An adaptive symbol mapping on 8-ary constellation for BICM-ID

Bit-interleaved coded modulation with iterative decoding (BICM-ID) is a spectral efficient coding technique. The technique is therefore very attractive for next generation of wireless communication. It has been shown that when interleaver and error-control code are fixed, symbol mapping which defined by the signal constellation and the bit labeling has a critical influence on the error performance of BICM-ID. An improved mapping which combines two QPSK with different radius can achieve excellent performance under high SNR but has adverse property at low SNR. This paper presents an adaptive symbol mapping scheme which respectively employs Gray and the improved mapping at different SNR regions to improve the performance at low SNR. Simulation results confirm that the adaptive mapping scheme can not only gets excellent performance at high SNR, but also outperforms the performance under low SNR of the improved mapping and be similar with Gray.