  We consider a two-user Gaussian multiple access channel with two independent
additive white Gaussian interferences. Each interference is known to exactly
one transmitter non-causally. Transmitters are allowed to cooperate through
finite-capacity links. The capacity region is characterized to within 3 and 1.5
bits for the stronger user and the weaker user respectively, regardless of
channel parameters. As a by-product, we characterize the capacity region of the
case without cooperation to within 1 and 0.5 bits for the stronger user and the
weaker user respectively. These results are based on a layered modulo-lattice
transmission architecture which realizes distributed interference cancellation.
