The application of optical fiber transmission technology in the intelligent system of the community <br> In the era of rapid development of information, the close cooperation of communication technology, computer technology and multimedia technology has given a powerful impetus to the development of the international community and the world economy. Transmission has undoubtedly become the focus of attention. Since the concept of fiber-optic communication was introduced in 1966, it has begun to develop rapidly. It plays an important role in constituting social information infrastructure and promoting the development of social science and technology. Today, the optical fiber transmission network is almost all over the world, and has become the main transmission mode of communication networks such as telecommunications, broadcasting and television, and computer networks. Because of the numerous advantages of fiber-optic transmission systems, it has won the favor of today's technology society. The fiber optic transmission system was used for long-distance telecommunications transmission at the beginning, and the radio and television system and computer network communication were rarely used in other aspects. At present, many companies at home and abroad have developed visual, audio and data optical transceivers for intelligent control systems and security systems based on the characteristics of optical fiber transmission, which has promoted the rapid development of the security community intelligent system.
Features and transmission principles of optical fiber transmission <br> Optical fiber transmission has the advantages of small attenuation, wide frequency band, strong anti-interference, high safety performance, small size and light weight, so it is incomparable in long-distance transmission and special environment. The advantages. The transmission medium is an important factor in determining the transmission loss, which determines the distance required to transmit the signal. The optical fiber as the transmission medium of the optical signal has the characteristics of low loss; the frequency band of the optical fiber can reach above 1.0 GHz, and the bandwidth of the general image is only 8 MHz. The image of one channel is more than enough to transmit by one core fiber, and it is more advantageous in transmitting voice, control signal or contact signal; the carrier in optical fiber transmission is light wave, and the light wave is electromagnetic wave with extremely high frequency, which is far more than that used in radio wave communication. The frequency is high, so it is not disturbed. And the glass material used in the optical fiber is non-conductive, and will not generate sparks due to disconnection, lightning strikes, etc., so it is safe and suitable for occasions such as flammable and explosive.
The optical fiber transmission system is mainly composed of three parts: a light source (also called an optical transmitter), a transmission medium, and a detector (also called an optical receiver). In the optical fiber transmission between computer networks, the work of the light source and the detector is generally completed by using a fiber optic transceiver, which is simply a device for connecting a twisted pair and an optical fiber, and its function is to twist the twisted pair. The transmitted signal is converted into a signal (optical signal) that can be transmitted through the optical fiber. Of course, it is also bidirectional. It can also convert the signal transmitted by the optical fiber into a signal that can be transmitted in the twisted pair to realize data transmission between the networks. In the ordinary video, audio, data and other transmission processes, the work of the light source and the detector is generally completed by the optical transceiver. The optical transceiver is a device that converts multiple E1 signals into optical signals and transmits them. The so-called E1 is a trunk line. The data transmission standard, the standard rate in China and Europe is 2.048Mbps, and the main function of the optical transceiver is to realize the electro-optical 'optical-electrical conversion. The conversion signal is divided into an analog optical transceiver and a digital optical transceiver. Therefore, the optical fiber transmission system can be classified into a digital transmission system and an analog transmission system according to transmission signals. The analog transmission system simulates the intensity of the light and changes the input signal into a continuous change in the amplitude (frequency or phase) of the transmitted signal. The digital transmission system converts the input signal into a "1", "0" pulse signal, and uses it as a transmission signal to be restored to the original signal at the receiving end. Of course, the equipment required varies with the fiber transmission signal. As a transmission medium, optical fiber is an important factor in optical fiber transmission systems. It can be classified in different ways: According to the transmission mode: Light is transmitted only along the inner core of the fiber, and only the main mode is transmitted as a single-mode fiber (Single-Mode). There are multiple modes of transmission in the fiber, which we call multimode.
Single mode fiber optic cable multimode fiber optic cable <br> According to the core diameter: slowly variable multimode fiber, slowly variable multimode fiber and slowly variable single mode fiber are divided according to the refractive index distribution of the fiber core: step fiber (Step Index fiber), referred to as SIF; Graded fiber, GIF; ring fiber; W fiber. Fiber optic cable: The connection between point-to-point fiber optic transmission systems is through fiber optic cables. The cable has one fiber (called single fiber), two fibers (called double fiber), or more.
Optical transmission technology in engineering applications <br> computer networks of optical fiber transmission <br> in our ordinary computer network twisted pair is widely used, such as in a home, an office building, are using double Stranded wires to network. However, the twisted pair can only transmit data within a distance of 100 meters. If it exceeds 100 meters, the data transmission speed and traffic will be seriously affected. Therefore, we need to use fiber-optic transmission. The fiber can realize the network connection with the longest distance of 100 kilometers, and has the advantage that the twisted pair can't match in terms of information transmission and security. In the residential and home networks, there are many connections that are not more than 100 meters. We still use twisted pairs, and fiber optic connections are used between the two points over 100 meters.
Optical fiber transmission between networks <br> Of course, the way optical transceivers are used is not just this one, users can use it according to their actual situation.
Optical fiber transmission of ordinary video, audio, data and other signals <br> In the current engineering applications, the transmission of video images in the surveillance system has been widely used in optical fiber transmission. In the field of traffic management, closed-circuit television monitoring, security, industrial automation, power and other fields, video, audio, data and other optical transceivers began to be widely used. In the initial stage of optical fiber transmission, the analog optical transceiver occupies a considerable proportion in the market. The transmission method is to modulate the video, audio, data and other signals of the baseband on a carrier frequency, transmit the optical fiber through the transmitting optical transceiver, and then receive through the other end. The optical transceiver performs demodulation and restores the corresponding baseband video, audio, and data signals. With the wide application of digital transmission, digital optical transceivers have been widely used in engineering at home and abroad. Digital optical transceivers use high-resolution digitization of video, audio and data of multi-channel analog baseband to form high-speed digital streams and multi-channel digital streams. It is multiplexed, transmitted by the transmitting optical transceiver, then received by the receiving optical transceiver at the other end, demultiplexed, restored to various digital signals, and then restored to analog video and audio by digital analog conversion (A/D analog-to-digital conversion). ,data. According to the current market situation, analog optical transceivers have gradually withdrawn from the market, and digital optical transceivers have begun to spread in the market. Digital transmission instead of analog transmission is a significant development trend of optical fiber communication technology.
Due to the advantages of optical fiber transmission, applications for optical transceivers are becoming more widespread. There are more and more applications in the project. The internal long distance and local area data communication, the network connection in the community, the remote line unit in the public switched telephone network, and the network terminal of the PABX group road in the network. Access to the network for general signal transmission and more. At present, the most widely used aspects of optical transceivers are long distance and data transmission. In the fields of security, transportation, banking, and the like, optical transmission technology is used to transmit video signals remotely. In addition, optical transceivers are widely used in many fields such as remote video conferencing, distance learning, and communication.
Optical fiber transmission in the intelligent system of the community <br> With the development of information technology, people's requirements for living environment have increased, and the intelligent construction of the community has gradually become a hot topic. Using computer technology, network communication technology, and multimedia technology to establish a multimedia integrated information exchange system between residents and service centers, residents and the outside world, providing an efficient and convenient service condition for the property management center, providing residents with a safe, Comfortable and convenient modern living environment. The construction of the community system network will become an important part of the construction of intelligent communities. The network system mainly includes a community broadband network system: a connection between a resident computer and a computer and the Internet.
Closed-circuit television monitoring system: mainly in the main entrance of the community, parking lot entrances and exits, elevators and main passages in the community, installing a TV monitoring system, implementing 24-hour surveillance and video recording, the monitoring center personnel can pass the monitoring center The TV screen can adjust the situation at any time. Once there is an alarm, it can be processed in time. At the same time, the recorded video can provide valuable image evidence for the police.
Video intercom system: install video intercom system at the entrance and exit of the community, the door of the residential building unit, and the door of the household. When the visitor comes to the entrance and exit of the community, the security call calls the visited user to confirm that someone is at home and the resident confirms the visitor. After the identity, the visitor can enter the community. At the door of the unit and at the door of the household, the visitor calls the household, and the household can enter the household unit or the household by remotely opening the electric lock after the second confirmation. The video intercom system can also be networked with the community monitoring center. When there are any alarms or special events, you can get in touch at any time.
Anti-theft alarm system: install infrared in the wall of the community, install infrared, door magnet, smoke, gas and other devices in the household. Once the corresponding alarm is found, the alarm information is transmitted to the management center through the intelligent terminal equipment. The security personnel can Promptly deal with it in a timely manner. Remote alarms are also available.
Home Intelligent System: A system that connects voice, video, Internet services, etc. through intelligent terminal devices to realize visual intercom, alarm and intelligent control of home electrical equipment.
Smart Card (IC Card) Management System: Replaces personal documents and cash payment methods used in community management and life with IC cards. Realizing the "one card" function of identity management and control of entrance and exit management, improving the living standard of residents and making property management more automated. The management center can control all the cards to make them effective or invalid in the security system, which is conducive to security. The management center can issue card encryption, logout and report loss for all cards.
There are also cable television systems, cell information systems, and so on. The signals transmitted in each system are different. The transmitted signals have analog signals as well as digital signals. For example, in closed-circuit television monitoring systems and video intercom systems, the transmitted analog signals mainly include audio signals and video signals. Digital signal transmission is becoming more and more popular, mainly including audio data, video data, and communication data. In the current community intelligence, the community requires an automated system for centralized management. Most of the network construction of the community adopts the mode of centralized management of the area plus the central area. The transmission of signals in the small area is mostly transmitted by means of twisted pair and coaxial cable transmission, and the transmission signals in the small area are concentrated to a "point". . The connection between the area and the area and between the area and the management center is equivalent to connecting the points. The connection method is usually different depending on the distance between the points. In the small area, the transmission of each signal can meet the requirements of the system by coaxial cable or twisted pair. However, with the development trend of large-scale and intelligent community, the functional requirements of each system are improved, and the central management requirements are required. To focus on intelligence. The connection between the area and the area, and the connection between the areas and the general management center, the transmission of video, audio and control data by conventional (coaxial or twisted pair transmission) is difficult to meet the system requirements. If high-quality images or sounds are not obtained in the presence of strong electrical interference or other conditions, even if a video signal amplifier or audio amplifier is added, effective transmission of video images and sounds can be ensured within a short distance. In the case where the transmission line distance is long, no matter how many signal video amplifiers are added, the image or sound signal is also attenuated, and even an image or sound signal cannot be obtained. This requires the use of fiber-optic transmission technology, fiber transmission solves all the problems, in the analog signal transmission part, the use of optical transceivers, the use of optical fiber for signal transmission, thus solving the loss of audio and video long-distance transmission. And far superior to coaxial cable transmission in anti-interference and security. In the digital signal transmission section, mainly the connection between the tile area and the tile area and the connection between each tile area and the general management center. A fiber optic transceiver is used to connect between cell broadband networks. Digital transmission is carried out to achieve the best requirements for the transmission band and safety performance of the signal. At present, the video, audio and control data in the community intelligentization have adopted a large number of optical fiber transmission technologies, and the optical fiber has been widely used in systems such as broadband network connection, closed circuit television monitoring system, video intercom system, and home intelligence.
Optical fiber transmission technology has been a good example in the community intelligent system. The signal transmission in the long-distance system is more widely used, such as SD-980 intelligent building video intercom and alarm network of Vision Technology Co., Ltd. Control system, which is a modern community-based intelligent video intercom network system developed by single-chip microcomputer control technology, video surveillance technology, digital communication technology, telephone technology and wireless anti-theft alarm technology. The whole system consists of three main parts: the security management center, the unit door access control host, and the indoor indoor extension. The system uses the SD-980M2/SD-980M3 management center and the central computer as the management and control center of the whole system, and connects the unit systems through the signal converter. A variety of functions such as calling, intercom, monitoring, unlocking, information release, and multi-function alarms. The system uses optical fiber transmission technology for long-distance video processing. In the past, the conventional video transmission uses coaxial cable. Due to the serious attenuation of the signal during the long-distance image transmission of the coaxial cable, the video intercom and the active monitoring image are not required, and the signal is transmitted over a long distance. There are many external interferences, such as video connections between the host, the occupants, and the management center. The SD-980 system uses the optical transceiver in the long-distance transmission process of the video to convert the analog image signal transmitted by the system into an optical signal. The optical signal is transmitted to the other end through the optical fiber, and the other end converts the optical signal into an analog image through the optical transceiver. The signal is input to the extension display. This greatly reduces the attenuation of the image signal and greatly improves the anti-interference. And in engineering use, wiring is more convenient, and fault detection is easier.
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Schematic diagram of SD-980 system <br> In the SD-2000Basic system of Vision Technology Industrial Co., Ltd., the international common TCP/IP transmission protocol user group management and open network structure are adopted. The video, audio, and control signals travel together in the broadband network of the cell, and the audio and video signals are compressed and converted into digital signals for transmission. The SD-2000Basic system still uses the original 980 system as a subsystem, and the backbone network uses Ethernet (community broadband/local area network) networking. The management center is replaced by a multimedia computer. All operations are performed on the computer. When communicating with the host computer, the image is directly displayed on the computer display. The management center computer directly accesses the backbone network through a hub or switch. The 980 subsystem is connected to the network by the access server (SD-2000AS01). The system divides the cell into several pieces, and the subsystem signals of each area are collectively compressed to the access server. The subsystem signals include audio signals, video signals, control signals, alarm signals, cell information and other signals. The access server accesses the network, and optical fiber transmission technology is adopted between the networks. A fiber optic transceiver is used between the switch and the switch and between the access server and the switch, converting the five types of line (twisted pair) signals of the ordinary network connection into optical signals transmitted in the optical fiber, and the optical signals at the other end. Converted to a signal transmitted in a Category 5 line. This makes the system have the characteristics of high speed, large system capacity, strong system expansion, simple construction and convenient operation.
Of course, the application of optical fiber transmission technology in cell intelligent is not only these, but also widely used in other systems, video surveillance technology, remote network monitoring, alarm and information transmission.
The advantages of optical fiber transmission technology make its own development more rapid. In the digital optical fiber transmission system, the nonlinearity of the light source has little influence on the digital code stream, and it is easy to adopt some coding error correction method in digital communication. The multiplex is realized, so the digital transmission system has a great advantage. The analog optical transceiver is gradually replaced by the digital optical transceiver. The digital optical transmission gradually replaces the analog optical transmission. Nowadays, the transmission of various signals on the market is increasing. In the intelligent area of ​​the community, there are many types of signals, and the use of optical fiber transmission is more and more extensive. Digital optical transmission is the main trend of signal transmission in cells.
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