An Improved Symbol Mapping on 8-ary Constellation for BICM-ID1

Bit-interleaved coded modulation (BICM) is a bandwidth-efficient coding technique, which can improve the bit error rate (BER) performance over the Rayleigh channel due to the increase of diversity order. However, it reduces the free squared Euclidean distance between symbol sequences, which degrades the performance over the additive white Gaussian noise (AWGN) channel. It has been found that BICM can be used to provide excellent performance over AWGN and Rayleigh channel with iterative decoding (BICM-ID). In addition, signal labeling has a critical influence on the performance of BICM-ID. This paper presents an improved symbol mapping which combines two QPSK with different radius. Through comparison with the conventional symbol mappings in terms of BER performance over Rayleigh channel, numerical results show that the new symbol mapping can improve the performance of BICM-ID system more than 0.2 dB when the BER is below 10-4.