  A reconfigurable intelligent surface (RIS) is capable of manipulating
electromagnetic waves with its flexibly configurable unit cells, thus is an
appealing technology to resist fast fading caused by multi-path in wireless
communications. In this paper, a two-path propagation model for RIS-assisted
wireless communications is proposed by considering both the direct path from
the transmitter to the receiver and the assisted path provided by the RIS. The
proposed propagation model unveils that the phase shifts of RISs can be
optimized by appropriate configuration for multi-path fading mitigation. In
particular, four types of RISs with different configuration capabilities are
introduced and their performances on improving received signal power in virtue
of the assisted path to resist fast fading are compared through extensive
simulation results. In addition, an RIS operating at 35 GHz is used for
experimental measurement. The experimental results verify that an RIS has the
ability to combat fast fading and thus improves the receiving performance,
which may lay a foundation for further researches.
