Power optimization for target localization with reconfigurable intelligent surfaces

Abstract

Target localization plays an indispensable role in wireless network and array signal processing. Generally, the traditional methods are restricted to the line of sight (LOS) transmission link assumption, and may fail in the non line of sight (NLOS) scenario. As a promising technology, reconfigurable intelligent surface (RIS) can customize the wireless channel and then overcome the performance degradation due to the lack of LOS. In this paper, we consider the power optimization problem of RIS localization, which is crucial for localization accuracy and energy consumption. In order to minimize the transmit power, we investigate several power optimization problems of the RIS localization under the constraints of the localization accuracy and the phase shift parameters of the RIS. Specifically, aiming at the RIS system with an anchor node (AN) and an target node (TN), we derive the Cramér-Rao bound (CRB) in terms of the location parameters of the TN, and prove the theoretic result of the relation between the optimal power and the phase parameters of the RIS. Based on these results, we formulate the corresponding power optimization problem, and derive the analytical solution of the optimization problem. Next, we obtain the convex form of the power optimization problem for the second scenario, that is, the RIS system with multiple TNs and single AN. Lastly, for the multiple ANs scenario with single TN, we solve the power optimization problem by using semidefinite release (SDR) method. Simulation results verify the feasibility of the proposed methods.