Optimized symbol mapping for bit-interleaved coded modulation with iterative decoding
ABSTRACT Symbol mapping is very crucial for the performance of bit-interleaved coded modulation with iterative decoding (BICM-ID). In this paper, a new scheme of symbol mapping called Cross-8PSK-Quasi-Gray is proposed. The optimization scheme of Cross-8PSK is composed of two QPSK with different radius and phases. Through analysis and comparisons with three previously mentioned symbol mappings in terms of channel capacity and error performance, simulation results show that Cross-8PSK-Quasi-Gray mapping significantly outperforms set partitioning, semi set partitioning labeling maps in the aspects of both channel capacity and error performance. The overall performance of Cross-8PSK-Quasi-Gray mapping is nearly close to gray mapping in conventional 8PSK. Thus, Cross-8PSK-Quasi-Gray mapping is a good scheme for designing the power-efficient BICM.
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ABSTRACT: Since BICM-ID is a concatenation between channel coding and mapping, its performances strongly depend on the matching between mapping rule and code structure. In our previous papers, we proposed a yet very simple, close Shannon-limit achieving BICM-ID system. It uses very simple codes, irregular repetition and single parity check codes, combined with extended mapping. Even though we know that the key role played towards the optimal design of the proposed code is the degree allocation for variable nodes, the irregular degree allocation to the node degrees were determined only empirically, by try-and-error. This paper shows that the problem of the optimal degree allocation for the proposed BICM-ID technique can be solved by using linear programming technique. Results shows we can achieve better matching between the de-mapper and decoder curves, by which we can achieve even closer threshold to the Shannon limit and also lower error floor.
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ABSTRACT: We consider a simple method to improve the adaptiveness and flexibility of bit-interleaved coded modulation (BICM) for various channel models. With state-of-the art adap- tive transmission techniques, the raw adaptation of the data rate to the channel characteristics is usually done by selecting an appropriate signal constellation and the fine adaptation is done by changing the code rate. To enable a fine adaptation also with the modulation, irregular modulation schemes have been introduced in (1). With irregular modulation, different signal constellations may be used within one code block, even if only the average channel state is known at the transmitter. In this paper, irregular modulation schemes are analyzed using EXIT charts, capacity, error bounds and error rate simulations. I. INTRODUCTION In most wireless mobile communication systems, the propagation environment and thus the channel characteristics are changing over the time. To maximize the achievable data rate over a time varying channel, the transmission scheme should be adapted using channel estimates available at the transmitter. The adaptation may be done by varying the transmitted power level, the size of the signal constellation