Information Theoretic Properties of OFDM with Index Modulation

Due to their potential to enhance spectral efficiency and energy efficiency, Index Modulation (IM) techniques in different domains (space, time, frequency) have gained significant attention in wireless communications, especially in systems with increasing volumes of teletraffic and constrained energy. In this paper, we provide an information theoretic foundation for IM systems. The entropy of an IM source has been derived in a closed form, moreover, we derive the maximum of the proposed entropy closed form, which is the first information theoretic quantity necessary to characterize other properties of IM sources such as the achievable rate and the channel capacity. Moreover, we extend our results to present an upper bound on the entropy of IM-OFDM, which is the first milestone defining the gain achieved by IM-OFDM over the convectional OFDM in both the spectral and energy efficiencies.