  For a fading Gaussian multiple access channel with user cooperation, we
obtain the optimal power allocation policies that maximize the rates achievable
by block Markov superposition coding. The optimal policies result in a coding
scheme that is simpler than the one for a general multiple access channel with
generalized feedback. This simpler coding scheme also leads to the possibility
of formulating an otherwise non-concave optimization problem as a concave one.
Using the channel state information at the transmitters to adapt the powers, we
demonstrate significant gains over the achievable rates for existing
cooperative systems.
