Spatial Lattice Modulation Techniques for MIMO Systems

This paper proposes spatial lattice modulation (SLM) for multiple-input-multiple-output (MIMO) systems. The key idea of SLM is to jointly exploit spatial, in-phase, and quadrature dimensions to modulate information bits into a multi- dimensional lattice. SLM achieves a higher spectral efficiency than the existing spatial modulation and spatial multiplex- ing methods under the constraint of M-ary pulse- amplitude- modulation (PAM) input signaling per dimension. In particular, it is shown that when the SLM signal set is constructed by using dense lattices, a significant signal-to- noise-ratio (SNR) gain, i.e., a nominal coding gain, is attainable compared to the existing methods. Additionally, a closed-form expression for the average mutual information of generic SLM is derived under Rayleigh- fading environments. Simulations verify the accuracy of the conducted analysis and demonstrate that the proposed SLM techniques achieve higher average mutual information and lower average symbol-vector-error-rate than do existing methods.