  Intelligent reflecting surface (IRS) and device-to-device (D2D) communication
are two promising technologies for improving transmission reliability between
transceivers in communication systems. In this paper, we consider the design of
reliable communication between the access point (AP) and actuators for a
downlink multiuser multiple-input single-output (MISO) system in the industrial
IoT (IIoT) scenario. We propose a two-stage protocol combining IRS with D2D
communication so that all actuators can successfully receive the message from
AP within a given delay. The superiority of the protocol is that the
communication reliability between AP and actuators is doubly augmented by the
IRS-aided first-stage transmission and the second-stage D2D transmission. A
joint optimization problem of active and passive beamforming is formulated,
which aims to maximize the number of actuators with successful decoding. We
study the joint beamforming problem for cases where the channel state
information (CSI) is perfect and imperfect. For each case, we develop efficient
algorithms that include convergence and complexity analysis. Simulation results
demonstrate the necessity and role of IRS with a well-optimized reflection
matrix, and the D2D network in promoting reliable communication. Moreover, the
proposed protocol can enable reliable communication even in the presence of
stringent latency requirements and CSI estimation errors.
