  Integrated sensing and communication (ISAC) is considered as a promising
solution for improving spectrum efficiency and relieving wireless spectrum
congestion. This paper systematically introduces the evolutionary path of ISAC
technologies, then sorts out and summarizes the current research status of ISAC
resource allocation. From the perspective of different integrated levels of
ISAC, we introduce and elaborate the research progress of resource allocation
in different stages, namely, resource separated, orthogonal, converged, and
collaborative stages. In addition, we give in-depth consideration to propose a
new resource allocation framework from a multi-granularity perspective.
Finally, we demonstrate the feasibility of our proposed framework with a case
of full-duplex ISAC system.
