Channel Estimation Technology In PDM-Co-OFDM Systems

Orthogonal Frequency Division Multiplexing (OFDM) technology has gained more and more interests in optical communication fields because it enables high frequency spectrum efficiency, adaptive modulation and simple channel equalization. Direct-detected optical OFDM (DDO-OFDM) and coherent-detected optical OFDM (CO-OFDM) are two forms of optical OFDM systems. CO-OFDM systems, with the advantages brought by coherent detection, maintain phase information and therefore adopt many digital signal processing (DSP) methods, which are greatly valued by researchers. Polarization-division-multiplexed CO-OFDM (PDM-CO-OFDM) systems can double the data rate, making them competitive candidates of beyond 100 Gb/s Ethernet.Among the various DSP technologies in PDM-CO-OFDM systems, channel estimation is an important one, which is the basis of depolarization. The Least Square Etismation is widely used because of its simplicity. However, it has a low tolerance of noise. Some improvements based on averaging in time and frequency domain have been proposed. But they are all problematic under certain conditions.In this paper, the principle of PDM-CO-OFDM system and its structure were researched and the optical fiber channel was analyzed. Using Matlab, a PDM-CO-OFDM system was built and the current channel estimation methods were inverstigated and simulated on the platform. Finally, the paper initiated a new noise-suppressing method based on channel impulse response filtering, greatly enhancing the estimation accuracy. Besides, the solution of applying adaptive weighted channel estimation (AWCE) algrithm to PDM-CO-OFDM system was proposed and the effect was confirmed by Matlab simulation on the platform.