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Tho Lun Mn Hc

K thut chuyn mch v tng i s

Ch :Tm hiu bo hiu knh kt hp-h thng

bo hiu R2Sv : Triu vn Mnh

Bi Vn ti

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1.1 KHI QUT

H thng bo hiu R2 l h thng bo hiu knh ring, c thit k phc v cho chc nng trao i thng tin gia cc tng i trongmng vin thng. H thng bo hiu ny c s dng cho c mng

quc gia v mng quc t.H thng bo hiu R2 cng thch hp cho cc phng thc t ng

v bn t ng. ng thi n c th p dng cho cc ng trung ktng t (Analog) hay trung k s (Digital).H thng bo hiu R2 c

phn thnh hai loi:Bo hiu ng dy.Bo hiu thanh ghi.

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1.2 phng thc truyn tn hiu ca bo hiu R2

H thng bo hiu R2 c thc hin theo giao thc btbuc. iu ny th hin ch tn hiu hng i c gi i

lin tc cho ti khi nhn c tn hiu hng v t tng iu kia. Vic bo hiu c thc hin gia b truyn m CS(Code Sender) v b nhn m CR (Code Receiver). Trong btruyn m CS, ngoi cc thit b truyn truyn tn hiu, bo

hiu cn c cc thit b nhn nhn tn hiu iu khin.Tng t nh vy, b nhn m CR cng c cc thit b nhn vthit b truyn tn hiu.Qu trnh truyn bt buc trong bo hiu R2 c thc hin

nh sau:

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s R SR

cs cR

a

c

b

f

e

d

g

Hnh 1.1 . Bo hiu bt buc

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a. Tn hiu c truyn lin tc di dng m a tn t b CSn b CR.

b. B CR sau khi nhn c tn hiu th nht ny s ra lnh chothit b truyn ca n gi v mt tn hiu iu khin theo hng

ngc li.c. Tn hiu iu khin di dng m a tn c truyn t b CR

v b CS.

d. B CS khi nhn c tn hiu iu khin s ngng truyn tnhiu th nht v bit rng CR nhn c tn hiu ny.

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e. B CR nhn thy b CS ngng truyn tn hiu th nht, nra lnh cho thit b truyn ca n ngng truyn tn hiu iu

khin v bit rng CS nhn c tn hiu ny.

f. B CS nhn thy tn hiu iu khin ngng truyn. Nchun b truyn tn hiu th hai.

g. B CS tip tc truyn tn hiu th hai v qu trnh trn li

c lp li.

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Bo hiu ng dy

Cc tn hiu ng dy hng i*Tn hiu chim

L tn hiu c gi i khi bt u cuc gi nhm thit lp litrng thi mch vo t trng thi ri sang trng thi b chim.* Tn hiu xo thun

L tn hiu c gi i kt thc cuc gi, nhm gii phngtng i b gi v cc khi chuyn mch ang tham gia phc

v cho cuc gi.

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Cc tn hiu ng dy hng v

* Tn hiu cng nhn chim

Sau khi nhn c tn hiu chim tng i b gi s pht tn hiucng nhn chim cho tng i gi xc nhn vic mch vo

chuyn t trng thi ri sang trng thi b chim.* Tn hiu tr li

Tn hiu ny c truyn t tng i b gi v tng i gi khithu bao b gi nhc t hp nhm phc v cho vic tnh cc

ca tng i gi.

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* Tn hiu xo ngcL tn hiu gi n tng i gi khi thu bao b gi t

my. Trong ch bn t ng, tn hiu ny thc hin chc nnggim st.

* Tn hiu gii phng hon tonTi tng i b gi sau khi nhn c tn hiu xo thun

s gi v tng i gi tn hiu gii phng hon ton xc nh sn sng phc v cc khi chuyn mch v tng i b gi

hon ton t do, sn sng phc v cho cuc gi khc.

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* Tn hiu kho mch

Tn hiu ny c gi trn cc mch ri ti tngi gi gy nn trng thi bn nhm bo v vic

chim mch tip theo.

Cc phin bn bo hiu ng dyTrong bo hiu ng dy c hai phin bn

(Version), mt phin bn dng cho bo hiu ng dytng t (Analog) v mt phin bn dng cho bo hiu

ng dy s (Digital).

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Phin bn bo hiu ng dy tng t:Nguyn tc truyn ca phin bn ny l c m hiu khi ri v

khng c m hiu khi bn.

Trong bo hiu ng dy kiu tng t, i vi mi hngtruyn dn cn phi c mt knh bo hiu s dng tn s ngoibng thoi l 3825Hz. Trng thi ng dy c phn nh qua

bng sau y:

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Cc iu kin thc hin bo hiu ng dy:Tn s bo hiu danh nh l 3825Hz.

Sai s so vi tn s trn khng vt qu 4Hz.Thi gian chuyn trng thi c m hiu sang khng c mhiu l 40 10 (ms).

Thi gian nh nht nhn bit c m hiu hng i v mtm hiu hng v l 250 50 (ms).

Phin bn bo hiu ng dy s:Trong h thng truyn dn s PCM 30/32 ngi ta s dng mtknh thoi (TS16) t chc hai knh bo hiu cc khung 1

15. S sp xp cc knh bo hiu trong khe thi gian TS16 ca hthng PCM 30 nh sau:

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Trong :

0000: ng chnh a khung.e : Bit cnh bo mt ng chnh a khung.

e = 0: Khng c cnh bo.

e = 1: C cnh bo.x : Bit d tr cha s dng.Thng thng ngi ta khng s dng ht 4 bit a, b, c, dcho bohiu m ch s dng hai bit a v b cn bit c v ds dng cho mc

ch khc.Hng i gm bit afv bit bf.Hng v gm bit ab v bit bb.

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Trong :-af::cho bit trng thihot ng ca cc thit b chuyn mchu gi ra vtrng thi ca ng dy thu bao gi.

-bf.: cho bit cs c trn hng t tng i gi ti tng i bgi.-ab: cho bit trng thi ca thu bao b gi.-bb: cho bit thit b chuyn mch tng i b gi ri hay bn.

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Bo hiu thanh ghi

Bo hiu thanh ghi trong h thng bo hiu R2 c s dng nc ta l kiu bo hiu b khng ch, ngha l bo hiu m victruyn thng tin gia cc tng i c thc hin ln lt theo

s hi p.

Trong bo hiu R2 ngi ta s dng m a tn l cc t hp haitrong su tn s truyn bo hiu thanh ghi gia cc tng i.Cc m a tn ny s c thu v pht bi cc thit b m a

tn.Th t cc t hp m theo hai hng c quy nh theo bng

sau y:

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B hi h i C hi h i hi h h h i h hi

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Bo hiu hng i: Cc tn hiu hng i c chia thnh hai nhm: tn hiunhm I v tn hiu nhm 2.

a) Bo hiu hng i nhm I:

Cc tn hiu nhm I ch yu mang thng tin v a ch ca thu bao b gi.

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b) Bo hiu hng i nhm II:

Cc tn hiu nhm II l tn hiu ch th v c tnh cuc gi v thubao ch gi.

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Bo hiu hng vBo hiu hng v c chia lm hai nhm: bo hiu hng v

nhm A v bo hiu hng v nhm B.a) Bo hiu hng v nhm A:

Cc tn hiu nhm A c s dng tr li xc nhn cho cc tnhiu hng i nhm I (trong mt s trng hp c dng

tr li cho cc tn hiu hng i nhm II) v thc hin chc nngchuyn a cc thng tin bo hiu.

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b) B hi h h B

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b) Bo hiu hng v nhm B:Cc tn hiu hng v nhm B cng dng tr li xc nhn cho mt hngi nhm II trong th tc bo hiu bt buc. ng thi cc tn hiu ny thchin chc nng chuyn a cc thng tin v trng thi thit b chuyn mch

hay trng thi ng dy thu bao b gi

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Cc phng php truyn tn hiu bo hiu thanh ghi

- Trong qu trnh kt ni cuc gi t tng i ch gi n tngi b gi c th c mt s tng i khc tham gia kt ni. V

bo hiu thanh ghi c ba phng php truyn nh sau:- Truyn bo hiu kiu tng chng (Link By Link).

- Truyn bo hiu kiu xuyn sut (End To End).

- Truyn bo hiu kiu hn hp (Mixed).

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1 Phng php truyn bo hiu kiu tng chngPhng php ny lin quan n vic truyn tn hiu gia cc

tng i k cn. Vi bo hiu kiu tng chng, s hiu cathu bao b gi s b gim dn qua mi tng i qu giang, ty cho n khi ch cn mt phn ca s b gi.

T A T B

T C T D

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Hnh 2.2. V d v bo hiu kiu Link By Link.

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* u im: D dng pht hin cc tn hiu (nhiu, mo dotr, mo do nhiu).

* Nhc im:

-Ti cc tng i qu giang, cc thanh ghi va phi c chc nngnhn s hiu va phi c chc nng gi s hiu. Do vy vicx l ti cc thanh ghi ny phc tp hn.

- Thi gian thit lp cuc gi lu v s cc s hiu truyn trn

tuyn ln.

- Khi s dng cc tn hiu thanh ghi hng v th thi gian chimcc thanh ghi qu giang tng ln do tt c cc thanh ghi trnmt kt ni nhiu lin kt phi c kt ni truyn v tn

hiu cui cng.

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2 Phng php truyn bo hiu kiu xuyn sutTrong bo hiu kiu xuyn sut, cc thanh ghi ca tng i qu

giang ch nhn cc s nh tuyn. Thanh ghi ca tng i xutpht cuc gi s lm vic trong sut thi gian thit lp cuc gi, n

cn c chun b d gi mt phn thng tin a ch khi c yu cubng cc tn hiu hng v. Thanh ghi qu giang s c gii

phng khi kt ni khi kt ni c pht trin ln pha trc ttng i qu giang .

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T A T B

T C T D

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Hnh 2.3. V d v bo hiu kiu End To End.

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u im:

- Cc thanh ghi ca tng di xut pht cuc gi c php iu khin thit lpcuc gi. T cho php cc kh nng nh tuyn t tng i xutpht.

- Ti cc tng i qu giang, cc thanh ghi ch c chc nng nhn mt phn shiu thu bao b gi ch khng cn gi. Do qu trnh x l ti cc thanhghi ny d dng hn.

- Thi gian thit lp cuc gi nhanh v s cc s hiu truyn trn tuyn t.- Thi gian chim cc thanh ghi ca cc tng i qu giang gim xung.

- Gim lng tr sau khi quay s v cc thanh ghi c gii phng sm hn,thng mch nhanh hn.

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3 Phng php truyn bo hiu kiu kt hp

y l phng php va s dng bo hiu kiu tng chng

va s dng bo hiu kiu xuyn sut.

T A T B T C T D

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Hnh 2.4. V d v bo hiu kiu kt hp.

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