Joint Beamforming and Deployment Design for UAV-Enabled ISAC Systems with Partially-Overlapped Subcarriers

In this paper, we consider an unmanned aerial vehicle (UAV)-enabled multi-carrier multiple-input multiple-output integrated sensing and communications scenario, where the UAV simultaneously provides downlink communication services to terrestrial communication users and detects terrestrial sensing targets. We propose a partially-overlapped (PO) subcarrier allocation scheme that allocates a dedicated fraction of subcarriers for sensing, while enabling communication across all the subcarriers. Based on the proposed PO subcarrier allocation scheme, we aim at maximizing the weighted throughput of the considered system, while simultaneously satisfying the sensing constraints. To this end, we formulate a joint beamforming, subcarrier allocation, and UAV deployment optimization problem. In order to solve this non-convex problem, we first transform it into a tractable form by leveraging mean square error approximation and multi-dimensional quadratic transformations. The reformulated problem is then decomposed into three subproblems, namely, the beamforming design subproblem, the subcarrier allocation subproblem, and the UAV deployment subproblem. These subproblems are solved by utilizing binary convex relaxation and successive convex approximation methods in an iterative manner. Through numerical results, we demonstrate that our proposed algorithm outperforms baseline schemes (i.e., the fullyoverlapped scheme and the non-overlapped scheme). In addition, it also achieves a comparable communication performance to the optimal solution obtained from the exhaustive search, showing how our proposed solution can improve the system performance by judiciously adjusting the beamforming, UAV deployment, as well as the fraction of overlapped subcarriers.