Friday, April 15, 2011

College】 【weak and analog video Optical Digital Optical difference】..

<br> in people's modern life and on the job, video surveillance systems have been widely used in optical fiber transmission-driven signal transmission. .The main advantages of optical fiber transmission: <BR> (1) low loss signal transmission, transmission distance. .Multi-mode fiber up to 5 km 80 km using single mode fiber and even farther; <BR> (2) TV signal has a wide frequency band, long-distance transmission is very difficult. .Optical fiber transmission of video signals, the transmission bandwidth of up to several hundreds of megabytes kilometers. .Can guarantee long-distance transmission of high signal to noise ratio, without high-frequency compensation. .This is a conventional cable can not match. .<BR> (3) strong anti-interference, electromagnetic radiation, no signal leakage, no ground and short circuit problems, the system power consumption. .<BR> (4) optical fiber transmission, long life, ordinary video cables up to 10-15 years, 30-50 years-long cable life. .<BR> Followed the highway, transportation, electronic police, surveillance, security, industrial automation, power, customs, water, banking and other areas of the video images, audio, data, Ethernet, telephone Optical begin .generally a large number of applications. .Early analog FM, AM, PM Optical in the market a considerable proportion of its transmission is baseband video, audio, data and other signals at a carrier frequency modulated by the firing Optical Fiber Transmission ., and then through the other end of the receiver to demodulate the Optical and restore into the corresponding baseband video, audio, data signals. .The domestic and foreign projects start large number of applications is the digital multi-channel Optical analog baseband video, audio, data, high-resolution digital, form a high-speed digital stream, then multiple multiplexed digital streams, through .Optical launch launch, and then the other end of the receiver by Optical receiving, demultiplexing, digital signal restored to separate ways, and through the digital to analog conversion (A / D analog-digital conversion) revert to analog video, audio, .data. .From the current market situation, the simulation Optical has gradually withdrawn from the market, and Digital Optical began mushrooming popularity in the market, a number instead of Moni, which is the optical fiber communication technology history of significant trends. .Optical transmission of digital signals with high quality, no analog frequency modulation, phase modulation, amplitude modulation Optical multi-channel signal transmission when the crosstalk with serious susceptible to environmental interference, poor transmission quality, long-term disadvantage of poor stability, .So many large and key projects has been widely used Digital Optical. .<BR> Optical and Digital Optical analog video what difference, which is the concern of many users, this paper discusses the following aspects are as follows: <BR> 1, optical fiber transmission signals in a different way .<BR> the name suggests, the simulation Optical emission of light on the head signal is modulated analog optical signal, which the carrier with the analog input signal amplitude, frequency, phase change caused by optical signal amplitude, frequency, phase changes are known as AM, FM ., Optical phase modulation. .The Digital Optical emission of light on the head signal is a digital signal that is 0 or 1 corresponds to the optical signal of strong and weak two states, different combinations of 0 and 1 represent different range of video, audio, and data signals. .<BR> 2, analog signal transmission input and output handling <BR> not the same, whether analog, digital optical transceiver, baseband input video, audio, and data signals must be processed. .The analog AM Optical, treatment is to video, audio, data on a high-frequency carrier signal amplitude modulation, the magnitude of the high frequency carrier signal with the video, audio, data rate changes; and digital light .client machine to the input baseband video, audio, data, high-resolution analog - digital converter, such as 1Vp-p amplitude range of range of the signal to digital signal using 12bits, said, 1V so into 4096, so after the analog-digital conversion .maximum voltage amplitude error caused by the 1/4096V (about 2.5mV), the error voltage is called quantization error voltage, the voltage amplitude value from a variety of 0V, 1/4096V, 2/4096V ... correspond to the maximum number of 1V .encoded 000000000000,000000000001,000000000010 ... 111 111 111 111. .Direct control of digital code signals emitted light signal head strong and weak two states (corresponding to 0 or 1), then the digital code received Optical digital - analog conversion, restored to the original baseband video, audio, data, .signal. .<BR> 3, dealing with different ways, causing the video, audio, and data signals signal distortion, aberration, interference due to the different simulation Optical <BR> for AM, FM, phase modulation, so the magnitude of the change in analog signal .and the carrier signal caused by amplitude modulation, frequency, phase changes correspond to the linear relationship between whether a good or bad to be the key Optical quality, so far, it is difficult to achieve true linear modulation, non-linear bound .cause signal distortion; also modulated carrier signal is also a good optical signal modulation, the nonlinear optical signal is also a very important factor, is well known that the nonlinear optical devices and the ambient temperature changes, voltage stability, light emission .Power has a great influence, it is required in the production of optical devices for 7-10 days of thermal cycling aging, and so screening process, aging, testing can only do this kind of change control in a certain range; optical signal in optical fiber .in the long haul, it will cause attenuation of optical signal power, transmission frequency shift, phase distortion, the same optical signal dispersion can also lead to optical signal distortion; optical signal reaches the receiver, the received optical devices still cause nonlinear distortion, by .photoelectric conversion into analog signals after the demodulation, modulation and demodulation will produce the same non-linear distortion. .So comprehensive simulation Optical, from the input signal modulation - electro-optic conversion - light output - energy conversion - the process of demodulation of these five would give rise to non-linear distortion, which signal distortion is inherent distortion, so it must not be eliminated .Therefore, the simulation Optical transmission of video images, audio quality, the effect of the data difficult to achieve very satisfactory results. .Optical digital only analog-digital conversion is only the quantization error (such as 1V when the video signal 12bits only 2.5mv), enough to cause signal distortion. .<BR> 4, simultaneous multi-channel signal intermodulation distortion caused by <BR> monitoring applications in the field, the user may have many various signals, such as video, audio, data, Ethernet, telephone or other user-defined .signals, each signal were used to transmit a pair of Optical inevitably expensive, so in order to improve fiber efficiency, reduce costs, the various signals to be multiplexed in the optical transceiver to a pair or a .optical fiber transmission. .On FM, AM, PM Optical speaking, 10/100M Ethernet signal or multiple transmit telephone signals is difficult to achieve high-speed, multi channel video or audio signal mixing frequency modulation, amplitude modulation, phase modulation in a .A carrier is bound to cause a variety of images, intermodulation interference. .So there were many well-known on the market of foreign brand FM, AM, PM Optical multi-channel video, audio, and data transmission often occurs with the phenomenon of interference, these instability phenomena are analog modulation technique has long been the .and difficult to solve the inherent problems and shortcomings. .So Analog Optical signal transmission capacity is limited, generally not more than 4 simultaneous signals. .The Digital Optical transmission of digital signals, it is easy to reuse and large-capacity interference does not occur. .Such as Shenzhen, South China Technology Co., Ltd all-digital Optical, can achieve up to 128 video, audio, data, Ethernet, telephone on the same fiber transmission without any crosstalk. .<BR> 5, the stability of the different analog modulation <BR> Optical modulation due to carrier, carrier and the shaved head is susceptible to environmental temperature. .The transfer quality varies with the shortcomings of the environment. .Because of such shortcomings, some large, important projects is concerned, the maintenance of Optical simulation has become a cause headache, which also brought a lot of contractors or owners of great dissatisfaction. .So a number of important projects selected Digital Optical is a wise choice. .<BR> 6, prices vary <BR> not the same as architecture, analog and digital Optical Optical slightly different prices, in general, single-channel video, audio, and data over a single Digital Optical .Analog Optical pricier, more than four-way video, audio, data, Optical Digital Optical contrast is much cheaper than analog, and that the transmission is much higher than analog video performance. .Therefore, the Digital Optical Optical cost-effective than analog. .<BR>.

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