How to significantly improve the spectral efficiency of linear modulations through time-frequency packing and advanced processing

We recently investigated the spectral efficiency, achievable with a symbol-by-symbol receiver, for linear modulations employing time-frequency packing. In this paper, we will investigate the improvements that can be obtained by increasing the receiver complexity. In the numerical results, we will mainly concentrate on time packing (an extension of the so called faster-than-Nyquist signaling technique) and on (i) receivers based on linear processing plus symbol-by-symbol detection or (ii) receivers based on a more sophisticated trellis processing with constrained complexity. Finally, the potential advantage of the proposed signalling scheme when combined with conventional low-density parity-check (LDPC) coding of the DVB-S2 air interface will be presented.