As the technical trends for the next-generation wireless network significantly extend the near-field region, a performance reevaluation of integrated sensing and communications (ISAC) with an appropriate channel model to account for the effects introduced by the near field becomes essential. In this paper, a near-field ISAC framework is proposed for both downlink and uplink scenarios based on an accurate channel model, where the impacts of the effective aperture and polarization of antennas are considered. For the downlink case, three distinct designs are studied: a communications-centric (C-C) design, a sensing-centric (S-C) design, and a Pareto optimal design. Regarding the uplink case, the C-C design, the S-C design and a 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 near-field ISAC are characterized. Numerical results reveal that 1) as the number of antennas grows, the SRs and CRs under our accurate model converges to constants, while those under conventional far- and near-field models exhibit unbounded growth; and 2) ISAC achieves a more extensive rate region than the conventional frequency-division S&C in both downlink and uplink cases.

翻译：随着下一代无线网络技术趋势显著扩展了近场区域，采用考虑近场效应的适当信道模型对集成感知与通信（ISAC）性能进行重新评估变得至关重要。本文基于精确信道模型，提出了适用于下行和上行场景的近场ISAC框架，其中考虑了天线的有效孔径和极化效应。针对下行链路，研究了三种不同的设计方案：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。针对上行链路，则考虑了C-C设计、S-C设计以及一种时分共享策略。在每种设计方案中，推导了感知速率（SR）和通信速率（CR）。为获得更深入认识，还分析了高信噪比斜率以及关于天线数量的速率缩放规律。最后，刻画了近场ISAC可达的SR-CR区域。数值结果表明：1) 随着天线数量增长，在本文精确模型下的SR和CR收敛至常数，而传统远场和近场模型下的SR和CR则呈现无界增长；2) 无论下行还是上行场景，ISAC均能实现比传统频分S&C更广泛的速率区域。