Dirty interference cancelation for multiple access channels

The state-dependent multiple access channel with a helper is investigated, in which transmitters 1 and 2 send two messages respectively to one receiver, which is corrupted by an independent and identically distributed (i.i.d.) state sequence. The state sequence is known to neither the transmitters nor the receiver, but is known to a helper noncausally. Thus, the helper assists the multi-access transmission by exploiting the state information. Our focus is on the Gaussian channel with additive state. An outer bound on the capacity region is first derived, and an inner bound is then obtained based on a dirty interference cancelation scheme. By comparing the inner and outer bounds, the full capacity region or segment on the boundary of the capacity region are characterized under various channel parameters. Practical motivation of the model and implication of the results are also discussed.