  We study the impact of heterogeneity of channel-state-information available
at the transmitters (CSIT) on the capacity of broadcast channels with a
multiple-antenna transmitter and $k$ single-antenna receivers (MISO BC). In
particular, we consider the $k$-user MISO BC, where the CSIT with respect to
each receiver can be either instantaneous/perfect, delayed, or not available;
and we study the impact of this heterogeneity of CSIT on the degrees-of-freedom
(DoF) of such network. We first focus on the $3$-user MISO BC; and we
completely characterize the DoF region for all possible heterogeneous CSIT
configurations, assuming linear encoding strategies at the transmitters. The
result shows that the state-of-the-art achievable schemes in the literature are
indeed sum-DoF optimal, when restricted to linear encoding schemes. To prove
the result, we develop a novel bound, called Interference Decomposition Bound,
which provides a lower bound on the interference dimension at a receiver which
supplies delayed CSIT based on the average dimension of constituents of that
interference, thereby decomposing the interference into its individual
components. Furthermore, we extend our outer bound on the DoF region to the
general $k$-user MISO BC, and demonstrate that it leads to an approximate
characterization of linear sum-DoF to within an additive gap of $0.5$ for a
broad range of CSIT configurations. Moreover, for the special case where only
one receiver supplies delayed CSIT, we completely characterize the linear
sum-DoF.
