Performance of duo‐binary turbo codes with optimized hierarchical modulation

Non‐binary turbo codes (TCs) have become an important class of TCs following the adoption of duo‐binary TCs (DBTCs) in the digital video broadcasting with return channel via satellite (DVB‐RCS) standard. Several hierarchical modulation (HM) schemes for binary TCs have been proposed with a view to enhancing their performance. However, the existing techniques make use of fixed parameters throughout the Eb/N0 range and have not been applied to non‐binary TCs. In this paper, optimum parameters have been derived from exhaustive simulations for performing HM with 8‐PSK integrated with DBTCs. To validate the improved error performances obtained with the optimized parameters for HM, EXIT charts have been generated. Moreover, a model that could predict the optimized parameters at each Eb/N0 using K‐nearest neighbor (K‐NN)‐based binary classification has been derived from the results of exhaustive simulations. Significant improvement in error performances have been observed with the proposed scheme. For example, with a couple length of 48, code rate of 1/3 or 1/2, and 8‐PSK modulation, a significant average gain of 0.5 dB is obtained over conventional DBTCs without HM.