Design And Implementation Of The Real-time DSP System Of Kramers-kronig Optical Receiver

Traditional coherent optical receiver supports advanced modulation format and digital signal processing,which can achieve higher transmission rate and longer transmission distance.In recent years,a popular Kramers-Kronig(KK)receiver is proposed,which uses single photodiode and realizes optical field reconstruction through digital signal processing technology,thus greatly reducing the cost and power consumption.Therefore,it has been intensively studied worldwide.The main tasks of the DSP system include optical field reconstruction and coherent demodulation.This thesis focuses on its working principle,algorithm design and hardware system development.(1)First,the system structure and working principle of KK receiver are studied.The numerical simulation system of KK receiver is established based on VPI Transmission Maker and Matlab.The effectiveness of the algorithms is validated.KK detection algorithm is used in optical field reconstruction,Gardner algorithm is used in clock recovery,CMA algorithm is used in polarization de-multiplexing,and Viterbi-Viterbi algorithm is used in carrier phase recovery.(2)This paper investigates time domain and frequency domain implementation methods of Hilbert transform(HT)which is the most difficult part of the KK detection algorithm.Then an overlap-block HT algorithm is proposed based on fast Fourier transform and inverse fast Fourier transform,taking the computational complexity and algorithm performance into account.The effects of HT window,overlap factor and bit width truncation on HT performance were analyzed.The algorithm is further optimized to realize real-time HT for high speed signals,meanwhile suppress the impact of edge effect and truncation error effectively.(3)Parallel pipelined optical field reconstruction module and coherent demodulation module were developed based on Xilinx FPGA development board and Vivado.The optical field reconstruction module is further optimized to simplify the hardware.Finally the two modules can realize most of the functions the KK receiver DSP system.Experiment shows that the DSP system can realize real-time optical field reconstruction and coherent demodulation of 10 GBaud quadrature phase shift keying(QPSK)signal.The output signal quality satisfies requirement of our project.