A near-field integrated sensing, positioning, and communication (ISPAC) framework is proposed, where a base station (BS) simultaneously serves multiple communication users and carries out target sensing and positioning. A novel double-array structure is proposed to enable the near-field ISPAC at the BS. Specifically, a small-scale assisting transceiver (AT) is attached to the large-scale main transceiver (MT) to empower the communication system with the ability of sensing and positioning. Based on the proposed framework, the joint angle and distance Cram\'er-Rao bound (CRB) is first derived. Then, the CRB is minimized subject to the minimum communication rate requirement in both downlink and uplink ISPAC scenarios: 1) For downlink ISPAC, a downlink target positioning algorithm is proposed and a penalty dual decomposition (PDD)-based double-loop algorithm is developed to tackle the non-convex optimization problem. 2) For uplink ISPAC, an uplink target positioning algorithm is proposed and an efficient alternating optimization algorithm is conceived to solve the non-convex CRB minimization problem with coupled user communication and target probing design. Both proposed optimization algorithms can converge to a stationary point of the CRB minimization problem. Numerical results show that: 1) The proposed ISPAC system can locate the target in both angle and distance domains merely relying on single BS and limited bandwidths; and 2) the positioning performance achieved by the hybrid-analog-and-digital ISPAC approaches that achieved by fully digital ISPAC when the communication rate requirement is not stringent.

翻译：提出了一种近场集成感知、定位与通信（ISPAC）框架，其中基站（BS）同时服务于多个通信用户并执行目标感知与定位。为在基站处实现近场ISPAC，提出了一种新型双阵列结构。具体而言，在小规模辅助收发器（AT）附加于大规模主收发器（MT）上，以赋予通信系统感知与定位能力。基于所提框架，首先推导了联合角度与距离的克拉美-罗界（CRB）。随后，在下行与上行ISPAC场景中，以最小通信速率要求为约束，对CRB进行最小化：1）针对下行ISPAC，提出了一种下行目标定位算法，并开发了基于罚对偶分解（PDD）的双层算法来处理非凸优化问题；2）针对上行ISPAC，提出了一种上行目标定位算法，并设计了一种高效的交替优化算法以求解用户通信与目标探测设计耦合的非凸CRB最小化问题。两种优化算法均能收敛至CRB最小化问题的驻点。数值结果表明：1）所提ISPAC系统仅依赖单个基站及有限带宽即可在角度与距离域对目标进行定位；2）当通信速率要求不严格时，混合模拟-数字ISPAC所实现的定位性能可接近全数字ISPAC的性能。