Quadrature Dual Mode Index Modulation

Dual mode index modulation-based orthogonal frequency division multiplexing (DM-OFDM) was recently proposed to enhance the spectral efficiency of the existing variants of OFDM with index modulation. In a DM-OFDM system, all subcarriers are activated and modulated by two distinct constellation diagrams. Consequently, additional information is implicitly carried through the subcarrier indices referring to the selected mapper diagram. In this letter, a novel transmission technique named quadrature dual-mode index modulation-based OFDM (QDM-OFDM) is proposed. To further improve the achievable spectral efficiency of DM-OFDM, QDM-OFDM independently performs dual mode index modulation on the in-phase and quadrature dimensions. Furthermore, error performance analysis of QDM-OFDM over Rayleigh and Rician fading channels is investigated. The pairwise error probability and a tight upper bound of the average bit error probability analytical expressions over generalized fading channels are established based on the maximum-likelihood detector. Finally, the enhancement of the proposed system is proven through the provided simulation results.