Improved BICM iterative decoding with hard-decision feedback

Bit-interleaved coded modulation (BlCM) enables power- and bandwidth-efficient transmission over fading channels. Power efficiency can be further improved if iterative decoding (ID) is applied, so-called BICM-ID. In this paper, we consider BICM-ID with hard-decision feedback as originally proposed by Li and Ritcey (1999) for low-complexity ID. We analyze the reliability of the soft output of the hard-decision feedback aided demapper, the inner decoder of BICM-ID. From this we find that a simple truncation of these output values significantly improves reliability in subsequent decoding iterations and thus, enhances convergence of ID. We propose two pragmatic truncation schemes and show by means of simulations that gains of more than 3 dB in power efficiency over conventional BICM-ID are achieved for the Rayleigh fading channel with no increase in decoding complexity.