Synchronization in Cognitive Overlay Systems_Vu Van Minh

8/13/2019 Synchronization in Cognitive Overlay Systems_Vu Van Minh

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im: ..... (b ng ch ..)

Ngy . thng . nm Gio vin h ng d n


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im: ...... (b ng ch ..)

Ngy . thng . nm

Gio vin ph n bi n


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L I C M N

ho n th nh n n y, em xin t lng bit n s u sc n c gio TH.S Ph m

Th Thy Hin, tn t nh h ng d n em trong su t qu tr nh vit n tt nghi p.

Em xin ch n th nh c m n nh tr ng to iu ki n gi p em c th ho nthnh n tt nghi p. C m n cc thy c trong khoa Vi n Th ng v cc thy ckhc trong H c Vi n C ng Ngh Bu Ch nh Vi n Th ng truyn t kin thc trongnhng n m hc t p ti tr ng. V i vn kin thc c ti p thu trong qu tr nh hc t pkhng ch l nn t ng cho qu tr nh nghi n cu n m cn l hnh trang qu bu em b c vo i mt cch vng chc v t tin.

Em c ng xin c m n gia nh v bn b lun ng vi n kh ch l , to mi iuki n tt nht trong qu tr nh hc t p, c ng nhqu tr nh thc hi n n.

Mc d em c gng nhi u nhng chc chn n cn nhiu thiu st. Emmong th y c ti p tc ch b o v gi p thm n ng y cng ho n thi n h n.


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MC L C

L I C M N ................................................................................................................ i MC L C .................................................................................................................... iii

DANH M C HNH V................................................................................................. v THU T NG VIT T T ........................................................................................... vi L I M U ................................................................................................................ 1 CHNG I TNG QUAN V V TUYN COGNITIVE ...................................... 3

1.1 GII THIU CHUNG ........................................................................................... 3

1.1.1 M c ch nghin cu mng v tuyn Cognitive ........................................... 3 1.1.2 c im ca mng CRN .............................................................................. 6

1.2 CNG NGH V TUY N COGNITIVE ............................................................ 7 1.2.1 Khi ni m v tuyn Cognitive ....................................................................... 7 1.2.2 Kh nng ca thit b u cui v tuyn Cognitive ...................................... 8 1.2.3 C u trc vt l ca thit b u cui CR ...................................................... 10

1.3 KI N TRC MNG V TUY N COGNITIVE ............................................. 12 1.3.1 Ph n loi kin tr c mng v tuyn Cognitive ............................................. 13 1.3.2 Ki n tr c mng v tuyn Cognitive ............................................................ 16

1.4 MT S K CH B N TRI N KHAI M NG V TUY N COGNITIVE ......... 18

1.4.1 M ng v tuyn Interweave Cognitive. ......................................................... 18 1.4.2 M ng v tuyn Underlay Cognitive. ............................................................ 19 1.4.3 M ng v tuyn Overlay Cognitive ............................................................... 20

1.5 NG D NG CA MNG V TUY N COGNITIVE .................................... 22 1.5.1 M ng cho thu.............................................................................................. 22 1.5.2 M ng l i Cognitive .................................................................................... 22 1.5.3 M ng khn c p ............................................................................................. 22

1.5.4 M ng qun s............................................................................................... 23 CHNG II CC NH H NG C A KNH TRUYN V TUYN ............... 24

2.1 GII THIU ........................................................................................................ 24

2.2 CC TC NG CA PH N CNG KHNG L T NG ......................... 24 2.3 CC THNG S CA KNH V TUY N ..................................................... 25

2.3.1 Tr tr i Excess Delay................................................................................. 26 2.3.2 L lch tr cng sut ..................................................................................... 27 2.3.3 Bng thng nht qun Bc .............................................................................. 28

2.3.4 Bng thng nht qun v tn hiu tham chu n min tn s.......................... 28 2.3.5 Tr i Doppler .................................................................................................. 29


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2.3.6 Th i gian nh t qun v cc tn hi u hoa tiu min th i gian ........................ 30 2.4 CC M HNH KNH TRONG H THNG THNG TIN V TUY N ...... 31

2.4.1 Knh Gauss................................................................................................... 31 2.4.2 Knh Rice..................................................................................................... 32 2.4.3 Knh pha inh Rayleigh............................................................................... 32

2.5 K T LU N ......................................................................................................... 33

CHNG III NG B TRONG H TH NG OVERLAY COGNITIVE ......... 34 3.1 NG B TRONG CC H THNG V TUYN THNG DNG VCOGNITIVE ............................................................................................................. 34

3.1.1 ng b trong cc h thng thngtin. ......................................................... 34 3.1.2 ng b thi gian v tn s trong h thng OFDM .................................... 36

3.1.3 ng b trong ng xung ca h thng LTE ........................................... 45

3.1.4 ng b trong h thng DVB-T ................................................................... 50 3.1.5 ng b trong h thng v tuyn Overlay Cognitive .................................. 54

3.2 O LNG V PHN TCH KT QU TRONG CC H TH NG LTE,DVB- T V OVERLAY COGNITIVE...................................................................... 56

3.2.1 ng b th i gian, t n s v tm trong h thng LTE ............................... 56 3.2.2 ng b th i gian, t n s trong h thng DVB-T ........................................ 62 3.2.3 ng b trong h thng Overlay Cognitive ................................................. 66

3.3 K T LU N ......................................................................................................... 71 K T LU N CHUNG ................................................................................................... 72

PH LC A .................................................................................................................. 73

PH LC B .................................................................................................................. 89

TI LIU THAM KH O ........................................................................................... 97


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DANH M C HNH V Hnh 1.1 S dng ph Berkerley, M ........................................................................... 4 Hnh 1.2 Khi nim h ph ............................................................................................ 5 Hnh 1.3 B thu pht CR ............................................................................................... 11

Hnh 1.4 u cui RF tuy n thu .................................................................................... 11 Hnh 1.5 Kin trc mng t p trung ................................................................................ 13 Hnh 1.6 Kin trc Ad-hoc ............................................................................................ 14 Hnh 1.7 Kin trc hnh l i.......................................................................................... 15 Hnh 1.8. Kin trc mng v tuyn Cognitive .............................................................. 16 Hnh 1.9 Chia s ph tn trong m ng Underlay Cognitive ........................................... 19 Hnh 1.10 Chia s ph tn trong m ng Overlay v Underlay Cognitive ...................... 21 Hnh 3.1 B iu ch BPSK v i cc thng s c c tnh....................................... 35 Hnh 3.2 S khi h thng truy n d n OFDM ......................................................... 37 Hnh 3.3 H s nh th i phn m u ca mt mng WLAN trn knh AWGN 20dB,chiu di FFT l 512 v chiu di CP l 64................................................................... 40 Hnh 3.4 H s nh thi v u ra lc phi h p ........................................................... 41 Hnh 3.5 M hnh ca k hiu OFDM trong mi n th i gian ......................................... 42 Hnh 3.6 Mt phn cc m u thu c tn hi u DVB-T ch 2K, kho ng b o v v i SNR l 20dB............................................................................................................ 44 Hnh 3.7 Cu trc l i ti nguyn khng gian th i gian tn s ca LTE. .................. 46 Hnh 3.8 Cc k hi u ng b s cp v th c p trong m t khung LTE ...................... 48 Hnh 3.9 Phn b sng mang ca DVB- T (cha chn khong b o v )......................... 51 Hnh 3.10. Phn b cc hoa tiu ca DVB-T ................................................................ 52 Hnh 3.11 l n v pha ca p ng tn s knh ti tr l 20 mu ............................. 55 Hnh 3.12 Kch b n m phng cho ng b v tm kim trong LTE......................... 57 Hnh 3.13 u ra tng quan cho ca tn hiu LTE v i cc chui s cp c ch s gc29, 25, 34 ....................................................................................................................... 58 Hnh 3.14 u ra c a thut ton pht hi n nh ............................................................ 59 Hnh 3.15 u ra tng quan cho ca tn hi u thu c v i cc chui th c p ......... 59 Hnh 3.16 Pha t tng quan ca tn hiu LTE sau khi hi u ch nh pha ........................ 60 Hnh 3.17 Chm sao BPSK ca tn hi u LTE sau khi ng b v cn bng ................. 61 Hnh 3.18 l n ca li do FO trong h thng DVB-T .............................................. 61 Hnh 3.19 u ra t tng quan ca tn hiu DVB-T ................................................... 63 Hnh 3.20 Pha u ra t tng quan ca tn hiu DVB-T ............................................. 63 Hnh 3.21 Pha u ra t tng quan sau khi hiu ch nh pha ......................................... 64 Hnh 3.22 l ncalidoFOtrongh thngDVB-T ....................................................... 64 Hnh 3.23 Pha do dch ly m u theo cc sng mang con.............................................. 65 Hnh 3.24 Cc k hi u chm sao 16QAM ca mt tn hiu DVB- T sau khi cn bng 65 Hnh 3.25 p ng pha c a knh overlay chuyn ti p ................................................. 66 Hnh 3.26 l n li i v i SNR cho cc FFO tng i tr c v sau khi b FFO .. 67 Hnh 3.27 Dch tn c tnh tng i v dch tn tng i ...................................... 68 Hnh 3.28 Cc k hi u chm sao s cp tr c (tri) v sau (phi) khi cn bng .......... 68 Hnh 3.29 Cc k hi u chm sao th cp tr c (tri) v sau (ph i) khi cn bng ........ 69 Hnh 3.30 Cc ng cong BER s cp (QPSK) v th c p (QPSK) v i cc gi tr tr khc nhau....................................................................................................................... 70


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THU T NG VIT T T

Cm t vit tt

T ting anhNgha ting vi t

(nu c)

3GPPThird Generation Partnership

Project

A

ADC Analog to Digital Converter B chuyn i t ng t sang s

BBPSK Binary Phase Shift Keying Kha dch pha nh phn

BS Base Station Tr m gc

C

CFO Carrier Frequency Offset D ch tn s sng mang

CP Cyclic Prefix Ti n t chu trnh

CR Cognitive Radio

D

DAC Digital to Analog Converter B chuyn i s sang t ng t

(I)DFT(Inverse) Discrete Fourier

TransformBin i Fourier r i r c (ng c)

DVB-TDigital Video Broadcasting-

Terrestrial Truyn h nh s mt t

F

FDD Frequency Division Duplex Song cng theo tn s FFO Fractional Frequency Offset Ph n th p ph n ca d ch tn s

(I)FFT (Inverse) Fast Fourier Transform Bi n i Fourier nhanh (ng c)

I

ICI Intercarrier Interference Nhi u lin sng mang


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IFO Integer Frequency Offset Ph n nguyn ca d ch tn s ISI InterSymbol Interference Nhiu lin k hiu

L

LO Local Oscillator B dao ng niLOS Line Of Sight

M

ML Maximum Likelihood

N

NLOS Non line Of Sight

O

OFDMOthorgonal Frequency Division

Multilplex

Ghp knh phn chia theo tns tr c giao

OFDMAOthorgonal Frequency Division

Multilplex Access

a truy nhp phn chia theo tns tr c giao

P

PDP Power Delay Prole L lch tr cng sut

PRBS Pseudo Random Binary Sequence Chu i nh phn gi ng u nhi nPSS Primary Synchronization Signal Tn hi u ng b s c p

Q

QAM Quadrature Amplitude Modulation iu ch bin cu phng QPSK Quadrature Phase Shift Keying Kha dch pha vung gc

R

SCFOSampling Carrier Frequency

Offset Dch tn s ly m u

S

SDR Software Dened RadioV tuyn nh ngh a bng phn

mm

SNIRSignal to Noise and Interference

ratio

T s tn hi u trn nhiu v t pm

SNR Signal to Noise Ratio T s tn hi u tr n t p m
http://en.wikipedia.org/wiki/Intersymbol_interferencehttp://en.wikipedia.org/wiki/Intersymbol_interference


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SSSSecondary Synchronization

SequenceChui ng b th c p

STO Symbol Time Offset D ch nh th i k hi u

TTDD Time Division Duplex Song cng theo th i gianTPS Transmission Parameter Signaling T n hi u th ng s truyn d n

U

UE User Equiment Thi t b ng i s dngUWB Ultra Wide Band Bng siu rng

W

WLAN Wireless Local Area Networks M ng kh ng d y cc b

Z

ZC Zadoff-Chu


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L I M U

Cc h thng th ng tin v tuyn hi n nay u c tr ng b i ch nh s ch c p ph t

ph tn c nh. Trong , hu ht cc d i tn s u c ph n chia c nh cho t ngng dng v tuyn c th. Tuy nhi n, mc d ph ng thc ph n chia t n s ny c nhiu nhiu u im nhng n cng g y ra s lng ph ngun ti nguy n s. Nhiucuc nghi n cu ch ra r ng c c d i tn s c c p ph p ang c s dng v ihi u sut r t th p. Theo nh y ban truy n th ng li n bang M FCC, hi u sut s dng c c d i tn s c c p ph p ch t c t 15% n 85% t ng s ph tnkh dng. Trong khi , cng v i s pht trin ca khoa h c cng ngh v nhu c u conng i, ng ycng c nhiu ng dng th ng tin v tuyn m i ra i v i hi l ng tns r t l n. Tuy nhi n, do h u ht cc d i tn s kh dng u c ph n chia chocc ng dng tr c nn nhng ng dng v tuyn m i kh c iu ki n ph t trin.iu n y i hi ph i c mt cng ngh mng m i ra i khai th c ph tn s hi nti mt cch hi u qu h n v p ng c c nhu c u ca cc ng dng m i.

t ng v mng v tuyn Cognitive c a ra nh m p ng nhu c u bc

thit tr n. Mng v tuyn Cognitive s khai th c nhng kho ng ph ang c b tr ng cung c p b ng th ng r ng cho c c ng dng v tuyn th ng qua c c kin tr c

phc t p v s dng c ng ngh cng ngh truy c p ph linh ho t. Do , vn c pthit t ra hi n nay l cn ph i nghi n cu, nm chc c im ca mng v tuynCognitive, t ng b c i v o nghi n cu c c ng dng ca n . Ch nh v vy, c ng v is nh h ng ca c gio Th.S Ph m Th Thy Hin, em chn ti nghin cung b trong h thng Overlay Cognitive cho n tt nghi p ca mnh. Ni dung

chnh ca ti l tm hiu mt trong nh ng hot ng quan tr ng v kh khn nhtca mng v tuyn Cognitive l ng b.

Ni dung ch nh ca n gm 3 ch ng:

Ch ng I: T ng quan v v tuy n Cognitive: Ch ng n y tr nh b y nhngvn c b n v mng v tuyn nhn thc bao g m: mc ch nghi n cu, c c cim ch nh, kin tr c ca mng v tuyn Cognitive.


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Ch ng II: C c nh h ng c a k nh truy n v tuy n : Ch ng n y t p trungm t cc tc ng ca phn cng khng l t ng, cc thng s ca k nh v tuyn v

m hnh ha cc nh h ng ca chng n knh v tuyn thng qua cc knh m hnh khc nhau nh m c tnh c tn hi u pht t tn hi u thu c ng th i c i thi nhi u nng h thng. y l c s cho th tc ngb trong cc h thng t hng tin v tuyn, t thc hi n ng b trong h thng Overlay Cognitive.

Ch ng III: ng b trong h th ng Overlay Cognitive : chngny trnh by v th tc ng b trong cc h thng thng tin v tuyn ni chung v trnh bychi tit v ng b trong h thng OFDM, ng xung ca h thng LTE, h thngDVB- T v h thng Overlay Cognitive. Bn cnh , chng cng a ra v phntch, nh gi cc kt qu m phng ng b trong cc h thng trn.

Mc d ht sc c gng, nhng do thi gian v kin thc c hn nn n chcchn cn nhiu thiu st. Em rt mong c s ng gp ca thy c ti c

hon thi n hn. Em xin trn trng c m n!

H Ni, ngy thng nm 2013

Sinh vin

V VnMinh


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CHNG I TNG QUAN V V TUYN COGNITIVE

1.1 GII THIU CHUNG

1.1.1 M c ch nghin c u m ng v tuyn Cognitive

Tn s l mt ngun ti nguyn v cng qu gi trong thng tin v tuyn. Hi nnay, t n s v n cn l mt ngun ti nguyn hn ch. Tnh cht hn ch y chiu l di tn s th v hn song con ng i m i ch c th s dng c kho ng100Ghz u tin truyn tn hi u v tuyn. Trong khi c rt nhiu ng dng vtuyn cng s dng ngu n ti nguyn hn ch ny. Chnh v vy m vic s dng tns ph i uc qu n l mt cch cn thn trong ph m vi m i quc gia v trn ton th gi i. phm vi m t quc gia, ngu n ti nguyn tn s c qu n l b i y ban qu n ltn s ca nh n c. y ban ny thc hi n vi c phn chia v c p gi y php quyn s dng cc di tn s khc nhau cho cc nh khai thc cung c p mt dch v nht

nh. y ban ny cng a ra cc quy nh tiu chun m b o khng xy ra s chng ln v gy nhiu l n nhau gi a cc mng ca cc nh khai thc . Vic c p pht cc di tn s cng ph i tun th cc nguyn tc chung mang tnh quc t nhmiu ha vic s dng tn s gia cc quc gia v vng lnh th v i nhau.

Hi n nay, cc mng v tuyn u c c im l s dng nhng d i tn s c nh. Tc l h thng u c thit k hot ng trn di tn m n c c p php. Tr c ht, mt s d i tn c n nh cho cc mc ch ti quan tr ng ca xhi nh cc dch v khn cp, m b o an ton, dch v hng khng Cc di tnkhc c n nh cho nh ng mc ch s dng mang tnh thng mi nh pht thanhtruyn hnh, in thoi di ng, Cui cng, c mt khi l ng nh ph tn s khngcn cp php v bt k ngi no cng c quyn s dng n. Mt v d in hnh caloi ny l di tn s dng cho cc mc ch cng nghi p, khoa h c v y t ISM.

Chnh sch cp pht ph tn c rt nhiu u im. u im u tin l tnh n

gi n trong qu n l. Do i v i mi d i tn s, quyn s dng c cp php cquyn cho cc mc ch c th nn khng cn x y ra tnh trng cnh tranh khng r


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rng v quyn c s dng d i tn . iu ny lm cho vic qu n l ph tn s d dng hn. Th hai, h u ht cc h thng thng tin v tuyn hi n nay u c thit k v ch lm vi c trong m t d i tn s xc nh. Chnh sch cp pht ph tn c nh

m b o quyn s dng c quyn v lu di mt d i tn s cho m t nh khai thcdch v. iu ny khuyn khch v to ra tm l yn tm cho cc nh u t b ranhng kho n vn ln xy dng h thng v u t cho vi c pht trin cc nghincu, c i tin nhm nng cao cht l ng d ch v. Do m cng ngy cng c nhiuloi hnh dch v cht lng cao, gi c cnh tranh n v i ng i s dng. Vy lng i s dng c h ng l i t tc ng ca chnh sch cp pht tn s c nh.Cui cng vic hot ng trong m t d i tn s lm cho cu trc thit b v vi c trinkhai h thng c iu ki n n gi n hn d n n cht l ng d ch v tt hn.

Mc d chnh sch cp pht tn s c nh c nhiu u im song n cng gyra s lng ph rt l n trong vi c s dng ngu n ti nguyn tn s. Hi n nay, nhi u cucnghin cu ch ra r ng cc di tn s c cp php ang c s dng v i hi usut r t thp. Theo nh y ban truy n thng lin bang M FCC, hiu sut s dng ccd i tn s c cp php ch t c t 15% n 85% t ng s ph tn kh dng vgi tr ny thay i theo c thi gian v v tr a l i v i tng d i tn. Hnh 1.1 chothy tnh hnh s dng tn s Berkerley, California, M trong di tn s t 1GHz n6Ghz. D a vo hnh trn, ta thy bn cnh nhng d i tn s 0- 2Ghz c s dng r thi u qu th nhng d i tn s t 3-5 GHz c s dng r t t. iu ny cho thy mtkhi l ng l n ph ang c s dng v i hi u sut r t th p.

Hnh 1.1S d ng ph Berkerley, M


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Ng i ta gi nhng d i tn s ang khng c s dng l nhng kho ng tr nghay h ph. S.Haykin a ra khi ni m y v h ph trong [3] nh sau:

Mt h ph l mt d i tn s c c p cho m t ng i s dng nhng ti

mt thi im no trong mt vng a l nht nh, d i tn s ny ang khng cs dng bi ngi .

Hnh 1.2 Khi nim h ph

Ngi c cp php s dng mt d i tn c gi l ng i s dng s c p PUhay ngi dng c cp php ca d i tn v nhng ng i s dng khc khngc php s dng d i tn ny cho d n ang c b tr ng nu khng c s ng ca PU. M t vn t ra hi n nay l lm sao tn dng c nhng h ph ny nhmnng cao hiu sut s dng ph gp phn gi i quyt ngun ti nguyn ngy cng thiunh hin nay. Do nh ng h ph th ng ch xut hi n mt cch ng u nhin nn chngta ch c th s dng chng theo c hi. Tc l ch c th s dng nhng d i tn

khi n ang c b tr ng v nhanh chng r i khi khi PU s dng n. c th tn dng c cc h ph, yu cu mt h thng ph i c kh nng

truy nh p ph r t linh ho t. Cc mng v tuyn hi n ti v i nhng giao th c c nhkhng th thc hi n c kh nng truy c p ph linh ho t nh vy. iu i hi

ph i c mt m hnh mng m i ra i c kh nng khai thc hiu qu nhng h ph.V vy, t ng v mng v tuyn Cognitive CRN c a ra k p thi p ng yucu ny. Mng CRN v i kh nng truy c p ph linh ho t DSA s khai thc cc h ph cung c p bng thng rng cho cc ng dng v tuyn thng qua cc kin trc phc


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t p. Nh ng ng i s dng trong CRN s ng vai tr nh ng i s dng th c p SUi v i nhng d i tn c cp php v c quyn u tin thp hnso v i cc PUtrong d i tn thuc s hu ca chng.

1.1.2 c im ca m ng CRN

Mc ch chnh l nng cao hi u qu s dng ph bng cch khai thc cc h ph nn CRN s c cc c im c b n lin quan n vi c s dng cc h ph . c th chia s ph v i cc PU m khng gy nh hng n h v p ng c yucu v cht l ng d ch v th CRN phi c nhng chc nng sau:

Cm bi n ph : Xc nh c cc di tn s ang trng v pht hi n mt cchk p th i s c mt ca cc PU trn di tn s khng gy nhiu cho h .

Qu n l ph: La chn knh tn s kh dng tt nht, ph h p v i cc yu cuca ng i s dng.

Chia s ph : Cung c p phng thc chia s ph tn s mt cch cng bnggia cc ng i s dng ca CRN.

Di chuy n ph : R i khi knh khi pht hin thy PU v duy tr cc yu cuthng tin mt cch lin mch trong su t qu trnh chuyn i sang d i tn s kh dng khc Hn th na, mc ch ca CRN khng ch n thun nng cao hiu qu s

dng tn s m h ng t i vi c ti u cht l ng hot ng ca ton mng c th cung c p mt d ch v thng tin cht lng cao cho ng i s dng. Do , CRN cnh ngha l mt h thng thng tin v tuyn Cognitive c nhiu ng i s dng, thc

hi n cc nhim v c b n nh sau: Nhn thc mi trng v tuyn bn ngoi bng cch ra l nh cho cc my thu

pht ca ng i s dng c m bin mi trng lin tc theo th i gian. Phn tchcc c im ca mi trng v thay i cc tham s hot ng ca mi mythu pht thch ng v i nhng thay i ng u nhin ca mi tr ng nh m t chtl ng hot ng tt nht.

To iu ki n thun l i cho vi c truyn tin gi a nhiu n g i s dng thng quavi c hp tc theo cch thc t t chc.


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iu khin cc qu trnh truyn tin gi a nhiu ng i s dng ang cng c nhucu thng qua vic cp pht chnh xc nhng ngu n ti nguyn kh dng phh p nht i v i tng yu cu ring bit ca tng ng dng.

Tt c cc nhi m v trn u c thc hi n theo th i gian th c nhm t c hai m c ch c bn. Th nht l cung c p vi c truyn tin v i tin cy cao chott c cc ng i s dng. Th hai l nng cao hiu qu s dng ph tn s v tuynthng qua vi c phn chia cng bng v ph h p v i cc ng dng.

c th thc hi n c cc chc nng ni trn th CRN yu cu mt thit b v tuyn ph i c kh nng rt mm do c th thay i mt cch nhanh chng ccchc nng giao thc khc nhau trong khi n di chuyn. Sau y chng ta s gi i thi umt cng ngh m i c tn l v tuyn Cognitive CR . y l cng ngh ng vai trthen ch t c th xy dng ln CRN.

1.2 C NG NGH V TUY N COGNITIVE

1.2.1 Khi nim v tuyn Cognitive

Cng ngh CR l mt s c i tin, pht trin ca cng ngh v tuyn c nhngha bng phn mm SDA. CR l mt cng ngh cho php c th thc hi n cSDA trong CRN.

Hi n nay c rt nhiu nh ngha khc nhau v CR. n gi n nh trong [4], CRc nh n h sau:CR l mt h thng v tuyn c th thay i cc tham s pht ca n da trn s

tng tc v i mi trng m n ang hot ng.Hoc nh theo S. Haykin trong [5] th CR c nh ngha l:

CR l mt h thng thng tin v tuyn thng minh ckh nng nhn thc v mitrng xung quanh n v s dng phng php lun hiu nh xy dng tm hiumi trng v thay i cc trng thi bn trong ca n thch ng v i cc thay i ng unhin ca cc tc ng RF u vo bng cch thay i tng ng c c tham s hotng nh: cng sut pht, tn s sng mang v phng thc iu ch theo th i gian


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thc, v i hai m c tiu c b n l: lun truyn tin v i tin cy cao b t c khi no cnn, s dng hi u qu tn s v tuyn.

1.2.2 Kh nng ca thi t b u cu i v tuyn Cognitive

Mt thit b c kh nng CR (gi tt l u cu i CR) c th l mt node m nghay m t u cui thng tin trong mng CRN. Nh ng kh nng ca u cui CR s c phn loi theo cc chc nng ca n da trn nh ngha v CR nu trn. Mtu cui CR s c m nhn mi tr ng (kh nng nhn thc); phn tch, nghin cuthng tin cm nhn c (kh nng t t chc) v thay i thch ng v i mi tr ng(kh nng t ti cu hnh).

1.2.2.1 Kh nng nhn th c

Kh nng nhn thc l kh nng m u cui CR c th nghe thng tin t mitrng bn ngoi. Chng ta c th tm tt kh nng nhn thc vo nhng nhi m v nh sau:

C m bin ph: Mt u cui CR c th c m nh n v pht hi n ra cc h ph cc d i tn s khc nhau m khng gy nh hng n PU c a d i tn .

Chia s ph: Mt u cui CR c th st nhp vo mt c cu m cho php chias ph theo m t s tha thun gia mt bn c cp php v mt bn th ba.Cc bn thm ch c th m phn vic s dng ph trn c s th i gian th choc kiu ad- hoc m khng cn s tha thun tr c.

Xc nh v tr: Mt u cui CR c th xc nh c v tr ca n v ca ccmy pht khc, sau la chn cc tham s hot ng ph hp nh cng sut pht v tn s cho php v tr .

Pht hi n cc h thng : M t thit b u cui CR c kh nng pht hi n ra cch thng, mng kh dng ang hot ng quanh n. V d khi m t u cui CRcn thc hi n mt cuc gi v pht hi n c mt tr m gc ca GSM gn yth c th thc hi n cuc gi thng qua kt ni tr c tip n tr m gc ny hoc


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9V Vn Minh D09VT5

thng qua cc u cui CR khc. Kh nng ny cho php u cui CR c th duy tr thng tin bt k v tr no.

Pht hi n ra d ch v: Pht hin ra d ch v lun i km v i kh nng pht hin ra

h thng. Cc nh khai thc h thng cung c p cc dch v thng qua cc mngtruy c p ca h. Mt u cui CR s tm thy cc dch v ph hp p ng ccnhu cu ca mnh.

1.2.2.2 Kh nng t ti cu hnh

Kh nng t ti cu hnh l kh nng iu ch nh cc tham s hot ng m khng cn c bt k s thay i no trn phn cng. Trong khi kh nng nhn thccung c p thng tin lin quan n tn s th kh nng t ti cu hnh cho php h thng c lp trnh mt cch linh hot bm theo mi trng v tuyn. C th hn l ucui CR c th c lp trnh truyn v nhn thng tin trn nhiu d i tn s v s dng cc cng ngh truy c p truy n d n khc nhau c h tr b i phn cng ca n.u cui CR c kh nng t cu hnh li i v i cc tham s nh sau:

Thay i tn s hot ng: M t u cui CR c th thay i r t nhanh t n s hot ng ca n. S thay i nhanh nh y ny k t h p v i mt phng thc lachn linh ho t tn s hot ng ph h p da vo thng tin t mi tr ng.

M ha/iu ch thch nghi: K thut iu ch v m ha c th c thay i lm thay i dng sng v c tnh truyn d n ca tn hi u thch nghi v imi trng v tuyn, lm cho tn s c s dng hi u qu hn v c th hotng song song cng v i cc h thng khc. Mt u cui CR c th la chn

phng thc iu ch ph v i mt h thng truy n d n nht nh cho php cch thng c th tng tc v i nhau.

iu khin cng sut: iu khin cng sut l mt c tnh cho php mt thit b c th thay i gia mt vi mc cng sut pht trong qu trnh truyn d nd li u. iu khin cng sut gip cho vic chia s ph ca u cui CR d dng hn.

Truy c p vo cc h thng m t cch linh hot: cc u cui CR c th truycp n nhiu h thng thng tin c cc giao thc khc nhau th kh nng t cu


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10V Vn Minh D09VT5

hnh li cho php u cui CR c th tng thch v i cc h thng ny khi cnthit. Kh nng ny rt hu ch khi u cui CR ho t ng trong cc mi tr ngm c nhiu h thng v tuyn cng tn ti.

1.2.2.3 Kh nng t t ch c

Kh nng t t chc ngha l CR s c kh nng t t chc vi c truyn tin c an da trn cc chc nng cm bin v cu hnh li:

Qu n l ti nguyn v tuyn: t chc v qu n l mt cch hiu qu thng tin v cc h ph gia cc CR th rt cn thit ph i c mt c cu qu n l ph hp l.

Qu n l kt ni v tnh di ng: do tnh khng ng nht ca CRNs nn thng tinv cu trc mng lin quan n vi c nh tuyn r t phc t p. Qu n l kt ni vtnh di ng tt c th gip vi c pht hi n ra cc h thng ln cn, pht hintruy c p internet kh dng v h tr vi c chuy n giao d c, gip cc CR lachn ng i v cc mng ph h p.

Qu n l an ninh/ m b o tnh tin cy: cc mng v tuyn nh n thc thc cht l

cc mng khng ng nht. S khng ng nht d n n r t nhiu ccvn anninh c n quan tm. Do , tin cy l mt iu ki n tin quyt cho cc hotng trong cc mng v tuyn nhn thc.

1.2.3 C u trc vt l ca thi t b u cu i CR

Mt b thu pht CR c cc thnh phn c bn ging nh mt b thu pht SDR

thng th ng, bao g m 2 ph n chnh l phn u cui RF (RF Front- End) v phn x l bng gc. Mi thnh phn c th c ti cu hnh thng qua mt bus iu khin c th thch ng v i s thay i theo th i gian c a mi trng v tuyn. Trong ph nx l bng gc, tn hi u c lc, iu ch/gi i iu ch v m ha/gi i m. Phn x l bng gc ca CR v c b n l ging v i cc thit b SDR thng th ng, tc l ckh nng cu hnh li thng qua lp trnh phn mm trn cc con chip x l tn hiu s DSP. Ph n to nn s khc bi t v tin b ca cc b thu pht CR l u cui RF. Dovy chng ta s tp trung tm hiu phn u cui cao t n.


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Cu trc ph bin ca mt thit b thu pht CR c th hi n trong hnh 1.3.

Hnh 1.3 B thu pht CR c im c bi t ca b thu pht CR l kh nng hot ng d i r ng ca phn

u cui RF. T t c cc thnh phn trong u cui RF u c kh nng hot ng trongmt d i tn r ng b thu pht CR c th hot ng trn tt c cc tn s m nmong mu n.

Hnh 1.4 u cu i RF tuy n thuHnh 1.4 miu t cu trc in hnh ca phn u cui RF trong my thu CR.

N bao gm cc khi c bn ging nh my thu thng thng. im khc bit ca CRl kh nng hot ng d i r ng v cc yu cu k thut phc t p. Khi th c hi n thutrong m t d i tn nht nh, do vi c la chn knh ch x y ra sau b i tn xung nn

mt thch thc m my thu CR ph i i mt l tnh trng bo ha my thu do cc tnhi u ngoi bng gy ra. iu ny c ngha l cc thnh phn ging nh b khuch i


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12V Vn Minh D09VT5

tp m thp LNA c th b bo ha do cc tn hiu nm trong d i dn hot ng camy thu nhng khng nm trong d i tn m my thu mun gi i iu ch trong m tth i gian nh t nh c cng qu mnh. Thch thc ny c th c khc phc

bng cch t cc mch lc kha cao tn c kh nng iu hng tr c LNA. Nhnggi thnhca cc b lc ny l rt cao v kh nng iu h ng ca n cng ch hnch mt gi i hn nht nh.

Mt khc, khi thc hi n c m bin ph th my thu CR s ph i thu tn hiu trongmt d i tn r ng. Anten s ph i thu cc tn hiu t nhiu my pht ang hot ng cc mc cng sut, trong cc di tn v cc v tr khc nhau. Tn hi u sau khi cx l phn cao t n s c a vo b ADC, m t s php o c thc hi n trn ccm u thu c c th pht hi n ra s hi n di n hay v ng m t ca cc PU. Cm bind i r ng yu cu mt b ADC c tc cao ln t i vi GHz. pht hi n cc tn hiuc cng nh trong d i ng r t l n ca tn hi u thu yu cu ADC ph i c phnd i r t cao, c th l 12 bit hoc l n hn. Mt b ADC p ng c cc yu cu nyc th khng ch to c. V vy, ta c th tm cch gim d i ng ca tn hiu thu

bng cch loi b nhng tn hi u c cng mnh trong d i tn thu m khng linquan n vi c c m bi n ph. Do nh ng tn hi u c cng mnh c th c t

bt k v tr no trong di tn r ng nn ta phi s dng cc mch lc kha c th iuhng loi b cc tn hi u ny.

Nhng gi i php k thut c th thc hi n c cc yu cu trn ca CR s lm cho thit b tr ln rt phc tp v chi ph rt cao. Chnh v vy vi c thc hi n ccgi i php phn cng ph hp, p ng c cc nhu cu CR l mt vn r t quantr ng cn ph i c gi i quyt c th trin khai c cc mng v tuyn Cognitive

vo thc t.

1.3 KI N TR C M NG V TUY N COGNITIVE

Ngo i vi c c m bi n ph nng cao hi u sut s dng tn s, thit CR trongCRN c n c th c m bin cc h thng th ng tin v cc mng kh dng xung quanhn. Chnhv vy m CRN kh ng ch n gi n l mt mng k t ni c c thit b CRv i nhau. CRN bao g m nhi u loi mng, h thngkh c nhau v c th xem nh l


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13V Vn Minh D09VT5

mt mng kh ng ng nht. T nh kh ng ng nht tn ti trong c c cng ngh truyc p v tuyn, c c mng, c c thit b u cui ca ng i s dng, c c ng dng v ccnh cung c p d ch v. Vi c thit k kin tr c mng v tuyn Cognitive s h ng t i

mc tiu l c i thi n hi u qu s dng ca to n b mng ch khng ch l nng caohi u qu s dng ph. V ph a ng i s dng, vi c s dng m ng c ngh a l h lu nlun c th thc hi n c c c y u cu ca m nh mi lc v mi n i th ng qua vi ctruy c p n CRN. V ph a nh khai th c, h c th cung c p nhng d ch v chtl ng cao cho ng i s dng v n nh t i nguy n mng v v tuyn truyn t i ccgi tin ca ng i dng v i hi u qu s dng ph cao h n.

1.3.1 Ph n lo i kin tr c m ng v tuy n Cognitive

Mng v tuyn Cognitive c th c trin khai theo nhi u dng kin tr c kh cnhau v c dng phc v nhu c u ca tt c cc ng dng c c p ph p c ngnh cha c c p ph p. C c th nh phn ch nh ca mt mng v tuyn Cognitive s

bao g m: m y di ng MS, tr mgc/imtruyc p BS/AP v mng l i. S k t h p ca ba th nh phn c b n ny s to ra ba lo i kin tr c mng v tuyn Cognitive kh cnhau, theo nh trong [7], bao g m: kin tr c t p trung, ki n tr c Ad-hoc v kin tr chnh l i. Sau y ch ng ta s tm hiu c im ca cc loi kin tr c mng n y.

1.3.1.1 Ki n tr c t p tru ng

Hnh 1.5 Kin trc mng t p trung


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Trong m ng kin tr c t p trung (hay c n gi l kin tr c h tng) nh c th hi n trong h nh 1.5, c c BS/AP c nh s phc v nhng MS trong ph m vi ph sngca n. Cc BS/AP c u th nh l n x ng sng cho m t mng kin tr c t p trung.

Nhng MS n m trong ph m vi truy n d n ca cng mt BS/AP s lin lc v inhau thng qua BS/AP . Vi c lin lc gia nhng MS n m trong cc t bo thuccc BS/AP khc nhau s c nh tuyn thng qua mng li. BS/AP c th thc hi nmt hoc nhiu giao th c truyn tin khc nhau p ng cc yu cu t cc MS. Mtu cui CR cng c th truy c p t i nhiu loi h thng thng tin khc nhau thngqua cc BS/AP ca chng.

1.3.1.2 Ki n trc Ad -hoc

Kin trc Ad-hoc c th hi n trong hnh 1.6 d i y

Hnh 1.6 Ki n trc Ad -hoc

Ng c li i v i kin trc t p trung, trong ki n trc Ad-hoc, cc MS t mnht chc mng mt cch t ng m khng cn c c s h tng h tr . Cc MS trongmt phm vi nh t nh c th t thit l p k t ni tr c ti p v i nhau d a trn cc giaothc hoc mt chun no to thnh mt mng Ad- hoc. Cc kt ni gia cc nodetrong m ng Ad- hoc c th c thit l p bng cc cng ngh truyn d n khc nhau.Hai u cui CR c th lin lc v i nhau b ng cch s dng cc giao thc thng tinhi n ti v cc h ph kh dng.


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1.3.1.3 Ki n trc hnh l i

Kin trc hnh l i l s k t h p ca kin trc tp trung v kin trc Ad-hocnh c th hi n trong hnh 1.7.

Hnh 1.7 Kin trc hnh l i

Trong d ng trc hnh l i, cc BS/AP c th lin lc tr c ti p v i nhau thngqua cc kt ni v tuyn. S c mt BS/AP c k t ni t i mng li v ng vai trnh mt cng MS c th lin lc v i cc mng bn ngoi. Cc BS/AP lm vicging nh cc b nh tuyn v tuyn v to thnh mng ng tr c v tuyn. MS c

th truy c p tr c tip n cc BS/AP hoc thng qua cc MS khc ng vai tr nh ccnode chuy n ti p nhiu chng. Do BS/AP c kh nng CR nn chng c th s dngcc h ph lin lc v i nhau. Hi n nay kh i lng cc h ph kh dng r t l n nndung l ng ca cc kt ni v tuyn gia cc BS/AP c th phc v nh mtmng ng tr c v tuyn. Do cc BS/AP khng cn k t ni tr c ti p t i mng li nnvi c quy ho ch v tr ca BS/AP s mm do hn v gi m chi ph trin khai m ng.


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1.3.2 Ki n tr c m ng v tuy n Cognitive

Kin tr c mng v tuyn Cognitive c tr nh b y tr n h nh 1.8

Hnh 1.8. Kin trc mng v tuy n CognitiveCc thnh phn chnh trong mng v tuyn Cognitive c th c chia thnh 2

nhm sau:

1.3.2.1 M ng s c p

Mng s cp PN i di n cho cc h thng mng hi n ti nh l cc mng t bo, mng truy n hnh... PN hot ng trong d i tn s c cp php v c quynu tin s dng cao nh t i v i d i tn s . Cc thnh phn c bn trong PN g m:

Ng i s dng s cp PU: Nh cp trong cc phn trn, PU l ng i

s dng c cp php hot ng trong m t d i ph nht nh. Cc PU khng


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17V Vn Minh D09VT5

cn bt k s thay i hoc ph i thm cc chc nng b sung no cng tnti v i cc trm gc v cc ng i dng c kh nng CR .

Tr m gc s c p PR- BS: l mt thnh phn h tng mng c nh ca PN c

php hot ng trong m t d i tn s no . V nguyn tc th trm gc s c pkhng cn b sung thm bt k mt chc nng no chia s ph v i cc ng idng CR. Tuy nhin, trm gc s cp c th c yu cu c thm cc giaothc m i phc v cho vi c truy c p vo mng c s ca cc ngi dng CR.

1.3.2.2 M ng v tuy n Cogniti ve CRN

CRN khng c giy php s dng hot ng trong d i tn s mong mu n.Ch nh v vy, vi c truy c p vo di tn mong mu n ch c th c cho php theokiu c hi. Trong hnh 1.8, CRN c trin khai theo c kiu kin trc t p trung (h tng) v kin trc kiu Ad- hoc. Cc thnh phn ca CRN g m c:

Ngi dng CR: l ng i d ng khng c cp php v ng vai tr nh mtng i s dng th hai (u tin thp hn) i v i mt d i tn s nht nh. Do

vy, ngi dng CR cn c cc kh nng nh trnh by cc phn tr c c th chia s d i tn s c cp php v i PU. Tr m gc CR-BS: Tr m gc CR l mt thnh phn h tng mng c cc kh

nng CR.Tr m gc CR cung c p k t ni n chng t i ngi dng CR. Thngqua k t ni ny mt ngi dng CR c th truy c p cc mng khc. Nu tr mgc CR c th s dng c cc giao thc ca cc mng s cp th n c th cung c p vi c truy c p d ch v mng t i cc PU.

B chia s , qu n l ph: l thc th mt trung tm. N thc hi n vai tr chia s ti nguyn tn s gia cc CRN khc nhau. N c k t ni t i tng CRN vc chc nng nh mt nh qu n l thng tin ph cho php s cng tn tica nhiu mng CRN.


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1.4 MT S K CH B N TRI N KHAI M NG V TUY N COGNITIVE

1.4.1 M ng v tuy n Interweave Cognitive.

Trong m hnh Interweave Cognitive, h thng th c p x c nh c c h ph haykho ng tr ng trong mi n th i gian, t n s hay v tr a l ang kh ng c s dng b ih thng s c p. t ng n y bt ngun t cc nghi n cu cho th y phn l n ph tnkhng c s dng trong h u ht th i gian m v d in h nh l cc kho ng tr ngtrong c c h thng truy n h nh.

Cc d ch v truyn h nh hot ng trong b ng tn UHF v VHF c c p ph p, c c c quan qu n l cm vi c s dng c c bng tn ny cho c c thit b khng c c p ph p. Tuy nhi n, do l i ch to l n ca truyn d n s nn vi c chuy n i cctr m truy n h nh ang s dng truy n d n t ng t l r t cn thit. M hon th nhvi c chuy n i sang truy n d n s DSO v o th ng 6 n m 2009, Anh l nm 2012Vi c chuy n i ny gi i ph ng mt l ng ng k ph tn cho c c d ch v khc.Mt l i ch quan tr ng kh c ca DSO l c hi s dng c c bng tn truyn

hnh cho c c thit b v tuyn kh ng c c p ph p khi PU ang kh ng s dngchng. C nhng v tr a l ph h p m vi c truy nh p k nh v n g y nhiu li n k nhhay ng k nh, nh ng tn ti mt s k nh c th c s dng b i cc thit b cngsut th p m khng nh h ng n PU. C c thit b th c p WSDs c kh nngnhn thc m u sc tr nh bt k nhiu c hi n o cho c c d ch v ang c b o v da tr n b n mu phm vi ph sng. Tr n b n ny, nh ng n i c mu kh c nhauth hi n mc tn hi u kh c nhau, nhng v ng kh ng c tn hi u truyn h nh s c

mu tr ng chng c gi l TVWS. Do ,TVWS c nh ngh a l: Khu vc al khng c tn hi u truyn h nh v d i tn ph t sng c th c s dng cho c c mcch th c p m khng g y bt k nhiu n o t i vi c ph t sng truy n h nh cc phncn li ca vng hay b t k dch v ng nhi m n o kh c.

chu u, TVWS n m d i tn 470-790MHz, m t d i tn hi u cht l ngcao, t t h n c cc t n hi u 3G hay Wifi m v n c kh nng truy n xa v xuyn thu.iu ny ha hn cho nhi u d ch v tim n ng nh truy nh p b ng r ng kh ng d ykho ng c ch l n cc v ng n ng th n. Kho ng c ch n y thay i theo th i gian v v


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tr a l v c th c khai th c b i nhng SU cho vi c truyn th ng ca h. Do vi c s dng ph tn c c i thi n bng c ch t i s dng c c h ph. K thutInterweave Cognitive y u cu nhn bit c hot ng trong ph tn ca nhng

ng i s dng sc p.

1.4.2 M ng v tuyn Underlay Cognitive.

Cch ti p cn Underlay Cognitive bao g m cc k thut thng tin v tuyn ckh nng nhn thc da trn gi nh r ng phn nhn thc c th kim sot c nhiugy ra bi my pht ca n t i my thu ca nhng PU. M t trong nh ng yu cu c

b n trong k ch b n trin khai ny lSU khng gy nhiu ng k t i thng tin cang i s dng chnh hin thi. Theo m hnh v tuyn Underlay Cognitive ny, truynd n cognitive v non-cognitive c th x y ra song song ch khi nhi u to ra cc thit

b cognitive i v i cc thit b chnh khng ko SNR chng xung d i mtng ng nht nh. Vi c hn ch nhiu cho ng i s dng chnh c th c p ng

bng cch s dng k thut a anten h ng cc tn hiu Co gnitive ra xa cc my thunon-cognitive ho c s dng bng tn r ng hn cc tn hiu C ognitive c th tr i

ph mc nhiu nn v sau gii tr i ph pha my thuCognitive , cng ngh ny da trn k thut tr i ph v truyn d n bng siu rng UWB. Hnh 1.9 th hi n cchchia s ph tn ca mng Underlay Cognitive.

Hnh 1.9 Chia s ph t n trong m ng Underlay Cognitive

Nhiu gy ra bi my pht th c p t i my thu chnh c th c tnh thng qua

tng h nu my pht th cp c th nghe c truyn t t my thu chnh. Ngoira, my pht th cp c th hn ch mc cng sut u ra m b o r ng nhi u gy


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21V Vn Minh D09VT5

cp php, ngi dngCognitive s c php chia s bng tn v i nhng ng i s dng c cp php v s khng gy nhiu v thm ch c th c i thi n cht l ngtruyn d n . Trong bng khng cp php, ngi dngCognitive s cho hi u nng ph

cao hn bng cch khai thc cc b n tin v b m gi m nhiuHnh 1.10 minh ha cch chia s ph tn trong m ng U nderlay vOverlay Cognitive .

Hnh 1.10 Chia s ph t n trong m ng Overlay v Underlay C ognitive

Tm li, mng Interweave C ognitive l mt h thng v tuyn thng minh thchi n qut ph nh k pht hi n s chim dng cc phn khc nhau trong ph tn t xc nh c hi truyn d n qua cc h ph v i nhiu nh nht cho nh ng ng idng hin ti. Trong khi m ng U nderlay vOverlay Cognitive cho php truyn d nsong song gi a cc thit b Cognitive v Non-cognitive th mc tiu chnh ca mngInterweave C ognitive l trnh truyn d n ng th i v i ng i s dng chnh. Cc h

thng Cognitive c n mt l ng l n thng tin bn l: mng Underlay Cognitive c n ccthng tin v nhiu gy ra bi my pht Cognitive cho ngi dng non-cognitive, m ngInterweave yu cu mt lng thng tin ng k v hot ng ca PU, m ng OverlayCognitive c n thng tin v b m cng nh kh nng c bn tin. Ngoi ra, cc gi i hncng sut ca thit b , cng sut truyn d n ca ngi dng Cognitive trong h thngUnderlay vOverlay Cognitive c quyt nh b i gi i hn nhiu v phm vi c ac m bin.


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22V Vn Minh D09VT5

Trong khi Interweave, Overlay v Underlay l ba cch ti p cn ca mng vtuyn C ognitive th cc d n lai cng c xy dng k t hp u im ca cc cchti p cn ny.

1.5 NG D NG CA M NG V TUY N COGNITIVE

Trong tng lai, CRN c th c ng dng trong m t s cc tr ng h p sau:

1.5.1 M ng cho thu

Mng s cp PN c th cung c p mt mng cho thu bng cch cho php victruy cp theo c hi n d i tn c cp php ca n v i s tha thun v i mt bnth 3 m khng lm nh hng n cht l ng d ch v ca PU. V d nh mng scp c th em cho thu quyn truy c p d i ph ca n v i nh khai thc mng di ngo MVNO. M ng s cp cng c th cung c p cc quyn truy c p ph ca n t i mt

cng ng a phng v i cc mc ch truy c p d i r ng.

1.5.2 M ng l i Cognitive

Cc mng khng dy dng hnh l i ang ni bt nh mt cng ngh mngem li l i nhun cao, cung c p nhng k t ni d i r ng cho ngi dng. Tuy nhin khimt mng tng ln v cc ng dng yu cu thng lng ngy cng nhiu hn thcc mng hnh l i s yu cu dung lng cao hn p ng cc yu cu ca cc

ng dng ny. Do cng ngh v tuyn Cognitive cho php truy c p t i khi l ng ph l n nn CRN c th c s dng trin khai cc mng hnh l i trong cc vng th ng c v yu cu lu l ng d ch v l n.

1.5.3 M ng kh n cp

Cc mng khn cp v m b o an ton cng cng l mt lnh vc khc c th ng dng CRN. Trong tr ng hp cc thm ha t nhin x y ra, ph hy tm thi c


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s h tng ca cc h thng thng tin hin ti v lc l ng cu h ang lm vic trongcc vng cn thit l p mt mng khn cp. Lc ny, do mng khn c p ph i xlcc thng tin v th m ha nn i hi vi c truyn tin ph i tin cy v yu cu th i gian

tr ph i r t nh. Hn na, truyn tin kh n cp yu cu mt l ng ph l n c th x l khi lng thng tin khng l bao g m m thanh, hnh nh v d li u lin quan nth m ha. Trong tr ng hp ny, CRN c th c trin khai gi i quyt cc vn trn.

1.5.4 M ng qun s

Mt trong nh ng ng dng ng quan tm nht ca CRN l trong mi tr ngqun s. CRN c th cho php cc i v tuyn qun s la bng tn s, cc dng iuch v cc kiu m ha bt k thch nghi v i mi trng v tuyn thay i cachin trng. Hn na, cc mng qun s c nhu cu b o mt r t cao tr c k ch.CRN cho php nhn vin qun s c th thc hi n chuy n giao ph mt cch linhhot, s dng nhng d i tn an ton nht cho chnh mnh v cc ng minh.


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n tt nghi p Chng II Cc nh h ng ca knh truyn v tuyn

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CHNG II CC NH H NG C A KNH TRUYN V TUYN

2.1 GII THIU

Theo ngha rng mt knh v tuyn c th c hiu l mi tr ng truy n sngv tuyn, bao g m c my pht v my thu, thng qua thng tin c pht, truyni, v nhn. Cc c tnh ca tn hi u v tuyn thay i khi n di chuyn t my phtthng qua cc knh n my thu. Nhng thay i ny ch yu l do cc hiu ng knh

nh s che t i, hi u ng a ng, v do phn cng khng l t ng my pht vmy thu, iu ny d n n vi c suy gi m cht l ng cc tn hi u thu c. i v i mt phin truyn d n c li x y ra, l n ca nhng suy gi m ny ph i c c tnh vxa b khi tn hi u thu c.

Trong h thng thng tin v tuyn di ng, thng tin c pht i d i dngmt tn hi u k thut s c iu ch tn s sng mang f c v c th biu din d idng ton hc nh sau:

trong sb(t) l hm phc cha thng tin iu ch. V ch c bin v pha ca tnhi u sng mang c iu ch nn chng ta c th phn tch sb(t)m khng mt tnhtng qut. Ngoi ra, ch trng hn vo suy yu do tc ng ca cc hiu ng knhv phn cng khng l tng nn chng ta b qua bi n dng do nhi u nn v cc nhiukhc. Hi n t ng mt ng cng c b qua v n t tc ng trong tr ng tm ca

n ny l ng b v c tnh knh.

2.2 C C TC NG CA PH N C NG KH NG L T NG

Trong v tuyn nh ngha bng phn mm (SDRs), h u ht vi c x l tn hiu c thc hi n d i dng s, do cc cc thit b v tuyn u cui t ti cu hnhs dng ti thiu cc thnh phn in t tng t m v n ph i m b o x l tn hiuc d i ng l n. Mt thit b chuyn i trc tip in hnh ca loi ny c th r t

(2.1)


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nhy c m v i sai l ch hay khi m khuy t trong thi t b u cui. Nhng khi m khuy tny do li s n xut, thay i nhi t hot ng t d n n cc thit b u cuikhng l tng nh mt cn bng pha; cc b khuch i v b chuyn i (ADC v

DAC) khng tuyn tnh; nhiu pha v dch tn do sai l ch b dao ng ni,Nucc thit b u cui khng l tng khng c c tnh v b, chng c th nhhng n cht lng v hi u nng ca cc thit b v tuyn v ton b cc lin kttruyn d n.

Mt s tr ng hp khng l t ng do n thit b u cui nh d i y: Cc b DAC, ADC v b ly m u: thng th ng s khng l t ng y l png bng thng khng l tng nh ph rng ca, nhiu l ng t, nhiu do s khng n nh ca ng h ly m u, mo phi tuyn do rt ngn (clipping) tnhi u trong ADC, dch ca cc mc l ng t ha trong ADC v DAC. S saikhc gia hai nhnh I v Q trong ADC v DAC gy ra mt cn bng IQ.

B tr n: thng thng khng l tng l cc bin dng phi tuy n nh cc s n phm iu ch giao thoa trong bng hay u ra bng iu ha. B tr n cng gyra s cch ly khng hon ton gia u vo, b dao ng ni v u ra, d ch tn

DC. S khc bi t tng i gia 2 nhnh I v Q trong b tr n cng gp phnlm mt cn bng IQ. B dao ng ni: s khng l t ng y thng l nhiu pha do s bin i

ng u nhin ca pha dao ng, d ch tn sng mang (CFO), d ch pha do s khc bi t gia b dao ng ni my pht v my thu.

B khuch i tp m th p LNA, b khuch i h s bin i VGA, b khuchi cng sut my pht: s khng l tng thng l cc hiu ng bin dng

phi tuy n nh nhiu trong bng, bin dng iu ha, bin dng iu ch giaothoa. S sai khc gia cc nhnh I v Q cng d n n mt cn bng IQ.

2.3 C C TH NG S CA K NH V TUY N

Bn cnh cc phn cng khng l tng c trnh by trn , truyn sng vtuyn di ng cn b nh hng ng k b i s bin ng kh l ng mc nng l ngca tn hiu thu c gy ra bi hin t ng truy n a ng v che ti. Truy n a


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ng l kt qu ca s ph n x, nhiu x v tn x khi truy n tn hiu t im phtn im thu . Hnh 2.1 l mt v d v truyn a ng. my thu, s bin thin cngsut khc nhau theo th i gian tuy n tnh l kt qu ca s chng ln cc tn hi u a

ng v i pha khng ng nht. Ngoi phn x, nhiu x v tn x, sng v tuyn cn b suy hao ng truy n . Cng tn hi u cng b thay i theo th i gian do s chuyn ng ca my thu hoc my pht. phn tch ta c th chia nh h ng catruyn sng v tuyn thnh hai loi: suy hao tn hiu phm vi r ng v mo tn hiu

phm vi h p. Suy hao tn hiu phm vi r ng do suy hao ng truy n v s che t imy pht v my thu cn mo tn hiu phm vi h p x y ra do truy n a ng.

Gi suy gi m v tr mi ng ln lt ln(t) v n(t). Tn hi u my thu cth c m t nh sau:

Thay tn hiu truyn d n d i dng bng gc phc vo (2) ta c:

Do , biu din dng bng gc phc ca tn hi u thu c l:

y nl pha ca ng truy n th n.T trn ta thy s r t kh m t mt knh v tuyn mt cch cht ch v n

b chi ph i b i mt s yu t khng th d on. V vy, c tnh thng k s dng ccthng s knh c trnh by d i y s cung c p ci nhn su sc nghin cutnh cht cc knh trong h thng thng tin v tuyn.

2.3.1 Tr tr i Excess Delay

Mt knh v tuyn c th c th hi n y b i p ng knhh(, t) ca nti thi im t cho xung tr delta Dirac p dng ti thi im t - . Thc t, tn hiu thu

(2.3)

(2.4)

(2.5)

(2.2)


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gi tr RMS l n hnhoc x p x v i kho ng thi gian k hi u th mt s th tc ph i c thc hi n hn ch s suy gi m hi u nng c th x y ra my thu.2.3.3 Bng thng nht qun Bc

Bng thng nht qun Bc c o bng thay i trong p ng tn s knhtrn mt kho ng cc thnh phn tn s mt thi im t no . Ni cch khc, bngthng nht qun l s o thng k di tn s m trong d i ny knh cho qua tt c ccthnh phn ph v i suy gi m gn nh bng nhau v pha tuyn tnh. p ng tn s knh ti mt thi im t c xc nh l bin i Fourier c a h(,t) i v i nh sau:

Tn hi u c ph t v i bng thngnh hn Bc, p ng tn s knh c cho b i cng thc (2. 9) c coi l phng trn ton b ph tn hi u. Mt khc, nu bngthng tn hiu truyn d n l n hn Bc, ph tn hi u s b mo. Trong tr ng hp ny,knh c gi l chn lc tn s. Do , mt knh l phng hay ch n lc tn s ch yu ph thuc vo bng thng ca tn hiu truyn d n. Thng th ng, mt knh c th c gi l chn lc tn s nu bng thng truyn d n ca n l n hn 50% bng thngnht qun.Tn ti mi quan h ngh ch o gia Bc v RMS nh sau:

y Bc(a) l bng thng nht qun ti thiu mPDP c t tng quan v i gi tr a .

2.3.4 Bng thng nht qun v tn hiu tham chu n mi n t n s

V d t cu trc khung LTE, chng ta bit r ng kho ng cch gia hai sngmang con ln cn l f space = 15 kHz [6]. Trong mi n tn s, k hi u hoa tiu c tti mi sng mang con th 6, do ,kho ng cch gia cc hoa tiu lin tip c th c a ra nh sau:

(2.11)

(2.9)

(2.10)


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Da vo cng thc (2. 10), bng thng Bc(a) trong knh khng i c xc nhti a = 0, 9 v trong knh thay i ti a = 0,5 khi. D a trn nhng gi nh trn, bngthng nht qun i v i gi tr t tng quan 0, 5 c tnh nh sau:

Tng t, i v i gi tr t tng quan ca 0,9 ta c:

Phng trnh (2.12) v (2.13) cho th y kho ng cch gia cc k hi u hoa tiutrong kho ng tn s tng ng v i bng thng trong knh l khng i, hn naknh c tnh t nht hai l n tr c khi t tng quan c gi tr 0,5.

2.3.5 Tr i Doppler

Trong cc mi tr ng truy n thng di ng, s chuyn ng ca my thu, my pht hoc cc i t ng xung quanh d n n vi c m r ng ph ca tn hi u thu c.Trong iu ki n truyn d n a ng, hi u ng Doppler gy ra dch tn s i v itng sng mang thnh phn.

Nu gi nh mt my thu di ng ang chuyn ng v i tc vrx m/s v sng c truyn t mt tr m gc tn s sng mang f c. Nu gc gia h ng chuy n ngca my thu v h ng n ca sng c gi nh l, dch Doppler f d ca thnh phntn s f c c nh ngha l:

v i f Dmax l tn s Doppler l n nht v c tnh bng

vrx l vn tc ca my thu vc l vn tc nh sng.

(2.12)

(2.13)

(2.14)

(2.15)

(2.16)


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Trong cc h thng truy n thng di ng, tr i Doppler l n nht c s dng m t tc thay i ca c tnh knh v tuyn. Kho ng thi gian m p ng xungknh l khng i c gi l th i gian nh t quan T c, th ng c tnh nh sau:

v i T c(a) l th i gian nh t qun gi tr t tng quan la trong mi n th i gian.

2.3.6 Th i gian nh t qun v cc tn hiu hoa tiu min th i gian

Dng h thng LTE l mt v d mt ln na gi i thch mi quan h giakho ng cch hoa tiu cc sng mang v th i gian nh t qun. T cu trc khung LTE,chng ta bit r ng th i gian c a mt khe l 0,5 ms [6]. C 6 k hiu OFDM trong m tkhe th i gian nn trong mt kho ng k hiu, T sym c th c tnh bng:

y Tslot l di khe v Nsym l s k hi u cho m i khe. K hiu tham chu nc t ti mi k hiu OFDM th t, nhng c phn b trn cc sng mang ph khc nhau. Tuy nhin, knh c th c c tnh sau mi k hiu OFDM th ba. Do, kho ng cch gia cc k hiu tham chu n trong mi n thi gian l:

T ref = 3.T sym = 0,25 ms

Gi nh m t my thu c tc ti a 120 km/h ti tn s sng mang 2,4 GHz th ta s nhn c mt d ch Doppler t i a 266,67 Hz. Da trn gi nh v s dng

cc mi quan h c m t trong m c 2.3.2, ta c th tnh th i gian nh t qunT ctngng v i cc gi tr t tng quana= 0,9 v 0,5 nh d i y:

T c(0,5) = arccos(0,5)

= arccos(0,5) = 0,623 ms

T c(0,9) = arccos(0,9) = 0,269 ms

(2.18)

(2.19)

(2.17)

(2.20)

(2.21)

(2.22)(2.22)


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Phng trnh (2.18) v (2.19) cho th y kho ng cch gia cc k hiu thamchunngn hn so v i th i gian nh t qun. Hn na, knh c c tnh t nht hai l ntr c khi t tng quan ca c tnh knh c gi tr 0,5.

2.4 CC M HNH KNH TRONG H TH NG THNG TIN V TUY N

Cc nh h ng ca cc thng s knh ni trn vo tn hi u thu c c th c m hnh ha sao cho cu hnh ca tn hi u thu c ti my thu c th tnh ton c t cu hnh ca tn hi u truyn i. M hnh ca mi tr ng gia my pht vmy thu c gi l m hnh knh. Da trn cc kch b n khc nhau ti my thu, ccm hnh knh khc nhau c th c pht trin nghin cu hi u nng h thng timy thu. Phn ny s cp n m hnh knh c th c p dng cho c hai tiuchun DVB- T v LTE.

2.4.1 Knh Gauss

M hnh mt knh Gaussian m t tr ng hp trong cc tn hi u c pht tr c ti p n my thu qua mt knh n; t n hi u thu c ph thuc vo mc canhiu; k nh ch b nh h ng b i nhiu Gauss tr ng cng (AWGN) ch yu l dochnh my thuto ra. V cc sng mang con ca tn hi u pht c chun ha ti my pht, t s tn hi u trn nhiu (SNR) c iu khin bng cch thay i bin nhiu,

. Nng lng trung bnh ca mt k hi u OFDM l:

Do , SNR s c thit l p bng t s ca E s v bin nhiu :

(2.23)

(2.24)


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2.4.2 Knh Rice

Trong m hnh Rice, tn hi u thu c thnh phn n nh v t tr i ca ng

truyn thng, ccthnh phn a ng ng u nhin n my thu theo cc gc khc nhauv x p chng ln tn hi u v t tr i ny. M hnh ny c dng ton hc nh phngtrnh sau, v i s(t) v r(t) l tn hi u u vo v u ra tng ng:

Trong :

p0 s(t) idi ncho ngtruy nthngLOS. N l s tia tn x i l dch pha t tn x ca ng th i i l suy hao ca ng th i il tr tng i ca ng th i H s Ricean K (t l cng sut ca ng truy n thng v i ng tn x) c tnh

bng:

2.4.3 Knh pha inh Rayleigh

Nh c p trong ph n 2.2, khi m t tn hi u c truyn qua mi tr ng cvt c n d n n khng th truyn thng (NLOS), s xut hi n cc ng truy n do

ph n x. Cc tn hiu my thu l s x p chng ca cc tn hi u thng qua cc ngkhc nhau v i tr v dch pha c a ring chng. Trn thc t, kho ng cch gia my pht v my thu l rt l n so v i di b c sng ca sng mang, do ta c th gi nh r ng d ch pha c phn b ng u t0n2 rad v pha ca mi ng l clp . Khi c s l ng l n cc ng, mi ng c th c m hnh ha nh mt

bin ng u nhin Gauss phc bng cch p dng nh l gi i hn trung tm [7]. Mhnh ny c gi l knh phading Rayleigh.

(2.25)

(2.26)


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Mt bin ng u nhin Gauss phc c dng: Z = X + jY , trong X v Y c trung bnh bng khng, c lp v phn phi ging bin ng u nhin Gaussian. Gi nh r ngcc bin ng u nhin l theo vng trn i xng, phn phi xc sut bin ca bin

ng u nhin ln lt l:

v i p(z) l phn b Rayleigh v z l h s pha- inh.Do , m hnh knh Rayleigh c th c to ra t phng trnh sau y v i

s(t) v r(t) l tn hi u u vo v u ra tng ng:

2.5 K T LU N

Nh vy, trong chng 2, n tp trung m t cc tc ng ca phn cngkhng l tng, cc thng s ca k nh v tuyn v m hnh ha cc nh h ng ca

chng n knh v tuyn thng qua cc knh m hnh khc nhau nhm c tnh ctn hi u pht t tn hi u thu c ng th i c i thi n hi u nng h thng. y l cs cho th tc ng b trong cc h thng thng tin v tuyn.

(2.27)

(2.28)


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n tt nghi p Chng III ng b trong h thng Overlay Cognitive

34V Vn Minh D09VT5

CH NG IIING B TRONG H TH NG OVERLAY COGNITIVE

3.1 NG B TRONG CC H TH NG V TUY N THNG D NG V COGNITIVE

3.1.1 ng b trong cc h th ng thng tin.

Trong b t k h thng thng tin lin lc no, qu trnh xy dng thng tin

my thu u cn bit mt s thng tin v tn hi u c pht v knhtruyn d n min hnh l p ng pha knh, tn s sng mang, nh thi thng tin n v pha sngmang. Tuy nhin, trong thc t, nhng thng tin khng c sn tr c v phic c tnh t tn hi u thu c. Tn s sng mng my thu b l ch so v i tn s sng mang ti my pht v nhiu l do. Hiu ng Doppler sinh ra t chuyn ng tngi ca my pht v i my thu l mt v d, hay ph n cng khng l tng c ptrong chng II cng gy ra nhng thay i trn. Do s khc bi t cc thng s

gia my pht v my thu cn c c tnh v hiu ch nh c i thi n hi u nng h thng mc c th ch p nhn c. Tng t nh vy, trong mi trng thng tinlin lc thc t, ph i mt mt l ng hu hn thi gian sng mang mang thng tin t my pht n my thu. Tr truyn d n do lan truy n trong mi tr ng d n dn khngkh p nh th i k hi u gia my pht v my thu. Do , chng ta cn ph i bit nhth i k hi u chnh xc my thu khc phc s xung c p hi u nng do khng kh pnh th i. D ch pha sng mang ca tn hi u thu c ch yu bao g m: p ng phaknh, pha do dch nh thi v nhiu pha t my pht dao ng ni. N cn c tnhton v b p trong tr ng h p gi i iu ch nht qun.

m hnh ha s khc bi t ni trn, chng ta cn ph i b sung cc m hnhknh khng phn tn n gi n m chng ta s dng trong cc chng tr c. Tn hi uthu c trong m hnh l:

(3.1)


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trong v(t) l tn hi u bng c s v cc thng s m i f v c s dng mhnh l ch ca tn s sng mang thu c t tn s sng mang danh nh v tr truyn d n tng ng. Qu trnh c tnh cc thng s ny c gi l ng b ha.

Phn n y tr nh b y v cc tc ng ca cc li ng b ha tn s v th i giann hi u nng ca mt h thng thng tin n gin bng cch ly mt h thng truy nd n BPSK nh mt v d.

Hnh 3.1 B i u ch BPSK vi cc thng s c c tnh Trong h thng BPSK tn hi u thu c c th c a ra nh sau:

r(t) = ApT (t ) cos[2(fc +f)(t + ) + ] + n(t) = ApT (t ) cos[2 (fc +f )t + ] + n(t)

trong n(t) l knh AWGN v i mt ph N 0 /2 v l s k t h p ca p ng pha,

pha do nh th i d ch v nhiu pha. Gi s chng ta c tnh c , v ca ccthng s f , v v i vi c s dng mt thut ton ng b no . Do , vi c b timy thu c th c thc hi n bng cch s dng cc thng s c c tnh th hi n trong s khi trong h nh 3.1 trn. Khi - T , xc sut li bit c th ctnh nh sau:

c gi tr nh hn hoc bng phn t n v, ng thc x y ra ch khi f = , =v = . Do , t phng trnh (3.5), chng ta th y r ng bt k li no trong cctham s c c tnh s y kh nng li bit ln trn xc sut li ti u. Ngoi ra,nu

li c tnh f, |f- | , nh hnr t nhiu so v i tc truyn t i d li u ( ) , v th:

(3.4)

(3.5)

(3.2)

(3.3)


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y = - v = - . Do li trong c tnh dch tn s v tr thi gian gyra s xung cp ng k trong hi u sut t l li bit. Cc s li u khc o hi u sutca thut ton ng b ha s c th o lun trong chng ny kt h p v i cc thutton ng b ha da trn OFDM.

3.1.2 ng b th i gian v tn s trong h th ng OFDM

3.1.2.1 Gi

i thi

u chung

OFDM ni ln nh mt trong nh ng cng ngh truy c p v tuyn ha hnnht trong hai th p nin qua. Phm vi ng dng ca n t truyn thng c dy nhDSL n mng cc b khng dy hay truyn pht m thanh v hnh nh k thut s.OFDM cng l mt nn t ng quan tr ng trong cng ngh truyn thng di ng nhWiMAX di ng v LTE.

Nguyn l ca OFDM l phn chia tng bng thng cn truyn vo mt s sngmang con c th truyn ng thi cc sng mang ny. Bng cch ny lung s tc cao c th c chia thnh nhiu lung tc thp hn. V th c th gi m nhh ng ca tr a ng v chuyn i knh pha inhchn lc thnh knh pha-inh

phng. Nh vy OFDM l mt gi i php cho tnh chn lc ca cc knh pha-inh.Vi c chia t ng bng thng thnh nhiu bng con v i cc sng mang con d n n gi m r ng bng con trong min tn s v v th tng di k hiu. S sng mang concng l n th di k hi u cng l n. iu ny c ngha l di k hiu l n hn sov i th i gian tr i r ng tr ca knh pha-inh phn tn theo thi gian, hay r ng bngtn tn hiu nh hn r ng bng tn nht qun ca knh. Trong cc s iu ch asng mang, cc bng con ph i nh v khng c chng ln ln nhau (cn ckho ng b o v ). Nhng trong OFDM cc knh con c th chng ln ln nhau, nhng

ph i tr c giao v i nhau, nh vy khng cn cc bng tn b o v v v th r t tit ki m

ph tn.

(3.6)


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Lung s cn truyn c phn thnh cc on di 2.log sc N M , trong , NSC l

s cc sng mang con s c s dng mang cc bit thng tin v M l s tr ng thica s iu ch. Sau b bin i S/P cc bit ca khi k c chuy n thnh NSC cm

z p,k v i (p=0,1. , NSC -1) v (k=-,; k biu th cho th i im pht on bit),mi mt cm c di 2logm M bit . Sau cc b MAP (s p xp tn hi u iu ch)

cm z p,k c s p xp ln 1 trong M vec t iu ch , p k x trong mi n th i gian. Sau b

DFT N SC m u min thi gian c chuy n i vo Nsc mu min tn s: , p k X . B s p

xp sng mang con thc hi n s p x p Nsc m u min tn s ln cc v tr quy nhtrong t p cc sng mang con u vo IFFT. C hai cch s p x p: s p xp khoanh vng

v s p xp phn b. trong cch s p x p th nht, N sc m u c s p xp ln mt vnglin tc cc sng mang con cn cch s p x p th 2 m u tn s c s p xp vo ccsng mang con phn b tr ong ton b bng tn. Sau cc mu tn s c b IFFTchuyn i t cc m u trong mi n tn s thnh cc mu trong mi n th i gian. Ti ptheo s chn V mu CP t i b chn CP Sau b bin i song song thnh ni ti p N+Vm u thi gian ny c chuy n i thnh dy xk ni ti p Sau b bin i s vo tngt ta c tn hiu s(t). pha thu qua trnh c thc hi n ng c li.

Hnh 3.2 S kh i h th ng truy n d n OFDM


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trnh nhiu lin k hiu (ISI), ti n t chu trnh c thm vo u ca mik hi u. iu ny c th c thc hi n bng cch sao chp mt phn cui cng cak hi u OFDM nh l mt tin t. di ca tin t chu trnh TG cn l n hn tr

tr i cc i ca knh trnh suy gim hi u sut do nhi u ISI . Do , di tng cak hi u OFDM l di tin t chu trnh TG cng v i di IFFT. Vi c chn tin t chu trnh c th cho php n gin trong vi c c tnh v cn bng knh trong mt cutrc knh song song trc giao tng ng. Mc d c s gia tng cng sut truyn t iv gi m tc d li u do ti n t chu trnh, nhng nhng li ch t chng v n c gi tr hn nhng bt li trn. Sau khi chn CP, cc k hi u OFDM c chuy n i ln tns v tuyn RF v truyn qua knh. Ti my thu, tn hi u c h tn xung n tn s

trung gian (IF) v thc hi n ng b ha xc nh th i gian xu t hi n ca cc khi u OFDM v iu ch nh cc dch tn s.

Truyn t i d li u trong cc bng con h p tr c giao hi u qu hn rt nhiu trongiu ki n knh pha-inh a ng v s c mt ca nhiu xung. Tuy nhin, n i hichi ph cho vi c ng b ha chnh xc cc tn s sng mang con my pht v mythu OFDM. B i v kho ng cch gia cc sng mang con nhn hp, tnh trc giao c acc sng mang con ny tr nn nhy c m hn v i dch tn s. Ngay c khi c tnhnh thi k hi u p dng vi c s dng cc tin t chu trnh m r ng cc k hi u th c tnh dch tn v n cn kh chnh xc trnh nhiu knh lin sng mang ICI. Mtkhc, nu cc c tnh nh thi k hi u khng vt qu chiu di CP th dch phatrong mi n tn s ch i hi mt qu trnh thng thng thng b li. D ch tn s lm mt tnh trc giao gi a cc sng mang con, do gy ra ICI. C ba li ng b ha chnh trong h thng OFDM: d ch nh thi k hiu (STO), d ch tn s sng mang

(CFO) v dch tn s xung l y m u (SCFO).C hai thng s cha bit ti my thu: thi im n ca k hi u OFDM v tn

s sng mang m n c truyn i. Thi im n ca k hi u c m phng nhtr trong cc p ng xung knh xung(k - ), trong l thi im n c gi tr nguyn cha bit ca k hiu. D ch tn s phn on c m phng nh s bin dng

bi phc ca d li u thu c trong mi n th i gian e j2 k/N , trong biu th s khc bi t gia cc my to dao ng my pht v my thu nh mt phn ca kho ng cchgia cc sng mang v N i di n cho chi u di FFT. Chng ta gi nh r ng my pht


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39V Vn Minh D09VT5

v my thu l n nh sao cho t t c cc sng mang con c s dch chuy n tng t nhau. D a trn gi nh tr c r ng cc knh l khng phn tn v tn hiu truyn ch b

nh h ng b i phc AWGN, cc tn hiu my thu c th c m hnh ha nh sau:

r(k) = s(k ) + n(k) y hai th ng s ng b ha kh c kh ng c t nh m hnh n y. u ti n,

dch pha c a s ng mang c th nh h ng n t l li k hi u iu ch nht qu ntrong tr ng h p kh ng c c t nh k nh. Tuy nhi n nu d li u c m ha theokiu kh c th hi u ng n y c loi b. Th hai l dch tn s ly m u c ng s nhh ng n hi u nng h thng. Ch ng ta gi nh r ng d ch l khng ng k .

Nhiu nghi n cu c thc hi n c tnh v iu ch nh d ch th i gian v tn s trong h thng OFDM d a tr n mt s ph ng ph p kh c nhau. H u ht ccthut to n ng b th i gian v tn s tn dng l i th ca t nh cht tun ho n ca t nhi u min th i gian hay s dng c c k hi u ng b c thit k c bi t cho m cch ng b. Mt s k thut ng b th i gian v tn s s c tr nh b y sau y.

3.1.2.2 C c k thu t ng b nh th i k hi u v t n s

Phn n y c p n cc ph ng ph p hi n c khc nhau c t nh th i gian bt u ca vi c truyn k hi u v dch nh th i. Trong [8 ], c tnh nh th i k hi u c thc hi n da tr n vi c tm kim mt chui ng b duy nh t v i hai n aging nhau trong th i hn mt na th i gian k hi u OFDM. M t chui nh th trongmin th i gian l k t qu ca vi c truyn chui Pseudo-Noise (PN) tr n tn s chn v s khng tr n cc tn s l.

Chui ng b duy nh t s c ph n t ch khi n n m y thu. Cho L l s l ng m u trong n a u ca chui ng b. Hai n a ca chui l ging h t nhaungoi tr s d ch pha g y ra b i d ch tn s gia m y ph t v my thu. T i mi im

bt u khung, t ng c c t ch ca L m u trong n a u v lin h p ca c c m u t ngng trong n a th hai c th c a ra nh sau:

(3.8)

(3.7)


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trong d l thi im c th bt u khung, r m l cc m u bng gc phc. imkhi u ca cc k hi u, cc tch ca mi c p m u ch ra cng sut ca cc m u v

pha g n nh khng i, 2f , tng t cho t t c cc tch. T phng trnh (3.7), m t

h s nh thi c th c nh ngha l:

Hnh 3.3 H s nh th i phn m u ca mt mng WLAN trn knh AWGN 20dB ,chiu di FFT l 512 v chi u d i CP l 64

Hnh 3.3 trn cho thy mt v d v mt h s nh th i ca tn hiu trong m tmng WLAN thng th ng (L = 512 v CP = 64) c truyn qua knh AWGN v iSNR t ng l 20 dB. Khi h s nh thi t n mt ngng c di tng ngv i chiu di ca kho ng b o v tr i tr i tr ca knh th th i gian b t u ca khungc th l bt c lc no trong phm vi c a ngng m khng gy bt k nhiu no.Tuy nhin s khng r rng ny trong vi c xc nh th i gian l y m u chnh xc t ravn trong vi c trin khai th c t. Mt s phng php x l tn hi u c s dng nhm trnh s khng r rng ny c c mt nh chi m u th tng ihp m c th d dng pht hi n. V d trong m ng WLAN c p trn, lc phihp u ra tngquan chu n ha v i mt b lc c h s thng nht c s dng c c mt nh n ti cnh ca ngng nh th hi n trong hnh 3.4 d i y:

(3.9)


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Hnh 3.4 H s nh thi v u ra l c ph i h pDch tn s c th c c tnh bng cch khai thc thc t sau y. S khc

bi t duy nh t gia hai m u cch nhau L/2 m u trong chu i PN l s khc bi t v pha:

My thu c th xc nh pha t i c c nh tm c (thi im bt u k hiu)v ti thi im cc m u tng quan ging h t nhau v pha ca u ra tng quan(nu c) l do dch tn s gia my pht v my thu. Do :

v do

Phng trnh(3.11 ) a ra c tnh cho phn thp phn ca d ch tn s. Bng

cch c tnh phn thp phn ca d ch tn s v sa cha n bng cch nhn cc muv i e-2jt / T chng ta c th trnh nhiu sng mang ln cn v duy tr trc giao gi a ccsng mang con lin tip. iu ny thng c gi l ng b ha tn s th. Cc thut ton ng b ha trong [8] i hi mt chui PN th hai c tnh s thayi trong cc frequency bins (phn nguyn dch tn s). Trong k thut ny, sau khi haichui PN c b tr cho ph n thp phn ca d ch tn s, chng c chuy n vomin tn s. FFTs c a chng l x1,k v x2,k v cho chui PN iu ch vi phn trn cctn s chn ca cc k hiu ng b th hai vk . Chui PN s xut hi n u ra tr khi

(3.10)

(3.11)

(3.12)

(3.13)


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n b d ch v tr do khng b dch tn ca 2z/T m z l mt s nguyn. Lu rng b iv c mt kho ng b o v v v n cn dch tn s, ngay c khi khng c iu ch vi phn gia cc k hiu ng b 1 v 2 (tc l chui PN), v n s l mt dch pha gi a

x1,k v x2,k ca 2(T+T g )2z/T . V th, thi im ny, phn nguyn v dch pha b sungny cha bit. Tuy nhin, v dch pha l nh nhau cho mi c p tn s, mt h s tngt v i phng trnh (37) c th c s dng. Cho X l t p h p ca cc ch s cho ccthnh phn tn s chn. S v tr chnb d ch c th c tnh bng cch tm cci ha:

v i vi c tng phm vi ph n nguyn ca cc dch tn c th v l s l ng tn s chnca chui PN. c tnh dch tn cui cng c th tnh nh sau:

V i cc d li u khng h tr loi ng b thi gian v tn s nh trong [9],

chng ta khai thc tnh cht theo chu k ca cc k hi u tm ra thi im bt u khi u v dch tn s. Phn d i y xem xt v th i gian h p l cc i v phng php c tnh dch tn da trn tin t chu trnh ca k hiu OFDM.

Hnh 3.5 M hnh ca k hiu OFDM trong mi n th i gian

(3.14)

(3.15)


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43V Vn Minh D09VT5

Gi s chng ta c M k hiu OFDM, m i k hiu c di N + L, t rong Nl di FFT v L l di CP. Thi im bt u ca mt k hiu nht nh trongtng khi l ng m u thu c l cha bit do s khng chc chn ti my thu v

tr truyn . Gi ch s ca cc mu thu c l a = {, +1, +2,, +L-1}. Ccm u ca cc ch s a v a + N tng quan l n nhau trong khi cc m u cn li khngtng quan. Do :

y k a , l cng sut k hi u v l chnh lch tn s sng mang gia my

pht v my thu. Da vo tnh cht tng quan ca cc k hi u quan st c trong r ,ta c hm log-likelihood c pht trin [8]:

v i

H s s dng c tnh v c th c tnh bng ly tng quan ca tnhi u thu c v i tr ca chnh n.

Hm likelihood t cc i theo khi cos t gi i hn bng mt trong cngthc 3.17 . Do , c tnh ML ca l:

(3.18)

(3.19)

(3.20)

(3.16)

(3.21)

(3.22)

(3.17)


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Thay phng trnh (50) vo phng trnh (46), ta c c hm likelihood nntheo nh sau:

Khi , c tnh ML ca v l:

Hi u sut ca c tnh likelihood cc i ch yu b nh h ng bi gi tr SNRv chiu di tin t chu trnh L. Khi tng chiu di ca tin t chu trnh, c tnh dchtn s c c i thi n tng ng. iu ny l do vic s dng trung bnh cc pha ca h s trong phng trnh (3.21) cc m u CP tm dch tn s. Khi tng SNR, kh nng pht hi n sai m t nh gi m tng ng, do lm tng hiu sut ca c tnh. Chiudi CP c bit my thu v SNR c th c c nh. V c b n, h s (m)

cung c p cc c tnh ca v . l n nng l ng chu n haca n xc nh ccnh l v tr im bt u k hiu. Pha t i mi im nh t l thun v i ML. Hnh 3.6cho th y u ra c a phng trnh (3.21) cho lu ng DVB-T th nghi m. Cc nh chothy cc c tnh nh th i cho m i k hi u. Cc pha ti thi im tng ng c s dng xc nh d ch tn s trong h thng.

Hnh 3.6 Mt phn cc m u thu c tn hiu DVB-T ch 2K, kho ng bo v vi SNR l 20dB.

(3.24)

(3.25)

(3.23)


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ti ny ch xt cho tr ng h p FDD . Hnh 3.7 cho thy cu trc l i ti nguyn khnggian th i gian tn s ca LTE.

Hnh 3.7 C u trc l i t i nguyn khng gian th i gian t n s ca LTE.

Nh th hi n trong hnh, cc k hiu OFDM trong mi n thi gian c cu trcthnh mt khung LTE. Khung LTE bao g m 10 khung con c th i gian 1ms. M ikhung con bao g m hai khe th i gian, m i khe 0,5ms. Trong m t khe th i gian, c 7k hi u OFDM v i phn th i gian h u ch l 0,067ms. Do , c tng s 140 k hiuOFDM trong m t khung th i gian 10ms.

3.1.3.2 Cc tn hiu ng b s cp v th c p

Nh cp trong cc phn tr c, cc tn hi u ng b s cp v th cp lr t quan tr ng trong tm kim LTE v th tc ng b nh thi khung. c l p v i bng thng knh c xc nh, 6 kh i ti nguyn xung quanh DC trong min tn s c dnh ring cho vic truyn t i cc tn hi u ng b. V i kho ng cch sng mangl 15 kHz, mt d i tn s c tng cng 6 12 15kHz = 1,08MHz c dnh ring


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47V Vn Minh D09VT5

xung quanh DC cho cc tn hi u ng b. V i 72 sng mang con dnh ring, 62 sngmang c s dng truyn cc tn hi u ng b. iu ny gip n gi n ho cctnh ton x l tn hiu ti cc thit b u cui bng cch cho php nh chiu di FFT

thp v thp hn t l ly m u. Trong mi n thi gian, chng c truyn mi khungcon th nm thc hi n ng b ha thi gian trn mi kho ng thi gian c s 5ms.Trong tiu chun 3GPP LTE, c ba chui ng b s c p duy nh t v 168 chui th c p. B i s xo trn cc chui th c p v i s cp, chng ta c th nhn c 504chui c th nhn dng mt duy nht trong m ng.

Cc tn hi u s cp c s dng thc hi n ng b nh th i 5ms gi a ccBS v UE. Chng c truyn trong k hiu OFDM cu i cng ca khe th i gian u

tin ca khung u tin (khung con 0) v khung con th nm trong mt khung vtuyn. Loi tn hi u c s dng ng b chnh l chui Zadoff-Chu (ZC) chuic tnh cht bin khng i v t tng quan bng khng. Thuc tnh bin khng i gip gim thiu t l nh trn trung bnh, trong khi t tng quan bngkhng t c cc tnh cht tt trong mi n thi gian. Phng trnh (3.27) cho th ycch to ra chu i ZC s dng ng b s c p:

trong u l ch s gc ph thuc vo ID a phng c chn. Trong cch ti pcn mng phn c p, m ng c chia thnh mt s nhm t bo, mi nhm cha ba .Cc trong mt nhm nht nh c mt ID nhn di n chng duy nht ti nhm .Tuy nhin cc ID c lp i l p li cho cc cc nhm t bo khc. Tiu chun3GPP LTE c 168 nhm t bo nh vy v 504 ID duy nht.

Sau khi th c hi n ng b nh th i 5ms b ng cch s dng tn hi u s c p, cctn hi u ng b th cp c s dng nhm xc nh nh thi khung v ID nhm xc nh duy nh t mt trong mng. Cc tn hiu th cp lun c truyn tr ccc tn hiu s c p trong m t k hi u OFDM nh trong hnh 3.8

(3.27)


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48V Vn Minh D09VT5

Hnh 3.8 Cc k hiu ng b s cp v th c p trong m t khung LTE

ng b cc chui th cp SSS c hnh thnh bng cch ghp xen k hai

chui c chiudi 31 l v , ph thuc vo s la chn ID a phng

nh trong tr ng h p ca cc chui ng b chnh PSS. Trong khung con u tin,

c nh x t i cc sng mang con chn v l nh x t i cc sng mang

con l v ng c li-trong khung con th su. S k t h p ca cc ch s m0 v m1 xcnh duy nh t mt nhm trong 168 nhm t bo. Ty thuc vo ch s sng mang con,

chn hay l m mt chui tr n khc c s dng cho cc chui v . Trong

tr ng h p ch s sng mang con l chn, chu i tr n s dng lc0(n) v ch s sngmang con l l th n lc1(n). Ty thuc vo s l ng khung con, chu i tr n cthm s dng cho chu i nh x t i cc sng mang con l. i v i khung con 0, n

l (n) v v i khung con th 5, (n) c s dng. M i chui trong hai chu i

tr n ny ph thuc vo cc ch s m0 v m1 xc nh nhm . Vic to ra c a SSS

c tm tt trong phng trnh (3.28 ) d i y:

(3.28a)

(3.28b)


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3.1.3.3 ng b th i gian

cc thit b u cui LTE trch xut thng tin h thng c truyn t cc

tr m gc v xc nh chnh xc v tr cc hoa tiu, nh th i khung gi a my pht vmy thu ph i c ng b. Nh cp trong cc phn tr c, tn hi u ng b scp ng vai tr quan trng trong vi c ng b nh thi khung. Qu trnh ng b c thc hi n bng t tng quan ca tn hi u thu c ca mi tn hi u ng b sc p trong mi n thi gian. Do tnh cht t tng quan mnh m ca cc tn hi u ng

b s c p trong mi n th i gian, my thu s xc c nh tr i ni t tn hi u ng b s c p, sau m i 5ms . Do , cc tnhi u s cp cho php t c ng b na

khung. Tuy nhin, tm ra thi im bt u ca ton b khung, chng ta cn khaithc cc tnh cht ca cc tn hi u ng b th c p. T phng trnh (3.28 ), do cc tnhi u th cp trong khung con u tin v th su c iu ch v i cc chui tr nkhc nhau, tng quan ca tn hi u thu c v i c hai chu i ny s cho bi t cc khi u trong khung con u tin hay th 6, do xc nh c thi im bt u cakhung.

3.1.3.4 ng b t n s

Truyn d n ng xung LTE s dng OFDM lm k thut l p vt l, cho phptruyn d n d li u tc cao trong cc kch b n pha- inh chn lc tn s. Tuy nhin,mt trong nh ng hn ch ca OFDMA l nhy c m v i dch tn s sng mang CFO.V i tn s sng mang 2,5GHz, mt d ch thng th ng 10ppm c a my to dao ng

ni cng gy ra dch 25kHz. H thng LTE s dng mt kho ng cch c nh gia ccsng mang con l 15kHz th dch CFO tng ng l1,67 kho ng cch sng mang con.Dch ny gy ra nhiu xuyn knh ICI v mo pha tn hi u nhn c nu khnghi u ch nh. Ph n ny s m t k hoch c tnh CFO cho ng xung LTE, g m 2 b c nh sau:

c tnh phn thp phn ca d ch tn s FFO: FFO gy ra ICI bng cch phhy tnh trc giao gi a cc sng mang con. V vy, n ph i c b tr c khitn hi u thu c c chuy n sang mi n tn s. Phng php c tnh


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likelihood c c i c p trong ph n 3.1.2.2 s c s dng c tnh FFO. c tnh ML ca FFO c a ra trong phng trnh (3.21 ) c th c m r ng cho m t khung co n nh sau:

y Nsf l s k hi u OFDM trong m t khung con.

c tnh phn nguyn ca d ch tn s IFO: Sau khi c tnh FFO c thchi n, chng ta gi nh cc phn thp phn ca CFO c sa cha hu ht.Phn nguyn ca cc CFO c hai tc ng vo cc tn hi u thu c. u tinl s d ch chuy n tn s khung, c ngha l, cc k hiu truyn trn sng mangcon k IFO li thu c trn sng mang con k. Tc ng th hai l xoay pha t l thun v i ch s OFDM. Hai tc ng trn c th c b p khi IFO c c tnh. Cc k hi u c s dng c tnh c th l mt trong hai hoa tiunh tr c hoc cc k hiu d li u iu ch PSK. Trong tr ng hp ny, ta

chn dng cc tn hi u ng b c tnh, dn t i c tnh IFO sau y:

y PSS v SSS tng ng l chui ng b s cp v th cp, k l ch s sng mang con ca cc chui ng b v Ng l chiu di bo v . V cc chui

ng b ch c tm thy trong cc khung con u tin v th su nn c tnhca IFO ch c th c thc hi n trong cc khung con .

3.1.4 ng b trong h th ng DVB-T

Trong m t m y thu DVB-T in h nh, giai on thu ti n FFT l cn thit cth nh th i k hi u OFDM v xc nh chi u di k hi u OFDM , l k ch th c

ca chuy n i Fourier nhanh FFT v chiu di tin t chu tr nh, n i m sau n y hai

(3.29)

(3.30)


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51V Vn Minh D09VT5

thng s c iu ch nh b i my ph t. Nguy n tc ng b tin FFT d a tr n s snc ca tin t chu tr nh trong c c k hi u OFDM trong khi theo d i v ng b tn s FFT li n quan n vi c s dng c c t n hi u tham chu n c ph n phi trong c c cu

tr c khung. C u tr c khung OFDM s c tr nh b y trong ph n ti p theo gi p gi ithch qu tr nh ng b trong h thng DVB-T.

3.1.4.1 C u tr c khung

Trong h thng DVB-T, t n hi u truyn i c t chc th nh c c khung, c 4khung li n ti p to th nh mt siu khung. M i khung ch a 68 k hi u OFDM trongmin th i gian ( c nh dut 0 n 67). M i k hi u ny cha hng ng n sngmang (6817 s ng mang v i ch 8K, v 1705sng mang v i ch 2K) n m d yc trong d i th ng 8 MHz (Vi t Nam ch n d i th ng 8MHz, ngo i ra c th chn d ithng 7MHz). H nh 3.9 d i y biu din ph n b sng mang c a DVB-T theo th igian v tn s.

Hnh 3.9 Phn b sng mang ca DVB- T (cha chn khong bo v ) Ngoi vic truyn d li u, mt khung OFDM cn cha cc sng mang hoa tiu

phn tn, cc sng mang hoa tiu lin tc v cc sng mang thng s truyn d n tnhi u TPS. Cc hoa tiu c th c s dng ng b khung, ng b tn s,


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3.1.4.2 ng b th i gian

Cc thut ton ng b thi gian thng khai thc s c mt ca mt tin t chu

trnh di tm ra thi im bt u ca mt k hiu. Thu t ton ny s dng phng php ML tho lun trong ph n 3.1.2.2. K t qu ca t tng quan gia tn hiu thuc v phin bn tr ca n ch ra nh chi m u th im bt u ca mi k hiu.Khi th i gian b t u ca k hi u c bit, chng ta c th xc nh v tr cc hoa tiuTPS trong cc k hi u v gi i m thng tin trong n xc nh th i gian b t u cakhung. Cc hoa tiu TPS c t chc thnh cc khi 68 bit, m i bit c truyn trnmt s sng mang con trong mt k hiu O FDM. Do , ng b khung yu cumtkho ng th i gian t 17 n 84 k hi u OFDM ty thuc vo k hi u OFDM u tinthu c trong khung.

3.1.4.3 ng b t n s

Ngoi c tnh dch nh th i, pha do d ch tn s phn on c th c xcnh v s dng sa FFO trong mi n thi gian. Do , ch c cc CFO l bi s cakho ng cch gia cc sng mang con s v n nm trong tn hiu OFDM trong mi n tns. Cc OFDM khi phc c chuy n i FFT, vi c ny tng t nh lc thch ngcho tn hi u OFDM. ng b FFT s thu c c tnh phn nguyn ca cc CFO vSCFO trong mi n tn s, m sau c b p trong tn hiu OFDM trong mi n th igian gi m ICI. S quay pha trong mi n tn s gy ra b i dch thi gian c ctnh v b p bng cch s dng cc hoa tiu lin tc.

Cc phng php ng b trnh by trn cho cc cng ngh khc nhau c th c s dng trong chia s ph v tuyn s c p, th c p trong Cognitive ho c cho c mnhn cc khong tr ng trong vng quang ph c cp php trong InterweaverCognitive ho c pht hin kho ng thi gian nh th i truyn t i trong phng phpOverlay Cognitive.


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Synchronization in Cognitive Overlay Systems_Vu Van Minh