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