Advanced Detection of Super-Nyquist WDM QPSK Signals with 5-bit/s/Hz Spectral Efficiency

We show that using a quadrature 4-level polybinary detection scheme together with maximum-likelihood-sequence estimation, we can achieve a 5-bit/s/Hz spectral efficiency for super-Nyquist WDM quadrature-phase-shift-keyed signals, with performance better than 16-ary quadrature-amplitude modulation