Modeling and Analysis of Near-Field ISAC

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.