  In this paper, we obtain a general achievable rate region and some certain
capacity theorems for multiple-access relay channel (MARC), using decode and
forward (DAF) strategy at the relay, superposition coding at the transmitters.
Our general rate region (i) generalizes the achievability part of Slepian-Wolf
multiple-access capacity theorem to the MARC, (ii) extends the Cover-El Gamal
best achievable rate for the relay channel with DAF strategy to the MARC, (iii)
gives the Kramer-Wijengaarden rate region for the MARC, (iv) meets max-flow
min-cut upper bound and leads to the capacity regions of some important classes
of the MARC.
