Research Baseband Modulation Technique In A Wireless Optical Fiber Fusion System

In recent years, along with the rise of the Internet, we have entered a new era-the age of the Internet, in which people’s demand for data is showing explosive growth. So, this requires the communication system has higher transmission rate and bandwidth, however, the conventional mobile communication system has been faced with the completed resources division in low frequency band, and the bottleneck of rate improvement. To solve this problem, researchers have been investigating the higher-frequency wireless communication technology and fiber access technology closely, achieving a significant breakthrough. Radio Over Fiber (ROF) technology, using optical fiber to transmit radio frequency signal, combined with high-capacity, low-loss and wireless communication flexible access characteristics, can be a good solution to the problem of the band depletion and be the focus of the wireless communication research in future, meanwhile it has a great potential for development. In this paper, baseband signal modulation technology in ROF system is in-depth research. The main work and achievements of this paper are as follows:Firstly, after having made a deep research and analysis on the ROF technology research status and development trend, I deeply understand the optical domain millimeter-wave signal generation technique, the optical detection technology, the base station simplified technology and baseband signal modulation technique in ROF, among which the baseband signal modulation technique is the focus of this study.Secondly, aiming at baseband modulation technique in ROF system, this paper studies the model of ROF system based on I/Q modulator and gives a detailed mathematical derivation for the system model. According to the characteristic of the system model,this system is divided into uplink and downlink and the simulation analysis is alone. I studied the impact of modulation index on system performance and the influence of I/Q modulator nonlinear characteristic on multiplexed signal under different modulation formats. And use a pre-distortion method to improve the effect of the modulator nonlinear characteristic on system performance.Then, based on I/Q modulator ROF system, build an experimental platform for research, finding the laser linewidth and frequency offset severely affect system performance. First of all, the paper studies the influence of the laser frequency offset and phase noise on system performance in means of simulation experiment. For frequency offset, this paper analyzes the two most commonly used frequency offset estimation algorithms in coherent transmission systems. For phase noise, in this paper, we adopt the differential phase detection method to suppress the influence caused by the phase noise on the system.Finally, in terms of experimental data, we use frequency offset estimation and differential detection for recovery processing, to study the different emitted optical power and the system performance under different carrier frequencies.