Wireless Power Transfer Reflection Policies for Multi-User Ambient Backscatter Communication

In this paper, we study a low-complexity wireless power transfer scheme based on the concept of retrodirective energy beamforming for multi-user ambient backscatter communication by considering signal spreading. After showing that the expression for the harvested energy at the energy receivers depends on the multi-user backscatter coefficients, we investigate various reflection strategies that achieve different design objectives. Specifically, we propose a scheme that maximizes the sum harvested energy in the network by optimizing the backscattering coefficients. Moreover, we evaluate a distributed power control algorithm that allows each energy receiver to adjust its backscatter coefficient iteratively based on its current harvested power, thereby achieving the desired user fairness.