy nhin, vic n nh li ph tnnhanh s gy nn nhng phc tp cho mng v mt thi gian mt mng truy nhp v tuyn cn thay i tn s thu pht cng nh bo hiu cho vic thay i . Ngoi ra khong thigian gia hai ln n nh li ti ph tn cng ng mt vai tr ht sc quan trng i vi tnh

chnh xc ca cc phng php d on. Thng thng tnh chnh xc s tng nu nh chu kgia hai ln n nh li knh gim.

n v trao i tn s ti thiu: Tham s ny quy nhph tn ti thiu cn phi ct i haythm vo cho mt mng truy nhp v tuyn. Ngha l, khng th n nh b rng ph tn chomt mng truy nhp mt cch ngu nhin.

Ri cuc gi:Trong cc thut ton phn b ti nguyn v tuyn ng th nu nh mt tn s


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sng mang no ang c kch hot truyn ti cc cuc gi th n khng c chim dng n nh li cho cc mng v tuyn khc. Quy nh ny m bo rng cuc gi khng b rido vic n nh li tn s gy ra. Tuy nhin, trong mt vi trng hp th thut ton phn b tinguyn s ti u nu nh chng ta chp nhn mt mc ri cuc gi no . Trong trng hpny th phn b ti nguyn v tuyn ng c nh hng trc tip ln t l tha mn ca cc

mng truy nhp dng chung ph tn do vic yu cu cc mng truy nhp v tuyn nh ri cucgi.

Chuyn giao gia cc tn s: Nu gi s rng cc mng truy nhp v tuyn cng nh cc userc kh nng chuyn giao tn s trong cng mt di tn s ca h thng mt cch d dng mkhng gy dn on cuc gi

S mng truy nhp v tuyn chia s cng mt ph tn : Mt cch tng qut th cc thut tonphn b ph tn ng khng giihn s mng truy nhp v tuyn dng chung ph tn.

Thch ng phn b ti nguyn khng gian: C th tng hiu qu ca gii thut phn b ph

tn theo thi gian th yu t khng gian cng phi c tnh n c mt thut ton thch ng.

S khi chc nng ca thut ton


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Cc khi chc nng trong thut ton phn b ti nguyn v tuyn ng theo thi gian gm c:

Kch hot n nh ti nguyn v tuyn ng : Khi chc nng ny c nhim v gim st thigian k t ln n nh ph tn ng trc .Sau kch hot chc nng phn b ti nguyn

ng n nh li ph tn trong cc chu k thi gian trong mt ngy. Chc nng kch hot nyc th cho php kch hot n nh ti nguyn ng theo nhu cu ca mng li.

Qun l lu lng sng mang: Chc nng qun l sng mang c thit k gia tng lngsng mang trng trong cc mng truy nhp v tuyn. Thut ton c th thc hin bng vic khavic s dng mt tn s sng mang no trong mt mng truy nhp v tuyn trc khi n cn nh li. Hoc nh gi s cuc gi m mt sng mang no truyn ti t xc nhliu hiu qu s dng ph tn c tng ln nu nh ct bt mt s cuc gi sang cc tn s sngmang cn trng khc. Ngoi ra, khi ny cn c nhim v m bo rng lu lng cc cuc gitrn mt sng mang no l ti a c th tit kim c nhiu tn s sng mang hn. Ssng mang s c tng thm na nu h thng phc tp c th thc hin chuyn giao

gia cc mng truy nhp.

D on v o lng ti: Khi chc nng ny c xy dng da trn lch s ti v chui thigian nh phn tch trn. Ngha l, da trn c s d liu v ti ca mng truy nhp trc thut ton d on s c tnh ti trng trong tng li ca mng.

Tnh ton yu cu sng mang: Chc nng ny dng cho cc mng truy nhp v tuyn bitc ti d on ca chng t xc nh s sng mang cn c cho mt mng truy nhp vtuyn.

n nh sng mang: Khi chc nng ny thc hin vic n nh sng mang cho cc mng truynhp v tuyn.

Phn b ti nguyn ng theo khng gian

Nhu cu ti ca mng truy nhp v tuyn khng ch thay i theo thi gian m n cn thay iv khc nhau theo tng khu vc. V d nh, dch v pht qung b s c nhu cu cao nhngni vui chi gii tr dch v im a im li c nhu cu cao nhng ni m nhu cu truynthng hai chiu c u tin la chn nh cc khu kinh doanh bun bn. iu , cho thy nhucu cp thit c mt thut ton phn b ti nguyn ng theo tng khu vc a l v ph tnc phn b u cho cc khu vc. Nhu cu lu lng ca cc mng v tuyn khc nhau s khcnhau theo khng gian c minh ha trong Hnh 13.

Hnh 13 Phn b ph tn ng theo khng gian


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Theo , ph tn phn b cho hai khu vc cnh nhau l khng chng ln ln nhau. Chin lcphn b ph tn ny c cho l hp l trong trng hp quy hoch cc mng truy nhp vtuyn l c lp (khng c s o kim trnh nhiu gia cc mng truy nhp v tuyn khcnhau nu chng hot ng cng di tn s)

Nhng yu cu i vi thut ton phn b ti nguyn theo khng gian :

Mc tiu ca cc yu cu i vi phn b ti nguyn v tuyn ng theo khng gian l khngc nhiu xy ra bin gia cc khu vc ca thut ton phn b ti nguyn v tuyn ng. Nhngyu cu ny phc v cho vic phi hp phn b ph tn gia cc khu vc phn b ph tnngbng vic chn thm cc khong bo v. Di y l cc yu cu c bn:

Lu lng thay i theo khng gian: cc thut ton phn b ti nguyn v tuyn theokhng gian hiu qu v mt ph tn, cc mng truy nhp v tuyn phi quan tm n c tnhlu lng ca mng theo tng khu vc a l khc nhau. Thut ton phn b ph tn ng theo

khng gian phi thc hin m hnh ha quy lut lu lng theo khng gian thc him vicnh gi got ng ca phng php thit k.

n v trao i tn s ti thiu: Cng ging nh thut ton phn b ti nguyn v tuyn theothi gian, thut ton phn b theo khng gian cng a ra quy nh v b rng ph ti thiu cthm vo hoc ct bt gia cc mng truy nhp v tuyn.

Thch ng ph theo khng gian: Phn b ph tn theo khng gian khng th thay i theo sthay i v nhu cu lu lng theo khng gian vi mt s thay i bt k no v mt khnggian. Phn gii khnggian m thch ng phn b ph tn theo khu vc c thc hin. Vicphn gii khng gian s dn n mt khi nim v kch thc phn b tn s ng khu vc, lkhu vc m nhu cu v lu lng khng thay i theo khng gian.

Mi quan h giaphn b ti nguyn khu vc v t bo ca cc mng truy nhp v tuyn :Phn b ti nguyn v tuyn khu vc dn n phn b a l cc thit b phn b ti nguyntrong mt mng truy nhp v tuyn thc t. Bi v, khi xem xt tn hiu bo hiu phn b tinguyn v tuyn, dng nh ch c mt node phn b ti nguyn trong mt khu vc phn b tinguyn. Khi thch ng ph tn c thc hin trn h thng cc my thu pht trong mng truynhp v tuyn, chiu ti thiu ca khu vc phn b ti nguyn s trng kch thc ca mt lnnht trong h thng v tuyn.

Dng chung nh gi ti lu lng gia cc khu vc phn b ti v tuyn ng khc nhau :Gi s rng cc thut ton phn b ti nguyn v tuyn ng khng gian m ti ca n cphn b gia cc phn b ti nguyn v tuyn khu vc ln cn. y l yu cu quan trng ivi cu trc ca phn b ti nguyn ng v c th phi hp n nh ph tn gia cc phn bti nguyn khu vc ln cn vi nhau, mi mt phn b ti nguyn v tuyn khu vc phi nhn thc c t nht cc mc lu lng ca cc cnh mnh. V vy, cn phi c tng tc mnggia cc node phn b ti nguyn khu vc i vi phn b thng tin ti lu lng chung.

Node phn b ti nguyn ng thng minh: Yu cu ny i vi cc thut ton phn b ti


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nguyn v tuyn ng trong trng hp khu vc bo v trong mi mt phn b ti nguyn khuvc hn ch vic chn vo cc ph tn s v tuyn khng s dng. thc hin c iuny, mi mt node phn bti nguyn ng phi c kh nng thit lp cc phn b tn s khcnhau trong cng mt khu vc phn b ti nguyn.

S mng truy nhp v tuyn chia s dng ph tn : Phn b ph tn ng theo khng gian vimc ch l pht trin cc thut ton n nh sng mang sao cho ph tn c th cp pht cho slng bt k cc mng truy nhp v tuyn.

S khi thut ton

Thut ton phn b ti nguyn v tuyn theo khng gian c cc khi chc nng chnh nh sau:

D on v nh gi ti: n gin, nhng kt qu ban u ca thut ton phn b tinguyn v tuyn theo khng gian c c vi gi thit rng cc phn b ti nguyn c kh nngd on ti mt cch hon ho sao cho mi mng truy nhp v tuyn c cung cp mt gi trxc nh ti trng. Gi thuyt ny l cn thit bi v khi nghin cu v thut ton phn b khnggian chng ta c nh i lng thi gian do rt kh c th m hnh ha mt k mtphng php d on ti no.

Tnh ton yu cu sng mang: Chc nng ca khi ny l t thng tin c c t d on titrng ca mng s tnh ton s sng mang cn thit cho mi mt mng truy nhp. Kt qu u raca khi chc nng ny s l u vo va thut ton n nh khng gian phn sau.

Th tc n nh sng mang: y l vn ht sc quan trong trong bt c mt thut ton phnb ti nguyn ng no n nh cc sng mang c th cho tng mng truy nhp v tuyn.

Hin nay, c nhiu cc phng php truy nhp ph tn ng c cc nhm nghin cu khcnhau trn th gii xut. Tuy nhin, mi phng php thng tp trung vo mt ng dng cth ch cha c mt m hnh truy nhp ph tn ng ph hp chung cho gii php v tuynthng minh. y vn ang l vn m cho cc nhm nghin cu trn th gii.


16/17

y ban truyn thng lin bang (FCC) M xut phng php truy cp ph tn ng theo mhnh nhit nhiu (Interference Temperature Model - ITM). Trong m hnh ny, thit b vtuyn s o nhit nhiu v xc nh gii hn nhit nhiu trc khi pht. Quan h gia nhit nhiu v bng tn, tn s sng mang c th hin nh sau [1]:

TI = PI(fc,B)/kB (1)

trong , TIl nhit nhiu (oK),PI(.)l cng sut nhiu trung bnh (W) ti tn sfcvi

rng bng tnB (Hz), v kl hng s Boltzman.

T thit b c th xc nh tham s rng bng tn v mc cng sut pht t c dunglng mong mun m khng vi phm gii hn nhit nhiu. Trong mng v tuyn thng minh,quyn truy nhp vo mng ca thit b da trn nhit nhiu. C ch ny hnh thnh nn mhnh a truy nhp theo nhit nhiu ITMA (Interference Temperature Multiple Access) .

Trc khi pht, nt mng tin hnh o nhit nhiu TI, l mt hm ca bng tn cn o nh (1). Sau , gi tr trn s phi hp cng vi gii hn nhit nhiu TL, dung lng cn thit Creqv tham s phm viL (c trng cho c tnh knh) tnh ton rng bng B v tc d liu.Qu trnh trn c lp li cho n khi gi trB hi t nh c m t Hnh 15.

Nu rng bngB cn thit truyn thnh cng gi tin c gi tr nh hnBmax, th gi tinc truyn. Ngc li, nuB >Bmaxgi tin khng c truyn, thit b v tuyn c cc lachn sau:

- i: Do xuyn nhiu trong thi gian ngn nn c th phi tm thi dng truyn tin.

- Gim C, gim tc d liu gi: Tuy nhin, do yu cu ca loi hnh dch v m khng thgim Cxung di mc ngng Cmin.

- TngL, gim phm vi v tuyn: Nu my thu ch xa, hoc b fading hoc b che chn, Lkhng th tng vt quLmax.

- C< Cmin,L >Lmaxv qu hn i, phng php cui l phi dch ton mng sang mt tn slm vic mi.


17/17

Hnh 15: Lu thut ton cho ITMA

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