  This contribution investigates the Degrees-of-Freedom region of a two-user
frequency correlated Multiple-Input-Single-Output (MISO) Broadcast Channel (BC)
with imperfect Channel State Information at the transmitter (CSIT). We assume
that the system consists of an arbitrary number of subbands, denoted as $L$.
Besides, the CSIT state varies across users and subbands. A tight outer-bound
is found as a function of the minimum average CSIT quality between the two
users. Based on the CSIT states across the subbands, the DoF region is
interpreted as a weighted sum of the optimal DoF regions in the scenarios where
the CSIT of both users are perfect, alternatively perfect and not known.
Inspired by the weighted-sum interpretation and identifying the benefit of the
optimal scheme for the unmatched CSIT proposed by Chen et al., we also design a
scheme achieving the upper-bound for the general $L$-subband scenario in
frequency domain BC, thus showing the optimality of the DoF region.
