06 – dhth8clt – tieu luan wireless networks

B CNG THNG TRNG I HC CNG NGHIP TP. H CH MINH

KHOA CNG NGH THNG TIN

TIU LUN MNG KHNG DY

TM HIU SC-FDE & SC-FDMA

Gio vin hng dn : ThS. ng Thanh Bnh

Sinh vin thc hin : 12018285 Hunh Ngc Ho

12164101 V Kim Hiu

12155411 Cao Vn i

12156671 Nguyn Thnh t

Lp : HTH8CLT

TP. H CH MINH, THNG 03 NM 2014

Tiu lun Mng Khng Dy TM HIU SC-FDE & SC-FDMA

2

NHN XT CA GIO VIN HNG DN

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Phn nh gi:

thc thc hin: ................................................................................................

Ni dung thc hin: ............................................................................................

Hnh thc trnh by: ...........................................................................................

Tng hp kt qu: ...............................................................................................

im bng s: .......................................... im bng

ch: ...................................................................

Tp. H Ch Minh, ngy thng nm

Gio vin hng dn


3

LI CM N

Trong sut qu trnh hc tp ti trng i Hc Cng Nghip Tp.HCM, nhm

em c nhng thy c gio trong khoa Cng Ngh Thng Tin truyn t, ch bo

nhit tnh nhng kin thc nn tng v chuyn mn trong chuyn ngnh v gip cho

chng em rn luyn tinh thn, nhanh chng ha nhp vi mi trng lm vic sau khi

ra trng, l nn tng vng chc gip chng em thnh cng trong s nghip sau ny.

Do thi gian lm Tiu lun c hn v kin thc cn hn ch nn khng th trnh

khi thiu st. Chng em rt mong nhn c s gp ca qu thy c bi bo

Tiu lun c hon thin hn.

Cui cng em xin gi li cm n chn thnh cc Thy ng Thanh Bnh

gip chng em hon thnh tiu lun ny. Knh chc cc thy sc khe, hnh phc v

vng bc trn con ng s nghip trng ngi vinh quang.

TP. H Ch Minh, ngy 30 thng 03 nm 2014

Nhm sinh vin thc hin


4

MC LC

1. Tng quan k thut iu ch OFDM .................................................................. 6 1.1 Cc u im ca OFDM ................................................................................. 7 1.2 Cc nhc im ca OFDM ........................................................................... 7 2. iu ch n sng mang vi cn bng min tn s SC-FDE ............................. 8 2.1 Cn bng min tn s ...................................................................................... 8 2.2 So snh vi OFDM ....................................................................................... 10 3. FDMA n sng mang ...................................................................................... 11 3.1 X l tn hiu SC-FDMA ............................................................................... 11 3.1.1 X l bn gi ............................................................................................. 11 3.1.2 X l pha bn nhn .................................................................................. 15 3.2 a truy cp phn chia theo tn s n sng mang ........................................ 23 3.2.1 SC-FDMA khoanh vng (LFDMA) ......................................................... 25 3.2.2 SC-FDMA phn b (DFDMA) ................................................................. 26 4. Lp lch ph thuc knh truyn (Channel-Dependent Scheduling CDS) ...... 27 4.1 Hiu sut SC-FDMA ..................................................................................... 28 4.2 Lp lch cp pht sng mang con .................................................................. 28 4.3 Kt qu lch biu ........................................................................................... 29 5. H thng MIMO SC-FDMA ............................................................................. 29 6. c tnh cng sut nh ca mt tn hiu SC-FDMA ....................................... 29 7. Kt lun v hng pht trin ............................................................................. 29 7.1 Kt lun ......................................................................................................... 29 7.2 Hng pht trin ........................................................................................... 30 Ti liu tham kho ................................................................................................. 31


5

DANH SCH NHM 06:

STT H & TN MSSV GHI CH

1 HUNH NGC HO 12018285

2 V KIM HIU 12164101

3 CAO VN I 12155411

4 NGUYN THNH T 12156671


6

1. Tng quan k thut iu ch OFDM

K thut OFDM (Orthogonal frequency-division multiplexing) l mt trng

hp c bit ca phng php iu ch a sng mang, trong cc sng mang ph

trc giao vi nhau, nh vy ph tnh hiu cc sng mang ph cho php chng ln

ln nhau m pha thu vn c th khi phc li tn hiu ban u. S chng ln ph tn

hiu lm cho h thng OFDM c hiu sut s dng ph ln hn nhiu so vi k thut

iu ch thng thng.

K thut iu ch OFDM do R.W Chang pht minh nm 1966 M [1]. Trong

nhng thp k va qua, nhiu cng trnh khoa hc v k thut ny c thc hin

khp ni trn th gii. c bit l cng trnh khoa hc ca Weistein v Ebert

chng minh rng php iu ch OFDM c th thc hin c thng qua php bin

i IDFT v php gii iu ch OFDM c th thc hin c bng php bin i

DFT[2]. Pht minh ny cng vi s pht trin ca k thut s lm cho k thut iu

ch OFDM c ng dng tr nn rng ri. Thay v s dng IDFT ngi ta c th s

dng php bin i nhan IFFT cho b iu ch OFDM, s dng FFT cho b gii iu

ch OFDM.

Ngy nay k thut OFDM cn kt hp vi phng php m knh s dng

trong thng tin v tuyn. Cc h thng ny cn c gi COFDM (code OFDM).

Trong h thng ny tn hiu trc khi c iu ch OFDM s c m knh vi cc

loi m khc nhau nhm mc ch chng li cc li ng truyn. Do cht lng

knh (fading v SNR) ca mi sng mang ph l khc nhau, ngi ta iu ch tn

hiu trn mi sng mang vi cc mc iu ch khc nhau. H thng ny m ra khi

nim v h thng truyn dn s dng k thut OFDM vi b iu ch tn hiu thch

ng. K thut ny c s dng trong h thng thng tin my tnh bng rng

HiperLAN/2 Chu u. Trn th gii h thng ny c chun ha theo tiu chun

IEEE.802.11a.


7

Hnh 1: So snh gia FDMA v OFDM

a) Ph FDMA v b) Ph OFDM

1.1 Cc u im ca OFDM

H thng OFDM c th loi b hon ton hin tng giao thoa gia cc k

hiu(ISI) nu di chui bo v (guard interval leght) ln hn tr truyn dn ln

nht ca knh.

Ph hp cho vic thit k h thng truyn dn bng rng, do nh hng ca

s phn tp v tn s i vi cht lng ca h thng c gim nhiu so vi h

thng truyn dn n sng mang.

OFDM ph hp cho vic thit k h thng truyn dn bng rng.

H thng c cu trc b thu n gin

1.2 Cc nhc im ca OFDM

ng bao bin ca tn hiu pht khng bng phng. iu ny gy ra mo

phi tuyn cc b khuych i cng sut my pht v my thu.

S dng chui bo v trnh c nhiu phn tp a ng nhng lm gim i

mt phn hiu sut s dng ng truyn, do bn thn chui bo v khng mang

thng tin c ch.


8

Do yu cu v iu kin trc giao gia cc sng mang ph, h thng OFDM

rt nhy cm vi hiu ng Doopler cng nh s dch tn (frequency offset) v dch

thi gian (time offset) do sai s ng b.

2. iu ch n sng mang vi cn bng min tn s SC-FDE (Single

Carrier modulation with Frequency Domain Equalization)

2.1 Cn bng min tn s

Hnh 1

Mt b cn bng s b li phn mo tuyn tnh gy ra do truyn sng a ng.

Vi cc knh bng rng, cc b cn bng trong min thi gian thng thng l khng

th thc hin do p ng xung kim ca knh rt di trong min thi gian. Cn bng

trong min tn s (Frequency Domain Equalization: FDE) l kh thi hn trong trng

hp ny. Cn bng knh thng thng l vic lc nghch o mo tuyn tnh gy ra

do truyn sng a ng. Vi mt h thng tuyn tnh bt bin theo thi gian, vic

lc tuyn tnh l mt php tch chp trong min thi gian v l php nhn trong min

tn s. Bin i Fourier bin i cc tn hiu trong min thi gian sang min tn s

m c th thc hin cn bng bng cch chia cho mt c tnh p ng tn s ca

knh. Hnh 1 ch ra php ton c bn ca vic cn bng trong min thi gian (tch

chp) v cn bng trong min tn s (php nhn).

S dng Discrete Fourier Transform (DFT), vic cn bng trong min tn s

c th d dng c thc hin bng cch s dng mt b x l tn hiu s hin i.


9

Do kch thc DFT khng tng tuyn tnh theo di ca p ng knh nn phc

tp ca FDE thp hn so vi b cn bng trong min tn s cho cc knh bng rng.

iu ch n sng mang vi cn bng trong min tn s (SC/FDE) l mt k

thut kh thi gim nh hiu ng fading chn lc tn s. N to ra hiu nng ging

nh OFDM vi cng mt phc tp, k c vi cc p ng xung kim ca knh di.

Mt b iu ch SC/FDE pht cc k hiu iu ch lin tip nhau. N chia chui cc

k hiu iu ch thnh cc khi v thm vo tin t tun hon (Cyclic Prefix: CP)

vo u mi khi. CP l bn sao ca phn cui cng ca cc khi. Nh trong OFDM,

CP gip trnh nhiu xuyn khi. N cng m bo rng tch chp ca p ng xung

kim ca knh vi cc k hiu iu ch c dng tch chp vng. iu ny thch hp

vi vic x l tn hiu c thc hin bi knh vi vic x l tn hiu c thc hin

bi FDE do php nhn trong min DFT tng ng vi tch chp vng trong min

thi gian. Bi ton dung ha vic x l tn hiu ti my thu vi vic chuyn i tn

hiu gy ra bi knh l mt bi ton tng qut cho vic cn bng trong min tn s

s dng cc php bin i ri rc. Khi tn hiu c truyn qua knh, n c nhn

tch chp tuyn tnh vi p ng xung kim ca knh. Do mt b cn bng knh lun

c gng thc hin nghch o li p ng xung kim ca knh, n nn thc hin cng

mt kiu tch chp ging nh knh, hoc tch chp tuyn tnh, hoc tch chp vng.

Cch gii quyt bi ton ny l thm mt CP my pht lm cho vic lc knh

ging nh mt php tch chp vng v thch hp n vi FDE da trn DFT.

Mt my thu SC/FDE chuyn i tn hiu thu c sang min tn s bng

cch s dng thut ton DFT. Sau khi thc hin cn bng trong min tn s, thut

ton IDFT chuyn i tn hiu n sng mang sang min thi gian v b tch sng

thc hin khi phc cc k hiu iu ch ban u. Ngc li, OFDM s dung mt b

tch sng ring bit cho tng sng mang con.


10

Hnh 2 B thu OFDM v SC/FDE

2.2 So snh vi OFDM

OFDM v SC/FDE kh ging nhau v cc phn t trong h thng. Tuy nhin,

cc im khc bit c bn gia chng l cc b cn bng. SC/FDE thc hin c 2

thut ton DFT v IDFT my thu, trong khi OFDM thc hin IDFT my pht v

DFT my thu.

Ti my thu, OFDM thc hin tch d liu trn tng sng mang con trong

min tn s trong khi SC/FDE thc hin tch d liu trong min thi gian sau khi

thm thut ton IDFT. Chu k ca cc k hiu iu ch trong min thi gian c

m rng trong trng hp ca OFDM khi truyn dn ng thi cc khi d liu trong

sut chu k thi gian c gin ra. H thng c rng bng tn BsHz c chia

thnh nhiu sng mang c rng bng tn nh hn v d liu c lp c truyn

ti trn mi sng mang con SC/FDE c nhng u im vt tri hn so vi OFDM

nh sau:

PAPR thp hn do iu ch n sng mang ti my pht.

t nhy cm vi dch tn s sng mang.

phc tp thp ti my pht, to nhiu thun li cho cc thit b u cui di

ng trong truyn thng ng ln.


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3. FDMA n sng mang

a truy cp phn chia theo tn s trc giao (OFDMA) v a truy cp phn

chia theo tn s n sng mang (SC-FDMA) l cc bn chnh sa ca cc k thut

OFDM v SC/FDE c gii thiu trn. Khc vi k thut trn, k thut a

truy cp c gii thiu trong phn ny truyn cc tn hiu khc nhau mt cch ng

thi. Tt c cc k thut phn chia theo tn s trc giao s dng mt b ri rc cc

sng mang con trc giao c cp pht trn mt bng thng h thng. Chng bao

gm cc bin i ri rc chuyn cc tn hiu gia min thi gian v tn s.

truyn cc tn hiu khc nhau mt cch ng thi, cc k thut a truy cp

s gn cc tn hiu vo cc b sng mang con tch bit nhau. V cc knh bng rng

phi chu Fading chn lc tn s, cc k thut FDMA c th s dng lp lch ph

thuc knh (Channel-dependent scheduling) c th phn tp ngi dng, v bi v

c tnh Fading ca cc thit b u cui nhng v tr khc nhau c lp thng k

vi nhau, cc k thut lp lch c th gn mi u cui vi nhng sng mang con c

c tnh truyn ph hp ti v tr ca thit b.

3.1 X l tn hiu SC-FDMA

3.1.1 X l bn gi

Time-Variant Multipath Propagation


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Hnh 3 Thi gian bin th lan truyn a tuyn

Thi gian bin th p ng xung knh

3.1.1.1 OFDM c bn (I)

Hnh 4 n sng mang so vi a sng mang

3.1.1.2 OFDM c bn (II)


13

Hnh 5 Sng mang con trc giao

3.1.1.1 OFDM c bn (III)

Cc bc x l


14

Hnh 6 Hiu qu thc hin c bng cch ca mt bin i Fourier ri

rc nghch o

3.1.1.4 OFDM c bn (IV)

Chn tin t tun hon

Hnh 7 Chn tin t tun hon

Mt bn sao ca ui tn hiu (chiu di T) c chn vo bt u ca mi

mu tn hiu OFDM.

Hp th cc thnh phn a ng.

3.1.1.5 OFDM c bn (V)

Hnh 8 i din thi gian min tn s OFDM

Thit k h thng OFDM

Khng xung t bn trong m symbol(inter-sumbol)

Bo v khong thi gian ln hn s chm tr lan truyn Td: GTc = Tg > Td


15

Hiu sut bng tn: thi gian Symbol ln hn nhiu so vi tr lan truyn:

NTc = Ts >> Td

Can thip gia cc sng mang: Tc Symbol cao hn nhiu so vi hiu

ng Doppler fD: 1/Ts>>fD

G chiu di chu k trong s cc chip

S lng N sng mang con

3.1.2 X l pha bn nhn

Gim chu k v tin hnh DFT

Knh phn vng trong N tn s song song cc knh ngang

Cn bng n gin tng phc tp vi N log (N)

Hnh 9 X l bn nhn

3.1.2.1 OFDMA (I)


16

Hnh 10 Mng li thi gian-tn s trc giao

3.1.2.2 OFDMA (II)

Time division multiple access (TDMA)

Hnh 11 Phn chia thi gian theo a truy cp

Frequency division multiple access (FDMA)


17

Hnh 12 Phn chia tn s a truy cp

Hnh 13 Cc tham s LTE (Downlink)


18

Hnh 14 Mng li ti nguyn LTE (Downlink)

Hnh 15 Ti nguyn khi LTE (Downlink)

3.1.2.3 OFDMA (III)


19

Hnh 16 Knh tn s c chn lc thi gian bin th

Hnh 17 M hnh thi gian tn s

Ti s dng tn s mm (I)


20

- Ti ranh gii cc t l tn hiu nhiu (SIR) l xp x. 0 dB do ti s

dng tn s 1

- DS-CDMA s dng bn giao mm ti ranh gii di ng

- Giao din khng kh OFDM da cho php ti s dng tn s mm cho

ngi s dng ti ranh gii di ng

Ti s dng tn s mm (II)

Hnh 18 Ti s dng tn s mm (II)

LTE Uplink

- Cng sut tiu th trong thit b s dng (UE) thit b u cui c

gii hn bi pin

- OFDM i hi phm vi hot ng ln do nh cao t l cng sut trung

bnh (PAPR)

- B khuch i in tuyn tnh vi phm vi rng c hiu qu xu


21

- n sng mang / frequecy phn chia nhiu truy cp (SC / FDMA) c

s dng cho cc ng ln trong LTE

So snh OFDMA so vi SC / FDM

Hnh 19 So snh OFDMA so vi SC / FDM

SC / FDMA phn tn so vi v tr

Hnh 20 SC / FDMA phn tn so vi v tr

SC / FDMA


22

Hnh 21 Cu trc bn gi v bn nhn ca h thng SC/FDMA v OFDMA

Cc bc x l

Hnh 22 Qu trnh x l


23

1.1.

Hnh 23 So snh PAPR(Peak To Average Power Ratio)

3.2 a truy cp phn chia theo tn s n sng mang

Trong cc ng dng thng tin di ng, OFDMA c u im quan trng l

khng nh hng bi truyn dn a ng. Kh nng ny t c l nh s dng

OFDM pht thng tin trn N sng mang con hot ng ti tc bit ch bng 1/N tc

bit ca thng tin cn truyn, tuy nhin c nhc im l Peak-to-Average Power

Ratio (PAPR) cao. Mt nhc im na ca OFDM trong h thng thng tin di ng

l cn dch cc tn s hoa tiu i vi cc u cui pht ng thi. Dch tn ph hoi

tnh trc giao ca cc cuc truyn dn OFDMA, ngha l xy ra nhiu a truy nhp.

khc phc nhc im ny, 3GPP xut s dng phng php a truy

nhp ng ln trong truyn dn DFTS-OFDM v c gi l a truy nhp phn chia

theo tn s n sng mang Single Carrier Frequency Division Multiple


24

Access (SC-FDMA) v c p dng cho LTE. khc phc nhc im

ny, 3GPP xut s dng phng php a truy nhp ng ln trong truyn dn

DFTS-OFDM v c gi l a truy nhp phn chia theo tn s n sng mang Single

Carrier Frequency Division Multiple Access (SC-FDMA) v c p dng cho LTE

thch ng min tn s phc ti ti BTS.

a) n nh bng thng bng nhau; b) n nh bng thng khc nhau

Hnh 24 M t nguyn l hot ng ca SC-FDMA

Hnh 24 M t trng hp a truy nhp ca 2 u cui c n nh bng

thng bng nhau (P1=P2), cn hnh 2b m t trng hp a truy nhp ca 2 u cui

c n nh bng thng khc nhau (P1#P2). Bng cc dch cc u ra ca DFT n

cc u vo thch hp ca IFFT, h thng c th pht tn hiu vo ng v tr min

tn s c quy nh theo lp biu.


25

OFDMA truyn song song, SC-FDMA truyn ni tip

Hnh 25 Th d minh ha s khc nhau trong vic truyn cc k hiu s

liu theo thi gian i vi OFDMA v SC-FDMA

Hnh 25 cho thy s khc nhau trong qu trnh truyn cc k hiu s liu theo

thi gian.Trn hnh ny ta gi thit rng, mi ngi s dng c 4 sng mang con

(P=4) vi bng thng bng 15KHz, trong mi k hiu OFDMA hoc SCFDMA

truyn 4 k hiu s liu c iu bin QPSK cho mi ngi s dng. Hnh 3 cho

thy vi OFDMA, 4 k hiu s liu ny c truyn ng thi vi bng con cho mi

k hiu bng 15KHz trong khong thi gian hiu dng TFFT ca 1 k hiu OFDMA,

cn i vi SC-FDMA 4 k hiu s liu ny c truyn ln lt trong khong thi

gian bng 1/P (1/4) thi gian hiu dng k hiu SC-FDMA vi bng thng bng P x

15KHz = 4 x 15KHz cho mi k hiu.

Ging nh OFDMA, thng lng SC-FDMA ph thuc vo cch sp xp cc k hiu

thng tin ln cc sng mang con. C 2 cch phn b sng mang con gia cc my

u cui nh sau:

3.2.1 SC-FDMA khoanh vng (LFDMA)

SC-FDMA khoanh vng (LFDMA: Locallized SC-FDMA) hay cn gi l

DFTS-OFDMA khoanh vng (locallized DFTS-OFDMA): mi u cui s dng 1


26

tp sng mang con lin k pht i k hiu ca mnh. V th bng thng truyn dn

ca LFDMA bng 1 phn bng thng h thng.

3.2.2 SC-FDMA phn b (DFDMA)

SC-FDMA phn b (DFDMA: Distrubuted FDMA) hay cn gi l DFTS-

OFDMA phn b (Distrubuted DFTS-OFDM) : cc sng mang con dnh cho 1 u

cui c phn b trn ton b bng tn tn hiu. Mt phng n ca SC-FDMA

phn b c gi l SC-FDMA an xen (IFDMA: Interleaved SC-FDMA), trong

cc sng mang c chim bi mt u cui cch u nhau v cc sng mang con

gia chng rng dnh cho cc u cui khc.

Hnh 26 Cc phng php n nh sng mang con cho nhiu ngi s dng

Hnh 26 cho thy 2 cch sp xp ni trn vi 3 u cui, mi u cui pht i

cc tn hiu trn 4 sng mang con trong 1 h thng 12 sng mang con. Hnh 4a vi

cch sp xp IFDMA (u cui 1 s dng 4 sng mang con gm 0,3,6,9; u cui 2

gm 1,4,7,10; u cui 3 gm 2,5,8,11); trong cch sp xp LFDMA, hnh 4b (u

cui 1 s dng cc song mang con 0,1,2,3; u cui 2 gm 4,5,6,7; u cui 3 gm

8,9,10,11)


27

Hnh 27 Hai kiu sp xp cc phn b sng mang con

Xt v kh nng khng i vi li truyn dn (iu ny nh hng ln thng

lng), SC-FDMA phn b (DFDMA) c kh nng khng phading chonk lc tn

s tt hn SC-FDMA khoanh vng (LFDMA), v thng tin cn truyn c tri rng

trn ton b bng tn tn hiu pht. Do , n cung cp kh nng phn tp tn s tt.

Tri li, SC-FDMA khoanh vng (LFDMA) cho php t c phn tp a ngi

dng khi xy ra phading chn lc tn s nu n n nh cho tng ngi s dng phn

bng tn, trong ngi s dng ny c c trng truyn dn tt nht ( li knh

cao). Phn tp a ngi s dng da trn vic phading c lp i vi cc my pht

khc nhau. H thng cng cn c b tp biu theo knh (CDS: Channel Dependent

Scheduler) cho cc sng mang. CDS i hi h thng gim st cht lng knh truyn

ph thuc tn s cho tng u cui v thch ng nh sng mang con thay i p

ng tn s knh ca tt c cc u cui.

4. Lp lch ph thuc knh truyn (Channel-Dependent Scheduling CDS)

CDS l mt dng ca mapping sng mang con c th c s dng trong cc

ng dng SC-FDMA v OFDMA. tng ca CDS l sp t vic truyn ca mi

u cui vi mt b cc sng mang con vi c tnh truyn thch hp.

Trong thc t, iu ny i hi mt b scheduler ti trm gc o lng cc

c tnh knh v yu cu truyn ca mi u cui. Scheduler sau thc hin thut

ton ti u cp pht sng mang con cho mi u cui. Cui cng, trm gc truyn


28

s cp pht ny ti cc u cui. Hnh 28 l mt s khi ca mt h thng SC-

FDMA nhn mnh hot ng scheduling ti trm gc.

Hnh 28 SC-FDMA vi CDS

4.1 Hiu sut SC-FDMA

Mapping sng mang con ph thuc knh truyn c th s dng bng thng v

cng sut dnh cho truyn thng tin ngi dng. Ngoi ra, u cui s dng nng

lng pin v bng thng h thng truyn cc tn hiu tham chiu thm d knh

truyn cho php trm gc c th o lng cht lng knh. Vic o lng ny

gip a ra mt trng thi l tng m khi trm gc bit c li knh ca tt

c sng mang con c sn. Tuy nhin, cch ny s rt tn km v mt bng thng h

thng v nng lng ca u cui. Trn thc t, phi xc nh c bao nhiu sng

mang con s dng cho thm d knh v mc thng xuyn thc hin truyn thm

d knh. Khi thc hin iu ny, h thng chp nhn mt s nh i gia lu lng

v cht lng knh ti trm gc.

4.2 Lp lch cp pht sng mang con

Cc h thng thc t cc sng mang con dng chunk (khoanh). Cng vi vic


29

n gin ha nhim v scheduling, truyn da trn cc chunk cn gip ci thin hiu

sut ca DFT trong b pht v IDFT trong b thu. Mt chunk bao gm cc sng mang

con lin tc trong LFDMA v trong IFDMA mt chunk bao gm cc sng mang con

cch u nhau trn ton di tn hiu. H thng LTE s dng LFDMA vi 12 sng

mang con/chunk.

4.3 Kt qu lch biu

CDS to kh nng cho nhiu u cui s dng cc sng mang con vi cc c

tnh truyn thch hp. Trong ng ln ca mt h thng di ng, thu thp thng tin

trng thi knh truyn. s dng bng thng h thng v u cui phi truyn cc tn

hiu thm d knh truyn tri rng trn ton b di tn ca knh, mc d cc tn hiu

thng tin ch chim gi mt phn ca di.

5. H thng MIMO SC-FDMA

Multiple Input Multiple Output (MIMO) l mt trong nhng phng php

gip ci thin hiu sut ca truyn thng di ng khng dy. K thut MIMO s dng

nhiu thnh phn anten ti b pht cng nh b thu ci thin cht lng kt ni

hoc dung lng truyn. Mt h thng MIMO c th cung cp hai loi li: li

phn tp khng gian (spatial diversity) v li ghp knh khng gian (spatial

multiplexing).

6. c tnh cng sut nh ca mt tn hiu SC-FDMA

T s cng sut nh trn trung bnh (PAPR) l mt phng php o lng

hiu sut biu th hiu qu cng sut ca b pht. Trong trng hp mt b khuch

i cng sut tuyn tnh l tng c th t c s khuch i tuyn tnh ln n

im bo ha, ta s c hiu qu cng sut ti a khi b khuch i hot ng ti im

bo ha.

7. Kt lun v hng pht trin

7.1 Kt lun

ti cng khi qut v hai cch khc nhau mapping sng mang con:

distributed (phn phi) v localized (cc b) cng nh khi qut v Lp lch ph

thuc knh (CDS) gip ci thin lu lng ca truyn SC-FDMA.


30

K thut MIMO vi nhiu thnh phn anten u pht v u thu ci thin

cht lng hoc dung lng truyn vi hai hng trong vic ci thin hiu sut: phn

tp khng gian v ghp knh khng gian cng c gii thiu s lc.

u im chnh ca SC-FDMA: PAPR thp hn so vi tn hiu OFDMA cng

c phn tch. Cng vi , ta cng cho thy DFDMA v LFDMA chu PAPR

cao hn so vi IFDMA nhng vn thp hn so vi OFDMA, mc d khng ng k.

C hai cch khc phc nhng nh hng ca knh truyn a ng. Cch

u tin l s dng iu ch a sng mang, nh OFDM, v cch cn li l s dng

b cn bng trong min thi gian (FDE).

7.2 Hng pht trin

Pht trin cc ng dng ca SC-FDMA.

Kt hp cng cc k thut khc.

31

TI LIU THAM KHO

[1]http://vi.wikipedia.org/wiki/Gh%C3%A9p_k%C3%AAnh_ph%C3%A2n_chia_t

heo_t%E1%BA%A7n_s%E1%BB%91_tr%E1%BB%B1c_giao

[2]http://4tech.com.vn/forums/showthread.php/10484-C%C3%A1c-

k%E1%BB%B9-thu%E1%BA%ADt-%C4%90a-Truy-C%E1%BA%ADp-

(Multiple-Access-Techniques)

[3] http://en.wikipedia.org/wiki/Single-carrier_FDMA

06 – dhth8clt – tieu luan wireless networks

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