  We introduce a resource theory of channels relevant to communication via
quantum channels, in which the set of constant channels --- useless channels
for communication tasks --- is considered as the free resource. We find that
our theory with such a simple structure is useful to address central problems
in quantum Shannon theory --- in particular, we provide a converse bound for
the one-shot non-signalling assisted classical capacity that naturally leads to
its strong converse property, as well as obtain the one-shot channel simulation
cost with non-signalling assistance. We clarify an intimate connection between
the non-signalling assistance and our formalism by identifying the
non-signalling assisted channel coding with the channel transformation under
the maximal set of resource non-generating superchannels, providing a physical
characterization of the latter. Our results provide new perspectives and
concise arguments to those problems, connecting the recently developed fields
of resource theories to `classic' settings in quantum information theory and
shedding light on the validity of resource theories of channels as effective
tools to address practical problems.
