Low-Complexity Design of Noninteger Fractionally Spaced Adaptive Equalizers for Coherent Optical Receivers

In this letter, we address the design of fractionally spaced adaptive equalizers when the input signal is sampled with noninteger, subsymbol sampling. We consider the problem of joint equalization and sample rate conversion and derive a stochastic gradient-based weight update algorithm for the equalizer. This enables us to decouple the equalization of channel impairments from that of fixed (periodic) distortion arising from noninteger, subsymbol sampling. This decoupling leads to a novel low-complexity architecture for the equalizer that shows superior or equal performance as compared to the existing architectures with higher complexity.