A simultaneously transmitting and reflecting surface (STARS) enabled integrated sensing and communications (ISAC) framework is proposed, where a novel bi-directional sensing-STARS architecture is devised to facilitate the full-space communication and sensing. Based on the proposed framework, a joint optimization problem is formulated, where the Cramer-Rao bound (CRB) for estimating the 2-dimension direction-of-arrival of the sensing target is minimized. Two cases are considered for sensing performance enhancement. 1) For the two-user case, an alternating optimization algorithm is proposed. In particular, the maximum number of deployable sensors is obtained in the closed-form expressions. 2) For the multi-user case, an extended CRB (ECRB) metric is proposed to characterize the impact of the number of sensors on the sensing performance. Based on the proposed metric, a novel penalty-based double-loop (PDL) algorithm is proposed to solve the ECRB minimization problem. To tackle the coupling of the ECRB, a general decoupling approach is proposed to convert it to a tractable weighted linear summation form. Simulation results reveal that 1) the proposed PDL algorithm can achieve a near-optimal performance with consideration of sensor deployment; 2) without violating the communication under the quality of service requirements, reducing the receive antennas at the BS does not deteriorate the sensing performance; and 3) it is preferable to deploy more passive elements than sensors in terms of achieving optimal sensing performance
QoS-Constrained Resource Pattern Design for V2X-ISAC Systems
Daegu Gyeongbuk Institute of Science and Technology (DGIST)（大邱庆尚北道科学技术院）；Institute of Innovation for Future Army, Republic of Korea Army（韩国陆军未来军队创新研究所）；Interdisciplinary Studies of Artificial Intelligence, DGIST（大邱庆尚北道科学技术院人工智能跨学科研究）；Autonomous Driving Intelligence Research Section, Electronics and Telecommunications Research Institute (ETRI)（电子通信研究院自动驾驶智能研究部）；Department of Electrical Engineering and Computer Science, DGIST（大邱庆尚北道科学技术院电气与计算机工程系）
