  In the setting of the two-user broadcast channel, recent work by Maddah-Ali
and Tse has shown that knowledge of prior channel state information at the
transmitter (CSIT) can be useful, even in the absence of any knowledge of
current CSIT. Very recent work by Kobayashi et al., Yang et al., and Gou and
Jafar, extended this to the case where, instead of no current CSIT knowledge,
the transmitter has partial knowledge, and where under a symmetry assumption,
the quality of this knowledge is identical for the different users' channels.
  Motivated by the fact that in multiuser settings, the quality of CSIT
feedback may vary across different links, we here generalize the above results
to the natural setting where the current CSIT quality varies for different
users' channels. For this setting we derive the optimal degrees-of-freedom
(DoF) region, and provide novel multi-phase broadcast schemes that achieve this
optimal region. Finally this generalization incorporates and generalizes the
corresponding result in Maleki et al. which considered the broadcast channel
with one user having perfect CSIT and the other only having prior CSIT.
