An Efficient Application of Turbo Coding for OFDM In-Phase/Quadrature Index Modulation

We present a method to efficiently apply turbo coding to OFDM in-phase/quadrature index modulation (OFDM-IQ-IM) for both cases of presence and absence of puncturing. We show that using the posterior probabilities of turbo-coded bits in the Bahl-Cocke-Jelinek-Raviv (BCJR) decoding algorithm yields the same decoding performance as using the likelihood probabilities of turbo-coded bits. We investigate the difference in error rate between systematic bits and parity check bits of systematic turbo coding and the difference in error rate between index selecting bits (ISBs) and symbol selecting bits (SSBs) of OFDM-IQ-IM. Based on the results, we devise a new bit mapping scheme that can efficiently split turbo-coded bits into ISBs and SSBs in OFDM-IQ-IM. Simulations show that the proposed bit mapping scheme improves the bit error rate (BER) of the turbo-coded 4QAM-based OFDM-IQ-IM approach and that the turbo-coded 4QAM-based OFDM-IQ-IM approach applying the proposed bit mapping scheme outperforms the turbo-coded 4QAM-based OFDM approach in the high signal-to-noise ratio (SNR) region.