Opportunistic relay networks, much like other forms of opportunism,
have simpler coding/decoding, as well as improved throughput compared
with open-loop systems. However, optimal opportunistic access in relay
networks requires the comparison of the instantaneous capacities of
sub-networks, which unfortunately are often unknown in closed form.
This is much more diffcult than, e.g., uplink or downlink diversity,
where it suffices to compare link gains or simple functions thereof.
We make advances in understanding the performance of a wide class of
opportunistic relay networks by developing a new formula for the
opportunistic diversity multiplexing tradeoff.