  In this paper, we propose a novel orthogonal frequency division multiplexing
with index modulation (OFDM-IM) scheme, which we call Q-ary multi-mode OFDM-IM
(Q-MM-OFDM-IM). In the proposed scheme, Q disjoint M-ary constellations are
used repeatedly on each subcarrier, and a maximum-distance separable code is
applied to the indices of these constellations to achieve the highest number of
index symbols. A low-complexity subcarrier-wise detection is shown possible for
the proposed scheme. Spectral efficiency (SE) and the error rate performance of
the proposed scheme are further analyzed. It is shown that the proposed scheme
exhibits a very flexible structure that is capable of encompassing conventional
OFDM as a special case. It is also shown that the proposed scheme is capable of
considerably outperforming the other OFDM-IM schemes and conventional OFDM in
terms of error and SE performance while preserving a low-complexity structure.
