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In fifth generation wireless networks, the escalating teletraffic and energy consumption has necessitated the development of green communication techniques in order to further enhance both the system's spectral efficiency and energy efficiency. In the past few years, the novel index modulation (IM) has emerged as a promising technology that is widely employed in wireless communications. In this paper, we present a survey on IM in order to provide the readers with a better understanding of its principles, advantages, and potential applications. We start with a comprehensive literature review, where the concept of IM is introduced, and various existing IM schemes are classified according to their signal domains, including the frequency domain, spatial domain, time domain and channel domain. Then the principles of different IM-aided systems are detailed, where the transceiver design is illustrated, followed by descriptions of typical systems and corresponding performance evaluation. A range of challenges and open issues on IM are discussed before we conclude this survey.

Abstract-Dual-mode index modulation aided orthogonal frequency division multiplexing (DM-OFDM) is recently proposed, where subcarriers are partitioned into OFDM subblocks, divided into two groups within each subblock, and modulated by two differentiable constellation alphabets. In DM-OFDM, additional bits can be transmitted through indices of subcarriers modulated by the same constellation alphabet. In this letter, generalized DM-OFDM (GDM-OFDM) is proposed, where the number of subcarriers modulated by the same constellation mode in each subblock is alterable. By applying such enhancement, the spectral efficiency can be improved at the cost of marginal performance loss. Moreover, since the BER performance of GDM-OFDM degrades at low signal-to-noise ratios (SNRs), an interleaving technique is employed to address this issue. At the receiver, a maximum-likelihood (ML) detector and a reduced-complexity log-likelihood ratio (LLR) detector are employed for demodulation. Simulation results demonstrate that the proposed GDM-OFDM is capable of enhancing the spectral efficiency compared with DM-OFDM at the cost of negligible performance loss, and the interleaved GDM-OFDM (IGDM-OFDM) can harvest on performance gain over GDM-OFDM.Index Terms-Orthogonal frequency division multiplexing (OFDM), index modulation, maximum likelihood detection, loglikelihood ratio based detection, interleaving technique.

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