Augmentation of a 3 x nR Hybrid Space-Time Block Code with Spatial Modulation

A simple technique to design MIMO space-time block codes that achieve both diversity and rate gains is to stack spatial multiplexing (V-BLAST) and transmit diversity (Alamouti) encoders; these are known as hybrid codes. We increase the spectral efficiency of a simple hybrid code with one V-BLAST layer and one Alamouti layer by using spatial modulation. In spatial modulation systems, information is transmitted, not only by radiating quadrature pulses, but by the selection of specific subsets of the available antennas. We also propose a nearly optimum, low complexity decoder algorithm, which uses heuristic calculations to reduce the search space. We present simulation results that show that the proposed decoder achieves lower error probability than other known decoders under uncorrelated and correlated channel conditions. We also show that the proposed decoder's complexity is lower than that of the tree-search QR-M algorithm, in uncorrelated and uniformly-correlated channels. In correlated channels with Laplacian distribution, the complexity tends to that of QR-M as the SNR increases.