MIMO Device-to-Device Communications via Cooperative Dual-Polarized Intelligent Surfaces

By making the propagation environment a programmable entity, reconfigurable intelligent surfaces (RIS) constitute a key enabler to fulfill the quality-of-service requirements of device-to-device (D2D) communications. In practice, however, a single RIS may not be able to establish a line-of-sight path between the devices, e.g., in environments with rich scattering or when devices are far apart. This can hinder the communications especially in applications that require the transfer of different data sets from a source to multiple destinations. Considering such type of applications, this letter proposes a dual-polarized cooperative RIS-assisted MIMO D2D communication scheme, where the beam routing path via multiple RISs is selected based on the maximum received signal-to-noise ratio and path constraints. Looking into system operation in indoor environments, and utilizing a realistic channel model, tractable expressions are obtained for the system's error rate and outage probability. An asymptotic analysis is also conducted to evaluate the diversity gain. The findings reveal significant advantages of the dual-polarized cooperative RIS scheme over other RIS-based schemes.