  In this letter, we analyze the spectral and energy efficiency of an
intelligent reflecting surface (IRS)-assisted multiple-input single-output
(MISO) downlink system with hardware impairments. An extended error vector
magnitude (EEVM) model is utilized to characterize the impact of
radio-frequency (RF) impairments at the access point (AP) and phase noise is
considered for the imperfect IRS. We show that the spectral efficiency is
limited due to the hardware impairments even when the numbers of AP antennas
and IRS elements grow infinitely large, which is in contrast with the
conventional case with ideal hardware. Moreover, the performance degradation at
high SNR is shown to be mainly affected by the AP hardware impairments rather
than the phase noise of IRS. We further obtain the optimal transmit power in
closed form for energy efficiency maximization. Simulation results are provided
to verify these results.
