  This paper demonstrates the significant gains that multi-access users can
achieve from sharing a single amplify-forward relay in slow fading
environments. The proposed protocol, namely the multi-access relay
amplify-forward, allows for a low-complexity relay and achieves the optimal
diversity-multiplexing trade-off at high multiplexing gains. Analysis of the
protocol reveals that it uniformly dominates the compress-forward strategy and
further outperforms the dynamic decode-forward protocol at high multiplexing
gains. An interesting feature of the proposed protocol is that, at high
multiplexing gains, it resembles a multiple-input single-output system, and at
low multiplexing gains, it provides each user with the same
diversity-multiplexing trade-off as if there is no contention for the relay
from the other users.
