We consider the MIMO fading broadcast channel, where until recently it was
taken
for granted that the sum degrees of freedom (DoF) cannot be improved beyond
TDMA, since the DoF-optimality of TDMA had been established when all receivers
have perfect CSIR, or when none of them have CSIR. Recently, it was discovered
that when users have unequal CSIR, TDMA is no longer optimal and a product
superposition with non-coherent (Grassmannian) signaling is DoF-optimal for
many
antenna configurations. This work extends product superpositions to the domain
of coherent signaling with pilots, showing that they can also achieve the
optimal DoF with product superposition. Furthermore, DoF optimality of product
superposition is established for a wider set of receiver antenna
configurations.