Tau ntsib cov tswv yim tshiab hauv lub neej niaj hnub, ntau tus sim nrhiav cov lus teb rau lawv cov lus nug. Nws yog rau qhov no tias nws yog ib qho tsim nyog los piav txog tej yam tshwm sim. Ib tug ntawm lawv yog xws li ib yam li modulation. Yuav tau tham ntxiv.
Kev piav qhia dav dav
Modulation yog tus txheej txheem ntawm kev hloov pauv ib lossis tag nrho cov txheej txheem siab oscillation tsis ua raws li txoj cai ntawm cov lus qhia tsawg zaus. Qhov tshwm sim ntawm qhov no yog kev hloov pauv ntawm spectrum ntawm kev tswj lub teeb liab mus rau thaj tsam siab, txij li kev tshaj tawm zoo rau hauv qhov chaw xav kom txhua tus transceivers ua haujlwm ntawm ntau zaus yam tsis muaj kev cuam tshuam ib leeg. Ua tsaug rau cov txheej txheem no, cov ntaub ntawv oscillations tau muab tso rau ntawm tus neeg nqa khoom paub txog qhov tseem ceeb. Lub teeb liab tswj muaj cov ntaub ntawv xa mus. High-frequency oscillation yuav siv lub luag haujlwm ntawm tus neeg nqa khoom ntawm cov ntaub ntawv, vim nws tau txais cov xwm txheej ntawm tus neeg nqa khoom. Lub teeb liab tswj muaj cov ntaub ntawv xa mus. Muaj ntau hom kev hloov kho, nyob ntawm seb qhov twg siv waveform: duab plaub, daim duab peb sab, lossis lwm yam. Nrog lub teeb liab discrete, nws yog kev cai los tham txog manipulation. Yog li ntawd,modulation yog ib txheej txheem uas muaj oscillations, yog li nws yuav ua tau zaus, amplitude, theem, thiab lwm yam.
Ntau yam
Tam sim no peb tuaj yeem xav txog yam dab tsi ntawm qhov tshwm sim muaj nyob. Hauv cov ntsiab lus, kev hloov pauv yog cov txheej txheem uas cov nthwv dej tsawg zaus yog nqa los ntawm cov nthwv dej siab. Cov hom hauv qab no feem ntau siv: zaus, amplitude thiab theem. Nrog kev hloov pauv zaus, kev hloov pauv ntawm zaus tshwm sim, nrog kev hloov pauv amplitude, lub amplitude, thiab nrog rau theem hloov kho, theem. Kuj tseem muaj ntau hom sib xyaw. Pulse modulation thiab hloov kho yog cais hom. Nyob rau hauv cov ntaub ntawv no, cov tsis tau ntawm high-frequency oscillation hloov discretely.
amplitude modulation
Hauv cov tshuab nrog hom kev hloov pauv no, qhov amplitude ntawm cov cab kuj hloov pauv ntawm qhov zaus siab nrog kev pab los ntawm kev hloov pauv nthwv dej. Thaum txheeb xyuas cov zaus ntawm qhov tso zis, tsis yog tsuas yog cov tswv yim zaus raug nthuav tawm, tab sis kuj lawv cov lej thiab qhov sib txawv. Nyob rau hauv cov ntaub ntawv no, yog hais tias tus modulation yog ib tug complex nthwv dej, xws li hais lus teeb liab uas muaj ntau zaus, ces cov sum thiab txawv frequencies yuav tsum tau ob bands, ib tug hauv qab cov cab kuj thiab ib tug saum toj no. Lawv hu ua lateral: sab sauv thiab qis. Thawj yog ib daim ntawv theej ntawm thawj lub suab teeb liab hloov los ntawm qee zaus. Qhov qis dua yog ib daim qauv ntawm cov teeb liab thawj zaug uas tau hloov pauv, uas yog, qhov qub siab zaus yog qhov qis dua nyob rau sab qis.
Lub sab sab qis yog daim iav duab ntawm sab sauv sab sauv txheeb ze rau tus neeg nqa khoom zaus. Qhov system siv amplitude modulation,kis tus cab kuj thiab ob sab yog hu ua ob txoj kev. Cov cab kuj tsis muaj cov ntaub ntawv tseem ceeb, yog li nws tuaj yeem raug tshem tawm, tab sis nyob rau hauv txhua rooj plaub, lub teeb liab bandwidth yuav yog ob zaug ntawm qhov qub. Qhov nqaim ntawm cov qhab yog ua tiav los ntawm kev hloov tsis tau tsuas yog cov cab kuj, tab sis kuj yog ib qho ntawm cov sab, vim lawv muaj ib cov ntaub ntawv. Hom no yog hu ua SSB modulation nrog suppressed cab kuj.
Demodulation
cov txheej txheem no yuav tsum muaj cov teeb liab hloov kho kom sib xyaw nrog cov neeg nqa khoom ntawm tib zaus raws li qhov tso tawm los ntawm lub modulator. Tom qab ntawd, thawj lub teeb liab tau txais raws li ib qho kev sib cais los yog ntau zaus, thiab tom qab ntawd lim los ntawm lwm cov cim. Qee lub sij hawm lub cim ntawm tus cab kuj rau demodulation tshwm sim nyob rau hauv situ, thiab nws tsis yog ib txwm coincide nrog cov cab kuj zaus ntawm lub modulator nws tus kheej. Vim muaj qhov sib txawv me me ntawm cov zaus, qhov tsis sib xws tshwm sim, uas yog ib qho ntawm cov xov tooj circuits.
Pulse modulation
Qhov no siv lub teeb liab digital baseband, txhais tau tias nws tso cai ntau tshaj ib me ntsis ib baud yuav tsum tau encoded los ntawm encoding ib tug binary cov ntaub ntawv teeb liab mus rau ib tug ntau theem teeb liab. Cov khoom ntawm binary signals qee zaum muab faib ua khub. Rau ib khub ntawm cov khoom, plaub qhov sib txuas tuaj yeem siv tau, nrog rau txhua tus khub tau sawv cev los ntawm ib qho ntawm plaub theem amplitude. Xws li lub teeb liab encoded yog tus cwj pwm los ntawm qhov tseeb tias qhov kev hloov pauv baud tus nqi yog ib nrab ntawm cov ntaub ntawv qub teeb liab, yog li nws tuaj yeem siv tau.amplitude modulation raws li ib txwm muaj. Nws pom nws daim ntawv thov hauv xov tooj cua sib txuas lus.
zaus hloov kho
Systems nrog qhov kev hloov kho no xav tias qhov zaus ntawm tus cab kuj yuav hloov raws li cov duab ntawm cov teeb liab modulating. Hom no yog qhov zoo tshaj plaws rau hom amplitude nyob rau hauv cov nqe lus ntawm kev tiv thaiv rau tej yam influences muaj nyob rau hauv lub xov tooj network, yog li nws yuav tsum tau siv nyob rau hauv qis speeds qhov twg tsis tas yuav nyiam ib tug loj zaus band.
Phase-amplitude modulation
txhawm rau nce tus lej ntawm ib qho baud, koj tuaj yeem ua ke theem thiab kev hloov pauv hloov pauv.
Ib qho ntawm cov txheej txheem niaj hnub no ntawm amplitude-theem kev hloov pauv tuaj yeem hu ua ib qho uas yog raws li kev sib kis ntawm ntau tus neeg nqa khoom. Piv txwv li, hauv qee daim ntawv thov, 48 tus neeg nqa khoom tau siv, sib cais los ntawm bandwidth ntawm 45 Hz. Los ntawm kev sib txuas AM thiab PM, txog li 32 lub xeev sib cais tau faib rau txhua tus neeg nqa khoom rau ib tus neeg lub sijhawm baud, yog li ntawd 5 khoom ib baud tuaj yeem nqa tau. Nws hloov tawm tias tag nrho cov teeb no tso cai rau koj hloov 240 khoom ib baud. Thaum ua haujlwm ntawm 9600 bps, qhov kev hloov pauv yuav tsum tsuas yog 40 baud. Xws li tus lej qis yog qhov ua siab ntev ntawm lub amplitude thiab theem dhia hauv lub hauv paus xov tooj.
PCM
Hom no feem ntau suav tias yog lub kaw lus rau tshaj tawm cov cim analog, xws li lub suab hauv daim ntawv digital. Cov txheej txheem modulation no tsis yog siv hauv modems. Ntawm no yog qhov rooj vag ntawm lub teeb liab analog nrogntawm ob zaug qhov siab tshaj plaws ntawm cov teeb liab analog. Thaum siv cov tshuab xws li hauv xov tooj, strobe tshwm sim 8000 zaug hauv ib ob. Txhua tus qauv yog qib voltage encoded nrog xya-ntsis code. Txhawm rau kom zoo tshaj plaws sawv cev rau cov lus hais, logarithmic coding yog siv. Xya khoom, ua ke nrog rau yim, uas qhia tias muaj lub teeb liab, tsim ib qho octet.
Kev hloov kho thiab tshawb pom yuav tsum tau rov qab kho cov lus teeb liab, uas yog, cov txheej txheem thim rov qab. Nyob rau hauv cov ntaub ntawv no, lub teeb liab yog hloov dua siab tshiab nyob rau hauv ib tug non-linear txoj kev. Cov ntsiab lus nonlinear txhawb nqa cov teeb liab tso zis spectrum nrog cov spectrum tshiab, thiab cov ntxaij lim dej yog siv los cais cov khoom siv tsawg zaus. Kev hloov kho thiab kev tshawb pom tuaj yeem ua tiav siv lub tshuab nqus tsev diodes, transistors, semiconductor diodes raws li cov ntsiab lus tsis-linear. Kev lig kev cai, taw tes semiconductor diodes yog siv, txij li cov tswv yim tswv yim capacitance yog qhov loj dua.
Modern Views
Digital modulation muab ntau cov ntaub ntawv muaj peev xwm thiab ua kom muaj kev sib raug zoo nrog ntau yam kev pabcuam cov ntaub ntawv digital. Tsis tas li ntawd, nws ua rau kom muaj kev ruaj ntseg ntawm cov ntaub ntawv, txhim kho kev sib txuas lus zoo, thiab ua kom lawv nkag tau sai.
Muaj ntau qhov kev txwv uas cov neeg tsim qauv ntawm txhua lub tshuab ntsib: lub zog tso cai thiab bandwidth, lub suab nrov ntawm kev sib txuas lus. Tus naj npawb ntawm cov neeg siv tau nce txhua hnubkev sib txuas lus tshuab, thiab qhov kev thov rau lawv kuj tseem loj hlob, uas yuav tsum muaj kev nce hauv xov tooj cua. Cov kev hloov pauv digital txawv ntawm qhov sib txawv hauv qhov uas tus neeg nqa khoom hauv nws xa cov ntaub ntawv ntau.
Yooj yim siv
Cov neeg tsim khoom ntawm cov xov tooj cua digital xov tooj cua ntsib lub luag haujlwm tseem ceeb - txhawm rau nrhiav kev sib haum xeeb ntawm bandwidth ntawm cov ntaub ntawv xa mus thiab qhov nyuaj ntawm cov txheej txheem hauv cov ntsiab lus. Rau qhov no, nws yog qhov tsim nyog los siv cov qauv sib txawv kom tau txais cov txiaj ntsig xav tau. Kev sib txuas lus hauv xov tooj cua kuj tseem tuaj yeem tsim los siv cov khoom siv yooj yim tshaj plaws thiab cov khoom siv hluav taws xob, tab sis rau kev sib txuas lus zoo li no, qhov zaus spectrum proportional rau tus naj npawb ntawm cov neeg siv yuav raug siv. Ntau cov neeg txais thiab cov khoom xa tawm xav tau tsawg dua bandwidth los tshaj tawm cov ntaub ntawv tib yam. Txhawm rau txav mus rau spectrally npaum txoj kev kis tau tus mob, nws yog ib qho tsim nyog yuav tsum ua kom cov khoom siv nyuaj kom haum. Qhov teeb meem no tsis yog nyob ntawm hom kev sib txuas lus.
lwm txoj kev xaiv
Pulse width modulation yog tus cwj pwm los ntawm qhov tseeb tias nws cov teeb liab nqa khoom yog ib theem ntawm pulses, thaum lub mem tes zaus tas li. Cov kev hloov pauv tsuas yog lub sijhawm ntawm txhua tus mem tes raws li lub teeb liab modulating.
Pulse-width modulation yog txawv ntawm zaus-theem kev hloov pauv. Cov tom kawg suav nrog kev hloov kho ntawm lub teeb liab hauv daim ntawv ntawm sinusoid. Nws yog tus cwj pwm los ntawm qhov amplitude tas li thiab hloov pauv zaus lossis theem. Pulse signals kuj tuaj yeem hloov kho hauv zaus. Tej zaum yuav ntevpulses yog tsau, thiab lawv zaus yog nyob rau hauv ib co nqi nruab nrab, tab sis lawv instantaneous tus nqi yuav txawv nyob ntawm seb modulating signals.
Cov Lus Qhia
Cov kev hloov pauv yooj yim tuaj yeem siv tau, tsuas yog ib qho kev hloov pauv raws li cov ntaub ntawv hloov pauv. Lub tswv yim sib xyaw ua ke uas siv rau hauv cov cuab yeej sib txuas lus niaj hnub no yog thaum ob qho tib si lub amplitude thiab theem ntawm cov cab kuj hloov ib txhij. Hauv cov tshuab niaj hnub no, ob peb lub subcarriers tuaj yeem siv tau, txhua tus siv qee hom kev hloov kho. Hauv qhov no, peb tab tom tham txog cov teeb liab modulation schemes. Lo lus no kuj tseem siv tau rau ntau theem kev pom, thaum muaj kev piav qhia ntxiv ntawm cov yam ntxwv xav tau rau cov ntaub ntawv nthuav dav.
Cov tshuab kev sib txuas lus niaj hnub siv hom kev hloov kho tau zoo tshaj plaws los txo qis bandwidth kom tso chaw ntau zaus rau lwm hom teeb liab. Qhov zoo ntawm kev sib txuas lus tsuas yog tau txais txiaj ntsig los ntawm qhov no, tab sis qhov nyuaj ntawm cov khoom siv hauv qhov no yog siab heev. Thaum kawg, qhov kev hloov pauv zaus muab qhov tshwm sim uas pom tau rau cov neeg siv kawg nkaus nkaus xwb hauv cov ntsiab lus ntawm kev siv yooj yim ntawm kev txhais tau tias.
