  Recently, the use of intelligent reflecting surface (IRS) has gained
considerable attention in wireless communications. By intelligently adjusting
the passive reflection angle, IRS is able to assist the base station (BS) to
extend the coverage and improve spectral efficiency. This paper considers a
joint symbol-level precoding (SLP) and IRS reflecting design to minimize the
symbol-error probability (SEP) of the intended users in an IRS-aided multiuser
MISO downlink. We formulate the SEP minimization problems to pursue uniformly
good performance for all users for both QAM and PSK constellations. The
resulting problem is non-convex and we resort to alternating minimization to
obtain a stationary solution. Simulation results demonstrate that under the aid
of IRS our proposed design indeed enhances the bit-error rate performance. In
particular, the performance improvement is significant when the number of IRS
elements is large.
