Space-Frequency Increment Index Modulation Approach for Fifth Generation and Beyond Wireless Communication Systems

Unlike the classical modulation, for instance, quadrature amplitude modulation (QAM) and others, where bits are transmitted via symbols particularly from modulation alphabets, in index modulation (IM), extra information bits can be conveyed via the indices of a particular transmit entities during the transmission process. Transmit antenna elements are example of transmit entities in multi-antenna systems which can be used to convey extra information bits. Recently, frequency diverse array (FDA), as a new type of transmit antenna array which differs from the traditional phased-array has been proposed in the literature. In FDA, the element indices has small frequency increment across them. In this paper, space-frequency increment IM is proposed. The proposed scheme utilizes the indices of the activated transmit FDA antennas and their respective corresponding frequency increments $\Delta f$ to convey additional information bits. The proposed scheme is inspired by the principle of quadrature spatial modulation (QSM) and no additional antenna activation is required. Compared with spatial modulation (SM) and QSM, it is shown that, the proposed scheme achieved higher spectral efficiency. Further, the average bit error rate (ABER), secrecy sum rate (SSR) and system capacity are derived and evaluated. Moreover, a low-complexity decoding algorithm is examined. Finally, via numerical results, the proposed scheme shows to be better than the comparative alternatives (QSM/SM), and may offer promising properties in various contexts.