Index Modulation with Space Domain Coding

Index Modulation (IM), and its variants, such as Space Shift Keying (SSK) and Spatial Modulation (SM), have been proposed for the next-generation wireless systems and are shown to provide high spectral/energy efficiencies and low implementation complexity. These systems utilize extra dimensions (e.g., spatial dimension), in addition to the conventional time/frequency dimensions, for information transmission. A simple Maximum Receive Ratio Combining (MRRC) based detector has been shown to be applicable for the IM decoding; however, it exhibits a significantly high antenna index detection error floor in the Rayleigh fading Multiple Input Multiple Output (MIMO) channels. Alternate schemes based on Maximum Likelihood (ML), Sphere Decoding (SD), or Hybrid Decoding (HD) reduce this error floor but at the cost of higher implementation complexity. This paper addresses reducing the antenna detection error in IM systems by proposing several new spatial domain forward error correction (FEC) schemes. In our first proposal, that we call Parity based SM (Pb-SM), the SM receiver uses the transmitted parity bits — sent via the modulated symbol on the selected transmit antenna — to estimate the antenna index. In the second proposal, that we call Antenna Encoding (AE), we form cosets of the transmit antennas (based either on the cross-correlation metric or on the Euclidean distance between the MIMO channel vectors) and use the coset index for information transfer. A simulation-based study presented in this paper demonstrates the effectiveness of the proposed schemes in reducing antenna detection errors.