Research On Digital RoF System Assisted By Digital Signal Processing

Radio over Fiber(RoF)is used for the transmission between the baseband processing units of the mobile communication central Office and the remote radio head due to its huge bandwidth,which has become a key technology in 5G research.Analog RoF is a RoF technology early concerned and deeply studied.Although its base station is simple,its requirement of modulator’s bandwidth and linearity is restrict.Since The high frequency signal is affected by the dispersion of fiber,and the high frequency microwave device and light modulator are greatly influenced by nonlinearity,the analog RoF technology can be suitable for short distance and large signal bandwidth transmission.However,the digital RoF moves the digital analog interface from central office to places between office and antenna.Although the processing load of the base station is increased,with the stability of digital optical fiber link,small and easily compensated nonlinearity and dispersion,digital RoF is suitable for long distance and high performance transmission.Therefore,the digital RoF is widely favored by the industrial world.We will study digital RoF system with the assistance of digital signal processing.This paper is organized as follows: firstly,the basic principle of RoF system and present situation is introduced.We mainly compare the advantages and disadvantages between analog RoF and digital RoF,as well as their suitable conditions.And band-pass sampling and OFDM modulation and demodulation are described in detail.Secondly,according to the principle of digital RoF communication system,we write part of encoding/decoding and digital signal processing program.Based on the OFDM modulation and demodulation technology,we establish a 1Gb/s digital RoF transmission system and do the Simulation verification with the Optisystem software.The paper summarizes the system characteristics of digital RoF and verifies that digital RoF has a good system performance in a certain dynamic range,which is in accordance with the previous theoretical study.Then,according to the high peak-to-average ratio(PAPR)in OFDM modulation,we study the generation mechanism of high PAPR and present a low complexity PAPR suppression technique with CAZAC consequence,which can reduce the PAPR,nonlinear effect and symbol error rate of the system effectively.We set up two digital RoF with the digital signal processing polarization solution multiplexing algorithm that based on the OOK signal direct detection polarization multiplexing system.By means of the polarization orthogonal multiplexing system,a method of using the simplified Stokes optical intensity detection at the receiver is presented,which can realize polarization DE multiplexing without Polarization tracking circuit.Simulation results prove that the system capacity is doubled.