Capacity region of a state dependent degraded broadcast channel with noncausal transmitter CSI

The capacity region for a state dependent degraded broadcast channel is derived. We study the case with noncausal channel state information (CSI) at the transmitter but no receiver CSI. For this model inner and outer bounds for the capacity region were known. We prove the achievability by introducing a new random coding scheme called the enhanced common randomness superposition coding. In this scheme, the stronger output terminal establishes more common randomness with the input terminal than that provided by the message intended for the degraded output receiver.