Differential Spatial Modulation Using New Index Bits

Spatial modulation (SM) has the potential to meet the requirements of 5G and beyond communication systems with features such as reduced hardware complexity and good trade-off between spectral efficiency and energy efficiency. In this study, an efficient non-square differential spatial modulation (DSM) scheme is presented in which the number of time slots is one more than the number of transmit antennas. The introduced scheme includes one empty time slot. At the other time slots, the time slots of the conventional DSM (CDSM) are used (the Gray code order (GCO) can also be used). There is one active antenna at each time slot of the proposed scheme. The index of empty time slot conveys information. Thus, in comparison with CDSM (or GCO), for the same number of transmit antennas, the introduced scheme has more energy-free bits (index bits). It is free of pilot overhead, channel estimation complexity, and potential channel state information (CSI) estimation errors. Further, a detector with no error propagation is presented. Analytical expressions for the bit error rate (BER) are derived at high signal-to-noise ratios (SNRs) and high SNRs per bit (SNRbs). Simulation results verify the theoretical evaluation and demonstrate the efficiency of the proposed scheme