  In this paper, we propose a novel integrated sensing and communications
(ISAC) framework for the sixth generation (6G) mobile networks, in which we
decompose the real physical world into static environment, dynamic targets, and
various object materials. The ubiquitous static environment occupies the vast
majority of the physical world, for which we design static environment
reconstruction (SER) scheme to obtain the layout and point cloud information of
static buildings. The dynamic targets floating in static environments create
the spatiotemporal transition of the physical world, for which we design
comprehensive dynamic target sensing (DTS) scheme to detect, estimate, track,
image and recognize the dynamic targets in real-time. The object materials
enrich the electromagnetic laws of the physical world, for which we develop
object material recognition (OMR) scheme to estimate the electromagnetic
coefficient of the objects. Besides, to integrate these sensing functions into
existing communications systems, we discuss the interference issues and
corresponding solutions for ISAC cellular networks. Furthermore, we develop an
ISAC hardware prototype platform that can reconstruct the environmental maps
and sense the dynamic targets while maintaining communications services. With
all these designs, the proposed ISAC framework can support multifarious
emerging applications, such as digital twins, low altitude economy, internet of
vehicles, marine management, deformation monitoring, etc.
