  Dual mode orthogonal frequency division multiplexing with index modulation
(DM-OFDM-IM) is recently proposed, which modulates all subcarriers to eliminate
the limits of spectrum efficiency in OFDM with index modulation (OFDM-IM). In
DM-OFDM-IM, the subcarriers within each subblock are divided into two groups,
which are modulated by two distinguishable constellation alphabets drawn from
the distinct two constellations.
  In this paper, a new constellation design for DM-OFDM-IM is proposed based on
the pairwise error probability (PEP) analysis. In previous works, the design of
the constellation pair is naive and induces much power. Also, a new bit mapping
scheme for DM-OFDM-IM is proposed. The proposed bit mapping scheme can relieve
the catastrophic effect of the index demodulation error incurring burst of
errors, which is the endemic problem of the index demodulation systems. The
simulation results show that the proposed constellation pair and the proposed
bit mapping scheme substantially enhance the BER performance of the DM-OFDM-IM
than the conventional DM-OFDM-IM.
