  We calculate the spectrum of large angle cosmic microwave background (CMB)
anisotropies due to quantum fluctuations of the gravitational wave modes in
one-bubble open inflation models. We find the bubble-wall fluctuation modes,
which had been thought to exist discretely in previous analyses, are actually
contained in the continuous spectrum of gravitational wave modes when the
gravitational coupling is correctly taken into account. Then we find that the
spectrum of the tensor CMB anisotropy can be decomposed into the part due to
the wall fluctuation modes and that due to the usual gravitational wave modes
in a way which is almost model-independent, even when the gravitational
coupling is strong. We also discuss observational constraints on the model
parameters. We find that an appreciable portion of the parameter space is
excluded but the remaining allowable region is still wide enough to leave the
one-bubble scenario viable.
