Research On Equalization Algorithm For PDM Coherent Detection System

With the explosive growth of various data and the limitation of bandwidth,optical communication system based on fiber amplifier and traditional dense wavelength division multiplexing(WDM)has been unable to meet the rapidly growing demand for information.The study on polarization multiplexing technology in recent years,using the two orthogonal polarization independent transmission of information,do not take the extra bandwidth needs,the transmission capacity increase based on existing multiplexing technology,and further improve the utilization rate of spectrum.It is widely used in modern high speed optical communication system.In optical communication system,with the application of fiber amplifier,the influence of fiber loss on the quality of communication can be ignored.At present,the dispersion compensation technology is mainly carried out in the optical domain,and the direct detection system can not meet the requirements of high-speed coherent optical communication.This paper will study the adaptive algorithm for digital processing module by using the algorithm to solve the convergence speed and precision of the opposite problem,and the use of higher order modulation algorithm is studied.The specific research contents are as follows:(1)This paper has done a lot of theoretical analysis on electric domain equalization algorithm,deduces the algorithm convergence speed and time problems,and introduces the present to solve the problem of two kinds of optimization scheme,through the analysis of the improved scheme that the computational complexity is higher than that of the fixed step length algorithm.So this paper puts forward the improved algorithm of piece wise iterative step,fixed step size and variable step size in two ways including segment step,the improved method is applied to the least square method and constant modulus algorithm.The feasibility of the scheme is verified by polarization multiplexing QPSK modulation system.The results show that the improved algorithm has better convergence speed and accuracy than the general improved algorithm.(2)For the 16 QAM modulation mode,in order to ensure the high spectral efficiency of the system,the current equalization algorithm is a constant modulus algorithm without reference sequence.But the 16 QAM modulation mode the number of values not only,the constant modulus algorithm cannot generally be used directly,so this paper proposed a improved algorithm based on the calculation of actual situation separately,this algorithm can reduce the number of die,but will not die as the only value,and the computation complexity is high.Therefore,in order to solve theseproblems,this paper proposes an improved constant modulus algorithm based on decision theory.Based on the analysis,the algorithm is simpler and more balanced,and the computational complexity is lower.