An improved pragmatic turbo encoding scheme for high spectral efficiency using constellation shaping

We propose a new turbo encoding scheme for high spectral efficiency with performance close to the Gaussian channel capacity. The scheme combines nonuniform signaling on a Gaussian channel, and pragmatic turbo coded modulation for simple and flexible implementation. A table is used to map equiprobable input symbols into nonequiprobable points in the QAM constellation. It is shown that the new scheme provides shaping gains of 0.6 dB and 0.93 dB, at rates 2 and 3 bits/dim respectively compared to the equiprobable pragmatic turbo coded modulation, and reach about 1 dB from the Gaussian channel capacity.