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A. Ni dung
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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.
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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
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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
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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
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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
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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
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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
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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
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II. c tnh knh v tuyn di ng
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II. c tnh knh v tuyn di ngBng 2.2 Cc c tnh knh trong ba min: khng gian, tn s v thi gian
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II. c tnh knh v tuyn di ng
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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
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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
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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:
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III. Nguyn l hot ng ca OFDM
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III. Nguyn l hot ng ca OFDM
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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
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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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III. Nguyn l hot ng ca OFDM
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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
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III. Nguyn l hot ng ca OFDM
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
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III. Nguyn l hot ng ca OFDM
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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)
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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
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III. Nguyn l hot ng ca OFDMHnh 3.16 Hiu qu ca khong bo v loi b ISI
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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
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III. Nguyn l hot ng ca OFDM
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III. Nguyn l hot ng ca OFDM
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III. Nguyn l hot ng ca OFDM
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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
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III. Nguyn l hot ng ca OFDM
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III. Nguyn l hot ng ca OFDM
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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
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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
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IV. iu ch OFDM 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
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IV. iu ch OFDM 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
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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
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IV. iu ch OFDM thch ng
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IV. iu ch OFDM thch ng
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IV. iu ch OFDM thch ng
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IV. iu ch OFDM thch ng
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IV. iu ch OFDM 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
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IV. iu ch OFDM thch ng
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IV. iu ch OFDM thch ng
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
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IV. iu ch OFDM thch 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
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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
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V. Chng trnh m phng
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V. Chng trnh m phng
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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
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V. Chng trnh m phng
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V. Chng trnh m phng
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V. Chng trnh m phng
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V. Chng trnh m phng
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Kt qu m phng khng dng c ch thch ng
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Kt qu m phng khng dng c ch thch ng
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Kt qu m phng khng dng c ch thch ng
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Kt qu m phng dng c ch thch ng mc iu ch
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Kt qu m phng dng c ch thch ng mc iu ch
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Kt qu m phng dng c ch thch ng mc iu ch
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Kt qu m phng dng c ch thch ng chn lc sng mang
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Kt qu m phng dng c ch thch ng chn lc sng mang
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Kt qu m phng dng c ch thch ng chn lc sng mang
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Kt qu m phng kt hp c ch thch ng chn lc sng mang v mc iu ch
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Kt qu m phng kt hp c ch thch ng chn lc sng mang v mc iu ch
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Kt qu m phng kt hp c ch thch ng chn lc sng mang v mc iu ch
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Kt qu m phng kt hp c ch thch ng chn lc sng mang v mc iu ch
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VI. nh gi hiu nng h thng OFDM thch ng
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VI. nh gi hiu nng h thng OFDM thch ng
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VI. nh gi hiu nng h thng OFDM thch ng
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VI. nh gi hiu nng h thng OFDM thch ng