I. Introduction
Orthogonal frequency division multiplexing with index modulation (OFDM-IM) has been regarded as a candidate multi-carrier transmission scheme for spectrum-and energy-efficient next generation wireless communication systems [1]. In OFDM-IM, differently from conventional OFDM, both the indices of active subcarriers and data symbols at the active subcarriers convey information, and these subcarriers are activated according to the incoming bit sequences. OFDM-IM offers attractive advantages over conventional OFDM, such as better bit error rate (BER) performance at low-to-mid level spectral efficiency values, higher robustness to inter-carrier interference (ICI), better ergodic achievable rate, and being more flexible based on different channel conditions and system requirements [2].