Performance analysis of RIS-assisted SM with I/Q imbalance

Abstract

The idea of utilizing reconfigurable intelligent surfaces (RISs) that employ an array of severally-controllable meta-material elements to scatter incoming data in a desirable way, in wireless communication systems has created new opportunities for transmission in various scenarios. For instance, RISs are envisioned as potential candidates to achieve smart radio environments in fifth generation (5G) network technology, which is usually described as incapable of controlling the environment. Nevertheless, existing studies analyzing RIS-empowered wireless networks generally discuss the cases with ideal hardware despite the fact that both physical transceiver and RISs suffer from unignorable hardware imperfections, which may exceedingly reduce the system performance in practical communication scenarios. This paper investigates the performance of an RIS-assisted spatial modulation (SM) scheme in the presence of in-phase/quadrature-phase imbalance (IQI) at the base station (BS) constituting a substantial impairment in direct-conversion transceivers. The concept of the RIS-assisted SM scheme is discussed by comparing three different implementation scenarios depending on the awareness of both the channel phases at the RIS and the severity of the IQI at the destination (D). The average bit error rate (ABER) is derived analytically by use of maximum likelihood (ML) detection method to tackle the distorting impact of the IQI taking the effects of path loss into account. Extensive computer simulation results, which verify theoretical findings, show that the performance of the traditional SM schemes with IQI can remarkably be improved by utilizing RISs, while having the knowledge of the adjusted phases at the receiver (Rx) provides substantial gain in terms of energy.