Capacity-achieving coding for cellular downlink with bidirectional communication

In this work we provide capacity achieving coding strategies for the cellular downlink with three users where two users want to communicate with each other. Due to the side information from the prior uplink, classical broadcast coding strategies can be beneficially combined with coding strategies for the bidirectional broadcast channel without and with random state non-causally known at the encoder. The single-user capacities are achievable, if additionally one decoder knows the independent and identically distributed additive channel state. The coding strategies depend on the relation of the channel gains. Converses can be proved for two of three cases.