Optical Coherent Detection Communication System And Research On Blind Equalization Algorithm For MSK Signal

Recently,minimum-shift keying(MSK)has paid more attention in the optical communication,owing to its constant amplitude and continuous phase at every bit transition instant and a narrow power spectrum.Meanwhile,in order to achieve higher spectral efficiency and electronic compensation of impairments,the MSK modulation in optical coherent system were widely investigated.However,the chromatic dispersion(CD),polarization mode dispersion(PMD)and amplified spontaneous emission(ASE)noise in MSK coherent optical communication system would result in a serious signal amplitude distortion and phase deviation.Blind equalization technology could eliminate the transmission impairments and does not need any training sequence,it could improve the bandwidth availability and low the demand of cooperativity between the transmitter and receiver.Hence,the adaptive blind equalization technology which is mature and low-cost is worthy to be applied in MSK coherent optical transmission at the receiver.In this paper,the performance of adaptive blind equalization was investigated in MSK coherent optical transmission system by simulation.the main achievements of the paper conclude as follows:Firstly,under the knowledge of basic principle of MSK modulation technology in the wireless communications,the key techniques,the advantages and disadvantages of MSK signals are briefly introduced.Then,the common adaptive blind equalization algorithms in coherent optical system are described and performance of these algorithms evaluation criteria in MSK coherent optical systems are also discussed.Secondly,in our paper the simulation of a 10-Gb/s optical MSK signal transmission and coherent detection digital communication system based on standard single-mode optical fiber(SSMF)is established.The baseband MSK signal is generated using MATLAB with off-line programming.Then,the baseband electrical MSK signal is modulated on an optical carrier with quadrature modulator(QM)over SSMF.In order to model the various transmission impairments,the laser phase noise,CD and EDFA ASE noise are taken into account.At the receiver,we use DSP to implement electronic compensation of varies impairments in digital domain.Finally,it is theoretically investigated the effects of impairments and blind equalization on MSK signal in coherent optical communication.After the classical constant modulus algorithm(CMA)equalization step,the output of the equalizer does not necessarily coincide with a delayed and rotated version of the input MSK signal.In our MSK coherent optical system,a novel blind equalization criterion is proposed to eliminate the latter indeterminacy.The proposed scheme,considering the constant modulus feature and the consecutiveness of the MSK signal simultaneously,it has better results than the classical CMA.Simulation results show that the 10-Gb/s MSK system successfully recovers MSK signal from various transmission impairments.