Reduced complexity Log-MAP algorithm with Jensen inequality based non-recursive max∗ operator for turbo TCM decoding

In this paper, a reduced complexity Log-MAP algorithm based on a non-recursive approximation of the max∗ operator is presented and studied for turbo trellis-coded modulation (TTCM) systems. In the algorithm, denoted as AvN Log-MAP, the max∗ operation is generalized and performed on n ≥ 2 arguments. The approximation is derived from the Jensen inequality. The non-recursive form of the max∗ calculations allows to achieve significant reduction in the decoding effort in comparison to the conventional Log-MAP algorithm. Bit-error rate performance simulation results for serial and parallel TTCM schemes in the additive white Gaussian noise and uncorrelated Rayleigh fading channels show that the AvN Log-MAP algorithm performs close to the Log-MAP. Performance and complexity comparisons of the AvN Log-MAP algorithm against the Log-MAP and several relevant reduced complexity turbo decoding algorithms proposed in the literature reveal, that it offers favorable low computational effort for the price of small performance degradation.