In this letter, we propose to deploy rotatable antennas (RAs) at the base station (BS) to enhance both communication and sensing (C&S) performances, by exploiting a new spatial degree-of-freedom (DoF) offered by array rotation. Specifically, we formulate a multi-objective optimization problem to simultaneously maximize the sum-rate of multiple communication users and minimize the Cram\'er-Rao bound (CRB) for target angle estimation, by jointly optimizing the transmit beamforming vectors and the array rotation angle at the BS. To solve this problem, we first equivalently decompose it into two subproblems, corresponding to an inner problem for beamforming optimization and an outer problem for array rotation optimization. Although these two subproblems are non-convex, we obtain their high-quality solutions by applying the block coordinate descent (BCD) technique and one-dimensional exhaustive search, respectively. Moreover, we show that for the communication-only case, RAs provide an additional rotation gain to improve communication performance; while for the sensing-only case, the equivalent spatial aperture can be enlarged by RAs for achieving higher sensing accuracy. Finally, numerical results are presented to showcase the performance gains of RAs over fixed-rotation antennas in integrated sensing and communications (ISAC).

翻译：本文提出在基站部署可旋转天线，通过利用阵列旋转提供的新空间自由度，同时提升通信与感知性能。具体而言，我们构建了一个多目标优化问题，通过联合优化基站的发射波束赋形向量与阵列旋转角度，在最大化多通信用户和速率的同时，最小化目标角度估计的克拉美-罗界。为解决该问题，我们首先将其等效分解为两个子问题：波束赋形优化的内层问题与阵列旋转优化的外层问题。尽管这两个子问题均为非凸，我们分别通过应用块坐标下降技术和一维穷举搜索获得了高质量解。此外，我们证明在纯通信场景中，可旋转天线通过提供额外的旋转增益以改善通信性能；而在纯感知场景中，可旋转天线可扩大等效空间孔径以实现更高的感知精度。最后，数值结果展示了在集成感知与通信系统中，可旋转天线相较于固定旋转天线的性能增益。