Research On Channel Estimation And Synchronization Algorithm In High-speed Optical Coherent Systems

With the popularization of data services having high-speed and high-quality,a much higher bandwidth of the access network and the backbone transmission network are required.Per wavelength channel rate up to 100Gb/s which will become the mainstream data transmission rate of the future high capacity optical communication.Therefore,the dispersion effects will be a important factor affected the transmission quality.In the future ultra-high-capacity optical transport network,combine with single carrier frequency domain equalization(SCFDE)technology,the polarization-division multiplexing(PDM)coherent optical communication system is a effective solution.Compared to orthogonal frequency division multiplexing(OFDM),SCFDE has similar performance and complexity to avoid the high peak-to-average power(PAPR)and sensitivity to phase noise and frequency offset in OFDM system.The main completed works are as follows:1.A channel estimation method in PDM-SCFDE systems based on a pairs of orthogonal training sequences(TSs)in the frequency domain(FD)are proposed.The orthogonality of these TSs is formed owing to different null frequency ton es in that pair of TSs.Therefore,such construction allow to obtain the full PDM channel state information by using only one block period of total training overhead combine with a reconstructive algorithm.Thus,the proposed method is extremely bandwidth efficient.Moreover,a 100-Gb/s PDM-SCFDE coherent communication system based on the proposed method is demonstrated by simulation.Additionally,in comparison with some conventional methods,the proposed method is robust in the condition of lower optical signal to noise ratio.2.Four traditional training-based timing synchronization algorithm are investigated.And the synchronization performance of these algorithms are combined in optical channel.The synchronization points are obtained by these algorithms deviate from the real one and the errors affected by dispersion.In this thesis propose a timing synchronization algorithm based on orthogonal TSs in the FD aimed at these problems mentioned above.For the algorithm,the accurate synchronization point is achieved by the method of local cross-correlation.Additionally,the training overhead of system is reduced because the TSs can be used for channel estimation.Meanwhile,the availability of the algorithm is demonstrated through numerical simulations in a 100-Gb/s PDM-SCFDE coherent communication system.3.The effects of training-based channel estimation performance induced by timing synchronization errors are analyzed.Then,a method that joint frame synchronization and channel estimation based on a pairs of orthogonal TSs in the FD is proposed in this thesis.The proposed method is extremely bandwidth efficient because these two algorithms only need one block period of total training sequence overhead.Furthermore,the frame synchronization algorithm can get the perfect synchronization point and channel distribution information.Moreover,channel estimation using the channel distribution information can further improve the performance.The accuracy and robustness of the proposed method are demonstrated by the simulation of a 100-Gb/s PDM-SCFDE coherent communication system.