Identification and Mitigation of Burst Errors for Partial Response Equalization in 256-Gb/s Intra-DCIs

Bandwidth limitation effect is increasingly serious for beyond 200-Gb/s per lane intensity modulation/direct detection (IM/DD) systems with 4-ary pulse amplitude modulation (PAM-4) format. Advanced equalizers have been used to deal with the bandwidth limitation effect. Partial response signaling is effective for signal shaping to suppress the signal's bandwidth, where a decoder is required to recover the original data. However, the straightforward 1/(1 + D) decoder leads to burst errors. In this paper, we propose and experimentally demonstrate the joint partial response equalization (PRE) with multiplication-free burst error canceller (BEC) in a 256-Gb/s PAM-4 transmission. We utilize an out-of-range detector to identify the end and polarity of error propagation resulted from 1/(1 + D) decoder. Then, BEC is activated to identify the beginning of error propagation based on the characteristic of PRE noise from previous sequence so that we can derive the whole error event and thus correct it. The whole process uses only adders and comparators rather than multipliers. The experimental results show that the BEC only requires a dozen of adders to eliminate the error propagation caused by 1/(1 + D) decoder, reducing the maximum length of burst errors from 15 to five. Moreover, the BEC outperforms the duobinary precoding with modulo4 decoder and even has a coincident performance as MLSE, where the receiver sensitivity penalty compared with MLSE is only 0.25 dB at the KP4-FEC threshold. With the benefit of the “Monitor-Activate-Correct” structure, the BEC processes only 1.6% of total symbols. This demonstrates that the proposed method has little complexity but can significantly suppress the error propagation.