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：提出了一种近场集成感知和通信（ISAC）框架，与传统的远场系统相比，引入了额外的距离维度，用于感知和通信。特别地，推导了近场联合距离和角度感知的Cramer-Rao下限，在最小化每个用户的最低通信速率要求的条件下进行优化。分别研究了全数字天线和混合数字和模拟天线。对于全数字天线，通过半定松弛获得了ISAC波形的全局最优解。对于混合天线，通过两阶段优化获得了高质量的解。数值结果表明，与远场ISAC相比，近场ISAC引入了额外的距离维度，提高了性能。