Design And Simulation Of The Novel And High Efficiency Optical OFDM Schemes

With the bandwidth requirement increasing, the transport network faces high pressure to enlarge its capacity. The fiber communication system is developing towards to100Gbits/s or higher bit rate. As a multi-carrier modulation technology, Orthogonal Frequency Division Multiplexing (OFDM) performs better than traditional Wavelength Division Multiplexing (WDM) for its high spectral efficiency (SE) and excellent robustness against chromatic dispersion (CD) and polarization mode dispersion (PMD). Now OFDM scheme is chose as one of the important solutions for future beyond100Gbit/s optical transmission systems. Though the study about OFDM technology is trending to refine, the subcarrier spacing can be further reduced after modifying the principles of OFDM scheme. Meanwhile, the bandwidth of OFDM system can be kept at a lower level.The technology mentioned before is named fast OFDM scheme. Presently, the study is focus on the DCT based fast OFDM scheme. However, DCT is not a commonly used method in optical transmission. Furthermore, a Hilbert transform is usually required after DCT to achieve single side band signals. If the DCT based fast OFDM scheme is adopted in future optical transmission, the construction of the transmitter and receivers of transmission system should be modified. The main creative work of the paper is the research about the DFT based fast OFDM scheme, which includes three parts as follows.(1) After carefully analyzing the principles of the proposed DFT based fast OFDM scheme, a fixed interference is found existing between the odd and even subcarriers. To mitigate this interference, three compensation methods is proposed:post-compensation method, centrally inserted pre-compensation method and4-based pre-compensation method. Finally, numerical simulation results prove the effectiveness of these three methods.(2) In the paper, the construction of the proposed DFT based fast OFDM scheme is also modified, which will make signal processing more convenient. The point of IFFT and FFT modules in the modified fast OFDM scheme will reduce to half. Meanwhile, the sampling multiple can also be improved. After that, the mitigation methods for interference proposed above also fit the modified fast OFDM scheme. Using both the modified construction and interference compensation method, the DFT based fast OFDM scheme will be more suitable for the future optical transmission system.(3) To investigate the compensation methods and the modified fast OFDM scheme, the simulation system based on VPI and matlab is built. This system can support40Gbit/s fast OFDM scheme perfectly.