Beamforming Design for Novel Relay-Assisted Multi-User Multi-Tag Symbiotic Radios

This letter considers a novel relay-assisted, multi-user multi-tag uplink symbiotic radio system, in which a relay node forwards multiple users' signals to a base station (BS), meanwhile powering multiple backscatter tags. We put forth a new joint transmit and receive beamforming design problem to minimize the relay's transmit power while satisfying the signal-to-interference-plus-noise ratio (SINR) constraints of both the primary users and the tags. An alternating optimization algorithm based on semi-definite programming (SDP) and zero-forcing is proposed to solve this non-convex power minimization problem. The proposed approach is also extended to jointly optimize the transmit/receive beamforming to maximize the minimal SINR of the tags under a given relay power budget. Numerical results show that the proposed beamforming designs significantly outperform the benchmarks.