Equalization Algorithm For Orthogonal Frequency Division Multiplexing Optical Signal Transmission System

The orthogonal frequency division multiplexing (OFDM) technologyhas received a lot of attentions and actively investigated in opticalcommunications due to its high spectrum efficiency, flexible spectrumallocation and anti-interference ability. It can provide the ability fortransmission and processing of high speed and large capacity to break the"bottleneck" of information transfer. So it will adapt to bandwidthrequirements for high-speed broadband services in a long time.TheO-OFDM system based on the direct detection (DDO-OFDM) is very easyto be implemented and has the merits of low cost and stability operation.This paper focuses on the selection of equalization algorithms inDDO-OFDM system. The main research results include:1. Optimize least square(LS) algorithms for OFDM system.Several key technologies and method of chanel equalization for OFDM arediscussed in detail. Analyses the principle and the insufficiency in LSalgorithm. Aiming at the drawbacks ofconventional algorithms, a improvement algorithm called LS+LPF was proposed. Moreover, theinfluences of system characteristics with different equalization scheme aresimulated, some valuable conclusions are shown. Synthesis results showthat the system with the novel algorithm has a better performance than LSequalizer. With adaptive filter, the improvement algorithm can restrain thenoise and maintain the primary energy of the channel,which has the samecomputation complexity as the conventional algorithms.2. Investigate the impact of fiber chromatic dispersion on thetransmission performance of an OFDM system. Fiber dispersion hasbecome a major limiting factor for long haul high bitrate optical fibertransmission system.The results show that fiber chromatic dispersion playsa stronger impact on high frequency subcarrier than low frequencysubcarrier. The proposed equalization method can effectivelycompensate the phase shift and amplitude attenuation caused by fiberchromatic dispersion.3. Propose a novel suitable equalization algorithm for theDDO-OFDM system. A novel time domain equalization (TEQ) in O-OFDM System was proposed and experimentally demonstrated.TheDD-LMS equalization principle was theoretically investigated． In thedirect-detection O-OFDM system, the experimented results confirmthat,compared with LS equalizer system,the decision direct least meansquare(DD-LMS) system performs1dB decreased on average,the bit errorrate(BER)of the system decreases a lot at the same receive power,a moreclearly received constellation could be abtained.Synthesis results showthat the system with the DD-LMS time domain equalizer has a betterdispersion compensation characteristics than LS frequency domainequalizer system.