Design of Iterative Demapping Schedules for Reduced-Complexity BICM-ID with Binary LDPC Codes and Orthogonal Modulations

Abstract : LDPC-coded modulations are attractive solutions for many communications links. BICM provides a very simple, flexible yet effective way of combining binary channel codes with non-binary modulations. However, iterative demapping is sometimes necessary to increase the coding gains. This is especially the case for orthogonal modulations where the "BICM capacity" falls far away from the coded modulation capacity. Unfortunately, iterative demapping results in a significant computational cost. A pragmatic solution to reduce this computational cost aims at restricting the number of demapping activations. In this article, a strategy to compute the minimum number of demapping activations necessary for a target estimated BER performance is presented and results are introduced for BICM-ID with binary LDPC-coded orthogonal modulations. Iterative demap-ping schedules optimized for a limited number of demapper activations are designed and evaluated in the finite code length regime.