  We explore the available degrees of freedom for various multiuser MIMO
communication scenarios such as the multiple access, broadcast, interference,
relay, X and Z channels. For the two user MIMO interference channel, we find a
general inner bound and a genie-aided outer bound that give us the exact number
of degrees of freedom in many cases. We also study a share-and-transmit scheme
for transmitter cooperation. For the share-and-transmit scheme, we show how the
gains of transmitter cooperation are entirely offset by the cost of enabling
that cooperation so that the available degrees of freedom are not increased.
