Direct-modulated Multiple Formats Optical OFDM System Based On Discrete Wavelaet Transform

Optical Orthogonal Frequency Division Multiplexing (OOFDM)communication system has the characteristics of high spectral efficiency and good transmission damage robustness, so it has received extensive attention. With a variety of services such as digital high-definition television, cloud computing and online games and other services, optical fiber communication system is also towards high efficiency, multiple service. In future communications, optical OFDM systems are also a very competitive alternative. However, the traditional Fourier transform based OFDM system is limited by the peak average power is relatively high,sensitive to frequency offset and timing bias and other shortcomings,limiting the application of OFDM. Therefore, on the basis of Fourier analysis, a frequency analysis method for dealing with non-stationary signals emerges, that is, wavelet analysis. Wavelet analysis has the ability of Fourier analysis to reflect the local frequency domain. Wavelet function can provide a series of orthogonal bases, which are very suitable for signal waveform design in communication system and orthogonal sub-channel division of multi-carrier transmission system And so on, in the communication system design is very potential. In this paper, the multi-carrier modulation based on discrete wavelet transform is used to replace the Fourier transform process in OFDM, and two improvement schemes are designed according to the system characteristics and optical fiber transmission characteristics. The transmission characteristics are studied by simulation. The main research work is as follows:(1)On the basis of studying the basic principle of OFDM technology,this paper focuses on some key technologies in OFDM technology. In view of the advantages and disadvantages of OFDM technology, the multi-carrier modulation based on discrete wavelet transform is proposed to replace the Fourier transform in OFDM, An OFDM transmission system based on discrete wavelet transform is designed, and the different wavelet bases, the number of layers and the redundancy are simulated. The simulation results show that the DWT-OFDM system proposed in this paper is superior to the FFT-OFDM system in terms of peak-to-average ratio and spectrum utilization. When different wavelet bases, resolution layers and redundancy are used, the performance of the system is different.(2)On the basis of studying the basic principle of DWT-OFDM, a multi-format modulation scheme is designed to improve the system. 32 channels system which is modulated by 8QAM, 16QAM and 64QAM ,is achieved by using the digital filter bank, and a simulation study is carried out. The results show that the multi-format system proposed in this paper has better bit error rate performance and has more flexibility in spectrum utilization and bit error rate performance than single-format system.(3)Based on the study of optical fiber transmission characteristics and the basic principle of DWT-OFDM system, a direct modulation scheme is designed by realizing the complex signal and directly modulating the laser.Finally, by combining with the multi-format scheme, the direct-modulated multiple formats optical OFDM system based on discrete wavelet transform is realized, and the simulation is carried out at the rate of 5Gb/s in 100km optical fiber. The results show that the system proposed in this paper has good bit error rate performance, which effectively reduces the complexity of the transceiver and improves the spectrum utilization rate.