Capacity of Gaussian MIMO Bidirectional Broadcast Channels
  We consider the broadcast phase of a three-node network, where a relay node establishes a bidirectional communication between two nodes using a spectrally efficient two-phase decode-and-forward protocol. In the first phase the two nodes transmit their messages to the relay node. Then the relay node decodes the messages and broadcasts a re-encoded composition of them in the second phase. We consider Gaussian MIMO channels and determine the capacity region for the second phase which we call the Gaussian MIMO bidirectional broadcast channel. 
Rafael F. Wyrembelski, Tobias J. Oechtering, Igor Bjelakovic, Clemens   Schnurr, Holger Boche