Multiuser Wirelessly Powered Backscatter Communications: Nonlinearity, Waveform Design, and SINR-Energy Tradeoff

Wireless power transfer and backscatter communications have emerged as promising solutions for energizing and communicating with power limited devices. Despite some progress in wirelessly powered backscatter communications, the focus has been on backscatter and energy harvesters (EHs). Recently, significant progress has been made on the design of the transmit multisine waveform, adaptive to the channel state information at the transmitter (CSIT), in a point-to-point backscatter system. In this paper, we leverage the work and study the design of the transmit multisine waveform in a multi-user backscatter system, made of one transmitter, one reader, and multiple tags active simultaneously. We derive an efficient algorithm to optimize the transmit waveform so as to identify the tradeoff between the amount of energy harvested at the tags and the reliability of the communication, measured in terms of signal-to-interference-plus-noise ratio (SINR) at the reader. The performance with the optimized waveform based on the linear and nonlinear EH models is studied. The numerical results demonstrate the benefits of accounting for the EH nonlinearity, multiuser diversity, frequency diversity, and multisine waveform adaptive to the CSIT to enlarge the SINR-energy region.