Research On Two-dimensional Optical Code Division Multiple Access Encoding And Decoding System

With the rapid development of super-clear video service,intelligent city and other integrated services,the communication network has been put forward higher requirements.Optical code division multiple access(OCDMA)technology has become one of the options to solve the "last kilometer" of passive optical network because of its random access,flexible capacity,high security,simple network management,strong confidentiality and so on.However,the lack of high performance optical address codes and practical codecs hinder the commercial use of optical code division multiple access systems.Therefore,it is an urgent need for the commercialization of OCDMA system to find a OCDMA codecs with good transmission performance,good reconfiguration and low cost.This paper focuses on the key technologies of two-dimensional(OCDMA)coding and decoding system.The main contents of this thesis are as follows:1.This paper summarizes the structure and working principle of several common two-dimensional incoherent OCDMA codec,and analyzes the performance of each kind of encoder and decoder.This paper analyzes and studies the PAM4 technology and its development status,designs a two-dimensional incoherent OCDMA coding and decoding system based on PAM4,and simulates a two-user codec system with a rate of 5Gbit/s and a transmission distance of 20 KM through Optisystem software.The performance and feasibility of the codec system are verified.The implementation of the system is relatively simple,the reconstruction is good,and the spectrum efficiency of the system is increased.2.The experiment of two-dimensional incoherent OCDMA coding and decoding system based on FPGA is carried out.Taking the Xilinx ML605 development board as hardware platform,the experiment of coding and decoding system is successfully carried out.The internal waveform of FPGA is observed by ChipScope IP core,and the function of each sub-module is verified.Two experimental platforms for user data transmission are built.The user data transmission rate is 250Mbit/s,the system transmission line rate is 5Gbit/s,the total amount of4-channel parallel transmission is 20Gbit/s,and the optical transmission distance is 10 KM.Observing data waveforms and eye diagrams with an optical oscilloscope.The experimentalresults show that the coding and decoding system has good performance and can recover the user data correctly.3.A QPSK-OCDMA two-dimensional coherent coding and decoding system is designed,and a two-user codec system with a rate of 5Gbit/s and a transmission distance of 10 KM is simulated by Optisystem software.The performance and feasibility of the codec system are verified by observing the decoded data waveform and eye diagram.The system adopts electro-optic combination coding and decoding technology to reduce the cost of the system,applies QPSK modulation technology to the OCDMA codec system,and alleviates the problem of low spectrum efficiency in the current OCDMA system.The coherent demodulation technology is used to suppress the multiple access interference(mai)problem in the system.