EXIT Chart Analysis of Turbo DeCodulation

Abstract

Turbo decodulation is the combination of iterative demodulation and iterative source-channel decoding to a single multiple turbo process. The receiver structures of bit-interleaved coded modulation with iterative decoding (BICM-ID), iterative source-channel decoding (ISCD), and iterative source coded modulation (ISCM) are merged to one novel turbo system, in which in two iterative loops reliability information is exchanged between the three single components, demodulator, channel decoder, and (softbit) source decoder. Simulations show quality improvements compared to the different previously known systems, which use iterative processing only for two components of the receiver. We propose the enhancement to turbo decodulation by an additional link for a direct supply of reliabilities from the softbit source decoder to the demodulator. We will demonstrate that using three-dimensional EXIT charts a convergence analysis of turbo decodulation similar to single turbo processes is possible