Cramér-Rao Bound Optimization for Joint Power Allocation in Multi-user ISAC Systems

Abstract: To improve the performance of both communication and sensing, this paper presents a coordinated power allocation strategy for a multi-user integrated sensing and communication (ISAC) system. The framework involves a central processor (CP) along with multiple base stations (BSs) that transmit both communication and specialized sensing signals. We introduce an innovative coordinated power allocation method for ISAC transmitters aimed at minimizing overall transmit power while ensuring that each communication user (CU) meets the signal-to-interference-plus-noise ratio (SINR) requirements. Additionally, this method seeks to achieve the optimal Cramér-Rao bound (CRB) for target sensing. Given that the coordinated power allocation challenge is non-convex, we reformulate it as a semi-definite programming problem by employing the semi-definite relaxation (SDR) technique. We then demonstrate that this method effectively guarantees the attainment of the global optimum. Numerical simulations indicate that our proposed strategy results in a reduction in transmit power compared to the CRBL-approximation method, underscoring significant performance enhancements.