Research On Trellis Coded Modulation Technology In Optical OFDM System

Because the emergence of services such as 4K/8K ultra-high-definition video,artificial intelligence,and the Internet of Things,optical communication systems have an increasing demand for speed.Orthogonal Frequency Division Multiplexing（OFDM）technology has high spectral efficiency and can resist inter-symbol interference,so it is regarded as one of the most suitable schemes in the future optical communication system.Besides,Trellis-Coded Modulation（TCM）can improve the receiver sensitivity without reduce the data rate,it provides a feasible scheme for improving system performance.However,in optical OFDM communication system with intensity modulation,the signal-to-noise ratio distribution of each data sub-carrier of the signals are unbalanced,which leads to the degradation of TCM performance.In this paper,the transmission performance of 4-dimensional TCM（4D TCM）signals combined with precoding technology is studied in the optical OFDM communication system based on intensity modulation.The main work is as follows:1.A method combining 4D TCM OFDM signals and Discrete Fourier Transform（DFT）precoding is proposed,and verified in the underwater optical wireless communication（UOWC）system.The proposed scheme alleviates the effect of power fading caused by scattering,attenuation and reflection in the UOWC system,and improves the system performance.The experimental results show that when the bit error rate is 3.8×10^-3,the receiver sensitivity of the 4D TCM 64-Quadrature Amplitude Modulation（QAM）-OFDM signals using DFT precoding is 1.28d B higher than that of the 64QAM-OFDM signals at the same data rate.2.A method combining 4D TCM OFDM signals and precoding technology is proposed and verified in W-band Radio-over Fiber（Ro F）system.The performance using DFT precoding,Constant Amplitude Zero Autocorrelation Sequence（CAZAC）precoding and Orthogonal Cyclic Transform（OCT）precoding are compared.The proposed scheme reduces the impact of frequency selective fading on 4D TCM 16QAM-OFDM signals.The experimental result show that after 50km single-mode fiber and 5m free space,for 4D TCM 16QAM-OFDM signals,OCT precoding has the worst performance,and CAZAC precoding can achieve the best performance.