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HC VIN CNG NGHBU CHNH VIN THNG

--------------------------------------------------------------------

Tng Hi

NGHIN CU GII PHP KT HP IU CHTHCH NGHI V CN BNG

NRON CI THIN HIU NNG TRUYN DLIU CHO HTHNG THNG

TIN DI NG BNG RNG

Chuyn ngnh: Kthut in t

M s: 60.52.70

TM TT LUN VN THC S

H NI - 2011

7/25/2019 SNR BER

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Lun vn c hon thnh ti:

HC VIN CNG NGH BU CHNH VIN THNG

Ngi hng dn khoa hc: PGS.TS. Trn Hng Qun

Phn bin 1:

Phn bin 2:

Lun vn s c bo v trc Hi ng chm lun vn thc s ti Hc vin Cng

ngh Bu chnh Vin thng

Vo lc: ....... gi ....... ngy ....... thng ....... .. nm .............

C th tm hiu lun vn ti:

- Th vin ca Hc vin Cng nghBu chnh Vin thng

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MU

Vi s ra i ca cc h thng thng tin di ng tc cao th fading cng tc

ng mnh n cht lng truyn dn ca h thng, cc knh thng biu hin cht

lng hu nh tc thi thay i theo thi gian. Do cc phng thc iu chcnh,

cn bng cin btc ng cc cm li. Mt trong nhng phng php c hiu qu

loi trcc nh hng c hi l iu ch thch nghi cc dng iu ch, m ha theo

cc tham sca h thng da vo thng tin cht lng knh gn nh tc thi do my thu

nhn c v phn hi trli my pht. chnh l phng php iu ch-m ha thch

nghi.

Ngoi ra, knh vn cn tc ng ca can nhiu do fading gy ra, nhng knh by

gil bng rng c tnh phi tuyn biu hin cc khe thng ging su trong bng tn. V

vy gim can nhiu by gi da vo cc b cn bng tuyn tnh thng thng s

khng cn hiu qu, m cn phi c bcn bng gii quyt c tnh phi tuyn ca knh,

phng php n gin, hiu qunht l cn bng mng nron.

Lun vn ny snghin cu iu chthch nghi-cn bng bng nron v kt hpchng trong mt gii php h thng duy nht nhm p ng yu cu thc tin cc h

thng di ng bng rng hin c v sc.

Phng php nghin cu:

- Trc ht nghin cu cc vn iu chthch nghi, cn bng mt cch ring

r. T chra l thuyt c bn ca iu chthch nghi, cn bng mng nron

v tc dng a li cho hthng.- Xy dng mt slut hc cho mt sbcn bng nron nhm chra cc tham

scho bcn bng.

- Da vo kt qum phng c ca cc tc gikhc, lun vn sphn tch,

nhn xt rt ra nhng khuyn nghp dng.

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ngha khoa hc ca ti:

- Xy dng mt sthut ton cho cn bng nron thun, phn hi v xuyn tm

n gin.

- nh gi n nh ca bcn bng

ngha thc tin:

- Khuyn ngh p dng cc phng thc iu ch vo nhng iu kin hon

cnh khc nhau.

Cng cnghin cu:

- Ton xc sut v i stuyn tnh.

- L thuyt truyn tin v mng nron.

Ni dung lun vn:

Chng 1: Tng quan vhthng thng tin thch nghi. Chng ny nhm chra

nt c bn c

a h

th

ng, cc cng trnh nghin c

u v

chng, hi

u nng trong knh.

Chng 2: iu chthch nghi v cn bng. Chng ny gii thiu cc gii php

iu chthch nghi v cn bng nhm lm c scho cc nghin cu mrng chng 3.

Chng 3: Kt hp iu ch thch nghi- cn bng nron. Trong chng ny trn

c sm hnh kt hp, lun vn snghin cu su hn bcn bng v cc thut ton o

to cho cn bng trong hon cnh kt hp.

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Chng 1

TNG QUAN VHTHNG THNG TIN THCH NGHI V HIU NNG

CA HTHNG

1.1

Gii thiu

i su vo nghin cu cc bi ton viu chv cn bng trong cc hthng

thch nghi, trc ht lun vn sgii thiu nhng nt c bn nht vhthng thch nghi,

hiu nng ca hthng trong knh nhiu Gauss, knh fading Rayleigh.

Lun vn cng s im qua mt s cng trnh nghin cu ni bt trn th gii

xung quanh lnh vc ny.

1.2 Nguyn l thch nghi

iu ch thch nghi AQAM l mt gii php thch hp cho thng tin gia trm

gc v my di ng. Thch nghi AQAM l hot ng ca my pht p ng cc iu

kin bin i theo thi gian ca knh. Nhm phn ng mt cch hiu qu cc bin i

cht lng knh, hthng thch nghi thc hin cc bc sau:

c lng cht lng knh

Chn cc tham struyn dn tip theo mt cch thch hp

Bo hiu hoc pht hin cc tham s c sdng

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1.3

Hiu nng ca hthng QAM trong knh nhiu Gauss

Hu ht c lng cht lng knh l tl li bit (BER Bit Error Rate), v n

phn nh cht lng knh khng kn ngun hoc bn cht ssuy gim cht lng.

1.4

Mt scng trnh ni bt nghin cu vcc hthng iu chthch nghi

v cn bng Nron.

Lun vn ny hc vin nhm theo hng nghin cu cc lut hc n gin v kt

hp iu chthch nghi vi cn bng nron. Cng a ra phn tch mt scng trnh

nghin cu trc vcc lnh vc ny.

Kt lun:

Qua cc ni dung trn ta thy c bc tranh tng qut thc hin c cc

hthng iu chthch nghi phi c nhng khu c bn no.

Tip , gii thiu hiu nng ca knh v tuyn m c trng lBER trong knh

nhiu Gauss ng vi cc loi iu chkhc nhau. Lun vn nghin cu BER trong

knh fading Rayleigh ng vi cc dng iu chkhc nhau. Qua gip nh hng

5

2

10-1

5

2

10-2

0 5 10 15 20 25 30 35 40 45 50 55 60

BPSK: L thuyt

BPSK: M phng

QPSK: L thuyt

QPSK: M phng

Hnh 1.1: Biu thBER i vi hthng BPSK, 4QAM, 16QAM, 64QAM trong knh fading phng Rayleigh.

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xc nh phng thc iu chkhi SNR thay i. Cui cng chng 1 im qua mt

s cng trnh tiu biu trong qu trnh nghin cu iu ch thch nghi-cn bng mng

nron qua nh hng bi ton theo nghin cu ca lun vn.

Chng 2

IU CHTHCH NGHI V CN BNG MNG NRON

2.1 iu chthch nghi

2.1.1 Gii thiu

iu chthch nghi l mt gii php rt hiu quthit lp cc hthng truyn

dn trn knh fading bin i theo thi gian. Nguyn l c bn ca n l phi c lng

knh ti my thu v phn hi c lng ny tr li my pht my pht thay i

phng php iu chtng ng vi sthay i cc c tnh ca knh truyn sao cho

duy tr c xc sut li u thu. Cc kthut iu chkhng thch nghi kp cc iu

kin ca fading m cn c dphng tuyn cnh duy tr hiu nng chp nhn

c khi cht lng knh xu. Nh vy cc hthng ny c thit lp p ng c cc

iu kin knh xu nht. Do thch nghi c vi knh fading cho nn n c thlm tng

thng qua trung bnh, gim cng sut pht cn thit, gim xc sut li bt trung bnh.

2.1.2 Tng quan hthng truyn dn thch nghi

My pht Knh My thu

r[i] y[i]x[i]

iu khinn un S i

M ha v iu

chthch nghiR i .C i

[i]

c lngknh

Gii mv gii iu ch

+X

[] n[i][i]

[i]

Tr

if

Knh phn hi

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Hnh 2.1: M hnh hthng truyn dn thch nghi.

2.1.3 iu chthch nghi bng bin i tc

Trong iu chbin i tc th tc sliu

(

)bin i theo li knh

.

Ngi ta thc hin iu ny bng cch cnh tc k hiu iu chRs = 1/Tsv s

dng gii php nhiu s iu chhoc cnhiu chm sao tn hiu iu chhoc c

nh s iu chv thay i tc k hiu.

2.1.4 iu chthch nghi bng bin i cng sut

b li sbin i SNR do fading, ngi ta thng dng phng php iu ch

thch nghi bin i cng sut pht. Mc tiu ca n l duy tr xc sut li bt cnh hoctng ng vi SNR thu khng i. Thch nghi cng sut pht ngha l b o ngc

fading knh sao cho knh sc biu hin nh mt knh AWGN i vi gii php iu

chv gii iu chny.

2.1.5 iu chthch nghi bin i tc v bin i cng sut trong hthng

MQAM.

mc ny, lun vn nghin cu mt dng iu chthch nghi c bit, l iuchbng cch bin i tc v cng sut ca hthng MQAM t cc i vhiu

sut phtrong lc vn p ng mc tiu pbtc thi cho. y lun vn cng chra

rng c mt khe hcng sut khng i gia hiu quphca kthut iu chMQAM

thch nghi ny v dung lng trong fading phng v khe hny c thkhp li mt phn

bng cch thm vo m li trong iu chthch nghi.

2.1.6 Thch nghi cng sut bng bin i ngc knh vi tc cnh

Hin nay, ngi ta cn nghin cu gii php thch nghi cng sut bng bin i

ngc knh duy tr SNR thu cnh. Sau spht tn hiu iu chMQAM tc

cnh duy nht t c mc tiu pb.

2.1.7 Thch nghi tc ri rc

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Khi thit kMQAM thch nghi cu phi xc nh cc bin ca Rj. Trong lc c

th ti u cc bin ny lm cc i hiu quph, vic ny chng ta s tr li bng

cch sdng phngphp cn ti u.

2.1.8 Hiu nng ca hthng iu chthch nghi

Trc khi i vo tnh ton xc sut li trung bnh ca hthng iu chthch nghi,

ta nh ngha xc sut li cho hthng iu chthch nghi tng qut:

= (2.1)

Khi hthng c tc bit thch nghi lin tc theo , k hiu tc l ()th xc sut li bit trung bnh by gil:

= ()()()()()

(2.2)

Trong trng hp hthng iu chchthch nghi vi tc ri rc th:

= ()() ()

(2.3)

Trong :

()l xc sut li bit bin i theo .p() l hm mt phn bxc sut ca .

2.2 Cn bng bng mng Nron

2.2.1 Gii thiu

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Trong mc ny chng ta a ra ci nhn tng quan v cn bng da vo mng

nron. Cn bng knh c thc xem di dng phn loi cc bi ton. Gii php ti

u bi ton ny l bi ton phi tuyn khng kt hp. Vy chng ta stho lun lm th

no cu trc phi tuyn ca mng nron nhn to c thnng cao hiu nng ca mt bcn bng knh so vi cch truyn thng v nghin cu cch thit kmng nron p

ng cn bng knh nh nhng mng o to nhiu lp (Multi-Layer Perceptron - MLP),

mng o to a thc (Polynomial Perceptron-PP) v mng nron xuyn tm (Radial

Basis Function - RBF).Chng ta nghin cu cu trc mng nron RBF chi tit p dng

cho cn bng knh. Hn na, chng ta sm ttng quan mng RBF v i vo cc ng

dng ca n.

2.2.2 M hnh knh

Mt knh bng thng gii hn to ra nhiu giao thoa lin k t (Inter Symbol

Interference ISI) c thc m tbi blc ngang ri rc c hm truyn t:

() = (2.4)

yp fn p ng xung thn ca knh v L+1 l chiu di ca ng ng xungknh (channel impulse respone CIR).

Z-1

Z-1 Z

-1{Ik}

{f0} {f0} {fL-1} {fL}

{}{}

Hnh 2.2: M hnh ri r c thi ian ca knh nhiu xu n k t v nhiu Gauss trn

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2.2.3 Cu trc mng cn bng

Trong phn ny chng ta schra rng cc c tnh ca dy pht c thc biu

thbng trng thi hu hn ca knh v xem xt bi ton cn bng nh l mt bi ton

thuc loi hnh hc.

Hnh 2.3: S cn bng tuyn tnh m t

2.2.4 Cu trc mng Nron

2.2.4.1 Gii thiu.

Mng nron nhn to l mt lp cc m hnh c gilp hthng thn kinh

ca con ngi. Cc m hnh ny bao gm cc yu txl c biu din bng cc

nron, mi nron c mt sdliu u vo v dliu u ra. Ngi ta sdng mt t

hp tuyn tnh tnh ra mt gi trttt cdliu u vo. Gi trny gi l tng trng

sca dliu u vo. Gi trtng trng stri gi trngng ca cc nron to ra

skhi ng ca nron. K hiu kch hot lm tham scho hm kch hot to ra d

liu u ra ca nron. Hm kch hot thng l hm phi tuyn tnh m n cho php mng

z-1

z-1

z-1

z-1

Cn bng quyt nh

vk

vk-1 vk-m+1

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nron gii quyt nhng bi ton phc tp. Hm kch hot c ba dng c bn: Hm mc,

hm phn on tuyn tnh, hm sigmoid.

2.2.4.2 Cu trc mng nron

Cu trc mng nron c xc nh bi vic sp xp cc nron trong mng. Cutrc khc nhau c nghin cu cho cc ng dng khc nhau.

Lp vo Lp ra Lp vo Lp raLpn

Perceptron n l(SLP) Perceptron a lp(MLP)

Hnh 2.5: Mng nron tin

u vo

Hm kch hot

Synaptic trng tm

Hnh 2.4: Mng Nron nhn to (nron thj)

()

w0j

w1j

wij

wIj

x0= 1

x1

xI

xi

vj yj

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Mng nron nhn to tin c cu trc cc lp nh Hnh 2.5, y tt cc ng

kt ni trc tip tu vo ti u ra khng c hi tip. Cc mng dng ny thng hot

ng khng n nh. c trng ca nron trong mi lp mng chc cc tn hiu ra lp

mng trc i vo u vo. C 2 loi cu trc mng perceptron thng sdng l:

- Mng perceptrong n lp (SLP): Mng c 1 lp mng nron

- Mng perceptron a lp(MLP): Mng c nhiu lp mng nron

Mng nron hi tip l dng mng nron nhn to tin nhng c Chng ta cng

xem xt n dng mng nron nhn to tin nhng c t nht mt vng phn hi.

V cng l mng nron nhn to dng li, mng c dng mng mt chiu, 2

chiu hay nhiu chiu dy nron.

Trong cc m hnh mng nron c c tnh c chra bi t tnh cc nt mng,

kiu mng v bi quy tc hun luyn v hc tp ca mng.

2.2.5 Cn bng trn c shun luyn a lp

Lp u vo

Lpn 1

Lpn 2

Lp u ra

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Hnh 2.6: M hnh cn bng hun luyn a lp m-t.

2.2.6 Cn bng trn c sa thc

Cu trc cn bng trn c sa thc (Polynomial Perceptron - PP) c Chen,

Gibson v Cowan nghin cu. Cn bng PP c cu trc n gin v vic tnh ton t

phc tp hn cu trc MLP. Vi cu trc a lp kt hp kthut a thc gn ng trong

gii php ti u cn bng phi tuyn gn ng.

Hnh 2.7: Cn bng trn c sa thc sdng bc m= 2 v a thc bc l=3

Xt mt m hnh a thc cp l = 3 hoc l = 5, cho vic gii thiu hot ng ca

hm sigma v kt qutnh ton ca hm. Xt cn bng trn c sa thc n gin vi

m=2, cp a thc l=3. Khi hm a thc quyt nh c dng:

() =( + + + + +

+

+

+

)

(2.5)

2.2.7 Thut ton to cm K-trung bnh

Lp u vo

Lp u ra

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Thng thng, chc nng ca thut ton K-trung bnh l chia phn vng chnh

thnh cc vector trong on K v sau tm vector trng tm, ci, i = 1,,K, vector l

i din tt nht cho tp vector trong mi khong hay on ring. Trong mng cn bng

da trn RBF thit kcc vector dng cm c cc vector trng thi nhiu ca knh vk, k =,,+quan st cn bng sdng cc kha vector hin ti.Cc bi ton kt hp sdng thut cm K-trung bnh thc hin cm xl c th

khng t ti ti u hay cu trc gn ti u. Thut ton chm bo cn ti u da trn

cn c xc lp trc.

2.2.8. Mng Nron xuyn rm RBF(Radial Basic Function)

2.2.8.1 Gii thiu

Hnh 2.8: Cu trc mng nron xuyn tm (RBF)

Mng RBF gm c 3 lp khc nhau, c chra nh Hnh 2.14. Lp vo c cu

thnh bi p nt ngun. Mt tp M hm kch hot phi tuyn , i = 1, , M, to thnh lpn th2. u ra ca mng c to nn bi lp th3, n bao gm cc nt ra. Cu trc

ny da trn thit kmng nron c bn. Hm kch hot trong lp n to nn hm xuyn

Lp u vo Lpn Lp u ra

=1 =

()

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tm RBF. Hm c c tnh l cc p ng c dng hm tng hoc gim u tnh ttm

im C.

2.2.9 Cn bng RBF trong Modem nhiu mc

Trong phn ny chng ta sm rng thit k cn bng RBF vi mc phc hp

Modem nhiu mc, y thng tin t tp gi trphc M, Ti, i = 1,2,,M. Trng thi

knh mong mun c thp ng vi phn vng trong M lp ln hn 2, theo gi trca

k ttruyn , c xc nh bi biu thc dng:, ={| = }

= ,,,, , =1,2,(2.6)

y rij, j = 1, ,nis, l trng thi knh ra mong mun ca vic truyn k t

= , =1,. R rng hn, snisl strng thi knh rijtrong tp , . Strngthi knh trong tp , l tt ck ttruyn , i = 1,2,M.

Mng RBF

Mng RBF

Mng con thM

Hnh 2.9: Cn bng mng modem trong M mc

Mng con th1

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phc tp tnh ton ca cn bng nhiu mc RBF ph thuc vo bc ca M

trong s iu ch, do vy snt n con RBF l = .Bng 2.3: phc tp tnh ton ca mng cn bng RBF bc m vi mu u

ra iu chM-ary. Tng snt n ca cn bng RBF l .Sphp cng tr

Sphp nhn

Sphp chia

Sm

Shm Max

2 (+1)

1

2.2.10 Cn bng thch nghi RBF

Nh ta bit u ra knh nhiu tdo l yu tcn xc nh ca hm quyt nh kt

hp, c lng trng thi knh c xc nh nh phn cu trc cn bng. Do vy trng

thi knh phi c hc trong qu trnh truyn d liu thc thoc c c trong qu

trnh o to. Cch thc ny c thc xy dng trn 2 phng php:

- Phng php c lng CIR yu cu

- Sdng thut ton cm K-trung bnh

Kt lun

Trong chng ny lun vn tm tt mng nron xuyn tm v m tvn cnbng. Kin trc ca cc mng RBF c trnh by v chng ti nu thit kca phn

tcn bng RBF da trn li gii phn tcn bng Bayes. Qu trnh so snh gia phn

tcn bng MSE v RBF chra rng phn tcn bng RBF c khnng a ra siu tnh

nng khi thm trnh tcn bng tng ng c xt n gia sphc tp ly tha m khi

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tng trnh tphn tcn bng. Phn tcn bng RBF c trnh tnp tin vi m= 9 sci

tin tnh nng 10dB v 20dB thng qua bcn bng MSE i vi knh Guass 2 ng v

3 ng thng v phn tcn bng RBF thhin c tnh BER d, nu knh nu ra rng

tng ng vi cc biu tng truyn pht khc nhau l khng thphn tch trong khongtrng quan st knh.

Tnh nng la chn ca phn tcn bng RBF sdng thut ton to chm tm

vector, thut ton to chm tm v hng v phn tc lng knh LMS sc so

snh. Tp hp ca thut ton to chm phthuc vo slng hsknh c la chn

v ph thuc vo m hnh module ha c sdng v ph thuc vo chiu di

CIR. Tuy nhin, tp hp kthut c lng lnh LMS chphthuc vo chiu di CIR

v do kthut ny ph hp hn vi cc s module ha trnh tcao v chiu di

CIR ln. iu ny c bit ng trong trng hp khi chmodule ha ca trnh to

to khc vi trnh tdliu, v di vi hthng QAM la chn, trong ssdng

chmodule ha mnh hn. K thut c lng knh LMS chc sdng t

c cc tm RBF tng ng v u ra knh mong mun sph hp hn i vi dys

dliu v o to. Sau phn hi quyt nh c a vo phn tcn bng RBF

gim s phc tp tnh ton ca n. Tnh nng ca n c ci thin, v khong cch

Euclidean gia knh nu rng tng ng vi cc biu tng truyn pht khc nhau c

tng ln, khi s DFE c sdng. Cn nhli rng cc tham sca RBF DFE c

la chn sl m = r + 1 v n = L trong m, n, r v L + 1 l trnh ttin, trnh thi

quy, trv chiu di CIR, trong a ra li gii hp l nht i vi phn tcn bng c

nh r. Nh mong mun, suy gim tnh nng do khnng xy ra li ra quyt nh stng

ln, khi BER tng ln, strnn quan trng hn i vi trnh tQAM c thhin. i

vi cc iu kin tt dn, suy gim tnh nng i vi cc s module ha trnh tcao scao hn, do chng sc nguy c hn do khong cch Euclidean gim gia cc trng

knh bn cnh.

Chng ta iu tra tnh cht ca phn tRBF la chn trong cc hon cnh tt

dn bt bin nhm li v biu tng. Chng ta quan st tc dng ca cc im to

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chm trng thi knh khng thphn tch i vi suy gim bt bin biu tng do tc

dng suy gim nhanh qua thi lng nhm li. Kt hp vi knh nghin cu phi tuyn

tnh, hin tng ny gii thch s c mt ca BER d. Do , chng ta cn lu rng

ngay ci vi cc knh suy gim chm.

Chng 3

KT HP

IU CHTHCH NGHI - CN BNG MNG NRON

3.1 Gii thiu

Trc y ngi ta thng nghin cu cc h thng iu ch thch nghi v h

thng sdng cn bng mt cch ring r. Tuy hthng iu chthch nghi gim ng

knh hng ca fading, nhng thc tvn khng thloi bhon ton c nh hng

ny. tip tc gim hn na nh hng ca fading cn li, u thu chng ta tip tc

dng thm mt gii php na l cn bng. y lun vn snghin cu trng hp

cn bng bng mng Nron xuyn tm v iu ch thch nghi do trng hp h thng

pht c s dng BPSK, 4QAM, 16QAM v 64QAM to cho cc b cn bng trong

trng hp: mng a lp, mng a thc v mng xuyn tm. Sau kt hp tnh ton

bng shiu qukhi sdng ng thi iu chthch nghi v cn bng.

3.2 M hnh iu chthch nghi - cn bng mng Nron

Hnh 3.1 biu thm hnh h thng sdng kt hp iu ch thch nghi v cn

bng mng nron xuyn tm. Trong pha pht s dng phng php chuyn mch

iu ch. Vnguyn tc c thc nhiu mch iu chkhc nhau M-QAM.

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Hnh 3.1: M hnh hthng kt hp iu chthch nghi v cn bng mng Nron

Chng 2 chng ta gii thiu tng qut vcn bng nron y, trong m hnhkt hp stnh ton cthhn hm nh xphi tuyn v tham sca n.

3.3 Xy dng lut hc cho gim st cn bng mng nron truyn thng n

gin

3.3.1 Gii thiu

Mng nron loi ny gm c cc phn t thch nghi tuyn tnh v l hthng t

hc thng minh n gin nht.

V cu trc b cn bng ny ch c mt nron tuyn tnh tn hiu vo X = [x1,

x2,xm]T

, mt tn hiu ra Y v cc vector trng sW = [w1,w2,wm]T, hm truyn t

a()c dng tuyn tnh.

x1

x2

xn

w1

w2

wm

f(v)

r=d-y

y

d- +

Chuyn iphng thc

iu chMy pht Knh My thu RBF DFE

c lngmc iu ch

Bng i chiuchuyn ngng

Dliu

Nhiu Cn bngdliu

Xc sutbit li ca

Burst dliuPhng thc

iu chcaBurst dliu

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Hnh 3.2: Cn bng mng nron truyn thng n gin hc c gim st

3.3.2 Xy dng lut hc

tn hiu ra bm c tn hiu tham chiu d ta cn iu chnh gi trvector trng

sw. Sau y lun vn gii thiu mt sphng php hc cho bcn bng ny.

Lut hc Adaline (Adaptor linear)

Lut hc LMS.

3.4 Cn bng knh phc bng mng perceptron hai lp

3.4.1 Cu trc bcn bng mng perceptron hai lp

khc phc iu y lun vn sa ra bcn bng knh phc, cng s

dng thtc o to phn hi ngc cho mng truyn thng hai lp, hai u vo v mt

u ra nh hnh 3.3.

a.S cu trc ca mng 2 lp truyn thng

w22

X1

X2

w11

w12

w21

w31

PE1

PE2

PE3

w32

y3

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b.S tnh ton ca mng 2 lp truyn thng

Hnh 3.3: Bcn bng knh phc mng perceptron 2 lp

3.4.2 Lut hc bcn bng Nron lan truyn ngc hai lp

Lut hc cho mng nron loi ny c Bryson v Ho xut nm 1969.

y lun vn ssdng vo hon cnh cth l bcn bng phc hai u ra mt u

vo, lut hc tng ng vi hnh 3.3.

3.5 Cn bng mng nron Hopfeld

3.5.1 c im

Trong h thng thng tin di ng mi dng kt hp iu ch thch nghi v cnbng ngi ta thng dng cn bng nron Hopfeld. l mt mng nron c mt vi

vng phn hi khnng ca n l thc hin nh xphi tuyn nhm gim can nhiu gia

cc k hiu do fading gy ra v mo phi tuyn c nhiu thut ton v cu trc thc

Nron 2

X1

X2

w22

w11

w12

w21

Nron 1

u1

u2

y2

y1w31

w32

y3 u3Nron 3

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hin cc mng nron ny nh perceptron a lp, mng pht xxuyn tm vic thc hin

phn hi tcc nron ra n lp vo, hoc tcc lp n n lp vo.

Hnh 3.4: M hnh hthng thng tin sdng cn bng Hopfeld

KnhMo phi

tuyn

Cn bng

Nron

Quyt

nh

Bto dy

o to

+

+

Tn hiu vo

-

+

{SM} {xn}

{yn}

{dn}

Tnhiu ra

n= -1

..

..

x1 y1

Xj yj

Xn yn

1= -1

j= -1

j1

jn

j

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Hnh 3.5: S cu trc cn bng dng Hopfield

c im ca n l mi nron thj u nhn tn hiu tbn ngoi xjv nh thin

kjvi j =1,2,n.

Tn hiu ra ca nron thj l yjc a ngc tr li u vo ca nron khc

vi trng swij: i =1, 2,, n v i .3.5.2 Lut hc cho cn bng Nron Hopfield ri rc

Trong phng thc ng b, cc trng s ca mi nron trong mng c cp

nht ng b. Trong phng thc khng ng b th trng s ca mt nron duy nht

c cp nht ti thi im tnh, v chc 1 nron c chn trong n nron c trongmng nn xc sut la chn l 1/n.

3.5.3 Tnh n nh ca bcn bng nron Hopfield

Nng lng trong mng khng tng khi trng thi ca cc nron trong mng thay

i, v vy bcn bng loi ny lun n nh. y l 1 u im ni tri ca bcn bng

ny.

3.6 Lut hc cho cn bng Nron xuyn tm

3.6.1. Cc hm truyn t

-Hm Gauss:

-Hm Multiquadric:

-Hm Multiquadric ngc:

-Hm Cauchy:

3.6.2 Lut hc cho mng nron xuyn tm

Gi c = {cki| k = 1, 2, , k; i = 1, 2, m}

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25/33

= {ki| k = 1, 2, , k; i = 1, 2, m}w = {wki| k = 1, 2, , k; i = 1, 2, m}

Cho N cp dliu vo-ra sdng mng nron xuyn tm hc cc cp dliu cho

trc, tc l cn xc nh mt gi tr k nh nht ca hm c s vi cc gi tr ti u

(c*,*, *) tn ti E(c*,*, *) < , vi E c xc nh:E(c,, w) = [] []

Trong []v []l u ra mong mun v u ra.

S

dng phng php gradient, cc thng s

i

u chnh c

a m

ng c tnh nh

sau:

[] = [ 1]

[] = [ 1]

[

] =

[

1]

Vi i = 1, 2, , m; k = 1, 2, , k; j = 1, 2, , n

h l thi im ly mu.

=

2

[] [] ((), ,)[[] ]

= 2

[] [] ((), ,)[[] ]

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=

[] [] ((),,)

Trong mt scng trnh trc y sdng phng php o to bnh phng

b nht trc giao OLS, y l phng php hiu qunhng kh thc hin. y lun

vn dng phng php Gradient n gin v dthc hin.

3.7 Phn tch kt qum phng kt hp ng thi iu chthch nghi v cn

bng nron RBF thch nghi

Mc ny lun vn s tm tt li kt qum phng h thng di ng siu ch

thch nghi MQAM kt hp cn bng thch nghi RBF ca tc gi.Sau lun vn sphn

tch v rt ra kt lun so snh vi nhng trng hp sdng ring riu ch v cn

bng.

3.7.1 Mt sgithit m phng

- My thu thc hin c lng trng thi knh hoc c lng tstn hiu can

nhiu sng mang. Cc trng thi knh squyt nh cc trung tm ca mng RBF.

- Tstn hiu trn can nhiu trong khong thi gian ca cm pht l khng thayi theo thi gian nhng sc bin i cm ny sang cm khc, iu ny tng ng coi

knh l bin i thun theo thi gian. Li u ra ca knh khi c can nhiu v p ng

ca bcn bng.

- My thu bit c phng thc iu chc sdng tng cm pht thu

c.

- Xc sut c lng li thi gian ngn Pbit l bit trc truyn tt ccc

phng thc iu chtrong hthng.

3.7.2 M hnh m phng

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- My pht pht cc k hiu gingu nhin vi nhng cm c di cnh cho

tt c cc phng thc iu ch qua knh bng rng khng bin i trong tng

cm.

- My thu thu mi cm sliu c cc phng thc iu chkhc nhau v cn bng

tng cm mt cch c lp.

- Xc sut li bit (hoc BER) tnh c cho mi phng thc iu ch:

= ()

Hnh 3.6: M hnh m phng iu chthch nghi kt hp cn bng RBF

Knh c

nh

Burst

BPSK

4QAM

16QAM

64QAM

RBF DFE

Btnh

ton BER

ngn hn

Bchn khung

vi chiu

chcao nht vi

BER ngn

hn

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3.7.3 Cc tham sm phng

Bng 3.1: Cc tham sm phng

Sk hiu trng mt cm, LD 144Sk hiu o to cho mt cm, LT 27

Tn spht 1,9GHz

Tc pht 2,6MBd

Tc my di ng 30 mph

Tn sDoppler chun 3,3 x 10-5

Cc trng sca knh 0,707 + 0,707z-1

Bc ca bcn bng thng 2

Bc ca bcn bng phn hi 1

Thi gian trquyt nh, 1

- M hnh knh truyn dn: Knh Fading Rayleigh hai tia.

3.7.4 Kt qum phng v nhn xt

BPSK BER

4 QAM BER

16 QAM BER

AQAM RBF DFE-BER:

Ch n TX

AQAM RBF DFE-BPS:

Ch n TX

10

10-1

10-2

10-3

10-4

10-5

-6

0 5 10 15 20 25 30 35 40 SNR(dB)

6

5

4

3

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a.

Mc tiu BER 10-2(BER trung bnh vi tc truyn)

b.Mc tiu BER 10-4(BER trung bnh vi dliu truyn)

Trng hp h thng dng truyn s liu c BER mc tiu = 10-4chra trn

Hnh 3.7(b).

BPSK BER

4 QAM BER

16 QAM BER

AQAM RBF DFE-BER:

Chn TX

AQAM RBF DFE-BPS:

Chn TX

10

10-1

10-2

10-3

10-4

10-5

10-6

0 5 10 15 20 25 30 35 40 SNR(dB)

6

5

4

3

2

Hnh 3.7: Kt qum phng hthng kt hp sdng cc phng thc iu chBPSK, 4-

QAM, 16-QAM, 64-QAM

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Trong trng hp ny xu th bin i c gi trBER, BPS tng t trn ch c

khong bin i SNR l c khc nhau. Tuy vy lu rng, vi khong SNR t8dB n

20dB th BER ca gii php thch nghi khng gin on pht s tt hn so vi BPSK.

Hin tng ny cng c nhn thy trong iu ch thch nghi bng hp v iu chthch nghi kt hp cn bng Nron. iu c gii thch nh sau:

BER trung bnh ca hthng l tstng cc bit li trn tng scc bit c pht

i . BER trung bnh ca hthng sgim khi gim sbit li v khi tng tng sbit pht

i trong cm sliu. Vi sk hiu pht cnh, khi sdng tng sbit pht trong cm

sliu pht l khng i, trong khi vi iu chQAM thch nghi, th tng sbit pht

trong cm sliu tng khi sdng AQAM bc cao. Nh vy trong trng hp ny BER

tng.

So snh kt qum phng trong hnh 3.7(a) v 3.7(a) nhn thy:

Vi truyn sliu, xc sut chn pht tng i cao nhm t BER mc tiu thp.

Khi SNR tng khong trn 16dB v 20dB vi BER = 10-2v BER = 10-7th xc sut chn

pht gn ti 0.

Tm li, phng php truyn kt hp iu chthch nghi v cn bng Nron c uvit hn khi so snh cc phng thc iu ch cnh ring r. Tuy vy phng php

iu chthch nghi khng chn pht th c tht c hiu nng mc tiu BER = 10-2

v BER = 10-4nu SNR ca knh cao hn 9dB v 18dB tng ng.

Mc tiu BER trung bnh khi truyn thoi BER = 10-2v truyn sliu BER = 10-

4t c i vi tt ccc SNR ca knh khi sdng trong chn pht.

3.8 So snh hiu nng BER trong trng hp cn bng thng thng v cnbng nron- iu chthch nghi kt hp

BER ca cn bng Nron v iu chthch nghi BPSK v 4-QAM tt hn so vi

cn bng thng thng ring rnu SNR tng.

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Tri li, hiu nng ca phng thc kt hp thp hn so vi hiu nng ca cn

bng thng thng trong trng hp 16 v 64-QAM. Tuy vy c thtng c hiu nng

bng cch tng cthi gian trquyt nh v bc ca bnron hng thun m.

Hnh 3.8: M phng hiu nng trng hp DFE thng thng v trng hp

kt hp RBF DFE

Da vo hnh 3.8 ta so snh hiu nng ca phng php iu ch thch nghi kt

hp cn bng nron:

- Vi BER mc tiu 10-2, th gii php kt hp cho hiu nng BER tt hn so

vi gii php khc.

DFE thng thng:

Tc truyn:

Hiu nng BER trung bnh

Hiu nng BPS trung bnh

Dliu truyn:

RBF DFE:

Tc truyn:

Hiu nng BER trung bnh

Hiu nng BPS trung bnh

Dliu truyn:

100

10-1

10-2

10-3

10-4

10-5

0 5 10 15 20 25 30 35 40

SNR(dB)

6

5

4

3

2

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- Vi mc tiu BER = 10-4, hiu nng BER ca phng php dng cn bng

nron kt hp iu chthch nghi so vi cn khc hon ton tng tnu

SNR nm trong khong 5dB n 12dB, nhng BPS th tt hn. Trong

khong SNR ny ch yu dng iu ch bc thp. V phng php cnbng nron kt hp iu chthch nghi cho hiu nng BER tt hn so vi

phng php ring ri vi cc phng php iu chbc thp.

Kt lun:

Sau khi nghin cu cc gii php iu chthch nghi, cc mng nron c bn,

lun vn nghin cu gii php kt hp iu chthch nghi v cn bng mng nron.

Trc ht, lun vn k tc m hnh tng qut c tnh cht nguyn l v h

thng kt hp c cc cng trnh trc y gii thiu. Lun vn i su nghin cu v

gii thiu mt sthut ton o to ho bcn bng dng:

- Mng nron truyn thng n gin.

- Cn bng knh phc bng mng perceptron hai lp.

- Cn bng bng mng Hopfield.

- Cn bng bng nron xuyn tm.

Cc thut ton ny tng i n gin. Phn cui cng ca chng gii thiu

mt skt qum phng ca cc tc gi trc c v lun vn phn tch, bnh

lun rt ra nhng hon cnh ng dng cthkhi p dng phng thc iu chthch

nghi kt hp cn bng nron.

KT LUN V HNG NGHIN CU TIP THEO

Lun vn nghin cu gii php kt hp iu chthch nghi v cn bng nron

ci thin hiu nng truyn dliu cho hthng thng tin di ng bng rng l mt trong

nhng khnghin cu v ang thu ht nhiu nh nghin cu.

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Sau khi gii thiu mt s l lun c bn vhiu nng ca h thng thng tin di

ng, iu ch thch nghi v mng nron thch hp vi h thng di ng bng rng v

theo phng n kt hp vi iu chthch nghi.

- Lun vn xy dng lut hc cho bcn bng bng mng nron truyn thng

n gin c gim st.

- Sdng cn bng phc bng mng perceptron hai lp v lut hc cho n.

- Xy dng lut hc cho cn bng mng nron Hopfield v nh gi n nh

cho n.

- ng dng mng nron xuyn tm cn bng knh v lut hc.

Cui cng lun vn gii thiu kt qu m phng h thng kt hp iu chthch nghi v cn bng nron xuyn tm. Trn c s lun vn phn tch, nhn xt

v rt ra cc hon cnh ng dng khi knh c sbin ng vSNR.

Hng nghin cu tip theo:

1. Nghin cu ng dng hiu qu mng nron trong cn bng knh truyn cc

cm tn hiu tc cao.

2. Cn bng nron c lut hc quyt nh