Achievable Rate Analyses and Phase Shift Optimizations on Intelligent Reflecting Surface with Hardware Impairments.

Intelligent reflecting surface (IRS) is envisioned as a promising hardware solution to hardware cost and energy consumption in the future fifth-generation (5G) mobile communication network. It exhibits great advantages in enhancing data transmission, but may suffer from performance degradations caused by inherent hardware impairments (HWI), which universally exist in the real-world communication systems. For analysing the achievable rate (ACR) and optimizing the phase shifts in the IRS-aided communication system with HWI, we consider that the HWI appear at both the IRS and the transceivers. By modelling the HWI at the IRS as phase errors and the HWI at the transceivers as distortion noises, we first mathematically derive the closed-form expression of the average ACR with HWI. Then, we formulate optimization problems to optimize the phase shifts of the IRS in the presence of HWI to improve the performance. The solution is obtained by transforming non-convex problems into convex semidefinite programming (SDP) problems. Subsequently, we theoretically compare the average ACR of the IRS-aided system with that of the decode-and-forward (DF) relay assisted system under two different conditions. Extensive simulations are carried out to verify the theoretical analyses. Results demonstrate that the average ACR of the IRS-aided system with HWI is lower than that without HWI, but can exceed that of the DF relay assisted system with HWI when the number of reflecting elements is large enough. It is concluded that the HWI has impact on the IRS, but still leaves opportunities for the IRS to surpass conventional DF relay.