Beamforming design for multi-antenna multi-tag symbiotic radio backscatter systems

In this paper, we consider a multi-tag symbiotic radio backscatter system, where a multi-antenna source node transmits its own message to a multi-antenna destination, while multiple backscatter tags transmit information to the destination by directly reflecting the incident signals from the source. We investigate the optimal beamforming design to minimize the transmit power at the source, subject to the signal-to-interference-plus -noise ratio (SINR) constraints for the signals of the source and the tags, and the harvested power constraints at the tags. The formulated min-power optimization problem is non-convex, and we propose a semi-definite programming (SDP) based alternating optimization algorithm to optimize the transmit beamforming vector at the source and the receive beamforming vector at the destination. Numerical results show that the proposed beamforming design algorithm converges fast and outperforms the counterpart scheme significantly.