Improved BER performance of hard-decision staircase code via geometric shaping

Staircase codes (SCCs) with hard decision (HD) decoding have attracted much attention in the optical communication community due to their outstanding performance and low decoding complexity [1]. Recently, an implementation agreement has been reached for using an SCC as an outer code in the baseline draft of 400G ZR [2]. To achieve high spectral efficiencies, forward error correction is typically combined with high order modulation formats. Additional gains can be obtained if regular quadrature amplitude modulation (QAM) constellations are replaced by constellations with geometric shaping (GS). In this paper, we consider GS with HD-SCC and analyze the post-SCC bit error rate (BER) performance of constellations with 64 points. Bose- Chaudhuri-Hocquenghem (BCH) codes are used as SCC component codes. The location of the constellation points is optimized by maximizing the achievable information rate. The simulation results show that the shaped constellations yield around 0.24 dB gains at a BER of 1e-6 when compared to regular 64QAM for different coding rates.