Index-Modulated MIMO-OFDM: Joint Space-Frequency Signal Design and Linear Precoding in Rapidly Time-Varying Channels

Abstract

In this paper, the application of index modulation (IM) to the multiple-input-multiple-output orthogonal frequency division multiplexing system is studied. Two index-modulated MIMO-OFDM schemes are proposed, named generalized joint space-frequency index modulation (G-JSFIM) and Kronecker product-based joint space-frequency index modulation (KP-JSFIM). In G-JSFIM, IM is applied directly in joint space-frequency resources. In KP-JSFIM, two component activation patterns (APs) are acquired by employing IM in space and frequency resources, respectively, and their Kronecker product is employed as the joint AP. Furthermore, for both proposed schemes, the linear precoding (LP) design is presented to alleviate the intercarrier interference in rapidly time-varying channels. In this LP design, a capacity lower bound is first derived, and then the precoding matrix is designed to maximize this bound. Specifically, utilizing the special signal character, an efficient LP matrix construction for KP-JSFIM is proposed through designing two component matrices in space and frequency dimensions separately. In general, the proposed G-JSFIM can achieve higher information rate and KP-JSFIM features lower implementation complexity. Simulation results show that G-JSFIM and KP-JSFIM can achieve better error performance in high and low transmit rates, respectively, compared with conventional schemes. Moreover, the effectiveness of the proposed LP design is also verified by computer simulations.