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A. Ni dung

B. C s l lunNhu cu s dng h thng thng tin di ng ngy cng gia tng, tc l nhu cu chim dng ti nguyn v tuyn gia tng. Hay ni cch khc tn ti mu thun ln gia nhu cu chim dng ti nguyn v ti nguyn vn c ca thng tin v tuyn.c im ca truyn dn v tuyn l ti nguyn hn ch, cht lng ph thuc nhiu vo mi trng: a hnh, thi tit dn n lm hn ch trin khai p ng nhu cu cho x hi ca cc nh cng nghip v dch v vin thng.

C. C s thc tinSong cc h thng s dng cng ngh OFDM hin nay nh: DAB, DVB, HDTV, HiperLANu khng s dng c ch thch ng, do cha ti u hiu nng cng nh cha i ph hiu qu i vi nhng nh hng bt li ca knh truyn v tuyn di ng.

Trn c s nh vy n chn ch nghin cu gii php iu ch thch ng tn hiu s trong h thng truyn dn s nhm t hiu sut s dng bng tn cao. T xy dng chng trnh m phng, c th l: M phng truyn dn OFDM thch ng trong thng tin v tuyn

I. Gii thiuHn ch ca cc k thut hin hnh

Cc k thut tri ph c kh nng chng li pha inh v nhiu, song tn ti nhng yu cu khng th thc hin c chng hn: Nu ngi dng cn c tc 20 Mb/s giao din v tuyn v h s tri ph l 128 (gi tr in hnh hin nay), dn n phi x l tc 2,56 Gb/s theo thi gian thc, v th cn c rng bng tn ln khng thc t.Cc k thut n sng mang i ph km hiu qu i vi pha inh v truyn lan a ng, c bit trong trng hp tc bit cao

I. Gii thiuYu cu

Truyn thng a phng tin khng nhng yu cu bng thng rng m cn QoS cao Lm th no truyn d liu tc cao qua giao din v tuyn m vn m bo QoS. Tuy c cc bin php nh cn bng thch ng song gp tr ngi v thi gian thc tc cao vi Mb/s vi chi ph thp

Gii php

Cn tm k thut iu ch c kh nng dung ha cc yu cu i ngc nhau theo cch tt nht c th

I. Gii thiuGhp knh phn chia theo tn s trc giao OFDM

OFDM l gii php phn tp tn s.OFDM t hiu sut s dng bng tn caoOFDM cho php gim nh hng ca tr a ng v v knh pha inh la chn tn sDo tri rng pha inh ln nhiu k hiu, nn lm ngu nhin ha li cmTnh kh thi ca OFDM cao do ng dng trit cng ngh x l tn hiu s v cng ngh vi mch VLSI

I. Gii thiuOFDM nhy cm vi dch Doppler cng nh lch tn gia cc b dao ng ni pht v thu

Vn ng b thi gian. Ti my thu kh quyt nh thi im bt u FFT

Gi tr PAPR cao

II. c tnh knh v tuyn di ngSuy hao (attenuation): Cng trng yu i theo khong cch, gi tr suy hao in hnh trong khong 50 150 dB ty vo khong cch. Suy hao gy pha inh phm vi rngChe chn (shadowing): Chng ngi vt gia my pht v my thuTp m (Noise): tp m nhit (cng c th tp m khc) xut hin trong tn hiu v lm gim cht lng vic tch tn hiuPha inh a ng v phn tn thi gian: Phn x v nhiu x lm mo tn hiu thu bng cch tri rng n theo thi gian. Ph thuc vo bng tn h thng, lm thay i cng tn hiu, c th gy ISI

II. c tnh knh v tuyn di ng

Nhiu (Interference): Cc my pht khc dng cng tn s hoc dng cc tn s ln cn vi n c th gy giao thoa vi cc k hiu mong mun.c tnh knh chn lc tn s: Mt tn s c tng cng trong khi cc tn s khc b suy haoCc knh v tuyn l cc knh mang tnh ngu nhin: n c th thay i t cc ng truyn thng n cc ng b che chn nghim trng i vi cc gi tr khc nhau

II. c tnh knh v tuyn di ngBng 2.2 Cc c tnh knh trong ba min: khng gian, tn s v thi gian

III. Nguyn l hot ng ca OFDMNguyn l

Phn chia ton b bng thng cn truyn vo nhiu sng mang con v truyn ng thi trn cc sng mang ny.

Lung s tc cao c chia thnh nhiu lung tc thp hn. V th c th gim nh hng ca tr a ng v chuyn i knh pha inh chn lc tn s thnh knh pha inh phng

III. Nguyn l hot ng ca OFDMTnh trc giao

OFDM truyn dn song song ng thi nhiu bng con chng ln nhau trn cng mt rng bng tn cp pht ca h thngLm th no tch cc bng con t bng tng chng ln hay ni cch khc chng khng giao thoa trong min tn s v min thi gianVn mu cht ca truyn dn OFDM l nh tnh trc giao ca cc sng mang con

III. Nguyn l hot ng ca OFDMNu k hiu cc sng mang con c dng trong h thng OFDM l si(t) v sj(t). m bo tnh trc giao cho OFDM, cc hm sin ca cc sng mang con phi tha mn:

III. Nguyn l hot ng ca OFDM

III. Nguyn l hot ng ca OFDMTn hiu OFDM pht phc bng tn gc c xc nh nh sau:T l di k hiu OFDMTFFT l thi gian FFT, phn hiu dng ca k hiu OFDMTG l thi gian bo v, thi gian ca tin t chu trnhTwin l thi gian m ca tin t v hu t to dng phf = 1/TFFT l phn cch tn s gia hai sng mangN l di FFT, s im FFTk l ch s v k hiu c truyn

III. Nguyn l hot ng ca OFDMTn hiu u ra ca b iu ch RF c xc nh nh sau:Trong fc l tn s sng mang RF


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Chuyn i Ni tip thnh Song song

IFFT

Khuch i cng sut v gii iu ch sng mang cao tn

iu ch sng mang con

Chn khong bo v

Chn t ng b khung

iu ch sng mang cao tn v khuch i cng sut

Loi b khong bo v

Tch khung

FFT

Gii iu ch sng mang con

Chuyn i Song song thnh Ni tip

...

...

D liu pht ni tip

D liu thu ni tip

Pha sng mang

Bin sng mang

I

Q

I

Q

I

Q

I

Q

I

Q

Sa li tn s

Tn hiu trong min thi gian

LO

Pha sng mang

Bin sng mang

My pht

My thu

Hnh 3.4 M hnh h thng truyn dn OFDM

ng b nh thi

Anten


iu ch sng mang con(D liu -> IQ vector)

IFFT

P/S

Zeros

Khong bo v

Tn s

Thi gian

Symbol start

Tn hiu OFDM phc bng tn c s u ra

Hnh 3.6. Tng IFFT + chn khong bo v, to tn hiu OFDM

D liu u vo

End

I

Q

III. Nguyn l hot ng ca OFDMHnh 3.27 Ph tn hiu OFDM 52 sng mang khng dng b lc (a) v dng b lc vi ca s Kaiser vi (b), [sim_ofdm_spectrum.m]Hnh 3.26 Ph ca tn hiu OFDM 52 sng mang (a) v 1536 sng mang con (b), khng dng b lc, [sim_ofdm_spectrum.m](a)(b)(a)(b)

III. Nguyn l hot ng ca OFDMCc nhn t nh hng ca knh pha inh ln hiu nng h thng truyn dn OFDM v cc gii php khc phc

Nguyn nhn: Do tnh chn lc, tnh ph thuc thi gian v tnh bt n nh ca knh pha inh gy ra giao thoa gia cc k hiu (ISI) truyn qua nHu qu: My thu quyt nh k hiu sai, kh khn trong vic khi phc nh thiGii php: Chn khong thi gian bo v

III. Nguyn l hot ng ca OFDMHnh 3.16 Hiu qu ca khong bo v loi b ISI

III. Nguyn l hot ng ca OFDMNguyn nhn: Do tnh chn lc tn s ca knh pha inh (ch yu l hin tng dch Doppler)

Hu qu: My thu khng phn bit c ranh gii gia cc k hiu truyn trn cc sng mang con (quyt nh sai k hiu mt tnh trc giao)

Gii php: Chn khong thi gian bo v mt cch tun hon, dng b cn bng PSAM

III. Nguyn l hot ng ca OFDMl mt phng php m cc im IQ cnh nhau trong chm sao s ch khc nhau mt bit. M ho Gray cho php ti u t s li bit v gim xc sut li nhiu bit xut hin trong mt k hiu n. Thng tin hnh m ho Gray khi iu ch M-QAM hay M-PSK

IV. iu ch OFDM thch ngKnh v tuyn thay i ngu nhin theo thi gian, gii hn hiu nng v thng lng truyn dnThch ng ng tham s iu ch ng vi cc tham s tc thi ca knhKnh tt cc gi tr ny s thay i cc tham s iu ch sao cho thu c thng lng h thng lnKnh xu cc gi tr s iu khin cc tham s iu ch sao cho gim thng lng h thng m bo QoSH thng khng dng iu ch thch ng, s dng cc tham s iu ch c nh m bo QoS ti trng thi ti nht ca knh v h thng s c thng lng nh nhau ti mi thi im

IV. iu ch OFDM thch ng

iu ch thch ng trong h thng TDAM

iu ch thch ng trong h thng CDAM

iu ch thch ng trong h thng OFDM

iu ch thch ng trong h thng MC-CDMA

CDMA thch ng

OFDM thch ng

MC-CDMA thch ng

La chn thch ng cc s a truy nhp

Hnh 5.1 S phn cp cc k thut iu ch thch ng


Knh

Hnh 5.2 Lu thut ton iu ch thch ng

Xc nh

Tham s iu ch = f (knh)

Thut ton iu ch thch ng


B iu ch

Hnh 5.3 Kin trc ca cc h thng iu ch thch ng

Thut ton iu ch thch ng

D liu

Thng tin v knh

B gii iu ch

D liu

Thng tin v knh hi tip

Tn hiu thng tin v cc tham s thit lp

My pht

My thu

IV. iu ch OFDM thch ngXy dng gii thut iu ch thch ng cho h thng truyn dn OFDM

Ti u hiu nng h thng truyn tin (thng lng, BER)Thch ng cc thng s iu ch theo cht lng knh hin thi

Da theo thng s iu ch c chn thch ng


Nitip - Song song

IFFT+Khong bo v+ song song - ni tip

Knh truyn

ni tip - song song +Loi b khong bo v+FFT

Song song - Ni tip

Tnh BER

...

...

D liu pht

D liuthu

Hnh 5.5 M hnh thut ton thch ng theo c ch chn lc sng mang cho h thng truyn dn OFDM

BER ngng

iu khin chn

iu khin gii chn

Quyt nh chn

1

2

N-1

N

N

N-1

2

1


text

text

BER ngngk = 1

k++

Bt u

Q(k) = 0

Q(k) = 1

Hnh 5.6 Lu thut ton ca khi quyt nh

ng

Sai

k = s sng mang

Kt thc

ng

Sai

BER

tb

ng

BER (k) >

BER

tb

ng


text

Bt u

n = s lng k hiu phtk = 1, u = 1, v = 0data_out = 0data_in = tn hiu pht

v = phn d (u/s sng mang)

v = 0

Q(v) = 0

v = s sng mang

data_out(u) = data_in(k)k++u++

data_out (u) = 0u ++

k = n

Kt thc

ng

sai

ng

sai

ng

sai

Hnh 5.7 Lu thut ton m t hot ng ca khi iu khin chn

V. Chng trnh m phng

c File nh

Chuyn d liu sang dng nh phn (tng khi 8 bit)

M ho M-QAM

Tx

KnhV tuyn

Rx

Gii m M-QAM

Chuyn d liu sang dng cc khi thp phn

Ghi File nh

To tp m Gauss

So snh d liu pht v d liu thu

Tnh li

Khi quyt nh

BER ngng

Chn sng mang

Gii chn sng mang

Khi iu khin chn, gii chn

Hnh 6.1 M hnh m phng h thng truyn dn OFDM thch ng

Khi tnh BER

V. Chng trnh m phng

V. Chng trnh m phng

1

0.32

0.28

0.13

Thi gian tr

0

5

8

17

Hnh 6.6 p ng xung kim ca knh

V. Chng trnh m phng

Kt qu m phng khng dng c ch thch ng

Kt qu m phng dng c ch thch ng mc iu ch

Kt qu m phng dng c ch thch ng chn lc sng mang

Kt qu m phng kt hp c ch thch ng chn lc sng mang v mc iu ch

VI. nh gi hiu nng h thng OFDM thch ng

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