China Atagba fidio Alailowaya COFDM ati olugba olupese ile-iṣẹ ni Shenzhen

OFDM le yanju daradara ikanni yiyan ipare ni multipath ayika, ṣugbọn ikanni alapin ipare (ti o jẹ, awọn ipare ninu eyi ti awọn titobi ti kọọkan ti ngbe gbọràn Rayleigh pinpin) ko ti bori daradara. OFDM ti o nlo ifaminsi ikanni lati yanju iṣoro yii ni a pe ni COFDM (Ti ṣe koodu OFDM). Awọn ipilẹ opo ni lati darapo igbohunsafẹfẹ yiyan iparẹ ikanni (ibugbe igbohunsafẹfẹ) ati awọn akoko-orisirisi alapin ipare ikanni (akoko ašẹ) papo lati dagba awọn akoko-igbohunsafẹfẹ ašẹ. Ni aaye yii, ifihan agbara lati ṣe atunṣe pẹlu oṣuwọn bit giga ti pin ni ibamu si awọn ofin kan ati lẹhinna interleaved ni akoko ati igbohunsafẹfẹ. 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. nitorina, the anti-error performance of the OFDM system is improved.

COFDM (se amin orthogonal igbohunsafẹfẹ pipin multiplexing), 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) tumọ si pe ifaminsi ikanni gba ọna ifaminsi convolutional pẹlu oṣuwọn ifaminsi iyipada lati pade awọn ibeere aabo ti data ti o ṣe pataki; Pipin Igbohunsafẹfẹ Orthogonal (OFD) ntokasi si awọn lilo ti kan ti o tobi nọmba ti ẹjẹ (subcarriers), eyi ti o ni dogba Aarin igbohunsafẹfẹ jẹ nọmba odidi kan ti igbohunsafẹfẹ oscillation ipilẹ; multiplexing (M) tumọ si pe awọn orisun data lọpọlọpọ ti wa ni interleaved ati pinpin lori nọmba nla ti a mẹnuba loke ti awọn gbigbe lati ṣe ikanni kan.

1. Ni arin ti o kẹhin orundun, eniyan dabaa kan olona-ti ngbe ibaraẹnisọrọ eni pẹlu igbohunsafẹfẹ iye aliasing, yiyan awọn loorekoore ti ngbe orthogonal ti ara ẹni bi awọn onijagidijagan, eyiti a pe ni COFDM. Eyi "orthogonality" n tọka si ibatan mathematiki gangan laarin awọn igbohunsafẹfẹ ti ngbe. 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) ọna ẹrọ. 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, ati be be lo, 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. mojuto. 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. O ti wa ni gbọgán nitori ti yi pataki ifihan agbara "tokun agbara" pe imọ-ẹrọ COFDM nifẹ pupọ ati itẹwọgba nipasẹ awọn olupese ẹrọ ibaraẹnisọrọ. Imọ-ẹrọ COFDM le ṣe atẹle nigbagbogbo iyipada lojiji ti awọn abuda ibaraẹnisọrọ lori alabọde gbigbe. Agbara ti ọna ibaraẹnisọrọ lati atagba data yoo yipada pẹlu akoko. COFDM le ṣe adaṣe ni agbara si rẹ, ki o si tan-an ati pa ẹrọ ti o baamu lati rii daju ilọsiwaju ilọsiwaju. aseyori iwe iroyin. Imọ-ẹrọ COFDM jẹ paapaa dara fun lilo ninu awọn ile giga, densely kún ati geographically oguna ibi, agbegbe ibi ti awọn ifihan agbara ti wa ni tan, ati awọn aaye nibiti a ti gbe data iyara-giga.

1. A o tobi iye ti data le tun ti wa ni rán labẹ dín bandiwidi: Imọ-ẹrọ COFDM le ya sọtọ ni o kere ju 1000 awọn ifihan agbara oni-nọmba ni akoko kanna, ati agbara lati ṣiṣẹ lailewu ni ayika awọn ifihan agbara kikọlu yoo ṣe ewu taara imọ-ẹrọ CDMA ti o ti di olokiki ni ọja loni.. Awọn aṣa ti siwaju idagbasoke ati idagbasoke jẹ gbọgán nitori ti yi pataki ifihan agbara "tokun agbara" ti o jẹ ki imọ-ẹrọ COFDM jẹ olokiki ati olokiki pẹlu awọn oniṣẹ ibaraẹnisọrọ Yuroopu ati awọn olupese foonu alagbeka, gẹgẹ bi awọn California Cisco Systems, New York Flarion Institute of Technology ati Lucent Institute of Technology ati awọn miiran ti bẹrẹ lati lo imọ-ẹrọ yii, ati Ile-iṣẹ Imọ-ẹrọ Wi-LAN ti Ilu Kanada ti tun bẹrẹ lati lo imọ-ẹrọ yii.
2. Imọ-ẹrọ COFDM le ṣe atẹle nigbagbogbo iyipada lojiji ti awọn abuda ibaraẹnisọrọ lori alabọde gbigbe: Niwọn igba ti agbara ti ọna ibaraẹnisọrọ lati atagba data yoo yipada ni akoko pupọ, 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. Imọ-ẹrọ COFDM jẹ paapaa dara fun lilo ninu awọn ile giga, densely kún ati geographically oguna ibi, 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, nikan awọn onijagidijagan ti o ṣubu ni ibanujẹ ẹgbẹ igbohunsafẹfẹ ati alaye ti o gbe nipasẹ wọn ni o kan, ati awọn miiran subcarriers ko baje, nitorinaa iṣẹ oṣuwọn aṣiṣe aṣiṣe gbogbogbo ti eto naa dara julọ ọpọlọpọ.
6. Nipasẹ awọn ifaminsi apapọ ti kọọkan subcarrier, o ni o ni lagbara egboogi-ipare agbara. Imọ-ẹrọ COFDM funrararẹ ti lo tẹlẹ iyatọ igbohunsafẹfẹ ti ikanni naa, ti o ba ti parẹ ni ko paapa pataki, ko si iwulo lati ṣafikun oluṣeto agbegbe akoko kan. Nipa fifi koodu paiwọn ikanni kọọkan, iṣẹ eto le dara si.
7. Imọ-ẹrọ COFDM jẹ sooro pupọ si kikọlu okun dín, nitori awọn kikọlu wọnyi nikan kan apakan kekere ti awọn ikanni iha.
8. Ọna imuse ti OFDM ti o da lori IFFT/FFT ni a le yan;
9. Oṣuwọn iṣamulo ikanni ga pupọ, 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" ati "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, yan ati idanwo awọn aaye fifiranṣẹ ati gbigba, satunṣe awọn itọsọna ti awọn eriali, ki o si ṣe iṣiro awọn iga ti awọn eriali, ati be be lo. , Ẹ̀rù iṣẹ́ náà wúwo gan-an, ó sì wúwo, eyiti kii ṣe taara taara ni ihamọ gbigbe ati gbigba ohun ati fidio, ṣugbọn tun dinku igbẹkẹle ati iṣẹ ṣiṣe ti eto naa.
    Awọn ohun elo aworan alailowaya COFDM ti yi ipo yii pada patapata. Nitori awọn abuda imọ-ẹrọ rẹ gẹgẹbi ọpọlọpọ ti ngbe, COFDM ẹrọ ni o ni awọn anfani ti "ti kii-ila-ti-oju" ati "diffraction" gbigbe. Ṣe idanimọ gbigbe awọn aworan iduroṣinṣin, ko ni ipa nipasẹ ayika tabi ni ipa nipasẹ ayika. Eto naa gba eriali omnidirectional, eyi ti o le ṣeto ọna asopọ gbigbe alailowaya ni akoko kukuru julọ. Ipari imudani ati ipari gbigba le tun gbe larọwọto laisi ihamọ nipasẹ itọsọna naa. Eto naa rọrun, gbẹkẹle, ati rọ ninu ohun elo.
12. O dara fun gbigbe alailowaya ti awọn aworan akoko gidi ni gbigbe iyara giga, ati ki o le lo makirowefu (oni makirowefu, itankale julọ.Oniranran makirowefu) ati ohun elo LAN alailowaya lori awọn iru ẹrọ bii awọn ọkọ, awọn ọkọ oju omi, ati awọn baalu kekere. Nitori awọn idi eto imọ-ẹrọ, ebute ohun-ini ko le ṣe aṣeyọri ni ominira Ati opin gbigba n gbe awọn aworan ni akoko gidi lakoko gbigbe iyara giga. Nigba lilo makirowefu ati ohun elo LAN alailowaya lori awọn ọkọ ati awọn ọkọ oju omi fun gbigbe aworan alailowaya, ojutu deede ni lati tunto afikun "servo idaduro" ẹrọ lati yanju awọn iṣoro bii iṣalaye igbi itanna, ipasẹ, ati imuduro, 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, awọn ọkọ oju omi, ati awọn baalu kekere. 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, ibi ipamọ, and editing.
    Each subcarrier of COFDM technology can choose high-speed modulation such as QPSK, 16QAM, 64QAM, ati be be lo, and the combined channel rate is generally greater than 4M bps. nitorina, high-quality codec images such as 4:2:0 ati 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, ibi ipamọ, 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, ati be be lo), 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.

Application of COFDM Wireless Transmission Technology in Video Surveillance
The wireless image transmission scheme using COFDM technology has good non-line-of-sight transmission and high-speed mobile transmission performance, and can provide real-time images and sounds of DVD quality. The on-site live audio and video can be transmitted flexibly and rapidly directly through vehicle-mounted or portable equipment or transmitted back to the command center through a relay station, optical fiber network, ati be be lo. The equipment can establish long-distance links with other microwave, satẹlaiti, and optical fiber communication equipment to build a practical and effective image transmission system. The main application environment of wireless image transmission equipment of COFDM technology is: urban building blocking environment, between buildings, inside and outside of buildings, between underground and ground of buildings; used in mobile; sea image, aerial image transmission, ati be be lo. It is a high-performance wireless image that is urgently needed by domestic public security, army, olopa ologun, ina Idaabobo, ilu air olugbeja (civil defense), itoju omi, maritime affairs, Awọn kọsitọmu, 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 / 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 "canyon communications", without antenna orientation. The product has the following characteristics: audio and video digital transmission, real-time image transmission, small volume of acquisition and transmitter, strong mobility, flexible and convenient, can be used by hand, encrypted transmission, good confidentiality, and the link transmission distance can reach 10KM-50KM.

The product is widely used in public security, ina Idaabobo, traffic police, civil air defense emergency, urban management law enforcement, environmental protection monitoring, fire emergency, water conservancy and flood control, electric power emergency, railway emergency, maritime law enforcement, sea surveillance inspection, customs border defense, dock monitoring, forest fire prevention, oil field anti-theft , military reconnaissance and other fields, suitable for real-time mobile transmission and monitoring of high-quality images in various complex environments such as urban areas, awọn okun, ati oke-nla.