  The increasing demand for higher data rates, better quality of service, fully
mobile and connected wireless networks lead the researchers to seek new
solutions beyond 4G wireless systems. It is anticipated that 5G wireless
networks, which are expected to be introduced around 2020, will achieve ten
times higher spectral and energy efficiency than current 4G wireless networks
and will support data rates up to 10 Gbps for low mobility users. The ambitious
goals set for 5G wireless networks require dramatic changes in the design of
different layers for next generation communications systems. Massive
multiple-input multiple-output (MIMO) systems, filter bank multi-carrier (FBMC)
modulation, relaying technologies, and millimeter-wave communications have been
considered as some of the strong candidates for the physical layer design of 5G
networks. In this article, we shed light on the potential and implementation of
index modulation (IM) techniques for MIMO and multi-carrier communications
systems which are expected to be two of the key technologies for 5G systems.
Specifically, we focus on two promising applications of IM: spatial modulation
(SM) and orthogonal frequency division multiplexing with IM (OFDM-IM), and we
discuss the recent advances and future research directions in IM technologies
towards spectral and energy-efficient 5G wireless networks.
