First, the demand for freeway video surveillance With the development of society and technological progress, and China's rapid economic demand for transportation, the construction of the highway has also developed at an unprecedented rate. As of last year, the total mileage of the expressway has already ranked second in the world. With the construction of expressways, the operation and management of expressways has become an urgent issue to be resolved. As the operation managers need to know and control the highway conditions in real time, the entire highway video surveillance system has emerged.
Highway video surveillance system is generally divided into toll monitoring and road monitoring in two parts. The charging monitoring system mainly focuses on the toll collection of the toll station lanes, toll plazas and toll booths, observes and records the types of vehicles that the toll lanes pass through, the operation procedures of the toll collectors, and the emergencies and special events during the toll collection process. Effective supervision. The road monitoring system is mainly to supervise key expressway sections such as highway trunk lines, interchange interchanges, and tunnels, and to master the traffic conditions of expressways, timely detect traffic blockage sections and illegal vehicles, and promptly provide guidance to ensure the safety of highways.
Second, the highway on the transmission mode selection and requirements 1, the characteristics of the highway monitoring system transmission According to the video surveillance of the highway monitoring system is divided into toll monitoring and road monitoring in two parts, in the monitoring of the charging signal, due to lane and fee management The distances are relatively close, generally between a few hundred meters to one kilometer. Toll monitoring often requires the transmission of real-time images with a large number of ways, often accompanied by multiple audio, data, intercom and Ethernet, etc. The quantity is mostly the basic feature of the charge monitoring; the road monitoring is relatively far from the highway monitoring transmission distance, high requirements for real-time image, a large number of video channels, the complex transmission structure on the road, the harsh environment is the basic characteristics of road monitoring.
Based on these characteristics, we propose to use transmission frequency bandwidth in expressway monitoring system, large communication capacity, long transmission distance, no electromagnetic interference, fine wire diameter, low weight and low cost, and easy-to-wire optical fiber + non- Compression video transmitter + coaxial cable to transmit. Toll monitoring often requires the transmission of many high-quality real-time images, often accompanied by multiple audio, data, intercom, and Ethernet networks. Therefore, it is recommended to select optical fibers with wide transmission bandwidth, large communication capacity, and low wiring complexity due to electromagnetic interference. Fiber optic cable plus non-compressed video optical transceiver for transmission.
2. Single-mode fiber should be used instead of multi-mode fiber. However, after we choose the transmission mode of optical fiber, we should pay attention to using single-mode fiber instead of multi-mode fiber. In past standards and usage habits, we should Often choose this transmission distance is less than 2km, choose multimode fiber, more than 2km use single-mode fiber. The reason is that in the early years when we were using optical fiber communication, due to defects in optical fiber manufacturing processes and optical devices, such as: 1. High cost due to the complicated manufacturing process of single-mode optical fibers; 2. Due to our commonly used light-receiving devices. When used in an environment where the transmission distance is short, saturation of the received power is likely to occur, resulting in poor compatibility of the equipment in use. Now these technical problems are no longer a problem. The price of single-mode fiber is already similar to that of multi-mode fiber. The dynamic range of optical devices can also be used stably from 0 to maximum transmission distance without adjustment. And single-mode optical fiber transmission rate is high, no inter-disturbance interference, there is no reflection and other defects, we can use single mode fiber transmission throughout. (In fact, most of the multi-mode optical transceivers have already adopted the single-mode device technology, so it is recommended to phase out multi-mode optical fibers when laying new optical fibers).
3, the choice of video transmission optical transceiver Here, we must consider the characteristics of the highway monitoring system to consider the choice of what kind of optical transceiver for transmission.
3.1 Charging monitoring The selection of optical transceivers The charging monitoring system is mainly responsible for the charging of the toll stations' lanes, toll plazas, and toll booths. Its image needs to be transmitted to the toll management office. It is close to the image, and its abundant business is its distinguishing feature. Therefore, we generally choose multi-channel digital video optical transceivers for point-to-point transmission.
3.2 Selection of outfield road monitoring optical transceivers The supervision of outfield road supervisors is more complex than the toll booths. Monitoring points need to be set up for interchanges and key road sections. A monitoring point should be set every 2km around the expressway section. A surveillance point is set every 150m in each direction in the tunnel. The camera control signal and the signal required for communication in the field are even more. Image signal, PTZ control, battery monitor, variable intelligence sign or information board, information induction Screens or information release screens, vehicle detectors, visibility detectors, meteorological detectors, monitoring points, etc. Enriched signals such as chassis security door magnetic switches need to be transmitted, hundreds of kilometers to hundreds of kilometers on the highway need to transmit hundreds of The road image and PTZ control signal also require a large number of other signals to be transmitted. The point-to-point transmission method will be limited by the distance and monitoring point dispersion conditions. We can choose to transmit the image to the nearest point through the point-to-point image optical transceiver. Toll station, and then at the toll station through the road number point-to-point optical transceiver to the high-speed public Road Management Center. In addition, we can also use a cascaded (or node) optical transceiver with more advanced technologies to collect the images of each point on the road, and then serially transmit all the videos to the monitoring center according to the order of the convergence points. The serial channels only occupy one core fiber, and each fiber link can set 10 to 16 aggregation nodes respectively. The distance between each two aggregation nodes can reach several tens of kilometers, and the large number of point-to-point video can also be solved. Optical transceivers cannot transmit hundreds of kilometers or even hundreds of kilometers of transmission, because each fiber link can access 10 to 16 images and several data accesses, and a highway with hundreds of images only needs several core fibers. All images can be sent back to the management center, which saves fiber resources.
3.4 Selection of optical transceiver performance Currently, multiple digital video optical transceivers on the market involve a wide variety of technical indicators. Most of the engineering vendors and users also lack the corresponding means to judge the rationality and authenticity of the technical indicators. Therefore, the products are selected. It's easy to get lost. However, in the expressway monitoring system, due to poorer environmental regulation, long transmission distances, higher requirements for images, and higher transmission and transmission requirements required by the country, we describe several items in the project. More critical and easily verifiable technical indicators, and focused on reliability and practicality, analyzed how to select digital video optical transceivers in security monitoring projects.
3.4.1 Technical Specifications Considering that multiplexed digital video optical transceivers can have multiple functions, each type of function has corresponding technical indicator requirements, such as video indicators, audio indicators, asynchronous data indicators, Ethernet indicators, and so on. Specific technical indicators can require manufacturers to provide third-party test certificates. Conditional contractors should conduct retesting in accordance with manufacturer-supplied specifications before purchasing equipment to verify the actual technical specifications of the equipment and the integrity of the manufacturer. Here, the following two video indicators are briefly described from the engineering perspective.
a. The video bandwidth is enough. The video bandwidth is a cliché problem. With insufficient video bandwidth, the details of the monitor screen are not clear enough, the horizontal resolution is low, and even serious color distortion or loss occurs. It is because of the importance of video bandwidth to image quality that some unscrupulous manufacturers intentionally exaggerate the video bandwidth of the product to deceive customers. A multi-channel digital video optical transceiver produced by a manufacturer claims its video bandwidth is 8M, but its externally announced video sampling frequency is 12.5M. In accordance with the Nyquist sampling law, to truly restore the signal, the sampling frequency should be at least twice the signal frequency. In this way, the theoretical video bandwidth of the optical transceiver of this manufacturer cannot exceed 6.25M in any case. Obviously, this is a lie that exaggerates the performance of deceiving customers, so that manufacturers with no commercial reputation should not be considered for inclusion in the scope of purchase. However, not all customers are able to accurately identify manufacturer's lies. For general contractors and users, the device's video bandwidth can be roughly judged by observing the details of the image.
b. The APL range is wide enough to have an APL, which is the average level of the image. Many builders are not paying attention or are not familiar with this indicator. However, if we talk about a problem encountered in some projects: the video signal is transmitted through the optical transceiver, when the screen has a large area of ​​white (such as when the camera is illuminated by a strong light) the monitor will horizontally shake, then The engineering staff is no stranger to it. This is because the APL range of video optical transceivers produced by some manufacturers is too narrow. When there is a large area of ​​white in an image signal, the DC component in each image signal increases, and the APL will increase, resulting in a decrease in the horizontal synchronization signal amplitude. Or, the monitor cannot detect line synchronization and screen jitter occurs.
3.4.2 Reliability considerations As a security monitoring project, equipment reliability should be the first consideration. The reliability of the equipment is the equipment manufacturer must consider when designing the product, however, some manufacturers may be unwilling to do or do not know how to do this work for some reasons. Here, the following issues are briefly discussed from the engineering perspective.
a. Convenient power supply, wide power supply range The power supply is the primary consideration for ensuring the reliability of digital video optical transceivers. The power supply cannot be guaranteed to be reliable and reasonable. The reliability of digital video optical transceivers has become a monthly basis. 220VAC-powered video optical transceivers are more convenient and reliable, and 220VAC-powered optical transceivers should be selected as much as possible. However, 220VAC power supply may be inconvenient in the field equipment, and 24VDC power supply will be used for solar power supply. In the solar power supply, it is necessary to consider the flexibility and power consumption of the power supply of the optical transceiver is not low enough.
3.4.3 Strong adaptability of temperature and humidity In some security monitoring projects, the working conditions of the optical transceivers are rather poor, the temperature variation range is wide, the air humidity is high, and some field monitoring points occasionally power outages. All of these require multiple digital video transceivers to have more consideration in the temperature range and allowable humidity, so as to ensure that they can work stably in harsh environments and adapt to security monitoring needs.
Highway video surveillance system is generally divided into toll monitoring and road monitoring in two parts. The charging monitoring system mainly focuses on the toll collection of the toll station lanes, toll plazas and toll booths, observes and records the types of vehicles that the toll lanes pass through, the operation procedures of the toll collectors, and the emergencies and special events during the toll collection process. Effective supervision. The road monitoring system is mainly to supervise key expressway sections such as highway trunk lines, interchange interchanges, and tunnels, and to master the traffic conditions of expressways, timely detect traffic blockage sections and illegal vehicles, and promptly provide guidance to ensure the safety of highways.
Second, the highway on the transmission mode selection and requirements 1, the characteristics of the highway monitoring system transmission According to the video surveillance of the highway monitoring system is divided into toll monitoring and road monitoring in two parts, in the monitoring of the charging signal, due to lane and fee management The distances are relatively close, generally between a few hundred meters to one kilometer. Toll monitoring often requires the transmission of real-time images with a large number of ways, often accompanied by multiple audio, data, intercom and Ethernet, etc. The quantity is mostly the basic feature of the charge monitoring; the road monitoring is relatively far from the highway monitoring transmission distance, high requirements for real-time image, a large number of video channels, the complex transmission structure on the road, the harsh environment is the basic characteristics of road monitoring.
Based on these characteristics, we propose to use transmission frequency bandwidth in expressway monitoring system, large communication capacity, long transmission distance, no electromagnetic interference, fine wire diameter, low weight and low cost, and easy-to-wire optical fiber + non- Compression video transmitter + coaxial cable to transmit. Toll monitoring often requires the transmission of many high-quality real-time images, often accompanied by multiple audio, data, intercom, and Ethernet networks. Therefore, it is recommended to select optical fibers with wide transmission bandwidth, large communication capacity, and low wiring complexity due to electromagnetic interference. Fiber optic cable plus non-compressed video optical transceiver for transmission.
2. Single-mode fiber should be used instead of multi-mode fiber. However, after we choose the transmission mode of optical fiber, we should pay attention to using single-mode fiber instead of multi-mode fiber. In past standards and usage habits, we should Often choose this transmission distance is less than 2km, choose multimode fiber, more than 2km use single-mode fiber. The reason is that in the early years when we were using optical fiber communication, due to defects in optical fiber manufacturing processes and optical devices, such as: 1. High cost due to the complicated manufacturing process of single-mode optical fibers; 2. Due to our commonly used light-receiving devices. When used in an environment where the transmission distance is short, saturation of the received power is likely to occur, resulting in poor compatibility of the equipment in use. Now these technical problems are no longer a problem. The price of single-mode fiber is already similar to that of multi-mode fiber. The dynamic range of optical devices can also be used stably from 0 to maximum transmission distance without adjustment. And single-mode optical fiber transmission rate is high, no inter-disturbance interference, there is no reflection and other defects, we can use single mode fiber transmission throughout. (In fact, most of the multi-mode optical transceivers have already adopted the single-mode device technology, so it is recommended to phase out multi-mode optical fibers when laying new optical fibers).
3, the choice of video transmission optical transceiver Here, we must consider the characteristics of the highway monitoring system to consider the choice of what kind of optical transceiver for transmission.
3.1 Charging monitoring The selection of optical transceivers The charging monitoring system is mainly responsible for the charging of the toll stations' lanes, toll plazas, and toll booths. Its image needs to be transmitted to the toll management office. It is close to the image, and its abundant business is its distinguishing feature. Therefore, we generally choose multi-channel digital video optical transceivers for point-to-point transmission.
3.2 Selection of outfield road monitoring optical transceivers The supervision of outfield road supervisors is more complex than the toll booths. Monitoring points need to be set up for interchanges and key road sections. A monitoring point should be set every 2km around the expressway section. A surveillance point is set every 150m in each direction in the tunnel. The camera control signal and the signal required for communication in the field are even more. Image signal, PTZ control, battery monitor, variable intelligence sign or information board, information induction Screens or information release screens, vehicle detectors, visibility detectors, meteorological detectors, monitoring points, etc. Enriched signals such as chassis security door magnetic switches need to be transmitted, hundreds of kilometers to hundreds of kilometers on the highway need to transmit hundreds of The road image and PTZ control signal also require a large number of other signals to be transmitted. The point-to-point transmission method will be limited by the distance and monitoring point dispersion conditions. We can choose to transmit the image to the nearest point through the point-to-point image optical transceiver. Toll station, and then at the toll station through the road number point-to-point optical transceiver to the high-speed public Road Management Center. In addition, we can also use a cascaded (or node) optical transceiver with more advanced technologies to collect the images of each point on the road, and then serially transmit all the videos to the monitoring center according to the order of the convergence points. The serial channels only occupy one core fiber, and each fiber link can set 10 to 16 aggregation nodes respectively. The distance between each two aggregation nodes can reach several tens of kilometers, and the large number of point-to-point video can also be solved. Optical transceivers cannot transmit hundreds of kilometers or even hundreds of kilometers of transmission, because each fiber link can access 10 to 16 images and several data accesses, and a highway with hundreds of images only needs several core fibers. All images can be sent back to the management center, which saves fiber resources.
3.4 Selection of optical transceiver performance Currently, multiple digital video optical transceivers on the market involve a wide variety of technical indicators. Most of the engineering vendors and users also lack the corresponding means to judge the rationality and authenticity of the technical indicators. Therefore, the products are selected. It's easy to get lost. However, in the expressway monitoring system, due to poorer environmental regulation, long transmission distances, higher requirements for images, and higher transmission and transmission requirements required by the country, we describe several items in the project. More critical and easily verifiable technical indicators, and focused on reliability and practicality, analyzed how to select digital video optical transceivers in security monitoring projects.
3.4.1 Technical Specifications Considering that multiplexed digital video optical transceivers can have multiple functions, each type of function has corresponding technical indicator requirements, such as video indicators, audio indicators, asynchronous data indicators, Ethernet indicators, and so on. Specific technical indicators can require manufacturers to provide third-party test certificates. Conditional contractors should conduct retesting in accordance with manufacturer-supplied specifications before purchasing equipment to verify the actual technical specifications of the equipment and the integrity of the manufacturer. Here, the following two video indicators are briefly described from the engineering perspective.
a. The video bandwidth is enough. The video bandwidth is a cliché problem. With insufficient video bandwidth, the details of the monitor screen are not clear enough, the horizontal resolution is low, and even serious color distortion or loss occurs. It is because of the importance of video bandwidth to image quality that some unscrupulous manufacturers intentionally exaggerate the video bandwidth of the product to deceive customers. A multi-channel digital video optical transceiver produced by a manufacturer claims its video bandwidth is 8M, but its externally announced video sampling frequency is 12.5M. In accordance with the Nyquist sampling law, to truly restore the signal, the sampling frequency should be at least twice the signal frequency. In this way, the theoretical video bandwidth of the optical transceiver of this manufacturer cannot exceed 6.25M in any case. Obviously, this is a lie that exaggerates the performance of deceiving customers, so that manufacturers with no commercial reputation should not be considered for inclusion in the scope of purchase. However, not all customers are able to accurately identify manufacturer's lies. For general contractors and users, the device's video bandwidth can be roughly judged by observing the details of the image.
b. The APL range is wide enough to have an APL, which is the average level of the image. Many builders are not paying attention or are not familiar with this indicator. However, if we talk about a problem encountered in some projects: the video signal is transmitted through the optical transceiver, when the screen has a large area of ​​white (such as when the camera is illuminated by a strong light) the monitor will horizontally shake, then The engineering staff is no stranger to it. This is because the APL range of video optical transceivers produced by some manufacturers is too narrow. When there is a large area of ​​white in an image signal, the DC component in each image signal increases, and the APL will increase, resulting in a decrease in the horizontal synchronization signal amplitude. Or, the monitor cannot detect line synchronization and screen jitter occurs.
3.4.2 Reliability considerations As a security monitoring project, equipment reliability should be the first consideration. The reliability of the equipment is the equipment manufacturer must consider when designing the product, however, some manufacturers may be unwilling to do or do not know how to do this work for some reasons. Here, the following issues are briefly discussed from the engineering perspective.
a. Convenient power supply, wide power supply range The power supply is the primary consideration for ensuring the reliability of digital video optical transceivers. The power supply cannot be guaranteed to be reliable and reasonable. The reliability of digital video optical transceivers has become a monthly basis. 220VAC-powered video optical transceivers are more convenient and reliable, and 220VAC-powered optical transceivers should be selected as much as possible. However, 220VAC power supply may be inconvenient in the field equipment, and 24VDC power supply will be used for solar power supply. In the solar power supply, it is necessary to consider the flexibility and power consumption of the power supply of the optical transceiver is not low enough.
3.4.3 Strong adaptability of temperature and humidity In some security monitoring projects, the working conditions of the optical transceivers are rather poor, the temperature variation range is wide, the air humidity is high, and some field monitoring points occasionally power outages. All of these require multiple digital video transceivers to have more consideration in the temperature range and allowable humidity, so as to ensure that they can work stably in harsh environments and adapt to security monitoring needs.
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