I HC TN C THNGKHOA IN- IN T

H THNG ViN THNG 1

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H THNG ViN THNG 1ThS. nh Thun

Dinh-Thuan Do 402018 - He thong vien thong 1

Chng 3: Knh truyn v tuyn Cc loi nhiu trong knh truyn v tuyn Hiu ng gn xa

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Nhiu a ng

Dinh-Thuan Do 402018 - He thong vien thong 1

Cc loi nhiu trong knh truyn v tuyn

3Dinh-Thuan Do 402018 - He thong vien thong 1

Cc loi nhiu trong knh truyn v tuyn

Nhiu xen k t ISI Nhiu xen k t c nh hng Mt phn nng lng k t (symbol) b chng ln vi k t bn

cnh gy ra nhiu xen k t ISI (intersymbol interference) ISI gim ng k kh nng tch sng (detector)

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Cc loi nhiu trong knh truyn v tuyn

Nhiu ISI Gi s c 2 ng tn hiu Tuyn ngn hn c chiu di d1,

tuyn cn li di d2 S khc nhau v tr truyn lan gia

2 ng ny nh th no?

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2 ng ny nh th no?

Dinh-Thuan Do 402018 - He thong vien thong 1

Cc loi nhiu trong knh truyn v tuyn

Cc nh hng trong truyn dn s

6Dinh-Thuan Do 402018 - He thong vien thong 1

Cc loi nhiu trong knh truyn v tuyn

Truyn dn qua mi trng v tuyn ni chung rt kh c tnh ha

Cc tn hiu EM thng b cn tr bi cc vt cn, gy ra phn x, tn x,

C 3 loi : Path Loss, Shadow fading, Multipath fading (or fast fading).

7Dinh-Thuan Do 402018 - He thong vien thong 1

Cc loi nhiu trong knh truyn v tuyn

Cc loi fading Phn loi: Flat Fading: knh c p ng l hng s cho bng thng

ln hn bng thng tn hiu

8Dinh-Thuan Do 402018 - He thong vien thong 1

Cc loi nhiu trong knh truyn v tuyn

Cc loi fading Frequency Selective Fading

9Dinh-Thuan Do 402018 - He thong vien thong 1

Cc loi nhiu trong knh truyn v tuyn

Cc loi fading Frequency Selective Fading Tn hiu thu c nhiu phin bn khc nhau, tr khc

nhau

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Cc loi nhiu trong knh truyn v tuyn

Cc loi fading Fast fading p ng xung ca knh truyn thay i

nhanh trong chu k k t (symbol) Ts

CS

DS

TTBB

>

Cc loi nhiu trong knh truyn v tuyn

Cc loi fading Tng hp cc loi fading

12Dinh-Thuan Do 402018 - He thong vien thong 1

Cc loi nhiu trong knh truyn v tuyn

Cc loi fading

13Dinh-Thuan Do 402018 - He thong vien thong 1

Cc loi nhiu trong knh truyn v tuyn

Hiu ng Doppler Khi my thu hay pht di chuyn, tn s b dch i f = v/

cos(), v l tc v l bc sng

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cm fc

vf = isshift maximum The

Cc loi nhiu trong knh truyn v tuyn

Hiu ng Doppler trit nh hng Doppler:

S dng tn s thp Pht theo cm tn hiu knh l hng s trong sut chu k cm

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Chn cc chui hun luyn trong mi khung tn hiu c th khi phc gi tr knh truyn

S dng mi trng truyn trong nh

Dinh-Thuan Do 402018 - He thong vien thong 1

Nhiu a ng

Tn hiu truyn bng nhiu ng n ch. Tr truyn lan theo mi ng l khc nhau

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Nhiu a ng

Cc nh hng ca nhiu a ng Ghost trong tn hiu truyn hnh. H thng nh v ton cu GPS tnh v tr khng chnh

xc. Fading la chn tn s (Frequency Selective Fading).

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Fading la chn tn s (Frequency Selective Fading). Nhiu ISI (Intersymbol interference).

Dinh-Thuan Do 402018 - He thong vien thong 1

Hiu ng xa gn

Khi nim hiu ng xa gn: Ngun gy nhiu gn thit b thu trong khi ngun tn hiu c ch th xa

V d: Nu d1Pr2. Ti my in thoi MS2 nhiu knh k tng do hiu ng gn xa

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M hnh knh Rayleigh, Rician

Mt knh Rayleigh tha nhn l tt c cc ng tn hiu c bin ngu nhin

Knh Rician tha nhn thnh phn tm nhn thng c bin ln nht

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Cc loi m ng truyn

M B8ZS (bipolar with 8-zeros substitution) Lut thay th: Nu 1 octet c 8 s 0 v xung pha trc

octet ny l +V, th 8 s 0 ny m ha thnh 000+-0-+ Nu 1 octet c 8 s 0 v xung pha trc octet ny l -V,

th 8 s 0 ny m ha thnh 000-+0+ -

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Cc loi m ng truyn

High-Density Bipolar-3 Zeros (HDB3) Lut thay th:

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Cc loi m ng truyn

M manchester: thay i mc in p gia chu k bit

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