Research On Symbol Synchronization And Channel Estimation In Broadband PDM-CO-OFDM System

With the development of cloud computing and Internet of Things,the emerging multimedia services bring about a great increase in the backbone transmission capacity.It poses a big pressure on information infrastructure.Improving the transmission rate and spectral efficiency in the fiber channel is a good way to reduce the transmission cost per information bit.It will lead to the promotion of optical-fiber network transmission capability.Taking the coherent optical orthogonal frequency division multiplexing technology combined with polarization division multiplexing technology can improve spectral efficiency.Morever,it will not at the expense of transmission distance.So it is able to meet the requirements of large capacity and long-distance optical communication in the future.Researching on the digital signal processing technology in PDM-CO-OFDM system and compensating for the system damage is the key to the development of ultra wideband optical communication system.Symbol synchronization and channel estimation algorithm in DSP module of PDM-CO-OFDM are studied.The main completed works are as follows:1.An improved symbol synchronization algorithm is proposed.It is able to solve the synchronization offset problem in the traditional symbol synchronization algorithm,which is affected by the dispersion in the optical fiber channel.The numerical simulation shows that the improved symbol synchronization algorithm is able to obtain an accurate symbol synchronization points.Morever,the training sequence used in this algorithm can be used in the channel estimation process.It decreases the training sequence overhead.2.A channel estimation algorithm based on a low overhead training sequence structure is proposed.It is specified to be utilized in the PDM-CO-OFDM system.This pair of training sequences on two polarization direction are orthogonal in frequency domain.It can obtain the PDM channel state information with utilizing one block of training sequences only.So it improved effective transmission rate.The numerical simulation shows that the improved algorithm can obtain a better performance than other traditional channel estimation al gorithm,especially at the low OSNR.3.Basing on the improved symbol synchronization algorithm and channel estimation algorithm,a joint symbol synchronization and channel estimation algorithm is proposed.This algorithm utilizing the channel information obtained by symbol synchronization process can futher improve the channel estimation performance.It is verified by numerical simulation.