  The fifth generation (5G) wireless communications brag both high spectrum
efficiency and high energy efficiency. To meet the requirements, various new
techniques have been proposed. Among these, the recently-emerging index
modulation has attracted significant interests. By judiciously activating a
subset of certain communication {building blocks, such as} antenna, subcarrier
and time slot, index modulation is claimed to have the potential to meet the
challenging 5G needs. In this article, we will discuss index modulation and its
general and specific representations, enhancements, and potential applications
in various 5G scenarios. The objective is to reveal whether, and how, index
modulation may strive for more performance gains with less medium resource
occupation.
