  Recently the second phase of Background Imaging of Cosmic Extragalactic
Polarization (BICEP2) claimed a detection of the tensor-to-scalar ratio ($r$)
of primordial fluctuation at $5\sigma$ confidence level. If it is true, this
large and measurable amplitude ($r \simeq 0.2$) of B-mode polarization
indicates that it is possible to measure the shape of CMB B-mode polarization
with future experiments. We forecast the precision of $r$ and the tensor
spectral index $n_{\rm t}$ measurements, with $n_{\rm t}$ as a free parameter,
from a {\it Planck}-like experiment, and from Spider and POLARBEAR given the
current understanding of their experimental noise and foreground contamination.
We quantitatively determine the signal-to-noise of the measurement in
$r$-$n_{\rm t}$ parameter space for the three experiments. The forecasted
signal-to-noise ratio of the B-mode polarization somewhat depends on $n_{\rm
t}$, but strongly depends on the true value of $r$.
