] CHUONG 4 Phan Nhat Minh

8/10/2019 ] CHUONG 4 Phan Nhat Minh

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CHNG 4: M PHNG H THNG MIMO-OFDM S DNG K THUTM HA KHNG GIAN-THI GIAN

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CHNG 4: M PHNG H THNG MIMO-OFDM S DNG K

THUT M HA KHNG GIAN - THI GIAN

4.1 Gii thiu chng cc chng trc chng ta tm hiu v h thng MIMO-OFDM, v k

thut m ha khng gian - thi gian trong h thng MIMO-OFDM. By gi chng

ta s i m phng h thng MIMO-OFDM s dng k thut m ha khng gian -

thi gian bng phn mm Matlab. Thng qua kt qu m phng chng ta c th rt

ra c nhn xt v nh gi v cht lng ca h thng.

4.2 Cc thng s m phng

Da vo s h thng cng nh cc tnh ton thit k mt h thng MIMO-OFDM s dng STBC nh cc chng trc, h thng MIMO-OFDM s dng

m ha khng gian - thi gian s c m phng vi cc thng s nh sau:

Thng s ca h thng thu pht OFDM:

- S anten pht l: TX= 1, 2, 4, 8

- S anten thu l: Rx = 1, 2, 4

- S k t OFDM trong mt khung truyn l : 7

- S k t pilot trong mt khung truyn l : 1

- Phng php iu ch s : 64-QAM

- Kch thc FFT/IFFT : 128

- di CP l: 10

- Cc ng phn ly L=7


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4.3 Lu thut ton

Bt u

Khi to cc thng s ban u

iu ch s

To chui bit

y = S*h + n

Gii m STC

Kh CP v bin i FFT d liu

c lng knh truyn

To knh truyn

Kt thc

i


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4.4 Kt qu m phng

4.4.1

So snh h thng SISO, m hnh MRC v m hnh Alamouti:

4.4.1.1Kt qu

Kt qu di dng s liu :

0 dB 1 dB 2 dB 3dB 4 dB 5 dB 6 dB 7 dB 8 dB

1x1 0.0991 0.0846 0.0691 0.0595 0.0493 0.0421 0.0331 0.0287 0.0237

1x2 0.0379 0.0273 0.0203 0.0147 0.0105 0.0072 0.0052 0.0034 0.0024

2x1 0.0764 0.0598 0.0456 0.0375 0.0273 0.0209 0.0155 0.0109 0.0080

Hnh v :

Hnh 4.1 So snh BER ca h thng SISO, m hnh MRC v m hnh

Alamouti4.4.1.2Nhn xt

- Qua th, ta thy cc gi tr BER u gim dn theo chiu SNR tng v khi

cng sut pht cng ln so vi cng nhiu th tn hiu thu c s tt hn.

0 1 2 3 4 5 6 7 810

-3

10-2

10-1

SNR (dB)

BER

No diversity, Transmitt er diversity and Receiver diversity Comparison

No diversity

Alamouti 2x1

MRC 1x2


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- Ta thy r ng th ca m hnh MRC v m hnh Alamouti u tt hn

so vi m hnh SISO, c ngha l s anten pht hoc anten thu tng th li phn

tp s tng nn s nng cao c cht lng h thng m khng cn phi tng cng

sut pht hay m rng bng thng. Nh vy c th thy tm quan trng ca vic

phn tp trong h thng thng tin nh ni chng 2.

- Vi cng bc phn tp l 2 nhng ta thy ng th ca m hnh MRC tt

hn so vi ng th ca m hnh Alamouti, do phng php phn tp thu s

cho c cht lng h thng tt hn so vi phng php phn tp pht vi cng

bc phn tp. Tuy nhin, trong thc t, vi cc thit b thu thng l nhng thit b

di ng nn vic c nhiu anten s lm cho phc tp ca thit b thu tng ln

cng nh cng knh hn, nh vy s kh khn cho vic di ng ca thit b thu.

- Vi vic s dng k thut m ha khi khng gian thi gian nn m hnh

Alamouti cho cht lng h thng tt hn so vi m hnh SISO khng c khi m

ha. Tuy m hnh MRC khng c khi m ha nhng nh phn tch trn th

phn tp thu tt hn phn tp pht nn m ha STBC khng c nh hng nhiu.

Tc dng ca k thut m ha STBC s c phn tch k mc sau.

4.4.2 H thng MIMO-OFDM s dng STBC vi 2 anten pht:

4.4.2.1

Kt quKt qu di dng s liu:


2x1 0.0764 0.0598 0.0456 0.0375 0.0273 0.0209 0.0155 0.0109 0.0080

2x2 0.0267 0.0176 0.0107 0.0071 0.0042 0.0023 0.0014 0.0008 0.0003

2x4 0.0045 0.0021 0.0009 0.0003 0.0001 4.449

*10-5

7.053

*10-6

1.085

*10-6

0


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Hnh v:

Hnh 4.2 BER ca h thng MIMO-OFDM s dng STBC vi 2 anten pht

4.4.2.2Nhn xt

Trong phn m phng ny, ta m phng m hnh h thng MIMO-OFDM s

dng m ha STBC vi 2 anten pht vi ln lt 1, 2, 4 anten thu. M hnh vi 2anten pht v 2 hoc 4 anten thu c pht trin t m hnh Alamouti 2x1. Gi s

nh ti SNR=5, trong khi vi 1 anten thu th t l bit li ch l xp x 10-2nhng khi

tng anten thu ln 2 th t l gim xung xp x 10-3v khi tng s anten thu ln

n 4 anten th t l bit li xp x 10 -5v n khi SNR l 8dB th t l li bit l 0,

t l bit li ny l tt trong h thng thng tin di ng. Nh vy, ta thy cht lng

h thng tt hn hn khi tng s lng anten thu. V khi li phn tp s tng

ln, ng thi vn gi c tc d liu ln nht nh s dng k thut m haSTBC. Tuy nhin, y ta ch xt n s lng anten pht l 2 nn n t c

phn tp ln nht cng nh tc d liu ln nht v ma trn m ha STBC l trc

giao, nu tng s anten pht ln th nhng iu trn c c p ng hay khng?

0 1 2 3 4 5 6 7 810

-6

10-5

10-4

10-3

10-2

10-1

SNR (dB)

BER

2xM order of STBC-OFDM in block multipath fading

2x1

2x2

2x4


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Vy ta phi xt n trng hp tng s anten pht ln l 4, v 8 kho st tc

dng ca m ha STBC.


4.4.3.1Kt qu

Kt qu di dng s liu:

0 dB 1 dB 2 dB 3dB 4 dB 5 dB 6 dB 7 dB 8 dB4x1 0.0423 0.0324 0.0227 0.0162 0.0128 0.0077 0.0054 0.0032 0.0018

4x2 0.0075 0.0043 0.0021 0.0011 0.0006 0.0002 0.0001 3.771*10-5

1.872*10-5

4x4 0.3030

*10-3

0.1015

*10-3

0.0277

*10-3

0.0011

*10-3

1.085

*10-6

0 0 0 0

Hnh v:


4.4.3.2Nhn xt

Qua th trn ta thy c vi cng s anten pht l 4 th tng s anten thu

ln s lm gim BER xung nh vi trng hp 2 anten pht trong khi phn tp

0 1 2 3 4 5 6 7 810

-6

10-5

10-4

10-3

10-2

10-1

SNR (dB)

BER

4xM order of STBC-OFDM in block mult ipath fading

4x1

4x2

4x4


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v tc d liu l ln nht. Nh trn th ta thy c khi tng s anten thu t 1

ln 2 th BER gim xung rt ng k khi SNR cng tng so vi trng hp 2 anten

pht trn. Nh vy vi vic tng s anten pht ln th khi tng s anten thu, BER

s gim xung nhanh hn so vi trng hp 2 anten pht trn. Vi 4 anten pht

v 4 anten thu th n SNR=5 t l bit li l 0. Tuy nhin quan trng nht y

chnh l tc dng ca m ha STBC. V vi s anten pht l 4 th nu vn s dng

phng php m ha trc giao v gii m nh 2 anten pht th s khng t c

phn tp ln nht v tc d liu ln nht. Do , ta phi s dng phng

php STBC gi trc giao a ma trn m ha v dng trc giao, nh vy vic

gii m cng n gin hn trong khi vn t c phn tp v tc d liu ln

nht. c th hiu r v m ha STBC gi trc giao th ta tip tc m phng h

thng vi 8 anten pht.


4.4.4.1Kt qu

Kt qu di dng s liu:


8x1 0.0244 0.0165 0.0103 0.0071 0.0042 0.0027 0.0016 0.0007 0.0005

8x2 0.0017 0.0007 0.0002 0.0001 3.594*10-5

1.221*10-5

2.848*10-6

1.492*10-6

0

8x4 0.8816

*10-5

0.1221

*10-5

0.0271

*10-5

0 0 0 0 0 0


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Hnh v :


4.4.4.2Nhn xt

Tng t nh cc trng hp trn th khi s anten pht l 8, khi ta tng santen thu ln th cht lng h thng tt hn. Nhng vi trng hp 8 anten pht th

t l bit li gim ng k hn so vi 2 trng hp trn ngay c khi s anten thu vn

l 1, 2 v 4. Ta d dng nhn thy vi 8 anten pht v 4 anten thu th ti SNR=3dB

t l bit li l 0, rt tt trong h thng thng tin di ng. Cng ging nh trng

hp 4 anten pht, trng hp ny cng s dng m ha STBC gi trc giao gim

c phc tp khi gii m v t c phn tp ln nht cng nh tc d

liu l ln nht.

0 1 2 3 4 5 6 7 810

-7

10-6

10-5

10-4

10-3

10-2

10-1

SNR (dB)

BER

8xM order of STBC-OFDM in block multipath fading

8x1

8x2

8x4


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4.4.5 H thng MIMO-OFDM s dng STBC vi M anten pht v 2 anten

thu

4.4.5.1Kt qu

Kt qu di dng s liu: Vi cc s liu BER ca h thng STBC-OFDM

2x2, 4x2, 8x2 c trn, ta c c hnh v di y.

Hnh v :

Hnh 4.5 M phng h thng MIMO-OFDM s dng STBC vi M anten pht

v 2 anten thu

4.4.5.2Nhn xt

Cui cng, ta s i so snh trng hp khi c nh anten thu m ch tng

anten pht ln vi s anten pht ln lt nh 3 trng hp m phng trn l 2, 4 v

8 anten thy r s khc bit khi tng s lng anten pht ln. Da vo th ta

thy ng th ca 8 anten pht tt hn nhiu so vi 4 anten pht v 2 anten

pht. ng th ca 4 anten pht vn tt hn so vi 2 anten pht. iu ny

chng t rng khi tng s anten pht ln th t l bit li s cng nh hn, do cht

lng h thng s tt hn. Tuy trng hp 4 anten pht v 8 anten pht khng tn

ti ma trn m ha STBC trc giao nhng ta c th s dng STBC gi trc giao

0 1 2 3 4 5 6 7 810

-6

10-5

10-4

10-3

10-2

10-1

SNR (dB)

BER

Mx2 of STBC-OFDM in block multipath fading

2x2

4x2

8x2


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a n v dng nh STBC trc giao, nh vy tc d liu cng nh phn tp

ca 2 trng hp ny u t ln nht nh trng hp 2 anten pht.

4.5 Kt lun chng

Qua chng ny, chng ta m phng c h thng MIMO-OFDM s

dng k thut m ha STBC c phn tch cc chng trc. Phn m phng

cho thy cht lng h thng thng tin di ng, cng nh tc dng ca k thut

phn tp v k thut m ha khng gian - thi gian ging nh trong l thuyt

trnh by.

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] CHUONG 4 Phan Nhat Minh