  Unmanned aerial vehicle (UAV) has high flexibility and controllable mobility,
therefore it is considered as a promising enabler for future integrated sensing
and communication (ISAC). In this paper, we propose a novel adaptable ISAC
(AISAC) mechanism in the UAV-enabled system, where the UAV performs sensing on
demand during communication and the sensing duration is configured flexibly
according to the application requirements rather than keeping the same with the
communication duration. Our designed mechanism avoids the excessive sensing and
waste of radio resources, therefore improving the resource utilization and
system performance. In the UAV-enabled AISAC system, we aim at maximizing the
average system throughput by optimizing the communication and sensing
beamforming as well as UAV trajectory while guaranteeing the quality-of-service
requirements of communication and sensing. To efficiently solve the considered
non-convex optimization problem, we first propose an efficient alternating
optimization algorithm to optimize the communication and sensing beamforming
for a given UAV location, and then develop a low-complexity joint beamforming
and UAV trajectory optimization algorithm that sequentially searches the
optimal UAV location until reaching the final location. Numerical results
validate the superiority of the proposed adaptable mechanism and the
effectiveness of the designed algorithm.
