Precoded Index Modulation for Multi-Input Multi-Output OFDM

Index modulated orthogonal frequency division multiplexing (IM-OFDM) is a novel multicarrier transmission scheme, which provides considerable performance improvement compared with classical OFDM by conveying information via the active subcarrier indices in conjugation with the constellation symbols. In this paper, we extend the idea of IM-OFDM to multi-input multi-output (MIMO) systems and propose precoded MIMO-OFDM (PIM-MIMO-OFDM). Based on the channel state information at the transmitter, PIM-MIMO-OFDM selects the active elements of the receiver-side space-frequency subblocks via linear precoding. The spectral efficiency enhancement method of in-phase/quadrature index modulation is also employed to construct PIM-MIMO-OFDM with in-phase quadrature modulation by selecting the active space-frequency elements in the in-phase and quadrature components of the constellation symbol. Thanks to the carefully designed precoding, the co-channel interference among received antennas can be completely eliminated. Consequently, low-complexity maximum likelihood and suboptimal detectors are devised with linear detection complexity. Both analytical and numerical results show that, with the help of precoding, PIM-MIMO-OFDM can achieve better bit error rateperformance than traditional precoded MIMO-OFDM (P-MIMO-OFDM) in various system configurations. In addition, the spectral efficiency can be also enhanced compared with the P-MIMO-OFDM under certain configurations.