Subcarrier Index Modulation for Future Wireless Networks: Principles, Applications, and Challenges

The unprecedented surge of mobile data traffic requires future wireless networks to support both high spectral efficiency and energy efficiency. To this end, index modulation (IM) emerges as a revolutionary modulation concept. As a realization of IM in frequency domain, subcarrier IM (SIM) has been receiving significant interest. In this article, we introduce the generic framework of SIM and its specific representatives. The potential applications of SIM are then investigated in a variety of scenarios, including cognitive radio, relay networks, downlink multiuser communications, and physical layer security. We finally discuss the challenges and possible research directions in SIM and its applications.