Dirty interference cancellation for Gaussian broadcast channels

The state-dependent broadcast channel with a helper is investigated, in which a transmitter wishes to send messages to two receivers via a broadcast channel. The channel is corrupted by an independent and identically distributed (i.i.d.) state sequence which is known to neither the transmitter nor the receivers. A helper that knows the state sequence noncausally assists the broadcast transmission to cancel state interference. Two scenarios are studied. In scenario 1, the transmitter sends one message to both receivers, and in scenario II, the transmitter sends two private messages respectively to two receivers. Our focus is on the Gaussian channel with additive state. Inner and outer bounds are derived for both scenarios. By comparing the inner and outer bounds, capacity/capacity region are characterized under various ranges of channel parameters. Practical impact of the model and results are discussed.