Energy Efficiency Analysis of Intelligent Reflecting Surface System with Hardware Impairments

Intelligent reflecting surface (IRS) technology has emerged as a promising way to improve the energy efficiency of wireless communication systems with less complexity and hardware cost. Most existing studies are conducted with ideal hardware, however, both physical transceiver and IRS suffer from non-negligible hardware impairments which may greatly degrade the system performance. In this paper, by considering hardware impairments, we focus on the energy efficiency analysis of IRS system. Our first contribution is to derive the optimal receive combining and transmit beamforming vectors. After that, we characterize the asymptotic channel capacity. With the derived asymptotic channel capacity and the power consumption model, the analytical upper and lower bounds on the maximal energy efficiency are provided. Our results show that an IRS system can achieve both high spectral efficiency and high energy efficiency with moderate number of antennas. This observation is encouraging for that there is no need to cost a lot on expensive high-quality antennas, which corresponds to the requirements of new communication paradigms.