  In this paper we explore the information-theoretic aspects of interference
alignment and its relation to channel state information (CSI). For the $K-$user
interference channel using different changing patterns between different users,
we propose several methods to align some parts of interferences and to increase
what is achieved by time sharing method. For more practical case when all the
channel links connected to the same destination have the same changing pattern,
we find an upper-bound and analyze it for the large interference channel
network. This result shows that when the size of the network increases, the
upper-bound value goes to $\frac{\sqrt{K}}{2}$. For the fast fading channel
when all the channels have the same changing pattern, we show that when the
direct links have different characteristic functions (channel permutation or
memory), in the absence of half part of CSI (cross links) at both transmitters
and receivers, one can achieve $K/2$ degrees-of-freedom (DoF). Also by the
converse proof we show that this is the minimum channel information to achieve
maximum DoF of $\frac{K}{2}$. Throughout this work, this fact has been
pinpointed to prove statements about more general partial state CSI and
achievable DoF. In other words, for the 3-user fully connected interference
channel we find out while $\frac{3}{2}$ lies in achievable DoF, we don't need
to know half part of the CSI. Also, the result has been extended to a more
general form for $K-$user interference channel and through the converse proof,
its functionality on channel state is proved to be optimum.
