  In this paper, we consider the problem of the interference alignment for the
$K$-user SISO interference channel with blind channel state information at
transmitters (CSIT). Our achievement in contrast to popular $K-$user
interference alignment (IA) scheme has more practical notions. In this case
every receiver is equipped with one reconfigurable antenna which tries to place
its desired signal in a subspace which is linearly independent from
interference signals. We show that if the channel values are known to the
receivers only, the sum degrees-of-freedom (DOF) rate region of the linear BIA
with staggered antenna switching is $\frac{Kr}{r^2-r+K}$, where $r = \left
\lceil{\frac{\sqrt{1+4K}-1}{2}} \right \rceil$. The result indicates that the
optimum DoF rate region of the $K-$user interference channel is to achieve the
DoF of $\frac{\sqrt{K}}{2}$ for an asymptotically large network. Thus, the DoF
of the $K$-user interference channel using staggered antenna switching grows
sub-linearly with the number of the users, whereas it grows linearly in the
case where transmitters access the CSI. In addition we propose both
achievability and converse proof so as to show that this is the DoF rate region
of blind interference alignment (BIA) with staggered antenna switching.
