MC LC

I. Quy hoch tn s v cc vn v gii hn bng tn s dng trong v tuynII. Tng quan cng ngh v tuyn nhn thc2.1 Gii thiu chung. 2.1.1 Truy cp ph v tuyn. 2.1.2 Vn khan him ph v hiu sut s dng ph. 2.1.3 Gii php v tuyn nhn thc v truy cp ph ng. 2.2 H thng v tuyn nhn thc. 2.2.1 Khi nim v tuyn nhn thc. 2.2.2 M hnh v tuyn nhn thc da trn SDR2.2.3 Chc nng ca v tuyn nhn thc2.2.3.1 cm bin ph2.2.3.2 2.2.4 Kin trc vt l 2.2.5 Cc chun ca h a, Chun IEEE SCC 41. b, Chun IEEE 802.22 cho khu vc mng khng dy. III. Phng thc chia s ph tn3.1 Cc bc chia s ph tn trong v tuyn nhn thc3.2 Cc phng php chia s ph tn trong v tuyn nhn thc3.2.1 chia s ph tn da trn kin trc3.2.2 chia s ph tn da trn cch thc cp pht ph3.2.3 chia s ph tn da trn cc cng ngh truy nhpIV. ng dng v thch thc ca mng v tuyn nhn thc4.1 ng dng thng tin khng dy nhn thc4.2 Thch thc V. Kt lun

II.Tng quang cng ngh v tuyn nhn thc2.1 Gii thiu chungS gia tng nhu cu ca thng tin khng dy ko theo nhu cu ci thin cht lng v lu lng, tnh tin cy, dch v... V vy m s lng thit b da vo cc chun khng dy v cng ngh s ngy cng gia tng trong tng lai. Nhng mt vn quan trng khc li ny sinh l ph tn s ca thng tin khng dy. Trong khi ti nguyn ph l c hn th s pht trin trn s dn ti tnh trng khan him ph. Do vy gii quyt c vn ny chng ta c th pht trin xa hn th trng vin thng cng nh tm ra c mt chun thc cht cho h thng thng tin tng lai ca chng ta.2.1.1 Truy cp ph v tuynTruy cp ph v tuyn hin nay b gii hn bi cc c quan qun l ph ca quc gia. Phn ln ph dnh cho cc dch v v tuyn c cp php. Truy cp m i vi hu ht ph ch c cho php vi cng sut truyn rt nh, trong ci gi l chia s lp di, v d nh s dng bng siu rng (UWB).Ch mt phn nh ca ph v tuyn dnh cho bng tn khng cn cp php. Bi v phn ph ny rt nh nn s khng sn c cho cc ph khng cn cp php mi. S chuyn i t ph c cp php sang ph khng cn cp php thc s kh khn v mt thi gian di. N i hi s kt hp gia t chc qun l ph chnh ph, nh pht trin cng ngh, nh cung cp dch v.Trong vng vi thp k qua, nhiu chun khng dy, cng ngh v dch v mi cho ph khng php mi ra i. Trong s ph bin l IEEE 802.11 WLAN, Wi-Fi v IEEE 802.15 WPANs. H thng ng dng khng dy trong ph khng php ny thc s thnh cng v thng mi. Ngy cng nhiu h thng v tuyn s dng khong ph ny, chng t rng n c th hu dng thay i cch qun l ph hin ti nhm hng ti truy cp ph m v linh hot.Gii hn v tr hon ca truy cp ph ang tht nghn v lm chm li qu trnh pht trin cc dch v v tuyn mi. Nhng h thng ny c th ci thin v an ninh, mi trng lm vic, gio dc, gii tr. S pht trin y ha hn v s lng thit b v tuyn da trn cc chun khng dy c th b tr hon bi nhng gii hn trn.2.1.2 Vn khan him ph v hiu sut s dng ph.Ph v tuyn l ti nguyn c hn. Cm t ph v tuyn ch khong tn s in t gia 3KHz v 300GHz. Hnh 1.1 minh ha khong tn s m thng ch ph tn s. Hu ht cc h thng thng tin v tuyn hin nay yu cu bo v cht ch chng li nhiu t cc h thng v tuyn khc. Ngy nay, ph cp php c bo v m bo khi nhiu.Phn ln ph v tuyn c cp cho cc h thng thng tin v dch v truyn thng xc nh trong hnh 1.2. Tuy nhin, ti nguyn ph li b lng ph bi nhiu l do. Hnh 1: Ph v tuyn t tn s 3KHz n 300GHzTh nht, s tht bi v kinh t ca cc dch v v h thng v tuyn cp php c th dn n ph khng s dng. V d, WiMax xut hin nhng khng thnh cng v thng mi. Ph WiMax c xc nh v cp php nhiu nc, nhng li khng c s dng trn din rng. Ph WiMax v th lm lng ph ti nguyn ph.Th hai, h thng v tuyn ca qun i cng nh cng an yu cu ph cho h thng m ch yu hot ng khi c bin c. Do vy thm phn lng ph ti nguyn ph.Th ba, s pht trin cng ngh dn n s ci thin hiu sut ph trong h thng thng tin cp php hin ti, v d nh pht sng tivi s. Do s yu cu t ph hn cung cp cng mt dch v.Ni tm li, mt phn ln ph ang c s dng khng hiu qu. Hn bao gi ht, cn tm ra mt cng ngh gip vic truy cp ph mt cch linh hot. Nh vy mi c th gii quyt vn khan him v lng ph ph hin nay.

Hnh 2: Ph v tuyn c cp cho cc h thng thng tin v dch v truyn thng.2.1.3 Gii php v tuyn nhn thc v truy cp ph ngNh chng ta bit, di tn s ca sng v tuyn l mt ti nguyn c qun l bi cc t chc vin thng ca chnh ph. V bt c h thng thu pht v tuyn no mun s dng tn s u phi c cp php bi cc t chc . Ngy nay, cng vi s pht trin ca khoa hc k thut ni chung v lnh vc in t - vin thng ni ring, di tn s ang dn tr nn cht hp bi s gia tng s lng cc h thng v tuyn cng nh cc chun giao tip nh FM, AM, TV, Mobile network,Wifi,Wimax... iu nghch l ch l mc d ph tn s ang ngy cng cht hp th hiu sut s dng ti nguyn tn s li rt thp. Theo thng k ca Hi ng vin thng lin bang ca M (FCC) th hiu sut s dng ti nguyn ph tn s ch vo khong 15% n 85%. Hiu sut ny thay i da vo c im h thng mng vin thng tng vng a l (mng dy c hay tha tht) v thi im s dng (gi cao im hay bnh thng).

Frequeney (GHz)0-11-22-33-44-55-6

Utilization (%)54.435.17.60.250.1284.6

Hnh 3: Hiu sut s dng di tn s.Da vo ph tn s v bng s liu v hiu sut s dng tn s, chng ta d dng nhn thy rng bn cnh nhng khong tn s c s dng kh hiu qu (0-2 Ghz) th vn c nhng khong tn s c s dng t hoc khng s dng (3-5 Ghz). Ngi ta nh ngha nhng khong tn s khng c s dng ny l khong trng (white space or spectrum hole). Vn t ra l lm sao tn dng c nhng khong trng ny nhm tng hiu sut s dng tn s cng nh gii quyt c vn cht hp ca di tn s hin nay. Kh khn ch nhng khong trng ny khng c nh m thay i lin tc ng vi s thay i ca hiu sut s dng m nguyn nhn c nu trn. Do vy nhu cu bc thit t ra i vi nn vin thng th gii l cho ra i mt h thng v tuyn thng minh c kh nng s dng nhng khong trng trong di tn s. S xut hin ca n s gii quyt c nhng kh khn trong vic s dng ti nguyn tn s.V tuyn nhn thc cng vi truy cp ph ng c th vut qua vn m ta cp trn. V tuyn nhn thc khng ch l cng ngh v tuyn mi m cn cha nhng thay i mang tnh cch mng trong vic qun l ph. V tuyn mi ny c thit k s dng v chia s linh hot ph m khng nh hng h thng v tuyn cp php.Cc h thng v tuyn nhn thc c th t ng phi hp trong vic s dng ph. Chng xc nh ph khi n khng c s dng bi h thng v tuyn cp php v s dng ph ny theo cch thng minh da vo vic quan st ph.H thng v tuyn mi cn kh nng thng minh p ng cht lng dch v (QoS) khi chia s ph vi h thng v tuyn khc v khi xut hin h thng m khng c kh nng cng tn ti. H thng v mng v tuyn nhn bit ca tng lai s t ng kt hp t yu cu QoS trong trng hp chia s ph, v d nh xut hin h thng khc, kh nng tranh chp, h thng v tuyn.Cng ngh v tuyn nhn thc c c v bi c quan d n nghin cu pht trin bo v (DARPA), thng tin th h tip theo (XG). Nhiu nghin cu v pht trin tp trung vo cng ngh mi ny. Chun mi dnh cho n ra i l IEEE 802.22. Chun ny l mt bin th ca IEEE 802.16 v dng cho WRAN. Mng ny hot ng vng nng thn ni m bng VHF/UHF khng s dng, v bao gm thit b bo v h thng v tuyn cp php (nh pht sng TV mt t) khi nhiu gy hi. Trc tin, cn phi ci tin ngay t vic qun l ph tn s. Hin nay, mi mt di bng tn mun c s dng u phi c s cho php ca mt t chc qun l tn s ca chnh ph. Ngi c cp php s dng di tn s c gi l primary user (PU) hay cn gi l licenced user v ch c php s dng di tn cng nh cc ngi s dng khc khng c php s dng di tn ny. Cch qun l tn s ny cng nhc v rt kh gii quyt nhng vn nu trn. FCC a ra chun IEEE 802.22 dng cho WRAN (Wireless Regional Area Network) cho php secondary user (SU) hay cn gi l unlicenced user s dng nhng khong trng trong di tn s. Thng 5/2004 FCC chnh thc ti s dng bng tn TiVi v SU c php s dng bng tn ny. Tuy nhin yu cu t ra l hot ng ca SU khng c nh hng n PU cng nh bt c lc no PU mun s dng li khong tn s trng th SU u phi nhng v chuyn sang tm khong trng khc. Do vy, mt h thng v tuyn nhn thc c kh nng cm bin khong trng cng nh kh nng thay i linh hot mi c th gii quyt kh khn ny.2.2 H thng v tuyn nhn thc. 2.2.1 Khi nim v tuyn nhn thc.H thng v tuyn nhn thc 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. Theo ,thit b v tuyn nh ngha bng phn mm SDR (Sotware Defined Radio) s l mt phn t quan trng trong h thng v tuyn nhn thc. V cc tham s ca thit b SDR c thay i mt cch linh ng bng phn mm m khng cn phi thay i cu trc phn cng. Mc ch ca v tuyn nhn thc l cho php cc thit b v tuyn khc hot ng trn cc di tn cn trng tm thi m khng gy can nhiu n cc h thng v tuyn c quyn u tin cao hn hot ng trn di tn . ch php tn dng ti a ti nguyn ph tn nh trn, v tuyn nhn thc phi c nhng tnh nng c bn sau: iu chnh tn s hot ng ca h thng mt cch tc th t mt bng tn ny n mt bng tn khc (cn trng) trn di tn cho php. 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 cu mi trng v tuyn, 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 ha sa li cho php t c thng lng tt nht c th. To bp sng v iu khin bp sng thch ng theo i tng truyn thng nhm gim thiu nhiu ng knh v ti a cng tn hiu thu.

hnh 4:khi nim h ph ri hnh thnh ln tng v v tuyn thng minh

2.2.2 M hnh v tuyn nhn thc da trn SDRM hnh v tuyn thng minh in hnh trn c s SDR nh hnh 2. Theo , cc chc nng v cc 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 cn trng mt cch tc th, anten di rng phi c kh nng qut tn s rt rng sao cho c th pht hin 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 nh ngha bng phn mm (SDR) s hot ng trn mt bng tn nh . Ngoi ra, h thng a anten c xut to bp sng v li phn tp nhm tng cng phn gii khng gian v ci thin hiu qu tch sng.Khi duplexer c dng nh hng (phnn b) tn hiu cho cc anten, hay ni cch khc n phn cch tn hiu thu v pht tn hiu pht.

Hnh 5: m hnh v tuyn nhn thc in hnh trn c s SDRKhi la chn tn s ng (Dynamic Frequency Selection DFS) l mt qu trnh la chn tn s t ng c dung trong v tuyn nhn thc trnh gy nhiu n cc h thng v tuyn khc c quyn u tin cao hn khi hot ng cng bng tn. Khi hot ng, ph tn s ch c la chn s dng khi n khng b chim dng bi thit b khc, v s dng chim dng ph tn ny nagy 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 ng thi trong module thu. Mi khi SDR c iu khin hot ng trong mt di tn nht nh thng qua phn mm m khng phi thay i cu trc phn cng. L do ca vic s dng nhiu mdule SDR song song thay v ch mt module SDR duy nht l gim phc tp cu thit b SDR. S liu u ra ca khi SDR c a vo cng mt khi chc nng, khi ny thc hin quyt nh ti u da trn nhng thng tin t cc SDR thnh phn, trong thc hin la chn va kt hp gia cc lung thng tin sau tch sng ti to lung thng tin cng 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 thit b v tuyn c quyn u tin cao hn da trn cc thng tin v: s phn b ph tn, thi im chim dng ph tn cu 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 kho chun mt cch chnh xc phc v cho qu trnh iu ch cao tn v chuynn i bng tn. Mun vy, 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 sut pht. Cc thng s ny cho php xc nh chnh xc mc cng sut pht nhm m bo v tuyn nhn thc 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 cng sut pht theo s thay i tn s lm vic ca thit b v tuyn nhn thc.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.2.2.3 Chc nng V tuyn nhn thc c 4 chc nng chnh:2.2.3.1 cm bin phTrc ht ta tm hiu v s pht hin tn hiu nh vo cm bin ph. R rng, vic cm bin ph l nhim v thit yu ca mng v tuyn nhn thc, n cho php ngi dng th cp c th pht hin ra khong ph trng v c c hi tn dng nhng khong tn s ny m khng nh hng g n h thng trn. V vn cm bin ph ny c trnh by nh sau. pht hin 1 tn hiu nm trong di bng thng B bit trc, ta c th th t vn v gi thit nh sau :H0: x(n) = v{n)H1 : x(n) = s(n) + v(n), n = 1,2, N y: H0 th hin s khng tn ti ca tn hiu, tc l ,tn hiu nhn c x(n) cha ng ch l nhiu Gauss trng cng tnh (AWGN),v(n) ~ CN(0,v2 ). H1 th hin cho s c mt ca tn hiu, tc l tn hiu nhn c x(n) gm 1 tn hiu s cp S(n) cng vi nhiu v(n). n tng ng ti s ln ly mu.Trong 4 chc nng ca CR l cm bin ph, qun l ph, s dng ph linh hot v chia s ph th cm bin ph l chc nng u tin v c vai tr quan trng trong ton b h thng ca CR. Cm bin ph s dng cc phng php x l tn hiu thu c a ra quyt nh v di tn s ang quan st l trng hay l c xut hin tn hiu PU. y l chc nng quan trng nht bi v n nh hng ln n quyt nh s dng hay khng s dng di tn s ang quan st. Mng CR cn da vo cc iu kin ca mi trng c th cm bin c di ph thch hp, qua a ra quyt nh chnh xc v vic s dng di ph no khng gy nh hng n PU.Mc d cm bin ph th c hiu theo truyn thng l tnh ton lng ph hay tnh ton nhiu nhit trong di ph, ni 1 cch tng qut hn l n l 1 thut ton m s dng nhiu c tnh phc tp nh thi gian, khng gian, tn s v m ha. ng thi n cng xc nh c loi tn hiu m chim gi ph (bao gm c iu ch, dng sng, bng thng, tn s sng mang v.v...). Tuy nhin, vic ny i hi phi mnh v k thut phn tch tn hiu vi cc tnh ton phc tp.Trong h thng CR c th chia cm bin ph ra lm 2 loi chnh sau: Occupancy sensing (cm bin s chim gi ph): pht hin s chim gi ph trong khu vc ln cn,qua xc nh c di ph no ang trng (white spaces) hoc ang di mc s dng (gray spaces). Mt v d v Occupancy sensing l b pht hin da vo nng lng (energy-based detection). Identity sensing (cm bin cc c trng): phn bit c di ph ang b chim gi bi primary user hay l ang b chim gi bi mt CR user khc. iu ny c bit quan trng i vi mi trng CR c nhiu user, khi white space phi c chia s cho nhiu user. Mt v d v Identity sensing l cm bin da vo c im (feature-based detection).Ta c s khi ca cc phng php trong qu trnh cm bin ph :

Hnh 5: S khi ca cm bin ph.Nh vy phng php cm bin c th c chia lm 2 loi: energy-based detection v feature-based detection.C 2 phng php energy-based detection v feature-based detection u c nhng u im v nhc im. Bi v a s CR thng c t thng tin v tn hiu ca PU nn vic s dng energy-based detection l iu tt yu, ch khi no CR c thng tin cn thit n mi c th s dng feature-based detection. i vi SNR cao th 2 phng php tng t nhau nhng i vi SNR thp th ch c cyclostationary feature detection l c kh nng hot ng tt vi xc sut pht hin cao. Da vo nhng u nhc im, ngi ta c th kt hp c 2 phng php ny vi nhau c th b sung cho nhau. Mt CR spectrum sensing c th chia lm 2 bc: cm bin th (coarse sensing) v cm bin tinh (fine sensing).Coarse sensing hng ti k thut energy-based detection. N c th d tm nhanh chng v khi qut di bng tn ph v xc nh mt s spectrum holes c kh nng s dng c. Sau spectrum holes s c x l bc th 2 l s dng fine sensing. N c thc hin da vo k thut feature-based detection.C 2 yu cu c bn trong vic cm bin ph trong lp vt l l: tin cy ca qu trnh cm bin v thi gian cm bin.Cht lng ca qu trnh cm bin l kh nng pht hin thnh cng tn hiu ca PU. Qu trnh pht hin c nh gi l khng cht lng khi chng ta khng pht hin c tn hiu PU hoc nhm tn hiu PU vi nhiu ca mi trng.Thi gian cm bin pht hin tn hiu c yu cu cng nh cng tt c th nhanh chng pht hin ra PU v thc hin nhng nhim v tip theo. Tuy nhin, vic cm bin t kt qu tt hn th chng ta cn phi s dng nhng gii thut DSP phc tp. iu ny i hi chng ta phi tn thi gian cm bin. Do , mt b pht hin ng tin cy c cht lng tt th n phi tn thi gian nhiu hn a ra c kt qu nh mong i. Thch thc t vic cm bin bng tn trng c tnh mc can nhiu:Kh khn ca m hnh tch da trn b thu l hiu qu ca tnh ton mc can nhiu. Mt thit b CR c th nhn thc c mc cng sut truyn v v tr chnh xc ca n thng qua s gip ca h thng nh v. Vi kh nng ny, th n li c th gy ra nh hng can nhiu ln cc hng xm ca n ti cng di tn s. Tuy nhin thc t th vn cha c cch no cho CR c th c tnh chnh xc mc can nhiu ti thit b Primary k cn. Mt thch thc quan trng khc l xc nh gii hn can nhiu, mt khi m thit b CR c gng iu khin truyn dn ca n theo gii hn ny th vic ra i mt m hnh cho vic xc nh gii hn can nhiu l cn thit. Tuy nhin, gi tr ti u ca gii hn ny ph thuc vo mt v c tnh lu lng ca mng Primary. Hn na, c tnh ca lp vt l cng nh hnh thc iu ch, cng sut pht v di tn s cng nh hng n gii hn ny. Cm bin bng tn trng trong mt mng a userTa thy thng thng mng CR c th cng tn ti trong mt mi trng nhiu thit b CR v Primary. Mi trng nhiu thit b khin n kh khn hn thc hin d tm thit b Primary v thc hin c tnh chnh xc nhiu thc s. Do nh hng truyn dn ca cc thit b CR khc m gy ra nh hng n mt CR ang c gng d tm tn hiu ca Primary. V th, hm d tm ph nn c pht trin c th d tm tt hn trong mi trng a user. gii quyt tt hn vn ny, th ta c th xem xt n k thut tch kt hp. Rng buc ca lp vt lK thut d tm ph tn s yu cu hiu qu kh nng ca lp vt l trong mi trng bng thng rng. Nh cp trn th trong thc t mng CR khng th thc hin ng thi cm bin v truyn l mt trong nhng yu t trong vic thit k thut ton d tm ph. Vic qut ton b bng ph s mt nhiu thi gian v yu cu chnh ca mng CR l thi gian d tm tn hiu PU i hi khong thi gian rt ngn. V k thut OFDM trong mng CR c bit nh l phng php tt nht ph hp vi kin trc vt l ca mng CR. Kh nng d tmTrong khi gii php mng trung tm tp trung vo vic la chn thng tin hiu qu t nhiu thit b d tm v nh v ph ti u cho cc user. Kin trc phn b dn n vic thng tin d tm c chuyn i tun hon gia cc thit b CR.ng kha cnh cc thit b Primary, cc thit b CR c th c xem l k chi xu v nghe ln knh truyn khi m thng tin trong mng primary ang trao i. Tuy nhin, k thut d tm ph tn s cn phi bit c c hay khng s hin din ca thit b Primary. Do , k thut d tm ph tn s nn c thit k chng c th bit c s hin ca cc thit b trong mng Primary m khng c c ni dung ca thng tin truyn i. Tnh an ton v tin cy d tm vng ph tn s:ng cch nhn ca cc thit b mng Primary th cc thit b CR l nhng k nghe ln, do bo qun tnh ring t ca cc thit b th k thut CR cn phi c thit k cn thn trnh r r thng tin trong mng primary.Vi mt bng ph hin c th thch thc u tin cho cc thit b CR l tin cy khi d tm ra s hin din ca tn hiu Primary hn ch n mc thp nht s can nhiu cho cc mng ang tn ti. Mt khi m tn hiu xut hin trong mi trng nhiu fading hay shadowning th rt kh khn cho vic phn bit gia mt ph trng v tn hiu c bin yu do knh truyn xu.2.2.3.2 qun l phTrong mng CR, bng tn ph v tuyn khng s dng s c tri trong khong tn s rng bao gm ph cp php v ph khng php. Vic pht hin nhng ph khng s dng ny thng qua cm bin ph. H thng v tuyn nhn thc s phi quyt nh ph tt nht p ng yu cu QoS trong s nhng ph sn c. cng chnh l l do h thng i hi phi c chc nng qun l ph. Chng ta s ln lt bn v hai chc nng ca qun l ph l phn tch ph v quyt nh ph. Trong khi cm bin ph nm lp vt l th phn tch ph v quyt nh ph li nm lp cao hn. a, phan tch phTrong mng v tuyn CR, cc khong ph trng thng thay i theo thi gian. V ngi s dng c trang b vi v tuyn nhn thc da vo lp vt l, nn tht quan trng hiu cc c im ca cc ph khc nhau. Nh c phn tch ph, h thng d dng la chn ph m p ng c yu cu ca ngi s dng. m t c bn cht ng ca mng th h mi, mi ph trng nn c c trng ha khng ch mi trng v tuyn thay i theo thi gian m cn hot ng ca PU v thng tin ph nh tn s hot ng v bng thng. V vy, cn thit xc nh cc thng s nh mc nhiu, tc li knh truyn, suy hao... m c th i din cho cht lng ca mt bng tn ph. C th l: Nhiu xuyn knh: Mt s bng tn ph th ng c hn so vi nhng ph khc. V vy, ph c dng xc nh c trng nhiu ca knh truyn. T s lng nhiu ti b nhn s cp (PR), cng sut cho php ca ngi dng CR c th c rt ra, t c th s dng c lng dung lng knh truyn. Suy hao: Suy hao s gia tng khi tn s hot ng tng. V vy, nu cng sut truyn ca ngi dng CR vn khng i th khong truyn ca n s gim tn s cao hn. Tng t, nu cng sut truyn tng b cho suy hao tng th kt qu s gy nhiu cho ngi dng khc. Li lin kt khng dy: ph thuc vo cch iu ch v mc nhiu ca bng tn ph, tc li ca knh truyn s thay i. Tr hon lp lin kt: xc nh suy hao, li lin kt khng dy v nhiu xuyn knh th c nhiu loi giao thc lin kt c yu cu ti nhng di ph khc nhau. iu ny dn n s tr hon ca cc gi truyn dn trong cc lp lin kt khc nhau. Thi gian chim gi: cc hot ng ca PU th c th nh hng n cht lng knh truyn ca h thng CR. Thi gian gi l khong thi gian mong i mt user trong h thng CR chim gi 1 di tn s c ng k trc khi b ngt i. R rng, thi gian chim gi cng lu th cht lng cng tt.Dung lng knh truyn c th c rt li t nhng thng s c gii thch trn, dung lng knh truyn l ch s quan trng nht trong cc c trng ca ph. Thng thng, t s SNR ti b nhn c dng cho vic c lng dung lng. Tuy nhin, v t s SNR dng nh ch l s theo di ca h thng CR, n th khng trnh c nhiu lin knh ca nhng PU. Do , c trng ca ph tn hiu th c tp trung vo s c lng dung lng ca knh truyn, da vo nhiu lin knh ti nhng b nhn c ng k. Gii hn nhiu lin knh th ch cho ta bit cn trn hay nh ca nng lng RF m n c th c gii thiu cho h thng CR c th s dng nhng khong tn s trn.Mt phng php c lng dung lng ph th c cp n da vo bng thng v cng sut truyn cho php. Theo , dung lng ph c tnh nh sau:C = B log2 (1 +)Trong B l bng thng, S l cng sut tn hiu nhn t CR user, N l cng sut nhiu ca b nhn, v I l cng sut nhiu xuyn knh ti b nhn CR b gy ra bi s truyn dn ca PU.Ngoi ra, vic tnh ton dung lng ca ph cng c cp n trong h thng v tuyn nhn thc OFDM. Theo , dung lng ph ca mng CR da vo OFDM c tnh theo:C = vi l tp hp ca cc vng ph khng s dng, G(f) l cng sut khuych i ti tn s f, S0 v N0 l cng sut ca tn hiu v nhiu trn mt n v tn s.Trong nhng cuc tho lun gn y v phn tch ph, ch yu tp trung vo phn tnh ton c lng dung lng ca ph. Tuy nhin, ngoi dung lng ra, chng ta cn ch n nhng yu t khc nh thi gian tr, tc li lin kt v thi gian chim gi cng nh hng n cht lng ca dch v. Hn na, dung lng th cng lin quan n c nhiu lin knh v suy hao. Cho ti nay, vic phn tch hon ton v m hnh ho ca ph trong h thng CR th ang c pht trin. Th nhng, tm ra mt khong ph thch hp cho nhiu ng dng khc nhau, i hi chng ta cn phi m thm nhiu nghin cu v cc di ph v kt ni tt c cc thng s c trng ca n a ra quyt nh hp l.b, quyt nh phDi ph hot ng thch hp th nn c thm vo h thng truyn dn hin ti m tho mn cc yu cu ca QoS v cc c trng ca ph. V vy, h thng qun l ph c th nhn bit c cc yu cu ca QoS.Da trn nhng yu cu ca ngi s dng th tc ca d liu, tc li c th chp nhn c, gii hn tr, cch thc truyn dn tn hiu v bng thng ca s truyn dn c th xc nh c. Sau ,theo lut quy nh, cc thit lp cho di ph tng thch cng c th c chn. Theo 1 s ti liu, th c 5 iu lut quy nh cho ph c ban hnh, v n c tp trung vo nhng thun li v gi thnh. Tuy nhin, cch thc ny th gi thit rng tt c cc knh truyn u c lu lng nh nhau.c, Nhng th thch ca vic qun l phC nhng tn ti trong qu trnh trin khai qu trnh nghin cu m ta cn phi gii quyt pht trin gii thut qun l ph ni trn.Cc th thch cn vt qua: Hnh thc quyt nhT s tn hiu trn nhiu SNR khng c trng cho h thng mng CR. Khng ch c SNR m cn c nhiu thng s c trng khc ca ph th nh hng ti cht lng ca vic qun l ph c nu trn. Do , lm th no kt hp tt c cc thng s c trng ny ca ph quyt nh kiu ph ph hp th vn ang tip tc c nghin cu v tho lun. tuy nhin, trong h thng OFDM m da vo h thng CR, nhiu di ph c th c s dng ng thi trong qu trnh truyn dn. T nhng nguyn nhn khung cng vic cho cc di ph trn c xy dng. S quyt nh nhiu di phTrong h thng CR, nhiu di ph c th c s dng ng thi trong qu trnh truyn dn. Thm na, h thng CR khng yu cu cc di ph m c chn phi lin tip nhau. V vy, ngi s dng trong h thng CR c th gi cc gi d liu thng qua nhng di ph khng lin tip ny. Truyn dn ph a knh ny ch ra s hn ch cht lng trong sut qu trnh chng ln ph khi so snh vi s truyn dn thng thng ch dng c mt knh. V d, nu tn hiu ca PU xut hin mt di bng no th h thng CR s phi b qua di bng ny v tm nhng c hi nhng di bng khc, th nhng khi cc di bng ny s bo tr, gi gn c knh truyn, lm cht lng ca knh truyn c n nh. Hn na, truyn dn a knh cho php tn hiu cng sut thp c s dng ti cc di bng. V vy,v tnh lm tng thm nhiu cho tn hiu PU. T nhng l do trn, th cng vic ca h thng qun l ph phi h tr cho kh nng quyt nh h thng truyn dn ph a knh. V d nh lm th no xc nh c s lng cc di bng v lm th no chn c di bng no ph hp vi h thng CR th vn cn ang nghin cu thc hin. Kt hp ti cu hnhK thut ca h thng CR cho php cc thng s ca sng thay i, ti cu hnh li h thng c th hot ng ti u trong vng trung tm ca di ph. V d nh, khi m t s SNR c xc lp th tc li bit BER c th c iu chnh duy tr, bo v dung lng knh truyn bng cch s dng li th ca kh nng thch nghi ca cng ngh. V vy, cng vic ca s kt hp ny l bao gm c vic quyt nh ph v ti cu hnh li. Quyt nh ph da trn cc bng tn ph hn tp, khng ng nhtR rng, ti trung tm di ph th lun c gn cho nhng mc ch khc nhau, do , khong ph c s dng bi h thng CR th gn nh l s kt hp gia ph c truy cp v ph khng c ng k. Trong trng hp ph ng k th ngi dng trong h thng CR phi xt n cc hot ng ca my PU trong phn tch ph v trong quyt nh ca mnh khng nh hng ti s truyn dn ca my PU. Ngc li, trong nhng di bng cha ng k, bi v tt c cc my trong h thng CR u c quyn truy cp nh nhau, chnh v vy m ta cn phi trang b mt h thng k thut ti tn chia ph cho hp l. Tuy nhin, quyt nh khong ph tt nht th cn phi qua mi trng phc tp, do , h thng CR cn h tr cho quyt nh ph trong c di bng ng k v di bng khng ng k.2.2.3.3 Linh ng phMc ch ca h thng CR l s dng ph tn s theo cch thc ng, c ngha l h thng CR s tm kim v hot ng ti bng tn s tt nht. tm c nhng khong ph trng tt nht th h thng CR phi thu thp cc khong ph trng ny. V th, s linh ng ph (spectrum mobility) c nh ngha nh l 1 cch thc m ngi dng trong h thng CR c th thay i tn s hot ng. Chng ta s m t nh ngha ca hin tng chng ln ph trong mng CR v bn v hng pht trin ca h thng ny.a, Chng ln phTrong h thng CR, s linh ng ph c thc hin khi m cc iu kin ca knh truyn tr nn xu i hay c s xut hin ca tn hiu PU. S linh ng ph s tng thm cc loi chng ph trong h thng CR v chnh l mc ch ca s chng ph. Cc giao thc t nhiu lp khc nhau trong h thng mng cn phi c thch nghi vi cc h s knh truyn ca tn s ang hot ng. Hn na, n th nn c xuyn sut c trong qu trnh chng ph v trong lc ch i c ghp ph.Ngay ti thi im bt u ca qu trnh ny, h thng CR cn phi thch nghi vi tn s hot ng, do mi ln mt my trong CR m thay i tn s hot ng ca n th cc giao thc mng cng phi thay i theo, chuyn sang mt ch hot ng khc. Mc ch ca s qun l linh ng cc ph ny trong h thng CR l chc chn rng s chuyn i tn s c thc hin mt cch sun s ngay khi c th cho cc ng dng ang chy trong mt my CR c th hot ng vi cht lng tt nht c th trong sut qu trnh chng ph. Vic cc giao thc ca qu trnh qun l linh ng bit trc cc thng tin trong sut qu trnh chng ph th cn thit. Cc thng tin ny th c cung cp bi gii thut cm bin.Kt qu, s qun l linh ng cc giao thc a tng ny c yu cu hon thin gii thut linh ng ph. Cc giao thc ny h tr cho h thng qun l linh ng s thch nghi i vi cc ng dng khc nhau. V d, mt kt ni TCP c th t mt trng thi i cho n khi s chng ph kt thc. Hn na, bi v cc thng s ca TCP s thay i sau khi s chng ph kt thc nn tht cn thit hc cc thng s mi v m bo rng qu trnh chuyn i t thng s c sang mi c thc hin mt cch nhanh chng. Cn i vi cc d liu thng tin, v d nh FTP, th cc giao thc qun l linh ng nn ci t cc thit b lu tr li cc gi thng tin m c truyn dn trong sut thi gian chng ph.b, Cc th thch t ra cho h thng qun l linh ng ph trong h thng CR Xt ti mt khong thi gian c bit no , c nhiu khong ph m c th s dng c cho mt ngi dng trong h thng CR. Gii thut c yu cu quyt nh khong ph no l tt nht th phi da trn cc c trng knh truyn ca cc khong ph trng ny v cc i hi ca cc ng dng m ang c dng trong my ca h thng CR. i khi, khi m khong ph trng tt nht c chn, th thch thc tip theo l lm th no thit kt mt h thng qun l linh ng ph mi gim tr v suy hao trong qu trnh chng ph. Khi m tn s ang hot ng bn khi m qu trnh truyn dn ang din ra bi mt my trong h thng CR, c th do my ng k s dng bt u dng tn s ny, khi , cc ng dng ang chy trn tn s ny phi chuyn sang mt tn s khc. Tuy nhin, chn c mt tn s khc chuyn th cn thi gian. V vy,cn c mt gii thut m bo rng cc ng dng ny khng b thit hi g trong qu trnh chuyn i. C nhiu s chng ln ph khc nhau cng tn ti trong h thng CR. Nu mt my trong h thng CR di chuyn t ni ny n ni khc th s chng ph c th khng xy ra bi v nhng di ph trng thay i. V th, yu cu i vi n chng ph l nn tp hp cc cm khu vc chng ph. Theo , s chng ph gia cc mng khc nhau th hng theo s chng ln theo chiu dc v n th ging nh nhng g m h thng CR ang lm. Di tc ng ca mi trng a dng, phc tp, n th cn thit ti chng ln ph c th c c tt c cc kh nng c cp. Kh nng linh ng ph trong min thi gian: h thng CR th thch nghi ph khng dy da trn nhng di bng trng ca ph. Bi v nhng knh trng ny thay i qu gi cho php, s cho php ca QoS trng mi trng th ang l thch thc. Kh nng linh ng ph trong khng gian: cc di bng trng th cng thay i khi m cc my di chuyn t ni ny qua ni khc. Do , vic phn phi ph tn hiu th tip tc l thch thc chnh trong h thng CR.2.2.3.4 chia s phTrong h thng CR, mt trong nhng thch thc chnh trong vic m c mt ph dng chnh l chia s ph. Chia s ph c th c coi nh l tng t vi s iu khin truy cp bt buc (MAC). Tuy nhin, khi chng ta nghin cu lnh vc ny, thc ra c nhiu thch thc khc cho vic chia s ph trong h thng CR. V s tn ti ng thi ca cc my ng k cng vi mt di ph trng rng chnh l hai nguyn nhn chnh cho nhng thch thc ny. Trong phn ny chng ta s tp trung vo nhng th thch c trng cho s chia s ph trong h thng CR, nu ln hng khc phc cc nhc im ny v tho lun v vic m rng hng nghin cu.Trc ht, cung cp mt danh mc nhng thch thc trong qu trnh chia s ph, chng ta cn phi lit k cc bc thc hin vic chia s ph trong h thng CR. Sau , nhng th thch ny v hng gii quyt chng s c trnh by mt cch chi tit hn. C 4 bc chia s ph nh sau: Cm bin ph (spectrum sensing): da vo s sn c ca ph, cc knh truyn c th c cho php s dng. S cho php ny khng ch ph thuc s sn c ca ph m n con ph thuc vo cc nguyn tc bn trong ca h thng. Do , vic thit k cho cc nguyn tc cho php ph hot ng tt hn l mt ch nghin cu quan trng. Truy cp ph (spectrum access): trong bc ny, mt vn chnh khc ca chia s ph l hnh nh. Bi v cc phn t ca h thng CR c gng truy cp vo cc ph, cc truy cp ny th c iu phi trnh s ng trong nhng phn chng ln ln nhau ca ph. S kt ni gia my pht v my thu (transmitter-receiver handshake): thit b nhn ca s lin lc my pht v my thu th c ch bo v thng tin ph c la chn. V vy, giao thc cho s kt ni gia my pht v my thu th cn thit cho h thng lin lc c hiu qu trong h thng CR. Ch rng, s hp tc kt ni y khng c ngha l lm hn ch giao thc ny gia my pht v my thu. S linh ng ph: mi nt trong h thng CR c xem nh khch mi ca ph tn s m n cho php. V th, nu cc c trng ca ph ang s dng m c yu cu bi my ng k th h thng lin lc cn tip tc duy tr vng ph trng khc. Do , s cm bin ph th cng quan trng cho s thnh cng ca qu trnh lin lc gia cc nt vi nhau.2.2.4 Kin trc vt lKin trc chung ca mt h thng thu pht CR c minh ha nh hnh 1.6. Trong cc b phn chnh ca h thng l phn u (RF Front-End) v phn x l bng gc (baseband processing unit). Mi b phn u c th c ti cu hnh thng qua ng iu khin (control) nhm thch ng vi cc iu kin thay i lin tc ca mi trng.

Hnh 6: B thu pht CR.Nu nh phn x l bng gc tng t nh cc h thng thu pht bnh thng th phn RF Front-End to nn s khc bit v tin b ca CR. Do vy, chng ta s tp trung tm hiu phn RF Front-End.

Hnh 7: Bng rng RF / kin trc analog front-end.u im ca phn RF Front-End trong h thng CR l kh nng cm bin bng rng, c th iu chnh n bt c phn no trong di tn s rng ln. Hn na n c th o lng cc thng tin ph t mi trng phc v cho chc nng cm bin ph. Cc b phn chnh ca khi RF Front-End gm c: RF Filter: c tc dng chn c khong bng thng mong mun bng cch cho tn hiu qua b lc thng di. LNA (Low noise amplifier): b khuch i nhiu thp c tc dng: loi nhiu tn s nh, khuch i nhiu thp tn hiu nh ng vo ca my thu ti mc cn thit i tn, tng nhy my thu. LNA thng c t mt n ba tng khuch i tuyn tnh, c iu hng chn lc tn s bng thng tn hiu mong mun. C tc dng khuch i tn hiu mong mun ng thi gim tn hiu nhiu. MIXER: ti b i tn th tn hiu thu c t my thu s c trn vi tn s gc c pht ra v c chuyn ti di bng gc hay tn s trung tn. VCO (Voltage controlled oscillator): c bit n nh l b iu chnh tn s bng in p. C tc dng nh b kha pha gip tn s ra n nh. Channel selection filter: c dng chn knh mong mun ng thi loi b knh k cn. C hai cch chn knh: direct convertion receiver v superheterodyne. AGC (Automatic gain control): l h thng hi tip iu chnh li my thu da vo bin tn hiu thu ng thi m rng di rng, cho php ta tng hoc gim khuch i khi tn hiu thu yu hay mnh bng cch thay i in p phn cc. PLL (Phase locked loop): l h thng hi tip vng kn. Tn hiu hi tip c dng kha tn s v pha ca tn hiu ra theo tn s v pha ca tn hiu vo.Thch thc i vi vic thit k kin trc cho CR l c th pht hin chnh xc tn hiu cng yu ca PU trong mt di ph rng.2.2.5 cc chun ca ha, Chun IEEE SCC 41T khi h thng qun l ph ph hp s dng SDR trong h thng CR bao gm nhiu k thut, nhiu phng php chun v nhng gi thit lin quan th tr nn quan trng. Nhng phng php x l chun v cc cuc kim tra ny c yu cu cho s pht trin v trin khai h thng mng CR. Tuy nhin, n by gi, hu ht cc nhm u ring r v lm vic c lp, do , kt qu th khng c s kt hp. gii quyt vn ny, th vic kt hp gia cc nhm li vi nhau v c trong cng nghip, v k nng v cc t chc khc l tht s cn thit. V chun IEEE Standards Coordinating Committee (SCC) 41 trong h thng CR v trong qun l ph c xy dng bt u mt chui cc chun lin quan gi l IEEE 1900. IEEE SCC 41 c xy dng nh a ch cho cc iu c ban hnh lin quan ti s pht trin, trin khai ci t v xy dng mt h thng CR v h thng qun l ph ph hp. IEEE SCC 41 th bao gm 4 nhm lm vic chnh v 1 nhm nghin cu. Mi nhm c nhim v cho mi chun cho cc kha cnh khc nhau ca h thng CR. Mi chun trong IEEE 1900 th c hng ti mi nhm lm vic. Sau khi hon thnh xong cc ti liu phc tho th cc nhm lm vic ny s gi cc bn tho ny ln cho IEEE bnh chn, vic bnh chn ny c thc hin bi IEEE Standards Association (SA). Nu m khng c bnh chn th h thng s loi tr bn tho ny. Sau khi quyt nh, bn tho s c bnh chn 1 ln na. Phng php ny th chc chn rng cc chun s c dng trong nhng cng vic khc nhau trong h thng CR. H thng IEEE 1900 bao gm: IEEE 1900.1: nhim v chnh ca tiu chun ny l xc nh v gii thch v nhng thut ng v nhng khi nim ca qun l ph, SDR, v tuyn thch nghi v nhng k thut khc. Tiu chun cng m t s tng tc gia nhng khi nim. Chun IEEE 1900.1 th c s dng nh l mt kt ni gia cc nhm lm vic trong IEEE SCC 41, bi v tt c cc nhm u nh ngha da trn tiu chun ny. IEEE 1900.2: tiu chun ny lin quan ti cc ngh trong thc t ca nhiu v s tn ti ng thi ca phn tch. Trong h thng CR, nhiu h thng khng dy v dch v c cho php cng tn ti trong cng mt v tr cng mt thi im. Cc thng s hot ng ti u ca cc h thng v cc dch v trn th l thng s ch yu qun l v trnh nhiu. Theo , mt khung cng vic cho tnh ton, nghin cu phn tch nhiu gia cc thit b khng dy v dch v th c gii thiu. Cc nhm ny s pht trin mt tiu chun gii quyt s xung t ng trong h thng CR. IEEE 1900.3: tiu chun ny th lin quan ti cc gi tr ph hp ca cu trc phn mm ca h thng SDR. Nhm cng vic ny s pht trin v nh ngha cc phng php cho vic tm gi tr ph hp ca cc cc b phn ca phn mm trong h thng SDR da trn cc thit b khng dy. Cng vc chnh ca tiu chun ny l m bo s tn ti ng thi v s ph hp trong phn mm. S ph hp ny c yu cu phi hp l v c chng nhn ca h thng CR. IEEE 1900.4: tiu chun ny th lin quan n s cung cp ng thi cho vic ti cu hnh cc giao din khng kh khng ng nht. S khng ng nht s l cha kho cho h thng khng dy m cc thit b di ng c th s dng k thut khng dy a knh mt cch ng thi. Nhm lm vic s nh ngha tt c kin trc ca h thng cng nh cng thc ca h thng. IEEE 1900.A: trch nhim ca tiu chun ny th lin quan ti s ph hp ca vic truy cp ph linh ng da vo thit b. Cc nhm nghin cu s nhn mnh s ph thuc v gi tr ca cc thng s ca thit b khng dy vi truy cp ph linh ng. Bi v mt thit b CR s phc tp hn so vi cc thit b c, nn mt gii thut hp l tr thnh mt th thch. Cc phng php mi cn c pht trin chc rng cc thit b s khng gy nhiu ln knh truyn ca thit b ng k. Vic nghin cu bao gm c s kh khn trong vic phn tch nguyn nhn ca nhiu. Nh sn xut phi trnh chng chc chn rng cc thit b s ph hp vi cc lut l.Cng c nhng tiu chun IEEE khc m cng lin quan ti cc lut l ca h thng khng dy v h thng CR nh IEEE 802.18, 19, 21, 22. IEEE 802.18 l mt tiu chun c dng cho cc nhm c trch nhim v s tham gia v s gim st qu trnh tin trin ca cc hot ng ca sng v tuyn trong nhiu h thng khc nhau v d nh IEEE 802.11 WLAN, IEEE 802.15 WPAN, IEEE 802.16 WMAN, IEEE 802.20 Mobile WLAN, IEEE 802.22 WRAN. Nhm tiu chun IEEE 802.18 ny c th a ra cc bnh lun n cc lut l ca b iu chnh thng tin ti cc nhu cu ca truy cp ph. IEEE 802.19 l nhm tiu chun dng trong s tn ti ng thi. Nhm ny s nh a ch cho cc gi thit tn ti ng thi gia cc h thng khng dy da trn tiu chun IEEE 802 (v d nh IEEE 802.11 v Bluetooth). Trong trng hp ny, khi mt tiu chun mi cho mt mng khng dy cha ng k c gii thiu, nhm tiu chun IEEE 802.19 s xt s m bo ca cc tiu chun chc chn rng tiu chun mi ny s cng tn ti vi s tn ti ca k thut ang hot ng trong cng 1 ph. Chun IEEE 802.21 l mt chun mi cung cp kh nng qun l ph linh ng cho c k thut ng b v khng ng b. N l tiu chun c bn cho h thng khng dy m cc thit b di ng c th s dng k thut khng dy ny. IEEE 802.22 l 1 k thut khng dy mi cung cp d liu thng tin trn mt khu vc rng ln. K thut ny s hot ng trn bng tn TV. Tuy nhin, chc chn rng cc dch v c khng b nhiu bi cc thit b IEEE 802.22, th h thng truy cp ph linh ng c cp ti. Mi quan h gia cc thnh phn IEEE SCC 41 nh trong hnh:

Hnh 1. 8: Mi quan h gia cc thnh phn IEEE SCC 41.b, Chun IEEE 802.22 cho khu vc mng khng dyC nhiu khong bng TV th cn trng rt nhiu trn nhiu khu vc. Nh bng TV 6 MHz c th s dng cho truyn d liu. Bi v cc bng TV th hu ht trong ph tn s thp (v d 54-862 MHz nam M v 41-910 MHz trn quc t) nn s truyn cc thng s th ph hp hn cho s truyn trong di di. Chun IEEE 802.22 c hng n k thut trong khu vc mang khng dy, m n ha hn s cung cp cho cc thit b di ng trong khu vc m bn knh c th ln n 100km. Bi v chun IEEE 802.22 th da trn h thng bng TV nn h thng CR ph hp s c dng trnh nhiu n cc dch v ng k.H thng kin trc ca chun IEEE 802.22 da trn WRAN th tng t nh mng truy cp khng dy bng rng (broadband wireless access (BWA)) nh IEEE 802.16 WiMAX. Trong thc t, mt WRAN th da trn kt ni im - a im m trong cc trm gc BS iu khin tt c cc kt ni. Lp vt l trong 802.22Trong lp vt l, s truyn dn ca chun IEEE 802.22 th hng n cc tn s m da vo truy cp dn tn s trc giao (OFDMA). Ghp cc bng TV c th c s dng 1 cch hp l tng cng dung lng ca h thng bng cch s dng k thut lin kt knh truyn. Knh truyn lin kt l k thut s dng b ghp knh cho s truyn dn ca dng d liu n. Mt k thut tng t c dng l chun IEEE 802.11 da trn WLAN. H thng v m ph hp t 0.5 bit/symbol/Hz n 5 bit/symbol/Hz s c cung cp cho chun ny. Mt mng IEEE 802.22 th c mong i s cung cp hn 10 ngi dng trn 1 mng t bo vi ng truyn ln v truyn xung vi lu lng ln lt l 1.5 Mbps v 384 kbps.

Hnh 9: Kt cu siu khung trong chun IEEE 802.22.

Hnh 10: Kt cu mt khung IEEE 802.22. Lp MAC trong 802.22Hnh trn ch ra cu trc khung ca lp MAC trong IEEE 802.22. Ti ni bt u ca khung, thng tin phn u ca khung superframe control header (SDH) th c truyn i bi BS trn nhng bng TV no c th. Phn m u c s dng bo v cc dch v truyn thng v trong khi SDH c s dng bi thit b s dng u tin CPE (consumer premise equipment) ng b vi BS. N bao gm tt c cc thng tin v CPE bt u kt ni. Ch rng, bi v theo yu cu ca FCC, th 2 bng TV cn li khng c s dng trnh nhiu cho dch v TV.V trong mt kt cu khung trong cc khung trn c a ra nh hnh. Truyn dn trong mi khung l cc khe thi gian v n da vo sng mang OFDM. Trong mt khung, c dng ln v dng xung ca khung con. Mt khung ph dng xung bao gm phn m u bt u mt khung. Sau , US-MAP v DS-MAP c dng chng t cu trc ca dng ln xung ca khung ph. Ch rng cu trc khung, siu khung, khung ph v khi li ca IEEE 802.22 th c iu khin bi BS. bt u mt kt ni vi BS, th mt CPE qut v xc nh cc bng TV trng m khng nh hng ti cc dch v khc. Da vo cc bng trng ny, CPE s qut tn hiu SCH nhn t BS. Sau khi nhn SCH, CPE c th bt u mt kt ni bng cch gi mt xc nhn ti BS. BS cho php truyn phn li v cho php CPE nhn trn khong trng ca ph. Cm bin knh trong chun IEEE 802.22Trong h thng 802.22, c BS v CPE thc hin cm bin knh theo chu k. Bi v cm bin knh c th trong khong bng hay ngoi khon bng nn c 2 giao din c yu cu ti CPE. Mt anten trc tip th c s dng kt ni vi BS, v mt anten ng hng th c dng cm bin ph. BS hng dn CPE cm bin bng TV, v kt qu cm bin s c gi tr li cho BS xy dng mt bn cc ph trng cho cc t bo m c dng qun l ph. Giao thc MAC cn c thit k cung cp cc yu cu ca qun l ph bao gm thay i knh truyn, s hon hay khi phc knh, s bao gm hay loi tr ca nhiu knh t mt knh truy cp. pht hin mt dch v TV truyn thng, h thng IEEE 802.22 cung cp my cm bin bng tn th v cm bin tinh nh hnh 1.11.

Hnh 11: C ch cm bin th v tinh trong h thng IEEE 802.22. ci thin h thng cho ph hp. Cm bin nhanh (hay gi l cm bin th), v d nh cm bin nng lng, th thc hin trong thi gian ngn gim s gin on trong truyn d liu. Kt qu ca s cm bin ny c s dng phn tch hot ng ca knh truyn. Nu c mt nng lng truyn dn c pht hin, th h thng cm bin tinh s hot ng. Gii thut ca cm bin tinh ny s tn thi gian xc nh cc tn hiu t dch v ngun. C 2 phng php cm bin th v tinh ny u p ng c yu cu ca chun IEEE 802.22. c bit, tn hiu TV s vi cng sut ngng l -116 dBm cng c pht hin vi xc sut pht hin gn 0.9 (gi tr ln nht ca xc sut bo sai l 0.1). H thng dch v th cn c pht hin trong vng khng qu 2 giy sau khi dch v ny bt u truyn d liu.

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III. Phng thc chia s ph tn3.1 Cc bc chia s ph tn trong v tuyn nhn thc c ci nhn tng qut vic chia s ph tn trong mng V tuyn thng minh chng ta s xem xt cc bc c c s chia s ph tn. Qu trnh chia s ph tn gm nm bc chnh:- Cm bin ph tn:Mt ngi s dng mng V tuyn thng minh ch c th chia s mt phn ph tn nu phn ph tn khng c s dng bi ngi s dng c giy php. Khi mt nt trong mng V tuyn thng minh quyt nh truyn trn ph tn no trc tin n phi nhn thc c s cn trng ca ph tn .- Phn b ph tn:Da trn cc thng tin v ph tn thu c t bc 1, cc nt mng sau c th phn b cho mt knh. Vic phn b ny khng ch ph thuc vo kh nng ca ph tn m cn da vo cc chnh sch ni mng cng nh ngoi mng.- Truy cp ph tn:Sau khi c c s phn b ph tn, cc mng truy nhp V tuyn thng minh tin hnh truy cp s dng ph tn. Vic truy cp ph tn cn m bo trnh s chng cho v ng gia cc thit b.- Bt tay gia cc thit b Thu-Pht:Khi ph tn c xc nh truyn thng, bn nhn trong qu trnh truyn c bit v ph tn c chn. Do , mt giao thc bt tay thu - pht rt cn thit cho thng tin trong mng V tuyn thng minh. Bt tay gia cc thit b gp phn m bo tc tuyn dn.Vic bt tay gia cc thit b Thu-Pht nhm lm tng hiu qu s dng ca mng V tuyn thng minh.- S dng ph tn linh hot:Khi m ngi s dng c cp php s dng li ph tn th cc nt mng V tuyn thng minh phi chuyn sang s dng ph tn mi m vn m bo QoS. S dng ph tn linh hot gp phn m bo qu trnh truyn dn khng b ngt qung.3.2 Cc phng php chia s ph tn trong v tuyn nhn thcTrong mngV tuyn thng minh,kh khn chnhkhi s dng ph tn m l vic chia s ph tn.Khng ging nh cm nhn ph lin quan chnh ti lp vt l, hay qun l ph lin quan ti cc dch v lp cao hn, cc chc nng chia s ph tng t vi cc cng ngh phn b ti nguyn v a truy nhp a ngi dng trong lp MAC ca cc h thng truyn thng ang tn ti. Vn chnh trong vic chia s ph l s cng tn ti ca cc ngi dng thng minh; ngi dng cp php v vic qun l cc bng thng khng lin tc c sn. C nhiu cch phn loi cc cng ngh chia s ph, nh da trn kin trc, da trn cch thc cp pht ph tn v da trn cc cng ngh truy nhp ph:

3.2.1 Cng ngh chia s ph tn da trn kin trc:-Chia s ph tn tp trung:Ton b cc nt trong mng gi thng tin cm nhn ph ca chng ti n v iu khin trung tm, sau n v iu khin trung tm s thit lp lc phn b ph. Chia s ph tn tp trung c th hin nh trong Hnh 2, mt u cui c cu hnh li ang c nhu cu s dng dch v video t mt server u xa thng qua cc mng con lin kt. Tt c cc mng con c iu khin bi mt b iu khin mng v tuyn (RNC). thit lp cc lung con, cc th tc sau cn c thc hin:+Bc 1: Bc bo hiu v khi to. RNC nhn mt ng dng t u cui di ng vi nhiu a ch truy nhp v tuyn. Sau khi c tnh c ti nguyn v tuyn hin c trong mng con c n iu khin, RNC s hi server u xa v tc trung bnh ch nh cho vic phn chia lu lng trn mi kt ni con (sub-link).+Bc 2:Lu lng c phn chia theo ng dng ca RNC (bc 1) v c gi n RNC. Cc lung con c dn nhn khc nhau.+Bc 3:RNC nhn c lu lng phn chia vi cc gi c dn nhn nh x vo cc mng con lin kt (v d lu lng vi nhn Vi ti WLAN, nhn Ai ti UMTS, i l ch s thng bo cho RNC v mi quan h v thi gian gia cc lung con). Cc dch v c th c p dng l:Cc lung con Video v Audio;HTTP vi s phn chia;HTTP vi s phn cng ca cc i tng chnh; Kh nng m rng lu lng Video; Lu lng thi gian thc v tn hiu iu khin ca n.+Bc 4: K thut ng b trong RNC lm gim tr c do mng v tuyn con gy ra bi cc nguyn nhn sau:Hot ng t ng lp li yu cu do cht lng kt ni khc nhau; Cc BTS khc nhau c cng sut x l khc nhau.

Hnh 13: Chia s ph tn tp trung-Chia s ph tn phn tn:Gii php ny thng c ngh trong trng hp m vic xy dng mt c s h tng l khng thch hp. phng php ny, khng cn mt thc th chia s ph tn trung tm m n yu cu cc knh iu khin trao i thng tin gia cc thu bao. Cc thu bao s t a ra cc quyt nh s dng ph tn c lp theo khu vc ni vng v m bo truyn dn tt nht v s dng t ph tn nht da trn cc thng s truyn tin. Gii php ny cho php pht trin mt loi mng mi t cu hnh nh l mng ad-hoc m khng cn bt k mt s thay i no trong cc h thng mng ang hot ng hin nay.3.2.2 Chia s ph tn da trn cch thc cp pht ph-Chia s ph tn hp tc:Mi nt chia s kt qu cm nhn ph ca n vi cc nt khc, sau thut ton phn b ph s quyt nh da trn cc thng tin ny. Gii php ny xem xt nh hng ca nt truyn vi cc nt khc. Ni cch khc, vic o c nhiu ca tng nt c chia s cho cc nt khc. Phng php chia s ph tn phn tn c th hin nh Hnh 3.Trong hnh, nt A, B, C hnh thnh nn mt nhm lin kt v s dng knh 1 nh l knh lin kt ca nhm. Cn nt C, D, E hnh thnh ln mt nhm lin kt khc s dng knh 2, cn cc nt D, F v G hnh thnh nn nhm th 3 v s dng knh 3. Bng cch t chc cc thu bao theo nhm, cc bn tin lin kt c phn b trn nhiu knh lin kt. iu c th gii quyt c s mt mt do nghn lu lng lin kt.

Hnh 3: Chia s ph tn theo c ch hp tc

- Chia s ph tn bt hp tc:Trivi c ch hp tc,chia s ph khng hp tc c ngha l cc nt t n quyt nh chia s ph.3.2.3 Chia s ph tn da trn cc cng ngh truy nhpTheo cng ngh truy nhp chia s ph tn c th chia thnh cng ngh chng ln (Overlay) v chm di (Underlay), c th hin nh trong Hnh 4.

Hnh 4: Chia s ph tn da trn cc cng ngh truy nhp

-Chia s ph tn chng ln:Trong phng php chia s ph tn chng ln, my thu pht V tuyn thng minh s ch c th truy cp vo phn ph tn c cp php khi ngi s dng c cp php khng s dng phn ph tn . Thc t th phng php ny chnh l vic ghp knh phn chia theo thi gian gia ngi s dng mng V tuyn thng minh v ngi s dng c cp php, do vy nhiu ti ngi s dng c cp php l nh nht. Phng php chia s chng ln c th hin nh Hnh 5.

-Chia s ph tn chm di (Underlay):Ngi s dng mng V tuyn thng minh s s dng cc cng ngh tri ph nh CDMA (a truy nhp phn chia theo m) hoc UWB (siu di ng bng rng) chia s bng tn vi ngi s dng c cp php.Vic s dng cc cng ngh tri ph s gip cho ngi s dng V tuyn thng minh c th dng trn ln bng tn ca ngi s dng c cp php bt k ngi s dng c cp php c s dng ph tn hay khng.Mt vn t ra trong phng php ny l ngi s dng V tuyn thng minh phi kim sot c cng sut pht ca mnh trnh gy nhiu ln ngi s dng c cp php. Cng ngh chia s ph tnchmthng c p dng i vi cc mng t ong v c minh ha nh Hnh 6.

Chng IV ng dng v thch thc ca v tuyn nhn thc4.1 ng dng thng tin khng dy nhn thcV tuyn nhn thc c ng dng rng ri trong vic ci thin hot ng h thng thng tin khng dy hin ti cng nh thit lp cc h thng thng tin khng dy mi.

Hnh 14: Phn loi ng dng v tuyn nhn thc.Nhm u tin bao gm cc ng dng v tuyn nhn thc ti u ha ti nguyn khng dy. Nhm th hai l ng dng ci thin cht lng thng tin. Nhm th ba v bn ln lt l ng dng trong kh nng tng kt v ng dng trong dch v.u th ca kh nng nhn thc trong h thng khng dy l khng c gii hn. Tuy nhin, v tuyn nhn thc cng i mt vi nhng thch thc. V d nh vic s dng ph yu cu phi xc nh nhng ph trng. Tuy nhin c th v tuyn nhn thc s khng pht hin ra s vng mt ca PU nu ch da vo mi SNR xc nh ph trng. Mt s mi trng fading nh hoc ln s lm gim cng tn hiu dn n pht hin sai. Vic pht hin c th tng tin cy thng qua h thng mng kt hp. Ngoi ra, SU cn thot khi ph ngay khi PU tr li. y cng l thch thc khng nh ca v tuyn nhn thc.

Hnh 15: Mt s ng dng v tuyn nhn thc v thch thc ca n.Qun l ph cng phc tp nh nh gi v la chn nhng ph mi thch hp cho nhu cu truyn hin ti. SU c th truy cp vo nhng on ph ring ti nhng v tr v thi gian khc nhau v truyn tn hiu cho cc h thng nhng khong ph khc. y cng l thch thc ca v tuyn nhn thc.Khi c nhiu ngi dng ng thi trong cng bng tn (v d nh bng ISM) th mc cng sut ca mi ngi dng phi c iu khin sao cho c th gim nh nhiu khng mong mun. Vic m ha d liu v ng truyn cng phi p ng nhu cu bo mt v bo v chng li s xm nhp.

Hnh 16: Mt s ng dng v tuyn nhn thc v thch thc ca n.Vic nh gi s dng ph cho SU cng l ti bn lun hin nay. Trong khi dch v ph cp php cung cp cho ngi dng vi c ch nh gi c thit lp t lu. trnh khai thc ph khng php khng cn thit v to cng bng cho ngi dng ph cp php th cn mt s c ch nh gi cho vic s dng ph khng php ny.Xt v lnh vc mng, ta cng c mt s thch thc cho v tuyn nhn thc nh xc nh v duy tr ng nh tuyn ti u, qun l mng hiu qu, thit lp knh iu khin tng thch. S linh ng ca ngi dng ph khng php cng to nn thch thc cho vic cu hnh mng ng. phc tp ca phn cng cng tng ln cng vi kh nng thng minh ca v tuyn nhn thc.V vy, kh nng v phc tp ca phn cng trong hin ti v tng lai l thch thc c th bin cc ng dng v tuyn nhn thc thnh hin thc. SDR c l ch l bc u tin trong qu trnh gii quyt vn ny. c th thc hin kt ni bt k ni u, thit b ca v tuyn nhn thc cn tun theo mt cch t ng vi chnh sch v qui nh thay i theo tng vng a l.Khi v tuyn nhn thc c a vo ng dng, cuc sng chng ta c th tr nn thoi mi, tin nghi, v d dng trong thng tin khng dy. Mun nh vy ta cn gii quyt cc thch thc v kh khn trong vic hin thc ha h thng v tuyn nhn thc.