Business Module Design Of Optical Communication System For Railway Section

Railway section communication is an important part of railway communication. They are the communications facilities which primarily provide external liaison for the railway workers. According to the needs of railway section communication, we have developed a set of railway section optical fiber communication system with optical time division multiple access technology. This paper describes the design of automatic telephone service and E1 data transmission service in the system.The system mainly consists of station-side equipment, terminals and communication links. Terminal service is realized by the connection of the service function part on the main control unit and the corresponding systems. In terms of automatic telephone services, it supports multiple terminals to use automatic telephone service simultaneously by accessing multiple automatic telephone service sub-board on the floor of control board. System's data processing module is a CPLD. The host protocol, forwarding through the CPLD communicate with the System terminal. At the same time, the host contacts with Subordinate MCU on the service board through RS-485 bus to realize the control of service. When the service is established, CPLD sends and receives the data between systems and the various service modules under the control of the host. Automatic telephone service board, which achieves the contact with the automatic telephone systems, mainly consists of the control module, voice codec module, the call circuit, dial-up circuit and ring detection circuits. In order to avoid the interference with telephone lines, telephone service board connects with automatic telephone system where the photoelectric isolation technology is used.In terms of E1 services, the host achieves the control of E1 services by registering and accessing the terminals on turn. The system data transmission code is NRZ, so in the E1 data transmission, through CPLD programming and polarity circuit to achieve the conversion between the HDB3 code and NRZ. Polarity conversion circuit uses the way of transformer coupled, with stable performance, simple structure. The output of the HDB3 code matches with the ITU-TG.703 specifications.