OFDM

、、、

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信道 自適應(yīng)技 使用

20世紀(jì)90

PRB

PRBTime-UserOne

WRAN：802.22IMT-Ad:

WHYDO強(qiáng)度 移動通信不得不處理多徑干擾 效應(yīng)：OFDM優(yōu)勢明顯

時(shí) 信 傳統(tǒng)頻分復(fù) 正交頻分復(fù) 信道傳輸函 信道傳輸函

HkOFDMt引入循環(huán)前綴CP（CyclicOFDMCodedmodulated 3210---1....0 001100

產(chǎn)生頻率差異，以提高 的能力x(k, xf(k,h(k,h(k,

yf(k, y(k,MMM1Inputto1

Guardx(k,n)IDFT(Xk n0,1,2,LN

xk,nxk,N nNg,Ng4Xk[X(k,0)X(k,1)LX(k,N4

33

Guardyf(k,n)xfk,nhk,nwk,

yk,nyfk,

Out Yk,m yk,m0,1,2,...,N

Y,H,)X,I,77?(k,m)Y(k, ?(k,

5MHzGuardGuard……s(t)N2dNexpj2fi0.5tiN2T1N1x(tx(t)iexpjTtdw22i

由于子載波的正交特性，可以采用一路子載波信k由于子載波的正交特性，可以采用一路子載波信k行解調(diào)，從而提取出這一路的數(shù)據(jù)。例如對第expexpkTt2dexpj2 dtiTN2i2Tk2??????fss

fFs FFT點(diǎn)數(shù)

TsT'T NcNc=F/Useful Useful

OFDM保護(hù)間隔

保護(hù)間隔OFDM具有天生的 符號周期短。TprefixTTpostfixTITTprefixTTpostfixTs t1Cyclic2CyclicPostfixorCyclicSuffic3CyclicPrefixandCyclicSufficOFDM插入“同步導(dǎo)頻”幫 OFDM對

D D H(k,(m1)Dfl)?(k,m)?P(k,m1)a?P(k,m2)(1

ad/D d

2c 2

1

l/c1

DataDataData ?R(?)G0TR(t) y(t)y*(t0?argmaxt

fn 累加 均比造成系統(tǒng)性能下降

？

Localized

00

fM/ 0 00DistributedBitBit

Bitto BitBit

0 0

Bitto

fM/

Add

BitBitBit

fM/ 0 0fM 00

信道帶寬35XXMX(k,NMsRFMx(k,NYkHXk信道h(t,YYMXY(k,NMy(k,2NDFT-IDFT- xnT

aejn

kk0kaej2kn/Nk0kN

ka'ej2kn/Nk0k

a'

0kNcNckNOFDM(with為7.68MHz，20MHz帶寬時(shí)為30.72MHz）35OneOFDMOnesubDOnesubDDDDDDDDDDDRD2

R1:FirstreferenceR2:Secondreference

D:DDDDDDDDDDDDDDDDDDDDDDDDDDDDDdensityisTBD(50%inthis staggeringbetweenfirstandsecondreferencesymbolsisTBD ,locatedinthefirstOFDMsymbolofthesub-Exact positionofsecondsymbolsis

ControlControld

Add Controlfor Controlfor Control Controlfor Controlfor Controlfor1 multiple multiple multiple DataforUE DataforUE ControlformultipleUEsDataforUEControlformultipleUEsDataforUEControlformultipleUEsDataforUE1resourceDataforUEADataUEDataUEControlDataforUECDataUEControlformultipleandDataforUEControlandDataforUEAControlformultipleUEsC