RIS-Assisted Advanced Spatial Modulation Techniques for Ambient Backscattering Communications

The dynamic control of wireless channels is a trending field of research which has been made possible by the advent of metamaterial-based reconfigurable intelligent surfaces (RIS). Moreover, for future applications in 5G and beyond, the device size constraints and power supply issues also need to be resolved before RIS can be deployed at large scale. Keeping these problems in mind, we propose RIS-assisted ambient backscattering (ABSc) communication framework utilizing advanced spatial modulation (ASM) techniques for spectral- and energy-efficient communication. Here, ABSc technique is leveraged for harnessing the power from ambient RF waves, while ASM techniques are deployed to ensure high spectral efficiencies by activating more than one but not the full set of antennas for transmission. Extensive performance analysis of ASM techniques are carried out, and upper-bounds on the ensuing error rates are derived. We corroborate the error rate upper-bound results with Monte-Carlo simulation results, and also provide comparative results to reveal the benefits of the proposed framework. In particular, it is shown that the ASM technique of improved quadrature spatial modulation (IQSM) can achieve the highest spectral efficiency. All the ASM techniques can perform better than the conventional spatial modulation technique by offering signal-to-noise power ratio gains of more than 2 dB. Additionally, RIS-assisted ASM techniques with ABSc perform better than the conventional frameworks without RIS.