MAP

The increasing demand for higher spectral efficiency in long-haul optical communications paved the way to advanced transmission techniques like orthogonal frequency domain multiplexing (OFDM) and Nyquist-WDM, and to the use of high-order modulation formats. We introduced the Time-Frequency Packing (TFP) technique, which goes beyond the paradigm of Nyquist frequency spacing, and allows QPSK to outperform M-QAM in terms of spectral efficiency at equal complexity. The use of bounds on the achievable information rate (AIR), numerically evaluated according to the auxiliary channel and mismatched decoding principles, provides a useful, fast and reliable estimation of the system performance, without reference to any specific employed code. We applied such an approach in the analysis of modern flexi-grid scenarios where cascaded wavelength selective switches (WSS) severely impair signal propagation. Results on the performance of practical low-density parity check (LDPC) codes were provided, and we showed their good agreement with the AIR bound