  This letter presents a detailed performance analysis of the intelligent
reflecting surface (IRS) aided single-input single-output communication
systems, taking into account of the direct link between the transmitter and
receiver. A closed-form upper bound is derived for the ergodic capacity, and an
accurate approximation is obtained for the outage probability. In addition,
simplified expressions are presented in the asymptotic regime. Numerical
results are provided to validate the correctness of the theoretical analysis.
It is found that increasing the number of reflecting elements can significantly
boost the ergodic capacity and outage probability performance, and a strong
line-of-sight component is also beneficial. In addition, it is desirable to
deploy the IRS close to the transmitter or receiver, rather than in the middle.
