Multi-Rate Kalman Filter for Carrier Phase Recovery in 200 Gbps PDM Coherent Optical Receivers

The Kalman filter is often used for tracking and estimation of effects such as LPN and NLPN in long haul coherent optical communication systems. However, real-time symbol-by-symbol estimation of these parameters is computationally challenging. We use a multi-rate Kalman filtering scheme that allows for different sampling and state update rates in the system. This scheme achieves high Q-factor by making use of maximum available samples while reducing computational load. Simulations are performed for 200 Gbps PDM-16-QAM system by transmitting 20000 symbols over 800 km optical channel. The filter has Q-factor of 17.25 dB with state estimates being updated after every 20 samples. The filter shows more than 1 dB improvement in Q-factor when compared to a KF where the intermediate samples are not utilised for phase estimation.