This article re-examines integrated sensing and communication (ISAC) systems operating in the near-field region of a large antenna array while exploiting a large bandwidth. We first reveal the fundamental characteristics of wideband sensing and communication (S&C) channels and highlight the key changes that occur during the transition from the far-field to the near-field region. Specifically, there are two fundamental changes in the near-field region: strong angular-delay correlation and element-specific Doppler frequencies. It is highlighted that the near-field effect can enable the wideband-like S&C functionalities in terms of signal multiplexing and range sensing due to the strong angular-delay correlation, thus allowing the trading of large antenna arrays for large bandwidths. Furthermore, it also introduces the wideband-unattainable functionalities in high mobility S&C scenarios by leveraging the element-specific Doppler frequencies. We then delineate certain paradigm shifts in thinking required to advance toward near-field wideband ISAC systems, with a particular emphasis on resource allocation, antenna array arrangement, and transceiver architecture. Lastly, some other promising directions are discussed.

翻译：本文重新审视了在大天线阵列近场区域运行且利用大带宽的集成感知与通信系统。我们首先揭示了宽带感知与通信信道的基本特性，并强调了从远场到近场区域过渡过程中发生的关键变化。具体而言，近场区域存在两个根本性变化：强角度-时延相关性以及单元特定的多普勒频率。研究表明，由于强角度-时延相关性，近场效应能够在信号复用和距离感知方面实现类宽带的感知与通信功能，从而允许以大规模天线阵列换取大带宽。此外，通过利用单元特定的多普勒频率，近场效应还可在高移动性感知与通信场景中引入宽带无法实现的功能。随后，我们阐述了推进近场宽带集成感知与通信系统所需的若干思维范式转变，特别强调资源分配、天线阵列布置和收发架构。最后，探讨了其他有前景的研究方向。