  Energy harvesting (EH) cognitive relays are an exciting solution to the
problem of inefficient use of spectrum while achieving green communications and
spatial diversity. In a spectrum sharing scenario, we investigate the
performance of a cognitive relay network, where a secondary source communicates
with its destination over Nakagami-$m$ channels via decode-and-forward EH
relays while maintaining the outage probability of the primary user below a
predefined threshold. Specifically, we derive a closed-form expression for the
secondary outage probability and show that it is a function of the probability
of an EH relay having sufficient energy for relaying, which in turn, depends on
the energy harvesting and consumption rates of the EH relay and the primary
outage probability threshold. We also show that relaxing the primary outage
constraint may not always benefit the cognitive EH relay network due to the
limitations imposed on the relay's transmit power by the energy constraint.
