Outer bounds for user cooperation

We obtain a dependence balance based outer bound on the capacity region of the two-user multiple access channel with generalized feedback (MAC-GF). We investigate a Gaussian MAC with user-cooperation (MAC-UC), where each transmitter receives an additive white Gaussian noise corrupted version of the channel input of the other transmitter. For all non-zero values of cooperation noise variances, our outer bound strictly improves upon the cut-set outer bound. Moreover, as the variances of the cooperation noises become large, our outer bound collapses to the capacity region of the Gaussian MAC without cooperation.