Selection of optical transceiver for the hottest E

2022-08-06
  • Detail

Selection of highway optical transceiver

using optical transceiver to transmit video, audio and control signals has become the preferred scheme in various engineering cases in the intelligent transportation neighborhood, especially in the highway. This article will introduce some experience of selecting optical transceiver in expressway for reference

with the continuous development of social economy, expressway construction is also increasingly extending in all directions. At the same time, the management of expressway is particularly important, so video surveillance plays a vital role in expressway management

Expressway video monitoring system is generally composed of toll station monitoring and road monitoring. The toll station monitoring system mainly includes real-time monitoring and recording of toll collection in toll station lanes, parking squares and toll booths. The road monitoring system is mainly used to conduct real-time monitoring on the expressway trunk lines, interchanges, tunnels and other key sections of the expressway, master the traffic conditions of the expressway, timely find out the traffic jam sections and illegal vehicles, and give guidance to ensure the safety and smoothness of the expressway

due to the long monitoring distance along the highway and the relatively poor environment, there are very high requirements for the anti-interference of signal transmission and the guarantee of long-distance transmission, so optical fiber is usually used as the medium for transmitting various signals. Of course, video optical transceiver has become the best choice for transmission equipment

signal transmission requirements of Expressway

1. Long distance signal is not easy to be affected by harsh environment

2. Voice communication and other multi service transmission requirements. Expressway management agencies. Real time mutual transmission of business and network information from the general management center, sub centers, sub centers to toll stations

3. Multi level transmission. Highway monitoring is generally composed of toll stations, monitoring sub centers and monitoring centers. When local collection points, toll booths and road monitoring points converge to a signal center, they also need to be transmitted to the next level center

4. Stability. In view of the actual situation of high-speed road environment, lightning protection and ensuring the stable transmission of video at monitoring points should be particularly emphasized

main solution of Expressway signal transmission

1. Overall structure diagram of the system

2. It can be seen from the overall structure diagram that monitoring points such as lanes, squares and lines are uniformly uploaded to the monitoring center of the station, and the monitoring center of the station then transmits to the superior sub center. Finally, all of them can be collected to the expressway management center to realize three cascade transmission. From the perspective of this architecture, the optical transceiver is the most important in each first level of monitoring, and it is also the most important link related to the effect of multi-level transmission. Its performance, long-term stability and adaptability to a variety of transmission modes all play a vital role in the highway monitoring center

3. The transmission to the monitoring center and the summary to the general control center are generally realized through network transmission. The e1/2m channel provided by telecom or Telecom is used to realize the transmission of audio and control signals, and the video browsing, control and centralized management are realized through the video server in the general monitoring center

characteristics of the special optical transceiver for Expressway

1. From the above requirements, the special optical transceiver for Expressway must have the following functional characteristics:

the video transmission room should have high transmission quality, the signal-to-noise ratio should be ≥ 67db, the full digital processing mode should be adopted, and the channels should not interfere with each other to ensure the optimal transmission effect. Expressway optical fiber lines are often staggered and complex. Many occasions involve transformation and upgrading. The original optical fiber may also be multimode. Therefore, it is required to integrate single multimode adaptive circuit in the optical transceiver to adapt to multimode optical fiber transmission

2. It is required to have a super dynamic range of at least 20dB, and the transmission distance can reach ≥ 40km, which can meet the requirements of long-distance transmission of expressway. The dynamic range will directly determine the transmission distance of the optical transceiver. According to the actual experience in the project, the transmission attenuation per kilometer is generally within 0.5dB, which belongs to the normal range. Therefore, the transmission of 40km can be guaranteed if 20dB is guaranteed

3. It is required to have a multi service interface. Besides video and data interfaces, voice, Ethernet and other signals can be accessed to ensure the needs of signal transmission in some special cases

4. The protection circuit is complete. Due to the complexity of the highway and the environment, lightning protection and other protection measures will be very important, and the data separation is small, which will directly affect whether the optical transceiver can operate stably for a long time

(1) communication interface protection

for the most widely used RS485 at present:

level 1: lightning discharge ----- discharge lightning or induced lightning energy, from thousands of volts to about 150V

level II: overcurrent protection, which makes the current impulse less than 1 ampere. If the current exceeds 1a, the protection circuit will be automatically disconnected to isolate the internal circuit from the interface; When the current returns to normal, the circuit will recover automatically

Level 3: reduce the 150V voltage of level 1 protection to 7-10v, providing a normal electrical voltage range for chip operation

(2) video protection circuit

the current video protection adopts the bridge +tvs protection mode. The protection level can reach 75V (the normal video signal is only 2V) at mpa=106pa, which can protect the video signal to more than 30 times

(3) power protection

power protection adopts two-level protection, and overvoltage protection adopts TVs mode; If the input current is more than 2 times of the normal working current value of the circuit board, the self recovery fuse will disconnect the power supply, the current is normal, and the self recovery fuse power supply returns to normal

summary:

as a part of urban security, some characteristics of highway optical transceiver also represent many demands of safe cities. The composition and complexity of urban monitoring system, urban traffic and extending in all directions all determine the indispensable position of optical transceiver in urban security

signal transmission is the key to building a safe city monitoring system with a sales volume of 40% (US $200million). The application of optical transceiver is a good way to achieve high cost performance and good transmission effect. It is used to describe that it will also play an increasingly important role by using fewer materials for production

Copyright © 2011 JIN SHI