Collaborative Positioning Optimization for Multiple Moving Users in UAV-Enabled ISAC

In this paper, we propose a joint real-time trajectory design, power control, and base station (BS) selection scheme in the unmanned aerial vehicle (UAV)-enabled integrated sensing and communication (ISAC) system, where multiple UAVs cooperate with BSs to provide communication and positioning functions for multiple moving users. Specifically, to optimize the sensing performance while guaranteeing the communication requirement, we adopt the Cramer-Rao bound (CRB) and communication spectrum efficiency (SE) of multiple users as the performance metric. Then, we formulate a mixed combinatorial and non-linear optimization problem to minimize the maximum position CRB of ISAC users under the constraints of communication SE, transmit power, UAV velocity, and collision avoidance among UAVs. To solve the non-convex original problem with the intractable expression form of CRB, we derive the position CRB into a simplified closed-form expression and employ the block coordinate descend (BCD) algorithm to alternatively optimize the trajectory design, power control, and BS selection variables. Then, we carry out several equivalent transformations and adopt the penalty function method and successive convex approximation (SCA) technology to make the optimization problem tractable. Finally, extensive simulations are conducted to validate and evaluate our proposed scheme.