Sequential decoding of trellis codes at high spectral efficiencies

A probabilistic algorithm is used to construct large constraint length trellis codes at high spectral efficiencies for use with sequential decoding. Linear trellis codes for two- and four-dimensional constellations with constraint lengths up to 19 are obtained. These codes can achieve 180/spl deg/ rotational invariance. To achieve full 90/spl deg/ rotational invariance, nonlinear trellis codes for four-dimensional constellations with constraint lengths up to 19 are obtained. In both cases it is shown that the channel cutoff rate bound can be achieved using constraint lengths between 16 and 19 with sequential decoding at a bit-error rate of 10/sup -5/-10/sup -6/ and that 4.9-5.8 dB real coding gains can be achieved over uncoded systems with the same spectral efficiency.