Research On Implement And Simulation Of OFDM In ROF System

With the growing demand of high data rate communication services, future communications tend to be with higher frequency and wider bandwidth. Radio-Over-Fiber system incorporates both feature of optical and high frequency radio wave transmission and could realize the long-haul transmission of high capacity and low cost radio-frequency signal and the ultra wide band wireless access which is more than 1Gbit/s.As one of the key technologies of the beyond third generation (B3G) or the fourth generation (4G) mobile communication system, OFDM could improve the spectral efficiency of wireless communications greatly and overcome the inter-symbol interference. The incorporation of these two technologies has become the hotspot of investigation for optical communications in recent years.This dissertation is about the research on the implement and simulation of OFDM in ROF system, divided into three parts:(1)The basic structure of ROF system and the key technologies of transmitter and receiver are discussed, especially the external modulation based on M-Z modulator and the coherent demodulation. The key technologies of OFDM are also discussed, including IFFT, cycle prefix and PAPR. We especially focused on the study of channel estimating via theory and simulation. The system performance before and after channel estimating were compared.(2)The structure of ROF-OFDM system was designed. OFDM radio frequency generating based on I/Q modulator and optical external modulation based on M-Z modulator were adopted in the transmitter. Coherent detection was adopted in the receiver. The system performance could be demonstrated with the simulation in VPI. Some schemes are proposed to improve the system, such as the compensation of the phase noise and the abstraction of the self carrier.(3)The structure of high speed WDM-OFDM system was designed. High speed optical transmission in despite of low speed RF signal was realized with polarization multiplexing and wavelength division multiplexing in the transmitter. The system was proved to be feasible via VPI simulation.In the last chapter the whole thesis was concluded.According to the research of capacity, coherent detection and multiplexing, we can conclude ROF-OFDM and WDM-OFDM systems hold the potential of enhancing spectral efficiency and capacity comparing with different systems. So ROF-OFDM will be regarded as an inevitable promising approach to exploit high frequency resources among many emerging technologies.