The technical trends for the next-generation wireless network significantly extend the near-field region, necessitating a reevaluation for the performance of integrated sensing and communications (ISAC) to account for the effects introduced by the near field. In this paper, a near-field ISAC framework is proposed with a more accurate channel model than the three conventional models (TCMs): uniform plane wave, uniform spherical wave, and non-uniform spherical wave, in which the effective aperture of the antenna is considered. Based on the proposed model, sensing and communication (S&C) performance in both downlink and uplink scenarios are analyzed. For the downlink case, three distinct designs are studied: the communications-centric (C-C) design, the sensing-centric (S-C) design, and the Pareto optimal design. Regarding the uplink case, the C-C design, the S-C design and the time-sharing strategy are considered. Within each design, sensing rates (SRs) and communication rates (CRs) are derived. To gain further insights, high signal-to-noise ratio slopes and rate scaling laws concerning the number of antennas are also examined. Finally, the attainable SR-CR regions of the near-field ISAC are characterized. Numerical results reveal that 1) as the number of antennas grows, the SRs and CRs of the proposed model converges to constants, while those of the TCMs increase unboundedly; 2) ISAC achieves a more extensive rate region than the conventional frequency-division S&C in both downlink and uplink cases.

翻译：下一代无线网络的技术趋势显著扩展了近场区域，这要求重新评估集成感知与通信（ISAC）的性能，以考虑近场引入的影响。本文提出了一种近场ISAC框架，其信道模型比三种传统模型（TCMs）：均匀平面波、均匀球面波和非均匀球面波更为精确，在该模型中考虑了天线的有效孔径。基于所提出的模型，分析了下行链路和上行链路场景中的感知与通信（S&C）性能。对于下行链路情况，研究了三种不同设计：以通信为中心（C-C）设计、以感知为中心（S-C）设计以及帕累托最优设计。对于上行链路情况，考虑了C-C设计、S-C设计以及时分策略。在每种设计中，推导了感知速率（SRs）和通信速率（CRs）。为获得更深入的见解，还研究了高信噪比斜率以及关于天线数量的速率缩放定律。最后，刻画了近场ISAC的可达SR-CR区域。数值结果表明：1）随着天线数量增加，所提模型的SRs和CRs收敛于常数，而TCMs的对应值无限增长；2）在下行链路和上行链路情况下，ISAC均实现了比传统频分S&C更广泛的速率区域。