  Enabling technologies of 5G and beyond wireless communication networks, such
as millimeter-wave communication, beamforming, and multiple-input
multiple-output (MIMO) antenna systems, are becoming increasingly dependent on
accurate information of the physical environment for optimized communication
performance. The acquisition of this information is a significant challenge,
which can be eased by knowledge of the radio environment. Radio environment
mapping (REM) has long been considered an enabler of cognitive radios (CRs).
However, the limitations of radios effectively confined the application of REM
to spectrum sensing and interference mapping. With the advent of more capable
software-defined radios and advanced networks, the idea of a truly intelligent
communication system empowered by enhanced REM can be realized. To this effect,
we propose the generalized radio environment monitoring (G-REM) concept to
include all aspects of the radio environment. We outline a general, self
contained framework which enables radio environment monitoring in standalone
devices. The presented G-REM framework comprises of different information
sources, sensing methods, sensing modes, and mapping techniques to enable the
realization of more reliable, secure, efficient, and faster future wireless
networks. The accompanying challenges and future research direction are also
provided.
