Researching On The Analysis And Reducting Method Of Nonlinear Distortion In OFDM-ROF System

The Radio-over-Fiber (ROF) system, combined the flexibility of wireless access and the high capacity, low cost fiber together; Orthogonal frequency division multiplexing (OFDM) technology has a lot of advantages, such as robust anti-interference capability, high spectral efficiency, large transmission capacity and so on. Therefore, both OFDM and ROF have been publicly regarded as kernel technology of 4G systems. The combination of OFDM and ROF, which also called OFDM-ROF optical transmission System, is a promising technology to apply to 4G networking, and it has become a research hotspot of current correspondence domain. We investigated the non-linear distortion of OFDM-ROF system by simulation and experiment. Specifically including:1. We constituted a theoretical model to reduce nonlinear distortion of the OFDM-ROF system by lowing the peak to average power ratio(PAPR) of the OFDM signal. Based on system simulation, we demonstrated and compared the performance of clipping and selective mapping (SLM) techniques in reducing nonlinear distortion, and analysed their advantage and disadvantage.2. A novel scheme employing an optical phase modulator to generate optical millimeter(mm)-wave with optical orthogonal frequency division multiplexing (OFDM) signal is theoretically analysed and experimentally investigated, studied the non-linear distortion of the generated optical signal on ROF system. And compared it with the scheme that the optical mm-wave with OFDM signals generated by an optical intensity modulator.The experimental results show that under the high optical power, after transmission over 50km standard single-mode fiber(SSMF),the power penalty of the optical mm-wave generated by the optical phase modulator is less than 0.5dB and the optical intensity modulator is more than 1dB. It demonstrated that the fiber transmission quality of optical mm-wave with OFDM signal generated by the optical phase modulator is better than the one generated by the optical intensity modulator.3. By introducing Turbo codes to optical OFDM signals, we have experimentally demonstrated the feasibility of the 60GHz OFDM-ROF system with Turbo coded and the data rate is 1.65Gb/s, then, studied the improvement of system performance employing Turbo code. We also have proposed and experimentally investigated a novel scheme based optical OFDM long-reach access system. This system provides high bit rate and reduce bandwidth demand by employing quadrature amplitude modulation (QAM)64 modulation for every subcarrier in OFDM signals, correctes the non-linear distortion, improves transmission performance and distance by employing Turbo code technique.