Research On The Phase Noise And SSB Modulation Technology For OFDM-ROF System

With the development of information technology and the populatization of mobile terminal,people for the requirement of communication network are also becoming higher and higher.Large-capacity,high-capacity and high-speed will be a hot spot in the development of information technology.Radio of Fiber(Radio-over-Fiber,ROF)system combines the advantages of high-capacity fiber-optic transmission and anti-electromagnetic interference,as well as the advantages of wireless transmission flexibility and simple equipment.It means that the efficiency and quality of information transmission will be improved,and the investment cost will be reduced.Therefore,ROF technology will play an important role in the development of future information technology.Orthogonal frequency division multiplexing(OFDM)is a multi-carrier modulation technology.It can effectively improve spectrum utilization in wireless communication and is the core technology of the fourth generation mobile communication system.The OFDM-ROF system,which combines the advantages of both technologies,has now become a hotspot in communication technology research.The main academic contributions are listed as follows:1.The related technologies of OFDM system have been in-depth studied and analyzed,mainly including its implementation method and numerical model.In order to demonstrate the advantages of spectral efficiency,we calculated and investigated the frequency spectrums and time domain waveforms of OFDM system.According to the modulation and demodulation model,we set up a numerical simulation platform for OFDM system,and studied the transmission performance of the system.Finally,the principle of single side band(SSB)modulation technology was elaborated and illustrated by numerical simulation.2.The impact of phase noise on OFDM-ROF system was investigated and suppressed by a pilot based method.The transmission performance of OFDM-ROF system under the influence of phase noise and suppression performance were simulated and analyzed by the simulation platform mentioned above.We compared the numerical results obtained before and after noise suppression,which shows that this method can effectively suppress the impact of phase noise.3.We proposed an optical coupling SSB modulation technology based on 120°hybrid coupler for the OFDM-ROF system.This system loads two radio frequency(RF)signals on the same optical carrier,and 120 ° hybrid coupler is used to combine two RF signals.Based on the numerical simulations,the factors of affecting the transmission performance,such as harmonic distortion and inter-modulation distortion,are theoretically analyzed.We compared the error vector magnitude(EVM)under different modulation index for OFDM-ROF systems based on120 ° hybrid coupler and 90 ° hybrid coupler.The obtained results show that the OFDM-ROF system based on 120 ° hybrid coupler has better performances in terms of EVM.After 40 kmtransmission,when the modulation index of the system is 0.2,the EVM is less than 0.05.When the OSNR is increased from 20 dB to30dB,the system of EVM is reduced gradually.The relationship of the power into the fiber and EVM shows that the EVM of the system can be very small.