  With the emerging Integrated Sensing and Communication (ISAC) technique,
exploiting the mobile communication system with multi-domain resources,
multiple network elements, and large-scale infrastructures to realize
cooperative sensing is a crucial approach satisfying the requirements of
high-accuracy and large-scale sensing in IoE. In this article, the deep
cooperation in ISAC system including three perspectives is investigated. In the
microscopic perspective, namely, within a single node, the sensing information
carried by time-frequency-space-code domain resources is processed, such as
phase compensation, coherent accumulation and other operations, thereby
improving the sensing accuracy. In the mesoscopic perspective, the sensing
accuracy could be improved through the cooperation of multiple nodes. We
explore various multi-node cooperative sensing scenarios and present the
corresponding challenges and future research trends. In the macroscopic
perspective, the massive number of infrastructures from the same operator or
different operators could perform cooperative sensing to extend the sensing
coverage and improve the sensing continuity. We investigate network
architecture, target tracking methods, and the large-scale sensing assisted
digital twin construction. Simulation results demonstrate the superiority of
multi-nodes and multi-resources cooperative sensing over single resource or
node sensing. This article may provide a deep and comprehensive view on the
cooperative sensing in ISAC system to enhance the performance of sensing,
supporting the applications of IoE.
