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Research On The Synchronization Algorithm Of Optical OFDM Transmission System

Posted on:2013-09-26Degree:MasterType:Thesis
Country:ChinaCandidate:X DiFull Text:PDF
GTID:2248330395985169Subject:Information and Communication Engineering
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With the rapid development of communication technology, people become more urgentto communication quality demand. How to realize information transmission with high speed,large capacity and high quality at limited bandwidth draws great attention of researchers. Asan important modulation technique, optical orthogonal frequency division multiplexing(OOFDM) with high spectral efficiency, and high tolerance of fiber dispersion andpolarization mode dispersion (PMD) has become a research hotspot.OOFDM systems require high performance of synchronization. Timing synchronizationerrors will cause inter-symbol interference (ISI), carrier frequency synchronization errors willcause inter-carrier interference (ICI), and sampling frequency errors will introduce ICI and ISI.These will make the performance of system decline seriously. At present a variety ofsynchronization methods have been proposed for the wireless channel OFDM systems.Optical fiber channel OFDM systems generally have a very high transmission rate. Theexistence of fiber channel nonlinearity and its intricate interaction with fiber dispersion,which is nonexistent in the wireless systems, lead to the uncertainty of synchronization ofOOFDM systems. Thus it is necessary to develop a synchronization method with excellentperformance and low computational complexity suitable for OOFDM system.According to different system structure, some OOFDM systems only need timingsynchronization, while others need timing synchronization and frequency synchronization.Based on the different structures of OOFDM systems, we discussed synchronizationalgorithms in direct detection OOFDM (DD-OOFDM) system and coherent optical OFDM(CO-OFDM) system. The innovation works are as follows:1. An intensity modulation (IM) DD-OOFDM experimental system based on standardsingle-mode optical fiber (SSMF) is established. We compared three typical timingsynchronization algorithms in wireless channel. Then an improved timing synchronizationalgorithm based on training sequence is proposed. Simulation and experimental results showthat the proposed algorithm can achieve higher timing synchronization accuracy andacquisition probability when the receiving power is low.2. The synchronization technology of CO-OFDM systems is studied. We analyzed theprinciple of frequency synchronization of Schmidl algorithm in CO-OFDM systems. Basedon this algorithm, we proposed an improved one-training-symbol joint timing and frequencysynchronization algorithm. The simulation platform of CO-OFDM system is constructed, andthen used to verify the proposed algorithm. Simulation results demonstrate that the proposed algorithm which requires only one training sequence can obtain better synchronizationperformance, reduce the system’s redundancy and improve the transmission efficiency.
Keywords/Search Tags:Optical communication, Orthogonal frequency division multiplexing (OFDM), Direct detection, Timing synchronization, Coherent optical OFDM, Frequencysynchronization, Training sequence
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