A Low-Complexity Carrier Phase Recovery Architecture Using Prefix-Sum and CT-MLE for Coherent Receivers

Hardware-efficient carrier phase recovery (CPR) is critical for coherent optical systems employing high-order quadrature amplitude modulation. This letter proposes a low-parallelism and low-complexity CPR architecture. It introduces a parallel prefix-sum engine that exploits the sparsity of the symbol distribution, enabling the hardware parallelism to be significantly reduced without information loss. Furthermore, the architecture features a multiplication-free maximum likelihood estimation to reduce intrinsic computational complexity. Implemented in 28 nm CMOS for 32 GBaud system, the proposed CPR estimator reduces area by 51% and power by 39% compared to a conventional mVV-CT-VV baseline, achieving state-of-the-art efficiencies with only 0.37 dB signal-to-noise ratio penalty.