  Hybrid relaying networks (HRNs) combining both a relay and an intelligent
reflective surface (IRS) can lead to enhanced rate performance compared to
non-hybrid relaying schemes, where only either an IRS or a relay is utilized.
However, utilizing both the relay and the IRS simultaneously results in higher
power consumption for the HRNs compared to their counterpart. In this work, we
study the required transmit power levels and the energy efficiency (EE) of HRNs
utilizing both a half-duplex decode-and-forward (HD-DF) relay and an IRS, and
compare their performance with non-hybrid relaying schemes. The impact of the
required channel estimation overheads is considered when the reflective
beamforming design (RBD) at the IRS is carried out under both instantaneous and
statistical channel state information models. Also, the investigation is
performed for both slow- and fast-changing environments. In terms of the
transmit power requirements, our results show that HRNs can lead to higher
power savings if the number of reflective elements at the IRS is not very
large. However, non-hybrid relaying schemes are shown to be more
energy-efficient, unless the targeted rate is high and the IRS is distant from
both transmitter and receiver but within a close proximity to the relay.
