  The performance of user-cooperation in a multi-access network is compared to
that of using a wireless relay. Using the total transmit and processing power
consumed at all nodes as a cost metric, the outage probabilities achieved by
dynamic decode-and-forward (DDF) and amplify-and-forward (AF) are compared for
the two networks. A geometry-inclusive high signal-to-noise ratio (SNR) outage
analysis in conjunction with area-averaged numerical simulations shows that
user and relay cooperation achieve a maximum diversity of K and 2 respectively
for a K-user multiaccess network under both DDF and AF. However, when
accounting for energy costs of processing and communication, relay cooperation
can be more energy efficient than user cooperation, i.e., relay cooperation
achieves coding (SNR) gains, particularly in the low SNR regime, that override
the diversity advantage of user cooperation.
