Propagation is not an insurmountable challenge.
Recent measurements indicate similar
general characteristics as at microwave frequencies,
including distance-dependent path loss and
the possibility of non-line-of-sight communication.
A main difference between microwave and
mmWave frequencies is the sensitivity to blockages:
the results in [11], for instance, indicate a
path loss exponent of 2 for line-of-sight propagation
but 4 (plus additional power loss) for nonline-of-sight.
MmWave cellular research will
need to incorporate sensitivity to blockages and
more complex channel models in the analysis,
and also study the effects of enablers such as
higher density infrastructure and relays. Another
enabler is the separation between control and
data planes, already mentioned.