Timing Recovery Algorithm Research Of MSK High-speed Coherent Optical Receiver

Optical fiber communication, which raises more claims for the transmission rate anddistance, occupies many fields in wire communication and becomes the main trend in thedevelopment of communication engineering. To obtain higher spectral efficiency, MSK hasbeen applied in coherent optical communication system with large capacity and high speed.In high-speed optical fiber communication systems based on MSK modulation, researchingtiming recovery algorithms with low complexity and reliable performance has great valuesin practical applications.Two kinds of basic timing recovery algorithms, based on feedback and feedforward,are presented in this paper respectively. According to the orthogonal modulation principle,MSK signal could be equivalent to QPSK signal. Detailed derivation and analysis about therealization of MSK timing recovery algorithms is offered. Timing recovery algorithmsbased on feedback and feedforward have been realized in Gauss channel and fiber channelwith MATLAB.In Gauss channel, the feedback timing recovery algorithm offers accurate timinginformation. But it suffers from oscillated delay and low convergence rate in the initial stageof the signal sequences transmission, which is by the iteration operation. The feedforwardtiming recovery algorithm can realize real-time location, showing better anti-interferenceperformance to Gaussian white noise. In fiber channel, although converging to zero, thefeedback timing recovery algorithm shows instability and its estimation error of the signalamplitude oscillates all the time. As the nonlinear factor increases, the error betweenestimated time delay and real time delay gradually grows in feedback algorithm, butgenerally stays stable in feedforward algorithm. Therefore feedfoward algorithm showsbetter performance in resisting nonlinear damages.