Joint Partial Response Equalization With Mapping-Rule-Based Simplified Maximum Likelihood Decoder for Intra-DCIs

As the explosive growth of global IP traffic, the bandwidth growth of optoelectronic devices in intensity modulation/direct detection (IM/DD) systems has begun lagging the capacity increasing of intra-datacenter interconnects (DCIs). The partial response (PR) signaling and various advanced equalizers have been introduced to solve the band-limited effect. In this paper, we propose and experimentally demonstrate a joint PR equalization (PRE) with mapping-rule-based simplified maximum likelihood sequence estimation (MRS-MLSE) scheme in a 256-Gb/s 4-ary pulse amplitude modulation (PAM-4) transmission system. The MRS-MLSE compresses the candidate alphabet of each PRE symbol according to the mapping rule of PRE signaling, resulting in a 41.2% computational complexity reduction compared to the traditional full-state MLSE. Moreover, we design a “Monitor-Activate-Correct” structure that activates the MRS-MLSE to correct errors when detecting error propagations caused by the fundamental 1/(1+D) decoder. The experimental results show that the proposed method can suppress the error propagation in the 1/(1+D) decoder effectively, and achieves a similar performance as the full-state MLSE decoder, which has only 0.3-dB receiver sensitivity penalty compared to it. The statistic results of various transmission scenes indicate that the MRS-MLSE is activated to process lower than 3.74% of total symbols at the KP4-FEC threshold of 2.4×10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup>.