  A Han-Kobayashi based achievable scheme is presented for ergodic fading
two-user Gaussian interference channels (IFCs) with perfect channel state
information at all nodes and Gaussian codebooks with no time-sharing. Using
max-min optimization techniques, it is shown that jointly coding across all
states performs at least as well as separable coding for the sub-classes of
uniformly weak (every sub-channel is weak) and hybrid (mix of strong and weak
sub-channels that do not achieve the interference-free sum-capacity) IFCs. For
the uniformly weak IFCs, sufficient conditions are obtained for which the
sum-rate is maximized when interference is ignored at both receivers.
