An application of a wringing lemma to the multiple access channel with cooperative encoders

The problem of communicating over a multiple access channel with cooperative encoders is studied. A new upper bound is derived on the capacity which is motivated by the regime of operation where the relays start to cooperate. The proof technique is based on a wringing lemma by Dueck and Ahlswede which was used for the multiple description problem with no excess rate. Previous upper bounds are shown to be loose in general, and may be improved.