Signature Spatial Modulation Using Dual-Polarized Antennas

Spatial modulation (SM) has a strong sensitivity to transmit antenna and channel correlations, because some of the information bits are assigned to active antenna selection, and the correlation limits the detection reliability of these bits. Recent approaches to solve this problem rely on either the use of unequal error protection through additional channel encoding/decoding or precoding in the form of antenna-dependent rotation (or joint rotation and amplitude scaling) of the signal constellation. The precoding based approaches achieve good results for small number of transmit antennas and for small constellations such as BPSK and QPSK, but the performance quickly degrades for higher-level signal constellations. Moreover, the complexity of the precoder optimization problem increases with the number of transmit antennas and the modulation order, making this approach not very practical to use for high spectral efficiencies. This paper introduces a novel approach to this problem, which is particularly suited for high-level signal constellations. This is achieved by the joint use of dual-polarized antennas and of active-antenna dependent signature constellations which are derived from each other through successive geometric interpolations. The theoretical analysis and the simulation results show that compared to previous methods it gives significant performance improvements in terms of robustness to transmit antenna correlation, particularly for Rician fading channels.