Research On Equalization Algorithm For PDM-SCFDE Optical Coherent Systems

With the development of mobile communication and digital multimedia business,much higher bandwidth of the access network and the backbone transmission network are required.Single carrier frequency domain equalization(SCFDE)technology has been paid more attention due to the advantage of low computation complexity in transmitter and favorable performance.To satisfy the requirement of ultra-high-capacity long-haul optical transport network,SCFDE combine with polarization-division multiplexing(PDM)becomes an effective solution.Currently,digital signal processing(DSP)replace optical domain compensation reduces device cost.However,the problem of signal redundancy and low equalization performance can not be ignored.In this thesis,DSP equalization and decision feedback algorithm is investigated and analyzed.The main works are as follows:1.A method of joint orthogonal training sequences and overlap frequency-domain equalization(OFDE)is proposed and demonstrated in PDM-SCFDE system.Orthogonal training sequences can be used to shorten signal redundancies at the transmitter.Meanwhile,favorable channel estimation accuracy can be implemented.By using OFDE method,no cyclic prefix(CP)is required at the transmitter to obtain favorable performance.And combined OFDE with orthogonal training sequences can improve bandwidth utility effectively.In addition,a 224-Gb/s PDM-SCFDE coherent optical communication system based on the proposed method is demonstrated by simulation.And the relationship of overlap length in OFDE and system performance is analyzed.Simulation result shows the proposed method has a better system performance and higher net bit rate.2.A method of residual inters interference(ISI)cancellation decision feedback equalization method based on the OFDE is proposed and demonstrated in PDM-SCFDE system.Minimum mean square error(MMSE)equalization has better noise reduction than zero forcing equalization in long-haul optical transport system,however there is residual ISI in equalized signal after MMSE.The proposed method of residual ISI cancellation based on OFDE is using decision feedback results to eliminate residual ISI after MMSE in PDM optical system.Simulation result shows the proposed method of residual ISI cancellation decision feedback combine with PDM based on OFDE can enhance bandwidth availability effectively and reduce bit error rate(BER)to improve system performance.