State constraints for the multiple-access arbitrarily varying channel

A discrete multiple-access arbitrarily varying channel with two transmitters and one receiver is considered. It has recently been shown that if such a channel is symmetrizable, then the capacity region has an empty interior. It is shown that if the channel is subject to a suitable state constraint, then the capacity region can contain certain open rectangles and thereby possess a nonempty interior, even if the channel is symmetrizable. A new weak converse under a state constraint is also proved. These results are then used to establish the capacity region of the two-user adder channel under state constraint 1/2