In 2010, when I started my Ph.D., this was the general consensus of the research community on forward error correction (FEC) for 100G long-haul coherent optical communications systems: Currently the Optical Internetworking Forum (OIF) has locked in on dual-polarisation quaternary phase shift keying (DP-QPSK) following digital coherent receivers for 100 Gb/s transport systems. System designers have shifted their interest to intensively search for even more powerful FEC schemes having an NCG of over 10 dB. . . . The candidates for this application are soft-decision and iterative decoding. The FEC redundancy in high-speed optical communications is limited by, among others, the availability of high-speed analog devices, the associated optical components, and the complexity of the digital circuitry. The industry consensus is that the maximum practical redundancy is currently not beyond 20 percent for 100 Gb/s digital coherent systems. The purpose of this work is to challenge this approach, in particular the choice of quadrature phase-shift keying (QPSK), the use of iterative decoding alone and the limit of 20% redundancy, which corresponds to a symbol rate of ≈ 31 GBd. The other building blocks, namely polarisation division multiplexing (PDM), coherent digital signal processing (DSP) and soft-decision (SD), will be maintained. I will present a solution for 100G long-haul non differentially encoded (NDE) coherent optical communications systems that achieves a net coding gain (NCG) over the uncoded QPSK of 11.8 dB. This solution is based on a larger constellation which allocates space for a higher redundancy of ≈ 60%, however having a smaller symbol rate of ≈ 28 GBd and hence occupying a narrower bandwidth. It uses available off-the-shelf building blocks with a complexity that, by now, should be more than feasible. I will also present a related solution for 100G long-haul differentially encoded (DE) coherent optical communications systems that achieves a NCG over the uncoded QPSK of 10.2 dB. These solutions are also perfectly scalable to 100G+ long-haul coherent optical communications systems, especially when the latters are realised increasing the symbol rate and hence the occupied bandwidth and not the size of the constellation.    «

In 2010, when I started my Ph.D., this was the general consensus of the research community on forward error correction (FEC) for 100G long-haul coherent optical communications systems: Currently the Optical Internetworking Forum (OIF) has locked in on dual-polarisation quaternary phase shift keying (DP-QPSK) following digital coherent receivers for 100 Gb/s transport systems. System designers have shifted their interest to intensively search for even more powerful FEC schemes having an NCG of ov...    »