M NG TRUYN (LINE CODING)GII THIU CC LOI M NG TRUYN

GII THIUTn hiu PCM l chui cc bit 1 v 0. Vic truyn tn hiu ny (t mt b ghp knh n b ghp knh cp cao hn, n gi my viba, hoc n gi my ca thit b quang) cho d c ly ngn nhng cng c th nhn chng b sai nu truyn khng ng dng line coding. Chuyn t mt dng m ny sang dng m khc trong thit b truyn PCM code converter.

GII THIU (tt)

Vic chn m ng truyn phi lu n:Thnh phn dc. Tn hiu nh thi ng b my pht v my thu. Bng thng. Gim st c cht lng.

GII THIU (tt)Yeu cau oi vi ma ng truyen (line code):Khong co thanh phan mot chieu (dc). Nng lng tn s thp phi nh. C nhiu cnh xung: khi phc xung clock b thu. Tn hiu m ho phi c kh nng gii m duy nht thnh tn hiu gc. Dai tan hep tiet kiem dai thong ng truyen. Bien oi co quy luat sao cho may thu kiem soat c loi bit.

CC LOI M NG TRUYNC hai loi m ng truyn chnh:Unipolar. Bipolar.

Xung m ng truyn c phn lm hai loi:Non Return to Zero (NRZ) Return to Zero (RZ)

CC LOI M NG TRUYN (tt)1 1 0 1 0 0 1 1 0 1 0 0 0 0 1 1 0 0 0 0 1 1 1 0 0 0 0 1 RZ NRZ AMI

HDB-3

CMI

CC LOI M NG TRUYN (tt) NRZ (100 % unipolar)Trn quan im mch: m NRZ l dng thng dng nht ca tn hiu s (ON-OFF). M NRZ c s dng trong thit b ghp knh, viba s, truyn dn quang. Tn hiu c m ha thnh 2 mc : +Bit 1 c m ha bi mc in p dng. +Bit 0 c m ha bi mc 0.

CC LOI M NG TRUYN (tt) NRZ (100 % unipolar) (tt)CLOCK T 1 V V/2 0 AMPLITUDE DC NRZ SPECTRUM 0 1 0 NRZ SIGNAL f=1/T

t

0

f/2

f

3f/2

2f

5f/2

3f

FREQUENCY

CC LOI M NG TRUYN (tt) NRZ (100 % unipolar) (tt)Ph c thnh phn DC. Gi tr trung bnh ca DC ph thuc vo t s s bit 1/0 ca chui tn hiu (t 0 volt V volt). V d: chui 10101010 c thnh phn DC l V/2. Thnh phn tn s c bn: f/2. Ch c hi bc l. Khng c bin tn hiu tn s clock (f) nn kh tch xung clock u thu. Nu c nhiu tc ng ln th khng th tch c.

CC LOI M NG TRUYN (tt) NRZ (100 % unipolar) (tt)M NRZ khng ph hp cho ng truyn cp ng. M NRZ c s dng cho h thng tc cao nh SONET/SDH (155Mbit/z hoc cao hn) nhng phi c ngu nhin ho (Scrambled)

M NRZ lng ccM ha vi hai mc in p + v Bit 1 tng ng mc in p + Bit 0 tng ng mc in p Mi xung c rng 1 chu k bit

CC LOI M NG TRUYN (tt) RZ (50 % unipolar)Ging nh m NRZ nhng rng xung gim cn mt na.

M RZ n ccM ha vi hai mc in p +, 0 Bit 1: na chu k u mc +, na chu k sau mc 0. Bit 0: mc 0. Mi xung c rng na chu k

M RZ lng ccM ha vi ba mc in p +, 0 ,Bit 1: na chu k u mc +, na chu k sau mc 0. Bit 0: na chu k bit u mc -, na chu k sau 0. Mi xung c rng na chu k

CC LOI M NG TRUYN (tt) RZ (50 % unipolar) (tt)CLOCK T 1 V DC AMPLITUDE DC RZ SPECTRUM 0 1 0 1 1 0 RZ SIGNAL

t

0

f

2f

3f

4f

5f

6f

FREQUENCY

CC LOI M NG TRUYN (tt) RZ (50 % unipolar) (tt)Cng tn ti thnh phn DC. Tn s c bn by gi trng vi tn s xung clock ca tn hiu c th tch xung clock u thu khi khng tn ti chui bit 0 ko di. Khng th pht hin li khi c nhiu. s dng c gii hn. Nhng m RZ bipolar c s dng rng ri.

CC LOI M NG TRUYN (tt) Alternative Mark Inversion AMI (bipolar code) Ma hai cc oi dau lan lt o rong xung bang na chu ky bit Khong cha thanh phan mot chieu Quy tac chuyen oi:Bit 1 trong ma goc chuyen thanh cac xung +V va V. rng xung: 50%. Bit 0 trong ma goc chuyn thnh 0 volt.

Cha giam c so bit 0 lien tiep Ch dung trong he thong 1,544Mbit/s (G.703)

CC LOI M NG TRUYN (tt) AMI (bipolar code) (tt)CLOCK T +V 1 0 1 0 1 1 0 AMI CODED SIGNAL

t

-V

AMPLITUDE

AMI SPECTRUM

0

f/2

f

3f/2

2f

5f/2

3f

FREQUENCY

MA NG TRUYEN TRONG PDHHDB-3 (High density binary) Ma hai cc co mat o xung dong cao o rong xung bang na chu ky bit Quy tac chuyen oi:+ Bit 1 trong ma goc chuyen thanh bit ngc dau vi bit trc o + Day 3 bit 0 tr xuong lien tiep trong ma goc van gi nguyen + Day 4 bit 0 tr len lien tiep th chia thanh tng nhom 4 bit 0 va chuyen thanh 4 bit A00V hoac 000V (A la bit trai dau vi bit trc o, V la bit cung dau vi bit trc o) theo quy nh sau: o 000V neu bit ng trc day 4 bit 0 trai dau vi bit V ng trc gan nhat o A00V neu bit ng trc day 4 bit 0 cung dau vi bit V ng trc gan nhat

MA NG TRUYEN TRONG PDH Ch ton tai cac day co 3 bit 0 lien tiep tr xuong Khong cha thanh phan mot chieu Ma HDB-3 co so bit 0 lien tiep t nhat so vi cac ma khac (mat o xung dong cao) Dung trong he thong 2Mbit/s va 34Mbit/s

CC LOI M NG TRUYN (tt) Coded Mark Inversion CMI (biphase)

Cc bit 1 lun phin o trng thi dng v m. Cc bit 0 trng thi m na chu k u v i trng thi na chu k cn li. M CMI c s dng trong cc h thng 139,264Mbit/s (G.703) v SDH 155,52Mbit/s giao tip in (STM-1e)

CC LOI M NG TRUYN (tt) CMI (biphase) (tt)CLOCK

1NRZ +0.5V CMI 0 -0.5V

0

1

1

0

0

1

0

0

0

1

0