Dirty-Paper Coding for the Multi-Access Channel with Conferencing

We derive the capacity region of the two-user dirtypaper Gaussian multi-access channel (MAC) with conferencing encoders. In this MAC, prior to each transmission block, the transmitters can hold a conference in which they can communicate with each other over error-free bit-pipes of given capacities. The received signal suffers not only from additive Gaussian noise but also from additive interference, which is known noncausally to the transmitters but not to the receiver. The additive interference is modeled as Gaussian or uniform over a sphere. We show that the interference can be perfectly mitigated, i.e., that the capacity region without interference can also be achieved in its presence. This holds irrespective of whether the transmitters learn the interference before or after the conference. It follows as a corollary that also for the MAC with degraded message sets— which is a special case of the MAC with conferencing encoders— the interference can be perfectly mitigated if it is known noncausally to the transmitters. To derive our results we generalize Costa’s single-user writing on dirty-paper achievability result to channels with dependent interference and not-necessarily-Gaussian noise.