New Design of Constellation and Bit Mapping for Dual Mode OFDM-IM

Dual mode orthogonal frequency division multiplexing with index modulation (DM-OFDMIM) is recently proposed, where the subcarriers within each subblock are divided into two groups, which are modulated by two distinguishable signal constellations. That is, the DM-OFDM-IM activates all subcarriers to convey data and eliminate the limits of spectrum efficiency in OFDM with index modulation (OFDM-IM). However, the conventional constellation pair in the DM-OFDM-IM is naively designed and thus induces much power increase. Also, there has been no discussion on symbol-to-bit mapping in the constellation pair. In this paper, a new constellation pair design and the corresponding bit mapping for the DM-OFDM-IM is proposed based on the average bit error probability (ABEP). Since the optimization problem of minimizing the ABEP is difficult to solve, we propose a suboptimal constellation pair through three steps; First, the shape of the constellation pair is design based on only the pairwise error probability (PEP) term in the ABEP. Second, a good bit mapping for the constellation pair is proposed. Third, we further modify the constellation pair by considering the ABEP. The simulation results show that the proposed constellation pair with the bit mapping substantially enhances the bit error rate (BER) performance of the DM-OFDM-IM compared with the conventional DM-OFDM-IM system.