Code IM-Assisted RIS for D2D Communications with Hardware Imperfections and Phase Noise

In practical communication systems, residual hardware imperfections often impose distortion noise that compromises the performance of the system. This paper investigates the effect of hardware limitations on the performance of coded index modulation (IM)-assisted reconfigurable intelligent surface (RIS) for device-to-device (D2D) communication systems. We show that the concept of coded IM can enhance both the spectrum efficiency and error performance of D2D communications in the presence of hardware imperfections, including hardware impairment at the D2D transceivers and phase noise at the RIS. In this system, spread code selection is applied to convey additional information and achieve a higher diversity gain. The D2D receiver performs detection employing a two-stage match correlation approach to reduce the high complexity of the maximum-likelihood (ML) detector. Our simulation results demonstrate the superiority of the coded IM-assisted RIS solution in improving spectral efficiency and error performance compared to the conventional RIS-assisted D2D system, while reducing the impact of hardware imperfections.