Research On Channel Estimation For PDM-CO-OFDM System

100 Gb/s rate optical communication systems are used on the market, the main focus on the optical communication system are more than 100 Gb/s. In high-speed optical transmission system, channel estimation and polarization multiplexing is more and more difficult to achieve because using the polarization multiplexing technology greatly reduces the system’s tolerance for the chromatic dispersion and polarization mode dispersion, laser linewidth. With the improvement of digital circuit chip production technology, it comes to truth that ADCs acquire the sampling rate and match the optical transmission rate. The Coherent Optical Orthogonal Frequency Division Multiplexing(CO-OFDM) systems offer improved receiver sensitivity, and DSP technique makes systems overcome the channel impairments, such as CD, PMD and so on.Among the various DSP(Digital Signal Processing) technologies in PDM-CO-OFDM systems, channel estimation is a significant one, which is the depolarization’s important basis. The Least Square Etismation algorithm is widely used owing to its simplicity. However, LS algorithm is sensitive to noise. Some improvements based on CIR(Channel Impluse Response) have been proposed. But they are all problematic under certain conditions.In this paper, we study the PDM-CO-OFDM(Polarization Division Multiplexing Coherent Optical Orthogonal Frequency Division Multiplexing) system.We analyse the signal and channel model, and use VPI Transmission MakerTM software to found a PDM-CO-OFDM optical transmission platform of 200 Gb/s rate. The communication platform is used for a simulation of chromatic dispersion and polarization mode dispersion, laser linewidth and ASE noise effect, etc. With the help of VPI Transmission MakerTM and MATLAB software, we found the DSP algorithm simulation platform. On the platform we simulate and analyse the PDM-CO-OFDM channel estimation algorithms, and according to its limitations, two improved methods based on DFT algorithm are proposed. Besides, this paper brings the first introduce of discrete cosine transform(DCT) which is widely used in the field of image processing into PDM-CO-OFDM system field. And the validity of DCT algorithm is verified on the VPI+MATLAB platform.