On the distribution of extrinsic L-values in gray-mapped 16-QAM

Authors:
Alex Alvarado;Leszek Szczecinski;Rodolfo Feick
Affiliations:
Chalmers University of Technology, Gothenburg, Sweden;INRS-EMT, Montreal, Canada;UTFSM, Valparaíso, Chile
Venue:
IWCMC '07 Proceedings of the 2007 international conference on Wireless communications and mobile computing
Year:
2007

Citing 3
Cited 0

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Abstract

In this paper we address the issue of probabilistic modelling of the extrinsic L-values, used as reliability metrics in the context of bit interleaved coded modulation with iterative demapping (BICM-ID). Starting with a simple piece-wise linear model of the L-values obtained via the max-log approximation, we derive the expressions for the cumulative distribution functions of the L-values, that differentiated produce the desired forms of the probability density functions for Gray-mapped 16-QAM. To illustrate the usefulness of our analytical expressions we applied them to efficiently compute the so-called EXIT functions of the demapper for different values of SNR. The proposed analytical expressions are also compared to thehistograms of the L-values obtained through time-consuming simulations.