There are many coding schemes that achieve the capacity of a class of multiple-access channels with feedback (MAC-FB).   In this talk, we investigate the necessity of certain forms of structures in capacity achieving codes for MAC-FB.
It is known that applications of Gacs-Korner-Witsenhausen common information leads to improvements in achievable rates in multi-user communication problems such as transmission of correlated sources over MAC and MAC-FB. We introduce a new common information which is called conferencing common information. As an intermediate step, we investigate how exploiting conferencing common information contributes to improvements over conventional coding schemes such as Cover- El Gamal – Salehi scheme. Next, we investigate the short-coming of existing codes based on unstructured random codes for MAC-FB. We show the necessity of certain forms of algebraic structures in capacity achieving codes and argue that the lack of such structures in the current coding schemes leads to their sub-optimality.