Txina COFDM Haririk gabeko Bideo Transmisore eta Hargailua factory supplier in Shenzhen

OFDM can well solve channel selective fading in multipath environment, but channel flat fading (hori da, the fading in which the amplitude of each carrier obeys the Rayleigh distribution) has not been well overcome. OFDM that uses channel coding to solve this problem is called COFDM (Coded OFDM). The basic principle is to combine the frequency selective fading channel (frequency domain) and the time-varying flat fading channel (time domain) together to form the time-frequency domain. In this domain, the signal to be modulated with a high bit rate is divided according to certain rules and then interleaved in time and frequency. Then they are connected with a convolutional code, so that the fading suffered by the coded data signal is statistically independent. If the signal suffers a negative echo loss at a certain carrier, statistically speaking, a positive echo will appear on another carrier, and the two compensate and cancel each other. Hori dela, the anti-error performance of the OFDM system is improved.

COFDM (maiztasun-zatiketa-multiplexazio ortogonal kodetua), the abbreviation of Coded Orthogonal Frequency Division Multiplexing, is currently the most advanced and most promising modulation technology in the world. Its basic principle is to convert the high-speed data stream into several sub-channels with lower transmission rate through serial-to-parallel conversion for transmission.

Kodetzea (C) means that the channel coding adopts a convolutional coding method with a variable coding rate to meet the protection requirements of data of different importance; Orthogonal Frequency Division (OFD) refers to the use of a large number of carriers (subcarriers), which have equal The frequency interval is an integer multiple of a basic oscillation frequency; multiplexing (M) means that multiple data sources are interleaved and distributed on the above-mentioned large number of carriers to form a channel.

1. In the middle of the last century, people proposed a multi-carrier communication scheme with frequency band aliasing, choosing mutually orthogonal carrier frequencies as subcarriers, which is what we call COFDM. Hau "orthogonality" refers to the exact mathematical relationship between carrier frequencies. According to this assumption, COFDM can not only make full use of channel bandwidth, but also avoid using high-speed equalization and anti-burst noise errors. COFDM is a special multi-carrier communication scheme. The information flow of a single user is serially/parallel converted into multiple low-rate code streams, and each code stream is sent with a subcarrier. Instead of using bandpass filters to separate subcarriers, COFDM uses Fast Fourier Transform (FFT) to select waveforms that remain orthogonal despite aliasing.
2. COFDM technology belongs to multi-carrier modulation (Multi-Carrier Modulation, MCM) teknologia. Some documents mix OFDM and MCM, which is actually not rigorous enough. MCM and COFDM are commonly used in 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.
3. 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, etc., based on the principle of the best balance between spectrum utilization and bit error rate. The COFDM technology uses adaptive modulation, and selects different modulation methods according to the quality of the channel. COFDM also adopts the coordinated working mode of power control and adaptive modulation. When the channel is good, the transmission power remains unchanged, and the modulation mode (such as 64QAM) can be enhanced, or the transmission power can be reduced when the modulation mode is low (such as QPSK).
4. COFDM technology is the basis of the HPA Alliance (HomePlug Powerline Alliance) industrial specification. It uses a discontinuous multi-tone technology to combine a large number of signals in different frequencies called carriers into a single signal to complete signal transmission. Because this technology has the ability to transmit signals under clutter interference, it is often used in transmission media that are susceptible to external interference or have poor ability to resist external interference.
5. COFDM is the abbreviation of Coded Orthogonal Frequency Division Multiplexing, which is the most advanced and most promising modulation technology in the world. Its practical value lies in supporting applications that break through the limit of line-of-sight. It is a technology that makes full use of radio spectrum resources and has good immunity to noise and interference. Diffraction and penetration of obstructions are COFDM technologies. core. Its basic principle is to convert the high-speed data stream into several sub-channels with lower transmission rate through serial-to-parallel conversion for transmission.
6. COFDM technology can separate multiple digital signals simultaneously and can operate safely around interfering signals. It is precisely because of this special signal "penetrating ability" that COFDM technology is deeply loved and welcomed by communication equipment manufacturers. COFDM technology can continuously monitor the sudden change of communication characteristics on the transmission medium. The ability of the communication path to transmit data will change with time. COFDM can dynamically adapt to it, and switch on and off the corresponding carrier to ensure continuous progress. successful newsletter. COFDM technology is especially suitable for use in high-rise buildings, densely populated and geographically prominent places, areas where signals are spread, and places where high-speed data is transmitted.

1. A large amount of data can also be sent under narrow bandwidth: COFDM technology can separate at least 1000 digital signals at the same time, and the ability to operate safely around interfering signals will directly threaten the CDMA technology that has become popular in the market today. The trend of further development and growth is precisely because of this special signal "penetrating ability" that makes COFDM technology popular and popular with European communication operators and mobile phone manufacturers, such as California Cisco Systems, New York Flarion Institute of Technology and Lucent Institute of Technology and others have begun to use this technology, and the Canadian Wi-LAN Institute of Technology has also begun to use this technology.
2. COFDM technology can continuously monitor the sudden change of communication characteristics on the transmission medium: Since the ability of the communication path to transmit data will change over time, COFDM can dynamically adapt to it and switch on and off the corresponding carrier To ensure continued successful communications;
3. This technology can automatically detect which specific carrier has high signal attenuation or interference pulse under the transmission medium, and then take appropriate modulation measures to enable the carrier at the specified frequency to communicate successfully;
4. COFDM technology is especially suitable for use in high-rise buildings, densely populated and geographically prominent places, and areas where signals are spread. Both high-speed data transmission and digital voice broadcasting hope to reduce the impact of multipath effects on signals.
5. It can effectively counter the interference between signal waveforms, and is suitable for high-speed data transmission in multipath environments and fading channels. When frequency selective fading occurs due to multipath transmission in the channel, only the subcarriers falling in the frequency band depression and the information carried by them are affected, and other subcarriers are not damaged, so the overall bit error rate performance of the system is much better many.
6. Through the joint coding of each subcarrier, it has strong anti-fading ability. The COFDM technology itself has already utilized the frequency diversity of the channel, if the fading is not particularly serious, there is no need to add a time domain equalizer. By jointly encoding each channel, the system performance can be improved.
7. COFDM technology is highly resistant to narrowband interference, because these interferences only affect a small part of the sub-channels.
8. The implementation method of OFDM based on IFFT/FFT can be selected;
9. The channel utilization rate is very high, 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.
10. The application of COFDM technology in wireless image transmission has the following unique advantages:
11. Applied in non-visible and obstructed environments, the excellent "diffraction" eta "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, select and test the sending and receiving points, adjust the direction of the antenna, and calculate the height of the antenna, etc. , the workload is very heavy and cumbersome, which not only directly restricts the transmission and reception of audio and video, but also greatly reduces the reliability and work efficiency of the system.
    COFDM wireless image equipment has completely changed this situation. Due to its technical characteristics such as multi-carrier, COFDM equipment has the advantages of "non-line-of-sight" eta "diffraction" transmisio. Realize the stable transmission of images, not affected by the environment or affected by the environment. The system adopts an omnidirectional antenna, which can set up a wireless transmission link in the shortest time. Eskuratze-muturra eta hartzaile-muturra ere libre mugi daitezke norabideak mugatu gabe. Sistema sinplea da, fidagarria, eta aplikazioan malgua.
12. Abiadura handiko mugimenduan denbora errealeko irudien haririk gabeko transmisiorako egokia da, eta mikrouhin-labea erabil dezake (mikrouhin digitala, espektro zabaleko mikrouhin-labea) eta haririk gabeko LAN ekipoak plataformetan, hala nola ibilgailuetan, ontziak, eta helikopteroak. Sistemaren arrazoi teknikoengatik, eskuratze terminala ezin da modu independentean gauzatu Eta hartzaileak denbora errealean irudiak transmititzen ditu abiadura handiko mugimenduan. Ibilgailuetan eta itsasontzietan mikrouhin-labea eta haririk gabeko LAN ekipoak erabiltzean hari gabeko irudiak transmititzeko, ohiko irtenbidea gehigarri bat konfiguratzea da "serbo egonkortzea" uhin elektromagnetikoen orientazioa bezalako arazoak konpontzeko gailua, jarraipena, eta egonkortzea, baina baldintza jakin batzuetan bakarrik erabil daiteke. Ingurunearen azpian puntu mugikorra puntu finkorako transmisioaz jabetzea, eta irudia askotan eten egiten da, transmisioaren eta harreraren eragina larriki eragiten duena. Ingeniaritza konplexua da, fidagarritasuna murrizten da, eta kostua oso altua da.
    Baina COFDM ekipoetarako, ez du gailu gehigarririk behar, eta finko-mugikorren artean erabil daiteke, mugikorra-mugikorra, eta oso egokia da plataforma mugikorretan instalatzeko, hala nola ibilgailuetan, ontziak, eta helikopteroak. Transmisioak ez ezik fidagarritasun handia du, baina kostu handiko errendimendua ere erakusten du.
13. Transmisio-banda zabalera handia da, bit-tasa altuko eta irudi kalitate handiko audio eta bideo transmisiorako egokia dena. Irudiaren bit-tasa, oro har, 4M bps baino handiagoa izan daiteke. Orokorrean mikrouhin digitalak eta espektro zabaleko mikrouhinen transmisio loturak, MPEG-2 kodeketa erabiltzen den arren, kanalak gehienbat 2M tasa hartzen du, hala nola, E1, horrela, deskodetutako irudiaren bereizmena 720×576ra iritsi daiteke, baina irudi konprimitutako kode-jarioa 1M besterik ez da ezkerretik eta eskuinera, ezin ditu audio- eta bideo-analisiaren osteko mutur hartzailearen eskakizun zehatzak bete, biltegiratze, eta edizioa.
    COFDM teknologiaren azpieramaile bakoitzak abiadura handiko modulazioa aukeratu dezake, hala nola QPSK, 16QAM, 64QAM, etc., eta kanal konbinatuaren tasa, oro har, 4M bps baino handiagoa da. Hori dela, Kalitate handiko codec irudiak adibidez 4:2:0 eta 4:2:2 MPEG-2n transmititu daiteke, muturraren hartzailearen irudiaren bereizmena 720 × 576 edo 720 × 480ra irits daiteke, eta kode korrontea 6M ingurukoa izan daiteke. Irudiaren kalitatea DVDaren hurbilekoa da, audio- eta bideo-analisiaren osteko mutur hartzailearen eskakizun zehatzak guztiz bete ditzakeena, biltegiratze, eta edizioa.
14. Ingurune elektromagnetiko konplexu batean, COFDM-k interferentziaren aurkako errendimendu bikaina du maiztasunaren desagerpen selektiboaren edo banda estuko interferentziaren eta seinale uhin formen arteko interferentziaren aurka.. Azpi-eramaile bakoitzaren kodeketa bateratuaren bidez, desagertzearen aurkako gaitasun handia du. Eramaile bakarreko sistemetan (esaterako, mikrouhin digitala, espektro zabaleko mikrouhin-labea, etc.), desagertze edo interferentzia bakar batek komunikazio-esteka osoa huts egitea eragin dezake, baina eramaile anitzeko COFDM sisteman, azpi-eramaileen zati txiki bat bakarrik oztopatzen da, eta azpieramaile hauek Kanalak erroreak zuzentzeko kodeak ere erabil ditzake akatsak zuzentzeko, transmisiorako bit errore-tasa baxua ziurtatzeko..

COFDM Haririk gabeko Transmisio Teknologiaren aplikazioa Bideo-zaintzan
COFDM teknologia erabiliz haririk gabeko irudien transmisio eskemak ikusmen-lerrorik gabeko transmisio ona du eta abiadura handiko transmisio mugikorren errendimendu ona du., eta denbora errealean DVD kalitateko irudiak eta soinuak eman ditzake. Lekuko zuzeneko audioa eta bideoa modu malgu eta azkar batean transmititu daitezke zuzenean ibilgailuan muntatutako edo eramangarriko ekipoen bidez edo komando zentrora itzul daitezke errelebo-estazio baten bidez., zuntz optikoko sarea, etc. Ekipamenduak distantzia luzeko loturak ezar ditzake beste mikrouhin batzuekin, satelite, eta zuntz optikoko komunikazio-ekipoak irudien transmisio-sistema praktiko eta eraginkor bat eraikitzeko. COFDM teknologiaren haririk gabeko irudiak transmititzeko ekipoen aplikazio ingurune nagusia da: hiri eraikuntza blokeatzeko ingurunea, eraikinen artean, eraikinen barruan eta kanpoan, lurpeko eta lurrazpiko eraikinen artean; mugikorrean erabiltzen da; itsasoko irudia, aireko irudien transmisioa, etc. Errendimendu handiko haririk gabeko irudia da, etxeko segurtasun publikoak premiazkoa duena, armada, polizia armatua, suteen babesa, aire defentsa zibila (defentsa zibila), uraren kontserbazioa, itsas gaiak, ohiturak, irratia eta telebista eta beste industria batzuk segurtasunean, eremuko komandoa, misioaren ezagutza, hondamendien erreskate, zuzeneko emisioa eta beste zereginak transmititzeko gailua.

hanhsx haririk gabeko irudiak denbora errealeko transmisioaren monitorizazio sistemak COFDM teknologia hartzen du, abiadura handiko mugimenduan transmisio egonkorra eta denbora errealeko monitorizazioa berma ditzakeena, desagertzearen aurkako eta bide anitzeko interferentziak (mugitzeko abiadura lor daiteke 150 km / h), eta definizio handiko emisio-mailako DVD kalitatezko Irudia eskaintzen, Ikusmen-lerroa ez den transmisio-gaitasun sendoa, Oso zaila deitzen den hiri-blokeo inguruneko aplikazioetarako aproposa "arroilaren komunikazioak", antena orientaziorik gabe. Produktuak honako ezaugarri hauek ditu: audio eta bideo transmisio digitala, irudien transmisioa denbora errealean, eskuratze eta igorle bolumen txikia, mugikortasun sendoa, malgua eta erosoa, eskuz erabil daiteke, transmisio zifratua, konfidentzialtasun ona, eta lotura transmisioaren distantzia 10KM-50KM izatera irits daiteke.

Produktua oso erabilia da segurtasun publikoan, suteen babesa, trafiko polizia, aireko defentsa zibileko larrialdia, hirigintza-kudeaketako legea betearaztea, ingurumena babesteko jarraipena, sute larrialdia, uraren kontserbazioa eta uholdeen kontrola, energia elektrikoko larrialdi, trenbide-larrialdia, itsas legea betearaztea, itsasoa zaintzeko ikuskapena, aduana-mugaren defentsa, kaian jarraipena, baso-suteen prebentzioa, petrolio eremuaren aurkako lapurreta , ezagutza militarra eta beste arlo batzuk, denbora errealean mugikorraren transmisiorako eta kalitate handiko irudiak monitorizatzeko egokia hainbat ingurune konplexutan, hala nola hiriguneetan, itsasoak, eta mendiak.