Analysis of the application of optical transceiver in urban traffic monitoring

With the rapid development of my country's economy and the rapid growth of urban population, many large and medium-sized cities are facing the problem of traffic congestion caused by the growth of urban population and vehicles. It has been proved that while strengthening urban traffic planning and urban road infrastructure, introducing advanced communication technology, monitoring concepts and control technology, and effectively controlling and guiding traffic in real time are the key and effective ways to solve the problem of urban traffic congestion. The key to solving this problem is to establish a modern and intelligent traffic monitoring and command system. In the urban traffic control system, optical transceivers play a very important role. This article will introduce the application of optical transceivers in urban road traffic monitoring.

Urban traffic monitoring system generally consists of three parts: video acquisition system, control system, and network transmission system. According to the functions completed, it is divided into subsystems such as video monitoring system, traffic light control system, electronic police system, and video detection. Its main functions are as follows:

Real-time monitoring of each intersection for unified command and dispatch

Detect traffic flow and traffic conditions

Record intersection scenes for a long time for processing and archiving

By controlling traffic light signals, traffic flow is regulated to effectively alleviate traffic congestion.

Electronic police can be set up at some intersections as needed.

Effectively detect traffic behavior and provide protection for combating vehicle violations

Timely discover and assist in handling public security incidents to maintain social stability and unity

From the perspective of the system composition of the urban traffic monitoring system, to complete the above functions, it is necessary for each component of the system to be able to independently complete its own functions and to work closely together: the video acquisition system needs to monitor the scenes of each intersection in real time, including analog video signals and image information collected by electronic police. The collected video information is transmitted to the monitoring center through the network transmission system. The control system of the monitoring center can timely understand the situation at the front end and save, record and process the video information; at the same time, the control system of the monitoring center must also control the front-end cameras, traffic lights, electronic police, etc. as needed. The control system of the monitoring center sends different control signals to various devices at the front end, and then sends them to various devices at the front end through the network transmission system to complete the control.

In the above process, each part of the system plays a very important role. Considering the functions completed by each part, you will find that whether it is a video surveillance system, a traffic light control system, or an electronic police system, they all share the same part, that is, the network transmission system. With the development and maturity of optical fiber communication, optical transceivers have become the first choice for network transmission systems. In video acquisition and central control systems, they use different equipment to complete different functions. The front end uses cameras and traffic lights, while the center uses matrices and hard disk recorders to process video information, and uses traffic light control software, electronic police software, etc. for control. The responsibility of communication and signal transmission between the front end and the monitoring center falls on the optical transceiver. A careful analysis of the functions of the entire system will tell you which signals the system needs to transmit:

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Video signal from surveillance camera

Control signal for controlling the camera

Data signal of traffic light network

Data signal of electronic police network

These signals are of different types, including analog signals, data signals, low-speed serial data, and high-speed Ethernet data. Such complex and diverse signals have brought us great trouble in network transmission. To transmit these signals, the traditional method requires different devices to transmit different types of signals separately, which requires more equipment and laying more lines, thereby increasing the investment and complexity of system construction. Today, as the optical fiber system has matured, the optical terminal can independently take on this important task.

Optical transceivers can be divided into analog optical transceivers and digital optical transceivers in terms of transmission mode. Regardless of the type of optical transceiver, it essentially converts the transmitted image, voice or data signal into electric light or photoelectricity. The optical transceiver is essentially an electrical signal to optical signal and optical signal to electrical signal converter. The purpose of the conversion is to allow various signals to be transmitted in optical fibers. The advantages of optical fiber transmission are: first, it has low attenuation. At present, optical transceivers can transmit images, data and voice signals over 100 kilometers without relay. Secondly, it has strong anti-interference ability. It is not affected by lightning strikes and electromagnetic radiation, which are not available in copper axis cable transmission and twisted pair transmission. Optical fiber also has the characteristics of large transmission capacity. Optical transceivers can not only realize the functions of transmitting images, voice and data on one optical fiber, but also realize the functions of transmitting telephone and computer network signals. It can be said that it covers almost all functions required in the field of monitoring.

The functions of optical transceivers are very powerful, and the types of signals they can transmit are also very diverse. Therefore, different types of optical transceivers should be selected in different situations. When choosing the model of optical transceiver, we should consider the following points:

1. What kind of fiber optic network is it based on? If you are expanding the capacity on the original network, it is best to use the same fiber, unless doing so cannot achieve the expected function. If it is a brand new project, it is best to use single-mode fiber. In traditional concepts, people always think that the cost of multi-mode systems is lower than that of single-mode systems over shorter distances (within 5 km). In fact, with the continuous popularization of optical fibers and the decline in equipment prices, the price advantage of multi-mode optical transceivers has long disappeared. In terms of transmission distance and effect, multi-mode equipment is inferior to single-mode, so at present, the cost performance of single-mode optical transceivers is higher than that of multi-mode optical transceivers.

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2. Which technology should be used for optical transceivers? From a technical point of view, digital optical transceivers are definitely better than analog optical transceivers. However, in practical applications, specific analysis is required. The implementation method of analog optical transceivers is simpler, and the system cost is relatively cheaper. At the same time, when only one or two video signals are transmitted, analog optical transceivers can transmit to a longer distance and obtain better signal quality, but if multiple video signals are transmitted, the transmission distance and signal quality will be greatly reduced. Digital optical transceivers are relatively complex, with high technical content and high price, but they can easily realize the mixed transmission of multiple channels and multiple signals. Therefore, when choosing one or two-channel image monitoring optical transceivers, the cost performance of analog optical transceivers is better than that of digital optical transceivers. In the series of four-channel and more than four-channel image monitoring optical transceivers, the cost performance of digital optical transceivers is better than that of analog optical transceivers.

3. Does the optical fiber system transmit video, audio, data, or a combination of these signals? According to the transmitted optical signal, optical transceivers can be divided into data (Data-RS232/RS422/RS485/Manchester/TTL/Biphase/Contactclosure) optical transceivers, video optical transceivers, audio optical transceivers, video/data optical transceivers, video/audio optical transceivers, video/data/audio optical transceivers, and multiplexed optical transceivers. At the same time, it is also necessary to consider whether the transmitted data is unidirectional or bidirectional.

Below we briefly introduce the use of optical transceivers in urban traffic monitoring systems through the actual case of a road monitoring system in a city in Zhejiang Province. This is a large-scale traffic monitoring system. The front end includes more than 270 fixed cameras, 60 fast integrated ball cameras, more than 300 video images, and the signal light control lines and electronic police data lines of the intersections are connected to more than 70 signal boxes at various traffic intersections in the city. In addition, one or more optical transceivers are installed in each signal box to transmit the video images of each intersection and the pictures taken by the electronic police to the monitoring center through optical fiber. The control center uses a large matrix to control the video, switch the image to the monitoring screen wall, and use a hard disk recorder to record and save all the images. At the same time, the control signal sent by the matrix host of the center to the ball camera, the data signal of the signal light control software and the electronic police software are also transmitted to the front-end intersections through the optical transceiver to control the angle, distance, aperture of the ball camera, the time of the signal light, and the setting of the electronic police, so as to better count and adjust the traffic flow and effectively alleviate traffic congestion. Since the front-end devices connected to the signal boxes at the front end are different, the signals that need to be transmitted are also different, so different types of optical transceivers are required. (As shown in the figure)

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In this system, we use the Infinova brand digital optical transceiver launched by Infinova Co., Ltd. (formerly NTK Corporation), USA. Its excellent circuit design and high-quality components make it have a sufficiently large optical link loss and dynamic range. We can use different types of optical transceivers according to the actual situation of the front end: some intersections only have monitoring images and no other equipment, so we use pure video optical transceivers; some have not only fixed cameras but also integrated ball cameras, so we use video plus reverse 422 control signal optical transceivers; there are also electronic police or traffic lights at the front end, so we use video plus data 232 control signal optical transceivers; some have computer networking, so we need to use Ethernet data optical transceivers; and there are optical transceivers that can transmit all the above data types together. No matter what kind of data is transmitted, it has real-time status indication, which is convenient for us to discover and solve problems. At the same time, when choosing optical transceivers, we also reserved some video and data channels to facilitate the overall expansion of the system and the networking between various city systems in the future.

It is not difficult to see from the above cases that optical transceivers play an indispensable role in traffic monitoring systems. At the same time, it is also crucial to choose different optical transceivers according to different signal types. It can help us monitor and solve traffic problems more effectively in real time.

At the beginning of the century, with the rapid development of urban transportation and road construction and the increasing maturity of optical fiber communication technology, we believe that the development prospects of optical transceivers in urban traffic monitoring will be broader.