  The impending spectrum congestion imposed by the emergence of new
bandwidth-thirsty applications may be mitigated by the integration of radar and
classic communications functionalities in a common system. Furthermore, the
merger of a sensing component into wireless communication networks has raised
interest in recent years and it may become a compelling design objective for
6G. This article presents the evolution of the hitherto separate radar and
communication systems towards their amalgam known as a joint radar and
communication (RADCOM) system. Explicitly, we propose to integrate a radio
sensing component into 6G. We consider an ultra-dense network (UDN) scenario
relying on an active multistatic radar configuration and on cooperation between
the access points across the entire coverage area. The technological trends
required to reach a feasible integration, the applications anticipated and the
open research challenges are identified, with an emphasis on high-accuracy
network synchronization. The successful integration of these technologies would
facilitate centimeter-level resolution, hence supporting compelling
high-resolution applications for next-generation networks, such as robotic cars
and industrial assembly lines.
