Generalized Polarization-Space Modulation in Reconfigurable Intelligent Surfaces

The recently proposed generalized polarization-space modulation (GPSM) for multiple-input multiple-output (MIMO) communications systems incorporates a limited number of radio frequency chains. It is a novel index modulation technique that has a potential for use in sixth-generation wireless communications. The conventional GPSM activates multiple dual-polarized transmit (Tx) antennas in the spatial domain and uses combinations of these indices to encode information bits. For each active DP antenna, the GPSM then selects one polarization state to transmit information. In this paper, we employ reconfigurable intelligent surfaces (RIS) to implement the GPSM transmitter to yield more than two polarization states while using a low-cost reconfigurable electromagnetic (EM) metasurface with a reduced form-factor compared to traditional MIMO antenna arrays. The method-of-moment full-wave simulations of our design of RIS-based Tx for GPSM using Barium Strontium Titanate film suggest feasibility and EM-compliance. Our numerical experiments using maximum likelihood detector at the receiver demonstrate that the BER performance of our RIS-aided GPSM is as good as or better than the conventional MIMO systems. The RIS-GPSM retains the same spectral efficiency as conventional MIMO but has a higher energy efficiency.