Shaping gain by non-uniform QAM constellation with binary turbo coded modulation

A non-uniform signal constellation can be used to obtain shaping gain. One typical way to design non-uniform constellation is make the output signal follow a Gaussian distribution by using equally like signals with unequal spacing. However, for binary turbo coded modulation (BTCM) with M-QAM system, this non-uniform constellation design criteria can be modified based on different impacts of various turbo encoded hits sequence on BER performance. In this paper, author points out that shaping gain for M-QAM with BTCM can be achieved integrated with optimization of mapping rule, performance of the proposed scheme outperforms over BTCM with uniform constellation, especially under low and moderate SNR region. Meanwhile, the effects of code rate, order of QAM constellation on shaping gain are investigated. Numeral results are provided to support the proposed scheme and analysis. The proposed scheme can be applied to high rate data service with hybrid ARQ, such as HSDPA system.