  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. A uniform planar array is
equipped at a base station, 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 examined. The attainable near-field SR-CR
regions of ISAC and the baseline frequency-division S&C are also characterized.
Numerical results reveal that, as the number of antennas in the array grows,
the SRs and CRs under our accurate model converge to finite values, while those
under conventional far- and near-field models exhibit unbounded growth,
highlighting the importance of precisely modeling the channels for near-field
ISAC.
