Multi-Mode Generalized Space-Time Index Modulation: A High-Rate Index Modulation Scheme for MIMO-ISI Channels

In this paper, a new index modulation technique, referred to as the multi-mode generalized space-time index modulation (MM-GSTIM) is presented. MM-GSTIM is a high-rate index modulation scheme for multiantenna inter-symbol interference (MIMO-ISI) channels. The proposed MM-GSTIM is a single carrier scheme with zero padding (ZP). MM-GSTIM performs 'mode-indexing' to efficiently increase the spectral efficiency. In a given MM-GSTIM frame, disjoint subsets of space-time slots are used to transmit modulation symbols from disjoint modulation alphabets (referred to as the modes). The choice of which space-time slots are used for transmission of a particular mode in an MM-GSTIM matrix conveys information bits. Thus, MM-GSTIM is a generalization of the well-known index modulation schemes such as spatial modulation (SM), generalized spatial modulation (GSM), and space-time index modulation. Here, an analytical characterization of the diversity order of the proposed MM-GSTIM scheme and the conditions required to maximize the transmission rate of multi-mode index modulation schemes are derived. Through simulations, it is shown that the proposed MM-GSTIM scheme can achieve better performance compared to other modulation schemes in MIMO-ISI channels.