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Low-complexity iterative decoding for bit-interleaved coded modulation Liu, Jeff Tai-Lin

Abstract

In this thesis, bandwidth-efficient transmission with bit-interleaved coded modulation (BICM) over fading channels is considered. The main focus of this work is on the design and analysis of iterative decoding schemes employing hard-decision feedback. Although suboptimum by nature, hard-decision feedback allows for low-complexity iterative decoders, which renders this approach advantageous for practical implementations. Two particular 16-ary modulation schemes with their corresponding decoders are considered for bandwidth-efficient transmission. The first scheme is 16-ary quadrature amplitude modulation (16QAM) with coherent iterative decoding (ID), so-called BICM-ID, which relies on (possibly imperfect) channel estimation. We analyze the reliability of the output of the demodulator, which is the inner component decoder in the iterative decoding scheme, and we propose the application of a metric truncation technique to improve the quality of the decision variable and thus the performance of hard-decision feedback iterative decoding. Simulation results for different variants of this metric truncation show notable gains in power efficiency, while decoding complexity is not increased. The second scheme we consider is so-called twisted absolute amplitude and differential phase-shift keying (TADPSK), which allows for iterative decoding without the need for channel estimation. We extend previous work on iterative decision-feedback decoding for TADPSK, so-called iterative decision-feedback differential demodulation (DFDM), and propose a sliding-window DFDM (SWDFDM) module as inner component decoder. Similar to the case of 16QAM, the application of metric truncation yields significant performance improvements also for TADPSK transmission. Finally, we compare 16QAM and TADPSK transmission by means of simulations. Depending on the quality of channel estimation, TADPSK with low-complexity iterative DFDM is shown to outperform 16QAM BICM-ID in some cases.

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