Simplified layered MLSE for PAM4 short-reach optical interconnects

To meet the high-speed and high-efficiency demands for optical interconnects, simplified layered maximum likelihood sequence estimation (MLSE) is proposed in this paper. Compared with the conventional MLSE, simplified layered MLSE reduces the processing delay from linear order to logarithmic order through the layered architecture, while simultaneously reducing the number of multipliers, adders, and comparators through the simplified scheme. The simplified layered MLSE is experimentally validated in a 112-Gbit/s PAM4 transmission over 2-km standard single-mode fiber. Compared with the conventional MLSE, the simplified layered MLSE achieves nearly identical bit error rate performance. Meanwhile, it reduces the processing delay from 34 clock cycles to 7 clock cycles, and also reduces the number of multipliers, adders, and comparators to 6.4%, 96.3%, and 32.8%, respectively.