M khi khng thi gian trc giao v iu ch li

Nguyn Th Hng

Trng i hc Cng ngh

Chuyn ngnh: K thut in t; M s: 60 52 70

Cn b hng dn khoa hc: PGS.TS. Trnh Anh V

Nm bo v: 2012

Abstract. Tng quan v h iu hnh Android. Nghin cu cc giao thc s dng: giao thc

TCP/IP; bn tin nhn ngn SMS. Tng quan v mng thng tin di ng (Vinaphone): cu trc,

cc thnh phn chc nng h thng GSM; cu trc, cc thnh phn chc nng h thng

GPRS/EDGE. cu trc, cc thnh phn chc nng h thng 3G. M hnh gii php v thit k

phn mm trn Android. a ra kt qu v hng pht trin tip theo.

Keywords: K thut in t; Phn mm; Android; in thoi di ng; Mng thng tin di ng

Content.

CHNG 1 : KNH FADING V K THUT PHN TP

1.1 Li trong knh Gauss v knh fading

Trong thng tin v tuyn bn cnh nhiu do tp m Gaus cn c can nhiu do fading lm trm

trng thm vic h hng bit thng tin trn ng truyn. Sau y ta nhc li nhng nt c trng c

bn ca 2 loi can nhiu ny.

1.1.1 Knh Gauss (AWGN)

Nhiu trng Gauss do tc ng ca chuyn ng nhit ln chuyn ng ca cc phn t ti in

trong cc thit b in t. y l mt qu trnh ngu nhin, mi mu l mt bin ngu nhin trung bnh

zezo G v ton b mt ph nng lng l phng trn ton b phm vi tn s f vi mc

N0/2.

Hnh 1.1. V d knh AWGN

Hnh 1.1. M t nhiu Gauss trng cng tnh

1.1.2 Knh Fading

1.1.2.1. Khi nim Fading

Fading l hin tng tn hiu ti im thu thay i ngu nhin theo thi gian v cng , pha

hoc tn s do tc ng ca mi trng truyn dn. in hnh l cc yu t : S thng ging ca tng

in ly i vi h thng sng ngn

S hp th gy bi cc phn t kh, hi ncS khc x gy bi s khng ng u ca mt

khng kh , S phn x sng t b mt tri t, t cc bt ng nht trong kh quyn, S phn x, tn

x v nhiu x t cc chng ngi trn ng truyn lan sng in t

1.1.2.2 Fading Rayleigh

Hm mt phn b Rayleigh c cho bi cng thc

Trong l gi tr hiu dng ca in th tn hiu nhn c trc b tch ng bao, 2 l cng

sut trung bnh theo thi gian

Minh ha hm mt phn b xc sut Rayleing

1.1.2.3. Fading Rice

Hm mt ph cng sut ca phn b Rician cho bi cng thc

2 222

02 20

0 0

r D

s s

r rDe I r

p r

r

Phn b Rician thng c m t bi thng s K c nh ngha nh l t s gia cng sut tn

hiu xc nh v cng sut cc thnh phn a ng

1.1.3. Li trong knh Gauss v knh fading

y ta so snh li ch theo k thut thu ng b

2 2/2

20

( )

0 0

rr e rp r

r

2

22

DK

Li trong knh Gauss

Xc sut li trung bnh i vi iu ch BPSK l

Li trong knh fading

Tnh trung bnh hm Q theo phn b ca h

theo cng thc Taylor

Nh vy,trong AWGN xc sut pht hin li suy gim vi hm m ca SNR, trong khi trong cc

knh fading n suy gim t l nghch vi SNR .

Hnh 1.5: So snh xc sut li qua fading Rayleigh v knh AWGN

1.2. K thut phn tp

1.2.1 Phn tp thi gian

0

20 1 2S Rbe

Ep Q Q N

N

2 1 R2 R 1

2 1 Re

SNp E Q h SN

SN

1

4S Rep

N

Phn tp thi gian thc hin bng cch pht i cc bn tin ging nhau trong cc khe thi gian

khc nhau, nhm phn tn bit thng tin trn nhng khong thi gian ln hn thi gian kt hp ca

knh

m bo cc k hiu m ha c pht qua fading c lp hay gn c lp th yu cu phi

ghp xen cc t m

1.2.2. Phn tp khng gian

L k thut c s dng ph bin trong thng tin v tuyn sng ngn. Trong phn tp khng gian

s dng nhiu anten hoc anten mng sp xp c khong cch i vi vic pht v nhn , yu cu v

sp xp l khc nhau i vi cao ca anten, mi trng lan truyn v tn s

1.2.3. Phn tp khng-thi gian

M khng gian-thi gian c phn ra lm 2 loi : M khi khng gian-thi gian STBC v m li

khng gian-thi gian STTC

CHNG 2 : M KHI KHNG THI GIAN TRC GIAo .

2.1 M Alamouti

M Alamouti to ra mt mu cho h thng 2x2 nhm t c li phn tp y vi thut ton

gii m ML n gin

S khi m ha Alamouti

Hnh 2.1 : Khi m ha Alamouti

u tin iu ch m bit thng tin vi m=log2M. Sau b m ha s ly 1 khi gm c 2 bit thng tin

k hiu x1, x2 trong mi ln m ha cho ra anten pht theo ma trn :

Ct u tin i din chu k pht u tin, ct th 2 i din cho chu k pht tip theo

Trong chu k u tin anten 1 pht x1, anten 2 pht x2 .

Trong chu k th 2 anten 1 pht x2* , anten 2 pht x1

* l lin hp phc ca x1

2.1.1. Trng hp s dng 2 anten pht v 1 anten thu

*1 2

*2 1

x

x

xX

x

Nu ta gi s c 1 antenna ti my thu th cc tn hiu nhn c c nh ngha nh sau :

Bng 2.1. Bng m ha v chui k hiu pht cho s phn tp pht 2 anten, 1 anten thu

Anten 1 Anten 2

Thi im t x1 x2

Thi im t +T -x2*

x1*

Bng 2.2. nh ngha cc knh gia 2 anten pht v anten thu

Anten thu

Anten pht 1 h1

Anten pht 2 h2

Bn 2.3. K hiu cc tn hiu thu ti anten thu

Anten thu

Thi im t r1

Thi im t +T r2

Mu phn tp pht 2 antenna ca Alamouti

Hnh 2.2. Mu phn tp pht 2 antenna ca Alamouti

2.1.2. Xt trng hp s dng 2 anten pht v 2 anten thu.

Ta c s phn tp

Hinh 2.3. S dng 2 anten pht v 2 anten thu.

2.1.3. Kt hp t s ti a MRC

Hnh 2.4. Kt hp t s ti a 1 Tx v 2Rx

M Alomuti khng cn s hi tip t my thu v my pht, khng lm tri rng bng thng, b gii

m n gin , khi ng dng th khng cn thit k li ton b h thng. Chng hot ng hiu qu

tng ng vi MRC nu tng cng sut pht x c gp i so vi h thng dng MRC. Nu cng

sut pht c gi khng i, mu ny s lm gim 3dB cng sut pht do cng sut pht c chia

nh cho 2 anten pht.

2.2 M khi khng thi gian trc giao

2.2.1. M khi khng thi gian STBC

M khng thi gian c nh ngha bi ma trn truyn dn X kch c nT x p, trong nT l s anten

pht, p la s chu k pht m khi trn anten pht , gi s s lng k hiu li vo ca STBC trong 1

ln m ha l k

Cu trc b m ha khng thi gian

Hnh 2.5. Cu trc b m ha khng thi gian

Hiu sut ph ca m STBC l

/ /b s

s

r r mR kmbits s Hz

B r p

Vi br v sr l tc bit v tc k hiu, B l di thng

Cc thnh phn ca ma trn X c chn sao cho chng l s kt hp tuyn tnh ca k symbol x1

.....xk v lin hp phc x1*xk

*.

22 2

1 2. ......H

nTkx x xX X c I

Vi c l hng s, MT l s antenna pht, XH l ma trn kim tra ca S v IMT

l ma trn n v

MTxMT. iu n to ra s phn tp MT mc. Cc ma trn truyn m ny c chn sao cho cc hng

v ct ca ma trn l trc giao nhau

2.2.2. M khi khng thi gian trc giao OSTBC

Vic xy dng m STBC phi da vo m trc giao. Ma trn truyn dn XnT c hng l trc

giao vi nhau. Tc l trong mi khi, tnh hiu pht t 2 anten phi l trc giao vi nhau. C ngha l

trong mi khi cc chui tn hiu t 2 anten pht bt k l trc giao nhau. V d chng ta gi s tn

hiu pht t anten th i l

,,0 ,1, ......,i i pi ix x x x Vi i=1,2,..., nT. Khi

*, ,1

. 0 , , 1,2,...,.p

i t j t Tt

i jx x x i j i j nx

Trong xi , xj k hiu tch v hng ca 2 chui xi, xj.

Tnh trc giao c th t c phn tp pht y vi mt s anten pht cho trc. N gip cho

vic thu tch cc tn hiu c n gin hn v do vy gii m ML n gin ch da trn x l tuyn

tnh tnh cc tn hiu thu

2.2.3. STBC cho cc tng quan tn hiu thc

Ta s phn tch qu trnh to ra cc ma trn thc

Xt cc ma trn vung tc l tng ng ng vi s lng anten pht MT = 2,4,8. Cc m ny l cc

m ton tc do ma trn l ma trn vung v phn tp pht y MT mc. Khi ma trn truyn:

Vi MT = 2 anten pht. Ta c th thy rng ma trn ny tha m iu kin trc giao theo phng trnh

3 4

4 3

1 2

2 1

1 2

2 14

3 4

4 3

x x x

x x xX

x x x

x x x

x

x

x

x

Vi MT = 4

2.2.4. STBC cho cc tng quan tn hiu phc

Cc ma trn trc giao phc c nh ngha l cc ma trn MTxp vi cc thnh phn phc s1, s2...sk

v lin hp phc ca chng tha m phng trnh trn. Cc ma trn tao ra s phn tp MT y vi

tc m k/p. Ma trn

*

2

*

1

12

2

xG

x

x

x

Ta phn tch cc ma trn truyn phc c kch thc MT =3, MT =4 vi tc m 1/2

1

1 22

2

xX

x

x

x

* * * *

3 4 1 2 3 4

* * * *

4 3 2 1 4 3

* * * *

1 2 3 4 1 2

1 2

3 2 1

3 4

x x x x x x x

G x x x x x x x

x x x x x x x

x

x

x

* * * *

3 4 1 2 3 4

* * * *

4 3 2 1 4 3

* * * *

1 2 3 4 1 2

* * * *

2 1 4 3 2 1

1 2

2 14

3 4

4 3

x x x x x x x

x x x x x x xG

x x x x x x x

x x x x x x x

x

x

x

x

2.2.5. Gii m STBC

Qu trnh gii m ny cng tng t nh trong qu trnh i vi mu Alamouti.

Khi cn tin hnh gii m STBC th cn phi tch c cc k hiu pht ni thu da vo tnh trc

giao ca cc tn hiu pht.

2.3 Xc sut li cp ca m khng thi gian

Gi s chiu di khung d liu pht i l L k t vi mi anten. Khi ta c t m khng thi gian

MTxL

1 2 1

1 1 1 2 2... ....T T TM M M

Le e e e e e e trong khi thc t tn hiu c pht i l

1 2 1 1

1 1 1 2 2... ... ...T T TM M M

L Lx x x x x x x x

iu ny xut hin nu tng cc k t, anten v chu k thi gian

Do li trong iu kin bit (hi,j) l

2, 0,

, 1,..., , 1,..., exp , / 42

i j T R s

d s eP s e h i M j M Q d s e E N

Khi li s l

,1 0

, 1,..., , 1,..., exp4

RMj j s

i j T R

j

A EP s e h i M j M

N

CHNG 3 : M LI KHNG THI GIAN

3.1. iu ch m li TCM

2 /2t

x

Q x e dt

Thng thng m ha tch bit vi iu ch ti b pht, v cng vy i vi gii m v gii

iu ch b thu. Vic sa li cung cp thm bit d ti b m ha lm chm tc thng tin trn

knh c rng bng c nh. Hiu sut ph c trao i vi hiu sut cng sut. c hiu sut

cao v ph v cng sut c th gp b m ha v iu ch vo mt khi chc nng thc hin cng mt

lc.

Hnh 3.1: Cu trc b iu ch li TCM

Hnh 3.2. Khng gian tn hiu 4-PSK v 8-PSK-TCM

3.1.1. Phn chia khng gian tn hiu

Da vo s khng gian tn hiu Ungerboeck xy dng k thut phn chia tp hp tn hiu

tng khong cch Euclide, trong khng gian M tn hiu ln lt chia thnh cc cp gim dn :

M/2,M/4, .... M/2m

, khong cch Euclide cc tiu ca cc tp tn hiu tng dn

dmin1

< dmin2

Hnh 3.3.Phn chia chm sao 8-PSK thnh 3 tp con

3.1.2. li m ha

li m ha ca h thng iu ch m li TCM c tnh theo cng thc :

2 2

min

2

min2

min

e e

free

D Pe

e

E

d d EG G G

E Ed

d

Trong e

freed l khong cch t do, min

ed l khong cch Euclide cc tiu, E

l nng lng tn

hiu iu ch TCM, GD l li v khong cch t do, GP l li v nng lng tn hiu iu ch.

Hnh 3.5. Gin khng gian tn hiu

Gin li trng thi ca 8PSK-TCM

Hnh 3.5. Gin li trng thi ca 8PSK-TCM

li m c tnh nh sau

li m tim cn tng theo s trng thi ca m chp. Gi tr t ti 6dB yu cu m vi s trng

thi rt ln

3.2. Gii m TCM

Gii m TCM c xy dng da theo thut Viterbi v li c s ca b m ha

Xt 1 chui tn hiu vo x= (x0, x1, ..., xm) hnh thnh mt tn hiu pht trn knh truyn c nhiu

AWGN v bng thng hn ch W th ti u thu tn hiu nhn c k hiu y(t) c cng thc sau :

y(t) = s1(t) + n(t)

Trong S1(t) l tn hiu pht, c cng thc 1

0

M

i k

k

S t x S t kT

n(t) l nhiu trng c mt ph cng sut l N0/2, nhim v b gii iu ch l da vo bin thu

y(t) khi phc li chui d liu x gn ging nht vi chui d liu pht da theo gi tr cc tiu

khong cc tn hiu ca php snh nh cng thc sau

21

0

min ;M

t k

k

y t x Y t kT x s t kT

0

min

0

min

0

(8 ) 2 sin / 8

(4 ) 2

2 sin / 8 2.586

2.5861.293 1.1

2

free

d PSK E

d PSK E

d E E

ED dB

E

trong y(t) l tn hiu thu sau b khi phc, xi l tn hiu pht

CHNG 4

M PHNG M KHI KHNG THI GIAN TRC GIAO V IU CH LI

4.1 Kch bn m phng

Thc hin kt ni gia m khi khng thi giao trc giao v iu ch li truyn thng tin trn h

a anten vo v ra, c th trong trng hp c 2 anten pht v 1 anten thu

M khi khng thi gian trc giao OSTBC l mt k thut s dng trong truyn thng khng dy

MIMO. Chng s dng phn tp khng gian thi gian v gii m nh b kt hp t l ti a ML. Tuy

nhin chng khng c li m. B kt hp OSTBC ti b thu cung cp thng tin ca k t pht, m

c th dng cho vic gii m hoc gii iu ch

M TCM l s tch hp m v iu ch cung cp li m ln.

OSTBC cung cp li phn tp, cn TCM cung cp li m. 2 thng s ny ch c hoc TCM

hoc OSTBC do ta kt hp TCM vi OSTBC tn dng c c 2 tham s.

Xy dng s khi kt ni gia m khi khng thi giao trc giao v iu ch li

Thng tin d liu t ngun d liu ra s c m ha bi b m ha li TCM, sau chng c

ghp xen v a vo khi m khi khng thi gian. Ti cc khe thi gian khc nhau, cc symbol u

ra c iu ch v pht tng ng trn cc anen pht khc nhau. Ti b thu, gii m khng thi gian

v tch xen nh thut ton Viterbi. Cui cng a vo gii m TCM c tn hiu u ra tng ng.

S thit k m phng qu trnh kt hp m TCM v OSTBC

Khi pht tn hiu ngu nhin : Khi to tn hiu ngu nhin Bernoulli to ra

ngun d liu khong 100 bit ngu nhin.

Khi iu ch li TCM : Thc hin iu ch nhng bn tin t khi pht tn hiu ngu nhin

Bernoulli trn chm sao PSK cho n khi c gi tr trung bnh. Trong qu trnh m phng s dng s

li 8-PSK vi 8 trng thi. Cu trc li s dng 2 ma trn u vo [2 3], [1 2 0; 4 1 2]. Khi ny

c 1 u ra khung d

liu di 50 tc l 2 bit u vo s to ra 1 k t

Khi gii m TCM M-PSK dng thut ton Viterbi. Cc tham s t l 30, so snh vi chiu

di hn ch ca TCM, l chiu di m bo khi thc hin th mt mt hu nh l khng c

u tin ta xt TCM trn knh Rayleigh Fading phng

Knh cn bng : khc phc nh hng ca knh fading ti b thu v u ra ca knh ii vo b

gii m M-PSK TCM gii m.

OSTBC 2x1 trn knh fading phng : Khi gii m OSTBC cho thng tin k t t b gii m

TCM bng cch dng m Almouti vi 2 anten pht. Tn hiu u ra ca khi ny l ma trn 50x2

Khi kt hp OSTBC ly tn hiu t anten thu vi thng tin trng thi knh ti u ra c

lng ca k t pht, sau a ti b gii m M-PSK TCM

Knh AWGN ti b thu

4.2 Kt qu m phng

10 12 14 16 18 20 22 2410

-4

10-3

10-2

10-1

100

SNR (dB)

FE

R

Concatenated OSTBC with TCM

TCM + OSTBC

TCM

OSTBC

4.3 nh gi so snh

Khi s dng iu ch TCM t l li ln hn so vi vic s dng, khi kt hp 2 m ny vi

nhau c c li v phn tp nn ng cong gim t l bit

KT LUN

Trong lun vn ny, cp n m khi khng thi gian trc giao v iu ch li. c bit

l qu trnh kt hp 2 m t c li phn tp cao.

Trong qu trnh nghin cu nu c tnh cp thit ca k thut phn tp gim fading v

tng tc truyn. Khi s nng cao c tin cy ca knh truyn v tuyn

References.

Ting vit

[1]. Nguyn Vit Knh, Trnh Anh V (2007), Thng tin s, Nh xut bn Gio dc.

[2]. Mai Hng Anh, Phn tp pht s dng m khi khng thi gian cu trc trc giao, Tp ch bu

chnh vin thng

[3]. Phan Hng Phng, Lm Chi Thng, K thut phn tp anten trong ci thin h thng dung

lng MIMO, Tp ch bu chnh vin thng

Ting Anh

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Jounal on Selected Areas in Communications, vol,16,no,8, Oct,1998

[2]. V.Tarokh,H.Jafarkhami, and A.R.Calderbank, Space-time block codes from orthogonal design,

IEEE Transactions on information theory, vol.45, no.5. Jul.1999

[3]. Yi Gong and K .B.Letaief, Concatiented space-time block coding with trellis coded modulation

in fading channels, IEEE Transactions on wireless communicationx, vol.1, no.4, Oct 2002