Research And Implementation Of Phase Compensation In IM/DD OOFDM System Based On Tunable DPLL

With the popularization of 5G networks,terminal equipment has increased the demand for traffic bandwidth,which will inevitably lead to backbone networks and metropolitan area networks with high-speed dynamic bandwidth allocation capabilities.Optical Orthogonal Frequency Division Multiplexing(OOFDM)has attracted the attention of scholars in the field of optical communications with its advantages of large capacity,high spectrum resource utilization and high dispersion tolerance.Synchronization technology is a very key technology in the OOFDM system,which can be divided into carrier synchronization,sampling clock synchronization and symbol synchronization,and the carrier frequency,clock and symbol are adjusted and aligned respectively.In recent years,research on OOFDM systems has focused on offline methods or simulation stages,and even in real-time hardware implementations,different algorithms target different complexity and hardware resources.A set of feasible algorithms with corresponding hardware complexity is extremely important for the realization of the OOFDM system.In this paper,a phase compensation algorithm based on dynamically tunable DPLL is proposed for real-time optical orthogonal frequency division multiplexing(IMDD OOFDM)system with direct detection of intensity modulation.In this experiment,we build an IMDD OOFDM system based on FPGA.We focus on the implementation of the key DSP modules of phase compensation,and evaluate the transmission performance of the system.The main research contents and achievements are as followsFirstly,the mathematical model,basic principle and key technologies of OFDM system are deduced.The basic structure of IMDD OOFDM system is introduced.Then the influence of sampling clock deviation on the system is analyzed theoretically.Secondly,several schemes of compensating sampling clock deviation are introduced,and their advantages and disadvantages are analyzed in detail.On this basis,an analog-to-digital hybrid phase compensation algorithm based on IMDD OOFDM system is proposed and verified by experiments.The experiments show that the phase compensation algorithm can effectively estimate and compensate the frequency offset error of real-time sampling clock,and the system frequency offset is stable within ±0.64ppm.Thirdly,based on FPGA and DPLL,a real-time high-speed IMDD OOFDM system is built.This research focuses on the overall scheme design,and introduces the design scheme of the key DSP module in detail.Based on the hardware,the transmission performance of the transmitter and receiver is simulated and estimated.The reliability of the system is verified by the feasibility analysis of the frequency offset signal value calculated by the captured phase compensation module in real time and the EVM.