| With the rapid development of optical communication technology, many devices differing in purpose and characteristic are used in optical communication system, which are composed of the basic elements such as optical transmitter, optical receiver and optical fiber. Optical transceiver is a predominant device of optical communication system. As a matter of fact, it is a switch that completes the transform between electronic signals and optical signals. In previous years, analog optical transceiver worked in frequency modulation, amplitude modulation, phase modulation has certain market share. The optical transmitter modulates video, audio and data signals in baseband to a carrier frequency, and transmits them into optical fiber. Optical transmitter are respond for transmitting optical fiber which will be received and moderated by the optical receiver in order to recover video, audio and data signals in baseband.. At present, digital optical transceiver is applied widely. Digital optical transceiver transforms analog video and audio signals into digital signals, and then merges signals with low rate from many channels into a high rate data, which can enlarge communication capacity and improve the rate of transfer, transforms them into optical signals finally. In the terminal the receiver transforms the optical signals into electronic signals, and recovers the low rate data from the high rate stream, and recovers the video and audio signals at last. Digital optical transceiver applied widely in video surveillance. Due to its wide applying range, video surveillance has attracted attention for many years. Video surveillance has the characteristics of intuitionistic, convenient, and abundant information. With the development of electronics and optical fiber communication technologies, and with the quantity of information transmitted becomes larger and larger, the video surveillance system also evolution from single channel to multi-channel. The techniques changes from analog to digital. The technology of transmitting several channels in one optical fiber has greatly saved the resource of optical fiber and reduced the cost per channel.This research is part of Jilin province highway bureau's transportation surveillance program. According to the program's requirement, this digital optical transceiver should accomplish the transmission of video signals, audio signals and the bidirectional transmission of data signals. The digital optical transceiver composed of transmitter and receiver, which is design by us, should support the transmission of four channel video signals, two channel audio signals and the bidirectional transmission of two channel data signals. The transmitter is composed of video processing module, data processing module, audio processing module, audio digital multiplexing module and system digital multiplexing and demultiplexing module. The system digital multiplexing and demultiplexing module is composed of CPLD one order multiplexing and demultiplexing module, video, audio and data transmitting module, backward data receiving module. The video processing module of the transmitter's function is to amplify the video signal, which is picked up by CCD cameras, and complete the transform from analog signals to digital signals. This module offers video digital signals which can be multiplex. The data processing module offers the interface between TTL/CMOS standard and RS-232/RS-485 standard. TTL/CMOS standard is applied in integrate circuit and RS-232/RS-485 standard applied in external data communication device. So the conversion is necessary. The audio processing module of the transmitter's function is to transform the analog audio signals, which is picked up by microphone, to digital signals, then send them into system digital multiplexing and demultiplexing module through audio digital multiplexing module. The system digital multiplexing and demultiplexing module is the hardcore of our designation. Its function is complete the digital multiplexing and demultiplexing of several channels digital signals by Time Division Multiple Access (TDMA). There are two steps of digital multiplexing and demultiplexing. It accomplished by CPLD and serializer/ deserializer chip separately. The receiver's structure matches the transmitter's structure. The receiver is composed of video processing module, data processing module, audio processing module, audio digital demultiplexing module and system digital multiplexing and demultiplexing module. The system digital multiplexing and demultiplexing module is composed of CPLD one order multiplexing and demultiplexing module, video, audio and data receiving module, backward data transmitting module. The video processing module of receiver's function is to transform 8-bit parallel digital signals to analog signals, which has completed the digital demultiplexing in CPLD. Then these analog signals are amplified and sent to video surveillance terminal. The function of data processing module of receiver is same to the data processing module of transmitter. It offers the interface between TTL/CMOS standard and RS-232/RS-485 standard. The audio processing module of receiver's function is to transform the digital audio signals, which has completed the digital demultiplexing in CPLD, to analog audio signals. The analog audio signals can be amplified by reproducer. The voice is recovered. The system digital multiplexing and demultiplexing module of receiver completes the digital multiplexing and demultiplexing which is matched with the corresponding module of transmitter.The essential part of the thesis is designing system digital multiplexing and demultiplexing module and programming CPLD in VHDL. Digital communication always develops towards high speed, huge capacity. With increasing of communication business, more and more digital terminal devices are appeared. It will be a great demand of digital multiplexing and transmission with huge capacity in order to use signal channel more sufficiently and economically. In the TDMA digital communication system, the high rate data stream can be merged by several channels low rate data stream. In fact the digital multiplexing is to apply TDMA to several channels low rate data stream. Different channels are transmitted in different time intervals, the different channels are separated by different time intervals in the terminal. This step is digital demultiplexing, which is the contrary process of digital multiplexing. Either forward data or backward data should complete multiplexing and demultiplexing twice. The forward data stream's first time multiplexing and second time demultiplexing is actualized in CPLD, and the forward data stream's second time multiplexing and first time demultiplexing is actualized in HDMP1032A/1034A chip. The backward data stream's first time multiplexing and second time demultiplexing is actualized in CPLD, and the backward data stream's second time multiplexing and first time demultiplexing is actualized in DS92LV1021A/1212A chip.In CPLD, The forward and backward data stream's first time multiplexing and second time demultiplexing is actualized. In transmitter the forward data stream complete the digital multiplexing. The video, audio and data signals clock in latches of CPLD with a low rate clock first, after timing and rate justification, they clock out in four time intervals, and prepared the second time digital multiplexing. In receiver, high rate data stream clock in latches of CPLD with a high rate clock in four intervals, after timing, rate justification and recovery, they clock out with several low rate clocks. The backward data stream's multiplexing and demultiplexing in CPLD is similar to the forward data stream. But because of the backward data is less than forward data, the high rate data stream clock in and clock out CPLD in two time intervals.The key part of this thesis is programming CPLD, and realizing of digital multiplexing and demultiplexing in CPLD, which is programmed by VHDL. Although this digital optical transceiver is designed for transportation surveillance program, it still has common use in designation and application. The designation of digital optical transceiver has extent functions which means it can be used in other area in case of change hardware and rewrite program of CPLD. As a result, the development of this project has a great applicable value. |
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