Generalized Space-Code Index Modulation for High Rate and Energy-Efficient MIMO Transmission

In this paper, we propose a spectrum-efficient and energy-saving multiple-input multiple-output (MIMO) scheme, which combines the code index modulation (CIM) and generalized spatial modulation (GSM), named generalized space-code index modulation (GSCIM). In our proposed scheme, the input information bits are transmitted not only by modulated symbols, but also by the activated transmit antennas pattern and the selected spreading code patterns for the in-phase and quadrature components. Due to the increase in index dimensions, more information bits can be implicitly transmitted, which improves spectrum and energy efficiency compared with SM, GSM, CIM spread spectrum (CIM-SS) and CIM-aided SM (CIM-SM). Considering the high computational complexity of maximum likelihood (ML) detection, two low-complexity detectors are proposed to implement GSCIM in practice. An analytical upper bound on the average bit error probability (ABEP) associated with ML detection is derived, which is verified by simulation results. Simulation results also show that the proposed GSCIM scheme outperforms SM, GSM, CIM-SS, CIM-SM and CIM-aided quadrature spatial modulation (CIM-QSM) schemes in terms of error performance.