  In existing communication systems, the channel state information of each UE
(user equipment) should be repeatedly estimated when it moves to a new position
or another UE takes its place. The underlying ambient information, including
the specific layout of potential reflectors, which provides more detailed
information about all UEs' channel structures, has not been fully explored and
exploited. In this paper, we rethink the mmWave channel estimation problem in a
new and indirect way, i.e., instead of estimating the resultant composite
channel response at each time and for any specific location, we first conduct
the ambient perception exploiting the fascinating radar capability of a mmWave
antenna array and then accomplish the location-based sparse channel
reconstruction. In this way, the sparse channel for a quasi-static UE arriving
at a specific location can be rapidly synthesized based on the perceived
ambient information, thus greatly reducing the signalling overhead and online
computational complexity. Based on the reconstructed mmWave channel,
single-beam mmWave communication is designed and evaluated which shows
excellent performance. Such an approach in fact integrates radar with
communication, which may possibly open a new paradigm for future communication
system design.
