- Nyob nruab nrab ntawm lub xyoo pua xeem, Cov neeg npaj tseg ib multi-carrier sib txuas lus tswvyim nrog frequency qhab aliasing, xaiv mutually orthogonal carrier frequencies li subcarriers, Nws yog dab tsi peb hu COFDM. No "orthogonality" xa mus rau lub caij nyoog mathematical kev sib raug zoo ntawm cov zauv. Raws li qhov kev xav no assumption, COFDM yuav tsis tsuas ua daim ntawv qhia txog kev siv channel bandwidth, Tiam sis kuj tsis txhob siv high-speed equalization thiab los tiv thaiv burst nrov yuam kev. COFDM yog ib tug tshwj xeeb multi-carrier sib txuas lus tswvyim. Cov ntaub ntawv ntws ntawm ib tug neeg siv yog serially/parallel converted rau hauv ntau yam tsawg-tus nqi code streams, Thiab txhua code stream yog xa nrog ib subcarrier subcarrier. Tsis txhob siv bandpass filters cais subcarriers, COFDM siv ceev Plaubier Transform (FFT) Xaiv waveforms uas nyob orthogonal txawm aliasing.
- COFDM tshuab belongs rau tej modulation (Multi-Carrier Modulation, MCM) Tej txuj ci tshiab. Tej cov ntaub ntawv muab OFDM thiab MCM, uas yog ua tau tsis rigorous txaus. MCM thiab COFDM feem ntau siv nyob rau hauv wireless channels. The difference between them is that COFDM technology specifically refers to dividing a channel into orthogonal sub-channels, which has a high channel utilization rate; while MCM can be more channel division methods.
- The introduction of COFDM technology is actually to improve the spectrum utilization of the carrier, or to improve the modulation of multi-carriers. Its characteristic is that each sub-carrier is orthogonal to each other, so that the spectrum after spread spectrum modulation can overlap each other, thereby reducing the Mutual interference between subcarriers. The modulation method used by each carrier of COFDM can be different. Each carrier can choose different modulation methods according to different channel conditions, such as BPSK, QPSK, 8PSK, 16Qam, 64Qam, thiab lwm yam., Raws li tus thawj xibfwb ntawm qhov nqi koj tshuav ntawm spectrum utilization thiab yuam kev tus nqi yuam kev. Lub COFDM tshuab siv adaptive modulation, Thiab xaiv cov modulation txoj kev raws li qhov zoo ntawm cov channel. COFDM kuj adopts lub coordinated ua hauj lwm hom hwj huam tswj thiab adaptive modulation. Thaum cov channel zoo, Lub hwj huam transmission tshua unchanged, thiab modulation mode (xws li 64QAM) yuav enhanced, los yog tus transmission yuav raug txo thaum lub modulation hom tsawg (xws li QPSK).
- COFDM tshuab yog lub hauv paus ntawm lub HPA Alliance (HomePlug Powerline Alliance) muaj kev hais lus. Nws siv ib discontinuous multi-tone tshuab combine ib tug xov tooj ntawm cov teeb liab sib txawv hu ua carriers rau hauv ib lub teeb liab kom tiav transmission. Vim hais tias lub tshuab no muaj peev xwm transmit signals nyob rau hauv clutter cuam tshuam, Feem ntau nws yog siv nyob rau hauv transmission tawm uas yog raug rau lwm cuam tshuam los yog tsis muaj peev xwm resist lwm cuam tshuam.
- COFDM yog cov abbreviation ntawm Coded Orthogonal Frequency Division Multiplexing, Nws yog tus tshaj plaws thiab feem ntau pheej modulation tshuab nyob hauv lub ntiaj teb. Nws tus nqi xyaum nyob rau hauv kev txhawb cov ntaub ntawv uas tawg los ntawm qhov txwv ntawm line-of-sight. Nws yog ib lub tshuab uas ua rau daim ntawv qhia txog kev siv xov tooj cua spectrum cov chaw muab kev pab thiab muaj zoo tiv thaiv kom nrov thiab cuam tshuam. Diffraction thiab penetration ntawm obstructions yog COFDM tshuab. tub ntxhais. Nws cov thawj xibfwb yooj yim yog los hloov cov ntaub ntawv high-speed stream rau ob peb sub-channels uas txo transmission tus nqi los ntawm serial-to-parallel conversion rau transmission.
- COFDM tshuab yuav cais ntau cov teeb liab simultaneously thiab yuav khiav lag luam zoo nyob ib ncig ntawm interfering teeb liab. Nws yog precisely vim yog qhov teeb meem tshwj xeeb "penetrating muaj peev xwm" Tias COFDM tshuab yog tsaug hlub thiab txais tos los ntawm kev sib txuas lus manufacturers. COFDM tshuab yuav continuously saib cov cia li hloov cov cim ntawm cov cim ntawm lub transmission nruab nrab. Muaj peev xwm sib txuas lus rau transmit cov ntaub ntawv yuav hloov nrog lub sij hawm. COFDM yuav dynamically adapt rau nws, thiab hloov ntawm tus corresponding carrier kom continuous kev kawm. ntawv xov xwm zoo. COFDM tshuab yog tshwj xeeb tshaj yog suitable siv nyob rau hauv high-sawv vaj tse, densely populated thiab geographically mas tej chaw, tej thaj chaw uas yuav kis tau tus kab mob no, thiab tej chaw uas muaj cov ntaub ntawv high-speed yog kis.
Kom zoo dua coFDM tshuab
- Ib tug nqi ntau cov ntaub ntawv kuj yuav muab xa mus nyob rau hauv nqaim bandwidth: COFDM tshuab yuav cais tsawg kawg yog 1000 Cov teeb liab tib lub sijhawm, thiab muaj peev xwm khiav lag luam muaj kev ruaj ntseg nyob ib ncig ntawm interfering teeb liab yuav ncaj qha mus rau CDMA tshuab uas kuj nrov nyob rau hauv lub lag luam hnub no. Qhov sib ntxiv kev loj hlob thiab kev loj hlob yog precisely vim yog qhov teeb meem tshwj xeeb "penetrating muaj peev xwm" Uas ua coFDM tshuab nrov thiab nrov nrog cov tswv nyob sab Europe sib txuas lus thiab txawb xov tooj manufacturers, xws li California Cisco Systems, New York Flarion lub koom haum uas tshuab thiab Lucent lub koom haum uas tshuab thiab lwm cov neeg muaj nyav siv tshuab no, thiab cov Canadian Wi-LAN lub koom haum uas tshuab muaj kuj pib siv tshuab no.
- COFDM tshuab yuav continuously saib cov cia li hloov cov cim ntawm cov cim ntawm lub transmission nruab nrab: Txij thaum muaj peev xwm sib txuas lus mus transmit cov ntaub ntawv yuav hloov lub sij hawm, COFDM yuav dynamically adapt rau nws thiab hloov ntawm thiab tua cov corresponding carrier kom txuas ntxiv mus txuas lus zoo;
- Lub tshuab no yuav automatically ntes uas muaj cov cab kuj muaj teeb liab attenuation los yog cuam tshuam pulse nyob rau hauv lub nruab nrab transmission nruab nrab, thiab ces coj cov modulation ntsuas kom muaj tus cab kuj tsawg zaus los sib txuas lus kom sib txuas lus;
- COFDM tshuab yog tshwj xeeb tshaj yog suitable siv nyob rau hauv high-sawv vaj tse, densely populated thiab geographically mas tej chaw, thiab tej thaj chaw uas muaj teeb liab yog kis. Ob leeg high-speed cov ntaub ntawv transmission thiab cov suab broadcasting vam cia kom txo tej yam uas multipath los ntawm cov teeb liab.
- Nws yuav zoo counter tus cuam tshuam ntawm teeb liab waveforms, thiab yog suitable rau cov ntaub ntawv high-speed transmission nyob multipath tej chaw thiab fading channels. Thaum frequency selective fading tshwm sim vim multipath transmission nyob rau hauv cov channel, Tsuas lub subcarriers ntog hauv lub frequency qhab kev nyuaj siab thiab cov ntaub ntawv ris los ntawm lawv muaj cuam tshuam dab tsi, Thiab lwm subcarriers yuav tsis puas ntsoog, Li ntawd, tag nrho me ntsis yuam kev ntawm lub kaw lus yog zoo npaum li cas.
- Los ntawm cov pob qij txha coding ntawm txhua subcarrier, Nws muaj zog los tiv thaiv fading muaj peev xwm. Lub COFDM tshuab nws tus kheej twb utilized lub frequency ntau haiv neeg lus ntawm cov channel, Yog hais tias cov fading tsis tshwj xeeb tshaj yog loj heev, Tsis muaj yuav tsum tau ntxiv ib lub sij hawm domain equalizer. Yog jointly encoding txhua channel, Lawv kev kawm tau zoo tuaj.
- COFDM tshuab yog resistant narrowband cuam tshuam, Vim hais tias cov cuam tshuam tsuas muaj feem xyuam rau ib feem me me ntawm cov channels sub-channels.
- Txoj kev siv ntawm OFDM raws li IFFT/FFT yuav xaiv tau;
- Cov channel utilization tus nqi yog siab heev, which is especially important in the wireless environment with limited spectrum resources; when the number of sub-carriers is large, the spectrum utilization rate of the system tends to be 2Baud/Hz.
- The application of COFDM technology in wireless image transmission has the following unique advantages:
- Applied in non-visible and obstructed environments, the excellent "diffraction" thiab "penetration" capabilities make it suitable for real-time wireless image transmission in urban areas, suburbs, and buildings. Traditional microwave equipment must be visible under visible conditions. (There must be no obstruction between the two sending and receiving points) to establish a wireless link channel, so the use is greatly restricted by the environment. It is necessary to inspect the application environment in advance, xaiv thiab kuaj cov ntsiab lus, kho cov kev taw qhia ntawm tus antenna, thiab laij qhov siab ntawm tus antenna, thiab lwm yam. , Lub workload yog hnyav heev thiab cumbersome, Uas tsis tsuas ncaj qha mus txwv cov transmission thiab txais tos ntawm audio thiab yees duab, Tiam sis kuj heev txo cov reliability thiab ua hauj lwm efficiency ntawm lub cev.
COFDM wireless duab khoom muaj kiag li hloov qhov teeb meem no. Vim nws cov cim xeeb ceem xws li multi-carrier, COFDM khoom muaj qhov kom zoo dua "tsis-ntawm-pom" thiab "diffraction" kis tau tus kab mob. Twb paub lawm tus ruaj khov transmission ntawm dluab, tsis cuam tshuam dab tsi los ntawm tej cheeb tsam los yog cuam tshuam dab tsi los ntawm ib puag ncig. Lawv adopts ib omnidirectional antenna, Uas yuav teeb ib wireless transmission txuas rau lub sij hawm luv luv. Tus tshaaj kawg thiab tau txais kawg yuav tau txav dawb do tsis tau txwv los ntawm cov kev taw qhia. Lub kaw lus no yooj yim, txhim khu kev qha, thiab yooj ywm rau hauv daim ntawv thov.
- Nws yog suitable rau wireless transmission ntawm real-time dluab hauv high-speed zog, thiab yuav siv tau microwave (cov microwave, kis spectrum microwave) thiab wireless LAN khoom rau platforms xws li tsheb, nkoj, thiab helicopters. Vim yog tej yam uas lawv ua tsis tau vim yog txoj kev, Lub tshaaj davhlau ya nyob twg tsis tau ywj siab pom tau hais thiab tau txais xaus transmits dluab nyob rau lub sij hawm tiag thaum high-speed zog. Thaum uas siv microwave thiab wireless LAN khoom rau tsheb thiab ships rau wireless duab transmission, Li ib txwm tov yog configure ntxiv "servo stabilization" ntaus kom daws tau teeb meem xws li electromagnetic yoj orientation, nrhiav, thiab stabilization, Tiam sis nws tsuas siv tau nyob rau hauv tej yam mob. Twb paub lawm tus transmission ntawm mobile taw tes rau tas taw tes nyob rau hauv qhov chaw, thiab cov duab no feem ntau cuam tshuam, uas tiag raug rau cov nyhuv transmission thiab txais tos. Tus engineering yog txoj, Lub reliability yog txo, thiab tus nqi yog ib qho tsis tshua muaj neeg.
Tab sis rau COFDM khoom, Nws tsis xav tau tej ntxiv li lawm, thiab nws yuav siv tau ntawm tsau-mobile, mobile-mobile, Thiab yog suitable rau plahaum rau mobile platforms xws li tsheb, nkoj, thiab helicopters. Tsis zoo xwb tus transmission muaj reliability, Tiam sis kuj qhia tau hais tias muaj nqi kev kawm.
- Tus transmission bandwidth yog siab, Uas yog suitable rau tus nqi siab thiab zoo duab zoo audio thiab yees duab transmission. Cov duab tom tus nqi yuav feem ntau dua 4M bps. Feem ntau cov microwave thiab kis spectrum microwave transmission txuas, Txawm tias MPEG-2 encoding siv, Cov channel feem coob adopts 2M tus nqi, xws li E1, Li ntawd, cov duab decoded yuav mus txog 720×576, Tab sis cov duab compressed code kwj yog tsuas 1M tshuav thiab txoj cai, Tsis tau raws li qhov uas yuav tsum tau txais xaus rau tom qab audio thiab yees duab tsom xam, cia, thiab editing.
Txhua subcarrier ntawm COFDM tshuab yuav xaiv high-speed modulation xws li QPSK, 16Qam, 64Qam, thiab lwm yam., Thiab lub neej coj channel tus nqi yog feem ntau dua 4M bps. Yog li ntawd, Dluab zoo codec dluab xws li 4:2:0 thiab 4:2:2 MPEG-2 yuav kis tau tus kab mob no, Cov duab uas tau txais xaus yuav mus txog 720×576 los yog 720×480, thiab cov kwj dej kwj yuav nyob ntawm 6M. Cov duab zoo yog ze ntawd DVD, which can fully meet the specific requirements of the receiving end for post-audio and video analysis, cia, thiab editing.
- In a complex electromagnetic environment, COFDM has excellent anti-interference performance against frequency selective fading or narrow-band interference and interference between signal waveforms. Through the joint coding of each sub-carrier, it has a strong anti-fading ability. In single-carrier systems (such as digital microwave, spread-spectrum microwave, thiab lwm yam.), a single fading or interference can cause the entire communication link to fail, but in a multi-carrier COFDM system, only a small part of the sub-carriers will be interfered, and these sub-carriers The channel can also use error-correcting codes for error correction to ensure a low bit error rate for transmission.
Daim ntawv thov coFDM Wireless Transmission tshuab hauv yees duab yoos
Cov duab wireless transmission tswvyim siv COFDM tshuab muaj zoo tsis-line-of-sight transmission thiab high-speed mobile transmission kev kawm, thiab yuav muab cov dluab real-time dluab thiab suab ntawm DVD zoo. Lub on-site nyob audio thiab yees duab yuav kis tau flexibly thiab ceev ncaj qha los ntawm lub tsheb-mounted los yog portable khoom los yog transmitted rov qab mus rau qhov chaw nres tsheb relay chaw nres tsheb, optical fiber network, thiab lwm yam. Cov khoom yuav tsim kom muaj kev mus sij hawm ntev mus nrog lwm microwave, satellite, thiab optical fiber sib txuas lus kom lawv muaj ib tug xyaum thiab zoo duab transmission lawv. Lub ntsiab daim ntawv thov ntawm wireless duab transmission khoom ntawm COFDM tshuab yog: lub tsev thaiv ib puag ncig, vaj tse, sab nraum lub tsev, underground thiab hauv pem teb ntawm vaj tse; siv mobile; duab, duab aerial transmission, thiab lwm yam. Nws yog ib tug duab high-kev kawm wireless duab uas yog urgently ntxiv los ntawm kev ruaj ntseg pej xeem ruaj ntseg, tub rog, tub ceev xwm armed, kev tiv thaiv hluav taws, kws muaj txuj ci civil kws muaj txuj ci (kws muaj txuj ci civil kws muaj txuj), dej haus, maritime affairs, kev cai dab qhuas, xov tooj cua thiab TV thiab lwm industries ruaj ntseg, hais kom ua, lub hom phiaj reconnaissance, kev puas tsuaj, Nyob tshaj tawm hauv xov thiab lwm yam tasks transmission ntaus ntawv.
hanhsx wireless duab real-time transmission xyuas lawv adopts COFDM tshuab, Uas yuav xyuas kom ruaj khov transmission thiab real-time xyuas nyob rau hauv high-speed zog, los tiv thaiv fading thiab txuj kev cuam tshuam (mus cuag 150 km/ntxov), thiab muab high-definition broadcast-level DVD zoo duab, Muaj zog tsis-ntawm-pom transmission muaj peev xwm, Zoo tagnrho rau urban blocking tej ntaub ntawv hu ua tsis tshua muaj neeg nyuaj heev "hav zoov", tsis muaj antenna orientation. Cov khoom muaj cov cim hauv qab no: Audio thiab yees duab transmission, Duab real-time duab transmission, ntim tshaaj thiab transmitter, muaj zog, yooj ywm thiab yooj yim, siv tau los ntawm tes, encrypted transmission, tsis pub lwm tus paub, thiab qhov txuas transmission nyob deb li cas yuav mus txog 10KM-50KM.
Cov khoom no lug siv nyob rau hauv pej xeem ruaj ntseg, kev tiv thaiv hluav taws, tub ceev xwm khiav, kws muaj txuj ci kws muaj txuj ci thaum muaj xwm ceev, kev tswj tub ceev xwm, kev tiv thaiv, hluav taws kub ceev, dej nyab thiab dej nyab, Fais fab tuag thaum muaj xwm ceev, railway thaum muaj xwm ceev, maritime tub ceev xwm, hiav txwv yoos soj ntsuam, ciam teb kws muaj txuj ci, dock xyuas, kev tiv thaiv hluav taws, roj teb los tiv thaiv tub sab , Tub rog reconnaissance thiab lwm teb, suitable rau real-time mobile transmission thiab xyuas cov dluab zoo dluab nyob rau ntau txoj kev xws li urban cheeb tsam xws li urban chaw, caij ntuj no, roob.
