Hybrid Double-RIS and DF-Relay for Outdoor-to-Indoor Communication

Reconfigurable intelligent surface (RIS) is a promising solution to enhance the energy and spectral efficiency of future wireless networks. The system with single RIS might not be able provide sufficient line-of-sight (LoS) links for outdoor-indoor communication, which often limit signal transmission distance coverage range. This paper first proposes novel hybrid double-RIS full-duplex (FD) decode-and-forward (DF) relay aided eliminate impact building occlusion penetration loss in communication. Expressions upper bound ergodic (ESE) are derived match simulation results well. To maximize ESE, two algorithms proposed passive beamforming RIS: optimal phase shifts (OPS) generalized cross-entropy (GCE) algorithm. Results show that OPS can power gain square elements’ number. GCE-based discrete algorithm achieve good performance on efficiency. An allocation (OPA) scheme between source also Numerical demonstrate advantage OPA over equal (EPA).