QAM kev hloov pauv xa ob lub suab lus analog lossis ob lub suab digital los ntawm kev sib txawv (modulating) lub amplitudes ntawm ob lub cab cab siv ib qho ASK lossis analog AM digital modulation scheme.
Txoj Cai Ua Haujlwm
Ob tus neeg nqa khoom nthwv dej ntawm tib zaus, feem ntau yog sinusoids, tawm ntawm theem nrog ib leeg los ntawm 90 ° thiab yog li hu ua quadrature carriers los yog quadrature Cheebtsam - li no lub npe Circuit Court. Modulated nthwv dej yog summed thiab qhov kawg waveform yog ib tug ua ke ntawm ob theem hloov keying (PSK) thiab amplitude shift keying (ASK), los yog nyob rau hauv lub analog case theem modulation (PM) thiab amplitude modulation.
Zoo li txhua qhov kev hloov pauv, QAM xa cov ntaub ntawv los ntawm kev hloov qee yam ntawm cov teeb liab nthwv dej (feem ntau yog sine yoj) hauv cov lus teb rau cov ntaub ntawv teeb liab. Nyob rau hauv cov ntaub ntawv ntawm QAM digital, ntau theem thiab ntau qhov qauv siv tau siv. Phase shift keying (PSK) yog ib daim ntawv yooj yim ntawm QAM uas cov cab kuj amplitude yog tas mus li thiab tsuas yog theem hloov.
Nyob rau hauv warpQAM kis tau tus mob, ib tug cab kuj yoj yog ib tug sau ntawm ob sine nthwv dej ntawm tib zaus, 90 ° nyob rau hauv theem ntawm ib leeg (nyob rau hauv quadrature). Cov no feem ntau hu ua "I" lossis hauv-theem tivthaiv, nrog rau "Q" lossis quadrature tivthaiv. Txhua lub zog nthwv dej yog amplitude modulated, lub ntsiab lus nws qhov amplitude tau hloov pauv los sawv cev rau cov ntaub ntawv uas yuav tsum tau hloov ua ntej nws tuaj yeem ua ke ua ke.
Daim ntawv thov
Txoj kev txiav txim siab ciam teb nyob rau hauv daim duab saum toj no qhia txog tus ciam teb ntawm qhov chaw (lossis "txoj kev txiav txim siab ciam teb", lus).
QAM (quadrature amplitude modulation) yog dav siv los ua ib qho kev hloov kho rau cov kev sib txuas lus digital xws li 802.11 Wi-Fi qauv. Arbitrary siab spectral efficiency tuaj yeem ua tiav nrog QAM los ntawm kev teeb tsa lub hnub qub uas tsim nyog, txwv tsuas yog los ntawm theem suab nrov thiab txuas cov kab sib txuas.
QAM kev hloov kho yog siv hauv cov tshuab fiber ntau optical raws li tus nqi nce ntxiv. QAM16 thiab QAM64 tuaj yeem hloov kho qhov muag nrog 3-channel interferometer.
Digital Technology
Hauv QAM digital, txhua qhov sib xyaw nthwv dej muaj cov qauv ntsuas qhov ntsuas tsis tu ncua, txhua qhov nyob ib ntus ib ntus, thiab qhov amplitude yog quantized, txwv rau ib qho ntawm cov qib tsis kawg uas sawv cev ib lossis ntau tus lej binary (ntsis) ntawm ib me ntsis digital. Hauv analog QAM, qhov amplitude ntawm txhua feem ntawm sine yoj hloov tsis tu ncuanyob rau lub sijhawm nrog lub teeb liab analog.
Phase modulation (analog PM) thiab keying (digital PSK) tuaj yeem suav tias yog qhov tshwj xeeb ntawm QAM, qhov twg qhov loj ntawm cov teeb liab modulating yog tas li, tsuas yog cov theem hloov. Quadrature modulation tseem tuaj yeem txuas ntxiv mus rau zaus hloov pauv (FM) thiab keying (FSK), vim lawv tuaj yeem suav tias yog nws cov subspecies.
Raws li nrog ntau cov qauv kev hloov pauv digital, cov duab kos duab muaj txiaj ntsig zoo rau QAM. Hauv QAM, cov ntsiab lus constellation feem ntau yog teem rau hauv ib daim phiaj xwmfab nrog sib npaug ntsug thiab kab rov tav qhov sib txawv, txawm hais tias lwm yam kev teeb tsa (xws li Hla-QAM) tuaj yeem ua tau. Txij li cov ntaub ntawv feem ntau yog binary hauv kev sib txuas lus digital, cov ntsiab lus hauv kab sib chaws feem ntau yog 2 (2, 4, 8, …).
Vim QAM feem ntau yog square, qee qhov tsis tshua muaj - feem ntau cov duab yog 16-QAM, 64-QAM thiab 256-QAM. Los ntawm kev txav mus rau qhov kev txiav txim siab dua, ntau cov khoom ib lub cim tuaj yeem kis tau. Txawm li cas los xij, yog tias lub zog nruab nrab ntawm lub hnub qub tseem zoo ib yam (los ntawm kev sib piv ncaj ncees), cov ntsiab lus yuav tsum nyob ze ua ke thiab yog li muaj kev cuam tshuam ntau rau lub suab nrov thiab lwm yam kev noj nyiaj txiag.
Qhov no ua rau muaj qhov yuam kev ntau dua thiab yog li qhov kev txiav txim siab dua QAM tuaj yeem muab cov ntaub ntawv ntau dua kev ntseeg siab dua li qhov kev txiav txim qis QAM rau qhov nruab nrab lub hnub qub tsis tu ncua. Kev siv cov kev txiav txim siab dua QAM yam tsis tau nce qhov yuam kev me ntsis yuav tsum tau siab duasignal-to-noise ratio (SNR) los ntawm kev ua kom lub zog teeb liab, txo suab nrov, lossis ob qho tib si.
Technical aids
Yog tias cov ntaub ntawv tus nqi ntau dhau ntawm cov uas tau muab los ntawm 8-PSK yog xav tau, nws yog qhov xav tau txav mus rau QAM vim nws ua tiav ntau dua ntawm cov ntsiab lus nyob ib sab hauv I-Q dav hlau, faib cov ntsiab lus ntau dua. Ib qho teeb meem nyuaj yog tias cov ntsiab lus tsis muaj tib lub amplitude, thiab yog li tus demodulator yuav tsum tam sim no raug kuaj pom ob theem thiab amplitude, tsis yog theem xwb.
TV
64-QAM thiab 256-QAM feem ntau siv hauv digital cable TV thiab cable modems. Hauv Tebchaws Meskas, 64-QAM thiab 256-QAM yog cov kev tso cai digital cable modulation schemes uas tau tsim los ntawm SCTE hauv ANSI/SCTE 07 2013 tus qauv. UK modulation QAM-64 yog siv rau digital terrestrial TV (Freeview) thiab 256-QAM yog siv rau Freeview-HD.
Cov kab ke sib txuas lus tsim los ua kom tiav qib siab ntawm spectral efficiency feem ntau siv cov zaus ntom ntom hauv cov koob no. Piv txwv li, tam sim no Powerplug AV2 500-Mbit Ethernet li siv 1024-QAM thiab 4096-QAM li, nrog rau cov khoom siv yav tom ntej siv ITU-T G.hn tus qauv los txuas rau cov xaim hauv tsev uas twb muaj lawm.(coaxial cable, xov tooj kab thiab kab hluav taws xob); 4096-QAM muab 12 me ntsis / cim.
Ib qho piv txwv yog ADSL thev naus laus zis rau kev sib tw-pair tooj liab, uas lub hnub qub loj ncav cuag 32768-QAM (hauv ADSL cov lus no yog hu ua me ntsis-loading lossis me ntsis ib lub suab, 32768-QAM yog sib npaug rau 15 khoom ib lub suab).
Ultra siab bandwidth kaw lub voj kaw kuj siv 1024-QAM. Los ntawm kev siv 1024-QAM, hloov kho coding thiab hloov kho (ACM) thiab XPIC, cov tuam txhab tuaj yeem ua tiav gigabit peev xwm hauv ib qho 56 MHz channel.
In SDR receiver
Nws paub tias 8-QAM ncig zaus yog qhov zoo tshaj plaws 8-QAM kev hloov kho hauv kev xav xav tau lub zog nruab nrab qis tshaj plaws rau qhov tsawg kawg nkaus Euclidean nrug. 16-QAM zaus yog qhov zoo tshaj plaws, txawm hais tias qhov kev pom zoo tuaj yeem tsim tau raws li cov kab tib yam li 8-QAM. Cov zaus no feem ntau siv thaum kho SDR receiver. Lwm zaus tuaj yeem rov tsim dua los ntawm kev tswj hwm qhov sib xws (lossis zoo sib xws) zaus. Cov kev zoo no tau nquag siv nyob rau niaj hnub SDR receivers thiab transceivers, routers, routers.
