Lê Đắc Nhường - Ky Thuat Truyen So Lieu

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TRNG I HC HNG HI KHOA CNG NGH THNG TIN B MN K THUT MY TNH

BI GING MN HC

K THUT TRUYN S LIU

Hi Phng 2009-1-

MC LC

Chng I: TNG QUAN .......................................................................................................................... 1. Mt s khi nim.................................................................................................................................. 2. M ha d liu ..................................................................................................................................... 3. Cch truyn thng tin trn ng dy ................................................................................................. 4. Nhng vn c bn trong truyn thng ............................................................................................ Chng II: H THNG TRUYN THNG ............................................................................................. 1. H thng truyn thng ......................................................................................................................... 2. Phng tin truyn tin. ........................................................................................................................ 3. Cc chun giao tip trong truyn thng ............................................................................................... 4. Mch iu khin truyn s liu ............................................................................................................ 5. Mng truyn thng ............................................................................................................................... Chng III: K THUT TRUYN S LIU ............................................................................................ 1. Khi qut ............................................................................................................................................. 2. Cc k thut truyn s liu ................................................................................................................... Chng IV: CC VN C BN TRONG TRUYN THNG............................................................. 1. M ho pht hin sai, sa sai .............................................................................................................. 2. Kim sot ng truyn ...................................................................................................................... Chng 5: MNG TRUYN S LIU ..................................................................................................... I. Tng quan ............................................................................................................................................ 1. Mng truyn s liu ............................................................................................................................. 2. Kin trc phn tng v m hnh OSI .................................................................................................... II. Mng truyn s liu ............................................................................................................................. 1. Phn loi mng theo k thut chuyn mch ......................................................................................... 2. K thut LAN ....................................................................................................................................... TI LIU THAM KHO ............................................................................................................................

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Mc ch mn hc: Hin nay vic truyn ti thng tin qua my tnh v ang c p dng rng ri. My tnh khng ch dng tnh ton, qun l, m phng, m cn c s dng truyn ti thng tin cng nh iu iu khin cc thit b thc trong thc t. Mn hc cung cp cc khi nim tng qut v k thut truyn s liu, mng truyn thng (Kh nng truyn ti, chn mng truyn, kim sot lung d liu, m ho)

Ni dung: (5 chng) 1. Tng quan 2. H thng truyn thng 3. K thut truyn s liu 4. Cc vn c bn trong truyn thng 5. Mng truyn s liu.

Yu cu 1. Tham d y cc tit hc 2. Thi hc tp tt trn lp 3. Thc hin cc bi kim tra gia k 4. Thi kt thc hc phn Z= 0,2X + 0,8Y

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Chng I: TNG QUAN

I. MT S KHI NIM: 1. Thng tin, tn hiu: - Thng tin: S cm hiu con ngi v th gii xung quanh - Nhu cu trao i thng tin: Rt ln - D liu: Dng biu din thng tin (ch vit, hnh nh, c ch, li ni...). c bit trn my tnh d liu c s ho c kh nng lu tr, x l, bin i, truyn gi... (Ch : Phn bit gia d liu v thng tin). - Thng tin khi truyn: Theo cc dng nng lng khc nhau: m, in, sng quang, sng in t... - Vt mang: Mi trng dng mang thng tin (L dng nng lng - C kh nng lu tr, truyn gi...) - Tn hiu: Vt mang cha thng tin trong n, L mt hm n tr bin thin theo thi gian hay tn s. - Tn hiu lin tc: L tn hiu bin thin lin tc theo thi gian v c bin bin thin lin tc (Nu v d) - Tn hiu ri rc: Tn hiu c bin c lp ri rc, ta c th thu tn hiu ri rc bng cch ly mu ri rc t tn hiu lin tc (tn hiu ly mu). - Tn hiu lng t: Tn hiu c bin ri rc theo cc mc lng t. - Tn hiu s: Tn hiu ri rc ho c v bin , tn s ln thi gian.

S(t)

S(t)

2. Tn s, ph, bng thng:

t

t

- Tn s: Tn s (f) ca tn hiu l s dao ng ca tn hiu trong mt n v thi gian (thng tnh bng giy) - Chu k: Chu k (T) ca tn hiu l khong thi gian tn hiu lp li mt ln. - Pha: L n v o v tr tng i ti mt thi im trong mt chu k n ca tn hiu, n c trng cho tnh tr. - Ph: Ph ca tn hiu l dy cc tn s m n c th cha. - Bng thng: Bng thng ca tn hiu l rng ca ph. - Tng quan gia tc truyn v bng thng: Do biu din tn hiu di dng sng theo tn s: s(t ) =

k sin 2kft nn khng c gii hn v tn s, dn n khng c gii hn v bng thng.k =1

1

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Bin cc xung thnh phn th k l 1/k, do vy nng lng ch tp trung mt s thnh phn ban u => tc truyn w (b/s) => bng thng yu cu 2w (Hz) II. M HO D LIU: Trong qu trnh lu tr v truyn gi, d liu lun phi c bin i, m ho sao cho ph hp vi vt mang, c kh nng truyn ti trn ng truyn, c kh nng bo v, trnh cc li c th sy ra, khi d liu thng m ho di dng tn hiu s hoc tng t tu thuc vo yu cu, mc ch. M ho: Lut nhn bit thng tin cn phi biu din vi dng tn ti nh phn. di m: ph thuc vo gi tr s ct nh phn ca k t mun biu din. Thng tin cn truyn: c m ha, trn thc t l tp cc gi tr phn t ca n. Biu din nh phn cc k t di1...din, thuc [0,1] ca k t Ci gi l t m.

Nguyn tc m ha: Tn dng mi kh nng biu din; Biu din trong h thp phn n gin; Thun tin, d sp xp; Cho php bo v hoc sa sai.

1. D liu s, tn hiu s: D liu s: D liu c bin ri rc ho v thi gian. Dng m ho n gin nht ca d liu s l t mt mc in p cho gi tr 1 nh phn v mt mc in p khc cho gi tr 0 nh phn. D liu nh phn c truyn bng cch m ho mi bt d liu bi xung tn hiu. Qu trnh nhn tn hiu bn thu ph thuc vo cc yu t: Ni nhn phi bit khong thi gian ca tng bt, ngha l phi bit chnh xc thi im bt u v kt thc Phi pht hin ra mc ca tn hiu Do nhiu v cc nguyn nhn khc, s c li xy ra.

Ba yu t chnh nh gi s thnh cng ca vic nhn tn hiu l: mc nhiu, tc truyn, kh nng ng truyn. Ngoi ra mt yu t khc dng nng cao hiu qu trong qu trnh truyn l m ho d liu, ngha l chuyn cc bt d liu thnh cc thnh phn ca tn hiu. Cc kiu m ho: a. M NRZ (None Return to Zero): + M NRZ-L (Level): y l phng php n gin nht, s dng hai mc in p khc nhau cho hai gi tr nh phn: Mc in p cao tng ng gi tr 0 nh phn Mc in p thp tng ng gi tr 1 nh phn Phng php ny s dng to v biu din d liu s bng cc thit b u cui v mt s thit b khc

+ M NRZ-I (Inverted) Phng php ny duy tr xung in p khng i trong sut thi gian tn ti bt. Bn thn d liu c m ho di dng c hay khng s thay i trng thi ti thi im u tin ca mt bt 1.-5-

+ u / nhc im: C tin cy cao trong vic pht hin ra s thay i trng thi trong iu kin c nhiu. Tn ti thnh phn 1 chiu, thiu kh nng ng b ho, Nu c s sai lch trong thi gian ng b gia hai bn s lm mt s ng b Do tnh n gin v c im c tn s tng i thp nn thng c s dng trong lu tr tn hiu s dng t

Chui bt

M NRZ-L

M NRZ-I

AMI

M 3 mc

M Manchester

b. M nh phn nhiu mc: Phng php ny s dng hn hai mc tn hiu + M lng cc AMI (Alternate Mark Invertion): Bt 0 c biu din bi tn hiu mc 0 Bt 1 c biu din bng xung c in p m hoc dng

+ M ba bc: Bt 1 c biu din bi tn hiu mc 0 Bt 0 c biu din bng xung c in p m hoc dng

+ u / nhc im: Khng lm mt s ng b nu c mt dy di m trong tt c l bit 1 (do da vo kh nng o pha trng thi bit 1). Tuy nhin nu c mt dy cc bit 0 lin tip vn c th to ra li Tn hiu khng c thnh phn 1 chiu C kh nng pht hin li n gin

c. M hai pha: M Manchester: S o trng thi gia khong thi gian bit: T thp ln cao biu din bt 1, t cao xung thp biu din bt 0.

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M Differential Manchester: S o trng thi gia khong thi gian bt dng ng b ho tn hiu bn nhn.

2. D liu s, tn hiu tng t: Ph bin nht l d liu truyn qua mng in thoi cng cng, mng chuyn mch v truyn tn hiu tng t trong tn s m thanh (khong t 300Hz n 3400Hz) Phng php m ho: Theo c trng v bin , tn s, gc pha. a. Phng php ASK (Amplitude Shift Keying) Hai gi tr nh phn i din cho 2 bin khc nhau:S (t ) = A . cos (2 f c t )S (t ) = 0

vi nh phn 1 vi nh phn 0

b. Phng php FSK (Frequency Shift Keying) Hai gi tr nh phn i din cho 2 tn s khc nhau ca tn s mang:S (t ) = A . cos (2 f 1 t )S (t ) = A . cos (2 f 2 t )

vi nh phn 1 vi nh phn 0

c. Phng php PSK (Phase Shift Keying) Hai gi tr nh phn i din cho 2 gc pha khc nhau ca tn s mang:S (t ) = A . cos (2 f c t +

)

vi nh phn 1 vi nh phn 0

S (t ) = A . cos (2 f c t )

Chui bit

ASK

FSK

PSK

3. D liu tng t, tn hiu s Phng php chuyn i d liu t tng t sang tn hiu s (s ho d liu) thng qua iu bin m xung a. Phng php PCM (Pulse Code Modulation):-7-

Da trn c s nh l ly mu Shannon: Nu mt tn hiu tng t f(t) c ly mu ti nhng khong thi gian bt k v fs>2fmax th nhng mu ny cha ton b thng tin ca tn hiu ban u. Hm f(t) c th c xy dng t nhng mu ny thng qua b lc thng thp. Cch thc: Ly mu d liu tng t vi t l thch hp. Mi mu c gn bng mt m n