Real-Time Polarization Demultiplexing by Multi-Thread Constant Modulus Algorithm for Fully Softwarized Access Networks

Optical access networks are replacing dedicated hardware-based architectures with architectures centered on general-purpose servers based on network function virtualization (NFV) and the software-defined network (SDN) in order to efficiently support various new services. To maximize the advantage of this new approach, studies are now targeting the fully softwarized access network which requires softwarization of digital signal processing (DSP). However, polarization demultiplexing includes sequential processing, and it is difficult to softwarize high-speed filter updates in a constant modulus algorithm (CMA) that supports real-world state of polarization (SOP) change. This paper proposes a novel multi-thread CMA that can track fast SOP changes by using multiple threads to implement filter convolution. It tracks faster SOP changes with the same filter update cycle as the conventional method by calculating multiple filters on multiple threads and averaging them. Its graphics processing unit (GPU) implementation adopts parallel reduction for averaging the filters and parallelizes the update of filters for tributaries X and Y in order to take advantage of many GPU threads. We evaluate the real-time bit error rate (BER) performance achieved by implementing the DSP functions with the proposal in a 5-Gb/s dual-polarization-quadrature phase-shift keying (DP-QPSK) system. The demonstration results show that the proposed algorithm supports 2,000 rd/s real-time performance for optical systems and offers high feasibility for application to the fully softwarized access network.