A near-field integrated sensing and communications (ISAC) framework is proposed, which introduces an additional distance dimension for both sensing and communications compared to the conventional far-field system. In particular, the Cramer-Rao bound for the near-field joint distance and angle sensing is derived, which is minimized subject to the minimum communication rate requirement of each user. Both fully digital antennas and hybrid digital and analog antennas are investigated. For fully digital antennas, a globally optimal solution of the ISAC waveform is obtained via semidefinite relaxation. For hybrid antennas, a high-quality solution is obtained through two-stage optimization. Numerical results demonstrate the performance gain introduced by the additional distance dimension of the near-field ISAC over the far-field ISAC.

翻译：本文提出了一种近场集成感知与通信（ISAC）框架，与传统远场系统相比，该框架为感知与通信引入了一个额外的距离维度。具体而言，推导了近场联合距离与角度感知的克拉美罗界，并在满足每个用户最低通信速率要求的条件下对其进行了最小化。同时研究了全数字天线与混合数模天线两种架构。对于全数字天线，通过半定松弛方法获得了ISAC波形的全局最优解；对于混合天线，通过两阶段优化得到了高质量解。数值结果证明了近场ISAC相较于远场ISAC在距离维度上的性能增益。