Research On Unipolar Optical Orthogonal Frequency Division Multiplexing Transmission Technology

Orthogonal frequency division multiplexing (OFDM) is used extensively in broadbandwired and wireless communication systems because it is an effective solution to intersymbolinterference caused by a dispersive channel. When OFDM is applied to opticalcommunication system employing intensity modulation with direct detection (IM/DD), wehave the problem that how converts the bipolar OFDM signal to the unipolar OFDM signal.So we study the transmission technology of unipolar optical OFDM (O-OFDM) in this paper.Firstly, we summarize the study progress on O-OFDM. Then we analyze the bit error ratio(BER) performance of asymmetrically clipped optical OFDM (ACO-OFDM) respectivelybased on discrete fourier transform (DFT) and discrete hartley transform (DHT) in additivewhite Gaussian noise (AWGN) channel. And we analyze the impact of2,1,7convolutional code on system performance of ACO-OFDM. Finally, we implement thetransmission of pulse amplitude modulated-discrete multitone (PAM-DMT) in AWGN andsingle mode fiber channel and analyze the system performance. The details are described asfollows:(1) ACO-OFDM based on DFT is investigated. We study the BER performance ofACO-OFDM based on IM/DD system in AWGN channel and compare it with DC-biasedoptical OFDM (DCO-OFDM). Then the convolutional code is applied to the ACO-OFDMsystem. We have the results that ACO-OFDM has greater power efficiency than DCO-OFDMfor a given normalized bandwidth. When the signal to noise ratio (SNR) is small, theconvolutional code may degrade system performance. However, the convolutional code canimprove system performance as the SNR increases. When the required BER is10-3, theconvolutional code makes the requirements on the SNR of ACO-OFDM with4QAMdecreased by about2dB.(2) ACO-OFDM based on DHT is investigated. We study the BER performance ofACO-OFDM based on DHT in AWGN channel and compare it with ACO-OFDM based onDFT. We analyze the impact of convolutional code on system performance of ACO-OFDMbased on DHT. We have the results that compared with ACO-OFDM based on DFT,ACO-OFDM based on DHT has a similar BER performance, but it has a simpler structure.When the required BER is10-3, the convolutional code makes the requirements on the SNR ofACO-OFDM based on DHT with4PAM decreased by about2.2dB.(3)The system performance of PAM-DMT is investigated. Firstly, the modulationprinciple of PAM-DMT is demonstrated. Then we study the BER performance of PAM-DMTin AWGN channel. We construct the simulation system by MATLAB and Optisystem7.0andimplement the transmission of PAM-DMT in single mode fiber through it. We have the resultsthat the maximum transmission distance of system can be improved by increasing opticalpower. And the BER performance of PAM-DMT is better than ACO-OFDM when the number of subcarriers is small. But with the number of subcarriers increasing, their performance isconsistent with each other gradually.