Energy consumption modeling and analysis for short-reach optical transmissions using irregular LDPC codes

As the transmission rate of data center (DC) related short-reach optical transmissions quickly increases to keep up with internet services' data demand pace, advanced FEC technology starts to establish its key role in short reach optical transmission systems. Coding strategy using Quasi-Cyclic LDPC (QC-LDPC) codes with hard-decision (HD) decoders stands out due to its excellent error correction ability and simple hardware implementation. Meanwhile, with the introduction of green communication concept and increasingly extensive applications of DC, energy consumption of short-reach links has become an urgent problem to be studied. Based on tanner-graph, energy consumption models of regular LDPC codes' HD decoding circuits over AWGN channel have been proposed. In this work, for the first time, we introduce energy consumption of optical transmitters and characteristics of short reach optical channels into energy consumption modeling. Besides, probability distributions of flipping operation as well as bit errors during irregular QC-LDPC codes' HD decoding iterations are analytically derived using density evolution algorithm. Based on our proposed model and post-layout circuit simulation, systems' total power when using four QC-LDPC codes in IEEE and 3GPP with Gallager A/B decoders together with the case of using no FEC are analyzed in two typical scenarios. Numerical results show that, in short range scenario with slight bandwidth limit, uncoded strategy is much more energy-saving than all adopted LDPC-coded strategies in 50Gbaud OOK and 25Gbaud PAM4 transmissions. While in severely band-limited case when FEC is necessary, a tradeoff between energy consumption of transmitters and decoders occurs in 70Gbaud OOK and 35Gbaud PAM4 transmissions. Besides, LDPC codes with longer length at similar rate are proved to consume less power for their better error correction ability. And in long range scenario, power differences among coding strategies grow significantly when pre-bit error rate (BER) approaches their error correction threshold, reflecting the great influence of error correction threshold on the energy consumption of LDPC decoders. Among all adopted coding strategies, a (19200, 15872) LDPC code with Gallager B decoder consumes minimum power in both two scenarios. However, it is also found that decoding algorithm minimizing the total power differs at different pre-BER if we concentrate on decoding algorithm, justifying the significance of our modeling in minimizing system energy consumption. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement