Optimal Transmit Signal and Beamforming Design for Integrated Sensing and Power Transfer Systems

Abstract

Integrating different functionalities, conventionally implemented as dedicated systems, into a single platform allows utilising the available resources more efficiently. We consider a frame-based integrated sensing and power transfer (ISAPT) system and propose the joint optimisation of the transmit beamforming vectors, the pulse duration, and the subframe durations to combine sensing and wireless power transfer (WPT) functionalities efficiently. In contrast to prior works, we adopt an accurate non-linear circuit-based energy harvesting (EH) model. We formulate and solve a non-convex optimisation problem for an arbitrary number of EH receivers and sensing targets (STs). The objective is to maximise the weighted sum of the average harvested powers at the EH receivers while ensuring the echo signals reflected by the ST targeted in the corresponding subframe are received with sufficient power for estimating the range to the ST with a prescribed accuracy within the considered coverage region. A method to determine the optimal solution to the problem is derived and two efficient suboptimal schemes are proposed. The performance gap between the upper-bound and the suboptimal schemes is shown to be small. The co-design of the sensing and WPT functionalities and the resulting optimised beampatterns are studied in detail. For high sensing accuracy requirements, the joint transmit signal and beamforming design is found to differ significantly from the optimal transmit signals dedicated to either sensing or WPT. A dedicated transmit signal for WPT is shown to enhance ISAPT system performance when the sensing requirements are less stringent.