  Processing of multiple communication flows in wireless systems has given rise
to a number of novel transmission techniques, notably the two-way relaying
based on wireless network coding. Recently, a related set of techniques has
emerged, termed coordinated direct and relay (CDR) transmissions, where the
constellation of traffic flows is more general than the two-way. Regardless of
the actual traffic flows, in a CDR scheme the relay has a central role in
managing the interference and boosting the overall system performance. In this
paper we investigate the novel transmission modes, based on
amplify-and-forward, that arise when the relay is equipped with multiple
antennas and can use beamforming.
