Research On DSP Algorithms For Minimum Shift Keying Signals In Optical Coherent Detection Communication Systems

Minimum shift keying(MSK)is widely used in wireless digital communication systems for its continual phase shifting,high spectrum efficiency,constant envelope and fast roll-off side-lobe spectrum.Recently,with the development of optical devices and digital signal processor,the electric signal processing method is more striking,because it enable compensate fiber impairment.In the thesis,it mainly focuses on the channel impairments of the MSK signals in optical coherent detection communication systems.And the channel impairment can be compensated by proposed DSP algorithms after coherent detection.The main research results are as follows:1.A new timing synchronization algorithm based on Golay complementary pair is proposed.The simulation has been studied in MSK coherent optical system.Compared with orthogonal frequency division multiplexing systems,the deviation of timing synchronization is more severely to the single carrier systems.Therefore,timing synchronization is crucial in single carrier systems.This thesis proposed a new symbol timing synchronization algorithm.We designed the training sequence and timing synchronization function by using the property of the Golay complementary pair.The performance of the proposed timing estimator is evaluated by mean and MSE,and is compared with those of Schmidl's,Minn's and Park's methods.The simulation results reveal that the new proposed algorithm can obtain excellent timing offset curve.Besides,it has much smaller mean and MSE than the other algorithms when the OSNR is low.2.The data-aided joint time-frequency channel estimation and equalization algorithm is proposed.The simulation has been studied in MSK coherent optical systems.In this thesis,the channel impairment can be equalized and compensated by DSP algorithm in the receiver.The amplified channel impulsive response samples can be obtained in the initial timing synchronization procedure.Then,the channel frequency estimates are acquired by Direct Fourier Transform.Subsequently,the signals processed by Laurent decomposition in the frequency domain.The simulation results verify the feasibility of the proposed method.5-Gb/s MSK signal transmit over 80km standard single mode fiber(SSMF).At the receiver,we propose the joint time-frequency channel estimation and equalization algorithm to compensate the impact of channel distortion.Besides,we analyze its performance characteristics compared with quadrature phase shift keying(QPSK)format.The simulation results reveal that MSK modulation format achieve better performance in low speed and short reach optical transmission compared with QPSK format.It will be a potential candidate for next-generation access network.