| Summary: | In this paper, we provide a comprehensive review of diverse index modulation (IM) architectures that operate in the space, time, and frequency domains, as well as their related technologies. We clarify that several IM-specific characteristics have explicit advantages over those of the conventional bandwidthefficient counterparts, such as spatial multiplexing, orthogonal frequency division multiplexing, and singlecarrier frequency division multiple access, which have been widely employed in the current wireless standards. While, for the next-generation wireless systems, multiple performance requirements that conflict with each other have been imposed, IM schemes have the potential of satisfying part of the requirements, in addition to enhancing bandwidth efficiency. More specifically, we characterize operational scenarios and system settings that specifically benefit from IM schemes versus their non-IM counterparts while clarifying the fundamental limitations and the open issues for IM schemes that have not been sufficiently explored previously. Furthermore, we also present the rationale of the recent novel IM scheme that amalgamates the time-domain IM scheme and the concept of faster-than-Nyquist signaling and attains a rate enhancement together with a low peak-to-average power ratio.
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