  This article proposes the concept of channel knowledge map (CKM) as an
enabler towards environment-aware wireless communications. CKM is a
site-specific database, tagged with the locations of the transmitters and/or
receivers, that contains whatever channel-related information useful to enhance
environmental-awareness and facilitate or even obviate sophisticated real-time
channel state information (CSI) acquisition. Therefore, CKM is expected to play
an important role for 6G networks targeting for super high capacity, extremely
low latency, and ultra-massive connectivity, by offering potential solutions to
practical challenges brought by the drastically increased channel dimensions
and training overhead. In this article, the motivations of
environmental-awareness enabled by CKM are firstly discussed, followed by the
key techniques to build and utilize CKM. In particular, it is highlighted that
CKM is especially appealing for four channel types: channels for yet-to-reach
locations, channels for non-cooperative nodes, channels with large dimensions,
and channels with severe hardware/processing limitations. Two case studies with
extensive numerical results are presented to demonstrate the great potential of
environment-aware communications enabled by CKM.
