Post-FEC BER Performance Analysis for Multistage PAM4 Systems

In a multi-stage link system where forward error correction (FEC) encoding/decoding is only used in the end devices of the end-to-end link, mixed mode errors (random and burst errors) from each sub-link stage collectively impact the end-to-end link performance. This paper introduces an analytical method for evaluating RS-FEC performance in multi-stage PAM4 systems. Typical application scenarios include links with retimer(s), and electrical-optical-electrical (E-O-E) links such as 200GAUI-n/400GAUI-n systems. Simulations are performed to study the impact of sub-link stages on the overall system post-FEC BER performance.