công suất đỉnh trên trung bình trong sc-fdma

7/28/2019 cng sut nh trn trung bnh trong SC-FDMA

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TRNG I HC THNH

KHOA CNKT IN T- VIN THNG---------------------------------------

N TT NGHIP

NGNH: Cng Ngh K Thut in T- Truyn Thng

M ngnh: 525203 ti:

CNG SUT NH TRN TRUNG BNH

TRONG SC-FDMA

Gio vin hng dn: Th.s L Th Ngc H

Sinh vin thc hin: Nguyn nh S

M sv: 0900895Lp: HT1 K1

H NI, NM 2013


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NHN T C GIO VIN PHN BIN

H v tn: Nn nh S M

L H T - K1 Kh

Ngh Cg gh h i - truyn thngTn ti: Cn t nh trn trung bnh trong SC-FDMA

Ni g g g hi hg C hg

h

Chn 1: Tng quan v cng ngh LTE

Chn 2: K thut a tr nhp phn chia theo tn sn n man (SC-

FDMA)

Chn 3: Cn t nh trn trung bnh trong SC-FDMA g hh

Ti i h h

1). H. G. Myung and D. J. Goodman ( 2008), Single Carrier FDMA: A New Air

Interface for Long Term Evolution, John Wiley & Sons.

2). Hyung G. Myung (2007), Single Carrier Orthogonal Multiple Access Technique

for Broadband Wireless Communications,UMI Dissertation Publishing.

Nhn t:

i.....

...........................................................................................................................................

Nh i......

...........................................................................................................................................

Kt n:...........................................................................................................................

...........................................................................................................................................nh i: ..........................................................................................................................

Ng hg

Ni vit nhn t

(k v ghi r h tn)
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Khoa CNKT in T-Vin Thng Lp HT1-K1

n tt nghip i

LI CM ON

E i Cg nh trn trung bnh trong SC-FDMA

cng trnh nghin cu v tm hiu l ca ring em. Cc s liu, kt quc ghi trong

n l trung th c ly t cc ti liu tham kho, n g hg g e i

chu hon ton trch nhim.

H Ni, g hg

Sinh vin

Nguy h S


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n tt nghip ii

LI CM N

S hc tp v nghin cu ti Tg i H Thh , e i h

thnh c h, n tnh ch dn, truy t cho em nhng kin thc, kinhnghim qu bu, lm nn tng cho cng vic sau ny .

Em xin chn thnh c gi ThS L Th Ng H, gi c tip

hng dn em thc hi i, gi em t ti li h hg h ghi

cu, cch vi n. hng kinh nghi g q gi i vi em.

Xin chn thnh c hg gi bn, nhg gi h g em

trong su qg g i hc.

H Ni, g hg

Sinh vin

Nguy h S


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n tt nghip iii

MC LC

LI CM ON ....................................................................................................... i

LI CM N .................................................................................................... ii

DANH MC CC TVIT TT .............................................................................. vDANH MC HNH NH ......................................................................................... viiiLI NI U ................................................................................................................ 1

Chn 1TNG QUAN V CNG NGH LTE

1.1. Gii thiu ................................................................................................................. 21.2. Khi qut truy nhp v tuyn LTE ...................................................................... 41.2.1. Cc s truyn dn: OFDM ng xung vSC-FDMA ng ln. ........... 41.2.2. Slp lch ph thuc knh vsthch nghi tc ........................................... 51.2.3. ARQ lai cng vi skt hp mm ....................................................................... 71.2.4. Htrnhiu anten ............................................................................................... 81.2.5. H

tr

a tr

m vqung b ................................................................................. 9

1.3. Cu trc giao din v tuyn LTE .......................................................................... 91.3.1. iu khin lin kt v tuyn (RLC) ................................................................... 111.3.2. iu khin truy nhp mi trng (MAC: Medium Acces Control) ................. 131.4. Tng kt ................................................................................................................. 21

Chn 2K THUT TRUY NHP PHN CHIA THEO TN SN SNG

MANG (SC-FDMA)2.1. Gii thiu ............................................................................................................... 222.2. Xl tn hiu SC-FDMA ..................................................................................... 232.3. nh x cc sng mang con ................................................................................... 272.4. Biu din trong min thi gian ca tn hiu SC-FDMA ................................... 292.4.1. Cc symbol trong min thi gian ca I FDMA .................................................. 302.4.2. Cc symbol trong min thi gian ca L FDMA ................................................. 322.4.3. Cc symbol trong min thi gian ca DFDMA ................................................ 332.4.4. So snh cc s nh x sng mang con ......................................................... 34


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n tt nghip iv

2.5. SC-FDM v a tr nhp phn chia theo tn s trc giao (OFDMA) ......... 362.6. SC-FDMA v CDMA vi b san bng min tn s........................................... 392.7. a tr nhp phn chia theo tn sm n n man (SC-CFDMA) ........ 412.8. Tng kt ................................................................................................................. 42

Chn 3CNG SUT NH TRN TRUNG BNH TRONG SC-FDMA

3.1. Gii thiu chung ................................................................................................... 443.2. Cc c tnh cng sut nh tn hi n n man........................................ 453.3. PAPR cc tn hiu truyn dn n anten........................................................... 493.4. PAPR cc tn hiu truyn dn a anten ............................................................. 533.5. Gim cng sut nh bng vic n bin symbol .......................................... 563.6. Tng kt ................................................................................................................. 60TNG KT .................................................................................................................. 61TI LIU THAM KHO ........................................................................................... 62


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n tt nghip v

DNH MC CC T VIT TT

3GPP

3rd Generation Partnership

Project D n hp tc th h th ba

B

BCCH Broadcast Control Channel Kh iu khin qung b

BPSK Binary Phase Shift Keying Kha dch pha nh phn

C

CDMA Code Division Multiple Access nhp phn chia theo

m

CP Cyclic Prefix Tin t vng

D

DFDMADistributed Frequency Division

Multiple Access

hp phn chia theo

tn s phn tn

DFT Discrete Fourier Transform Bi i Fourier ri rc

F

FDD Frequency Division DuplexSong cng phn chia theo tn

s

FDE Frequency Domain Equalization San bng trong min tn s

FDMAFrequency Division Multiple

Access

hp phn chia theo

tn s

I

ICI Inter-Carrier Interference Nhiu xuyn knh

IDFT Inverse Discrete FourierTransform Bi i Fourier ri r gc


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n tt nghip vi

IFDMAInterleave Distributed Frequency

Division Multiple Access

hp phn chia theo

tn s e

IP Internet Protocol Giao thc Internet

ISI Inter-Symbol Interference Nhiu xuyn k hiu

L

LFDMALocalized Frequency Division

Multiple Access

hp phn chia theo

tn s cc b (tp trung)

LTE Long Term Evolution S pht trin di hn

O

OFDMOrthogonal Frequency Division

Multiplexing

Ghp knh phn chia theo tn

s trc giao

OFDMAOrthogonal Frequency Division

Multiple Access

hp phn chia theo

tn s trc giao

P

PAPR Peak-to-Average Power RatioT s cng su nh trn

cng sut trung bnh

PCH Paging Channel Knh tm gi

PDCCHPhysical Downlink Control

Channel

Kh iu khin ng xung

vt l

PDSCHPhysical Downlink Shared

Channel

Knh chia sng xung vt

l

PS Pulse Shaping nh dng xung

Q

QAM Quadrature amplitude modulation iu chi vung gc


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n tt nghip vii

QPSKQuaternary Phase Shift Keying Kha dch pha c hg

S

SC-

CFDMA

Single Carrier Code-Frequency


hp phn chia theo

tn s h g g

SC-

FDMA

Single Carrier Frequency


hp phn chia theo

tn s g g

SNR Signal-to-Noise Ratio T s tn hiu trn tp m

T

TDD Time Division DuplexSong cng phn chia theo thi

gian

TDMA Time Division Multiple Access hp phn chia thi

gian

U

UE User Equipment Thit bgi dng

UMTSUniversal Mobile

Telecommunications System

H thng vi hg i ng

ton cu


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n tt nghip viii

DNH MC HNH NH

Hnh 1.1: Cc h thg hg i i ng pht trin ln ti 4G ................................... 3Hnh 1.2: Kin trc mng LTE ..................................................................................... 3Hnh 1.3: Lp lch ph thu h ng xung trong min thi gian v tn s........ 6Hnh 1.4: Cu trc giao thc LTE ................................................................................ 11Hh Ph n v ni ghp RLC ......................................................................... 12Hnh 1.6: V d v s nh x ca cc knh logic ti cc knh truyn ti .................... 15Hnh 1.7: La ch hg hc truy ng xug ng ln .......................... 17Hnh 1.8: Giao th ARQ i ng b hg ng b ............................................ 19Hh l ARQ song song ............................................................................ 20Hnh 2.1: Cu trc my pht v my thu ca cc h thng SC-FDMA v OFDMA. [2]...................................................................................................................................... 24Hnh 2.2: Th h ca SC-FDMA truy , N g g g M (


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n tt nghip ix

Hh M = iu ch t Q = 3 thit bu cui; thi gian symbol l Tgi; g hg gn l

sourceB Hz. [2] ....................................................................... 37

Hh OFDMA g hg liu c nhn ti sourceB /4 Hz v mrngthigian ti 4T giy. [2] ...................................................................................................... 37Hnh 2.15: SC-FDMA mrg g hg i 3channel SourceB B ; n nn thi gian

symbol cn T/3 giy. [2] .............................................................................................. 38Hnh 2.16: OFDMA v SC-FDMA; tch sng v san bng. [2] .................................. 38Hnh 2.17: DS-CDMA vi b san bng min tn s (FDE). [2] .................................. 39Hnh 2.18: Tri ph vi cc vai tr ca chui d liu v chui tn hi i

cho tn hi c tri ph. [2] ...................................................................................... 40Hnh 2.19: nh x sng mang con truyn thng v nh x sng mang con lai ghp. [1]...................................................................................................................................... 41Hnh 2.20: Bi khi ca h thg hp phn chia theo tn s gmang (SC-CFDMA). [2] .............................................................................................. 42Hnh 2.21: So snh gia SC-FDMA v SC-CFDMA g iu kin cc sn mang con

b chi g h g t sgi s dng. [1] ..................................................... 42

Hnh 3.1: Mi quan h v mt l thuyt gia PAPR v hiu qu cng su h i vicc b khuh i lp A v l B ng. [1] ........................................................... 44

Hnh 3.2: CCDF ca cng sut tc thi i vi iu ch BPSK v cc gi tr h s un

l h h; ng chm chm l kt qu thc nghi ng lin l

gii hn trn. [2] ........................................................................................................... 48

Hnh 3.3: Cng sut tc thi CCDF i vi g g hiu OFDM vi

biu din d liu gc BPSK trn cng th h h i vi cc tn hi g

mang, chng ta xt h s un lc c , , ; i vi OFDM, cc sng mang g s dng cc s N l 32, 128, v 512. [2] ....................................................... 49

Hnh 3.4: So snh CCDF c PAPR i vi IFDMA, DFDMA, LFDMA, v OFDMA

vi tng s cc sng mang con N = 512, s c u vo cc symbols M = 128,

IFDMA vi h s tri ph Q = 4, DFDMA c h s tri ph Q = , (h s un

lc) = 0.22 : (a) QPSK; (b) 16- QAM. [1] .................................................................... 51

Hnh 3.5: so snh gia CCDF c PAPR i vi IFDMA v LFDMA vi tng s cc

sng mang con N = 256, s ca cc h thg u vo M = 64, h s lan truyn Q = 4,v (h s un lc) ca 0, 0.2, 0.4, 0.6, 0.8, v 1: (a) QPSK; (b) 16-QAM. [1] ......... 53


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n tt nghip x

Hnh 3.6: Ly m c trn min tn s l tch chp v php tng trong min thi

gian. Ch skquy vo s sng mang con. [1] .............................................................. 54

Hnh 3.7: CCDF ca PAPR cho 2 x 2 ly m ng nht TxBF. [1] ................. 54

Hnh 3.8: h hng ca sng t ha v ly trung bnh ca ly m c ma trn

trong PAPR. [1] ............................................................................................................ 55

Hh S h PAPR i MIMO khc. [1] ......................................... 56

Hnh 3.10: Ba loi gii h i . [1] ....................................................................... 57

Hh khi c hg h i i vi truyn dn SC-

FDMA MIMO. [2] ........................................................................................................ 58

Hnh 3.12: CCDF ca cng sut symbol sau khi xn.ymg ng vi k hi g

g ng nt d g ng vi CCDF i vi e g hh g

g CCDF i vi anten 2. [1] ..................................................................................... 58

Hnh 3.13: Biu hin mc lin kt cho xn : (a) gii m BER; (b) m ha FER. [1]...59

Hnh 3.14: PSD cc tn hi [] ....................................................................... 59


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n tt nghip 1

LI NI U

Ng , hg i i g g h in rt mnh m v khng ngng

c ci tin nh ng nhu c i hg i hg h ng ca congi. Hin ti hi hng s dng cng nghFDMA g h h h

gih c chng trong cc mg hg i i ng t bo th h k tip. Trong khi

WiMAX, c chun ha bi t chc IEEE s dng cng ngh OFDMA cho truyn

d g ng xung th mt cng ngh tim tng khc l LTE (Long Term

Evolution-S pht trin di h) hun ha bi t chc hp tc th h th 3

(3GPP) li ch s dng OFDMA cho truyn d ng xug, g hi ng ln s

dng cng ngh hp phn chia theo tn s g g (SC-FDMA).

Nhg h i v mt thc thi h thng ca SC-FDMA so vi OFDMA g n ti

vic cng su nh h i.

Nhn thc r nhng yu c iu khin gim cng sut trong cc mng thng

i i g, c bit l tnh kh thi trong cc h thg LTE g g i, g i

kin th hc t c ti i H Thh hg h hng ca c gio

Ths. L Th Ng H, e h i h n tt nghi i hc Cg t

nh trn trung bnh trong SC-FDMA

n g hg

Chn 1: Tng quan v cng ngh LTE

Chn 2: K thut a tr nhp phn chia theo tn s n n man(SC-FDMA).

Chn 3: Cng sut nh trn trung bnh trong SC-FDMA

c s q gi v ch bo tn tnh trong qu trnh nghin cu v

cung cp ti liu ca c gio Ths. L Th Ng H, c hon thnh vi ni

dung m nh h T hi h v thi gian c h, n chc chn

khng chn khi nhng sai st, knh mong cc thy c gio v cc b ih i g

gp kin chnh s hng pht trin ti he n hon thi h

H Ni, ngy 25 thng 5 nm 2013

Ngi n

Sinh vin: Nguy h S


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n tt nghip 2

Chn 1

TNG QUAN V CNG NGH LTE

1.1. Gii thiu

LTE l th h th t g i a chun UMTS do 3GPP pht trin. UMTS th

h th ba d WCDMA c trin khai trn ton th gii m bo tnh

cnh tranh cho h thg g g i, hg / GPP u d n

nhm x h c pht trin v lu di cho cng nghi ng UMTS vi tn gi

Long Term Evolution (LTE). C nhiu ty ch nng cp mng hin ti ln LTE

cho c cc cng ngh 3GPP v phi 3GPP. C ng tin ln LTE d thy nht l t

GSM ln EDGE, tip theo ln WCDMA ri HSPA v cui cng l ln 3GPP LTE.

GPP t ra yu cu cao cho LTE, bao gm gim chi ph cho mi bit thng tin,

cung cp dch v t h, dng linh ho g n hi g n mi,

gin ha kin trc mng vi cc giao tip mv gi g g ng tiu th

thit bu cui. Cc mc tiu ca cng ngh ny l:

T nh tc thi vi g hg MHz.- Uplink: 50 Mbps.- Downlink: 100 Mbps.

Dung lng d liu truyn ti trung bnh ca mt ngi dng trn 1MHz sovi mng HSDPA Rel.6.

- Uplink: g n 3 ln.

- Downlink: g n 4 ln.

Ho ng ti i t di chuyn ca thu bao l 0-15 Km/h. Vn hotng tt vi t t 15-120 Km/h. V c ho ng khi thu bao di

chuyn vi t t 120-350 Km/h (thm ch 500 K/h g n).

Cc ch tiu trn phi m bo trong bn knh vng ph sng 5Km, gim cht t

trong ph i n 30Km. T 30-100Km th khng hn ch.

i g hg ih ht: c th ho ng vi g n 1.25MHz, 1.6

MHz, 10MHz, 15MHz v 20MHz c chiu ln v chiu xung. H trc hai trng

h i g g ng bng nhau hoc khng.


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n tt nghip 3

Hnh 1.1: Cc h thn thn tin di ng pht trin ln ti 4G

Hnh 1.2: Kin trc mng LTE


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n tt nghip 4

c mc tiu ny, s c rt nhi ht mi c p dg, g

ni b ht v tuy OFDMA ( p phn chia theo tn s tr gi),

thut anten MIMO (Multiple Input Multiple Output). Ngoi ra h thng ny s chyhon ton trn nn IP (all-IP Network), v h trc hai ch FDD v TDD.

1.2. Khi qut truy nhp v tuyn LTE

1.2.1. Cc s truyn dn: OFDM ng xung vSC-FDMA ng ln.

S truyn d ng xung d OFDM. OFDM l mt

truyn d ng xung hp dn v mt vi l do. Do thi gian symbol

OFDM g i di kt hp vi mt tin t tun hon, OFDM c sc ch ng cao

v mt chng li chn lc tn s knh. Mc d s sai lc tn hiu do mt knh lachn theo tn s v nguyn l c thc x l bng cch san bng bn thu, s

phc tp ca vic san bng b u trnn khng hp d thc thi trong mt thit

bu cui i ng ti rg g MHz V y, OFDM cng vi sc chu

ng vn c c i vi h ih hn lc theo tn s hp d h ng

xug, c bi hi c kt hp cng vi s ghp khng gian.

Cc li ch khi dng OFDM gm c:

- OFDM cung cp s truy nhp ti min tn s, he h h h h t do cho b lp lch trnh ph thuc knh so vi HSPA. Cc s phn chia di thng

mm d c h trmt cch d dng bi OFDM, bng cch bi i sng cc

sng mang con OFDM c s dng cho truyn dn. Tuy nhin, ch rng s h tr

v cc s phn chia nhiu ph g i hi vic lc RF mm do l vic lm m

khng ph h h truyn dn chnh xc. Tuy nhin n li cho php duy tr cu

trc x g gc ging h, hg q rng c g hg,

gin vic th hi u cui.

- S truyn dn qug / g hg i gig h c pht

t nhiu trm g, c thc hin d dng nhOFDM.

i vi ng ln LTE, s truyn d g g OFDM

tri DFT (DFTS-OFDM) c s dng. Vic s dng s iu ch g g

g g h y nht s cng sut nh trn trung bnh ca tn hiu

c truyn th h i vic truyn d g g h OFDM T s

cng sut nh trn trung bnh ca tn hi c pht nhh cho php cng sut

truyn d g h h i vi mt b khuh i h c. V vy, s truyn

d g g h h dng b khuh i cng sut hiu qu h,


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n tt nghip 5

i g g i vng phg g i c bit quan trg i vi

u cui b gii hn cng su ng thi, vic san bng cn thi x l nhiu ca

tn hi g g h-ih hn lc theo tn s khng thnh v trongng ln do cc ti nguyn x l tn hiu ti trm gc t b hn chh i u

cui i ng.

Ngc li vi ng ln WCDMA/HSPA l khng tr gi g a vo

s truyn d g g h ng ln trong LTE d phn tch trc

giao nhg gi s dng v thi gian v tn s. Sh h gi dng trc

giao c ch trong nhi ng h g ga nhiu ni t bo. Tuy nhin, s

cp pht mt ti nguyn di thng tc thi rt ln cho m gi g l mt

chi c khng hiu qu ng h g d liu ch yu b

gii hn bi cng sut truy h i thng. Trong hon ch h h, m u cui

ch c cp pht mt phn ca tng di thng truyn d u cui

khc c th pht song song trn phn cn li ca ph The h , ng ln LTE

ny bao gm thnh ph hp min tn s, k hoch truyn d ng

LTE i hi g c gi FDMA g (SC-FDMA).

1.2.2. Slp lch ph thuc knh vsthch nghi tc

im ch yu c truyn dn LTE l vic s dng truyn dn knh

hg, g gn ti nguyn thi gian v tn sc chia s m h ng gia

nhg gi s dng. Vic s dng truyn dn knh chung thch ng tt vi cc yu

cu ngu i g h i m h hh hg ra bi d liu gi v

g h h t vi cng ngh then ch h c s dng bi LTE. Trong mi

khong thi gian ngn, b lp lh iu khi nh nhg gi dng cc ti

g c chia s N g q nh t d li c dng cho mi lin

kt, tc l s thch nghi t v c th e h t phn ca b lp lch trnhny. B lp lch l mt phn t ch cht v quy nh l n hiu sut ton bng

xug, c bit l trong mt mng ti mc cao. C s truyn d he ng xung

l ng i ng cho s lp lch cht. S g g g ng

h thng c th c n iu kin vh h q nh

lp lh, c gi l lp lch ph thu h i c khai thc trong

HSPA, i m b lp lh ng xung ny pht ti m gi g hi iu kin

knh thun li ti h d liu, v ph i g hg hc

hi i vi g c nng cao. Tuy nhin, thm vo min thi gian ny LTEg truy nhp ti min tn s, nhc s dg OFDM g ng xung v


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n tt nghip 6

Hnh 1.3: Lp lch ph thuc knh ng xung trong min thi gian v tn s

DFTS-OFDM g ng ln. Cho nn, vi mi min tn s, b lp lch trnh c th

la ch gi dng cng vi iu kin knh tt nht. Ni cch khc, vic lp lch

trong LTE khng ch c th bi i knh vo tnh ton min thi gi h

HSPA m cn trong c min tn s. i c minh ho trong Hnh 1.3.

Khg i vi vic lp lch ph thuc knh min tn s l c ch nht ticc t u cui th, i h h hi h g h i mt cch chm

chp theo thi gian. Vic lp lch ph thuc knh da vo cc s bi i ch ng

knh gia nhg gi g c vi g g ng trong h thg i vi

cc dch v nhy vi tr, mt b lp lch min thi gian duy nht c thc bt

bu lp m gi dng c th, bt chp ch ng knh khng ti nh ca n.

Trong hon ch h y, vic li dng cc s bi i ch ng knh c trong min

tn s s gip ci thin hiu sut ca ton b h thg i vi LTE, cc quy nh lp

lch biu c thc ly c mi l chi ti Hz i g hphp cc s bi i h g i nhah c theo di nhb lp lch ny.

Lp lch ng xungng xung, mi u cui thng bo mt s h gi v ch ng knh tc

thi ti trm g C h gi h c nhh a vo mt tn hiu chun

c pht bi trm g g c dng cho cc m h iu ch. D h

gi cht ng knh, b lp lch ng xung c thn nh cc ngun ti nguyn cho

nhng gi s dng, h ng knh vo tnh ton. V nguyn l, m u


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n tt nghip 7

cui c lp lch trnh c thc n nh mt b bt k ca cc khi ti nguyn rng

180 kHz trong mi khong thi gian lp lch 1ms.

Lp lch ng lng LTE c da vo s phn tch trc giao ca nhg gi s dng

v n l nhim v ca b lp lh g nh cc ti nguyn trong c

min thi gian ln min tn s (kt hp TDMA v FDMA) cho nhg gi

dng khc nhau. Cc quy nh lp lh t ln cho mi iu

khi u cui i g c php pht bn trong mt t bo trong mt

khong thi gi h nhng ti nguyn tn s truyn dn s thc hin v

nhng t d li ng ln m s dng. Ch rng ch mt min tn s k nhauc h h u cui i g g g h h qu ca vic dng

truyn d g g ng xung LTE.

C iu kin knh c th g h rong qu trnh

x l lp lh ng ln gig h ic lp lh h ng xung. Tuy nhin, thng

i h c v iu ki h ng ln ny l mt nhim v khng quan

trng. V v, hg h h h c s phn t ng ln l

iu quan trg h t s b xung trong cc hon cnh m s lp lch ph thuc

h hg c s dng.

Ch rng vic lp to nhiu lin t bo l mt chi c lp lch ch yu,

h hh g bo lng ging vo trong tnh ton D , lp to

nhiu lin t bo l mt v b xung mrng v va mi nhn th g c

im k thu i g n rng s lp to nhiu c thc ng dng

ch cho mt tp cc t c la chn, ph thuc vo cc yu cu b tr theo tng

s trin khai c th.

1.2.3. ARQ lai cng vi skt hp mm

ARQ lai nhanh kt hp m c s dng trong LTE vi cc l do rt ging

h g HSPA, th h h u cui yu cu truyn li mt cch nhanh

chng cc khi truyn ti h c b nhm v cung cp mt cng c cho s thch

nghi t ngm. Giao th g ging vi i g i vi HSPA-

nhiu qu trnh x l ARQ lai dg i song song. Nhng s truyn li c thc

yu cu nhanh chng sau s truyn mi gi gi gi g h hi c

kt hp mm v cc bm cc bit mm my thu c th thc hin s kt hp mmgia cc ln th.


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n tt nghip 8

1.2.4. Htrnhiu anten

LTE h tr nhiu anten ti c trm gc l u cui h t b phn

khng th thiu c c tnh k thut. V nhiu kha cnh vic s dng nhiuanten l k thut ch y h hiu sut LTE ln. Nhiu anten c th

c s dng theo nhiu cch khc nhau cho cc m h h h

- Nhiu anten thu c thc dng cho phn t h i vi cc s truyn dn

g , i c s dng trong nhiu h thng t bo cho nhi Tuy

nhin, hai anten thu l chun (baseline) cho tt c u cui LTE, hiu su ng

xug g c ci thi Ch gin nht ca vic s dng nhiu anten thu l s

phn tp thu ci trit pha-ig, hg g h h h ctrong kch bn hn ch nhiu n e g c dng khng ch cung cp s

phn tp chng pha-ig kh nhiu.

- Nhiu anten pht ti trm gc c th dng cho phn tp pht v cc loi khc v

to chm. M h hh a t h ci thin SNR (Signal-to-Noise Ratio)

v/hoc SIR (Signal-to-Interference Ratio) thu c, cui cng l ci thin dung

ng h thng v vng ph sng.

- Ghp khng gian (Spatial multiplexing), thnh thog c gi l MIMO,s dng nhiu anten c my pht l h c h trbi LTE. Ghp khng gian

d n kt qu t d li g, h h iu kin v knh trong cc

ng hp b gii hn di thng bng cch to mt vi knh song song.

Nhn chung, cc k thut nhi e h h h g ng

hp khc nhau. V d, ti SNR v SIR g i th h i cao hoc ti ra t bo

th vic ghp khng gian cho cc li h g i hn ch thay th, trong cc

ng h h h nhiu anten ti h g g SNR/SIR

nh hg h a to chm. M h, g ng h t

SNR SIR g i cao, v d trong cc t bo nh, vi g h ng tn hiu

h a cung cp cc li h g i nh v cc t d liu c th c b

gii hn bi di hg hh h b gii hn bi SIR/SNR Tg ng

h h h, gh hg gi g hi h iu kin knh

t S nhi e g iu khin bi trm gc, do vy c th chn mt

ph hp cho mi s truyn dn.


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n tt nghip 9

1.2.5. Htra trm vqung b

Qung b nhiu t n s truyn dn ca cc thng tin ging nhau t

nhiu t bo. Bg h hi h iu ny ti u cui, vic s dng mt cch hiuqu cng sut tn hiu t nhiu v tr t bo lc d tm c tht c mt s ci thin

g v m ph sng (hoc cc t qug h) i c

hi h g WCDMA, g , ng hp qug / m nhiu t bo, mt

u cui i ng c th thu cc tn hiu t nhiu t bo v kt hp mm mt cch tch

cc bn trong my thu.

LTE thc hi iu ny m h cung cp s qung b nhiu

t bo hiu qu cao. Bng cch truyn khng ch cc tn hiu ging nhau t nhiu vtr t bo (vi m v s iu ch ging h), ng b ho thi gian

truyn gia cc t bo, tn hiu ti u cui i ng s hin di g h t tn

hi h i mt v tr t v l thu ng truy

ng. Do sc ch ng c OFDM i vi ng truy ng nn s truyn

dn nhiu t h g c gi l mng mt tn s m qung b

(MBSFN: Multicast-Broadcast Single-Feqe New) i g c

gi l mng tn s (SFN Sige Feqe Network) mc d trong 3GPP s vit

t MBFSN c dng v SFN l s vit tt ca System Frame Number), sau khng ch ci thi g tn hiu thu, m cn loi tr nhiu lin t bo. V

vy, cng vi OFDM, g t qug / m nhiu t bo cui cng cn b

hn ch duy nht bi tp nhi g ng hp cc t bo th hiu sut c th

t cc cao. Nn ch rng vic s dng truyn dn MBSFN cho qug / m

phi m bo sng b kht khe v sng chnh thi gian ca cc tn hi c

pht t i t t bo khc nhau.

1.3. Cu trc giao din v tuyn LTETg vi WCDMA/HSPA, g h t c cc h thng thng tin hi i

khc, qu trnh x i vi LTE c kt cu thnh cc lp giao thc khc nhau.

Mc d mt vi l g vi nhg i g g WCDMA/HSPA, hg

g t vi s khc bit, v d do cc s khc nhau trong cu trc ton th

gia WCDMA/HSPA v LTE. Phn ny bao gm s din t v:

Cc lp mng pha trn lp vt l. S ng ln nhau ca chng. Giao din vi lp vt l.


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n tt nghip 10

Trong phn ny ch ni ti cu trc truy nhp v tuyn LTE gm c mt nt

eNodeB (Evolved-Universal Terrestrial Radio Access NodeB).

Tng qut chung v cu trc giao th LTE i vi ng xug cminh ho trong Hnh 1.4 Nhg hg hi tt c cc thc th ih h

trong Hnh 1.4 c thng dng tt c cc hon cnh. V d, khng phi s lp lch

MAC g hg hi ARQ lai cng vi s kt hp m c s dng cho qung

b v thng tin h thg H a, cu trc giao thc LTE lin quan ti cc s truyn

d he g g vi c ng xung trong hnh 1.4, mc d c

cc s khc nhau v vic la chn khun dng truyn ti v s truyn dn nhiu anten

sc tho lun.

D li c truy he ng xung ti hh i dng cc gi IP da vo

mt trong cc dch v mng SAE (SAE: System Architecture Evolution bearers).

Tc khi truyn dn qua giao din v tuy, gi IP c cho qua nhiu thc

th giao thc mg c din t chi ti h g h

- Giao thc hi t d liu gi (PDCP) thc hin vi IP gim

sng bt cn thi pht trn giao din v tuyn. C h u da trn

s u mnh ROHC (Robust Header Compression)- mt thut

c tiu chu h g g WCDMA g h t vi cc

tiu chu hg i i g h PDCP g h him m mt v bo v

nguyn vn v d li c pht. Ti bn thu, giao thc PDCP thc hin gii m mt

v cc ho ng gii g ng.

iu khin lin kt v tuyn (RLC: Radio Link Control) c trch nhim phn

n/mc ni, x l truyn li v phn pht theo chui ni tip ti cc lp cao

h Kh i WCDMA, giao th RLC g eNeB h l mt

loi e trong cu trc mng truy nhp v tuyn LTE. RLC cung cp ccdch vh PDCP i dng cc gi mang v tuyn (radio bearers). C mt thc th

RLC cho mi dch v mang v tuy hit lp cu hnh cho m u cui.

- iu khin truy nh i g (MAC Mei Ae C) iu khin

cc s truyn li ARQ lai v lp lh g ng xung. Ch g

lp lh h t trong eNodeB, ci m c mt thc th MAC cho mi

t i vi c g ng xung. Thnh phn giao thc ARQ lai

c hin din trong cu pht ln thu ca giao thc MAC. MAC cung cp cc

dch vh RLC i dng cc knh logic.


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n tt nghip 11

Hnh 1.4: Cu trc giao thc LTE

- Lp vt l (PHY: Physical Layer) x l vic m ho/gii , iu ch/ gii iu

ch, s nh x nhiu anten, v cc ch g p v in hnh khc. Lp vt l

cung cp cc dch v cho l MAC i dng cc knh truyn ti (transport channel).

Cc ph gm s din t c th h cc giao thc RLCv MAC ca LTE.

1.3.1.iu khin lin kt v tuyn (RLC)

RLC LTE g vi WCDMA/HSPA chu trch nhim v phn chia

( ) gi IP g c bi h RLC-SDUs (RLC-Service

Data Unit ) t PDCP hh h nh h RLC- PDUs (RLC-Protocol

Data Unit). Vi ch l thc th d liu t/ti mt lp giao th h c bit

h t SDU v thc th g ng ti/t mt lp giao thc th h iu thPDU N g l vic truyn li ca cc PDUs bh i, g h ic xo b bn


24/74


n tt nghip 12

sao v mc ni cc PDUs thu c. Cui g, RLC m bo phn pht ni tip

cc SDUs cho cc lp pha trn.

C h truyn li RLC chu trch nhim cho s phn pht khng b li ca dliu cho cc l iu ny, mt giao thc truyn li ho ng gia

cc thc th RLC trong my thu v my pht. Bng cch gim st chui cc ch si

vo, RLC thu c th nhn ra cc PDUs b li. Cc thng bo trg hi c quay tr

li RLC pht, yu cu truyn li cc PDUs b li. Da vo thng bo cc trng thi thu

c, thc th RLC my pht c th hh ng ph hp v truyn li PDUs

li n c yu c Khi RLC nh c hh yu cu cc s truyn li cc

PDUs li h , c ni l ho ng trong ch bo nhn (AM:

Acknwege Me) i g vi h g g g g

WCDMA/HSPA AM g in hnh trong cc dch v TCP (Transmission

C P) h fie g ic phn pht d liu khng b li

iu quan trg hg u.

Tg vi WCDMA/HSPA, RLC g h nh cu hnh theo ch

khng bo nhn (UM: Unacknowledged Mode) v ch trong sut (TM:

Transparent Mode). Trong UM, s phn pht ni tip ti cc l h c cung

c hg hg n li cc PDUs li c yu c UM g in hnh chocc dch vh VIP g phn pht khng b li l t quan trg i vi thi

gian phn pht ngn. TM, m h trsong ch dng cho cc m h c bit

h hp ngu nhin.

Hnh 1.5: Phn on v ni ghp RLC

Mc d RLC c th x l cc li truyn dn do tp m, cc s bi i knh

khng d c, trong tt c ng h c x l bi giao thc ARQi MAC D vi g h truyn li trong RLC c the h

khng cn thit. Tuy nhin, sg h truyn li trong cRLC MAC


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n tt nghip 13

bn do c cc s khc nhau v bo hiu phn hi. Cng vi s thm vo vic x l

truyn li v phn pht ni tip, RLC g m nhim sh n v mc ni h

c minh ho trong Hnh 1.5. Ph thuc vo quy nh b lp trnh th mt sng a d li c la chn cho vic truyn dn t b m RLC SDU cn

SDU h n/ghp ni to thnh RLC PDU. V v, i vi LTE

h hc RLC PDU bi i m h g i vi cc t d liu cao, mt

h hc PDU ln d u nhh g i Tg hi i vi cc tc

d liu thp, m h hc PDU nhc yu cu nu khng th ti trng c th

qu ln. V cc t d liu LTE c th ti i/ n trn m Mi/

h h PDU g h y cho LTE. Do tt c RLC, b lp trnh v cc

h thch nghi t t trong eNodeB nn cc kch h PDU g ch trmt cch dg i vi LTE.

1.3.2.iu khin truy nhp mi trng (MAC: Medium Acces Control)

Lp MAC x l vic ghp knh logic, truyn li ARQ lai, v lp lh ng

ng xug Tg hn vi HSPA, ci m dng phn t ng ln

v v v nh r c t bo phc v ln t bo khng phc v trong khi LTE ch

nh r mt t bo phc v v khng c phn t ng ln. T bo phc

v l t u cui i g c kt ni ti v l t bo m chu trch nhim chovic lp lch v s ho ng ARQ lai.

Cc knh logic v cc knh truyn tiMAC cung cp cc dch vh RLC i dng cc knh logic. Mt knh logic

nh nhvo loi hg i g c phn loi trong cc knh

iu khi, c dng cho vic truyn d iu khin v cc thng tin v t chc

cn thit cho mt h thng LTE ho g, h ng dng cho d liu

gi dng. Tp cc loi h gi hnh cho LTE bao gm:

- Knh iu khin qung b (BCCH: Broadcast Control Channel) dng cho s

truyn d hg i iu khin h thng t mng ti tt c u cui i ng

trong t Tc khi truy nhp h thng, mt u cui di ng cn c thng tin

c truyn h tm hiu h thg nh c hh h h no v

dh i thng ca h thng.

- Kh iu khin tm gi (PCCH Pgig C Che) g tm gi

u cui i ng m v tr ca n trn c t hg c nhnbit v mng v v th thng bo tm gi c c truyn cho nhiu t bo.


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n tt nghip 14

- Knh iu khin dnh ring (DCCH: Dedicated Control Channel) dng truyn

thng tin iu khin ti/t mt u cui di g Kh g nh cu hnh

ring c u cui i g h hg hn giao cuc gi khc nhau.- Kh iu khi m (MCCH: Multicast Control channel) dng cho s

truyn d hg i iu khin cn thit cho vic thu ca MTCH.

- Kh ng dnh ring (DTCH: Dedicated Traffic Channel) s dng cho

vic truyn dn d li gi dng t/ti m u cui i g i knh logic

g truyn dn cho tt c d li gi g ng ln v d li gi dng

ng xung m khng phi l MBMS (Multimedia Broadcast/Multicast Service).

- Kh g (MTCH Mi Tffi Che) c dng chotruyn d ng xung ca cc dch v MBMS. Mt c h gi g

t c dng cho WCDMA/HSPA. Tuy nhin, so vi WCDMA/HSPA, cu trc

knh logic LTE ny c ph gin, cng vi vic gim sng cc loi knh

logic. T lp vt l, lp MAC s dng cc dch v i dng cc knh truyn ti

(transport channel). Mt knh truyn ti h gh i c tnh v thng tin

c truyn qua giao din v tuyn. D liu trn mt knh truyn ti c sp

xp thnh cc khi truyn ti (transport blocks). Trong mi khong thi gian truyn

TTI (TTI: Transmission Time Interval), ti t khi truyn ti h hc no

c truyn qua giao din v tuyn khi khng c s ghp khng gian. Nu c

gh hg gi (MIMO) h ln ti hai khi truyn ti cho mi TTI.

c kt hp cng vi mi khi truyn ti l mt khun dng truyn ti (TF:

T F) nh r khi truyn ti h h no s c truyn qua giao

din v tuyn. Khun dng truyn ti (TF) cha thng tin vh hc khi truyn

ti, iu ch, v nh x anten. Cng vi s nh ti nguyn, kt qu t m

c th suy ra t khun dng truyn ti (TF). Nhs bi i cc khun dng truynti, lp MAC c thh c cc t d liu khc nhau. V v, iu khin t

g c bi h la chn dng truyn ti.

Tp cc loi knh truyn ti hnh cho LTE gm c:- Knh qung b (BCH: Broadcast Channel) c mt khun dng truyn ti c

h, c cung cp bi im k thu N g truyn dn thng tin

trn knh logic BCCH.

- Knh tm gi (PCH Pgig he) g truyn thng tin tm gi trn

knh logic PCCH. PCH h tr s h gi n (DRX: Discontinuous Reception)


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n tt nghip 15

h h u cui i ng tit kim ngun pin nhvo ch ng v thc d thu

PCH ny chcc thi i h c. Knh chia sng xung (DL-SCH:

Downlink Shared Channel) l knh truyn ti c dng cho vic truyn dn d liung xung trong LTE. N h trcc h LTE h thch nghi t ng v

vic lp lch ph thuc knh trong min thi gian v min tn s, ARQ lai, v ghp

khng gian. N cung h trDRX gim s tiu th ngu u cui i ng. DL-

SCH TTI (DL-SCH Transmision Time Interval) l 1 ms.

- Kh hg (MCH Mi Che) g h trMBMS.

N g i mt khun dng truyn ti h (ei-static transport

format) v s lp lh h (ei-i heig) Tg ng hp truyn

dn nhiu t bo bng cch dng MBSFN, vic lp lch v cu hnh khun dng truyn

ti c lp to gia cc t bo tham gia vo s truyn d MBSFN

- Knh chia sng ln (UL-SCH: Uplink Shared Channel) l ph i xng vi

DL-SCH.

Nhim v ca ch g MAC gh h gi h h h cc

knh logic cho cc knh truyn ti thch hp. MAC trong LTE h tr vic ghp ca

RLC PDUs t dch v mng v tuyn (radio bears) khc nhau thnh khi truyn ti

ging nhau. V c mt s s lin quan gia loi hg i h c pht nn c

cc s gii h g ic nh x ca cc knh logic ti cc knh truyn ti. Mt

v d v s nh x cc knh locgc ti cc knh truyn ti c cho trong Hnh 1.6.

Hnh 1.6: V d v snh x ca cc knh logic ti cc knh truyn ti

Vic lp lch ng lnCh g bn ca b lp lch g g thng xung, c th

h ng, cho mi khong 1ms, nhng thit bu cui i ng no truyn

d liu trn UL-SCH v trn nhng ti g ng ln ny. Vic lp lh ng ln


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n tt nghip 16

g c s dng cho HSPA, hg khc nhau c hg c

s dng, nn c mt s s khc nhau quan trng gia HSPA v LTE v kha cnh ny.

Trong HSPA, chia s i g ng ln ch yu c th chp nh cnhiu ti tr . B lp lh ng ln trong HSPA cht gii trn ca sng

ca nhi ng ln cho php thi i i g u cui c t C trn gii

hn ny, thit bi g u cui la ch c l nh dng truyn ph hp. Chin

g gh h ng ln khng tr gi h ng hp

HSPA. Thit b i g u cui khng dng cho tt c nhg i g h y

bt buc truyn ti cng sut th, gim bt nhiu trong t D , hi

nhng ti nguyn khng dng cho mt thit bi g u cui c th khai thc theo

thit bi ng u cui khc thng qua b dn knh. T vi nh dng truyn

c chn lc v tr thit bi g u cui h HSPA ng ln, ngoi di tn hiu

cn t khai bo nt B la chn g h c thc hin.

V phn LTE, ng ln trc giao v chia s ti nguyn c iu khin bi

eNodeB b lp lh h ti nguyn thi gian tn s. Vic gn ti nguyn khng

phi hon ton cho thit bu cui i ng khng th dng c tng phn cho thit

bu cui i ng h D , ng ln trc giao, m h g c li h

trong vic la chn thit b u cui i g h nh dng truyn c so snhvi HSPA. Bi vy, ngoi vic gn nhng ti nguyn thi gian tn s cho thit bu

cui i ng, b lp lch eNodeB chu trch nhi iu khi nh dng truy ( ln

trng ti, iu ch) ca thit bu cui i ng sc s dg Khi gi lp

lch bit nhg nh dng truyn cho thit bu cui i ng mun s dng khi pht,

hg n thi h iu khin tn hiu ngoi di t thit bu cui i g n

eNeB iu ny c li thg in ph sng c h n chi ph, mi bt c iu

khin pht thng tin ngoi di c th h h g so vi gi thnh ca

truyn d li h iu khin tn hiu cn thu vi tin c h Mc d vic b

lp lch eNeB h nh dng truyn ti cho thit bu cui i ng, cn

phi ch dn gii quyt vic lp lh ng ln ly theo thit bu cui i ng v

khng qua v tuyn truy hg Nh y, mc d vi gi lp lch eNeB iu

khin trng ti ca tr u cui i ng trong vic lp lch, thit b u cui

vn phi chu trch nhim cho s la chn t v tuyn truyn thng d li c ly.

Nh y, thit bu cui i ng x c lp dn knh logi i c minh

ho bn phi ca Hnh 1.7, gi lp lch iu khi eNeB nh dng truyn ti iu khin thit bu cui i ng dn knh logic. so snh, trg hi ng


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n tt nghip 17

xung gng, NeB iu khin cho chi nh dng truyn ti v dn knh

gi, c miu t bn tri ca hnh.

Hnh 1.7: La chn phn thc truyn ng xun v ng ln

Ghp knh trong thi i u cui i ng khng theo nhng quy tc, nhng

tham s ca n c thnh cu hnh bi tn hiu RRC t eNodeB. Mi dch v mng

c gn mt quy i i bt. Thit bu cui i ng s thc

hin ghp knh v dy dch v mng khng tho mn th t i n t bt ca

h. Ti nguyn cn li, nu c, sau khi thc hi i d liu da vo th

t i g gh h

gi b lp lh ng ln, thit bu cui i ng c th lp lp truyn

hg i n eNode B s dng tin nhn MAC. R rng, thng tin c thc truyn

nu thit bu cui i ng nu c sng lp lch hp l.

Lp lch ph thu h g s dng cho ng xung. V nguyn l, n

c thc s dng cho cg T hi, h gi h ng h ng

ln khng d lm ging h ng xung. iu ki h ng xung c thc

nh bi tt c cc thit b u cui i ng trong mt t c quan st d

dng khi tham chiu vic truyn tn hiu chun v pha eNode B v tt c nhng thit

bu cui i ng c th chia s gig h hiu tham chiu ti kt quh gich g h h gi h g h ng ln, tuy nhin, cn tn hiu chun

h mi mt thit bu cui i ng cho eNode B mu ng cht


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n tt nghip 18

g h g Nh y tn hiu tham chi c h trbi LTE. Cho nn,

bi h cung c h g g h t s b xung hay khc ti vic

lp lch ph thu h ng ln trnn quan trng. ARQ lai

ARQ lai LTE cng vi s kt hp m chng li cc li truyn dn. V

cc s truyn li ARQ lai l nhanh nn nhiu dch vh h i vi mt hoc

nhiu s truyn li, he h hh hh h iu khin t ngm

(g ), g h HSPA, giao thc ARQ lai l b phn ca lp MAC, trong khi

, h ng kt hp m c x l bi lp vt l.

R rng, ARQ lai khng thng dg c cho tt c cc loi ng.V d, cc s truyn dn qug g hg i ging nhau dnh cho nhiu

gi dng lm vic khng da vo ARQ lai. V th ARQ chc h trcho DL-

SCH v UL-SCH.

Giao thc ARQ lai LTE bao gm nhiu qu trnh x l dg i song song.

Da vo s thu ca mt khi truyn ti, my thu thc hin th gii m khi truyn ti

ny v thng bo cho my pht bit v kt qu ca ho ng gii m thng qua mt

ACK/NAK biu th s gii m thnh cng hoc nu s truyn li ca mtkhi truyn ti c yu c ti thi h u, m ACK/NAK

l c s dng. R rng my thu nht thit phi bi c m ACK/NAK

h c kt hp vi q h ARQ i i c gii quyt nhs tnh ton

thi im c ACK/NAK g kt hp ACK/NAK ny vi mt qu trnh

ARQ h c minh ho trong Hnh 1.8. Ch rg, g ng hp

ho ng TDD, mi quan h v thi gian gia s thu ca d liu theo mt qu

h ARQ i pht ca ACK/NAK g h hng bi s phn chia

g /ng xung.

LTE, mt giao th hg ng b cho s ho g ARQ i ng

xung. V vy, cc s truyn li ng xung c th xy ra ti bt c thi gian no

sau ln truy u tin v h s qu trnh x ARQ i ch th qu trnh x

g c ch tm vo. Mt khc, cc s truyn li he ng ln d

giao th ng b v s truyn li xy ra mt thi im xc nh c sau s truyn

dn u tin. Hai ng h c minh ho trong Hnh 1.8.


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n tt nghip 19

Hnh 1.8: Giao thc RQ ai ng bv khn ng b giao th ARQ i hg ng b, cc s truyn li c lp lch v nguyn

t n ging vi cc s truy u tin. Mt khc, trong giao th ng b, thi

im cho cc s truyn li c cnh sau khi vic truyn l i c lp lch.

Tuy nhin, ch rng b lp lch nhn bit t thc th ARQ trong eNodeB m u

cui i ng s thc hin s truyn li hay khng.


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n tt nghip 20

Hnh 1.9: a l ARQ song song

Vic s dng nhi q h ARQ i g g c minh ho trong Hnh

, i vi mi gi dng c th d n d li h hi he h ARQlai khng theo trnh t no. V d, khi truyn ti 5 trong hnh minh ho c gii

m thnh cng tc khi truyn ti i u mt s truyn li. Sau khi gii

m thnh cng khi truyn ti c phn thnh cc knh logic thch hp v s sp xp

li c lm trn mi knh logic bng cch dng chui cc ch s ny.

C h ARQ lai s sa cc li truyn gy bi tp m hoc cc bi i knh

khng th d Nh ho lun , h RLC g hg hc hin

i vi cc yu cu truyn li. Tuy nhin, t khi cc s truyn li RLC l cn thi chARQ i n c khng sa hu ht cc li truyn dn hg i hi ARQ

lai c th hg khg cp pht cc khi d liu khng c li (error-

free) cho RLC do mt k hchui ca cc khi d liu khng c li c phn pht

ti RLC. iu ny xy ra do bo hiu hi tip v sai, v d mtNAK c din dch

hg g hh t ACK bi my pht, gy mt d liu. Xc su x iu

ny c th l khong 1%; Mt xc sut li hg q i vi cc dch v TCP

bn (Transmission Control Protocol) l cn thit cho s cp pht cc gi TCP h h

khng c li. Mt cch c thh, i vi cc t d li t qu 100 Mbit/s yucu xc sut mt mt gi d li i 510 . V n, TCP coi ton b cc li gi l


33/74


n tt nghip 21

do s tc nghn. V vy, cc li gi khi s mt qu trnh trnh tc cng vi mt s

gi g ng cc t d li duy tr hiu sut tt ti cc t d liu cao

th RLC-AM phc v nhm m h q g b m phn pht d liukhng c li cho TCP.

V h ARQ lai c mc tiu cho cc s truyn li r hh i hi gi

mt bt thng bo trng thi ACK/NAK ti my pht tht nhanh c th thc hin

ch trn mt TTI. Mc d v nguyn l c th c xc sut li thp tu

ca thng tin phn hi ACK/NAK hg gi hi tr l c n cng sut pht

g i cao. Vic gi s tr gi ny mt cch h n mt t l li hi tip

khong 1% ci m quy nh t l li ARQ i V hng bo

trg hi RLC c truy h ACK/NAK ARQ i h g nn s tr

gi c s tin cy 510 hay th h g i nh. V vy s kt hp ca

ARQ i RLC c mt s kt hp tt v thi gian kh hi nh v m u

hi tip va phi g hi hh hn ny b xung ln nhau.

V RLC ARQ i t cng mt node nn sg ht ch gia

hi i iu c th xy ra. V d n h ARQ lai pht hin mt li khng

th khi phc li c th vic truyn ca mt thng bo trng thi RLC c thc

khi s ngay lp t h i truyn mt thng bo trng hi he nh k iuny s d n vic truyn li RLC ca cc PDU b li hh h V y, vi m

h ic kt hp ca ARQ lai v RLC c the h h truyn li vi

hi h phn hi trng thi.

1.4. Tng kt

Tg hg , h t s im cbn ca mg LTE h c

nh tc thi ca uplink v downlink thc t vi g hg MHz, i g

thng linh hot: c th ho ng vi g n 1.25MHz, 1.6 MHz, 10MHz, 15MHzv 20MHz c chiu ln v chiu xung. C ng tin ln LTE l t GSM ln EDGE,

tip theo ln WCDMA ri HSPA v cui cng l ln 3GPP LTE c nhng

khi qut truy nhp v tuy g LTE h ng xung dng k thut OFDMA,

ng ln dng k thut SC-FDMA, lp lh ng ln ng xung, h tr

qung b v nhiu anten cng vi ARQ lai kt hp mm. Cu trc giao din v tuyn

gm c cc giao th iu khin lin kt v tuy RLC, iu khin truy nh i ng

MAC hi h g LTE, hg e trnh by v k thut SC-

FDMA vi vic nh x sng mang con, x l tn hiu, so snh SC-FDMA vi OFDMA.


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n tt nghip 22

Chn 2

K THUT TRUY NHP PHN CHIA THEO TN SN SNG

MANG (SC-FDMA)

2.1. Gii thiu

hp phn chia theo tn s tr gi (OFDMA) y nhp phn

chia theo tn s g g (SC-FDMA) l phin bn ci bin ca OFDM. Tt c

cc k thut phn chia tn s trc giao s dng mt tp hp ri rc cc sng mang con

tr gi c phn bq rg g n h thng. Bao gm cc bi i ri rc

chuyn cc tn hiu gia min thi gian v min tn s h ng thi mt vi

tn hiu cc k thu hp gn cc tn hiu cho mt tp cc sng mang conhg g h V h g hg ng chu pha-ih hn lc theo tn s,

nn cc k thut FDMA c th s dng lp lch ph thu h nh c phn tp

gi g, gi , c tnh pha-ih a cc thit bu cui ti cc v tr

h h c lp thng k vi nhau, nn cc k thut lp lch c th gn cc sng

mang con cho mi thit bu cui vi c tnh truyn dn thch hp ti v tr ca thit

bu cui.

Cc h thng t bo WiMAX s dg OFDMA truyn cc tn hiu t cctrm g g h hit bu cui i g Ngc li, GPP q nh OFDMA

cho truyn d ng xung v SC-FDMA cho truyn d ng ln trong cc h

thng t bo (LTE) lm cho cc thit bu cui i ng trnn hiu qu cng sut.

Vic bi c phin b g i a h thng CDMA hin ti, d n hp tc 3GPP2

g hc hin SC-FDMA s dng m tri i vi i g g i ng (UMB).

M h im ca OFDMA l t s cng su h g h (PAPR) , iu

g gi hh gim hiu qu ca b khuh i cng sut ca my

pht. Vi PAPR thp, cc b khuh i cng sut ti cc thit bu cui i ng sdng SC-FDMA gi h hiu qu h i vic chng s dng truyn

dn OFDMA. Mt khc, vi t bo hiu cao, b san bng trn min tn s ca

ng truyn SC-FDMA phc t h hiu so vi b san bng OFDMA. Vi truyn

dn SC-FDMA c gii hn vi ng ln LTE, cc b san bng phc tp chc

yu cu ti cc trm gc m khng yu cu thit bu cui i ng.


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n tt nghip 23

2.2. Xl tn hiu SC-FDMA

Hnh 2.1 m t mt my pht SC-FDMA gi mt khi d li n my thu.

u vo c h u ra c h iu ch phc. Cc hthng thc t c kh g hh ghi t cch t ng k thu iu ch vi cht

ng knh, bng s dng kha dch pha nh phn (BPSK) trong cc knh ch ng

iu chi i trc giao 64 mc (64-QAM) trong cc knh cht

ng tt. Khi d liu bao gm M iu ch ph c to ra vi t

giysymbolRsource / . Hnh 2.2 cung cp cc chi tit ba thnh phn trung tm ca my

pht trong Hnh 2.1. Bi i Fourier ri rc M-im (DFT) to ra M symbol trn

min tn siu chMsng mang trong sNsng mang con trc giao tri

rg g hg :

HzfNWchannel 0 (2.1)

Tg f0 [Hz] l khong cch gia cc sng mang con. T knh truyn dn l

giysymbolRM

NR sourcechannel / (2.2)

Nu k hiu Q l h s tri phg hg, gh

M

N

R

RQ

sourc e

channel (2.3)

S , h thng SC-FDMA c thiu khin Q tn hiu ngun trc giao vi

mi ngun chim tp M sng mang con trc giao khc nhau. Trong ch thch ca Hnh

2.2, )1,...,1,0( Mmxm biu din cc symbol ngu iu ch v

)1,.....,1,0( MkXk biu dinMmu DFT ca mx . )1,.....,1,0( NlYl biu din cc

mu trn min tn s sau khi nh x sng mang con v )1,.....,1,0( Nnyn biu dincc symbol trn min thi gi c pht, nh c t vic bi i Fourier ri

r gc IDFT cal

Y . Khi nh x khi sng mang con trn Hnh 2.1 v 2.2 gn cc

iu ch trn min tn s cho cc sng mang con. Qu trnh nh xi hi

c gi l lp lch.


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n tt nghip 24

Hnh 2.1: Cu trc my pht v my thu ca cc h thng SC-FDMA v OFDMA. [2]

Bi v cc thit bu cui b phn tn v mt khng gian c cc knh pha-ih

c lp vi nhau, SC-FDMA v OFDMA c th c li t vic lp lch ph thucknh. Bi i Fourier ri r gc (IDFT) trong Hnh 2.1 v 2.2 to ra vic biu

din trn min thi gian, ny , ca N symbol sng mang con. B bi i song song ni

tip b tr 0 1 1, ,..... Ny y y ph hp vi vi iu ch sng mang tn s v tuyn v

truy n my thu.

My pht trong Hnh 2.1 thc hin hai qu trnh x l tn hi h c khi

truyn d h t t c gi l tin tg (CP) cung cp

thi gian bo v g hn nhiu gia cc khi d liu (IBI) do truyn d g M h g hc hin ho ng lc tuy h c gi l to dg g

gi g ng tn hiu ngoi di g Tin t vng l bn sao chp ca phn cui

cng ca khi d li N c chn vo v u tin ca mi khi d liu v hai l

do. Th nh, CP g i h hng thi gian phng v gia cc khi lin k.

N di ca CP li h i tr ln nht ca knh, hay ni m h i khi l,

chiu di c ng xung knh truyn th khng c IBI.


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n tt nghip 25

Hnh 2.2: Th h ca SC-FDMA truyn symbol, cNn man con tron M (


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n tt nghip 26

Hnh 2.3: B lc cosine nng. [1]

Hnh 2.3 minh ha v mt hnh hc cc b lc cosine nng trn min tn s v

trn min thi gian. H s un l m trong khong t iu khi ng

bc x ngoi di g Vi = , lc l mt b lc di hg ng kh ton b

bc x ngoi di g Khi g, c x ngoi di g g g The in

thi gian, cc bp sng bn cnh c ng xung b l g hi gi iuny lm tg g nh ca tn hi h i hi o dng xung. V vy,

s la chn ca h s b lc un lc yu cu s dung ha gia cc m h c x

ngoi di g hp v t l cng su nh trn trung bnh thp. DFT trong my thu

Hnh 2.1 bin i tn hi h c min tn s trong ch phc hiNsng mang

con. Vic gii nh x thc hin tch M mu trong min tn s ca mi tn hiu ngun.

Bi v SC-FDMA s dg iu ch g g, gp phi mo tuyn tnh thc

ch c hi h hiu lin symbol (ISI). B san bng trong min tn s s trit

b ISI. Khi IDFT ti h h g Hh i i c sanbng trli min thi gi, c mt b tch sng lm nhim v nhn l t

M iu ch.

Hnh 2.4 minh ha ho ng my thu SC-FDMA t mt phi cnh truy nhp

gi g g g Tc khi thc hin qu trnh gii iu ch SC-FDMA

n, trm g h hi gi dng trong min tn s trong qu trnh gii nh x

sng mang con.

Hnh 2.1 ch ra rng kt hp SC-FDMA x l tn hiu trong cc phn t caOFDMA v cng thm khi DFT u vo c h g ng l khi IDFT

u ra ca my thu. V my pht SC-FDMA c nhim v mrng g hg


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n tt nghip 27

hi bao phg hg a knh, SC-FDMA i hi c gi l OFDMA

tri bi DFT.

Hnh 2.4: Cu trc my thu SC-FDMA tmt phi cnh truy nhp a ni dung vi

Q thit bu cui tron ng ln. [2]

2.3. nh x cc sng mang con

Hnh 2.5 m thi hg h gn M iu ch trong mintn s ti cc sng mang con: nh x sng mang con phn tn v nh x sng mang

con tp trung. Tg hg h h cc sng mang con tp trung, cc symbol

iu chc gn cho M sng mang con lin k. Trong ch phn tn, cc symbol

h u trn ton bg hg h Tg hai ch th khi IDFT ti

my pht sg i bng 0 cho N M sng mang con khng b chi g T

gi ch nh x cc sng mang con tp trung ca SC-FDMA l FDMA tp trung

(LFDMA) v ch nh x cc sng mang con phn tn ca SC-FDMA l FDMA

phn tn (DFDMA) Tng hp N Q M cho ch phn tn vi cc khong cchu nhau gia cc sng mang con b chi hg c gi l FDMA ghp xen


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n tt nghip 28

(IFDMA) IFDMA ng h c bit ca SC-FDMA v n rt hiu qu khi my

pht c thiu ch tn hiu mt cch nghim ngt trong min thi gian m khng cn

s dng DFT v IDFT. Trong phn 2.4, ta m t cho IFDMA, s kt hp DFT vIDFT s gim bt mt php nhn ph gi, g g i vic quay pha ca

mi iu ch ti u vo ca my pht.

Hnh 2.5: Cc ch nh x cc sng mang con ( phn tn v tp trung). [2]

Hnh 2.6: V d nh x cc sng mang con khc nhau vi M =4, Q =3, v N =12.[2]

Hnh 2.6 minh ha ba v d v cc symbol pht SC-FDMA trong min tn s

vi 4M symbol trn khi, 12N sng mang con v 3Q N M thit bu cui.Trong ch tp trung, b iu ch chim cc sng mang con 0, 1, 2 v 3:


41/74


n tt nghip 29

00 XY , 11 XY , 22 XY , 33 XY , v 0iY cho i 0, 1, 2, 3.. Trong ch phn tn

vi iu ch h u nhau trn tt c cc sng mang con th 00 XY

, 12 XY , 24 XY , 36 XY v trong ch ghp xen th 00 XY , 13 XY , 26 XY ,

39 XY .

Hnh 2.7 m t IFDMA v LFDMA biu th cc tn hiu ca 3 thit bu cui

khc nhau giao nhau ti mt trm gc b chi g n nhau c chn lc cc tp

sng mang con.

Hnh 2.7: Cc phn php phn bcc n man con a ni sdng. [1]

Tq im ca vic phn bi g, hg h h sng mang hi h g hg h p lh h hg h p

lch ph thuc knh (CDS). CDS gn cc sng mang con ti nhi gi s dng theo

ng tn s knh ca mi gi s dng. Vi chi hg h p lch, vic nh

x cc sng mang con phn tn s d n vic phn tp tn s v tn hi h i

c tri trn ton bg hng. Vi vic nh x phn tn, CDS s gip ci thin

hiu su Ngc li, CDS c li ch l h i nh x sng mang con tp trung bi

v n cung cp phn t gi g g .

2.4. Biu din trong min thi gian ca tn hiu SC-FDMA

Vi IFDMA, LFDMA v DFDMA, ba ho ng trong Hnh 2.2 c thc

e h t php ton tuyn tnh trn chui iu ch { nxm :

,,,, 1M } D , i thnh phn chui u ra { nyn : ,,,, 1N }

l mt tng trng s ca cc thnh phn chui , g ng s l cc s

ph Tg ng hp IFDMA, cc trng su bng 0, ngoi tr mt thnh phn

ca chui u vo. Tp hp cc php ton s d n vic nhn mi u vo

vi mt s ph i v lp li chui u vo vi g Q ln quay pha,

vi Q l h s mrg g hg


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n tt nghip 30

Phn 2.4.1 s suy ra tnh cht ny t v d vi 4M symbol/khi, 12N sng

mang con v 3Q thit bu cui. Ph g bg th ca chui tri

ph v chui thi gian ca mt khi tn hiu IFDMA. Cc cng thc cho cc chuithi gian ca LFDMA v DFDMA th phc t h i IFDMA. Phn 2.4.2 v

2.4.3 m t ph ca hai k thut nh x sng mang con cng vi cc cng thc cho cc

phn t ca chui thi gian.

2.4.1. Cc symbol tr ong min thi gian ca IFDMA

Vi IFDMA, vic kt hp hai khi DFT v IDFT trong my pht ca Hnh 2.1

v 2.2 s d n cc php ton x l tn hi gin bng vic nhn mi symbol

u vo bi mt s phc vi i v lp li chui u vo vi g Q ln

Hnh 2.8: Minh ha nh x sng mang con IFDMA viM = 4 symbol/ khi,

Q =3 thit bu cui, v N Q M = 12 thit bu cui. [2]

quay pha, vi Q l h s mrg g hg Ph h g g i vicquay pha mi iu ch phc trong khi truyn d ki iu ny l

g, h n hai tnh cht ca DFT v IDFT: (a) Cc m h hg h u


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n tt nghip 31

nhau trong mt mi g ng ti mt chui c chu k trong mt min khc; v (b)

dh i t khong r trong min tn sg ng vi mt php quay pha ca mi

mu thi gian. Vi q h c thc hin bng cch nhn mi mu vi exp 2j rn N , g N l s im trong bi i gc, r l gi tr ca dch

chuyn tn s, v n l s m u ra trong min thi gi i t

trnh by ton hc chi tit ca tnh cht ny. Hnh 2.8 l mt minh ha cho v d vi

4M symbol/khi, 12N sng mang con v 3Q thit b u cui, v

12 MQN sng mang con.

Cho mt tn hi u vo, : 0,1,..., 1lY l N l ph ca chui SC-FDMA c

truyn biu th mt khi d liu : 0,1,2,..., 1mx m M . Vi IFDMA, ph ca M

thnh ph h hg h u nhau, vi cc mu ln c c phn cch bi cc

mu 1Q trong min tn s. Tn hiu min thi gi g ng : 0,1,2,..., 1ny n N

l tun hon vi bn sao Q c phn b ln thi gian 0,1,2,..., 1 1n M N Q v

vi s quay pha ca exp 2j rn N . Xt mt tn hi u vo : 0,1,2,..., 1mx m M

chim cc sng mang con 0, ,2 ,..., ( 1).l Q Q M Q . Tn hiu thi gi c pht tun

h g ng ti tri ph ca tn hiu ny c chui 0 1 1, ,..., Mx Q x Q x Q c lpli Q ln (gc quay l 0 radian). By gita xt tn hiu t mt thit bu cui khc

: 0,1,2,..., 1mu m M iu ch tp ti he g g h u

nhau 1, 1, 2 1,..., ( 1). 1n Q Q M Q .

Ph ca tn hiu ny : 0,1,2,..., 1lV l N g ging vi ph lY hg dch

i hh hn khc khng bi mt mt sng mang con. S dch chuyn ny trong

min thi gi g ng vi php nhn trong min thi gian exp 2j n N D ,

chui min thi gi c truyn l Qu /0 , QNnju /)/2exp(1 ,, 1Mu exp

QNnj /)/2( c lp li Q ln vi gc quay thch hp. Tng qut, vi mt tn hiu

u vo : 0,1,2,..., 1mx m M iu ch vi cc sng mang con ti

, ,2 ,..., ( 1).n r Q r Q r M Q r th tn hi c truyn dn s l

: 0,1,2,..., 1mx m M c lp li Q ln vi gc quay pha ca exp 2j rn N .

Cc cng thc ton h g ng ti s miu t u tin l cc symbol

min tn s l:


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n tt nghip 32

/, 0 1

0, trng h p khc

l Q

l

X l Q k k MY (2.6)

Vi 0 1l N v .N Q M t . 0 1,0 1n M q m q Q m M th:

1 1 1

0 0 0

1 1

0 0

22 2

2 2

(mod )

1 1 1 1

1 1 1 1

1 1

n

N N M

l l Q k

l l k

M M

k k

k k

m n

Mq m

nn n j Qkj l j lQMN N

Mq m mj k j k

M M

M

y y

Y e X e X eN N Q M

X e X eQ M Q M

x xQ Q

(2.7)

Kt qu cc symbol thi gian ny l s lp li u vo gc mx

vi h s t l l 1 Q trong min thi gi g h hg i .

Khi b u phn tn sng mang con t sng mang con th r 0 1r Q th:

, . 0 1

0, trng h p khc

l Q r

l

X l Q k r k MY (2.8)

Tg ng vi biu thc (2.7), cc symbol thi gian ny c thc vit li

h

( )

2

mod

1.

n n

rnj

N

My x e

Q

(2.9)

C th thy t biu thc (1.9), s c thm mt ln quay pha l exp 2j rn N

h c k hiu khi b u phn tn sng mang con t sng mang con th rthay v sng mang con khng. Vic quay pha ny sg ng ti nh x

cc sng mang con khc.

2.4.2. Cc symbol tr ong min thi gian ca LFDMA

Hnh 2.9 l bi ca nh x sng mang con LFDMA. N m t cc symbol

iu ch chim 12 sng mang con lY trong v d.


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n tt nghip 33

X0 X1 X2 X3

X0 X1 X2 X3

X0 X1 X2 X3

T

DFTx0, x1, x2, x3 X0, X1, X2, X3

Y0

Y1

Y2

Y3

Y4

Y5

Y6

Y7

Y8

Y9

Y10

Y11

i 1

(r = 0)

i 2

(r = 1)

i 3

(r = 2)

Hnh 2.9: Minh ha nh x sng mang con LFDMA viM = 4 symbol/ khi,

Q = 3 thit bu cui, v N Q M = 12 thit bu cui. [2]

Cc mu min thi gian ca tn hiu LFDMA c thc biu di h

mod

12

20

1, 0

1 11 , 0

1

Mn

q Mn Qm q jpQ

m p qjpM QM

x qQ

y y xe q

Q Me

(2.10)

Nh h thy trong cng thc (2.10) tn hiu LFDMA trong min thi gian

i hi cc bn sao ca cc symbol thi gi u vo vi h s t l1 Q ti v tr mu

l bi s nguyn ca Q . Cc gi tr tc thi l tng trng s ca tt c cc symbol thi

gian ca khi u vo.

2.4.3. Cc symbol tr ong min thi gian ca DFDMA

Hnh 1.10 l mt bi ca nh x sng mang con DFDMA. N m tiuch cc symbol chim 12 sng mang con, lY trong v d.


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n tt nghip 34

X0 X1 X2 X3

X0 X1 X2 X3

X0 X1 X2 X3

Tns

DFTx0,x1,x2,x3 X0,X1,X2,X3

Y0 Y1 Y2 Y3 Y4 Y5 Y6 Y7 Y8 Y9 Y10 Y11ucui1

(r=0)

ucui2

(r=1)

ucui3

(r=2)

Hnh 2.10: Minh ha nh x sng mang con DFDMA vi M 4 symbol/ khi,

Q 3 thit bu cui, v N Q M = 12 thit bu cui. [2]

mod

mod

12

20

1, 0

1 11 , 0

1

nM

M

Q

Qqn Qm q MjpQ

Qm p Qqjp

M QM

x qQ

y yx

e qQ M

e

(2.11)

Tg 1Q Q Q l h s tri thc. Cc mu trong min thi gian ca

DFDMA c cu trc gig h g LFDMA

2.4.4.So snh cc s nh x sng mang con

Hnh 2.11 m t cc mu trong min thi gian cho mi nh x sng mang con

c miu t ngay tu. Tn hiu IFDMA duy tr cc symbol thi gi u vo ti

mi mu trong khi LFDMA v DFDMA c cc mu thi gian phc t h ngtrng s phc ca cc iu ny d n cng su nh s h

c cho rng vi cc tn hiu LFDMA v DFDMA. Hnh 2.12 m t mt v d ca

i ca cc mu cho mi nh x sng mang con choN= 64 sng mang con,M=16

sng mang con trn khi, Q =4 h s tri ph cho IFDMA vi bn thit bu cui, v

Q=3 h s tri ph cho DFDMA vi ba thit bu cui.

Trong Hnh 2.12 khng c to dg g i vi h Hh g

t g dg g OFDMA C u vo ring bi h iu ch SC-

FDMA c s dg QPSK i vi IFDMA, chng ta c thq i khng

i m xut pht t vic duy tr tnh ch g hg i c QPSK i vi


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n tt nghip 35

LFDMA v DFDMA, chng ta c th thy bi g h h h B

gm, tt c nh xg g g g h hin cng su nh

th h OFDMA

Hnh 2.11: Bin ca cc mu SC-FDM v OFDM cho iu chu vo QPSK

khng c to dng xung. [2]


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n tt nghip 36

x0 x1 x2 x3 x0 x1 x2 x3 x0 x1 x2 x3

x0 * * x1 * * x2 * * x3 * *

x0 * * x2 * * x0 * * x2 * *

x0 x1 x2 x3

Thigian

IFDMA

DFDMA

LFDMA

mx

. nQ y

3

,

0

*k m k

k

c x

(ck,m:Trngsphc)

Hnh 2.12: Cc m nh x sng mang con khc nhau trn min thi gian. [2]

2.5. SC-FDM v a tr nhp phn chia theo tn s trc giao (OFDMA)

C mt mi lin h g gia OFDMA v SC-FDMA cho truyn dn cctn hi c lp t cc thit bu cui h n mt trm g Hh

ch ra rng cc my pht v my thu SC-FDMA v OFDMA thc hin nhiu hm x

l tn hiu chung. Hai k thu u c cc tnh cht sau:

iu ch v truyn dn d liu trong cc khi gm c M iu ch;Ph hi g hg truyn d hh g n con vi hg i c

mang trn cc sng mang con ri rc;

B san bng knh min tn s;S dng mt tin tg trnh nhiu lin khi.

Tuy nhin, c nhng s khc nhau ring bit li d n hiu sut khc bit.

Hu ht im khc nhau r rng l OFDMA pht mt tn hi g g g hi

SC-FDMA pht mt tn hi g g Bi iu ny, SC-FDMA c mt t l

cng su nh trn trung bnh (PAPR) th h OFDMA

Trong min thi gian, khong thi gian ca cc sym iu chc mrg g ng hp ca OFDMA. Khi c M symbol trn mt khi v N sng

mang con tri g hg h thng, c hai SC-FDMA OFDMA u c th pht


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n tt nghip 37

cc tn hiu t Q N M thit bu cui ng thi. Hnh 2.14 m t, cho M = 4,

12N , v Q = 3, nu khong thi gi iu ch l Tgiy, th khong

thi gian symbol OFDMA l M T giy. S mrng v mt thi gian ny s lm gimnhi i (ISI), g im chnh c OFDMA Ngc li, SC-

FDMA li iu ch trong min thi gian. Khong thi gian ca

cc symbol SC-FDMA l T Q giy h g t h thng TDMA. SC-FDMA s

dng b san bng min tn s ti trm g kh ISI.

Hnh 2.13 m t cc khi gm 4M iu ch t 3Q thit

bu cui mi khong thi gian l T (s) chim m rg g hg SourceB Hz.

i 1

i 2

i 3

T giy

Bsource

Hz

Hnh 2.13: M = 4mbo iu ch tQ = 3 thit bu cui; thi gian symbol l Tgiy;

bn thn nn lsource

B Hz. [2]

4T giy

BchannelHz

Hnh 2.14: OFDM nn bn thn dliu c nhn tisource

B /4 Hz v mrng

thi gian ti 4Tgiy. [2]


50/74


n tt nghip 38

4Tgiy

Bch

annelHz

T/3giy

Hnh 2.15: SC-FDMA mrn bn thn ti 3channel SourceB B ; n nn thi gian symbol

cn T/3 giy. [2]

Hnh 2.16: OFDMA v SC-FDMA; tch sng v san bng. [2]

Hnh 2.14 m t mt tn hiu OFDMA vi 12N sng mang con, vi mi

g hg 4SourceB Hz. Mi sng mang con mang m iu ch cho

4Tgiy. Hnh 2.15 m t mt tn hiu SC-FDMA, s dng lp lch IFDMA. , i

iu ch chim ton bg hg 3channel SourceB B Hz D , hng

thi gian symbol gim xung cn 3T giy.

Hnh 2.16 m t OFDM thc hin san bng v tch sng ring bit cho mi

g g Ngc li, SC-FDMA thc hin san bng trn ton bg hg

knh S , dg IDFT bi i tn hiu t mt thit bu cui sang min

thi gi hi h g iu ch. IDFT thc hi c

khi tch sng symbol l cn thit v ngoi tr vi IFDMA th cc tn hi c pht


51/74


n tt nghip 39

gm c mt tng trng s ca tt c cc symbol trong mt khi, h c m t trong

phn 2.4. IDFT l u t mt tn hiu hn hp. V SC-FDMA c

hiu qu tri ph mi iu ch trn ton bg hg h, hyvi pha-ig chn lc tn s h OFDMA, hi iu ch pht

g g hp. M im c OFDMA t qua SC-FDMA l bit sng

mang con thch ng knh v cng sut ti c th chp nh c. Bg hh ghi iu

ch symbol v cng sut cho cc sng mang con ring bit, OFDMA c thn gn

vi gii hn trn ca s gii h ng cho mt knh c th.

2.6. SC-FDMA v CDMA vi b san bng min tn s

hp phn chia theo m chui trc tip (DS-CDMA) vi b san bngmin tn s (FDE) thay th h e, hg c s dg g q c DS-

CDMA, vi b san bng min tn s. Mt my thu rake gm c mt di sa li, c

ng b ha vi mt thnh ph ng ca tn hi c yu cu. Khi sg

g g, hn lc tn s trog h g g hc tp ca biu hp rake

g g Vic s dng FDE thay cho biu hp rake c th lm gim bt cc vn

phc tp trong DS-CDMA. Hnh 2.17 l mt bi khi ca CDMA chui trc

tip vi FDE.

Hnh 2.17: DS-CDMA vi b san bng min tn s (FDE). [2]

My pht ca DS-CDMA/FDE l gig h DS-CDMA hg hng ngoi trvic b sung mt tin t vng. Vic tri cc tn hi g gc to ra mt chui cc

chip vi vic tri g hg di g a knh. FDE trong my thu kh


52/74


n tt nghip 40

nhiu lin chip trong tn hi h i vi cc h s tri ph nh, hiu sut ca

my thu rake gi g bi v nhi i ng v FDE c mt hiu sut t h

i vi h s tri ph ln, chi u c hiu sut ging nhau.SC-FDMA v DS-CDMA/FDE l ging nhau bi v c hai k thu c x

li t tri ph d li g hp thnh m g ng. Chi u duy tr PAPR

thp bi v truyn d g g

Mt mi lin quan ch gia DS-CDMA trc giao v IFDMA l bng s trao

i vai tr ca chui tri ph v chui d li, iu ch DS-CDMA tr hh iu ch

IFDMA. Mt v d ca vi q c minh ha trong Hnh 1.18. Chng ta

c th thy rng kt qu ca tri ph vi i i trong cc mu ca iu ch IFDMA.

Hnh 2.18: Tri ph vi cc vai tr ca chui dliu v chui tn hi c trao i cho

tn hi c tri ph. [2]

M im ca SC-FDMA qua DS-CDMA/FDE l lp lch ngun ph thuc

knh l c th khai thc s la chn tn s ca knh.


53/74


n tt nghip 41

2.7. a tr nhp phn chia theo tn sm n n man (SC-CFDMA)

SC-FDMA truyn thng khng ho g c vi mt s thit bu cui s

dng lp lch tp trung v s dng lp lch phn tn khc nhau bi c tnhtrc giao ca cc ngun bng mi sng mang con b chi g i khng nhi h

mt thit b u cui ti bt k thi gian no. Bng cch s dng k thut tri ph

chui trc tip tr gi c khi ti iu ch SC-FDMA, c hai nh x c th cng

tn ti vi cc sng mang con chg h h c minh ha trong Hnh 2.19. Chng

ta tham kho ti h h hp phn chia theo tn s

sng mang (SC-CFDMA), khi m c th e h kt hp ca DS-CDMA

v SC-FDMA. Mu ny ca SC-FDMA c s dg g ng ln 3GPP2

UMB h iu khin tn hiu.

Hnh 2.20 m t bi khi ca mt h thng SC-FDMA v Hnh 2.21 so

snh SC-FDMA v SC-CFDMA g iu kin ca cc sng mang con b chi g

cho cng mt sgi s dng. Trong Hnh 2.19 v 2.21 tham chiu cc khi ng

k ngang theo chiu dc ti m tri ph 1 v tham chiu cc khi ng k ngang theo

chiu ngang ti m tri ph 2. Trong SC-FDMA ho OFDMA, gi g c

phn tch hon ton trong min tn sg hi gi dng SC-FDMA phn tch

khc nhau trong c hai min tn v min thi gian.

Hnh 2.19: nh x sng mang con truyn thng v nh x sng mang con lai ghp. [1]


54/74


n tt nghip 42

Hnh 2.20: Bi khi ca h thn a tr nhp phn chia theo tn sm n n

mang (SC-CFDMA). [2]

Hnh 2.21: So snh gia SC-FDMA v SC-CFDM tron iu kin cc sn mang con b

chim n cho cn mt sni sdng. [1]

2.8. Tng kt

FDMA g g (SC-FDMA) l mt k thu hp m s dng

iu ch g g, gh h n s trc giao, v b san bng min tn s.OFDM v SC/FDE l hai k thut x l tn hiu trong min tn s kh ging nhau v

cc thnh phn cu trc nhg h ng li khc nhau, SC/FDE c thm cc b san


55/74


n tt nghip 43

bng knh pha thu. V mt cu trc h thng, SC-FDMA khc vi OFDMA l c

thm khi DFT pha pht v IDFT pha thu. SC-FDMA c hai m hnh nh x

sng mang con l FDMA tp trung (L-FDMA) v FDMA phn tn (D-FDMA) ving h c bi FDMA gh e (IFDMA) im ca SC-FDMA l c t s

cng su nh trn cng sut trung bnh (PAPR) th h i OFDMA g

hh SC-FDMA c la chn l cng ngh hp ng ln

trong h thng 3GPP-LTE.


56/74


n tt nghip 44

Chn 3

CNG SUT NH TRN TRUNG BNH TRONG SC-FDMA

3.1. Gii thiu chung

Cng su h g h (PAPR) h ng ch ng, biu th

hiu sut ca cng sut pht tn hi Tg ng hp, mt b khuh i cng sut

tuy h g i h c s khuh i tuyn tnh ti im bo ha,

ta s c hiu sut cng sut c i khi b khuh i thc hin ti im bo

h PAPR B g gh hg n m li cng su ho ng

trong min tuyn tnh ca b khuh i cng sut. Chng ta c th biu din theo l

thuyt mi quan h gia PAPR [dB] v hiu sut cng su h h

20ax

.10

PAPR

m

(3.1)

Tg hiu sut cng su max l hiu sut cng sut ti B khuch

i cng sut ti l A, max l 50% v ti lp B l 78.5%. Hnh 3.1 cho thy mi quan

h th v n l hin nhin t PAPR cao lm gim hiu qu ch ng cng

sut pht.

Hnh 3.1: Mi quan h v mt l thuyt gia PAPR v hiu qu cng sut pht i vi

cc b khuch i lp A v lp B tng. [1]


57/74


n tt nghip 45

M im ni bt ca SC-FDMA so vi OFDMA l PAPR th h u

g g n c ca n. PAPR th h t thun li trong cc thng tin

ng i hit bu cui i g h Nh c trnh by mc2.4, cc mu trn min thi gian ca cc tn hiu SC-FDMA iu ch l khc

nhau, ph thu nh x sng mang con v chng ta c thg i c

tnh PAPRh h i vi nh x sng mang con khc.

Tg hg , hg i gii thiu v s phn tch gii h im

cng su h i vi mt tn hi g g hg hng. ti mc 3.3, ta m t

i PAPR i vi vic truyn dn e a SC-FDMA v kh c

h PAPR i vi nh x sng mang con khc nhau. Ti mc 3.4, ta phn tch

i PAPR i vi truyn d -ten. c bit, chng ta phn tch s

ng ch g h h (CCDF) a PAPRi vi 2 x 2 truyn m ha

ht to chm ring (TxBF) h thng SC-FDMA c m t trong hg

6. Ti mc 3.5, ta m t m hg h i gim cng su nh.

Chng ti cho thy m ho ng lin kt v cc kha cnh trn min tn s ca

hg h xut.

3.2. Cc c tnh cng sut nh tn hi n n man

Cng su nh ca bt k tn hiu ( )x t g h hg a n

l ln nht 2| ( ) |x t . Tuy nhin,hg h h h ngu nhin lin tc, c th khng

b gii bi 2| ( ) |x t ti M h hg h h h ngu nhin vi cc gi tr ri

rc b chn 2| ( ) |x t ti , h xy ra vi xc sut rt thp. S phn b ca2| ( ) |x t l mt ch s hiu sut h h h hg i n vi xc sut gii hn

b. Vi w h c, gii hn xc su h gh 2 2| ( )|Pr{| ( ) | } ( )x tx t w F w ,

g 2| ( )| ( )x tF w c ch g hbh (CDF) a2

| ( ) |x t , v xc sut giihn b l 2 22| ( )|Pr{| ( ) | } 1 ( ).Pr{| ( ) | }x tx t w F w x t w g c gi l ch g

phn bh (CCDF)

Wih Gfe i c g g (SC) iu ch

tn hiu khng phn bGi i h h gii hh g ng ca

s phn b h hg a chn, h gii thch thg h gii hn trn

khi b sung tch lu ca gii h Cheff g dng cng sut lin tc. chng ta

i he nh ca h m t cng su nh v mt gii h i vi tn hiug g iu ch truyn thng.


58/74


n tt nghip 46

Ta xt m i di g gc ca tn hi iu ch SC truyn thng

( )k kk k

s p t kT a

(3.2)

Tg { }k ks

c truyn dn symbols, s = [, s-1, s0,s1,], p(t) l b lc

dng xung, v T l khong thi gian symbol. Sk thuc biu di iu ch tp hp C ca

h h B, gh , { : 1}k b

s C c b B c phn bu. chng ta gi s

mi { }sks c lp khc nhau.

Chg h gh t bin ng hi Z cho t0[,T) h

Z x(t0, s) = ( )k kk k

s p t kT a

(3.3)

Tg ak=skp(t0-kT).{ak}s khng ph thuc vi nhau ti {sk}s c lp vi

nhau. Tik

s c phn bu trn Cv thg h ()

Pr[ak= cbp(t0 - kT)] = Pr[sk= cb] =1

B(3.4)

Tg B-1.

M h hg m tCCDF h

Pr[|x(t0, s)|2 w] = Pr[|Z|

2 w] = Pr[|Z| ] (3.5)

Vi w 0 v w . Gi s ta bit tp h iu ch tp C l c tht v tp

h i i xng qh im gc. vy th,

Pr[|Z| ] = Pr [ Z ] + Pr[Z -]

= 2Pr[Z ] (3.6)

Bng cch s dng gii hn Chernoff, vy b ng thc sau cha:

Pr[ ] { }v vZZ e E e (3.7)

Tg v l gii php c hg h

E{ZevZ}.E {e

vZ} = 0 (3.8)

Bng vic mrng bi E{ZevZ} v E{evZ}, hg h () thnh

{ }

{ }k

vak

vakk

E a e

E e

(3.9)


59/74


n tt nghip 47

i vi v v gii hg h (), hg c v thay cho . Ti

hg h () hg g g, hg h gi gii php v mt s hc.

Chng c th gii hn trn cc CCDF 20r[|x(t , )| w]P s h hg

trnh (3.5), (3.6), v (3.7).

2

0 .Pr[| ( , ) | ] 2 { }kvav

ub sc

k

x t s w e E e P

(3.10)

h hg h () () x l bng s, chng ta gii hn

i bi mt kin rng -Kmax k Kmax . Tg ng hp ca IFDMA, min l

h hc khi u vo N l l h iKmax, s phn b cng sut tc thi ca tn

hiu IFDMA s c cng gii hn trn l tn hiu SC truyn thng bi u vo symbols

qua li c lp nhau trong khong thi gian ca -Kmax k Kmax.

X iu chBPSK i vi BPSK, chng ta s dng theo tp hp dy:

CBPSK= {-1,1} (3.11)

Cg , he g i g g hg h

2 2 2

sin( / ) cos( / )( ) .

/ 1 4 /

t T t T p t

t T t T

(3.12)

Vi 0 1 l h s un lc.

Khi , hg h () thnh

0 0max

max

( ) ( )0 0

( ) ( )0 0

1 1( ) ( )

2 21 1

2 2

K

k K

vp t kT vp t kT

vp t kT vp t kT

p t kT e p t kT e

e e

(3.13)

S hi nh thg h (), gii h g hg h(3.10) trthnh

( )

.

BPSK

ub SCP max

2 max ( ) ( )0 0

max

1

( )2

K Kvp t kT vp t kT

k K

ve e e

(3.14)

V chng ta c gii hn trn ca CCDF l

( ) 2 ( )

0 .Pr[| ( , ) | ]BPSK BPSK

ub SCx t s w P (3.15)

Hnh 3.2 cho thy( )

.

BPSK

ub SCP vi ,T = 1, v 0 / 2 0.5t T cng vi cc kt qu thcnghim s dng m phng Monte Carlo. chng ta coi h s un lc ca0, 0.2,


60/74


n tt nghip 48

, i vi m phng Monte Carlo, chng to ra 1000 khi BPSK c

iu ch ngu nhin vi mi khi , c to ra ph c.

chng ta c th thy gii h g hg h () gi cso snh vi cc kt qu thc nghi g h gii h h h i vng

cui cng ca phn b trong phn chng ta quan tm nht. Vic quan st th v khc

gh hc t l cng su nh nh c khi h s un lc ca b lc cosin nng

n ti ( = g ng vi b lc di hg ng).

g ng hp ca mt tn hi g g OFDM, hg h

gin biu din CCDF ca PAPRi vi N sng mang con vi t ly mu Nyquist

h

Pr{ } 1 (1 )w NPAPR w e (3.16)

C ng nu ly m q c p dng hoc s ca sng mang con nh,

th biu thc ny khng chnh xc.

Hnh 3.2: CCDF ca cng sut tc thi i vi iu ch BPSK v cc gi tr h s un

lc khc nha; cc ng chm chm l kt qu thc nghim v cc ng lin l gii

hn trn. [2]


61/74


n tt nghip 49

3.3. PAPR cc tn hiu truyn dn n anten

Trong phn ny, chng ta phn tch PAPR ca tn hiu SC-FDMA i vi mi

hg hc nh x sng mang con. i vi {x :m=0,1,...,M-1}m l cc symbol d liu c iu ch S ,

Hnh 3.3: Cng sut tc thi CCDF i vi n n man v cc tn hiu OFDM vi

biu din dliu gc BPSK trn cng thc phn tch: i vi cc tn hi n n

mang, chng ta xt h s un lc ca 0, 0.2, v 0.4; i vi OFDM, cc sng mang con

an dng cc s N l 32, 128, v 512. [2]

{Xk = , ,, M - 1} l cc mu trn min tn s sau khi DFT {xm = , , ,

M - 1}, { X : l= , , , N - 1} l cc mu trn min tn s sau khi nh x sng mang

con, v { nx = , , , N - 1} l cc symbol thi gian sau khi IDFT ca { nX : l= 0,, , N - 1}. Chng ta biu din tn hiu pht thng di phc SC-FDMA ( )x t i vi

khi ca d liu l:

1

0

( ) ( )N

nn

j tcx t e x p t nT

(3.17)

Tg c

g g h hg, () g g g, T l

hg hi gi nx hg g

i g (RC) hi ie g (RRC), g g

g g i g hg hg


62/74


n tt nghip 50

Hnh 3.3 so snhh h gii h CCDF i i i h

hi g g i h CCDF i i OFDM i i hi g

g, hg h h g , , i i OFDM, hg g g g g N , , , hg hg

g g g g Chg h g h i h

BPSK Th hg h h hi g g g h

h h i h h i OFDM

Theo biu thc thi gian v tn s cho 2 dng xung:

1,0 | |

2

1 1 1( ) 1 cos | | , | |

2 2 2 2

10,| |

2

RC

T fT

T TP f f f

T T T

fT

(3.18)

2 2

2

sin .cos

( )4

. 1

RC

t t

T TP t

t t

T T

(3.19)

( ) ( )RC RC

P f P f (3.20)

2 2

2

sin (1 ) 4 .cos (1 )

( )16

. 1

RRC

t t t

T T TP t

t

T T

(3.21)

Chg h gh PAPR h , i vi tn hiu pht x(t):

=

2

0

2

0

max | ( ) |

1| ( ) |

t NT

NT

x t

x t dtNT

(3.22)

Khng c to dng xung, t ly mu symbol s cho cng PAPR v tn hiu

SC-FDMA iu ch trn mt sng mang con. Do , hg iu din

PAPR m khng c to dng xung vi t ly m h

2

12

0,1,..., 1

0

| |R

1| |

ax nN

n

n N

n

xPAP

xN

m

(3.23)


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n tt nghip 51

(a)

(b)

Hnh 3.4: So snh CCDF ca PPR i vi IFDMA, DFDMA, LFDMA, v OFDMA vi

tng s cc sng mang con N = 512, s ca u vo cc symbols M = 128, IFDMA vi h

s tri ph Q = 4, DFDMA c h s tri ph Q = 2, v (h s un lc) = 0.22 : (a)

QPSK; (b) 16- QAM. [1]


64/74


n tt nghip 52

Nh i , i ca mt tn hi g g iu chm khng c phn b Gaussian, khc vi cc tn hiu OFDM v r h phn tchdng phn b chnh xc. Chng ti phn tch s nghin cu cc thuc tnh PAPRi vi cc tn hiu SC-FDMA.

S dng m phng Monte Carlo, chng ta tnh ton CCDF (chc g h

tch l b ) c PAPR, PAPR h i mt s PAPR gi tr

PAPR0 (Pr{PAPR > PAPR0}) Chg h gi h CSDF PAPR i vi

IFDMA, DFDMA, LFDMA, v OFDMA. Thit lp m phng v gi thi h

Chng ta to ra 104 khi d li u ng hi c CCDF ca PAPR. Chng ta xt cc chm symbol QPSK v 16-QAM. Rt ng g g gc p(t) vi cc khong thi gian t -6T n 6T , chng ta

ly mu qu n bng 8 ln, v chng ta s dg g hg n ti l 5MHz.

Chng ta xt cc khc lin t i vi LFDMA. Chng ta khng p dng bt k to dg g g ng hp ca

OFDMA.

Hnh 3.4 bao g im CCDF c PAPR i vi IFDMA, DFDMA,

LFDMA, OFDMA i vi tng s ca cc sng mang con N = 512, s symbols

u vo M = 128, IFDMA vi h s tri ph Q = 4, v DFDMA vi h s tri ph

2Q . Chng ta so snh gi tr PAPR tri vi xc sut th h %3

0( r{PAPR>PAPR =10 })P , hoc PAPR 99,9 % phn v. Chng ta k hiu 99.9 %

PAPR l PAPR99.9%. bng 3.1 tng kt PAPR 99.9% phn v i vi mi nh x

sng mang con.

Bng 3.1: PAPR 99% i vi IFDMA, DFDMA, LFDMA, v OFDMA

iu ch Dng xung IFDMA(db)

DFDMA(db)

LFDMA(db)

OFDMA(db)

QPSK

None

RC

RRC

0

6.2

5.3

7.7

7.7

7.8

7.0

8.0

8.7

11.1

N/A

N/A

16-QAM

None

RC

RRC

3.2

7.8

7.2

8.7

8.7

8.7

8.7

9.0

9.5

11.1

N/A

N/A

RC : to dng xung cosin nng; RRC: to dg g i g c hai; h s un

lc = 0.22.


65/74


n tt nghip 53

Chng ta c th thy tt c ng hp SC-FDMA c PAPR thc s thp

h i OFDMA. Ngoi ra, IFDMA c PAPR thp nh, g h DFDMA

LFDMA c cc mc PAPR ging nhau.3.4. PAPR cc tn hiu truyn dn a anten

Trong ph , hg h h im PAPR ca truyn d -

e i vi h thng SC-FDMA. C th, chng ta kh h c truyn.

dn to chm ring (TxBF) cho 2 an-ten pht. T nhg h h t pht t vic

h h PAPR, hg g n vic phn tch s s dng m phng Monte Carlo

h h c tnh PAPR ca h thng MIMO SC-FDMA

Hnh 3.5 cho thy h hng ca h s un l g PAPR hi dng todg g i g i vi N= 256, M =64, v Q = 4. Chng ta c th thy n nh

hg g h g ng hp c IFDMA Nh gi i h s un lc t 1

ho , PAPR g g vi IFDMA. Khi h s un lc gim t 1 xung 0,

PAPR g t cch g i vi IFDMA iu ny cho thy rng c s cn bng

gia ch ng PAPR vi bc x ngoi di g c x ngoi gii g g

vi h s un l g

Hnh 3.5: so snh gia CCDF ca PPR i vi IFDMA v LFDMA vi tng s cc

sng mang con N = 256, s ca cc h thn u vo M = 64, h s lan truyn Q = 4, v

(h s un lc) ca 0, 0.2, 0.4, 0.6, 0.8, v 1: (a) QPSK; (b) 16-QAM. [1]

Chng ta p dg h ht trn min tn s sau DFT. M ha

c trn min tn s l tch chp v php ly tng trn min thi gi h g hh3.6. V vy, chng ta hy vg thy sg a cng su nh do cc b lc v

ly tng.


66/74


n tt nghip 54

hnh 3.7, th hin CCDF ca PAPR cho 2x2 ly m ht TxBF.

11. 12. 1.

21. 22. 2.

11. 12. 1.

21. 22. 2.

11. 1. 12. 2.

21. 1. 22. 2.

,

.

.

. .

. .

k k k

k k

k k k

k k k

k k k

k k k

k k k k

k k k k

V V S

V SV V S

X V S

V V S

V V S

V S V S

V S V S

Min tn s

Vij = {Vij.0, Vij.1,, V1ij.M-}

S1 = { S1.0, S1.1, , S1.M-1}

Vij = IDFT{Vij},

Si = IDFT{Si}

11 1 12 2

21 1 22 2

. .

. .

V S V S X

V S V S

Min thi gian

Hnh 3.6: Ly m trc trn min tn s l tch chp v php tng trong min thi

gian. Ch skquy vo s sng mang con. [1]

kim chng rng vic lc ca ly m c l nhn t ch y g g

PAPR, chng ta s th hin kt qug ng hp ny khi ch c vic lc bng vic

i t c ch tn hiu an-ten th 2 v, =, i vi ng hp khi ch c vic

ly tng bng vic c thay th tch ch hh h h hng vi thnh phn

u tin l vij. Vi ly m c, chng ta c th thy rng vi g B h -ten

u v 2.6 dB cho an-ten th 2 trong PAPR99.9%.

Hnh 3.7: CCDF ca PAPR cho 2 x 2 ly m trc ng nht TxBF. [1]


67/74


n tt nghip 55

Chng ta c th quan st rng vic lc, gp phn chnh trong ma trn ly mu

c trn nhg c tnh ca PAPR.

Hnh 3.8: nh hng

công suất đỉnh trên trung bình trong sc-fdma

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