Simplified Log-MAP decoding with max* approximation based on the Jensen inequality

In the paper, a modified Log-MAP algorithm based on a novel approximation of the max^* operator derived from the Jensen inequality is proposed. In this approach, the max^* operation is performed on n≥2 arguments, thus the recursive calculations are avoided and significant reduction in the number of operations performed per decoding step, as compared with the conventional Log-MAP, is achieved. Simulation results of BER performance for both turbo codes and turbo trellis-coded modulation (TTCM) employing the new algorithm are given, showing the near-optimal performance of the proposed algorithm.