Backscatter Communication System for Integrated Sensing and Communications

This paper studies a multi-user backscatter communication (BackCom) system for integrated sensing and communications (ISAC), where the ISAC transmitter sends excitation signals to power multiple passive backscatter devices (BD), and the ISAC receiver performs joint sensing (localization) and communication tasks based on the backscattered signals from all BDs. Specifically, the localization performance is characterized by the Cramér-Rao bound (CRB) on the transmission delay and direction of arrival (DoA) of the backscattered signals, whose closed-form expression is obtained by deriving the corresponding Fisher information matrix (FIM), and the communication performance is characterized by the sum transmission rate of all BDs. Then, a CRB minimization problem is formulated by considering the communication rate constraint, and is shown to be non-convex in general. To solve this problem, we propose an approach that combines fractional programming (FP) and Schur complement techniques to transform the original problem into an equivalent convex form. Finally, numerical results reveal the trade-off between the localization and communication performances.