chap2 -...

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Unformatted text preview: ________________________________________________________________ ____________________ Ch ng 2 M ha v i u ch II - 1 $ CH NG 2 M HA V I U CH PH T N C A TN HI U Ph t n gin o n Ph t n lin t c M HA Cc d ng m ph bi n K thu t ng u nhin ha I U CH Bin Gc Xung Trong truy n thng, tin t c v d li u l t t c nh ng g c n trao i, chng c th l ti ng ni, hnh nh, t p h p cc con s , cc k hi u, cc i l ng o l ng . . . c a vo my pht pht i hay nh n c my thu. Tn hi u chnh l tin t c c x l c th truy n i trn h th ng thng tin. Vi c x l bao g m chuy n i, m ha v i u ch . Chuy n i l bi n cc tin t c d i d ng khng i n thnh ra tn hi u i n. M ha l gn cho tn hi u m t gi tr nh phn v c tr ng b i cc m c i n p c th c th truy n trn knh truy n v ph c h i my thu. i u ch l dng tn hi u c n truy n lm thay i m t thng s no c a m t tn hi u khc, tn hi u ny th c hi n nhi m v mang tn hi u c n truy n n n i thu nn c g i l sng mang (carrier wave). M c ch c a s i u ch l d i ph t n c a tn hi u c n truy n n m t vng ph t n khc thch h p v i tnh ch t c a ng truy n v nh t l c th truy n ng th i nhi u knh cng m t lc ( a h p phn t n s ). Ch ng ny c p n s i u ch v m ha. Nh ng tr c tin, chng ta c n nh c l i m t s tnh ch t c a tn hi u qua vi c phn tch tn hi u khng sin thnh t ng c a cc tn hi u hnh sin v l u n m i quan h t n s -th i gian c a tn hi u. 2 . 1 ph t n c a tn hi u Trong m t h th ng thng tin t n t i 3 d ng tn hi u v i ph t n khc nhau: - Lo i th nh t l cc tn hi u c tnh tu n hon c d ng hnh sin ho c khng. M t tn hi u khng sin l t ng h p c a nhi u tn hi u hnh sin c t n s khc nhau. K t qu ny c c b ng cch dng chu i Fourier phn tch tn hi u....
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chap2 -...

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