Study On Applications Of Digital Predistortion Technology In ROF System

With the rapid development of wireless communication technology, great changes take part in peoples'communication methods.The increasing number of users and the emergence of new services require higher transmission quality and boarder bandwidth.Non-constant envelope modulation formats,such as OFDM can cope with severe channel conditions such as narrowband interference and frequency-selective fading due to multipath,while RoF system can provide abundant bandwidth due to the relevant characteristics of optical fiber. RoF system with OFDM signal became an attractive solution in future wireless communication field.However, non-constant envelope modulation signals are especially vulnerable to the nonlinear distortions due to their high PAPRs.The biggest limitation of OFDM-RoF system is limited dynamic range.This thesis attempt to solve the problem by using DPD technology to reduce nonlinearity of RoF link.The network architecture, characteristics and advantages of RoF system are introduced at first. Then the thesis points out the limitation when it carries OFDM signal and introduces digital predistortion (DPD) technology as a solution. After that, linearization technologies especially DPD technology are discussed. Then the nonlinearity of RoF link is analyzed and a DPD algorithm model based on Volterra series is created.An implementation scheme of DPD is proposed and simulation results show the feasibility of the scheme. Finally, the implementation of the scheme on an FPGA demo board is illuminated in detail with the guidance of software defined radio(SDR) and the test on the hardware testbench shows the DPD works well.For the test source WiMax signal 8.5dB EVM improvement and about 13dB ACPR improvement are obtained.