Partial response DFE guided ultra-low complexity FTN signaling for high spectral efficiency intra-DCI

Faster-than-Nyquist (FTN) signaling is deemed a promising candidate for enabling high spectral efficiency in next-generation optical data center interconnects (DCIs). Trellis-based sequence detectors, such as maximum likelihood sequence estimation (MLSE) and maximum a posteriori (MAP) sequence estimation, operating with long memory lengths, are by far the most commonly adopted strategy for deciphering the original symbol from severe inter-symbol interference (ISI). Nevertheless, the inherent high complexity of this approach poses significant challenges to its practical implementation. In this paper, a partial-response decision feedback equalizer (PR-DFE) is proposed to realize ultra-low complexity and high-performance FTN signaling. The fundamental principle of the proposed scheme involves combining the transmitter-side precoding and receiver-side partial response equalization criteria, which significantly reduces the occurrence of the error propagation issue of the typical DFE in the FTN system. The effectiveness of the proposed scheme is experimentally verified in a 56Gbaud FTN 4-ary pulse amplitude modulation (PAM4) system with a compression factor of 0.8. According to the experimental results, PR-DFE achieves 2.4 dB and 1.5 dB receiver sensitivity improvement compared to the typical DFE and PR-FFE at a bit-error-rate (BER) of 4.5 × 10^-3 (BER threshold of 6.7% overhead staircase hard-decision forward error correction code). Moreover, the implementation of the PR-DFE has successfully reduced the probability of two consecutive symbol errors from 4.83 × 10^-3 to 0 compared to the typical DFE. According to experimental results, the proposed PR-DFE FTN signaling scheme is a promising candidate for ultra-low complexity and high spectral efficiency intra-datacenter interconnect (intra-DCI) applications.