Chương 1

Chng 1 TNG QUAN V H THNG THNG TIN DI NG

Gii thiu chngTrong chng ny s trnh by cc vn Lch s pht trin h thng thng tin di ng Cc vn c bn trong thng tin di ng M hnh knh pha inh a ng Lch s pht trin ca h thng thng tin di ng S gia tng ca cc thit b di ng thng minh thc u s tng trng ca cc dch v p ng nhu cu trao i thng tin gia ngi vi ngi, hi h thng thng tin di ng phi c nhng bc pht trin tng ng. Tnh n nay, h thng thng tin di ng tri qua ba th h, ang s dng rng ri th h th ba (3G), chun b ph bin th h th t (4G) v ang tng bc th nghim th h th nm (5G) .Th h th nht (1G) c xy dng theo quy m mng li quc gia v lm vic da trn nn tng cng ngh tng t. Nhng h thng 1G c xem nh nn mng, nh hng cho vic xy dng cc th h thng tin di ng sau ny.Th h th hai (2G) l th h u tin s dng cng ngh k thut s. H thng 2G a ngi s dng trao i thng tin vt qua ranh gii mt s quc gia nh cc thng s c tiu chun ha ton cu theo cc Cng c quc t.Ngoi vic truyn ting ni, 2G cn cn m ra cc loi hnh truyn s liu tc thp v nh du s ra i ca h thng v tuyn in, radio di ng, WLAN. S xut hin ca nhng dch v a phng tin di ng l bc tin gip con ngi tip cn gn hn n th h th ba (3G).Cng ngh truyn thng 3G l th h th ba ca chun cng ngh in thoi di ng, cho php truyn c d liu thoi v ngoi thoi (ti d liu, gi email, hnh nh).im mnh ca cng ngh 3G so vi cng ngh 2G l cho php truyn nhn cc d liu, m thanh, hnh nh cht lng cao cho c thu bao c nh v thu bao ang di chuyn cc tc khc nhau.Yu cu ca h thng 3G l:Tng dung lng h thng.Tng thch vi cc h thng thng tin di ng trc y (2G).H tr a phng tin.Dch v d liu gi tc cao.Vi thng tin v tinh (kh nng ph sng rng) tc ng truyn s liu c kh nng thay i.Cng ngh 3G l mt chun IMT-2000 ca T chc Vin Thng Th Gii (ITU). Tuy nhin, trn thc t cc nh sn xut thit b vin thng ln trn th gii xy dng thnh 4 chun 3G thng mi chnh: W-CDMA: Da trn k thut CDMA tri ph, l gii php thch hp vi cc nh khai thc dch v di dng s dng GSM,tp trung ch yu chu u v mt phn chu ( trong c Vit Nam). CDMA 2000: L th h k tip ca 2G CDMA. CDMA 2000 cung caaos tc d liu t 144 kbit/s ti trn 3 Mbit/s. Chun ny c chp nhn bi ITU. TD-CDMA: L mt chun da trn k thut song cng phn chia theo thi gian (Time-division duplex). y l mt chun thng mi p dng hn hp ca TDMA v CDMA nhm cung cp cht lng dch v tt hn cho truyn thng a phng tin. TD-SCDMA: c xem nh l mt gii php thay th cho W-CDMA. TD-SCDMA pht trin da trn giao thc ca S-CDMA.Do hn ch ca 3G v tc ng truyn v kh nng truy cp khi ngi dng di chuyn vi tc ln, nhng nghin cu gn y ang tp trung vo vic ng dng cng ngh 4G ti mt s ni trn th gii nh Nht Bn, Hn Quc,Vi cng ngh ny, tc d liu t trn 2M v c th ln ti 155Mbps trong mt s iu kin mi trng nht nh, m rng cc loi hnh dch v, ng dng, nng cao cht lng h thng v hiu qu s dng bng thng.Mng 4G t c nhng c im vt tri so vi 3G nh:Kh nng truy cp mi lc, mi ni, bt k ngi s dng thit b di ng no.Mng 4G s l s hi t u im ca cc cng ngh hin c. Ly ngi dng lm tm im. Mng 4G cung cp kt ni bng rng v bo m cht lng h thng trong iu kin mi trng thay i cho cc dch v a phng tin trong thi gian thc.Gii thiu 1 cht v mng 5G

Cc vn c bn trong thng tin di ng Suy hao ng truyn (Path Loss)S suy hao trn ng truyn l s suy gim mt ng nng lng ca sng in t khi n lan truyn trong khng gian. Suy hao trn ng truyn c th do nhiu nguyn nhn: do s m rng, lan truyn v mi hng ca sng v tuyn trong khng gian t do, hoc do sng in t b hp th v phn x bi nc, mt t, cy ci, cc ta nh v nhng vt th xung quanh khc. Khi tn hiu c truyn t mt pht qua khng gian n my thu, gi s rng khng c bt k mt vt chn no v tn hiu truyn trn mt ng thng t my pht n my thu (y gi l s lan truyn ca tn hiu trong khng gian t do). Khi , cng sut tn hiu thu c ti my thu l (2.5)Trong : (2.6)(2.7)Hiu ng bng rm (Shadowing)Nu ch c s nh hng ca suy hao trn ng truyn, cng sut tn hiu nhn c s bng nhau ti cc im cch my pht cng mt khong cch. Trn thc t, iu ny khng xy ra v ngoi suy hao ng truyn cn c cc yu t nh hng khc. Cc vt chn trn ng truyn t cc ta nh, cy ci lm sng in t b phn x nhiu ng khc nhau, nhiu trn nhng ng n cng khc nhau lm cng sut n cng khc nhau. Vic cng sut nhn c khc nhau trong cng mt khong cch cn gi l Shadowing. Vn Shadowing s gy nh hng chm khi ngi dng i t v tr ny sang v tr khc. V do nh hng chm nn Shadowing cn c gi l Slow fading.Hiu ng DopplerKhi c s chuyn ng tng i gia my thu, tn s thu c s thay i tng ln hay gim i ty thuc vo s di chuyn hng vo nhau hay ra xa nhau gia my pht v my thu. Hin tng ny c gi l hiu ng Doppler. Hiu ng Doppler lm cho ph tn s bn thu b lch so vi tn s trung tm mt khong, gi l tn s Doppler.Tn s Doppler (1.3.3)Fading a ng Fading c nh ngha l s thay i cng tn hiu sng mang cao tn ti anten thu do s thay i khng ng u v ch s bc x kh quyn, phn x mt t, nc trn ng truyn sng.Cc yu t gy ra hin tng fading bao gm: S hp th ca mi trng (cc phn t kh, hi nc, sng m). Mc suy hao ph thuc vo di tn s ta chn d truyn sng in t. S thay i chit sut ca tng in ly nh hng n h thng truyn tin s dng bc sng ngn Phn x nhiu ng t mt t, nc v vt cn trn b mt Tri t gy ra s lan truyn a ng. Cc hin tng khc x, tn x, nhiu x, sng in t khi gp vt cn gy nn giao thoa v tr ng truyn ca cc tn hiu. Phn x: Khi sng p vo cc b mt bng phng. Tn x: Khi sng p vo cc b mt khng bng phng v cc vt ny c chiu di so snh c vi chiu di bc sng Nhiu x: Khi sng va chm vo cc vt c chiu di ln hn nhiu so vi chiu di bc sng.Fading phng v fading la chn tn sFading phng (Flat fading)L fading m suy hao ph thuc vo tn s khng ng k v hu nh l hng s vi ton b bng tn hiu dng ca tn hiu. Fading phng do truyn dn a ng:Hnh thnh do phn x ti vt cn, s thay i ca khc x kh quyn v s di chuyn trong qu trnh truyn dn lm cho cng trng thu c u thu b suy gim.Trong cc h thng chuyn tip s, s bin thin ca khc x l nguyn nhn ch yu dn n hin tng truyn dn a ng m kt qu ca n l tn hao fading thay i theo tn s.Tuy nhin, h thng c bng tn hiu nh nn tn hiu suy hao fading a ng nh, do c th b qua v fading a ng c xem l fading phng. Fading phng do hp th:L hin tng sng in t b hp th v b tn x do ma, tuyt, sng m, hay cc phn t khc tn ti trong mi trng truyn dn nn tn hiu vo u thu b suy gim. Hin tng fading ny thay i ph thuc vo thi gian.Hnh (1.4)nh hng ca fading tc ng ln ton b di tn tn hiu truyn trn knh l nh nhau, do vic tnh ton d tr fading (fading margin) d dng hn (cc tn s trong bng tn u b tc ng nh nhau nn ch vic tng thm cng sut pht cho tt c bng tn). Fading la chn tn s (Frequency-selecting fading)L fading m suy hao thay i ph thuc vo tn s, xy ra khi bng tn ca tn hiu ln hn bng thng ca knh truyn. Do h thng tc va v ln c rng bng tn hiu ln (ln hn rng knh) s chu nhiu tc ng ca loi fading ny.Tc hi ln nht ca loi fading ny l gy nhiu lin k t ISI. Fading chn lc tn s tc ng ln cc tn s khc nhau l khc nhau, do vic d tr nh fading phng l khng th. Do khc phc n, ngi ta s dng mt s bin php: Phn tp (diversity): L mt phng php nng cao tin cy ca vic truyn tn hiu bng cch truyn mt tn hiu ging nhau trn nhiu knh truyn khc nhau my thu c th chn hoc kt hp nhng tn hiu thu c thnh mt tn hiu tt nht. Li dng vic truyn trn nhiu knh m ta c c i li phn tp, thng c o bng dB. S dng m sa li gim BER. Tri ph tn hiu: K thut tri ph v c bn l s dng mt m c bit tri ph tn hiu trong bng thng hp (thm ch rt hp) ra mt bng thng cc rng lm cho tn hiu truyn i rt ging nhiu trng c trong t nhin.

( on ni thiu tri tr vi cc loi nhiu)Thng tin trng thi knh truyn Trong truyn thng khng dy, thng tin trng thi knh truyn (CSI) cp n cc thuc tnh knh bit ca mt ng truyn vin thng. Thng tin ny m t cch mt tn hiu truyn t my pht n my thu v i din cho hiu ng kt hp, v d nh tn x, fadingCSI cn c c lng my thu, thng c lng t ha v a tr li my pht. V vy, my pht v my thu c th c CSI khc nhau, i khi c gi l CSIT v CSIR, mt cch tng ng.V c bn c hai mc CSI l CSI tc thi (instantaneous CSI) v CSI thng k (statiscal CSI).M hnh knh fading a ngKt lun chng Qua chng ny chng ta c ci nhn tng quan v lch s pht trin v cc vn trong thng tin di ng nh cc yu t gy suy hao tn hiu, mt s loi nhiu thng gp v m hnh ca mt knh fading a ng c c mt h thng thng tin di ng hin nay, ngnh vin thng tri qua nhiu bc bin chuyn ng k, t th h u 1G s khai da trn nn tng cng ngh tng t, n th h 2G c s ha t tc 50Kbps v hin nay cng ngh 4G tng tc bit ln ti 1Gbps (vi thu bao ng yn), tc l tng gp 20.000 ln. Vi nhiu u im vt tri, m rng loi hnh dch v v ti u ha cht lng, h thng thng tin di ng ang phc v tt nhu cu trao i thng tin ca con ngi thi k hin i.Cht lng tn hiu qua knh truyn v tuyn b tc ng bi nhiu yu t, nhng nh hng ln nht l fading, c bit l fading la chn tn s do s kh khn trong vic tnh ton c lng cht lng knh cng nh gim t l li bit bn thu. i vi cc mng di ng th h sau (3G, 4G), do yu cu tc bt ln nn cng cn phi tch hp nhiu k thut vo qu trnh truyn (m ha, phn tp ) nhm m bo cht lng dch v. Tt c nhng khi nim trong chng ny l nn tng xy dng m hnh m phng cho chng sau.

Chng 2 GII THIU S LC V H THNG IN BAND FULL DUPLEX

Gii thiu chng IBFD c gii thiu nh l mt gii php kh hp dn tng thng lng trong h thng thng tin lin lc v mng li khng dy. Vi IBFD, mt thit b khng dy cho php c truyn v nhn tn hiu ng thi trong cng mt bng tn s. < khc ni phi gii thiu IBFD l chi chi , tnh cht nh rng.>Chng ny trnh by v cc ni dung sau Gii thiu s lc v h thng In band full duplex (IBFD). H thng IBFD c th xy dng thnh cng trong thc t. nh hng ca self-interference ln IBFD v cch suy gim n.C hi tn dng Full Duplex nh gi cao li t IBFD, ta xem xt ba cu trc ( m hnh ) c bn trong hnh Fig 3 (a) Relay topology, (b) Bidirectional topology v (c) basestation topology Trong mi trng hp, cc thit b u cui c th c nhiu anten v s anten c th khc nhau. Ba cu trc lin kt c bn c ly cn hng t mng ad hoc v nn tng c s h tng (infrastructure-based)( v d: cell v WiFi). Trong mng ad hoc vi thit b IBFD, m hnh lu lng khc nhau dn n cu trc lin kt biu hin cc thnh phn khc nhau. Tng t nh th, cc cu trc bi-directional v base station c th c trong mng infrastructure-based vi thit b u cui IBFD.u tin xem xt cc cu trc lin kt relay th hin trong Hnh 3a, u cui R hot ng nh mt relay cho php cc dng d liu n gi t ngun S ti ch D. Nu relay R ch s dng trong knh truyn half-duplex th n s cn lun phin gia tn hiu nhn c t u cui S v chuyn tip sang u cui D nh th hin trong hnh 3a. Tuy nhin, nu u cui R s dng trong knh truyn IBFD, n c th nhn v chuyn tip ng thi (trn cng mt tn s), nh th hin trn hnh 3a. Nh vy, bng cch hot ng ch IBFD, mng relay c th tng gp i hiu qu quang ph tng i ( the spectral efficiency) ( n v bit/s/Hz) so vi half-duplex. Ch rng, mng relay IBFD yu cu ch c relay R l hot ng ch full-duplex, cn S v D khng nht thit phi thu pht ng thi.Tip theo xem xt cu trc hai chiu hnh 3b, ni c 2 lung d liu: u A gi d liu n u cui B v u cui B gi d liu cho u A. Nu mt trong hai thit b A hoc B ch c th hot ng ch half-duplex, th giao tip gia AB khng th xy ra ng thi nh giao tip BA c, v 2 giao tip ny phi c thc hin qua 2 khe thi gian trc giao, nh trong hnh 3b. Tuy nhin, nu thit b u cui A v B cng h tr IBFD, th thng tin t AB c th truyn ng thi vi chiu ngc li. Do c kh nng tng gp i hiu qu quang ph so vi half-duplex.Cui cng, xt trn cu trc cc trm gc ca hnh 3c, ni cng tn ti 2 lung d liu: thit b u cui TU gi d liu trn ng uplink n trm gc BS v BS gi d liu trn ng downlink c lp n thit b u cui TD. Nu BS ch half-duplex th n phi lun phin gia tn hiu thu c t u cui TU trong 1 khe thi gian v tn hiu pht t u cui TD trong khe thi gian trc giao vi n (nh hnh 3c). Tuy nhin, nu BS c th hot ng ch IBFD, th n c th h tr ng thi trong bng tn uplink v downlink,lm tng gp i hiu qu quang ph. Ging nh cu trc relay, ch phn t BS mi cn h tr IBFD, thit b u cui TU v TD khng cn phi truyn nhn ng thi.Self-interferenceTrong hnh 3, mi tn en i din cho tn hiu mong mun truyn i v mi tn ch s giao thoa.C 2 trng hp giao thoa, mt l self-interference xy ra khi cc tn hiu c truyn bi thit b u cui IBFD cn tr vic tip nhn cc tn hiu mong mun ti cng u thu. Hai l inter-terminal interference xy ra trong h thng gia cc thit b u cui khng h tr IBFD. V d, trong cu trc relay hnh 3a, truyn tn hiu u cui S c th gy nhiu giao thoa n u thu D, trong khi cu trc trm gc, hnh 3c, u pht TU c th gy nhiu cho u thu TD, inter-terminal interference khng th pht sinh trong cc mng ny khi ch half-duplex. t c gp 2 hiu sut quang ph l tng trong IBFD, yu cu phi kim sot c c self-interference v inter-terminal interference. V t can nhiu l yu t hn ch ca mng IBFD ( nhiu hn hn inter-terminal interference) nn trong n ny, ta s tp trung tm hiu v self-interference. Mt s phng php suy gim self-interferenceCu to ca mt b thu pht IBFDCu to ca mt thit b u cui IBFD nguyn mu v mi trng hot ng ca n c biu din hnh bn di. Hnh 4a trnh by s mt anten tch IBFD vi nhiu anten pht v nhiu anten thu. M hnh anten shared cng c cu trc tng t ngoi tr mi cp anten pht thu trong hnh 4 s thay th bi mt circulator gn lin vi mt anten thng, nh trong hnh 2b. S khc bit gia anten tch v anten shared s c trnh by phn tip theoa v y ci BFD system vi anten share..

Cc thit b u cui IBFD chp nhn mt dng bit truyn c m ha v iu ch trong min s, to ra mt tn hiu s di nn ring bit cho mi anten pht. Mi tn hiu s ny u c chuyn i sang analog vi b DAC, upconverted n mt tn s sng mang cao, khuch i bng b khuch i cng sut cao (HPA), v bc x ra mi trng bng anten. Trong thc t, qu trnh ny s a vo mt s non-idealities trong tn hiu pht (v d, DAC lng t ting n, nhiu dao ng pha v khuch i mo), dn n cc khc bit nh, nhng quan trng gia tn hiu truyn thc t (actual) v tn hiu d nh (intended).ng thi, cng mt bng tn s, cc chc nng ca thit b u cui IBFD nh l mt my thu. Mi tn hiu c chn bi anten thu l thng lng vo ca chui phn cng ring bit, trong bao gm b khuch i tp m thp (LNA),downconverter,v analog-to-digital converter (ADC). Cc kt qu tn hiu s di nn s c x l trong min s (lin quan n gii iu ch, cancellation self-interference, v gii m bt) cung cp cc dng bit nhn. Mt khc, cc mch Canceler c th nhn thy trong hnh 4, cng nh cc ty chn khc khng th nhn thy t s s c tho lun trong phn tip theo.% C hai cch pht v thu x l dy chuyn c th c giao tip vi anten. Mt l kin trc (cu trc) anten-tch, minh ha trong hnh 2b. Trong kin trc anten tch, mi chui truyn s dng mt anten bc x chuyn dng v mi chui nhn c n nh mt anten cm bin. Trong khi cu trc anten shared, mi cp chui pht/ chui thu chia s anten chung. Shared anten hot ng i hi mt b song cng mi nh tuyn tn hiu pht t my pht ti anten v nh tuyn tn hiu thu trn anten ti my thu, trong khi c lp tt c cc chui my thu n chui my pht. Mt phn quan trng trong anten shared song cng l circulator, l mt thit b ferrite, c th nh tuyn trc tip bng cch khai thc truyn dn phi tuyn tnh trong vt liu t tnh[]. Cc thit b ng dn sng nh: b ghp nh hng, my bin p Hybrid cng c th c s dng nhn ra mt anten shared song cng.% ci ni a ln trn, u mcMt thit b u cui IBFD vi N chui pht v N chui thu s yu cu 2N anten trong h thng anten tch hay N anten cng N circulator trong h thng anten shared. Propagation-domain Self-interference SuppressionK thut c lp truyn lan khng dy nhm mc ch in t ha c lp cc chui pht t chui thutc l, ngn chn self-interference trc khi n xut hin trong chui mch thu. u im u tin thc hin suy gim self-interference trong min lan truyn l phn cng cc dng downstream thu c khng cn phi x l tn hiu 1 cch trung thc vi phm vi hot ng rt ln. Trong cc h thng anten tch, min lan truyn cch ly c hon thnh bng cch kt hp ng path loss, phn cc cho, v anten directionality, trong khi h thng anten shared thc hin bng cch s dng mt circulator.Trong h thng anten tch, suy hao ng truyn gia cc thit b u cui IBFD ca anten pht v thu (hoc anten mng) c th c tng ln bng cch t khe chn hp th gia chng. Mc d k thut path loss rt hp dn v l do n gin, nhng vn b mt s hn ch nh: cc thit b nh hn, phng thc hin cc k thut khng c nhiu.Analog-circuit-domain Self-interference Cancellation K thut analog circuit domain cancellation nhm mc ch ngn chn self-interference trong chui thu analog, trc b ADC. S ngn chn ny c th xy ra trc hoc sau b downconverter v LNA. Hnh 4 cho thy, khi tn hiu pht c khai thc ti ngun cp anten pht, x l trong min analog v tr vo ngun cp d liu anten thu hy b self-interference. % Nhng c mt vi cch khc, chng hn nh khai thc tn hiu pht trong min s, p dng nhng iu chnh cn thit nh li, pha,tr. Sau chuyn i n sang min analog circuit s dng trong self-interference cancellation.% thuyt trnh%.Ging nh cc i tc trong min lan truyn, k thut cancellation analog circuit domain hoc c th l knh nhn thc hay l knh v thc. K thut knh v thc ch c th hy b interference trn ng dn trc tip, cn k thut knh nhn thc c kh nng hy b c interference trc tip v phn x. i vi tn hiu hp, cc self-interference (trc tip hoc phn x) c th c m hnh ha nh mt h s phc v tr gia mi cp anten pht v thu. Trong trng hp ny, mt anten ring bit thit b u cui IBFD vi anten thu pht n ch iu chnh h s ko nn phc n v tr n. Knh truyn v thc s iu chnh 1 ln, khi h thng c thit k/hiu chun, trong khi knh nhn thc s iu chnh lin tc h s ny v tr b p cho nhng thay i trong knh phn x. i vi tn hiu bng rng, cc ng dn trc tip t can nhiu c th c gim nh bng cch s dng cng mt k thut analog circuit domain m t trn nu li anten v p ng pha thit k c tn s phng. Knh truyn phn x t giao thoa s l knh chn lc tn s nh kt qu ca truyn lan a ng. Vic la chn tn s ny s lm cho mch analog circuit domain cancellation ( mch hy b can nhiu min tng t) thm nhiu thch thc, c bit khi cc tn hiu truyn ti c khai thc v x l trong min analog, k t n s yu cu mt b lc tng t thch ng cho mi cp anten thu pht. Mt khc, khai thc tn hiu truyn trong min k thut s to iu kin cho vic s dng thch ng lc k thut s cho ng cancellation phn x thng d dng hn nhiu, nht l trong cc tn hiu bng rng nh OFDM.Digital-domain Self-interference CancellationK thut hy b cancellation nhiu min s nhm mc ch hy b cancellation nhiu sau khi ADC bng cch p dng k thut x l tn hiu (DSP) phc tp vo cc tn hiu nhn c. u im ca vic lm ny trong lnh vc k thut s l x l phc tp tr nn tng i d dng. V d, trong khi nhn c chm tia (beamforming) trn nguyn tc c th thc hin trong mch tng t, n ph bin hn trong thc t thc hin bng k thut s, v nhng l do mch phc tp v cng sut tiu th. Tuy nhin, nhc im ca mch hy b k thut s l vng hot ng ca ADC gii hn s lng self-interference c th ngn chn.Bc u thit k mt b hy b cancellation nhiu k thut s l xy dng mt m hnh h thng ri rc m gi li tt c mi th gia DAC v ADC ca IBFD u cui, k c k thut lc b giao thoa trong min truyn lan v min tng t c m t trc . Mt m hnh chnh xc s cn phi nm bt khng ch bn thn thit b u cui IBFD m cn gia cc knh truyn lan anten, thm ch c cc thit b nm ngoi mng IBFD.

Chng 3 C LNG KNH TRUYN TRONG H THNG FULL DUPLEX

Gii thiu chng H thng ful duplex trong thc t rt kh c to ra do phn ln nh hng ca self-interference, kh c hon ton self-interference trong h thng ta cn thit phi bit c p ng knh truyn gia my pht v my thu. V th, chng ny chng ta s tp trung c lng knh truyn ti di nn trong mt b thu pht duplex.K thut tin m ha Zero Forcing (ZF)V c bn, cc c lng d self-interference c tr vo tn hiu nhn c trong min s. Mt s k thut s self IC s dng li trung bnh bnh phng v a anten, nh zero forcing.Trong truyn dn v tuyn, s phn tp ngi dng l yu t chnh lm tng nh k lu lng h thng. Do cn c nhng k thut m ha ti u pht trc khi pht tn hiu i trn knh truyn t c li v thng lng. c gi l k thut tin m ha.C hai loi tin m ha chnh: tin m ha khng tuyn tnh (nhiu lon vector..) v tin m ha tuyn tnh ( ti thiu bnh phng li MMSE, zero-forcing ZF)Sau y ta ch kho st k thut tin m ha tuyn tnh ZFTn hiu thu c ti anten thu c th c biu din nh sau:

Trong , l thnh phn can nhiu, lm suy gim ng k hiu sut ca h thng.

Nhim v khi thc hin k thut tin m ha l tm cc trng s sao cho tha iu kin sau ti thiu ha thnh phn can nhiu:

tm c cc trng s, ta biu din di dng vector nh sau:

Vi

ti thiu ha can nhiu ma trn tin m ha W c th c tm bng cng thc:

Do : Vector y c th vit li

Vi l dng vector ca tn hiu c pht i ti M anten trm gc.

V trm gc c gii hn cng sut pht ti a l . Do vy vic xc nh ma trn W phi tha mn iu kin

Vi

Voi Sau tin m ha ZF, tn hiu nhn c ti D la

Thit k ma trn tin m ha Vic thit k ma trn tin m ha ti S v D phi tha mn hai iu kin: Cng sut pht phi tha mn iu kin gii hn Mi thu bao khng thu c thng tin ca thu bao khc Thit k ma trn tin m ha ti S - PMa trn tin m ha P c xc nh:

Ds l ma trn ng cho c tc dng m bo cng sut pht ti trm gc tha iu kin gii hn. Khi , tn hiu thu c ti D

Cng sut pht tng cng ti trm gc vi ma trn tin m ha P:

Mi anten c cng sut pht bng 1, ta chn

Khi tng cng sut pht ti trm gc

tha yu cu gii hn cng sut.Thit k ma trn tin m ha ti D - Wm bo khng c nhiu xuyn knh ti thu bao s dng ma trn tin m ha W ti ch.Ti ch, bn tin c pht i c dng

Trong cng khe thi gian, tn hiu thu c ti u S l:

tha cc iu kin, ma trn W c thit k l

Dr L ma trn ng cho tha iu kin gii hn cng sut. Khi cng sut pht ti D

Trong , l t s tn hiu trn nhiu SNR, du xp x xy ra khi t s SNR ln.Trace c tnh cht hon v vng nn ta c

V cng sut pht ti mi anten bng 1, nn iu kin gii hn cng sut l Pow M. t iu kin ny, ta chn

Cc k thut c lng Trong h thng khng dy full duplex, chui bit thng tin c iu ch thnh cc k t PSK/QAM, truyn qua knh truyn khng dy. Tn hiu nhn c thng b mo do cc c tnh ca knh truyn. Do cc k thut c lng c a ra xc nh p ng knh, nhm khi phc li chui bit truyn i mt cch chnh xc nht.c lng 1D c lng 1D l k thut dng cc thng tin mt chiu, thi gian hoc tn s c lng. Trong min tn s gm cc k thut c lng: c lng bnh phng ti hiu (LS estimator) Thut ton ni xung p ng xung hu hn FIR c lng ti thiu sai li trung bnh bnh phng (MMSE estimator) c lng Gaus-Markov.Di y s gii thiu v k thut c lng LS v MMSE c lng bnh phng ti thiu (Least Square estimator)Cc k t dn ng (pilot symbol) c m t bng ma trn

X l ma trn ng cho vi cc phn t ca x

c lng LS s tm p ng knh h bng cch ti thiu bnh phng li

Trong

T suy ra p ng xung c lng ca knh truyn

Trong

Chuyn qua min tn s, p ng tn s ca knh truyn

T

Vi X l ma trn cha cc k t dn ng v y l k t nhn c th k thut c lng LS trong min tn s c n gin bng cch chia bin i Fourier ca k t nhn c cho k t dn ng truyn i.c lng ti thiu sai li trung bnh bnh phng (MMSE)MMSE l k thut ti thiu ha sai li trung bnh bnh phng cho tt c cc c lng tuyn tnh.B c lng MMSE c m t mt cch tng qut:

Trong

Tt c cc k t block u l k t dn ng, do p ng knh ti v tr cc k t dn ng trong min tn s cng l p ng ton b knh .

c lng 2DNhng phng php c lng trn ch dng hm tng quan gia cc sng mang con trong mt mc thi gian c lng. Vic c lng s chnh xc hn nu ta s dng thng tin c hai min thi gian v tn s, l k thut c lng 2D.Cch tip cn xy dng b c lng 2D n gin nht l dng hai b c lng 1D, mt b c lng knh trong min thi gian, mt b c lng knh trong min tn s. Trong vic c lng trong min thi gian c thc hin trc. Sau y l thut ton c lng n gin:

Trong

c lng thch nghiB c lng thch nghi l b c lng thng xuyn cp nht cc thng s ca knh truyn do h qu ca vic thay i h thng knh truyn. l im khc bit c bn nht so vi c lng 1D v 2D nh trnh by trn. Trong n, phn ny ch mang tnh cht gii thiu.c lng knh truyn trong h thng full duplex M t h thng

M hnh h thng n gin c m t nh trn Trong , ti my pht v my thu bao gm mt anten pht v mt anten thu. Gi s ng truyn ca hai thit b u cui l ng truyn trc tip. Tn hiu s c giao tip ch trong cng pha, trong cng mt khe thi gian v cng tn s.u tin, my pht truyn tn hiu thng qua anten T1 n anten R2 ca my thu, cng lc ti my thu cng pht tn hiu t anten T2 n anten R1 ca my pht.Tn hiu nhn c ti anten R2 ca ngoi tn hiu mong mun, cn c thnh phn t can nhiu bi chnh anten T2 nm trong n. c biu din nh sau:

Trong x1, x2 l tn hiu truyn i t v , H1 v H2 l p ng knh truyn gia Trong cng thi im, anten T2 bn my thu pht tn hiu qua R1. Tn hiu nhn c c biu din

Nu u cui bit c ma trn p ng knh H1 v H2 n c th trit c nhiu trn ng truyn m n nhn c. V vy chng ta tp trung vo cc thng s trng thi knh thu ti R1 ti u cui.

Phn sau chng ta s c lng H da vo k thut c lng LS.c lng knh truyn s dng k thut c lng LS c lng knh truyn, c hai u cui truyn i chui Np k t dn ng vi Tn hiu nhn c ti R2 c biu din

Trong X1,X2 l ma trn k t dn ng c xc nh

t

c lng LS my thu l

Vi : p ng knh c lng ca H1 v H2X l ma trn gi o ca ma trn XDa vo c lng H1,H2 ,tn hiu dn ng ti R2 s c truyn v ti u cui R1Tn hiu nhn c ti u cui R1 c biu din

Khi , c lng ton b knh truyn s l

Vi iu kin Np>M1+M2 pilot, chng ta c lng c p ng knh H1 v H2 ti my thu, p ng knh H11 v H21 ti my pht.Kt lun chng chng ny, ta tm hiu c k thut c lng c bn v p dng k thut LS c lng p ng knh truyn ca h thng thng tin hot ng trong ch full duplex. H thng ny vn cn kh mi vi hin ti, nhng c nhiu trin vng trong tng lai. c bit em li li ch gp hai ln hiu qu quang ph.Trong h thng Full Dupex a anten, gim t l li bit m gip cho h thng hot ng tt hn, phi s dng k thut tin m ha loi b can nhiu t cc sng mang ln cn. C nhiu k thut tin m ha khc nhau, nhng trong phm vi n ch tm hiu k thut tin m ha Zero-Forcing, tc l trc khi pht, tn hiu s c nhn vi mt ma trn bit trc, c tnh ton sao cho bn thu c th phc hi li tn hiu ban u, cn thnh phn can nhiu t tn hiu khc s b trit tiu.H thng vin thng v tuyn no cng cn phi thc hin vic c lng knh nh gi kh nng phc v knh c tt hay khng. Trong trng hp ny l phc v cho vic loi b self-interference trong h thng full duplex. c lng knh truyn s m phng trong chng sau, em chn k thut c lng dng thut ton LS, mt thut ton khng qu phc tp nhng so snh, nh gi cht lng knh truyn khi thay i thng s ca knh.Chng tip theo s tin hnh m phng h thng knh truyn full duplex ta thy r hn nhng g tm hiu.

Chng 4 M PHNG

Gii thiu chng Chng ny s trnh by cc kt qu m phng c lng knh truyn trong h thng full duplex Kho st cht lng h thng full duplex khi thay i s lng bit pilot Kho st cht lng h thng full duplex khi thay i kiu iu ch Kho st cht lng h thng full duplex khi thay i knh trynMc chnh xac ca c lng LS trong h thng full duplexThit lp cc iu kin ca knh truyn m phng:1.Ti my pht v my thu, mi bn dng 1 anten pht v 1 anten thu2.iu ch theo kiu QPSK3.Thc hin knh truyn CSI bit, so snh vi knh truyn s dng c lng LS v knh khng dng k thut c lng 4. Trao i thng tin vi 2 thit b u cui. Tnh BER c thc hin ti my pht 5. S dng p ng knh theo m hnh knh truyn Rayleigh fading, c xt n tc ng ca AWGN.