Ntxinä Transmisor ne receptor vídeo inalámbrico COFDM factory supplier in Shenzhen

OFDM can well solve channel selective fading in multipath environment, but channel flat fading (that is, 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. Ir, the anti-error performance of the OFDM system is improved.

COFDM (multiplexación ya división frecuencia ortogonal codificada), 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.

Coding (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, Ya jä'i propuso 'nar esquema comunicación multiportadora ko alias 'me̲i frecuencias, Ar nt'ets'i frecuencias portadoras mutuamente ortogonales komongu ar subportadoras, nä'ä ge'ä nä'ä llamamos COFDM. Nuna "ortogonalidad" ar refiere ar nthe matemática exacta ja ya frecuencias portadoras. Ir nge nuna ar supuesto, COFDM hingi Honto to aprovechar ja ar máximo ancho 'me̲i ar 'ñuu, pe 'nehe evite njapu'befi ecualización mextha ar velocidad ne ar errores mafi anti-ráfaga. COFDM ge 'nar esquema hontho comunicación multiportadora. Flujo ungumfädi Honto 'nar usuario ar bi pa̲ti jar serie yá paralelo jar múltiples flujos ar código xí hñets'i'i velocidad, ne ya flujo código ar envía ko 'nar subportadora. En lugar de utilizar filtros bi thogi 'me̲i da separar ya subportadoras, COFDM gi japu̲'be̲fi ar transformada ngut'a ar Fourier (FFT) pa seleccionar formas ar onda da permanezcan ortogonales a pesar de ar solapamiento.
2. Ar tecnología COFDM pertenece ar modulación multiportadora (Modulación multiportadora, MCM) Tecnología. 'Ra ya documentos mezclan OFDM ne MCM, nä'ä pe hingi ar suficientemente nä'ä riguroso. MCM ne COFDM ar utilizan comúnmente jar canales inalámbricos. Diferencia entre nu'u̲ es ke ar tecnología COFDM ar refiere específicamente ja ar división 'nar 'ñuu jar subcanales ortogonales, Gi pe̲ts'i 'nar mextha tasa utilización ar 'ñuu; Mente da MCM to da mäs nt'ot'e división canales.
3. Ar Nthuts'i ñut'i ar tecnología COFDM ar pe pa mejorar ar utilización ar espectro ar portadora, o da mejorar ar modulación ya multiportadoras. Ár característica ar da Kadu ar subportadora xí ortogonal entre hä, ja modo da espectro 'mefa xta modulación espectro ensanchado pa superponer ar entre hä, reduciendo nja'bu̲ ar interferencia mutua ja ya subportadoras. Ar nt'ot'e modulación utilizado ir nge ya portadora COFDM to da diferente. Nu'bu̲ portadora to da 'ñets'i 'na'ño nt'ot'e modulación ir nge ya 'na'ño nkohi ar 'ñuu, ngu BPSK, QPSK, 8Psk, 16QAM, 64QAM, etcetera., basado jár ndui xi hño ar equilibrio entre ár utilización ar espectro ne ar tasa bits erróneos. Ar tecnología COFDM gi japu̲'be̲fi modulación adaptativa, ne selecciona 'na'ño nt'ot'e ar modulación nä'ä mä ar hño ar ar 'ñuu. COFDM 'nehe adopta ar modo ar 'be̲fi coordinado control nts'edi ne modulación adaptativa. Nu'bu̲ ar 'ñuu ar za̲, Ár nts'edi transmisión permanece inalterada, ne ar modo modulación (ngu 64QAM) ar tsa̲ da mejorar, wa ár nts'edi transmisión ar tsa̲ da reducir nu'bu̲ modo modulación xí hñets'i'i (ngu QPSK).
4. Ar tecnología COFDM ar base ar Alianza HPA (Alianza HomePlug Powerline) Especificaciones industriales. 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. núcleo. 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" ne "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, etcetera. , 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 "'ñotho ar 'ñu visión" ne "diffraction" Transmisión. 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. The acquisition end and the receiving end can also move freely without being restricted by the direction. The system is simple, fidedigno, and flexible in application.
12. It is suitable for wireless transmission of real-time images in high-speed movement, and can use microwave (digital microwave, spread spectrum microwave) and wireless LAN equipment on platforms such as vehicles, buques, and helicopters. Due to technical system reasons, the acquisition terminal cannot be independently realized And the receiving end transmits images in real time during high-speed movement. When using microwave and wireless LAN equipment on vehicles and ships for wireless image transmission, the usual solution is to configure an additional "servo stabilization" device to solve problems such as electromagnetic wave orientation, tracking, and stabilization, but it can only be used under certain conditions. Realize the transmission of mobile point to fixed point under the environment, and the image is often interrupted, which seriously affects the effect of transmission and reception. The engineering is complex, the reliability is reduced, and the cost is extremely high.
    But for COFDM equipment, it does not need any additional devices, and it can be used between fixed-mobile, mobile-mobile, and is very suitable for installation on mobile platforms such as vehicles, buques, and helicopters. Not only the transmission has high reliability, but also shows high cost performance.
13. The transmission bandwidth is high, which is suitable for high bit rate and high image quality audio and video transmission. The image bit rate can generally be greater than 4M bps. In general digital microwave and spread spectrum microwave transmission links, although MPEG-2 encoding is used, the channel mostly adopts 2M rate, such as E1, so that the decoded image resolution can reach 720×576, but the image compressed code stream is only 1M Left and right, unable to meet the specific requirements of the receiving end for post-audio and video analysis, Almacenamiento, and editing.
    Each subcarrier of COFDM technology can choose high-speed modulation such as QPSK, 16QAM, 64QAM, etcetera., and the combined channel rate is generally greater than 4M bps. Ir, high-quality codec images such as 4:2:0 ne 4:2:2 in MPEG-2 can be transmitted, the image resolution of the receiving end can reach 720×576 or 720×480, and the code stream can be around 6M. The image quality is close to that of DVD, which can fully meet the specific requirements of the receiving end for post-audio and video analysis, Almacenamiento, and editing.
14. 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, etcetera.), 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.

Nt'ot'e tecnología transmisión inalámbrica COFDM jar videovigilancia
Esquema transmisión inalámbrica ar imágenes nä'ä gi japu̲'be̲fi ar tecnología COFDM pe̲ts'i 'nar hogu̲ma̲ rendimiento transmisión hinda 'ñu visión ne transmisión móvil mextha velocidad, ne ar tsa̲ da proporcionar imágenes ne ya nzu̲nt'i jar pa real ko ya DVD. Ar audio ne ar video vivo ja ar sitio ar xi ungumfädi bí flexible ne ngut'a ar Hmunts'i a través de equipos portátiles wa montados ja ar vehículo wa ungumfädi ar ar pengu̲hmäga̲ made ts'edi a través de 'nar estación retransmisión, Red fibra óptica, etcetera. Ar equipo to da t'ot'e enlaces xi maki mbi ko ma 'ra ya microondas, satélite, ne equipos comunicación ya fibra óptica pa gu̲ts'i 'nar ko ya transmisión imágenes práctico ne xi hño. Ar principal ar entorno ya nt'ot'e ja ya equipos transmisión inalámbrica imágenes ar tecnología COFDM: Nguu urbano da bloquea ar entorno, entre ar edificios, inside and outside of buildings, between underground and ground of buildings; used in mobile; sea image, aerial image transmission, etcetera. It is a high-performance wireless image that is urgently needed by domestic public security, army, Ar polisiya tsa, mfats'i ngatho ja ya incendios, civil air defense (mfats'i civil), conservación ar dehe, maritime affairs, aduana, radio and television and other industries in security, field command, mission reconnaissance, disaster rescue, live broadcast and other tasks transmission device.

hanhsx wireless image real-time transmission monitoring system adopts COFDM technology, which can ensure stable transmission and real-time monitoring under high-speed movement, anti-fading and multi-path interference (moving speed can reach 150 Km yá h), and provide high-definition broadcast-level DVD quality Image, strong non-line-of-sight transmission capability, ideal for urban blocking environment applications known as extremely difficult "Comunicaciones ar cañón", 'ñotho ar orientación antena. Ar producto pe̲ts'i nuya ya características: Transmisión ar 'bede audio ne video, Transmisión imágenes jar pa real, Pequeño volumen adquisición ne transmisor, Xí nze̲di movilidad, Flexible ne mahyoni, Ar tsa̲ da utilizar tso̲kwa mano, Transmisión encriptada, Hño confidencialidad, ne mbi transmisión ar enlace tsa̲ da alcanzar ya 10 km bí 50 ar km.

Ar producto ar ampliamente utilizado jar ntsuni pública, mfats'i ngatho ja ya incendios, Ar polisiya Tránsito, Emergencia mfats'i Aérea Civil, Nt'ot'e ar ley gestión urbana, Monitoreo ár mfa̲ts'i ar nt'uni mbo jar ximha̲i, emergencia ya incendio, Conservación ar dehe ne control inundaciones, Emergencia energía eléctrica, Emergencia ferroviaria, Nt'ot'e ar ley marítima, Inspección ja ya marítima, Mfats'i ar frontera aduanera, Monitoreo muelles, Prevención incendios forestales, Antirrobo yacimientos petrolíferos , Reconocimiento militar ne ma'ra ya campos, Mfädi pa ar transmisión móvil jar pa real ne monitoreo ar imágenes mextha hño ja yá entornos complejos, komongu áreas urbanas, Mares, ne t'o̲ho̲.