Carrier Phase Recovery of 64 GBd Optical 16-QAM Using Extensive Parallelization on an FPGA

Carrier phase recovery (CPR) for phase noise mitigation is a vital part of modern coherent optical systems. As higher order M-QAM modulation formats are being employed to increase network capacity, CPR complexity grows as well, and more powerful chips are needed to cope with the advanced DSP. In this paper we present an FPGA-based flexible architecture of the Nonlinear Least Squares (NLS) CPR algorithm, targeting present-day and future generation systems. We describe optimization approaches at the algorithmic and HW levels to facilitate HW efficiency, while we combine multiple parallelization techniques to achieve high-throughput processing. Considering various FPGA devices, we perform fine-grain exploration with respect to cost, throughput and accuracy to support up to 64 GBd 16-QAM links with less than 1 dB SNR penalty.