Analysis of BICM-ID receivers exploiting transformations of extrinsic information

In this article we analyze a novel idea to increase the applicability of Bit Interleaved Coded Modulation with Iterative Decoding (BICM-ID) to legacy waveforms. One essential design parameter of BICM-ID receivers with respect to the error correcting capabilities is the symbol mapping of the digital modulation scheme. A so-called Semi-Set Partitioning (SSP) symbol mapping is well known to provide higher stepwise gains in robustness in every iteration than a Gray encoded symbol mapping. The novel approach is based on the idea to make in a first step of BICM-ID the deliberately false assumption that a well performing symbol mapping has been used at the transmitter, even though in reality a less powerful symbol mapping was applied. In a second step, the mismatch in both symbol mappings is compensated by an innovative Transformation of Extrinsic Information (TEI). After having reviewed the innovative TEI idea in more detail, we will discuss the fundamentals of the required signal processing. In addition, as a novelty of this article we will analyze three different ways to implement the TEI approach. Several simulation results will be shown which demonstrate the theoretically achievable performance gains.